Abstract
Intrinsically photosensitive retinal ganglion cells (ipRGCs) respond to light and play roles in non-image forming vision, such as circadian rhythms, pupil responses, and sleep regulation, or image forming vision, such as processing visual information and directing eye movements in response to visual clues. The purpose of the present study was to identify the distribution, types, and proportion of melanopsin-immunoreactive (IR) cells in the retina of a nocturnal animal, i.e., the microbat (Rhinolophus ferrumequinum). Three types of melanopsin-IR cells were observed in the present study. The M1 type had dendritic arbors that extended into the OFF sublayer of the inner plexiform layer (IPL). M1 soma locations were identified either in the ganglion cell layer (GCL, M1c; 21.00%) or in the inner nuclear layer (INL, M1d; 5.15%). The M2 type had monostratified dendrites in the ON sublayer of the IPL and their cell bodies lay in the GCL (M2; 5.79%). The M3 type was bistratified cells with dendrites in both the ON and OFF sublayers of the IPL. M3 soma locations were either in the GCL (M3c; 26.66%) or INL (M3d; 4.69%). Additionally, some M3c cells had curved dendrites leading up towards the OFF sublayer of the IPL and down to the ON sublayer of the IPL (M3c-crv; 7.67%). Melanopsin-IR cells displayed a medium soma size and medium dendritic field diameters. There were 2–5 primary dendrites and sparsely branched dendrites with varicosities. The total number of the neurons in the GCL was 12,254.17 ± 660.39 and that of the optic nerve axons was 5,179.04 ± 208.00 in the R. ferrumequinum retina. The total number of melanopsin-IR cells was 819.74 ± 52.03. The ipRGCs constituted approximately 15.83% of the total RGC population. This study demonstrated that the nocturnal microbat, R. ferrumequinum, has a much higher density of melanopsin-IR cells than documented in diurnal animals.
Highlights
The intrinsically photosensitive retinal ganglion cells are retinal ganglion cells (RGCs) that are considered a third class of photoreceptors, which respond to light
Cells were classified according to the location of the cell body as follows: cell bodies conventionally located in the ganglion cell layer (GCL) and cell bodies displaced in the in black (GCL) and green (INL)
The present study revealed several important features of melanopsin-IR cells in the R. ferrumequinum retina
Summary
The intrinsically photosensitive retinal ganglion cells (ipRGCs) are retinal ganglion cells (RGCs) that are considered a third class of photoreceptors, which respond to light. Melanopsin-immunoreactive cells in microbat retina functional characteristics have been revealed [1,2,3,4,5] These retinal cells innervate many brain areas, including the suprachiasmatic nucleus (SCN), ventral subparaventricular zone (vSPZ), intergeniculate leaflet (IGL), pretectal area (PTA), olivary pretectal nucleus (OPN), and ventrolateral preoptic nucleus (VLPO). These areas contribute to non-image forming responses to light, which include the regulation of circadian rhythm, pupil constriction, and sleep regulation [6,7,8,9,10,11,12]. Recent studies demonstrated that ipRGCs contribute to vision projecting to vision-related areas such as the lateral geniculate nucleus (LGN) and superior colliculus (SC) [13,14,15,16]
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