Retinal Projections to the Pretectum, Accessory Optic System and Superior Colliculus in Pigmented and Albino Ferrets

Abstract

Retinal projections to the pretectal nuclei, accessory optic system and superior colliculus in pigmented and albino ferrets were studied using anterograde tracing techniques. Both Nissl- and myelin-stained material was used to identify the pretectal nuclei, nuclei of the accessory optic system and the layers of the superior colliculus. Following monocular injection of either horseradish peroxidase or rhodamine-B-isothiocyanate, four pretectal nuclei, including the nucleus of the optic tract, posterior pretectal nucleus, anterior pretectal nucleus and the olivary pretectal nucleus, could be identified to receive direct retinal input in both pigmented and albino strains. In the accessory optic system, retinal terminals were observed in the dorsal, lateral and medial terminal nuclei as well as in the interstitial nucleus of the superior fasciculus, posterior fibres. The retinal projection to the superior colliculus was found to innervate the three superficial layers. The retinal projections to the pretectal nuclei and nuclei of the accessory optic system in the pigmented animals were bilateral, although the label was most dense contralateral to the injected eye. Ipsilateral retinal projections to the pretectal nuclei and nuclei of the accessory optic system appeared to be absent in albino ferrets, i.e. they were invisible with our methods. In both pigmented and albino ferrets retinal terminals in the contralateral superior colliculus densely innervated the three superficial layers. In both strains the ipsilateral projection appeared as clusters which were absent in rostral and caudal poles. In pigmented animals the ipsilateral projection was much denser and more extensive than in albinos. Following injection of retrograde tracers into the brainstem at the level of the dorsal cap of the inferior olive, retrogradely labelled neurons in the pretectum were found in the ipsilateral nucleus of the optic tract. Their somata overlapped mainly with scattered retinal terminals close to the pretectal surface and rarely or not all with the deeper prominent terminal clusters. In the accessory optic system, inferior olive projecting neurons were observed in all four ipsilateral nuclei and fully coincided with the retino-recipient zones. In the superior colliculus, retrogradely labelled neurons were found contralateral to the injection site in the deep layers.

Optokinetic Deficits in Albino Ferrets (Mustela putorius furo): A Behavioral and Electrophysiological Study

“…There are several retinal aberrations caused by albinism (Jeffery, 1997), a reduction of ipsilaterally projecting retinofugal axons (Morgan et al, 1987;Zhang and Hoffmann 1993), an aberrant, albeit well developed retinal projection to subcortical visual structures, a distorted retinotopic map in visual cortex but not in the superior colliculus (Quevedo et al, 1996;Akerman et al, 2003), as well as a lack of binocular neurons in visual cortex. None of these changes seem to have direct bearing on the lack of OKR.…”

Experimentally Induced Retinal Projections to the Ferret Auditory Thalamus: Development of Clustered Eye-Specific Patterns in a Novel Target

“…Thus for example, the ferret retinogeniculate projection (Fig. 12 A) segregates into parallel eye-specific layers (Linden et al, 1981) and on /off sublayers (Stryker and Zahs, 1983;Hahm and Sur, 1988;Hahm et al, 1991), whereas the retinocollicular projection segregates into a periodic pattern of eye-specific clusters (Zhang and Hoffmann, 1993). The generation of specific terminal patterns might depend on intrinsic features of the target.…”

Laminar profile of visual response properties in ferret superior colliculus

“…In the cat, superficial collicular layers additionally receive direct inputs from early visuotopically organized cortical areas such as cytoarchitectonic areas 17, 18, 19, and to a lesser extent area 21a (Harting et al 1992). In contrast to superficial collicular layers, in both cats (Berson 1988) and ferrets (Zhang and Hoffmann 1993), there is virtually no direct retinal input to the deep layers. Furthermore, unlike superficial layers, direct cortical inputs to deep collicular layers in both cats (Harting et al 1992) and ferrets (Manger et al 2010) originate from the "higher-order" visuotopically organized cortical areas.…”

“…The sources of afferent pathways innervating superficial and deep layers reflect the functional dichotomy within the SC, with superficial layers being innervated predominantly by retinal and early visual cortical projections, and deeper layers receiving higher visual and motor cortical projections (Harting et al 1992;Manger et al 2010;Zhang and Hoffmann 1993). In addition to extensive horizontal connections within individual layers, superficial neurons form axon collaterals that terminate in deep layers, forming a direct superficial-to-deep connection in the SC (Grantyn et al 1984;Lee 1993, 1997;Isa et al 1998).…”