NADPH-DIAPHORASE IN THE DEVELOPING BRAIN OF THE DEGU (OCTODON-DEGUS),RELATION TO AMINERGIC TRANSMITTERS

The cellular and spatial distribution of the presumptive retrograde tr ansmitter nitric oxide, detected by NADPH-diaphorase histochemistry an d of immunocytochemically labeled monoaminergic fiber systems was comp ared in regions of the medial prefrontal cortex of the precocious rode nt Octodon degus. The staining patterns at two postnatal stages (P0 an d P14) were compared to those found in adult animals (P90). At birth, NADPH-diaphorase positive neurons were found in all cortical layers of the anterior cingulate, infralimbic and prelimbic cortex. During post natal development the number of diaphorase-positive cells gradually de creased in layers Il-VI and remained unchanged in layer I of these cor tical regions. All NADPH-diaphorase positive neurons appeared to be sp ineless and pyramidal cells never contained NADPH-diaphorase. No coloc alization of NADPH-diaphorase with either serotonin or TH was detectab le. However, at all developmental stages the somata and proximal dendr itic shafts of some of the NADPH-diaphorase containing bi-or multipola r neurons in layers V-VI were contacted by serotonin-and tyrosine hydr oxylase-immunoreactive fibers. In a subpopulation of GABAergic interne urons in the deeper layers (V-VI) NADPH-diaphorase activity was coloca lized with calbindin-D 28 k immunoreactivity. The abundance of nitride rgic systems in regions of the medial prefrontal cortex already at bir th together with their close spatial relationship with monoaminergic a fferent systems as well as local GABAergic units may indicate a yet to determine role of these transmitter systems in early learning.