Motor responses to microstimulation of the medullary pyramidal tract in the cat

Substantia nigra influences on the reticulospinal neurons: an electrophysiological and ionophoretic study in cats and rats

The influences exerted by the substantia nigra on reticulospinal neurons and the nature of the synaptic transmitter subserving these projections have been studied in adult cats and rats. Nigral stimulation evokes discharge changes in a significant number of reticulospinal cells (32.4% in cats and 39.1% in rats) on both ipsi- and contralateral sides. The responses were short-latency inhibitions (69.5% in cats and 76.5% in rats), short-latency excitations (22.2% in cats and 23.6% in rats) and in the remaining few cases long-latency excitations. Short-latency excitations, quite similar to the nigra-induced ones, were the predominant response pattern (95.2% in cats and 96.9% in rats) elicited on reticulospinal cells following stimulation of cerebral peduncle. The stimulation of substantia nigra in rats submitted to chronic ablation of sensorimotor cortex elicited only inhibitory responses while stimulation of nigral area in rats with intranigral injection of kainic acid was still capable of evoking short-latency excitations but not short-latency inhibitions. Therefore, the former can be ascribed to activation of corticoreticular fibers running in the cerebral peduncle whereas the latter can be considered as depending on activation of nigral efferents. The nigra-influenced cells were both 'fast' and 'slow' reticulospinal neurons and resulted mainly located in most rostral regions of reticular formation. Ionophoretic application of GABA suppressed the spontaneous firing of reticulospinal cells while no effect was observed following application of dopamine. The nigra-induced inhibitions were abolished by GABA-antagonist bicuculline and not by dopamine-antagonist fluphenazine.(ABSTRACT TRUNCATED AT 250 WORDS)

Influences of pyramidal tract on the subthalamic nucleus in the cat

In adult cats, with mesencephalic decerebration sparing the cerebral peduncles and ablation of the sensorimotor cortex, changes in firing of single cells of subthalamic nucleus (STN) were analyzed upon stimulation of ipsilateral medullary pyramidal tract (PT). Twenty-two out of 44 of the STN cells exhibited, following PT stimulation, discharge changes that in the greatest part of cases (91%) were excitatory in nature. Excitations, always followed by inhibitory rebound, appeared with latency values compatible with a monosynaptic linkage.

Pyramidal influences on ventral thalamic nuclei in the cat

In pericruciate cortex-ablated 'pyramidal cats', discharge changes in single neurons of ventral thalamic nuclei were studied, following stimulation of ipsilateral medullary (MPT) and contralateral cervical (CPT) pyramidal tract. It was seen that cells in ventrolateral nucleus, ventroanterior nucleus and ventromedial nucleus were not significantly (2.2%) modified by impulses coming from MPT and CPT. Conversely, a very high percentage (58.8%) of cells in ventrobasal complex (VB) responded to MPT stimulation (64.4% in ventroposterolateral nucleus, VPL, and 40.7% in ventroposteromedial nucleus, VPM). A considerable number (34.8%) of VPL cells responsive to MPT, were influenced by CPT, while none of the cells in VPM were. The most frequent effect observed in VB neurons, on MPT and CPT stimulation, was excitation followed by depression of discharge.

Pyramidal input to the intracerebellar nuclei of the cat

In unanesthetized cats it has been found that pyramidal volleys elicited upon medullary pyramidal tract stimulation were capable of modifying the discharge of 41% of intracerebellar nuclear cells, via pontocerebellar systems impinging predominantly on the lateral cerebellar cortex. The incidence of responsive cells was 80% in the dentate nucleus compared with 10% in the fastigial nucleus, 11% in the anterior and 12% in the posterior division of the interpositus nucleus. The response was in 59% of the cases excitation followed by inhibition, in 30% of the cases a pure excitation and in 11% of the cases a pure inhibition. Excitation, pure or followed by inhibition, had a mean latency of 5.78 ms and a mean duration of 12.21 ms, while inhibition displayed a mean latency of 9.03 ms and a mean duration of 34.64 ms. The possible functional significance of the pyramidal input to the lateral cerebellum is briefly discussed in relation to a possible convergence of pyramidal and associative impulses in single cerebellar neurons.