Intern. J . Neuroscience, 1972, Vol. 3, pp. 285-290 0 Gordon and Breach Science Publishers Ltd. Printed in Birkenhead, England

NUCLEUS FASTIGII INFLUENCES ON BLOOD FLOW AND BLOOD PRESSURE

J. MITRA and RAY S . SNIDER

Center for Brain Research, University of Rochester Medical Center, Rochester, New York 14642

(Received March 21, 1972)

Electrical excitation of the nucleus fastigii in the cat can produce a change in blood flow (BF) to an extremity either with or without a change in systemic blood pressure (BPI. Characteristically, there is decreased BF and increased BP during stimulation followed by rebound enhancement of BF at the end of stimulation in intact and bilateral vagotomized animals. This post stimulatory effect can last 2 to 3 minutes. The usual BP change was a pressor response less than 50 mm Hg. EKG changes usually accompanied the higher BP changes as did increased heart rate. Slowing of the 3-5/sec EEG tracings taken from the hippocampus was seen in several preparations during the stimulatory interval. A cerebellar role in the inter organ redistribution of blood is discussed.

INTRODUCTION

Cerebellar influences on visceral motor structures are not only more difficult to demonstrate than those on somatic musculature, but the conflicting data collected by relatively few investigators make it difficult to decide what the cerebellar influences are. The early studies of Moruzzi (1938, 1940) were done carefully and showed that vasomotor and carotid sinus reflexes could be modified by cere- bellar stimulation in precollicular decerebrated cats. Zanchetti and Zoccolini (1954) using cats with transections at lower medullary levels, showed that cerebellar stimulation could alter pressor responses associated with sham rage. Ban (1959) saw similar effects in rabbits under urethane anesthesia. Sawyer and co-workers (1 96 1) con- sidered an intact hypothalamus to be necessary for the cardiovascular changes produced by cerebellar stimulation although they did not do studies on animals with discrete hypothalamic lesions. In view of the above mentioned findings and the variable changes in heart rate and blood pressure which we saw occasionally during stimu- lation procedures on the cerebellar cortex, questions were asked concerning the effects of nuclear rather than cortical stimulation on such visceral functions as blood flow and blood pressure. These questions became more pertinent with the timely appearance of the publication by Miura and Reiss (1969) showing the existence of a fastigial pathway to the reticular formation which sub- serves pressor function.

METHODS

Thirty-five cats weighing between 2.5 and 3.5 kg were used and the data from 18 of these animals, which were considered most typical and most frequently observed, forms the basis of the present report. All cats were anesthetized by the short- acting barbiturate Surital (12.5 mg/kg) and surgically prepared for the electrical recording and stimulation experiments. A cannula was usually placed in one femoral artery and the 1.5 mm trans- ducer for the B & L electromagnetic flow meter #410 (carrier frequency = sine wave, 400 cps) was placed around the other one. The animal was then attached to a mechanical respirator and given Flaxedil (4.0 mg/kg) medication. At no time was the rectal temperature allowed to fall below 35°C. All animals were protected from pain by the following precautions : 1 % novocain was infiltrated in the tissues around all incised areas every 1-2 hours. 1 % novocaine was also injected around pressure points, i.e. ear bars and eye bars. Addi- tional surgery was not attempted without giving additional doses of Surital.

Bipolar insulated 26 gauge nichrome wire elec- trodes stereotaxically oriented were used as stimulating and recording electrodes in deep neural structures. Ink writing oscillographs were used to record EEG, EKG, blood flow, and blood pressure tracings. The 2 mm probe of the electromagnetic flow meter was sutured to surrounding tissue to minimize movement. Zero flow was arbitrarily marked when temporary (less than 3 sec) total

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286 J. MITRA AND R. S. SNIDER

occlusion of a blood vessel was made distal to the probe. Flow rate was also calibrated with serum passing through the blood vessel and dropping into a graduated cylinder while the probe was surrounding the blood vessel.

The blood pressure records were taken via a Statham P23 AC pressure transducer attached to the cannulated femoral artery. The recording equipment was calibrated against a mercury manometer. Vascular resistance was calculated by the simple method of dividing the numerical

value of blood flow per minute into the mean pulse pressure expressed in mm mercury.

A Grass S4 electronic stimulator was used with repetitive biphasic pulses ranging between 10 and 300/sec (0.1 msec duration). Since frequencies between 200 and 300/sec required the least voltage these were usually employed (voltage range 3-12 V). A milliammeter was used to monitor current flow during stimulation.

At the end of each experiment the brain was dissected free of bone and dura and immersed in

LO

o n * 1 A- B C I FIGURE 1 Changes produced in blood flow record, EEG, EKG, and blood pressure record by electrical stimula- tion of nucleus fastigii. 200 pA electrical pulses (300/sec and 0.1 msec duration) applied for 10 sec to lateral margin of left nucleus fastigii in bilateral vagotomized cat (on-off) in a, b, c. a : Blood flow tracing taken from left femoral artery. b: EKG. Vertical calibration marks: a, 0-10 ml/min; b, 0.02 mV/cm. c: Blood pressure (100-190 mm Hg; maximal change = 50 mm) tracing taken from right femoral artery. A = 2 sec; B = 16 sec; C-52 sec. Length of horizontal black lines = 2 sec. Records d, e, f were taken from animal with intact vagi and intact leg. 800 p A electrical pulses (300/sec and 0.1 msec duration) for 10 sec applied to central area of left nucleus fastigii. (720 pA was threshold.) Tracings removed at A = 2 sec; B = 12 sec; C = 86 sec. d: EEG tracing taken from right posterior hippocampus. e: Blood flow tracing taken from right femoral artery. f: EKG 0.02 mV/cm. Blood pressure (not shown) in the left femoral artery remained at 108 mm during the recording. In records a, c the vascular resistance changed from 21 (prestimulation) to 28 (stimulation) to 17 (20 sec after stimulation) to 20 (1 min after stimulation). [n record e the vascular resistance changed from 21 (prestimulation) to 20 (end of stimulation) to 22.5 (1 min after stimulation).

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FASTIGIAL INFLUENCES ON BLOOD CIRCULATION 287

10% formalin for a minimum of four days and freehand sections were made transversely through the brain stem to determine the approximate location of the electrode tip. Then Nissl stained histological sections were prepared and studied for more accurate localization.

RESULTS

The data are divided into two sections: 1) changes in blood flow (BF) and blood pressure (BP) and 2) electroencephalographic (EEG) and electro- cardiographic (EKG) changes. In order to reduce the effects of cutaneous blood flow the paw was ligated and, unless otherwise indicated, each animal’s rear leg below the blood flow probe was carefully separated from the skin and the skin rewrapped around the leg.

Blood Flow and Blood Pressure

Figure l a shows the effects on BF of stimulating the nucleus fastigii in bilaterally vagotomized animals. Note that BF fell from 5.7 ml to 5.2 ml/min during stimulation and rose to 6.3 ml/min in the early poststimulatory period. The total altered effect lasted 75 sec. As shown in Figure lc, BP rose 5 mm during stimulation and fell 26 sec after withdrawal of stimuli to 2 mm below the prestimulatory level before returning to that level. Note that changes in B F and BP run parallel time coiirses.

As shown in Figure le there was a fall in blood flow during stimulation followed by a post stimu- latory increase. In this animal the vagi were intact and although the record is not shown, the blood pressure remained unaltered during stimulation. These data are interpreted to indicate that blood flow and blood pressure changes induced by cerebellar stimulation are not being mediated by vagal pathways.

Figure 2 shows simultaneous blood pressure and blood flow tracings taken before (a and b) and after (c and d) 0.2 ml application of 2% novocain in saline to the stimulation site via 30 gauge needle adjacent to stereotaxic electrode. Note that white matter is being stimulated and that after treatment with novocain the magnitude and duration of blood flow changes were reduced considerably, while blood pressure showed less alteration. A second application of 0.2 ml novocain prevented both effects even when 800 pA stimulating current

was used. These data are interpreted to indicate that spread of current to brain stem was not the cause of the changes. It is not known why it is more difficult to block the blood pressure changes than the blood flow changes. Although not shown in this record, the blood pressure changes recover faster from novocain depression than do the blood flow changes.

Figure 2e shows changes in blood flow in an animal with intact vagi. Note that the changes are similar to those shown in Figure 1 namely stimula- tory depression and post stimulatory enhancement resulting from nuclear stimulation.

EEG and EKG

That alterations in the EEG and EKG accompany the changes in blood flow and blood pressure are shown in Figures 1 and 2 (see lb, Id, lf, 2f, and 2g). Records taken from the posterior hippo- campus (Id) when the contralateral N F was stimulated indicate that 2 to 3/sec slow waves are changed to faster frequencies (3 to 4/sec) during stimulation. The EEG returns quickly to pre- stimulatory levels following ‘off’. In Figure 2g a similar record is shown except the 5 per second prestimulatory waves change to 6 to 7/sec during stimulation.

Occurring simultaneously with the EEG altera- tions are EKG changes which may or may not accompany changes in heart rate. (See Figures Ib and If). A systematic study of EKG changes could not be done since a lead I (arm-to-arm) electrode array was used to collect the data. Slowing of the heart rate was never observed. However, frequently increased amplitude of components of EKG (Figure lb, If) accompanied by increased rate (If), or less frequently with no rate change (Ib) was observed during stimulation. Ten animals were studied following bilateral vagotomy. Fusion of the T-P waves was observed in all of them (see Figure lb). However, since shortening of the T-P interval was seen in some animals with intact vagi (Figure If) it was impossible to generalize as to the mechanisms involved which mediate the cerebellar influence.

DISCUSSION

In view of the studies by Hoffer and co-workers (1966) it was not surprising to observe a reciprocal relationship between changes in BP and BF. For

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288 J. MITRA AND R. S . SNIDER

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FIGURE 2 Changes produced in blood pressure and blood flow records by electrical stimulation of nucleus fastigii. 500 pA (300/sec and 0.1 msec duration) electrical pulses applied to white matter just dorsal to right nucleus fastigii for 10 sec in bilateral vagotomized cat (on-off). At A, 10 sec and at B, 85 sec of tracing was removed. a : Blood pressure taken from right femoral artery. b: Blood flow taken from left femoral artery (0-5.0 ml/min vertical calibra- tion). Total duration of blood pressure change was 110 sec with maximal rise of 20 mm. Heart rate changed from 216 to 228. c: Blood pressure (100-150 mm). d: Blood flow; as above, except 0.2 ml of 2 % novocain was applied to stimulation site before stimulation. At A, 5 sec and at B, 40 sec of record was removed. The horizontal black line = 5 sec. In a and b the vascular resistance changed from 26.2 (prestimulation) to 19.4 (end of stimulation) to 16.2 (20 sec later). In c and d the vascular resistance changed from 22.0 (prestimulation) to 20.7 (at end of stimulation).

In e, f, g, the stimulation site was changed to ventral margin of left nucleus fastigii. The vagi were intact. (300/sec, 0.1 msec duration; 400 PA). Tracings removed A = 25 sec, B = 50 sec, C = 30 sec. In e blood flow (0-5.0 ml/min). f: EKG -.05 mV/cm g : EEG-left posterior hippocampus (100 pV/cm). The horizontal line = 3 seconds.

example, during the stimulation period there was an initial decrease in BF in the femoral artery while BP was rising. Hoffer 1965 has shown that the cerebellum can influence the redistribution of blood to the viscera and to skeletal muscle in a manner which allows increased BF in one region while decreased BF is occurring in another without alteration of systemic BP. The functional signi- ficance of this mechanism during exercise, for example, may deserve additional consideration.

That the present results are not due in artefactual

spread of current to the brain stem, is shown by the data in Figure 2 where focal injection of novocaine caused a diminution of the effects of electrical activation. Also shown in Figure 2a, 2b are the effects of stimulating afferents to the nuclei. These data resemble those published by Hoffer (1965) who stimulated the cerebellar cortex exclusively.

The data in Figure l a and l c also indicate that the same stimulation can induce both decreased B F and increased BP. Thus, there appears to be an overlap of representation of these two functions

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FASTIGIAL INFLUENCES ON BLOOD CIRCULATION 289

within NF. This must not be interpreted to mean that one is dependent on the other since Figure 2e shows that it is possible to obtain BF alterations without recordable evidences of BP changes. The recent studies of Miura and Reis (1969) indicate that the fastigial nucleus can mediate a pressor response which is relayed through the medullary paramedian reticular nucleus. Since this same nucleus receives a projection from the carotid sinus, then it can be said that there exists both anatomical and physiological evidence for the present report on changes in BP. The present observations made on changes in BF are more difficult to explain especially in view of the recent findings by Hockman, Livingston, and Talesnik (1972) that cerebellar stimulation can inhibit reflex vagal bradycardia and that forebrain structures are involved.

Originally, it was planned to use the EKG data obtained from the arm-to-arm leads only as a monitor for heart rate. However. EKG changes were consistently observed during periods of more prominent changes in BF and/or BP (Figure 1). Since BF and BP changes could be observed with- out accompanying EKG changes, the data would indicate that the EKG changes were not due to direct cerebellar influences on cardiac musculature but were due to unknown interactions between cardiovascular centers and the cerebellum. The prominent increase in size of the T wave (Figure lb) in the bilateral vagotomized animals, and the previous studies of Hoffer (1965) with methylatro- pine and phentolamine can be interpreted to indicate that prominent effects on the sympathetic nervous system can result from fastigial stimula- tion. It is recognized that a shift of the axis of the heart can account for small changes, but the prominent EKG changes shown in Figure 1 cannot be due solely to heart axis shifts.

EEG changes in the hippocampus were observed in approximately 1/3 of the animals (see Figures 1, 2). When present, an increased number of slow waves (2-5/sec) during the latter part of stimulation and/or early poststimulatory period was observed. Occasionally, the slow waves became more prominent following ‘off’ but they never continued for the total duration of the pressor change. They

were slightly faster in frequency than the pulse in the initial stimulatory and initial poststimulatory periods and were more prominent during the period of increased blood flow. However, this relationship was a capricious one since frequencies almost double the frequency of the pulse (Figure 1) could be found. Previous studies by Iwata and Snider (1959) have shown that cerebello-hippo- campal electrical interactions do exist but they have not yet been related to measurable changes in BF and BP. It is beyond the scope of the present paper to attempt this study.

ACKNOWLEDGMENTS

Supported by Public Health Service Grants NB 04592 and NB 04596.

REFERENCES

Ban, T., 1959, Cerebellarautonomicfunction. RecentAdvances in Research on the Nervous System 3 : 555-576.

Hockman, C. H., Livingston, K. E., and Talesnik, J., Cerebellar Modulation of Reflex Vagal Bradycardia. (In Press).

Hoffer, B. J., 1965, The effects of stimulation of the cere- bellum on the circulatory system. Ph.D. dissertation, University of Rochester.

Hoffer, B. J., Ratcheson, R., and Snider, R. S., 1966, The effects of stimulation of the cerebellum on the circula- tory system. Fed. Proc. 25: 701.

Iwata, K., and Snider, R. S., 1959, Cerebello-hippocampal influences on the electroencephalogram. Electroenceph. d in . Neurophysiol. 11: 439-446.

Miura, M., and Reis, D. J., 1969, Cerebellum: A pressor response elicited from the fastigial nucleus and its efferent pathway in brain stem. Brain Research 13: 595-599.

Moruzzi, G., 1938, Sur les rapports entre le paleocervelet et les reflexes vasomoteurs. Ann. Physiol. 14: 605-612.

Moruzzi, G., 1940, Paleocerebellar inhibition of vasomotor and respiratory carotid sinus reflexes. J. Neurophysiol. 3: 20-32.

Moruzzi, G., 1950, Problems in Cerebellar Physiology, Charles C. Thomas, Springfield, Ill.

Sawyer, C. H., Hilliard, J., and Ban, T., 1961, Autonomic and EEG responses to cerebellar stimulation in rabbits. Amer. J. Physiol. 200: 405412.

Zanchetti, A., and Zoccolini, A., 1954, Autonomic hypo- thalamic outbursts elicited by cerebellar stimulation. J. Neurophysiol. 17: 475483.

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