INFLUENCE OF DIFFERENT PUTATIVE NEUROTRANSMITTERS ON ACh RELEASE FROM THE BRAIN AND SPINAL CORD

Abstract

The influence of putative neurotransmitters on acetylcholine (ACh) output from cholinergic fibres of the mammalian brain and of the frog spinal cord is discussed. The following effects can be listed as based on existing evidence. Drugs which stimulate dopamine release or dopamine receptors enhance ACh output from the cerebral cortex but decrease ACh output from the caudate nucleus. Opposite effects are seen by administering dopamine antagonists. Noradrenergic systems seem to depress ACh output in the cerebral cortex and spinal cord. No clear effect of the serotoninergic system on spontaneous ACh output has been demonstrated; however, indirect evidence suggests a modulating influence of 5HT on the cholinergic neurons ascending to the cortex. The addition of GABA to the bathing medium brings about a decrease in ACh output from the frog spinal cord. Opposite effects are seen following the addition of GABA antagonists (Picrotoxin and tutin). An increase in ACh output from the spinal cord also follows the application of excitatory aminoacids such as glutamic acid and its agonist kainic acid.