Selective specificity of calcium-binding proteins calbindin and calretinin expression in the magnocellular neurosecretory hypothalamic nuclei of tortoises and turtles.

We have studied the distribution of calcium-binding proteins in the magnocellular neurosecretory nuclei of nonapeptidergic neurosecretory nuclei of the preoptic-hypothalamic complex in a tortoise (Testudo horsfieldi) and a pond turtle (Emys orbicularis) using immunohistochemistry. We have found that different types of cells in the paraventricular and supraoptic nuclei predominantly express calbindin and, to a lesser extent, calretinin, but not parvalbumin. The selective calbindin/calretinin control of the neurohormone secretion in these hypothalamic nuclei is an evolutionary conservative feature typical of reptiles and mammals.

Distribution of calcium-binding proteins, parvalbumin and calbindin, in the midbrain auditory center (MLd) of a pigeon.

Immunohistochemical distribution of calcium-binding proteins, parvalbumin (PV) and calbindin (CB), has been studied in the mesencephalic auditory center (MLd) of pigeon (Columba livia). In the central region of the MLd (core, ICC), an overlap in distribution of the PVand CB-immunopositive (ip) neurons and neuropil has been observed, with different patterns in the central and peripheral parts. In the peripheral region of the MLd (belt, ICS, and ICX), both neurons and neuropil contained only CB. A selective CB chemospecificity of the belt, ICS, and ICX is an evolutionary conserved feature characteristic of all avian species. Interspecies differences in the distribution of PV and CB immunoreactivity in the ICC are a result of adaptive functional specialization, which provides specific processing of different aspects of the auditory information.

[NEURONS IN VISUAL THALAMIC CENTERS OF TURTLES, PROJECTING UPON THE TELENCEPHALON, EXPRESS DIFFERENT TYPES OF CALCIUM-BINDING PROTEINS: COMBINED IMMUNOHISTOCHEMICAL AND TRACER STUDY].

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.

[Calcium-binding proteins and cytochrome oxidase activity in the turtle optic tectum characterzing the visual tectofugal pathway].

Using immunohistochemistry and tracer technique, we studied in the optic tectum of turtles (Emys orbicularis and Testudo horsfieldi) the distribution of CaBPr (parvalbumin, PV, calbindin, CB, calretinin, CR) before and after horseradish peroxidase delivery into nucleus rotundus (Rot). In parallel, activity of cytochrome oxidase (CO) was studied. In the main link of the tectofugal visual pathway (the central gray layer, SGC) in the both chelonian species rare PV-ir, as well CB- and CR-ir neurons were found to vary significantly both in the number and the immunoreactivity degree of their bodies and dendrites. The superficial (SGFS) and deep periventricular (SGP) tectal layers, on the contrary, contained numerous cells immunoreactive to all three CaBPr in different quantitative proportions. Only a small part of the retrogradely labeled tectorotundal neurons contained PV, CB or CR. Very large PV-ir neurons were not retrogradely labeled; by their morphological characteristics, they corresponded to efferent neurons with descending projections. SFC neurons of two chelonian species differed in the degree of CO activity. In SGFS, dense immunoreactivity of neuropil to all three CaBPr and the high CO activity were observed in both species with some differences in sublaminar distribution for every of proteins. Peculiarities of distribution of CaBPr-ir and of CO activity in various segments of SGC neurons are discussed with respect to laminar organization of the turtle tectum and to patterns of its retinal innervations. It was proposed that in projectional tectorotundal SGC neurons, the studied CaBPr are concentrated mainly in their distal dendrites contacting with retinal afferents in the superficial retinorecipient tectal layer.

[Calcium-binding proteins and metabolic activity in thalamotelencephalic parts of the turtle visual system].

Distribution of three calcium-binding proteins (CaBPr) calbindin (CB), calretinin (CR) and parvalbumin (PV) in parallel with metabolic activity (cytochrome oxidase, CO) was studied in telencephalic projection zones of the tecto- and thalamofugal visual pathways in experiments on the Horsfield's terrapin Testudo horsfieldi and the pond turtle Emys orbicularis. It was shown that the nucleus rotundus (Rot) and dorsal lateral geniculate nucleus (GLd) terminal fields in both zones (dorsolateral region of the anterior ventricular ridge, Advrdl and dorsolateral cortex, Cxdl, respectively) were CB-immunoreactive (-ir) in the both studied turtle species. The highest density of CB-ir terminals and the focus of rotundal projections in the Advrdl core coincided precisely. The GLd terminal field in Cxdl also was CR-ir. The PV contribution to innervation of both projectional zones was much lower, especially to innervation of Cxdl from GLd. In spite of similar CB-ir innervation, the projectional field of the tectofugal pathway of Advrdl had the much higher CO activity than of that of the thalamofugal pathway in Cxdl. The neurons immunoreactive to all three CaBPr types were distributed in Cxdl in different ratios in each of layers. In the visual Advrdl area the overwhelming majority were PV-ir neurons, whereas CB-ir neurons were absent. The conclusion is made that in spite of the CB- or CB/CR-immunoreactivity predominates over the PV-immunoreactivity in both thalamotelencephalic pathways of the visual system, the tectofugal (rotundo-Advrdl) pathway having the higher metabolic activity.

[Activity of cytochrome oxidase in centers of tectofugal and thalamofugal channels of the visual system of pigeon Columba livia].

By using a histochemical method of determination of activity of cytochrome oxidase (CO), the level of metabolic activity in pigeons has been shown to be higher in centers of the tectofugal visual channel (pretectal nuclei: Pr, SP, SP/IPS, thalamic nucleus Rot, telencephalic entopallidum) than in centers of the thalamofugal visual channel (GLd, visual area of the hyperpallium Wulst). These data agree with the concept of the dominating role of the tectofugal visual channel in organization of the bird everyday behavior. The high CO activity is also characteristic of the mesencephalic structures (EM, isthmus nuclei: IMc, IPc, SLu) modulating transduction of visual information in tectum, Rot and GLd. Similar differences in the metabolic activities between two visual system channels have been shown earlier in reptiles, which indicates the evolutionary conservatism of the tectofugal visual channel among the sauropside amniotes. However, in pigeons the level of the CO activity in some GLd nuclei approaches that in Rot, which allows us to suggest a rise in birds of the role of the thalamofugal channel in processing of information necessary for performance of complex visual functions.

[Components of the pigeon tectothalamic visual pathway, revealed with aid of study of cytochrome oxidase and immunoreactivity to calcium-binding proteins].

Distribution of activity of cytochrome oxidase (CO) and immunoreactivity to parvalbumin (Pv) and calbindin (Cb) was studied in the optic tectum of the pigeon (Columba livia). In the first link of the tectofugal pathway in the central gray layer (SGC = layer 13), small amounts of the CO-active and Pv-immunoreactive (Pv-ir) cellular bodies were revealed in its internal part (sublayer 13b). Some of these neurons located along the SGC lower boundary had long dendritic processes ascending into the superficial tectum layer (SGF). In the retinorecipient SGF sublayers and particularly in neuropil of the sublayers 4 and 7, the high CO activity correlating with Pv-immunoreactivity was found. It is suggested that a great contribution to metabolic activity of these sublayers is made by the largely branching dendritic processes of Pv-ir neurons of sublayer 13b. The projectional neurons SGC located in its external part (sublayer 13a) were CO-inactive and contained Cb. They sent long dendrites into sublayer 5b; in its neuropil, the high density of Cb-immunoreactivity and a moderate CO activity were detected. Thus, the tectal link of the pigeon tectofugal visual channel consists of two components--the Pv-specific, highly metabolically active and the Cb-specific, metabolically less active ones that transduce visual information from different retinorecipient SGF sublayers. The absence of the significant amount of CO-positive bodies of projectional neurons in SGC can be due to that metabolically more active are their dendritic arborizations in the SGF sublayers.

[Metabolic activity of thalamic and telencephalic auditory centers in the pigeon].

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.

[Evolutionary significance of reciprocal connections in the turtle tectofugal visual system].

In two turtle species--Emys orbicularis and Testudo horsfieldi--by the method of anterograde and retrograde traicing method at the light and electron microscopy level, the existence is proven of direct descending projections from the thalamic nucleus of the tectofugal visual system n. rotunds (Rot) to the optic tectum. After injection of tracers into Rot alone and into Rot with involvement of the tectothalamic tract (Trtth), occasional labeled fibers with varicosities and terminals are revealed predominantly in the deep sublayers of SGFS of the rostral optic tectum, while in the lower amount in other tectal layers. After the tracer injections into the optic tectum, a few retrogradely labeled neurons were found mainly in the Rot ventral parts and within Trtth. Their localization coincides with that of GABA-immunoreactive cells. Electron microscopy showed the existence of many retrogradely labeled dendrites throughout the whole Rot; a few labeled cell bodies were also present there, some of them being also GABA-immunoreactive. These results allow us to conclude about the existence of reciprocal connections between the optic tectum and Rot in turtles, these connections being able to affect processing of visual information in tectum. We suggest that reciprocity of tectothalamic connections might be the ancestral feature of the vertebrate brain; in the course of amniote evolution the functional significance of this feature can be decreased and even lost in parallel with a rise of the role of direct corticotectal projections.

[Distribution of metabolic activity (cytochrome oxidase) and immunoreactivity to calcium-binding proteins in turtle brainstem auditory nuclei].

Using histochemical and immunohistochemical techniques, distribution of activity of oxidative mitochondrial enzyme cytochrome oxidase (CO) and of immunoreactivity to calcium-binding proteins has been studied in spiral ganglion and auditory nuclei of brainstem in two turtle species. It has been shown that immunoreactivity to calbindin, parvalbumin, and calretinin in neurons and neuropil of nuclei of cochlear and superior olivary complexes, in nucleus of lateral lemniscus, and in spiral ganglion neurons coincides topographically with the high CO activity. The similarity of the studied metabolic and neurochemical characteristics of these auditory centers in reptiles, birds, and mammals indicates the existence of some common principles of their organization in amniotes in spite of phylogenetic differences and peculiarities of specialization of the auditory system in different species.

[The level of metabolic activity (cytochrome oxidase) as an index of functional significance of tectofugal and thalamofugal channels of the reptilian visual system].

Using histochemical determination of activity of the mitochondrial oxidative enzyme cytochrome oxidase (CO) in brain structures, metabolic activity both in turtles and in lizards has been shown to be higher in centers of the tectofugal channel (the tectal stratum griseum centrale, SGC; nucleus pretectalis ventralis, Ptv; thalamic nucleus rotundus, Rot; telencephalic visual area of the anterior dorsal ventricular ridge, Advr) than in the thalamofugal channel centers (the thalamic nucleus geniculatus lateralis pars dorsalis, GLd; cortex dorsolateralis, Cxdl; and pallial thickening, Path) of the visual system. Some interspecies differences in distribution of the CO activity in the tectal, thalamic, and telencephalic visual centers between terrestrial and pond turtles and lizards were revealed. The obtained data confirm the idea on the dominating role of the tectofugal channel over the thalamofugal channel of the visual system in information processing and organization of the day-to-day behavior of reptiles.

The evolution of the centrifugal visual system of vertebrates. A cladistic analysis and new hypotheses.

In a recent review of the available data concerning the centrifugal visual system (CVS) of vertebrates [Repérant, J., Ward, R., Miceli, D., Rio, J.P., Médina, M., Kenigfest, N.B., Vesselkin, N.P., 2006. The centrifugal visual system of vertebrates: a comparative analysis of its functional anatomical organization, Brain Res. Rev. 52, 1-57], we have shown that this feature of the visual system is not a particularity of birds, but is a permanent component of the vertebrate central nervous system which nevertheless shows considerable morphological and functional variation from one taxonomic group to another. Given these findings, the primary objective of the present article is an attempt to specify the evolutionary significance of this phylogenetic diversity. We begin by drawing up an inventory of this variation under several headings: the intracerebral location of the retinopetal neurons; the mode of intra-retinal arborizations of the centrifugal fibres and the nature of their targets; their neurochemical properties; and the afferent supplies of these neurons. We subsequently discuss these variations, particularly that of the intracerebral location of the retinopetal neurons during development and in adult forms, using the neuromeric terminology and in the framework of cladistic analysis, and seek to interpret them in a phylogenetic context. From this analysis, it becomes evident that the CVS is not a homogeneous entity formed by neurons with a common embryological origin, but rather a collection of at least eight distinct subsystems arising in very different regions of the neuraxis. These are the olfacto-retinal, dorsal thalamo-retinal, ventral thalamo-retinal, pretecto-retinal, tecto-retinal, tegmento-mesencephalo-retinal, dorsal isthmo-retinal and ventral isthmo-retinal systems. The olfacto-retinal system, which is probably absent in Agnatha, appears to be a pleisiomorphic characteristic of all Gnathostomata, while on the other hand the tegmento-mesencephalo-retinal system appears to be present only in Agnatha. Our cladistic analysis also shows that the remaining six subsystems are polyphyletic in origin and have arisen independently on several occasions in different radiations of Gnathostoma. In conclusion, we suggest that, in the course of the palaeontological history of vertebrates, these different retinopetal pathways have been selected on the basis of widely different environmental pressures which remain to be identified.

The centrifugal visual system of vertebrates: a comparative analysis of its functional anatomical organization.

The present review is a detailed survey of our present knowledge of the centrifugal visual system (CVS) of vertebrates. Over the last 20 years, the use of experimental hodological and immunocytochemical techniques has led to a considerable augmentation of this knowledge. Contrary to long-held belief, the CVS is not a unique property of birds but a constant component of the central nervous system which appears to exist in all vertebrate groups. However, it does not form a single homogeneous entity but shows a high degree of variation from one group to the next. Thus, depending on the group in question, the somata of retinopetal neurons can be located in the septo-preoptic terminal nerve complex, the ventral or dorsal thalamus, the pretectum, the optic tectum, the mesencephalic tegmentum, the dorsal isthmus, the raphé, or other rhombencephalic areas. The centrifugal visual fibers are unmyelinated or myelinated, and their number varies by a factor of 1000 (10 or fewer in man, 10,000 or more in the chicken). They generally form divergent terminals in the retina and rarely convergent ones. Their retinal targets also vary, being primarily amacrine cells with various morphological and neurochemical properties, occasionally interplexiform cells and displaced retinal ganglion cells, and more rarely orthotopic ganglion cells and bipolar cells. The neurochemical signature of the centrifugal visual neurons also varies both between and within groups: thus, several neuroactive substances used by these neurons have been identified; GABA, glutamate, aspartate, acetylcholine, serotonin, dopamine, histamine, nitric oxide, GnRH, FMRF-amide-like peptides, Substance P, NPY and met-enkephalin. In some cases, the retinopetal neurons form part of a feedback loop, relaying information from a primary visual center back to the retina, while in other, cases they do not. The evolutionary significance of this variation remains to be elucidated, and, while many attempts have been made to explain the functional role of the CVS, opinions vary as to the manner in which retinal activity is modified by this system.

[Extrinsic cells, immunoreactive to Ca-binding protein, as sources of thalamic visual centres in tortoises].

Extrinsic sources of calcium-binding proteins involved in immunoreactive innervation of the visual thalamic nuclei Rot and GLd in turtles (Testudo horsfieldi and Emys orbicularis) were studied using HRP tracing method and immunohistochemistry. In 1.5-4.5 months after monocular enucleation calbindin (Calb)-, parvalbumin (Parv)- and calretinin (Calr)-labeling was found in fragments of degenerated retinal fibers in the contralateral optic tract and in some retinorecipient structures (optic tectum, GLd and GLv). Changes in GLd were detected in its neuropil part. in 2.0-3.5 months after unilateral ablation of tectum and pretectum, the densities of Parv-, Calb- and Aclr-immunoreactivity terminals and fibers were diminisched in the ipsilateral n. Rot, with the maximum effect seen in Parv. Following HRP injection into the visual thalamus (Rot and GLd), retrogradely labeled cells with Parv label only, were revealed in the ventrothalamic nucleus Enta, pretectal nucleus Ptv, and in all types of Ca-binding proteins (CaBPr) in separately labeled cells of the optic tectum. Thus, it has been shown that thalamic visual centers in turtles have multiple extrinsic cells, which serve as sources of CaBPr projections. The present data suggest that organization of CaBPr inputs to visual thalamus in reptiles (turtle) and higher amniotes are fundamentally similar.