Precise Localisation of 5-HT_2A Receptors in the Rat Substantia Nigra

Abstract

The implications of the action of 5-hydroxytryptamine (5-HT) in substantia nigra function are poorly understood, although nigral 5-HT does appear to play a role in motor control, partly independent of dopamine (Oberlander et al., 1981). The substantia nigra receives 5-HT input from the dorsal raphe nucleus (Corvaja et al., 1993), and 5-HTimmunopositive axon terminals are in synaptic contact with both dopaminergic and nondopaminergic, postsynaptic, structures in the substantia nigra (Nedergaard et al., 1988; Moukhles et al., 1997). Experiments performed in vivo in the substantia nigra pars reticulata indicate a primarily inhibitory effect of 5-HT (Collingridge and Davies, 1981; Dray et al., 1976; Fibiger and Miller, 1977; Oberlander et al., 1981), whereas in in vitro studies 5-HT excited over three quarters of pars reticulata GABAergic cells (Rick et al., 1995). The action of 5-HT on pars compacta neurons is excitatory, acting through an inward rectifier current (Nedergaard et al., 1988; Nedergaard et al., 1991), although it can often have opposing effects on different neurons of the same class in the substantia nigra, and its overall physiological effect is far from simple (Dray et al., 1976; Collingridge and Davies, 1981; Nedergaard et al., 1988; Rick et al., 1995).