Data from: Co-expression of two subtypes of melatonin receptor on rat M1-type intrinsically photosensitive retinal ganglion cells

Intrinsically photosensitive retinal ganglion cells (ipRGCs) are involved
in circadian and other non-image forming visual responses. An open
question is whether the activity of these neurons may also be under the
regulation mediated by the neurohormone melatonin. In the present work, by
double-staining immunohistochemical technique, we studied the expression
of MT1 and MT2, two known subtypes of mammalian melatonin receptors, in
rat ipRGCs. A single subset of retinal ganglion cells labeled by the
specific antibody against melanopsin exhibited the morphology typical of
M1-type ipRGCs. Immunoreactivity for both MT1 and MT2 receptors was
clearly seen in the cytoplasm of all labeled ipRGCs, indicating that these
two receptors were co-expressed in each of these neurons. Furthermore,
labeling for both the receptors were found in neonatal M1 cells as early
as the day of birth. It is therefore highly plausible that retinal
melatonin may directly modulate the activity of ipRGCs, thus regulating
non-image forming visual functions.