Raphe Stimulation-Evoked Modulation of Postsynaptic Responses by Neurons of the Cat Somatosensory Cortex Activated by Stimulation of Nociceptors |
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Authors: | T Sh Labakhua T K Janashia G I Gedevanishvili |
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Institution: | (1) Department of Neurosurgery, Experimental Neurosurgery Section, Medical Faculty, RWTH Aachen University, Pauwelsstrasse 30, 52074 Aachen, Germany; |
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Abstract: | We studied the effects of electrical stimulation of the raphe nuclei (RN) of the cat brain on postsynaptic potentials developing
in somatosensory cortex neurons activated by nociceptive influences. Intracellular records were obtained from 15 cells, which
were either selectively excited by stimulation of nociceptors (intense electrical stimulation of the dental pulp) or activated
by both the above nociceptive and non-nociceptive (moderate stimulations of the infraorbital nerve or thalamic ventroposteromedial
nucleus, VPMN) influences. In neurons of both groups, stimulation of both nociceptive afferents and the VPMN evoked complex
responses (EPSP–AP–IPSP; IPSPs were 200 to 300 msec long). In some studied cortical neurons, isolated electrical stimulation
of the RN (which caused the release of serotonin, 5-HT, in the cortex) resulted in relatively short-latency synaptic excitation,
while inhibition was observed in other cells. In the case where stimulation of the RN was used as conditioning influence,
such stimulation (independently of the kind of the initial response to RN stimulation) led to long-latency and long-lasting
suppression of all components of the synaptic reactions evoked by excitation of nociceptors. The maximum of inhibition was
observed at test intervals of 300 to 800 msec. The mechanisms underlying modulatory influences coming from the 5-HT-ergic
brainstem system to neurons of the somatosensory cortex, which are activated by excitation of high-threshold (nociceptive)
afferent inputs, are discussed. |
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Keywords: | |
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