Morphology and location of tectal projection neurons in frogs: A study with hrp and cobalt‐filling

Abstract

Tectal projection neurons were labeled by retrograde transport of horseradish peroxidase (HRP) or cobaltic-lysine. The tracer substances were delivered iontophoretically or by pressure injection or diffusion into various regions of the brain or spinal cord. Histochemical procedures allowed identification of labeled cells projecting to the injected regions. Many neurons were filled with cobaltic-lysine, resulting in a Golgi-like staining. After cobalt injections in the diencephalon most of the labeled cells, identified as small piriform neurons, were located in layer 8 of the tectum. Two types of small piriform neurons were distinguished. Type 1 neurons have flat dendritic arborizations confined to lamina D, while the dendrites of type 2 cells may span all of the superficial tectal strata. In smaller numbers large piriform, pyramidal, and ganglionic cells of the periventricular tectal layers were labeled after diencephalic injections. Rhombencephalic cobalt and HRP injections labeled cells whose axons form the tectobulbospinal tract. The neurons most frequently labeled were large ganglionic cells. Ipsilaterally, the majority of their somata were located in layer 7, and their dendrites arborized mainly in lamina F. Contralaterally, labeled ganglionic cell somata occupied the top of layer 6, and most of their dendritic end-branches entered lamina B. The possible functional significance of this anatomical arrangement is discussed. After tectal cobalt injections the topography of the tectoisthmic projection and the terminals of tectal efferent fibers in the diencephalon and brainstem were observed. It is concluded that the organization of frog tectofugal pathways is very similar to that of mammals.

An intracellular study of pretectal influence on the optic tectum of the frog, Rana catesbeiana

“…They were activated antidromically by the electric stimulation applied to the pretectal Lpd/P region. Neuroanatomical and some physiological characteristics of the tecto-thalamic projection have been described by others [1,21,[31][32][33] . Our data provide further physiological proof for the existence of reciprocal connections between the tectum and particular pretectal nuclei as suggested by Székely and Lázár [25] .…”

“…Previous immunocytochemical studies [21] have revealed that the pretectal Lpd/P nuclei contain neuropeptide Y (NPY)-like immunoreactivity cells whose fibers distribute in the superficial layers of the ipsilateral tectum (except lamina A), where they partially overlap retinal recipient laminae [22,23] . Because it is known that NPY can reduce the excitatory input, as observed in the rat hippocampus [24] , it is likely that the inhibitory inputs from pretectal cells are attributable to NPY-like immunoreactivity.…”

Immunohistochemical localization of cocaine‐ and amphetamine‐regulated transcript peptide in the central nervous system of the frog Rana esculenta

“…The main target of the tectothalamic projection is the lateral thalamic neuropil (Lázá r et al, 1983;Montgomery and Fite, 1991).…”

Morphology, axonal projection pattern, and response types of tectal neurons in plethodontid salamanders. I: Tracer study of projection neurons and their pathways

“…Cobaltic lysine studies in frogs (Lázár et al, 1983;Antal et al, 1986;Roth et al, 1990) have demonstrated morphological details of projection neurons comparable to those obtained with biocytin but have not produced a complete picture of the number and course of the efferent pathways. In the present study, the use of isolated brain preparations made a locally restricted application of biocytin possible.…”

“…The latter plays an important role in visual functions of reptiles and birds (Hodos and Karten, 1966;Reiner and Powers, 1978;Powers and Frank, 1983); in mammals it is involved in visual attention (Robinson and Petersen, 1992). It is unclear whether similar tracts projecting to different diencephalic targets exist in amphibians (Lázár et al, 1983).…”