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EFFECT OF COOLING THE DENTATE NUCLEUS ON HAND MOVEMENT OF THE MONKEY. TO RU_T§UJ!MgT_OI±_HI§AE_GEMBA ~ _ _ ~ _ § ~ § ~ ! . . . . . ~ £ ~ e ~ n ~ _ ~ ! _ ~ b ~ § J ~ 2 ~ ± _ ! ~ ! ~ _ ~ g L ~ £ ~ i _ ~ n _ ~ b ~ _ ~ _ 9 ~ _ _ ~ ! ~ ! ~ K#oto Univers i tz , K~oto 606, Japan.

- The-f~nct ional-- r -o~e-of- the--ce~ebel lum in voluntary movement was invest igated in two Japanese monkeys performing v i s u a l l y - i n i t i a t e d react ion- t ime hand movement and s e l f - i n i t i a t e d movement tasks. Electrodes fo r recording cor t i ca l f i e l d po ten t ia ls were chron ica l l y implanted on the surface and at about 2.5-3.0mm depth in the cortex and guide tubes fo r a cool ing probe were set aiming a t the den ta te nucleus. The coo l i ng probe has a vacuum j a c k e t so as to generate low temperatures only at i t s very t i p . In the v isual task, cool ing the dentate nucleus i p s i l a t e r a l to the operant hand (O°C at the t i p ) revers ib l y increased the react ion time and reduced the size of sur face-negat ive, depth-pos i t ive (s-N, d-P) premevement f i e l d po ten t ia l s in the motor cortex con t ra la te ra l to the hand. This s-N, d-P potent ia l is movement-related and is fol lowed by movement with an almost constant in te rva l o f about lOOms in the normal condi t ion, but during cool ing the i n t e r v a l was remarkab ly pro longed and dev ia ted . By s h i f t i n g the coo l i ng probe to d i f f e r e n t distances from the nucleus, there was found a close co r re la t i on between the decrease in size of the potent ia l and delay in react ion time. Also, in the s e l f - i n i t i a t e d movement task, the cool ing reduced the size of the s-N, d-P readiness potent ia l in the motor cortex. In both tasks, no changes were observed in the po ten t ia ls in other co r t i ca l areas such as p re f ron ta l , premotor, and somatosensory cor t ices. These f ind ings support the idea that the motor command fo r these tasks comes to the motor cortex through the cerebe l lo - tha lamo-cor t i ca l pathway including the dentate nucleus and produces the s-N, d-P potent ia l as EPSP currents in pyramidal neurons.

THALAMIC PROJECTIONS TO THE POSTERIOR PARIETAL CORTEX IN JAPANESE MONKEYS (Macaca fuscata). KATSUMA NAKANO, TETSURO KAYAHARA, YOSHIHIRO KUGA, AND TATSUHIRO SAWADA, Department of Anatomy, School of Medicine, Mie University, Tsu, Mie 514, Japan.

Using anterograde and retrograde axonal transport techniques of wheat germ agglutinin conjugat- ed peroxidase (WGA-HRP), we investigated thalamic projections to the posterior parietal cortex in Japanese monkeys (Macaca fuscata). Experiments were performed on 9 monkeys under ketamine and nembutal anesthesia with specific precautions. Neurons projecting to area 7 were observed in the nucleus ventralis anterior pars magnocellularis, nucleus pulvinaris medialis (Pul m), intralaminar nuclei, and the medial parts of nucleus ventralis lateral is pars caudalis (VLc) and nucleus ven- t ra l is lateral is pars postrema (VLps). Neurons projecting to area 5 were seen in the nucleus ventralis lateral is pars oral is, nucleus ventralis lateral is pars medialis, nucleus pulvinaris oralis (Pul o), nucleus centrum medianum, intralaminar nuclei, and the lateral parts of nucleus lateral is posterior (LP), VLps and VLc. Terminal labels transported anterogradely were also ob- served in the LP, VLc, VLps and Pul o with area 5 injection, and in the Pul m, VLps, nucleus cen- t ra l is lateralis, of intralaminar nuclei, and in the ventral part of nucleus lateral is dorsalis with area 7 injection. Our data suggest that some motor information relay via the motor thalamic nuclei to the posterior parietal lobe where higher order neural function appear to engage.

INPUT-OUTPUT PROPERTIES OF RETICULAR NEURONS AROUND THE TRIGEMINAL MOTOR NUCLEUS IN THE RAT. TOMIO INOUE*, YUJI MASUDA*, OSAMU SAITO*, TADASHI NAGASHIMA* AND TOSHIFUMI MORI~OTO, Dept. Oral Phy~o-r~.,-Osa-~i-~__~-ac. Dent., Suita, ~a~

Previous study has shown that cortically-induced rhythmic jaw movements (CRJMs) are modulated by intraoral stimulation. To analyze the neuronal mechanisms underlying this modulation, neurons showing a rhythmic alteration in firing frequency during CRJMs were examined in the brain stem of anesthetized rats. Forty-three rhythmically-activated neurons were found in the supratrigeminal area and reticular formation medial to the oral nucleus of the trigeminal spinal nucleus. Most of these neurons responded either to stimulation of the trigeminal sensory branches and/or passive jaw opening. Nine of these neurons responded to antidromic stimulation of the ipsilateral masseteric motoneuron pool. The field potential in the ipsilateral masseteric motoneuron pool was averaged after spike potentials from four single neurons of antidromically-activated neurons. Negative or positive potentials were revealed in all cases and monosynaptic connection of these neurons to masseteric motoneurons are suggested. Antidromically-activated neurons might play a role in the control of jaw movements.