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

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.