Edward R. Gruberg

Anatomy and physiology of a binocular system in the frograna pipiens

Abstract The locations of tectal neurons projecting to nucleus isthmi (n. isthmi) were found by iontophoretic injection of horseradish peroxidase (HRP) into n. isthmi. After retrograde transport, stained tectal somata are found to lie almost exclusively in layer 6 and below of the ipsilateral tectum. Many cells are colored throughout the extent of their dendrites into the fine rami, giving the appearance of a Golgi stain. Nucleus isthmi receives projections from the ipsilateral tectum and from no other region. Nucleus isthmi units recorded electrically respond to visual stimuli and are arranged in a topographic map of the visual field. There are two types of receptive fields, those with small centers and those with large centers. The small centers are about 3-5° in diameter, similar to type 2 optic nerve fibers. Their response is to many of the same geometric features of stimulus as excite type 2 fibers. The large centers are at least 7-10° in diameter and respond to many of the same features as excite types 3 and 4 optic nerve fibers. The responsiveness of small and large center n. isthmi units is very similar to the elements of the ipsilateral visual field projection onto tectum, i.e. the neuropilar units recorded in layers A and 8 of the tectum when the contralateral eye is occluded. These are in strong contrast to those of tectal cells of layer 6 and below, which have large receptive fields, show far less vivacious response, adapt extremely rapidly to repeated stimuli and are hard to describe in terms of characteristic stimuli because they are unresponsive most of the time. We suggest, therefore, that the axons of tecto-isthmic cells are quite active and that their cell bodies, located in layer 6 and below, only fire occasionally on the firing of their axons.

A forebrain visual projection in the frog (Rana pipiens)

Abstract In the frog (Rana pipiens) using a modification of the Fink-Heimer degeneration stain, a projection was traced from the lateral anterior thalamus via the lateral forebrain bundle to the ipsilateral striatum in the ventrolateral area of the forebrain. Striatal degeneration extended from the anterior commissure to the olfactory bulb. Single-unit microelectrode recording revealed that this area contained visual units that responded to the on and off of light.

Influencing and Interpreting Visual Input: The Role of a Visual Feedback System

Vertebrates are able to visually identify moving objects and orient toward attractive ones or escape if the objects seem threatening. When there is more than one object in the visual field, they can attend to a particular object. The optic tectum (superior colliculus in mammals) (OT/SC) has long

The serotonergic somatosensory projection to the tectum of normal and eyeless salamanders

The spinotectal somatosensory projection was compared in normal, genetically eyeless, and embryonically manipulated salamanders. In normal animals, serotonin fluorescence was restricted to the intermediate tectalneuropil. This same region showed both high levels of serotonin uptake and somatosensory single unit electrical activity. In mutant eyeless salamanders and in normal animals enucleated early in development, serotonin fluorescence, serotonin uptake, and somatosensory activity were present in the superficial tectal neuropil. One‐eyed animals, either genetically normal axolotls with one eye enucleated embryonically or genetically eyeless animals in which a normal eye had been transplanted, showed normal intermediate serotonin fluroescence and somatosensory physiology in the visually innervated half‐tectum. In the visually uninnervated half‐tectum, they showed superficial serotonin fluorescence and somatosensory physiology.

The distribution of succinic semialdehyde dehydrogenase in the brain and retina of the tiger salamander (Ambystoma tigrinum)

Abstract With the use of tetrazolium salt the distribution of succinic semialdehyde dehydrogenase, the final enzyme in the degradative pathway of GABA, was investigated in the brain and retina of the tiger salamander. In the brain it was found in discrete neural areas, including the neuropil of the acoustico-lateral area, the magnocellular area of the medulla, the neuropil of the cerebellum, the mesencephalic V nucleus, the third nerve nucleus, the epiphysis, the subcommissural organ, the fasciculus retroflexus, and the neuropil of the habenulla. In addition there was a diffuse distribution due to ependymal cells. In the retina the enzyme was seen in Mu¨ller cells, ellipsoid bodies and possibly Landolt club processes.

Removal of retinal input fails to elicit isthmo-tectal sprouting in the frog.

The retina and nucleus isthmi both project in laminar fashion to the superficial layers of the frogs tectum. In order to determine whether isthmo-tectal axons show collateral sprouting after retinotectal input is removed, we injected [3H] proline into the nucleus isthmi and measured the volume of the crossed isthmo-tectal projection. We found no evidence of collateral sprouting.

Connections of Anterior Thalamic Visual Centers in the Leopard Frog, Rana pipiens

The amphibian retina projects to two discrete regions of neuropil in the anterior thalamus: the neuropil of Bellonci and the corpus geniculatum. These retinorecipient areas are encompassed within a larger zone of surrounding neuropil we call the NCZ (for neuropil of Bellonci/corpus geniculatum zone). The NCZ is characterized electrophysiologically by a distinctive tonic oscillatory response to blue light; it appears to be a visual module involved in processing the stationary visual environment. Using horseradish peroxidase (HRP), we mapped the connections of the NCZ. Retrogradely labeled cell bodies are found in: (1) the contralateral anterior thalamus; (2) both retinas; and (3) the posterior medial dorsal thalamus (PMDT). Anterogradely labeled fibers are found in: (1) the contralateral anterior thalamus; (2) the ipsilateral PMDT; (3) the ipsilateral neuropil lateral to the posterior tuberculum in the ventrolateral posterior thalamus; and (4) the ipsilateral anterior medulla. There are no direct connections between the NCZ and the telencephalon, the tectum, or the suprachiasmatic nucleus. Applying HRP to the PMDT, we found that its inputs are limited to the contralateral and ipsilateral NCZ and the contralateral PMDT. Thus, PMDT appears to be a satellite of the NCZ. Blue light elicits tonic oscillatory electrical responses in the PMDT quite similar to the responses to blue light in the NCZ. We discuss how the leopard frog NCZ and the mammalian ventral lateral geniculate nucleus share anatomical and physiological properties.