Intraspinal amino acid neurotransmitter activities are involved in the generation of rhythmic sympathetic nerve discharge in newborn rat spinal cord

Endogenous neurotransmitter activities underlying the sympathetic nerve dis charge (SND) generated by newborn rat spinal cord in vitro were investigate d using glutamatergic, glycinergic, and GABAergic antagonists. Under contro l conditions, the SND power spectrum had two major frequency components: sy nchronous bursting SND (bSND) with power dominant at <0.1 Hz and quasiperio dic SND (qSND) oscillating at 1-2 Hz. Using high Mg2+ solution (12-24 mM) t o block Ca2+-dependent synaptic transmission reversibly abolished SND. An i nterruption of glutamatergic neurotransmission by CNQX (non-NMDA receptor b locker) or L-AP4 (reducing the synaptic release of glutamate) failed to aff ect qSND, but consistently reduced bSND. Application of kynurenate, a broad -spectrum ionotropic glutamate receptor blocker, only caused an unstable SN D but did not reduce SND. In contrast, strychnine (Stry, glycine receptor a ntagonist) consistently reduced qSND in a dose-dependent manner. Bicucullin e (Bic, GAB(A), receptor antagonist) induced a synchronous bSND of irregula r rhythm, which could be further regularized by adding Stry. Bic-induced bS ND was reversibly abolished by CNQX or L-AP4. In conclusion, intraspinal gl ycinergic, GABAergic, and glutamatergic activities are involved in the gene ration of the spinal cord-derived SND in newborn rats. Intraspinal GABAergi c interneurons may tonically inhibit the glutamatergic bursting neurons tha t generate a synchronous bSND. Activities of these glutamatergic bursting n eurons may also be modulated by intraspinal glycinergic interneurons. (C) 2 001 Published by Elsevier Science B.V.