Dendro axonic transmission. I. Evidence from receptor binding of dopaminergic and cholinergic agents

Spiroperidol binding in the substantia nigra and QNB and a-bungarotoxin ( a-Btx) binding in the neostriatum were measured in rats with lesions designed to produce selective alterations in pre- and postsynaptic neuronal processes. The objective was to determine whether presynaptic receptor sites may exist for dendritically released transmitters. Spiroperidol was used to measure dopaminergic receptor sites while QNB and a-Btx were used to measure muscarinic and nicotinic cholinergic receptor sites, respectively. The binding results were correlated with measurements on the individual striata of tyrosine hydroxylase (as an index of the integrity of nigrostriatal dopaminergic neurons) and of glutamic acid decar☐ylase (as an index of the integrity of striatal interneurons and descending striatonigral pathways). The results indicate that muscarinic receptor sites in the striatum are on neuronal perikarya or dendrites but nicotinic receptor sites are on afferent dopaminergic and corticostriatal neurons; in the substantia nigra spiroperidol binding is on afferent striatonigral neurons. The results, together with available biochemical and morphological data, are used to support the hypothesis that communication at many CNS synapses may involve a neurotransmitter dialog rather than a monolog. If true, this will affect interpretations of many pharmacological, behavioral and physiological experiments.