Retinofugal projections in the mouse

Abstract

The laboratory mouse is increasingly a subject for visual system investigation, but there has been no comprehensive evaluation of this species’ visual projections. Here, projections were visualized and mapped following intraocular injection of cholera toxin B subunit. Tissue was processed using standard procedures applied to 30 Am free floating sections with diaminobenzidine as the chromogen. The mouse retina projects to approximately 46 brain regions, including 14 not previously described in this species. These include two amygdaloid nuclei, the horizontal limb of the diagonal band, the paraventricular hypothalamic nucleus, several visual thalamic nuclei, the paranigral nucleus, several pretectal nuclei, and the dorsal cortex of the inferior colliculus. Dense retinal patches were also observed in a narrow portion of the ipsilateral intermediate layer of the superior colliculus. The superior fasciculus of the accessory optic tract, which innervates the medial terminal nucleus, was also determined to be a terminal zone throughout its length. The results are compared with previous descriptions of projections from mouse intrinsically photoreceptive retinal ganglion cells, and with data from the hamster, Nile grass rat and laboratory rat. The retinal projection patterns are similar in all four species, although there are many differences with respect to the details. The specific visual functions of most retinorecipient areas are unknown, but there is substantial convergence of retinal projections onto regions concerned with olfaction and audition.

Signalling by melanopsin (OPN4) expressing photosensitive retinal ganglion cells

“…For example, it is unclear to what extent the properties of light responses vary between the distinct subclasses of M1-type pRGCs that project to the SCN and the OPN, and how these responses may be tailored to meet the different physiological roles performed by these cells. Indeed it should be noted that in total, pRGC innervations are detected for as many as 32 distinct brain regions, 32,33,80 and in the majority of these cases the subtypes of pRGCs innervating these areas, and the specific properties of light responses transmitted to these regions has received little attention. There are also significant gaps in our understanding of the melanopsin phototransduction signalling pathway.…”

Do the anterior and lateral thalamic nuclei make distinct contributions to spatial representation and memory?

“…The lateral thalami receive inputs from tectal-pretectal pathways, such as the superior colliculus, lateral geniculate nucleus, reticular thalamus, and direct retinal inputs (Morin & Studholme, 2014;Thompson & Robertson, 1987). The superior colliculus rests within secondary visual pathways often associated with the production of movements that orient, or reflexively attend, a subject toward visual targets (Grieve et al, 2000;Milnar & Goodale, 1984;Reep & Corwin, 2009), but these pathways have also been linked to a high degree of multi-modal processing, especially from somatosensory cues, which in rodents stem from the vibrissae (Bezdudnaya & Keller, 2008;Cooper et al, 1998;Robertson et al, 1980;Weldon & Best, 1992).…”

Architecture of retinal projections to the central circadian pacemaker

“…In addition, the SCN is the only region in the mouse brain that receives nearly equal inputs from the ipsilateral and contralateral eyes. This is quite surprising because all other retinorecipient brain regions are innervated ∼95% contralaterally (23). The importance of and the mechanism of how the SCN receives equal input from both eyes are essentially unexplored.…”

“…Furthermore, this simple demarcation of the SCN was challenged by studies showing that the entire mouse SCN receives dense innervation from ipRGCs (11). Because of the dense retinal innervation pattern, it has been difficult to decipher the identity of SCN neurons innervated by ipRGCs (22)(23)(24). Therefore, little is known about which cell types in the SCN receive retinal input.…”