[Coexistence of cholinergic and nitrergic neurotransmitters in the spinal cord of rabbits]

Nitric oxide (NO) plays a major role as a neuronal messenger molecule. NO has been assumed to act as a retrograde signalling molecule that modulates transmitter release. Acetylcholine (ACh) is known to function as a typical neurotransmitter. In the present work the presence of both transmitters (NO and ACh) and their possible relations in the rabbit spinal cord were examined. In our experiments histochemical methods for the visualisation of acetylcholinesterase (AChE) and NADPH diaphorase (NADPH-d) were used. Both histochemical methods were performed separately and together on the same sections of the thoracic spinal cord. NADPH-d positive dark blue stained neurons were mainly detected in superficial and deep layers of dorsal horn, preganglionic autonomic neurons and pericentral area (1). The presence of AChE positive amber yellow neurons was confirmed mostly in motoneurons located in ventral horns and then in neurons of the intermediate zone. Except for the above mentioned also double-labeled neurons containing both yellow and dark blue histochemical product were noticed. Their presence was confirmed in the intermediate zone and in the pericentral area. Thus, the coexistence of NADPH-d and AChE was confirmed in the area of interneurons. These observations suggest that NO may play a role in the control of cholinergic neuronal activity and that NO can be involved in the modulation of synaptic transmission. (Fig. 9, Ref. 21.)