Tegmento-thalamic relations in turtles

A focus of evoked potentials and the largest number of spike responses of single units to tegmental stimulation were found in immobilized turtles (Emys orbicularis), lightly anesthetized with chloralose, in the ventral region of the thalamus, which is a heterosensory zone of predominantly somatosensory modality. Incomplete separation of lateral- and medial-tegmental projections between the dorsal and ventral portions of the ventral thalamic region respectively was discovered. Tegmental stimulation, coinciding with or preceding electrodermal or photic stimulation, causes predominant depression of somatic single unit responses, but has less effect on visual responses. The possibility of comparison of tegmento-thalamic systems in reptiles and mammals is discussed.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 12, No. 2, pp. 165–174, March–April, 1980.     

Tegmento-telencephalic relations in turtles

Electrophysiological characteristics of tegmental projections in the forebrain were studied in immobilized turtles (Emys orbicularis), anesthetized with chloralose. The main zone of representation of the tegmentum is located in the striatum, where evoked responses with shorter latencies were recorded and a larger number of units responding distinctly to tegmental stimulation was concentrated than in the dorsal ventricular ridge and general cortex. At the striatal level predominance of lateral tegmental projections was found in the lateral zone and of medial tegmental projections in the medial zone of the striatum. An inhibitory action of conditioning stimulation of the tegmentum on somatic evoked potentials and single unit responses was established. An attempt was made to compare the tegmento-telencephalic system in reptiles and mammals.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 12, No. 3, pp. 255–263, May–June, 1980.     

The tecto-thalamo-telencephalic system of the tortoise (electrophysiological investigation)

Using tortoises immobilized with diplacin to which chloralose had been added, or under chloralose — nembutal narcosis, we investigated the distribution of evoked potentials and neuronal responses in the thalamus and forebrain induced by electrical excitation of the optic tectum and by flashes of light. In the thalamus the main mass of cells that reacted to these stimuli was concentrated in the nucleus rotundus and the tecto-thalamic tract; in the forebrain it was concentrated in the general cortex, the pallial thickening, and the neostriatum. In the two latter structures responses with shorter latent periods than those in the general cortex predominated. Visual and tectal neuronal responses, especially those of convergent cells, displayed correlation in their latent periods and types of response, which was more clearly shown in the thalamus. Submaximal tetanization of the optic tectum had a facilitating effect on cortical responses produced by light flashes and excitation of the nucleus rotundus. Complete blocking of transmission of tectal impulsation to the forebrain was observed on destruction of the tecto-thalamic tract region bounded by the lateral bundle of the forebrain, the lateral geniculate body, and the nucleus rotundus. High-frequency excitation of the nucleus rotundus produced only partial blocking of transmission (of the late components). It is concluded that there are various pathways of tectal impulsation through the thalamus to the forebrain.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 2, No. 3, pp. 296–306, May–June, 1970.     

Calcium-Binding Proteins in Pretectum of Turtles (Immunohistochemical Study)

An immunohistochemical study was carried out to reveal distribution of immunoreactivity (IR) against Ca-binding proteins (CaBPr): calbindin (Calb), calretinin (Calr), and parvalbumin (Parv) in pretectum of the Central Asian terrestrial turtles (Testudo horsfieldi) and the pond turtles (Emys orbicularis). A wide distribution of CaBPr-IR neurons and terminals with a significant overlapping was established in most of pretectal nuclei (Lm, Pd, Pe, Po, and ndCP) with some differences in density of IR elements for various proteins. The alternative distribution of Parv-IR (a high density of IR neurons) and Calb/Calr-IR (a most low content of IR neurons and terminals) was found in the non-retinorecipient nucleus Ptv. Comparison of data obtained in turtles with literature data obtained in other species of reptiles and mammals has revealed a significant variability in the CaBPr distribution in some, presumably homologous, pretectal nuclei among various representatives of amniotes. The conclusion is made that in the process of evolution of amniotes, apart from conservatism of CaBPr-IR characteristics, there occurred their plastic rearrangements due to morpho-functional specialization of pretectal nuclei.     

Neurochemical organization of reptilian thalamus. Comparative analysis of amniote optical centers

Study of neurochemical characteristics of the turtle thalamus was performed using antibodies against several biologically active compounds; monoamines (5-HT, TH), neuropeptides (SP, m-Enk, NPY), against ChAT and by histochemical detection of NADPH-d. Based on our own results and literature data obtained on other representatives of reptiles, birds, and mammals, a comparative analysis was carried out of neurochemical organization of two thalamic optical centers—relay nuclei of thalamofugal (GLd) and tectofugal (Rot/LP-Pulv) systems of amniotes. Features of similarities and differences of these centers in representatives of non-mammalian and mammalian amniotes are revealed. GLd has a great similarity of the studied neurochemical characteristics in all amniotes. It receives innervation from all studied transmitter-modulatory systems with predominance of serotonin-, choline- and NPY-ergic projections. Neurochemical organization of Rot comparable with the tectorecipient part of mammalian LP-Pulv has a great resemblance in reptiles and birds, with considerable interspecies differences inside each class. In the majority of the studied systems, Rot is characterized by scant innervation. On the contrary, LP-Pulv receives sufficiently massive innervation from these systems. The most characteristic of this complex are rich SP- and cholinergic projections that are scant in Rot of reptiles and birds. The similar feature of Rot and LP-Pulv is the presence of massive serotonin- and NO-ergic (NADPH-positive) projections. The revealed similarities and differences of the neurochemical characteristics of thalamic optical centers among amniotes seem to reflect various transformations of thalamo- and tectofugal visual systems in the course of phylogenetic and adaptive evolution.