A Dual Immunoperoxidase Labelling Method to Study the Ultrastructural Relationships between Choline Acetyltransferase- and Neuropeptide Y-Containing Neurons in the Rat Striatum

Abstract

In the striatum, neuropeptide Y (NPY) and choline acetyltransferase (ChAT) are to be found in populations of aspiny neurons with distinct morphological features. Indeed, immunocytochemical studies using selective antibodies have indicated that NPY-labelled neurons are medium-sized type IV aspiny neurons (Vuillet et al., 1989b), whereas ChAT-labelled neurons belong mainly to the category of large neurons in the striatum (Bolam et al., 1984). Neurochemical studies in combination with lesion experiments and morphological studies have provided evidence that both NPY- and ChAT- containing neuronal populations represent interneurons, receive afferents from extrinsic origin (Chang, 1988; Vuillet et al., 1989a; 1989b), and provide synaptic input to medium-sized spiny neurons that are predominantly striatal output neurons (Izzo and Bolam., 1988; Vuillet et al, 1989b). These data suggest that both cholinergic and NPY interneurons in the striatum may play an integrative role which may be of particular relevance in the control of sensorimotor function. The question of whether or not synaptic interactions exist between those NPY and cholinergic interneurons then appears of great interest for further functional resolution of the striatal network. Two major difficulties emerge to answer this question: both types of neurons represent less than one percent of the total striatal neuron population; in addition, besides the paucity of NPY terminals, both ChAT and NPY axonal boutons form predominantly symmetrical type synapses that are difficult to characterize.