Journal of Physiology (1988), 399, pp. 177-189 177With 7 text-figuresPrinted in Great Britain

STIMULATION OF VASOPRESSIN RELEASE IN THE VENTRAL SEPTUMOF THE RAT BRAIN SUPPRESSES PROSTAGLANDIN El FEVER

BY A. M. NAYLOR*, Q. J. PITTMAN AND W. L. VEALEFrom the Department of Medical Physiology, Faculty of Medicine,The University of Calgary, Calgary, Alberta, Canada T2N 4N1

(Received 15 June 1987)

SUMMARY

1. Infusion of prostaglandin E1 (PGE1) into a lateral cerebral ventricle of the ratevoked a rise in core temperature which could be attenuated by electrical stimulationof the bed nucleus of the stria terminalis (BST). Electrical stimulation of the BST inthe absence of PGE1 did not alter body temperature in the afebrile rat.

2. When the intracerebroventricular (i.c.v.) infusion of PGE1 was preceded by abilateral injection of saline or vasopressin V2 antagonist d(CH2)5D-ValVAVP into theventral septal area (VSA), electrical stimulation of the BST suppressed the PGE1hyperthermia. However, when the vasopressin V1 antagonist d(CH2)5Tyr(Me)AVPwas injected into the VSA prior to i.c.v. infusion of PGE1, electrical stimulation ofthe BST did not alter the hyperthermic response to PGE1.

3. These actions were site specific in that the suppression of PGE1 hyperthermiawas observed only when the electrode tips were located in the area of the BST.Similarly, the V1 antagonist only blocked the effect of electrical stimulation wheninjected into the VSA.

4. When the vasopressin V1 antagonist was injected into the VSA, the PGE1 feverwas prolonged when compared to the controls with saline.

5. Injection of saline, vasopressin V1 and V2 antagonist into the VSA, withoutPGE1 or BST stimulation, did not evoke any significant change in the coretemperature of the rats.

6. These data are consistent with the hypothesis that vasopressin may functionwithin the brain as an endogenous antipyretic and that vasopressin may act in aBST-VSA neuronal pathway concerned with endogenous antipyresis.

INTRODUCTION

Arginine vasopressin (AVP) is present in neurones over widespread areas of thecentral nervous system (CNS) (Swanson, 1977; Buijs, 1978; Buijs, Swaab, Dogterom& Van Leeuwen, 1978; Van Leeuwen & Caffe, 1983; De Vries, Buijs, Van Leeuwen,Caffe & Swaab, 1985) and there is now considerable evidence that this peptidefunctions as a neurotransmitter or neuromodulator in the brain (Riphagen &

* Current address: MRC Reproductive Biology Unit, 37 Chalmers Street, Edinburgh EH39EW.

A. M. NAYLOR, Q. J. PITTMAN AND W. L. VEALE

Pittman, 1986). In particular, AVP appears to act in the ventral septal area (VSA)of the brain as a neurotransmitter involved in endogenous antipyresis (Kasting,Veale & Cooper, 1982; Naylor, Cooper & Veale, 1987 a for reviews). Thus, perfusionof vasopressin through the VSA suppresses the rise in core temperature evoked byperipheral administration of a pyrogen (Kasting, Veale & Cooper, 1979; Naylor,Ruwe, Kohut & Veale, 1985), and central administration of a pyrogen (Naylor et al.1985) or prostaglandin E2 (Ruwe, Naylor & Veale, 1985).The central receptor mediating the antipyretic action of vasopressin resembles the

V1 (vasopressor) rather than the V2 (antidiuretic) subtype of peripheral vasopressinreceptor, in that an antagonist of the V1 receptor, d(CH2)5Tyr(Me)AVP (Kruszynski,Lammek, Manning, Seto, Haldar & Sawyer, 1980), prevented the antipyretic actionof exogenously administered AVP (Kasting & Wilkinson, 1986; Naylor, Gubitz,Dinarello & Veale, 1987b) whereas a V2 agonist DDAVP (1-desamino-8-D-argininevasopressin) (Sawyer, Acosta & Manning, 1974) did not alter fever when injected intothe brain (Naylor et al. 1987 b).

Evidence to support the hypothesis that AVP functions within the VSA as anantipyretic under physiological conditions has been obtained from release studiesand from experiments in which the effects of endogenously released AVP have beenblocked either with AVP antagonists or specific antibodies. Therefore, during fever,the release of vasopressin was altered within the same sites where exogenouslyadministered vasopressin suppressed fever, the amount of peptide releasedcorrelating negatively with febrile changes in body temperature (Cooper, Kasting,Lederis & Veale, 1979; Malkinson, Bridges, Lederis & Veale, 1987). Furthermore,either the injection of a vasopressin V1 antagonist, d(CH2)5Tyr(Me)AVP (Cooper,Naylor & Veale, 1987), or perfusion of specific AVP antisera (Malkinson et al. 1987)within the VSA, enhanced the febrile response to a pyrogen challenge. In the case ofthe V1 antagonist, the enhancement of fever was specific since the similaradministration of a vasopressin V2 antagonist, d(CH2)5D-ValVAVP (Manning, Klis,Olma, Seto & Sawyer, 1982) did not alter the time course or magnitude of fever(Cooper et al. 1987).

Currently the neuroanatomical source ofvasopressin responsible for the antipyreticactions of AVP in the VSA has not been established. However, the major source ofvasopressin to the VSA is from a vasopressinergic pathway originating in the BST(De Vries & Buijs, 1983; De Vries et al. 1985; Disturnal, Veale & Pittman, 1985). Theexperiments reported in this paper were undertaken firstly, to determine if electricalstimulation of the BST would attenuate the fever evoked by ic.v. PGE1, andsecondly, to determine if the effects of BST stimulation could be modified byvasopressin (V1 and V2) antagonists injected into the VSA.

METHODS

Male Sprague-Dawley rats (180-320 g) were used for the experiments. Under pentobarbitoneanaesthesia (65-75 mg/kg i.P.) bilateral 20 gauge (thin-wall) stainless-steel guide cannulae wereimplanted stereotaxically (Pellegrino, Pellegrino & Cushman, 1979) so that the tips remained 4 mmabove the intended site of injection in the VSA. A single guide cannula was implanted above alateral cerebral ventricle. In addition, monopolar stimulating electrodes (stainless-steel insert pin,00 size, tip exposure of 100 ,um) were implanted bilaterally within the BST and a ground electrode

178

CENTRAL VASOPRESSIN AND FEVER SUPPRESSION

was placed on the surface of cortex. All cannulae and electrodes were secured to the skull asdescribed previously (Ruwe et al. 1985). Following surgery, each rat recovered for a period of7-10 days.During experiments, each rat was placed individually in a plastic cage without restraint. The

body temperature of each rat was monitored continuously with a precalibrated transmitter(VM-FM disc; Minimitter Inc., Sun River, OR, U.S.A.), placed into the peritoneal cavity at thetime of cannulae implantation, and a receiver (RAIOIO). Body temperature was recorded on-line(Dataquest III, Data Sciences Inc., Minneapolis, MN, U.S.A.) at 5 min intervals using a Zenith ATcomputer.

Baseline recordings of body temperature were made for at least 2 h before injection of thePGE1, vasopressin antagonists (see later) or the control solution (sterile physiological saline).Febrile body temperatures were induced by infusing PGE1 (200 ng in 10-0 Iud) (Upjohn), by gravityflow, into a lateral cerebral ventricle. Fifteen minutes prior to the PGE1 infusion, saline (1-0 4ul) orthe vasopressin antagonists (400 pmol in 10 ulu) were injected bilaterally into the VSA over a30-45 s period using a 27 gauge injector needle connected by PE-20 tubing to a Harvard infusionpump. A cross-over design was used for the order of injection. Bilateral electrical stimulation of theBST (Grass Instruments; monophasic square-wave pulses, 0 5 ms duration at 20 Hz, 10 s on, 10 soff, 10-50 ,uA) was typically for 10 min before and 20 min following the i.c.v. injection of PGE1.The two vasopressin antagonists, 1-(,8-mercapto-fl,fl-cyclopentamethylene proprionic acid),2-(O-methyl) tyrosine arginine vasopressin and 1-(,8-mercapto-/,fl-cyclopentamethylene proprionicacid), 2-D-valine, 4-valine arginine vasopressin were supplied by Dr M. Manning. (Abbreviated asd(CH2)5Tyr(Me)AVP and d(CH2)5D-ValVAVP respectively.)Upon completion of the experiments, each rat was anaesthetized deeply with sodium

pentobarbitone. The brain was then perfused with saline followed by neutral formalin. The tissuewas blocked in the coronal plane and sectioned at 50 ,am on a sledge microtome. Each section wasstained with neutral red and the injection sites localized by light microscopy.

Results were assessed statistically using an analysis of variance followed by the Scheffe post-hoctest. The fever indices were expressed as areas under the fever curves in °C h.

RESULTS

Intracerebroventricular infusion of PGE1 evoked a rise in core temperature whichwas maximal 20-30 min after injection. When the i.c.v. administration of PGE1 wasaccompanied by electrical stimulation of the BST, the PGE1 hyperthermia wasattenuated significantly (1 h fever index: PGE1 alone, 0-87 + 040 °C h; PGE1 andBST stimulation, 0-16+0-10 °C h; P < 0-001). Electrical stimulation of the BST inthe absence of PGE1 did not reduce body temperature in the afebrile rat (Fig. 1,lower panel). In addition, at the currents delivered, there were no behavioural ormotor abnormalities observed. In those instances where electrical stimulation of theBST reduced the response to PGE1, the normal behavioural changes associated withfever (e.g. blanched skin, huddled posture and piloerection) were not observed.Instead, the rats lay quietly, explored or groomed.

In another group of animals, when the i.c.v. administration ofPGE1 was precededby a bilateral injection of saline into the VSA, electrical stimulation of the BSTprevented the normal rise in body temperature associated with the centraladministration of PGE1 (Fig. 2). However, in these same animals, when thevasopressin V1 antagonist, d(CH2)5Tyr(Me)AVP, was injected similarly into the VSA15 min prior to PGE1, fever was evoked which was not altered by electricalstimulation of the BST (Fig. 2). Indeed, the temperature response was notsignificantly different from that observed with PGE1 alone (1 h fever index; seeFig. 3).

179

180 A. M. NAYLOR, Q. J. PITTMAN AND W. L. VEALE

In the same group of rats as those described above, a different vasopressinantagonist, d(CH2)5D-ValVAVP, was injected into the VSA. This antagonist, whichis specific for the V2 receptor, did not prevent the antipyretic response resulting from

Stimulation periodI I~~~~~~~~~~~~~~~~~~~~

1-5h

No stimulation

PGE,

n = 6

I

Stimulation period

II~~~~~~~~~~~~~~~~~~~~~~~~~~

n = 8

-15 0 15 30 45 60

Time (min)

Fig. 1. Upper panel: mean temperature responses (±S.E.M.) evoked by an intra-cerebroventricular (i.c.v.) infusion of prostaglandin E1 (PGE1; 200 ng/10 ,u) at time zero

(@; mean+ S.E.M. zero value, 37-47 + 0 33 TC). Electrical stimulation of the bed nucleus ofthe stria terminalis (BST) (bar) suppressed significantly the PGE1 fever (0; mean+ S.E.M.zero value, 37-90+ 0 30 °C) (1 h fever index). Lower panel: mean temperature responses

(+S.E.M.) evoked by stimulation of the BST. Mean+s.E.M. zero value, 37-43+0-20 'C.

electrical stimulation of the BST (Fig. 2). Both the magnitude and duration of feverwere identical to that seen when saline was injected into the VSA.

In Fig. 3, the fever indices (°C h for 1 h) for the four treatment groups are

illustrated. The fever indices obtained from the rats that were treated with thevasopressin V1 antagonist and received BST stimulation were not different from thefever indices produced by the i.c.v. infusion of PGE1 alone (with no stimulation of

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CENTRAL VASOPRESSIN AND FEVER SUPPRESSION 181

the BST). In contrast, when either saline or the vasopressin V2 antagonist wereinjected bilaterally into the VSA prior to i.c.v. injection of PGE1, electricalstimulation of the BST produced fever indices that were significantly reduced whencompared to either the PGE fever alone or the V1 antagonist-treated group(P <0001).

Figure 4 illustrates the time course ofPGE1 hyperthermia and the stimulation andinjection sites for various treatments in an individual animal. In this case, the

20

Stimulation period

15

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0

0 *

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0E * Saline (n =8)E

oV, antagonist (n = 8)

-0 V2 antagonist (n = 7)

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Fig. 2. Mean temperature responses (±S.E.M.) to the intracerebroventricular (i.c.v.)infusion of prostaglandin El (PGE1; 200 ng/10 ,ul) at time zero during electricalstimulation of the bed nucleus of the stria terminalis. Either saline (10 ,ul), vasopressinV1 antagonist (400 pmol) or vasopressin V2 antagonist (400 pmol) were injected bilaterallyinto the ventral septal area (VSA; first arrow) 15 min before the PGE1. Mean+ S.E.M.zero values: saline treated, 37-85 + 021 °C; V1 antagonist treated, 37-50+ 0-20 °C;V2 antagonist treated, 37-83 + 0-20 °C.

injection of the vasopressin V1 antagonist was made outside the VSA (see histologicalinsets). Under these circumstances, electrical stimulation of the BST prevented thePGE fever, that is, the V1 antagonist was ineffective in blocking the antipyretic effectof BST stimulation when injected outside the VSA.

Since d(CH2)5Tyr(Me)AVP has been reported to enhance the later stages ofinterleukin-1 fever (Cooper et al. 1987), the effects of this antagonist on PGE1 feveralone were investigated. Figure 5 illustrates the effects of injection of saline andvasopressin V1 antagonist into the VSA on PGE1 hyperthermia (Fig. 5, upper panel)and also on resting body temperature (Fig. 5, lower panel). The vasopressin V1antagonist enhanced the later stages of PGE1 hyperthermia but did not alter the

A. M.NA YLOR, Q. J. PITTMAN AND W. L. VEALE

initial time course of the fever (Fig. 5, upper panel). An analysis of the fever indicesfor the two treatments over the first and second hours revealed the following. Overthe first 60 min there was no significant difference between the fever indices, whereasbetween 60 and 120 min, the presence of the vasopressin V1 antagonist in the VSAenhanced PGE1 hyperthermia (P < 0-05) when compared to the control responsewith saline (Fig. 6). Injection of saline or vasopressin V1 antagonist into the VSAwithout PGE1 resulted in no significant alterations in core temperature (Fig. 5, lowerpanel). Similarly, the vasopressin V2 antagonist did not alter resting bodytemperature in the afebrile rat (data not shown).

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VI-VSA Sal.-VSA V2-VSABST stim. BST stim. BST stim.

Fig. 3. Fever indices showing the effects of two vasopressin antagonists and saline,injected into the ventral septal area (VSA), on the stimulation-induced suppression ofprostaglandin E1 (200 ng/100 ,ul intracerebroventricularly) fever. Electrical stimulation ofthe bed nucleus of the stria terminalis (BST) suppressed significantly PGE1 fever whensaline or V2 antagonist were injected bilaterally into the ventral septal area (VSA)(*P < 0-001 compared to PGE1 alone or V1 antagonist-treated group). In contrast whenthe V1 antagonist was injected into the VSA, electrical stimulation of the BST did notalter significantly the PGE1 fever when compared to PGE1 alone (n.s.: not significantlydifferent).

The areas in the forebrain where electrical stimulation of the BST suppressedPGE1 hyperthermia were located predominantly in the area of the BST, above theanterior commissure and also caudally towards and bordering on the fornix (Fig. 7,upper panel). Sites where stimulation did not affect PGE fever include the lateralseptum, anterior commissure, preoptic area and ventral fornix (Fig. 7, upper panel).The loci of injections where the vasopressin V1 antagonist altered PGE1 hyperthermiaand reversed the effects of BST stimulation are indicated in Fig. 7 (lower panel).These were located predominantly in the VSA, in an area bounded by the diagonalbands of Broca. In addition, there were some sites located more rostrally. Areaswhere injection of the antagonist was without effect were located more dorsal andlateral to the active sites (Fig. 7, lower panel).

182

CENTRAL VASOPRESSIN AND FEVER SUPPRESSION 183

DISCUSSION

Infusion of PGE1 into a lateral ventricle of the rat evoked a prompt hyperthermicresponse which returned towards baseline after about 30 min. This hyperthermicresponse could be attenuated significantly upon electrical stimulation of the BST butnot of other nearby areas. Although the possibility cannot be excluded that these

20

Stimulation period a

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Fig. 4. Temperature responses obtained from an individual rat to the intracerebro-ventricular (i.c.v.) infusion of prostaglandin E1 (PGE1; 200 ng/10 ,ul; El) withoutelectrical stimulation (zero value, 37-62 °C) and during stimulation of the BST. Bilateralinjection of vasopressin V1 antagonist (400 pmol; 0; zero value 38-32 °C) into an area

outside of the ventral septal area (VSA; 15 min prior to PGE1) did not block the BSTstimulation-induced suppression of fever when compared to the response with saline(1-0 41; *; zero value 37-72 C). Sites of injection (left) and bed nucleus of the striaterminalis stimulation (right) are shown on the histological insets. Abbreviations: see

legend for Fig. 7.

responses were due to stimulation of fibres of passage rather than cell bodies in theBST, this area is known to provide significant afferent input to the VSA (De Vries& Buijs, 1983; Disturnal, Veale & Pittman, 1985; De Vries et al. 1985).

Electrical stimulation of the brain, in particular the rostral hypothalamus(Beaton, McKinley, Berry & Ranson, 1948) evokes a fall in body temperature in anumber of species (Andersson, Grant & Larsson, 1956). Therefore, ifBST stimulationelicited a non-specific hypothermia by activating heat loss effectors then this could

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184 A. M. NAYLOR, Q. J. PITTMAN AND W. L. VEALE

account for the antipyretic effect of BST stimulation. However, since electricalstimulation of the BST did not evoke hypothermia in the afebrile rat, such an effectis unlikely to account for the BST stimulation-induced reduction in PGE1 fever.

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k

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Fig. 5. Upper panel: mean temperature responses (± S.E.M.) to the intracerebroventricular(i.c.v.) infusion of prostaglandin E1 (PGE1; 200 ng/10 pl). Fifteen minutes prior to this(first arrow), either saline (lO, l) or the vasopressin V1 antagonist (400 pmol) wereinjected bilaterally into the ventral septal area (VSA). Mean+ S.E.M. zero values: salinetreated, 38&38 + 0 30 °C; V1 antagonist treated, 37-92 + 0-25 'C. Lower panel: meantemperature responses (± S.E.M.) to the injection of saline (0; mean+ S.E.M. zerovalue, 38&53+0±20 °C) and vasopressin V1 antagonist (0; mean+s .E.M. zero value,3813 + 0-38 °C) into the ventral septal area (VSA; first arrow). There was no significantdifference between the two treatments.

The VSA contains a number ofneurotransmitters (De Olmos, Alheid & Beltramino,1985) which could be released upon electrical stimulation of the BST and thereforecould mediate the antipyretic action of BST stimulation. However, in view of theantipyretic effect of vasopressin in the VSA (Ruwe et al. 1985), and the observation

CENTRAL VASOPRESSIN AND FEVER SUPPRESSION

that the major source of AVP to the VSA originates in the BST (De Vries & Buijs,1983; De Vries et al. 1985), the possibility that BST stimulation reduced PGE1hyperthermia by releasing vasopressin in the VSA was investigated. On injectioninto the ventral septum, the vasopressin V1 antagonist prevented electricalstimulation of the BST from suppressing the PGE1 hyperthermia. In contrast to this,the V2 antagonist did not block the PGE1 hyperthermia upon BST stimulation.Therefore, an explanation of these data may be that the V1 antagonist blocks AVPreceptors in the VSA, thereby preventing the BST stimulation-induced release ofvasopressin from interacting with receptors in the VSA. In this way the V1antagonist, but not the V2 antagonist, is capable of preventing the antipyretic effect

n.s. P<O005I I , r

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0 ~~~0-60min 60-120minFig. 6. Fever indices showing that the vasopressin V1 antagonist enhanced prostaglandinE1 (PGE1; 200 ng/10 Al) fever on injection into the ventral septal area (VSA) whencompared to the control response with saline. This enhancement was evident in the laterstages ofPGE1 fever (60-120 min; P < 0-05). Initially (0-60 min), there was no significant(n.s.) difference between the two treatments.

of BST stimulation. This suggests that AVP, acting in a BST-VSA neuronalpathway, may be responsible for vasopressin-induced endogenous antipyresis. Insupport of this view, the V1 antagonist used in this study has been shown previouslyto prevent the antipyretic effect of both exogenously administered (Kasting &Wilkinson, 1986; Naylor et al. 1987 b) and endogenously released AVP (Cooper et al.1987).The absolute specificities of the vasopressin antagonists (V1 and V2) used in this

study have not been verified thoroughly. Although both are relatively specific totheir respective vasopressin receptor, their pharmacological specificities have notbeen determined in detail. The vasopressin V1 antagonist may also interact withoxytocin receptors (Kruszynski et al. 1980) but this is unlikely to account for thepresent observations since oxytocin does not suppress pyrogen fever (Kovacs &DeWied, 1983). In addition, a non-specific neurodepressant action has beenattributed to d(CH2)5Tyr(Me)AVP (Porter & Brody, 1986). However, a neuro-

185

A. M. NAYLOR, Q. J. PITTMAN AND W. L. VEALE

depressant action is unlikely to explain these results since, firstly, the structurallysimilar V2 antagonist did not mimick the V, antagonist and, secondly, the V1antagonist can preferentially block the cardiovascular actions of spinal AVP but notthose of substance P (C. L. Riphagen & Q. J. Pittman, unpublished observations). In

Stimulation sites

Injection sites

Fig. 7. Upper panel: schematic histological sections of the rat forebrain showing siteswhere electrical stimulation suppressed (U, n = 14) or did not alter (Ol, n = 6)prostaglandin E1 fever. Lower panel: schematic histological sections showing sites in andnear the VSA where injection of vasopressin V1 antagonist either enhanced prostaglandinEl fever or prevented the antipyretic effect of bed nucleus of the stria terminalisstimulation (@, n = 14). Sites where injection of the vasopressin V1 antagonist had noeffect are also shown (0, n = 7). Abbreviations: AC, anterior commissure; AH, anteriorhypothalamus; BST, bed nucleus of the stria terminalis; CC, corpus callosum; CP,caudate putamen; FX, fornix; IC, internal capsule; LO, lateral olfactory tract; LC orLCV, lateral ventricle; LS, lateral septum; NA, nucleus accumbens; OC, opfic chiasm;POA, preoptic area; SI, substantia innominata; ST, stria terminalis; 2n, optic tracts; 3V,third ventricle.

addition, d(CH2)5Tyr(Me)AVP applied onto neurones in the VSA (Disturnal, Veale& Pittman, 1987) or hippocampus (Burnard, Veale & Pittman, 1987) did not producedepression.The ability of the V1 antagonist to prevent electrical stimulation of the BST from

suppressing PGE1 fever was site specific in that the antagonist blocked the action ofBST stimulation only when injected into the VSA. In this regard, when the Vantagonist was injected outside the VSA, BST stimulation suppressed the PGE1hyperthermia. A similar site specificity exists in the VSA for the antipyretic action

186

CENTRAL VASOPRESSIN AND FEVER SUPPRESSION

of exogenously administered vasopressin (Naylor et al. 1987 a for review). Indeed, theareas in the forebrain where the V1 antagonist and AVP modify fever are verysimilar.As well as projecting to the VSA, the BST also projects to many other sites in the

brain including diencephalic and brain-stem areas (De Olmos et al. 1985). Amongother possible functions of these pathways, there is evidence that the BST mayparticipate in the control of neuroendocrine function (Beltramino & Taleisnik, 1980;Dunn, 1987). Since the effects of electrical stimulation of the BST may be blocked inthe CNS with a vasopressin V1 antagonist, it is unlikely that alterations in the plasmalevels of hormones are primarily responsible for the present observations. Similarly,possible release of AVP into the periphery is unlikely to contribute to the antipyreticresponse since intravenous vasopressin does not modulate fever (Cooper et al.1979).When the V1 antagonist was infused into the VSA, the resulting PGE1 fever was

prolonged and enhanced. This observation agrees with a previous study indicating arole for endogenous vasopressin in fever suppression (Cooper et al. 1987). However,the enhancement ofPGE1 fever by the V1 antagonist raises a potential interpretativeproblem concerning the reversal by the V1 antagonist of BST stimulation-inducedfever suppression. That is, the antagonist could be enhancing PGE1 fever byantagonizing the antipyretic action of endogenous vasopressin released in responseto the febrile signal rather than as a result of BST stimulation. Because of thisproblem, the time course of PGE1 fever in the presence of the V1 antagonist wasexamined. As indicated in Fig. 6, the V1 antagonist enhanced the latter stages ofPGE1 fever (between 60-120 min), but did not alter fever during the first 60 min. Yetit is precisely during this first 60 min that BST stimulation-induced antipyresis wasreversed by the V1 antagonist. Thus, this analysis reinforces the conclusion that BSTstimulation suppresses fever by releasing AVP into the VSA. Furthermore, theenhancement of the latter stages of fever by the V1 antagonist provides furtherevidence that endogenously released vasopressin may be important in limiting theduration of fever.

In conclusion, these data support and strengthen the hypothesis that AVP mayfunction in the brain as an endogenous antipyretic. In addition, it is likely thatvasopressin released during fever in the VSA may originate from neurones located inthe BST. Future studies will address the question of how the BST system is activatedto release vasopressin during fever.

This work was supported by the Medical Research Council of Canada. A. M. N. holds astudentship from the Alberta Heritage Foundation for Medical Research. Q. J. P. is an MRCScientist and AHFMR Scholar. The vasopressin antagonists were supplied by Dr M. Manning(Toledo, OH, U.S.A.). We thank Mrs Grace Olmstead for typing the manuscript.

REFERENCES

ANDERSSON, B., GRANT, R. & LARSSON, S. (1956). Central control of heat loss mechanisms in thegoat. Acta phy8iologica scandmnavica 37, 261-279.

BEATON, L. E., MCKINLEY, W. A., BERRY, C. M. & HANSON, S. W. (1948). Localization of acerebral center activating heat-loss mechanisms in monkeys. Journal of Neurophysiology 4,478-485.

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BELTRAMINO, C. & TALEISNIK, S. (1980). Dual action of electrochemical stimulation of the bednucleus of the stria terminalis on the release of lutenizing hormone. Neuroendocrinology 30,238-242.

Buijs, R. M. (1978). Intra- and extrahypothalamic vasopressin and oxytocin pathways in the rat.Cell Tissue Research 192, 423-435.

Buijs, R. M., SWAAB, D. F., DOGTEROM, J. & VAN LEEUWEN, F. W. (1978). Intra- and extra-hypothalamic vasopressin and oxytocin pathways in the cat. Cell Tissue Research 186,423-433.

BURNARD, D. M., VEALE, W. L. & PITTMAN, Q. J. (1987). Altered sensitivity to arginine vaso-

pressin (AVP) in area CA1 of the hippocampal slice following pretreatment of rats with AVP.Brain Research 422, 11-16.

COOPER, K. E., KASTING, N. W., LEDERIS, K. & VEALE, W. L. (1979). Evidence supporting a rolefor endogenous vasopressin in natural suppression of fever in the sheep. Journal of Physiology295, 33-45.

COOPER, K. E., NAYLOR, A. M. & VEALE, W. L. (1987). Evidence supporting a role for endogenousvasopressin in fever suppression in the rat. Journal of Physiology 387, 163-172.

DE OLMOS, J., ALHEID, G. F. & BELTRAMINO, C. A. (1985). Amygdala. In The Rat Nervous System,vol. 1, Forebrain and Midbrain, ed. PAXINOS, G., pp. 223-234. Australia: Academic Press.

DE VRIES, G. J. & Buijs, R. M. (1983). The origin of the vasopressinergic and oxytocinergicinnervation of the rat brain with special reference to the lateral septum. Brain Research 273,307-317.

DE VRIES, G. J., Buijs, R. M., VAN LEEUWEN, F. W., CAFFE, A. R. & SWAAB, D. F. (1985). Thevasopressinergic innervation of the brain in normal and castrated rats. Journal of ComparativeNeurology 233, 236-254.

DISTURNAL, J. E., VEALE, W. L. & PITTMAN, Q. J. (1985). Electrophysiological analysis ofpotential arginine vasopressin projections to the ventral septal area of the rat. Brain Research342, 162-167.

DISTURNAL, J. E., VEALE, W. L. & PITTMAN, Q. J. (1987). Modulation by AVP of glutamateexcitation in the ventral septal area of the rat brain. Canadian Journal of Physiology andPharmacology 65, 30-35.

DUNN, J. D. (1987). Plasma corticosterone responses to electrical stimulation of the bed nucleus ofthe stria terminalis. Brain Research 407, 327-331.

KASTING, N. W., VEALE, E. L. & COOPER, K. E. (1979). Antipyresis following perfusion of brainsites with vasopressin. Experientia 35, 208-209.

KASTING, N. W., VEALE, W. L. & COOPER, K. E. (1982). Vasopressin: A homeostatic effector in thefebrile process. Neuroscience and Biobehavioural Reviews 6, 215-222.

KASTING, N. W. & WILKINSON, M. F. (1986). An antagonist to the antipyretic effects ofintracerebroventricularly administered vasopressin in the rat. In Homeostasis and ThermalStress, ed. COOPER, K. E., LOMAX, P., SCHONBAUM, E. & VEALE, W. L., pp. 137-139. Basel:Karger.

KOVACS, G. L. & DEWIED, D. (1983). Hormonally active vasopressin suppresses endotoxin-induced fever in rats. Lack of effect of oxytocin and a behaviorally active vasopressin fragment.Neuroendocrinology 37, 258-261.

KRUSZYNSKI, M., LAMMEK, B., MANNING, M., SETO, J., HALDAR, J. & SAWYER, W. H. (1980).[1-(/J-Mercapto-,8,,l-cyclopentamethylenepropionic acid) 2-(O-methyl)tyrosine] arginine vaso-

pressin and [1-(f-mercapto-,8,,8-cyclopentamethylenepropionic acid)] arginine vasopressin, twohighly potent antagonists of the vasopressor response to arginine vasopressin. Journal ofMedicinal Chemistry 23, 364-368.

MALKINSON, T. J., BRIDGES, T. E., LEDERIS, K. & VEALE, W. L. (1987). Perfusion of the septum ofthe rabbit with vasopressin antiserum enhances endotoxin fever. Peptides 8, 385-389.

MANNING, M., KLIS, W. A., OLMA, A., SETO, J. & SAWYER, W. H. (1982). Design of more potentand selective antagonists of the antidiuretic responses to arginine-vasopressin devoid ofantidiuretic agonism. Journal of Medicinal Chemistry 25, 414-419.

NAYLOR, A. M., COOPER, K. E. & VEALE, W. L. (1987a). Vasopressin and fever: Evidencesupporting the existence of an endogenous antipyretic system in the brain. Canadian Journal ofPhysiology and Pharmacology 65, 1333-1338.

188

CENTRAL VASOPRESSIN AND FEVER SUPPRESSION 189

NAYLOR, A. M., GUBITZ, G. A., DINARELLO, C. A. & VEALE, W. L. (1987b). Central effects ofvasopressin and 1-desamino-D-arginine vasopressin (DDAVP) on interleukin-1 fever in the rat.Brain Research 401, 173-177.

NAYLOR, A. M., RUWE, W. D., KOHUT, A. F. & VEALE, W. L. (1985). Perfusion of vasopressinwithin the ventral septum of the rabbit suppresses endotoxin fever. Brain Research Bulletin 15,209-213.

PELLEGRINO, L. J., PELLEGRINO, A. S. & CUSHMAN, A. J. (1979). A Stereotaxic Atlas of the RatBrain, 2nd edn. New York: Plenum Press.

PORTER, J. P. & BRODY, M. J. (1986). A V1 vasopressin receptor antagonist has nonspecificneurodepressant actions in the spinal cord. Neuroendocrinology 43, 75-78.

RIPHAGEN, C. L. & PITTMAN, Q. J. (1986). Arginine vasopressin as a central neurotransmitter.Federation Proceedings 45, 2318-2322.

RUWE, W. D., NAYLOR, A. M. & VEALE, W. L. (1985). Perfusion of vasopressin within the rat brainsuppresses prostaglandin E-hyperthermia. Brain Research 338, 219-224.

SAWYER, W. H., AcOSTA, M. & MANNING, M. (1974). Structural changes in the arginine vasopressinmolecule that prolong its antidiuretic action. Endocrinology 95, 140-149.

SWANSON, L. W. (1977). Immunohistochemical evidence for a neurophysin-containing autonomicpathway arising in the paraventricular nucleus of the hypothalamus. Brain Research 128,346-353.

VAN LEEUWEN, F. & CAFFE, R. (1983). Vasopressin-immunoreactive cell bodies in the bed nucleusof the stria terminalis of the rat. Cell Tissue Research 228, 525-534.