Expression of a sarcoma proto-oncogene, c-lyn, was mapped in the adult
rat brain using immunohistochemistry. Lyn protein was prevalent in re
stricted cell populations of the olfactory bulb and the basal forebrai
n which included nuclei of accumbens, fundal striatum, bed stria, vent
ral pallidum and central amygdala as well as deep entorhinal and pyrif
orm cortices. Tightly packed Lyn-positive cells formed discrete multip
le stripes crossing perpendicular to the rostral limb of the anterior
commissure, and intense masses surrounding the caudal limb. In the tha
lamus, the habenula, anterodorsal nucleus and medial geniculate body,
together with the paraventricular hypothalamic nuclei, had prominent r
eactive neuronal somata and dendrites in the neuropil. The lateral sep
tal nucleus also had intense Lyn-positive neurons with overlapping den
dritic fields. In addition, scattered neurons were evenly distributed
throughout the striatum. The red, interpeduncular, auditory and trigem
inal tract nuclei were intensely reactive. The cerebellar molecular la
yer was uniformly labeled except for a few isolated fiber bundles in t
he lowest part of this layer. The granule cells adjacent to the Purkin
je cell layer appeared in reactive patches. In the spinal cord, the po
steromarginal nucleus had intense labeling. The significance of this h
ighly localized distribution pattern of Lyn protein may be related to
connections forming functional compartments serving signal transductio
n within specific central nervous system circuitry.