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.     

Components of the pigeon tectothalamic visual pathway, revealed with aid of study of cytochrome oxidase activity 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 retino-recipient 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.     

Neurochemical characteristics of the turtle optic tectum: comparison with other reptilian species and birds

Data on distribution of biologically active substances in the turtle optic tectum are compared with results of similar experiments on other reptilian as well as on avian species. In two turtle species (Testudo horsfield and Emys orbicularis), immunoreactivity to monoamines (5-HT and TH), NPY, as well as NADPH-d activity were similarly distributed in neuropil of the SGFS retinorecipient part and in that of the SGP/SAP periventricular layers. Immunoreactivity to neuropeptides SP and m-Enk was maximal in neuropil of the SGFS non-retinorecipient part. The periventricular layers were characterized by the abundant radial SP- and mENK-ir as well as the NADPH-d-positive neurons. Diffusely dispersed ChAT-ir elements and many ir fibers perpenducilar to the tectal surface were observed in the SGFS retinorecipient part; the SGFS non-retinorecipient part contained a dense plexus of thick ir fibers and diffusely distributed ir terminals. The GABA ir cells were the most numerous in the tectum; they were spread in all tectal layers. Thus, various biologically active substance located in superficial retinorecipient tectal sublayers could affect processing and transmission of information via ascending dendrites of neurons in deeper layers. The cells containing SP, m-Enk, and NADPH-d had laminar organization in SGP; via the system of ascending and descending axons, they are able to affect other structures within and outside of the optic tectum. Putative sources of tectal modulatory innervation are discussed. In all studied reptilian and avian species, the principal similarity is revealed in the neurochemical organization. Some differences might be explained by the level of tectal differentiation due to factors of phylogenetic evolution and/or adaptive specialization.     

Distribution of calcium-binding proteins parvalbumin and calbindin in the thalamic auditory center in pigeons

Distribution of calcium-binding proteins (CaBPr) parvalbumin (PV) and calbindin (CB) in the thalamic auditory center (nucleus ovoidalis, Ov) was studied in the pigeon (Columba livia). Two parts of Ov were distinguished on the basis of their cytoarchitectonics and distribution of PV and CB immunoreactivity. The central lemniscal region (core, nCe) contains both dense PV-ir neuropil and PV-ir neurons overlapped with scant CB-ir neuropil and weaker stained CB-ir neurons. The peripheral extralemniscal region (belt), consisting of peri/paraovoidal nuclei (Ovl, Ovm, SPO), contains only CB-ir neuropil and strongly stained CB-ir neurons morphologically differing from CB-ir neurons in the nCe. A comparative analysis of our data on the distribution of PV and CB immunoreactivity in the thalamic auditory relay center in pigeons and related literature data obtained on other avian, reptilian and mammalian species indicates high evolutionary conservatism of its extralemniscal region across all sauropside amniotеs and mammals in contrast to plasticity of its central lemniscal region due to adaptive, ecologically dependent transformations during the evolution.     

Neurochemical characteristics of the turtle optic tectum: Comparison with other reptilian species and birds

Data on distribution of biologically active substances in the turtle optic tectum are compared with results of similar experiments on other reptilian as well as on avian species. In two turtle species (Testudo horsfield and Emys orbicularis), immunoreactivity to monoamines (5-HT and TH), NPY, as well as NADPH-d activity were similarly distributed in neuropil of the SGFS retinorecipient part and in that of the SGP/SAP periventricular layers. Immunoreactivity to neuropeptides SP and m-Enk was maximal in neuropil of the SGFS non-retinorecipient part. The periventricular layers were characterized by the abundant radial SP- and mENK-ir as well as the NADPH-d-positive neurons. Diffusely dispersed ChAT-ir elements and many ir fibers perpenducilar to the tectal surface were observed in the SGFS retinorecipient part; the SGFS non-retinorecipient part contained a dense plexus of thick ir fibers and diffusely distributed ir terminals. The GABA ir cells were the most numerous in the tectum; they were spread in all tectal layers. Thus, various biologically active substances located in superficial retinorecipient tectal sublayers could affect processing and transmission of information via ascending dendrites of neurons in deeper layers. The cells containing SP, m-Enk, and NADPH-d had laminar organization in SGP; via the system of ascending and descending axons, they are able to affect other structures within and outside of the optic tectum. Putative sources of tectal modulatory innervation are discussed. In all studied reptilian and avian species, the principal similarity is revealed in the neurochemical organization. Some differences might be explained by the level of tectal differentiation due to factors of phylogenetic evolution and/or adaptive specialization.     

Neurons of visual thalamic nuclei projecting to telencephalon express different types of calcium-binding proteins: A combined immunocytochemical and tracer study

In turtles (Testudo horsfieldi, Emys orbicularis), immunoreactivity to calbindin (CB), parvalbumin (PV), calretinin (CR) and co-localization of CB and PV were studied in neurons of the visual thalamic nuclei (Rot, GLd) projecting to the telencephalon using a combination of immunohistochemical and tracer methods. The prevalence of CB-immunoreactive (-ir) neurons in Rot, CB-ir and CR-ir neurons in GLd, and a smaller number of PV-ir neurons in both nuclei was shown. Double immunofluorescent labeling revealed that within both nuclei PV and CB are colocalized in most PV-ir and fewer CB-ir neurons. After injection of horseradish peroxidase into the Rot and GLs telencephalic projection fields, retrograde labeling was found in corresponding thalamic projection neurons immunoreactive to all the three proteins. After introduction of the fluorescent tracer Fluo-gold into the same telencephalic regions, retrograde labeling was detected in Rot and GLd neurons immunoreactive only to PV and CB as well as in neurons with colocalization of both proteins. These findings provide further evidence that in turtles the CB component prevails in the rotundo-telencephalic pathway while the CB/CR component is dominant in the geniculotelencephalic pathway. The role of functional specialization in segregation of neurons expressing distinct types of calcium-binding proteins is postulated.     

Evolutionary evaluation of reciprocity of connections in the turtle tectofugal visual system

In two turtle species—Emys orbicularis and Testudo horsfieldi—by the method of anterograde and retrograde traicing 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 calcium-binding proteins parvalbumin and calbindin in the pigeon telencephalic auditory center

Immunoreactivity for calcium-binding proteins parvalbumin (PV) and calbindin (CB) was studied in the pigeon (Columba livia) telencephalic auditory center. All its regions displayed overlapping distribution patterns of PV and CB immunoreactivity, although in the central (L2) vs. peripheral (L1, L3, CMM) layers they were dissimilar. L2 and the inner L1 sublayer (L1i) were distinguished by a higher immunoreactivity of neuropil for both proteins and the presence (in L2) of numerous small densely packed granular-type cells: heavily stained PV-ir and, as a rule, poorly stained CB-ir neurons. In Lli, the number of neurons and the density of neuropil immunoreactive to both proteins decreased. The outer L1 sublayer (L1e) as well as L3 and CMM were characterized by a generally lesser density and irregular distribution of immunoreactive neuropil and a heterogenous repertoire of PV-ir and CB-ir neurons referring to diverse morphological types, with an increased number of large multipolar cells. The differences in PV and CB immunoreactivity among different regions of the pigeon telencephalic auditory center revealed the similarity of the latter to the laminar auditory cortex in mammals.     

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.     

Changes of calcium binding protein expression in spinothalamic tract neurons after peripheral inflammation

Specific neuronal populations are known to express calcium binding proteins (CBP) such as calbindin (CB), parvalbumin (PV) and calretinin (CR). These CBP can act as calcium buffers that modify spatiotemporal characteristics of intracellular calcium transients and affect calcium homeostasis in neurons. It was recently shown that changes in neuronal CBP expression can have significant modulatory effect on synaptic transmission. Spinothalamic tract (STT) neurons form a major nociceptive pathway and they become sensitized after peripheral inflammation. In our experiments, expression of CBP in STT neurons was studied in a model of unilateral acute knee joint arthritis in rats. Altogether 377, 374 and 358 STT neurons in the segments L3-4 were evaluated for the presence of CB, PV and CR. On the contralateral (control) side 1%, 9% and 47% of the retrogradely labeled STT neurons expressed CB, PV and CR, respectively. On the ipsilateral (arthritic) side there was significantly more CB (23%) and PV (25%) expressing STT neurons, while the number of CR positive neurons (50%) did not differ. Our results show increased expression of fast (CB) and slow (PV) calcium binding proteins in STT neurons after induction of experimental arthritis. This suggests that change in CBP expression could have a significant effect on calcium homeostasis and possibly modulation of synaptic activity in STT neurons.     

Influence of the "open field" exposure on calbindin D28K, calretinin, and parvalbumin containing cells in the rat midbrain - developmental study.

The aim of our study was to analyze the influence of the open field (OF) exposure on: 1. Distribution of c-Fos positive nuclei in: ventral tegmental area, substantia nigra, periaqueductal gray. 2. Appearance of calbindin-D28k, calretinin and parvalbumin in midbrain neurons that are engaged in the stress response. 3. Changes of c-Fos and calcium-binding proteins expression during maturation. The material consisted of Wistar rats of age between 0 and 90 days. The OF exposure was applied throughout 10 min and 90 min before the death of the animals. The brain sections were double stained using the antibodies against c-Fos, CB, CR or PV. Our results showed that in all studied nuclei age-related increase of c-Fos expression (without changing of its distribution properties) was found. PV didn't show any co-localization with c-Fos in neurons of studied regions at any ages, however some PV-immunoreactive (PV-ir) basket-like structures around c-Fos-immunoreactive (c-Fos-ir) neurons were observed. In the youngest group of rats c-Fos-ir cells and cells immunoreactive for CB and CR constituted separate neuronal populations. During maturation increases in the level of their co-localization with c-Fos was observed. We may conclude that in adult rat midbrain structures CB-immunoreactive (CB-ir) and CR-immunoreactive (CR-ir) cells (probably projection neurons) are mainly activated in the stress response following OF exposure. In the contrary PV-ir cells has only an indirect (modulatory) influence upon the c-Fos-ir cells.     

Morphological properties of tectal neurons that project to the nucleus geniculatus lateralis,pars ventralis (GLv) and the surrounding ventral thalamus in chicks

Layer 10 neurons of the chick tectum were morphologically investigated. The layer 10 neurons displayed heterogeneous immunoreactivities to calcium-binding proteins (CaBPs). Calbindin (CB)-immunoreactive (ir) neurons had pyramidal or round somata, primarily found in layers 5, 9, and 13. Parvalbumin (PV)-ir neurons were of various shapes with small to large somata (109.7 ± 48.6 μm²) that were located mainly in layers 4 and 10. Calretinin (CR)-ir neurons had small to middle-sized somata (79.3 ± 9.7 μm²) located primarily in layers 10 and 13, and most of them were similar to typical radial cells in size and shape. Two distinct types of neurons that projected to the nucleus geniculatus lateralis, pars ventralis (GLv) and ventral thalamus were demonstrated in layer 10. Type 1 cells had small to middle-sized somata (74.3 ± 33 μm²), and each cell had a single apical dendrite that ramified into bush-like branches in layer 7. These cells corresponded to CR-ir neurons and radial cells in size and shape. Type 2 cells had larger somata (124.7 ± 52.6 μm²), and their shapes were pyramidal, polygonal, or oval. They had multiple obliquely ascending dendrites that ramified into bush-like branches in layer 7. These cells often appeared similar to PV-ir neurons.     

Polarity and laminar formation of the optic tectum in relation to retinal projection

The mes-metencephalic boundary (isthmus) works as an organizer for the tectum, and the organizing molecule may be Fgf8. The region where Otx2, En1, and Pax2 are expressed overlappingly may differentiate into the mesencephalon. The di-mesencephalic and mes-metencephalic boundaries are determined by repressive interaction of Pax6 and En1/Pax2 and of Otx2 and Gbx2, respectively. The optic tectum is a visual center in lower vertebrates. The tectum and the retina should be regionalized and be positionally specialized for the proper retinotopic projection. Gradient of En2 plays a crucial role in rostrocaudal polarity formation of the tectum. En2 confers caudal characteristics of the retina by inducing ephrinA2 and A5, which are the repellant molecules for the growth cones of temporal retinal ganglion cells. Grg4 antagonizes the isthmus-related genes, and is involved in the formation of di-mesencephalic boundary and tectal polarity formation at an early phase of development. Then, Grg4 plays a role in tectal laminar formation by controlling the migration pathway. Migration pathway of tectal postmitotic cells changes after E5. The late migratory cells split the early migratory neurons to form laminae h-j of SGFS. Grg4 is expressed in the ventricular layer after E5, and forces postmitotic cells to follow the late migratory pathway, though retinal fibers terminate at laminae a-f of SGFS. Misexpression of Grg4 disrupts the lamina g, and in such tecta retinal arbors invade deep into the tectal layer, indicating that lamina g is a nonpermissive lamina for the retinal arbors.     

Co-existence of protein kinase C gamma and calcium-binding proteins in neurons of the medullary dorsal horn of the rat

Protein kinase C gamma isoform (PKCgamma) is present at high levels in the spinal and medullary dorsal horns and is thought to play a role in the sensitization of dorsal horn neurons in certain pain states. Calbindin-D28k (CB), calretinin (CR) and parvalbumin (PV) are the most commonly expressed calcium-binding proteins and are located abundantly in the medullary dorsal horn (also called the caudal subnucleus of the spinal trigeminal nucleus). In the present study, immunofluorescence histochemical double staining for PKCgamma and CB, CR or PV was performed in the rat medullary dorsal horn. Most of the PKCgamma-, CB-, CR- and PV-immunoreactive neurons were observed in lamina II; some were also encountered in lamina I and lamina III of the medullary dorsal horn. Neurons co-expressing CB/PKCgamma, CR/PKCgamma and PV/PKCgamma were also mainly found in lamina II, while in lamina I and lamina III, only a few neurons co-expressing CB/PKCgamma, CR/PKCgamma and PV/PKCgamma were encountered. The percentages of neurons co-expressing CB/PKCgamma in the total numbers of CB- and PKCgamma-immunoreactive neurons were 6.7 and 5.9%, respectively. Of the total numbers of CR- and PKCgamma-immunoreactive neurons, 5.0 and 5.6%, respectively, showed both CR and PKCgamma immunoreactivities. The percentages of neurons co-expressing PV/PKCgamma in the total numbers of PV- and PKCgamma-immunoreactive neurons were 25.7 and 4.1%, respectively. Most of these neurons co-expressing CB/PKCgamma, CR/PKCgamma and PV/PKCgamma were small (/=36 microm) multipolar neurons were infrequently seen. The present results indicate that there are some neurons co-expressing CB/PKCgamma, CR/PKCgamma and PV/PKCgamma in the medullary dorsal horn. These neurons might play important roles in the nociceptive modulation from the oro-facial region.     

NADPH-diaphorase and calcium binding proteins in the trigeminal nucleus oralis of rats

We have examined the distribution of nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) and the calcium binding proteins (CBPs), calbindin D-28k (CB), calretinin (CR) and parvalbumin (PV), in the trigeminal nucleus oralis (Sp5O). NADPH-d was detected by histochemistry while CBP was detected by immunohistochemistry. NADPH-d-positive neurons were distributed in the medial rostro-dorsomedial part (RDMsp5O) and dorsomedial part (DMsp5O) of Sp5O, and the rostrolateral part of the nucleus of the solitary tract (NTS). CB- and CR-positive neurons were mainly distributed in the dorsal part of Sp5O. In contrast, PV-positive neurons were mainly distributed in the ventral part of Sp5O. NADPH-d colocalized with CB (40%) and CR (20%) but not with PV in neurons of DMsp5O/NTS. The mean cell sizes of neurons in RDMsp5O were larger than those in DMsp5O/NTS. PV-positive neurons were larger than NADPH-d-positive neurons. NADPH-d-, CB- and CR-positive neurons were generally small in RDMsp5O and DMsp5O/NTS. Few neurons were retrogradely labeled in RDMsp5O and DMsp5O from the thalamus, when numerous labeled neurons were in the principal and interpolar nuclei. These data indicate that NADPH-d histochemistry and CB, CR and PV immunohistochemistry identify a discrete cell population in Sp5O. Those labeled neurons in RDMsp5O and DMsp5O/NTS were considered to be involved in sensorimotor reflexive function of the intra-oral structures.     

NADPH-diaphorase and calcium binding proteins in the trigeminal nucleus oralis of rats

We have examined the distribution of nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) and the calcium binding proteins (CBPs), calbindin D-28k (CB), calretinin (CR) and parvalbumin (PV), in the trigeminal nucleus oralis (Sp5O). NADPH-d was detected by histochemistry while CBP was detected by immunohistochemistry. NADPH-d-positive neurons were distributed in the medial rostro-dorsomedial part (RDMsp5O) and dorsomedial part (DMsp5O) of Sp5O, and the rostrolateral part of the nucleus of the solitary tract (NTS). CB- and CR-positive neurons were mainly distributed in the dorsal part of Sp5O. In contrast, PV-positive neurons were mainly distributed in the ventral part of Sp5O. NADPH-d colocalized with CB (40%) and CR (20%) but not with PV in neurons of DMsp5O/ NTS. The mean cell sizes of neurons in RDMsp5O were larger than those in DMsp5O/NTS. PV-positive neurons were larger than NADPH-d-positive neurons. NADPH-d-, CB- and CR-positive neurons were generally small in RDMsp5O and DMsp5O/NTS. Few neurons were retrogradely labeled in RDMsp5O and DMsp5O from the thalamus, when numerous labeled neurons were in the principal and interpolar nuclei. These data indicate that NADPH-d histochemistry and CB, CR and PV immunohistochemistry identify a discrete cell population in Sp5O. Those labeled neurons in RDMsp5O and DMsp5O/NTS were considered to be involved in sensorimotor reflexive function of the intra-oral structures.     

Ontogeny of Neurons Containing Calcium‐Binding Proteins in the Preoptic Area of the Guinea Pig: Sexually Dimorphic Development of Calbindin

This study characterizes for the first time the distribution and coexistence patterns of calbindin (CB), calretinin (CR), and parvalbumin (PV) in the female and male guinea pig preoptic area (POA) during brain development, using immunohistochemistry and quantitative real‐time PCR techniques. The results show that the prenatal development of the guinea pig POA takes place in elevated levels of CB and CR immunoreactivity with the peak at embryonic day 50 (E50) and generally in newborns both these proteins reach an adult‐like pattern of immunoreactivity, contrary to PV which appears later, peaks at postnatal day (PND) 10 (P10), and stabilizes at P20. CB and CR have also overlapping distributions which differed from that of PV, and much higher expressions at mRNA and protein levels. However, CB‐positive (+), CR+ and PV+ neurons create in the guinea pig POA separate populations as CB and CR coexisted only in a small number of neurons and CB+ cells never coexpressed PV. Moreover, the density of CB+ neurons, contrary to CR+ and PV+ cells, is sexually dimorphic favoring males at all the examined stages. In conclusion, elevated levels of CR and CB at the time of intense cell migration, differentiation, myelination, and synaptogenesis in the guinea pig brain suggest that these proteins may be engaged in similar processes in the POA, while late onset of PV may be rather linked with POA maturation. As the population of CB+ cells in the POA is very large, its dimorphic development may have huge impact on the sexual differentiation of this brain region.     

Nucleus isthmi of the frog: structure and tecto-isthmic projection.

The morphology of neurons in the isthmic nucleus was studied with the Golgi technique. Most of the neurons have thick dendrites covered with lamelliform dendritic processes. The tecto-isthmic projection was investigated with the Fink--Heimer technique after partial tectal lesions. The anteromedial part of the tectum projects on the dorsal and anterior part, the caudomedial tectal region on the dorsal and posterior part of the nucleus. The posterolateral tectal area projects on the anterolateral part of the nucleus, and the axons originating in the anterolateral tectal quadrant terminate in its ventral and caudal part.     

Acetylcholinesterase activity in the normal and retino-deprived optic tectum of the quail

Summary Acetylcholinesterase localization has been studied by electron microscopic histochemistry in the quail optic tectum. Ultrastructural analysis reveals that the different neuronal types in the tectum possess the metabolic pathways for AChE synthesis to different degrees. From the site of synthesis in cell bodies the enzyme spreads towards areas of neuropil. In the neuropil of AChE-rich areas a balance seems to exist between enzyme stored in dendrites (and sometimes axon terminals) and enzyme released into the extracellular spaces. Precise identification of cholinergic synapses by means of AChE localization is in most cases impossible, due to extensive spread of the enzyme through the extracellular compartments of the neuropil.Unilateral ocular ablation causes disappearance of the stratum opticum and decrease in thickness of the superficial tectal layers in the contralateral optic tectum, but only minor modifications in AChE localization. This finding is in agreement with biochemical results which show equivalence of the relative concentration of AChE in the right and left optic tectum 1 or 2 months after ablation of the right eye. The experimental evidence suggests that cholinergic mechanisms are not related to the discharge of retinal afferents on receptive tectal neurons, but more likely to intrinsic neural circuits which might be involved in the modulation of tectal activity.     

The calcium binding proteins calbindin,parvalbumin, and calretinin have specific patterns of expression in the gray matter of cat spinal cord

Calcium binding proteins (CBPs) regulate intracellular levels of calcium (Ca²⁺) ions. CBPs are particularly interesting from a morphological standpoint, because they are differentially expressed in certain sub-populations of cells in the nervous system of various species of vertebrate animals. However, knowledge on the cellular regulation governing such cell-specific CBP expression is still incomplete. In this work on the L7 segment of the cat spinal cord, we analyzed the localization and morphology of neurons expressing the CBPs calbindin-28 KD (CB), parvalbumin (PV), and calretinin (CR), and co-expressing CB and PV, CB and CR, and PV and CR. Single CBP-positive (⁺) neurons showed specific distributions: (1) CB was present in small neurons localized in laminae I, II, III and X, in small to medium size neurons in laminae III–VI, and in medium to large neurons in laminae VI–VIII; (2) PV was present in small size neurons in laminae III and IV and in medial portions of laminae V and VI, medium neurons and in lamina X at the border with lamina VII, in medium to large neurons in laminae VII and VIII; (3) CR labeling was detected in small size neurons in laminae I, II, III and VIII, in medium to large size neurons in laminae I and III–VII, and in small to medium size neurons in lamina X. Double labeled neurons were a small minority of the CBP⁺ cells. Co-expression of CB and PV was seen in 1 to 2% of the CBP⁺ cells, and they were detected in the ventral and intermediate portions of lamina VII and in lamina X. Co-localization of CB and CR was present in 0.3% of the cells and these cells were localized in lamina II. Double labeling for PV and CR occurred in 6% of the cells, and the cells were localized in ventral part of lamina VII and in lamina VIII. Overall, these results revealed distinct and reproducible patterns of localization of the neurons expressing single CBPs and co-expressing two of them. Distinct differences of CBP expression between cat and other species are discussed. Possible relations between the cat L7 neurons expressing different CBPs with the neurons previously analyzed in cat and other animals are suggested.