Thalamic projections to the posterior parietal cortex in Japanese monkeys (Macaca fuscata)

$68 EFFECT OF COOLING THE DENTATENUCLEUSON HANDMOVEMENTOF THE MONKEY. TORU_T§UJ!MgT_OI±_HI§AE_GEMBA ~__~_§~§~! ..... ~£~e~n~_~!_~b~§J~2~±_!~!~_~gL~£~i_~n_~b~_~_9~__~!~!~ K#oto U n i v e r s i t z , K~oto 606, Japan. The-f~nctional--r-o~e-of-the--ce~ebellum in voluntary movement was investigated in two Japanese monkeys performing v i s u a l l y - i n i t i a t e d r e a c t i o n - t i m e hand movement and s e l f - i n i t i a t e d movement tasks. Electrodes f o r recording c o r t i c a l f i e l d p o t e n t i a l s were c h r o n i c a l l y implanted on the surface and at about 2.5-3.0mm depth in the cortex and guide tubes f o r a cooling probe were set aiming a t the d e n t a t e nucleus. The c o o l i n g probe has a vacuum j a c k e t so as t o g e n e r a t e low temperatures only at i t s very t i p . In the visual task, cooling 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 ) r e v e r s i b l y increased the reaction time and reduced the size of surface-negative, d e p t h - p o s i t i v e (s-N, d-P) premevement f i e l d p o t e n t i a l s in the motor cortex c o n t r a l a t e r a l to the hand. This s-N, d-P p o t e n t i a l is movement-related and is followed by movement with an almost constant i n t e r v a l of about lOOms in the normal condition, but during cooling the i n t e r v a l was r e m a r k a b l y p r o l o n g e d and d e v i a t e d . By s h i f t i n g the c o o l i n g probe t o d i f f e r e n t distances from the nucleus, there was found a close c o r r e l a t i o n between the decrease in size of the p o t e n t i a l and delay in reaction time. Also, in the s e l f - i n i t i a t e d movement task, the cooling reduced the size of the s-N, d-P readiness p o t e n t i a l in the motor cortex. In both tasks, no changes were observed in the p o t e n t i a l s in other c o r t i c a l areas such as p r e f r o n t a l , premotor, and somatosensory c o r t i c e s . These f i n d i n g s support the idea that the motor command f o r these tasks comes to the motor cortex through the c e r e b e l l o - t h a l a m o - c o r t i c a l pathway including the dentate nucleus and produces the s-N, d-P p o t e n t i a l as EPSP currents in pyramidal neurons. -

THALAMIC PROJECTIONSTO THE POSTERIORPARIETAL CORTEX IN JAPANESEMONKEYS(Macaca fuscata). KATSUMA NAKANO, TETSUROKAYAHARA, YOSHIHIROKUGA, AND TATSUHIROSAWADA, Department of Anatomy, School of Medicine, Mie University, Tsu, Mie 514, Japan. Using anterograde and retrograde axonal transport techniques of wheat germ agglutinin conjugated 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 lateralis pars caudalis (VLc) and nucleus vent r a l i s lateralis p a r s postrema (VLps). Neurons projecting to area 5 were seen in the nucleus ventralis l a t e r a l i s pars oralis, nucleus ventralis lateralis pars medialis, nucleus pulvinaris oralis (Pul o), nucleus centrum medianum, intralaminar nuclei, and the lateral parts of nucleus lateralis posterior (LP), VLps and VLc. Terminal labels transported anterogradely were also observed in the LP, VLc, VLps and Pul o with area 5 injection, and in the Pul m, VLps, nucleus cent r a l i s lateralis, of intralaminar nuclei, and in the ventral part of nucleus lateralis 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.