Interaction between cholinergic and catecholaminergic neurones in rat brain

Abstract

With the help of histochemical, biochemical and functional analyses of DA and NA in the rat central nervous system after treatment with various types of anti-cholinergic drugs, the interaction between cholinergic and catecholaminergic neurones has been studied. The histochemical analyses showed that the DA depletion induced by tyrosine hydroxylase inhibition from the neostriatal and limbic but not the median eminence DA nerve terminals was slightly reduced by the anticholinergic drugs. On the contrary the NA depletion induced by tyrosine hydroxylase (H44/68) inhibition was increased in the hypothalamic and cortical NA nerve terminals. After DA-β-hydroxylase inhibition with FLA-63, an increased depletion of NA was observed only in the cortical NA nerve terminals. It is suggested that the amine turnover is slightly reduced in the telencephalic DA nerve terminals and increased in the NA nerve terminals. The neuroleptic-induced increase in DA turnover seen after H44/68 was partly reduced by anticholinergic drugs. The increase in NA turnover, however, was not influenced by either selective DA or combined DA and NA receptor blockade. The anticholinergics counteracted neuroleptic-induced cataleptic behaviour in various functional tests, whereas the immobilization was not affected. The interpretation is given that neostriatal cholinergic synapses mainly act independently of the DA synapses and that the cholinergic neostriatal projection has a modulatory effect on locomotor activities induced by the nigro-neostriatal DA system. In this connexion, the limited beneficial effects of anticholinergic therapy in Parkinson's disease is discussed. The results suggest that the activity in the ascending DA neurones can partly be regulated by two cholinergic systems, one to the neostriatum and one striato-nigral cholinergic tract.