Original Article

Involvement of medullary tail-flick related neurons in descending facilitation evoked by chemical stimulation of rat lateral habenular nucleus

Authors: Luo-Xiu Huang, Zhen-Feng Cheng

Abstract

AIM: To study effects of sodium L-glutamate microinjection into lateral habenular nucleus (LHN) of rats on the firing of medullary tail-flick related neurons and tail-flick reflex (TF).
METHODS: Using synchronous recording of unitary neuronal discharges and TF induced by noxious heat.
RESULTS: Chemical stimulation of LHN induced an excitement of the on-cell spontaneous activity, an inhibition of the off-cell spontaneous activity with an enhancement of their TF related responses. The spontaneous firing rate of on-cells increased from 5.8 +/- 2.2 Hz to 10.9 +/- 3.4 Hz while the spontaneous firing rate of off-cells decreased from 11.8 +/- 2.2 Hz to 6.1 +/- 2.2 Hz. Meanwhile the TFL was shortened from 4.04 +/- 0.17 s to 2.97 +/- 0.13 s.
CONCLUSION: The chemical stimulation of LHN produced a facilitating action on nociceptive spinal defensive reflex. This effect is brought out by the cooperation of on- and off-cells.
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