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Multichannel processing of environmental information constitutes a fundamental basis of functioning of sensory systems in the vertebrate brain. Two distinct parallel visual systems - the tectofugal and thalamofugal exist in all amniotes. The vertebrate central nervous system contains high concentrations of intracellular calcium-binding proteins (CaBPrs) and each of them has a restricted expression pattern in different brain regions and specific neuronal subpopulations. This study aimed at describing the patterns of distribution of parvalbumin (PV) and calbindin (CB) in the visual thalamic and mesencephalic centers of the pigeon (Columba livia). We used a combination of immunohistochemistry and double labeling immunofluorescent technique. Structures studied included the thalamic relay centers involved in the tectofugal (nucleus rotundus, Rot) and thalamofugal (nucleus geniculatus lateralis, pars dorsalis, GLd) visual pathways as well as pretectal, mesencephalic, isthmic and thalamic structures inducing the driver and/or modulatory action to the visual processing. We showed that neither of these proteins was unique to the Rot or GLd. The Rot contained i) numerous PV-immunoreactive (ir) neurons and a dense neuropil, and ii) a few CB-ir neurons mostly located in the anterior dorsal part and associated with a light neuropil. These latter neurons partially overlapped with the former and some of them colocalized both proteins. The distinct subnuclei of the GLd were also characterized by different patterns of distribution of CaBPrs. Some (nucleus dorsolateralis anterior, pars magnocellularis, DLAmc; pars lateralis, DLL; pars rostrolateralis, DLAlr; nucleus lateralis anterior thalami, LA) contained both CB- and PV-ir neurons in different proportions with a predominance of the former in the DLAmc and DLL. The nucleus lateralis dorsalis of nuclei optici principalis thalami only contained PV-ir neurons and a neuropil similar to the interstitial pretectal/thalamic nuclei of the tectothalamic tract, nucleus pretectalis and thalamic reticular nucleus. The overlapping distribution of PV and CB immunoreactivity was typical for the pretectal nucleus lentiformis mesencephali and the nucleus ectomamillaris as well as for the visual isthmic nuclei. The findings are discussed in the light of the contributive role of the phylogenetic and functional factors determining the circuits׳ specificity of the different CaBPr types., (Copyright © 2015 Elsevier B.V. All rights reserved.)

In turtles (Testudo horsfieldi, Emys orbicularis) the immunoreactivity for calbindin (CB), parvalbumin (PV), calretinin (CR), and colocalization of PV and CB in neurons of visual thalamic nuclei (Rot, GLD) projecting to the telencephalon were studied using combined immunohistochemical and tracer method. The predominance of CB-ir neurons in Rot, CB-ir and CR-ir neurons in GLD and a lower amount of PV-ir neurons in both nuclei were shown. With double labeling fluoroimmunohistochemistry technique the colocalization of PV with CB was revealed in the majority of PV-ir neurons and in a fewer number of CB-ir neurons within both nuclei. After delivery of horseradish peroxidase into the telencephalic projection fields of Rot and GLD, retrograde labeling was found in the corresponding thalamic projection neurons immunoreactive for every protein investigated. After fluorescent tracer (Fluoro Gold) injection into the same telencephalic regions retrograde labeling was observed in Rot and GLD neurons, immunoreactive only for PV or CB, as well in neurons with colocalization of the both proteins. These data support predominance of CB-ir component in the rotundo-telencephalic pathway and CB/CR components in the geniculo-telencephalic pathway in turtles. The role of functional specialization in segregation of neurons expressing different types of calcium-binding proteins is postulated.

The distribution of immunoreactivity to the calcium-binding proteins parvalbumin, calbindin and calretinin and of cytochrome oxidase activity was studied in the mesencephalic (torus semicircularis), thalamic (nucleus reuniens) and telencephalic (ventromedial part of the anterior dorsal ventricular ridge) auditory centres of two chelonian species Emys orbicularis and Testudo horsfieldi. In the torus semicircularis, the central nucleus (core) showed intense parvalbumin immunoreactivity and high cytochrome oxidase activity, whereas the laminar nucleus (belt) showed low cytochrome oxidase activity and dense calbindin/calretinin immunoreactivity. Within the central nucleus, the central and peripheral areas could be distinguished by a higher density of parvalbumin immunoreactivity and cytochrome oxidase activity in the core than in the peripheral area. In the nucleus reuniens, the dorsal and ventromedial (core) regions showed high cytochrome oxidase activity and immunoreactivity to all three calcium-binding proteins, while its ventrolateral part (belt) was weakly immunoreactive and showed lower cytochrome oxidase activity. In the telencephalic auditory centre, on the other hand, no particular region differed in either immunoreactivity or cytochrome oxidase activity. Our findings provide additional arguments in favour of the hypothesis of a core-and-belt organisation of the auditory sensory centres in non-mammalian amniotes though this organisation is less evident in higher order centres. The data are discussed in terms of the evolution of the auditory system in amniotes., (Copyright 2010 Elsevier B.V. All rights reserved.)

Distribution of activity of the mitochondrial oxidative enzyme cytochrome oxidase C was studied in the thalamic (Ov) and telencephalic (field L) auditory centers in pigeons. The CO activity level has been shown to differ in the central (core) and peripheral (belt) subdivisions of these centers: the high CO activity in the former (nCe, L2) and the much lower or absent in the latter (Ovl, Ovm, SPO). Comparison of our data with those of various avian and reptile species confirms the concept of the common plan of rostral auditory centers in sauropsid amniotes by the principle of the center-periphery (core-belt), which is characteristic of the corresponding mammalian centers. The separation of the central and peripheral parts of these centers is better pronounced in birds than in reptiles.

Projections of the pretectal region to forebrain and midbrain structures were examined in two species of turtles (Testudo horsfieldi and Emys orbicularis) by axonal tracing and immunocytochemical methods. Two ascending gamma-aminobutyric acid (GABA)ergic pathways to thalamic visual centers were revealed: a weak projection from the retinorecipient nucleus lentiformis mesencephali to the ipsilateral nucleus geniculatus lateralis pars dorsalis and a considerably stronger projection from the nonretinorecipient nucleus pretectalis ventralis to the nucleus rotundus. The latter is primarily ipsilateral, with a weak contralateral component. The interstitial nucleus of the tectothalamic tract is also involved in reciprocal projections of the pretectum and nucleus rotundus. In addition, the pretectal nuclei project reciprocally to the optic tectum and possibly to the telencephalic isocortical homologues. Comparison of these findings with previous work on other species reveals striking similarities between the pretectorotundal pathway in turtles and birds and in the pretectogeniculate pathway in turtles, birds, and mammals., (Copyright 2000 Wiley-Liss, Inc.)

Reciprocal connections of the hypothalamus with the ventral nucleus of the lateral geniculate body and ventrolateral (subthalamic) nucleus were demonstrated in the lizard Ophisaurus apodus using the retrograde and anterograde axonal tracing method following local HRP injection into the mamillary complex.

Data on the evolution of the visual system in the phylogenetic scale of vertebrates are reported. Visual projections in the telencephalon of cyclostomes (lampreys) and retinothalamo-telencephalic channel in elasmobranches (skates) are shown. In amphibians (frogs) and reptiles (turtles) the existence of two visual subsystems (retino-thalamo-telencephalic and retino-tecto-thalamo-telencephalic) is determined, both being overlapped partially at the level of n. geniculatus lateralis and totally in the telencephalon. In turtles earlier visual and tectal impulses towards the telencephalon proved to be relayed in n. geniculatus lateralis and later ones--in n. rotundus. In mammals (rats) visual tecto-cortical connections are shown to have one synaptic relay in thalamic structures since cortical potentials evoked by stimulation of the colliculus superior in rats posses a rather short latency. Significant latency shortening of tectal visual responses in monkeys, as compared with the latency of the respective potentials in turtles (chronic identical experiments), supports the idea of the progressive development of the tectal division of the visual system in the vertebrate phylogony. It is concluded that both divisions of the visual system--retino-thalamic and retino-tectal underwent corticalization at earlier evolutionary stages.

Thalamic structures relaying impulses originating from optic stimulation of the retina and electric stimulation of the tectum on the way to the general cortex, hyperstriatum dorsal ventricular ridge and striatum were studied in turtles Emys orbicularis. Anodal polarization of the n. rotundus temporarily, and the lesion of this nucleus irreversibly, suppressed the main negative component of responses evoked by tectal stimulation and light flashes in the dorsal ventricular ridge without affecting them in the general cortex. Polarization and lesions of the lateral thalamic region, including nucleus geniculatum lateralis produced an opposite effect. A conditioning single stimulation of the tectum or n. rotundus suppressed flash-evoked potentials in the hyperstriatum. However evoked potentials and single unit responses appeared following stimulation of the lateral thalamic region. They exhibited blocking interactions with the tectum-evoked responses. A conclusion is made that in the turtle the main pathways conducting visual information to the cortex and hyperstriatum are different: in the former case it is relayed in the lateral geniculatum region in the latter--in n. rotundus, although an overlap of the projections in dorsal ventricular ridge and striatum can be suggested.

The organization of auditory projections at the mesencephalic, thalamic and telencephalic brain levels was studied utilizing the method of horseradish peroxidase (HRP) transport in two species of the turtle--Emys orbicularis and Testudo horsfieldi. It was shown that the torus semicircularis receives bilateral afferents from the brain stem auditory centers. They arise predominantly from the contralateral cochlear nuclei, the ipsilateral superior olive, the dorsal and ventral nuclei of the lateral lemniscus and from the symmetrical torus semicircularis. These connections appear to be reciprocal. After the enzyme injections correspondingly into the torus semicircularis and n. reuniens anterograde and retrograde HRP transports show that the central nucleus of the torus semicircularis projects to n. reuniens throughout its rostro-caudal extent mainly ipsilaterally. In turn, n. reuniens projects to the medioventral part of the dorsal ventricular ridge. A following common principle of the organization of the auditory system was revealed at the three brain levels explored. Auditory relay centers occupy the most medial positions at every level (n. centralis of the torus semicircularis, n. reuniens, the medioventral part of the dorsal ventricular ridge). Immediately lateral to them are somatic centers (correspondingly, n. intercollicularis, n. ventralis, the central part of the dorsal ventricular ridge). These together with the auditory centers form united functional complexes at every level. In these complexes auditory and somatic projections overlap, thus constituting a basis for the interaction between auditory and somatic afferent inputs. Mesencephalic and thalamic auditory centers were shown to receive direct somatic (cervical spinal) projections and non-direct from the underlying somatic center as well as from the adjacent somatic center at the same level (n. intercollicularis in the mesencephalon, n. ventralis in the thalamus). Somatic centers in the complexes described get no direct auditory projections. Auditory impulses however can enter them via two pathways: along neuron axons from the neighbouring auditory center reaching the adjacent somatic center and along somatic neuron dendrites which pass into the adjacent auditory center. The morphological basis for the auditory-somatic interactions primarily in the auditory center and also in the somatic center was demonstrated in Golgi-like HRP labeled and Golgi-impregnated neurons of these centers. The organization of the auditory-somatic projections at the three brain levels in turtles in to a degree comparable to the auditory system in mammals which is structured according to the core-belt principle.(ABSTRACT TRUNCATED AT 400 WORDS)

In the turtles Emys orbicularis and Testudo horsfieldi connections of the thalamic (n. reuniens) and telencephalic (medio-ventral part of the dorsal ventricular edge--DVE) centers of the auditory system have been revealed by means of the retrograde and anterograde horseradish peroxidase (HP) transport method. At a local HP administration into the n. reuniens, the labelled neurons are detected bilaterally in the midbrain: in the auditory center (n. centralis of the torus) and predominantly in the somatic nucleus (n. intercollicularis); in the thalamus--ipsilaterally among the marked fibers of the dorsal peduncle of the forebrain lateral bundle, in the anterior and posterior parts of the suprapeduncular nucleus, in the nucleus of the ventral supraoptic chiasm. The HP anterograde transport is followed in the thalamic n. anterior and n. ventralis, in the forebrain lateral bundle as far as the medial part of the DVE. When HP is injected into the DVE auditory zone, retrogradely labelled neurons are revealed ipsilaterally along the whole pathway of the auditory center (n. reuniens), as well as in the n. anterior and n. ventralis, in the posterior part of the suprapeduncular nucleus, in the posterior commissure nucleus, in the caudal nucleus. Most of these thalamic nuclei are connected with the somatosensory system. The principle of the structural-functional organization of the auditory system in reptiles is discussed; it ensures the interaction between the auditory and somatic impulses making a necessary base for the audition-controlled behaviour.