LOW EXPRESSION OF EXTRACELLULAR-MATRIX COMPONENTS IN RAT-BRAIN STEM REGIONS CONTAINING MODULATORY AMINERGIC NEURONS

Extracellular matrix proteoglycans, particularly those accumulated in perineuronal nets (PNs), have been shown to form characteristic distri bution patterns in cortical and subcortical regions of adult mammals. Their involvement in sustaining mechanisms that are especially related to fast activities of neurons has been discussed as one of the possib le functions. The present study deals with the spatial organization of extracellular matrix proteoglycans in brain stem regions that contain aminergic neurons, such as substantia nigra, ventral tegmental area ( VTA), raphe nuclei and locus coeruleus (LC). As these nuclei are known to influence brain activity by modulatory functions exerting patterns of slow electric activity, it could be expected that PNs would be abs ent around aminergic cells. The staining of PNs with Wisteria floribun da agglutinin (WFA) was combined with the detection of catecholaminerg ic neurons by tyrosine hydroxylase immunoreactivity and of serotonergi c neurons by tryptophan hydroxylase (TH) immunoreactivity using double fluorescence microscopy. It was found that the catecholaminergic and serotonergic neurons in the nuclear accumulations, as well as those sc attered in adjacent regions, were not ensheathed by PNs. In contrast, several non-aminergic neurons intermingled with aminergic neurons in t he raphe nuclei, in the substantia nigra pars compacta (SNC) and in th e VTA, as well as many cells in the reticular part of the substantia n igra, were found to be surrounded by PNs. It can be concluded from the se results that the absence of PNs around aminergic brain stem neurons , also previously shown for cholinergic basal forebrain neurons, appea rs as a characteristic feature common to cells that exert slow modulat ory functions. (C) 1998 Elsevier Science B.V. All rights reserved.