Chemically specific retinal ganglion cells collateralize to the pars ventralis of the lateral geniculate nucleus and optic tectum in the pigeon (Columba livia).

Immunohistochemical and retrograde tracing techniques were combined to study the retinal ganglion cells which project to the pars ventralis of the lateral geniculate nucleus (GLv) in the pigeon. Using two different fluorescent tracers, two histochemically-distinct populations of ganglion cells were found to project to both the GLv and the optic tectum. The first population of ganglion cells exhibited tyrosine hydroxylase-like immunoreactivity and represented about 20% of all ganglion cells which were retrogradely labeled from the GLv.

The rat accessory optic system: effects of cortical lesions on the directional selectivity of units within the medial terminal nucleus.

Single units within the medial terminal nucleus of the accessory optic system were recorded and examined for their responses to a moving pattern, in both intact and decorticated urethane-anesthetized rats. The preferred directions of motion in control rats were mainly upward with a temporal component and downward with a nasal component. The responses to upward motion were almost absent after cortical ablation, with most units now preferring temporal or downward-nasal directions.

Catecholaminergic subpopulation of retinal displaced ganglion cells projects to the accessory optic nucleus in the pigeon (Columba livia).

In birds, displaced ganglion cells (DGCs) constitute the exclusive source of retinal input to the nucleus of the basal optic root (nBOR) of the accessory optic system. Tyrosine-hydroxylase (TH) immunoreactivity was examined in the pigeon retina after injections of rhodamine-labeled microspheres into the nBOR. A population of about 400 DGCs was observed in each case to exhibit both TH immunoreactivity and rhodamine bead fluorescence.

Telencephalic and pretectal modulation of the directional selectivity of accessory optic neurons in the pigeon.

Direction-selective units within the accessory optic system of the pigeon were shown to respond more strongly to motion along two main directions, downward-nasal and upward-temporal. Following ipsilateral telencephalic or pretectal lesions, these directions were modified in a systematic way. In the former, the principal response directions were downward-nasal and temporal and in the latter, downward-temporal and upward-temporal.

The pretectal nucleus of the optic tract modulates the direction selectivity of accessory optic neurons in rats.

Direction-selective single units within the medial terminal nucleus of the rat were shown to prefer motion in upward-temporal or downward-nasal directions. Lesions of the optic tract nucleus practically abolished responses to the nasal direction of motion and increased the directional bias toward the temporal direction. Such results suggest a significant role of that pretectal nucleus in the determination of direction selectivity of accessory optic neurons.

Interocular transfer of habituation in pigeons: mediation by tectal and/or posterior commissures.

Interocular transfer of the habituation to diffuse photic stimuli was demonstrated to be almost complete in pigeons. Birds submitted to visual Wulst ablation or supraoptic commissure lesion performed in much the same way. In contrast, when the tectal and posterior commissures were lesioned, pigeons failed to show interocular transfer of that learning process.

A pretectal projection upon the accessory optic nucleus in the pigeon: an anatomical and electrophysiological study.

Neurons of the nucleus lentiformis mesencephali, the avian homologue of the optic tract nucleus, were retrogradely filled with horseradish peroxidase after injections of the enzyme into the accessory optic nucleus in pigeons. The projection appeared exclusively ipsilaterally, and was confirmed by unitary and evoked potential recordings. Together with previous reports in both birds and mammals, the present study contributes information linking the accessory optic system to the pretectal nucleus of the optic tract and thence to horizontal optomotor mechanisms.

Retinal ganglion cells of the pigeon accessory optic system.

After the demonstration of its involvement in visuomotor coordination, the accessory optic system has been the subject of renewed interest. An interesting feature of its functional organization is that the retinal ganglion cells generating projections to accessory optic nuclei appear to be, at least in birds, the displaced ganglion cells of Dogiel. Retinal extracellular unit recordings were performed for 21 pigeons.

The accessory optic system in pigeons: receptive field properties of identified neurons.

Visual receptive fields of neurons in the nucleus of the basal optic root were investigated in pigeons. Their projections could be traced to vestibulo-cerebellum and oculomotor complex by means of antidromic activation. Units in that nucleus showed large peripheral receptive fields and appeared highly sensitive to moving targets, with the majority displaying axis specificity and direction selectivity.

Inhibition of tectal neurons from telencephalic visual areas in pigeons.

The author investigated the influence of efferent projections of visual telencephalic areas upon the optic tectum, in locally anesthetized, paralyzed and artificially ventilated pigeons, using extracellular unit recording and electrical stimulation by means of stereotaxically implanted bipolar electrodes. Despite the fact that some neurons located at superficial tectal layers could be driven by telencephalic shocks, the most consistent data are the inhibitory effects observed throughout the tectum, but mainly at deep layers. This effect was observed either on spontaneous activity or on electrically elicited spikes, by stimulating the optic tract.