Both monoaminergic and cholinergic afferent
projections to the neocortex putatively modulate
cortical morphogenesis and plasticity. Previously
we showed that neonatal,electrolytic lesions:
the cholinergic nucleus basalis magnocel!ularis
(nBM) projections to the neocortex result in
significant decreases-of cortical layer width that
correlate with cognitive alterations. Such electrolytic
lesions, performed for lack of a selective
neurotoxin in mice, may affect mono- aminergic
fibers of passage. Here, we investigate the effects
of neonatal 5,7 dihydroxytryptamine (5,7-DHT)
focal injections into the nBM region on cortical
laminar morphology in adult male and female
mice. 5,7-DHT lesions on the first postnatal day
resulted in significant cortical depletion of both
serotonin and norepinephrine that attenuated
with age. Generally, cortical layer widths
increased in response to the lesion; the effects
were layer, region, and sex specific. Previous
reports from our laboratories described longterm
behavioral alterations after comparable
focal, neonatal 5,7-DHT lesions. The studies
described here provide an anatomical basis for
such behavioral alterations. Our data suggest
that monoaminergic and cholinergic projections to the cortex may have opposite effects on the
developing cortical neuropil. Jointly, our
morphological and behavioral findings may
have important implications for a variety of
developmental disorders in humans and
provide some insights into sex differences in the
penetrance of these disorders.