Ka. Coleman et J. Mitrofanis, ORGANIZATION OF THE VISUAL RETICULAR THALAMIC NUCLEUS OF THE RAT, European journal of neuroscience, 8(2), 1996, pp. 388-404
The visual sector of the reticular thalamic nucleus has come under som
e intense scrutiny over recent years, principally because of the key r
ole that the nucleus plays in the processing of visual information. De
spite this scrutiny, we know very little of how the connections betwee
n the reticular nucleus and the different areas of visual cortex and t
he different visual dorsal thalamic nuclei are organized. This study e
xamines the patterns of reticular connections with the visual cortex a
nd the dorsal thalamus in the rat, a species where the visual pathways
have been well documented. Biotinylated dextran, an anterograde and r
etrograde tracer, was injected into different visual cortical areas [1
7; rostral 18a: presumed area AL (anterolateral); caudal 18a: presumed
area LM (lateromedial); rostral 18b: presumed area AM (anteromedial);
caudal 18b: presumed area PM (posteromedial)] and into the different
visual dorsal thalamic nuclei (posterior thalamic, lateral posterior,
lateral geniculate nuclei), and the patterns of anterograde and retrog
rade labelling in the reticular nucleus were examined. From the cortic
al injections, we find that the visual sector of the reticular nucleus
is divided into subsectors that each receive an input from a distinct
visual cortical area, with little or no overlap. Further, the resulti
ng pattern of cortical terminations in the reticular nucleus reflects
largely the patterns of termination in the dorsal thalamus. That is, e
ach cortical area projects to a largely distinct subsector of the reti
cular nucleus, as it does to a largely distinct dorsal thalamic nucleu
s. As with each of the visual cortical areas, each of the visual dorsa
l thalamic (lateral geniculate, lateral posterior, posterior thalamic)
nuclei relate to a separate territory of the reticular nucleus, with
little or no overlap. Each of these dorsal thalamic territories within
the reticular nucleus receives inputs from one or more of the visual
cortical areas. For instance, the region of the reticular nucleus that
is labelled after an injection into the lateral geniculate nucleus en
compasses the reticular regions which receive afferents from cortical
areas 17, rostral 18b and caudal 18b. These results suggest that indiv
idual cortical areas may influence the activity of different dorsal th
alamic nuclei through their reticular connections.