Pattern of striate cortical projections to the pretectal complex in the guinea pig

Abstract

The primary goal of this study was to determine whether the striate cortex (Oc 1) of the guinea pig projects to the pretectal nucleus of the optic tract (NOT), the first postretinal station of the horizontal optokinetic pathway, and, if so, to analyze the anatomical organization of this cortico-NOT projection. Other goals of this investigation are to identify other pretectal nuclear projections from the visual cortex in the guinea pig, and to determine whether there is any visuotopic organization in this pathway. Axonal tracers (biocytin or 3H-leucine) were injected into the striate cortex (Oc 1), and the tissue processed with histochemical or light autoradiographic techniques. All subcortical terminal labeling is ipsilateral in the basal ganglia and thalamic nuclei. Furthermore, projections are traced to the ipsilateral brainstem, including two areas of the pretectal complex: (1) one in the NOT, extending in some cases to the adjacent lateral portion of the posterior pretectal nucleus (PPN), and (2) one in the pars compacta of the anterior pretectal nucleus (APNc). The terminal fields in the APN are consistently located rostrally in the dorsolateral portion of the nucleus, independently of the injection site in Oc 1, whereas in the NOT the terminal fields shift slightly after injections placed in different locations in the striate cortex. A correlation of the injection sites in Oc 1 and terminal fields in the NOT reveals a loose topographic organization in the cortico-NOT projection; accordingly, the rostrocaudal axis of the striate cortex projects to the lateromedial axis of the NOT, with a 90 degrees rotation, whereas lateral parts of the striate cortex project diffusely throughout the rostrocaudal extent of the NOT. These data show for the first time that the NOT in the guinea pig receives a substantial projection from the visual cortex. Given the fact that in the guinea pig the optokinetic nystagmus shares some of the characteristics found in cat and monkey (i.e., consistent initial fast rise in the slow phase velocity and reduced asymmetry in monocular stimulation), the present findings lend support to the hypothesis that a cortical input to the NOT is a necessary condition for these oculomotor properties to be present.

The accessory optic system: basic organization with an update on connectivity, neurochemistry, and function

“…However, connection studies have not revealed a direct projection in rabbits and guinea pigs (Giolli et al, 1978(Giolli et al, , 1988aHollander et al, 1979;Lui et al, 1994). Apparently, the same may be true for rats (Nauta and Bucher, 1954;Benzinger and Massopust, 1983), although the AOS is not explicitly mentioned in these papers.…”

“…In fact, some studies deal with these two nuclei as a single complex (e.g., Schmidt et al, 1993). However, when the two structures have been distinguished histologically, a visual cortical input is found only on the NOT, and not the DTN (Lui et al, 1994).…”

Mammals

“…The nucleus of the optic tract receives a bilateral projection from the ventral geniculate (Edwards et al 1974) and strong projections from the nuclei of the accessory optic system (see below). The visual cortex in primates , cat (areas 17-19, 21; Updyke 1977), rat (Schmidt et al 1993) and guinea pig (Lui et al 1994) projects to the nucleus of the optic tract and the adjacent dorsal terminal nucleus of the accessory optic system (see Sect. 22.8.3.4), but this connection was disputed in the tree shrew (Harting and Noback 1971;Weber 1985) and is absent in the rabbit (Giolli et al 1978).…”

Galvanic stimulation of the vestibular periphery in guinea pigs during passive whole body rotation and self-generated head movement

“…However, in contrast to previous findings in primates (Blazquez and Highstein 2007;Waespe and Henn 1979), mouse vestibular-only cells ("VO neurons") do not exhibit activity related to either the visual motion stimulus or eye movement during OKN. The guinea pig has been previously shown to have neural circuitry intermediate to that of primates compared with mice or rabbits for OKN (Lui et al 1994), and so further electrophysiological studies are needed to determine whether the effects of GVS on VOR show species-specific differences for this animal.…”