• The Korean Journal of Physiology and Pharmacology
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• v.8 no.3
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• pp.129-132
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• 2004

Single unit responses of the ventral posterior medial (VPM) thalamic neurons to stimulation were monitored in anesthetized rats during activation of contralateral primary somatosensory (SI) cortex by GABA antagonist. The temporal changes of afferent sensory transmission were quantitatively analyzed by poststimulus time histogram (PSTH). Mainly, afferent sensory transmission to VPM thalamus was facilitated (15 neurons of total 23) by GABA antagonist (bicuculline) applied to contralateral cortex, while 7 neurons were suppressed. However, when ipsilateral cortex was inactivated by GABA agonist, musimol, there was significant suppression of afferent sensory transmission of VPM thalamus. This suppressed responsiveness by ipsilateral musimol was not affected by bicuculline applied to contralateral cortex. These results suggest that afferent transmission to VPM thalamus may be subjected to the interhemispheric modulation via ipsilateral cortex during inactivation of GABAergic neurons in contralateral SI cortex.

• Journal of Korean Neurosurgical Society
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• v.29 no.8
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• pp.985-994
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• 2000

Objective : There are some advantages of trigeminal evoked potential(TEP) recording compared to other somatosensory evoked potential(SSEP) recordings. The trigeminal sensory pathway has a pure sensory nerve branch, a broader receptive field in cerebral cortex, and a shorter pathway. Despite these advantages, there is little agreement as to what constitutes a normal response and what wave forms truly characterize the intraoperative TEP. This study presents the normative data of TEP recorded on the epidural surface of the rat with a platinum ball electrode. Materials & Methods : Under general anesthesia with urethane, the adult Sprague-Dawley male rats(300-350g) were given electrical stimulation with two stainless steel electrodes which were inserted into the subcutaneous layer of the area around whiskers. A reference electrode was positioned in the temporalis muscle ipsilateral to the recording site. Results : TEPs were recorded in the Par I area of somatosensory cortex and recorded most apparently on the point of 2mm posterior from the bregma and 6mm lateral from the midline. The typical wave form consisted of 5 peaks (N1-P1-N2-P2-N3 according to emerging order, upward negativity). Each latency to corresponding peaks was not influenced by the different intensities of stimulation, especially from 1 to 5mA. Average latencies of 5 peaks were in the following order ; 7.7, 11.1, 15, 22.3, 29.4ms. There was also no significant difference between latencies before and after administration of muscle relaxant(pancuronium). For the electrophysiological localization of recorded waves, the action potential of a single unit was recorded with glass microelectrode(filled with 2M NaCl, $3-5M{\Omega}$) in the thalamus of rat. A sharp wave was recorded in the VPM nucleus, in which the latency was shorter than that of N1. This suggests that all 5 peaks were generated by neural activities in the suprathalamic pathway. Conclusion : In terms of recording near-field potentials, our data also suggests that TEP in the rat may be superior to other SSEPs. In overall, these results may afford normative data for the studies of supratentorial lesions such as hydrocephalus or cerebral ischemia which can have an influence on near-field potentials.