N. Lavine et al., A POPULATION OF NICOTINIC RECEPTORS IS ASSOCIATED WITH THALAMOCORTICAL AFFERENTS IN THE ADULT-RAT - LAMINAL AND AREAL ANALYSIS, Journal of comparative neurology, 380(2), 1997, pp. 175-190
In the adult rat brain, a prominent population of nicotinic cholinocep
tors binds H-3-nicotine with nanomolar affinity. These receptors are a
bundant in most thalamic nuclei and in neocortical layers 3/4, which r
eceive a major thalamic input. To test whether cortical nicotinic rece
ptors are associated with thalamocortical afferents, unilateral excito
toxic (N-methyl-D-aspartate) lesions were made in one of four thalamic
nuclear groups (anterior, ventral, medial geniculate, or dorsal later
al geniculate) or in temporal cortex. After 1 or 4 weeks of survival,
cortical H-3-nicotine binding was quantified via autoradiography. Thal
amic lesions resulted in a partial loss of H-3-nicotine binding in ips
ilateral cerebral cortex. In each thalamic lesion group, the greatest
decrease (35-45%) occurred within the cortical layers and area (i.e.,
cingulate, parietal, temporal, or occipital cortex) receiving the dens
est thalamocortical innervation. Binding of H-3-nicotine was also redu
ced within the thalamus local to the lesion, particularly at the longe
r survival time. Saturation analysis, performed in frontoparietal cort
ical tissue homogenates following ventral thalamic lesions, revealed a
significant (34%) reduction in receptor density but not affinity. Dir
ect excitotoxic lesions of the neocortex (temporal cortex) tended to p
reserve H-3-nicotine binding in layers 3/4, despite local neuronal los
s. These results, taken with other published findings, suggest that so
me nicotinic cholinoceptors in adult rat cerebral cortex are located o
n thalamocortical terminals. This organizing principle appears to appl
y not only to sensory and motor relay projections but also to associat
ion nuclei that project to allocortical areas. These receptors may pro
vide a local mechanism for nicotinic cholinergic modulation of thalamo
cortical input. (C) 1997 Wiley-Liss, Inc.