The pretectal nucleus Lentiformis mesencephali of Rana pipiens

Abstract

The pretectal nucleus lentiformis mesencephali (nLM) of Rana pipiens was investigated with autoradiographic, horseradish peroxidase (HRP), and Golgi techniques. Retinal afferents to nLM originate primarily from the central retina. The primary projection is contralateral with a small ipsilateral component. Following optic nerve transection and HRP impregnation, contralateral retinal afferents show a restricted, dense core of HRP label in the superficial portion of the nucleus with sparser HRP label in the surround. Ipsilateral retinal afferents arborize throughout nLM, except in the dense-core region. Additional afferents to nLM originate from the ipsilateral tectum, the nucleus rotundus, the mesencephalic pretectal gray, the contralateral nLM, and the nucleus of the basal optic root. Afferents from the accessory optic system arborize only in the dense-core region, following HRP injections into the nucleus of the basal optic root, while afferents from the mesencephalic pretectal gray arborize in all parts of nLM except the dense core. Afferents from the tectum and anterior thalamus appear to arborize throughout the nucleus without discernible pattern. The lamination of afferent terminals in nLM was correlated with Nissl-stained cytoarchitectural material in which the majority of large neurons cluster around the dense core of nLM. Three types of neurons occur in nLM: large neurons (25-micron dia.), fusiform neurons (12.5-micron dia.), and stellate neurons (10-micron dia.). Additionally, two cell groups outside nLM which send dendrites into the nucleus were observed: cells of the posterior lateral nucleus and cells of the posterior thalamic pretectal gray. Both large and fusiform neurons project to the deep layers of the optic tectum as well as to the ventral rhombencephalon superficial to the abducens nucleus. While a small number of fusiform neurons project to the nucleus of the basal optic root, the stellate neurons appear to be intrinsic to nLM. The anuran nLM strongly resembles the nucleus of the optic tract in mammals in terms of the site of origin of its retinal afferents, lamination of afferent terminations, its central connections, and its demonstrated involvement in horizontal optokinetic nystagmus.

Pretectum and Accessory Optic System in the Filefish <i>Navodon modestus </i>(Balistidae, Teleostei) with Special Reference to Visual Projections to the Cerebellum and Oculomotor Nuclei

“…Similar projections from the pretectum have been reported in leopard frogs [Montgomery et al, 1981[Montgomery et al, , 1985. However, APv projects also to the oc ulomotor complex, unlike the pretectal nuclei of other vertebrates.…”

Microiontophoresis and Single-Unit Analysis of Cholinergic Drugs in the Optic Tectum of Frog

“…These neurons are postsynaptic to retinal axons and afferents from other sources [i.e. nucleus isthmi, pretectum] which terminate in the superfi cial tectal laminae [Wang et al, 1982;Wilczynski and Northcutt, 1977;Lazar, 1984;Montgomery et al, 1985;Wang et al, in press]. By comparison, units iso lated in the more superficial laminae showed brisk reponses to visual stimula tion and response characteristics typical of primary optic afferents, but showed little or no change in responsiveness fol lowing iontophoresis of ACh, atropine or curare.…”

Neurophysiological Investigation of the Pretectal Nucleus lentiformis mesencephali in <i>Rana pipiens</i>

“…Direction-selective visual units have also been recorded in the nLM of pigeons [32,37] and in the pretectal region of amphibians [8, 23, ' Supported by NEI EYO-4577 and NSF BNS-8209026. 27,35], However, the exact location of direction-se lective visual neurons has not always been specified in relation to the primary terminal zones of optic ax ons (i.e., posterior thalamic neuropil, nLM, and unci nate neuropil), each of which receives an indepen dent, retinofugal projection [30,31]. The large-celled nLM also receives a major projection from large ganglionic neurons of the nucleus of the basal optic root (nBOR); nLM, in turn, projects to the optic tec tum and peri-nBOR region [30].…”