Distribution of somatostatin receptors in the cat and monkey visual cortex demonstrated by in vitro receptor autoradiography

Receptor architecture of macaque and human early visual areas: not equal, but comparable

Existing cytoarchitectonic maps of the human and macaque posterior occipital cortex differ in the number of areas they display, thus hampering identification of homolog structures. We applied quantitative in vitro receptor autoradiography to characterize the receptor architecture of the primary visual and early extrastriate cortex in macaque and human brains, using previously published cytoarchitectonic criteria as starting point of our analysis. We identified 8 receptor architectonically distinct areas in the macaque brain (mV1d, mV1v, mV2d, mV2v, mV3d, mV3v, mV3A, mV4v), and their respective counterpart areas in the human brain (hV1d, hV1v, hV2d, hV2v, hV3d, hV3v, hV3A, hV4v). Mean densities of 14 neurotransmitter receptors were quantified in each area, and ensuing receptor fingerprints used for multivariate analyses. The 1st principal component segregated macaque and human early visual areas differ. However, the 2nd principal component showed that within each species, area-specific differences in receptor fingerprints were associated with the hierarchical processing level of each area. Subdivisions of V2 and V3 were found to cluster together in both species and were segregated from subdivisions of V1 and from V4v. Thus, comparative studies like this provide valuable architectonic insights into how differences in underlying microstructure impact evolutionary changes in functional processing of the primate brain and, at the same time, provide strong arguments for use of macaque monkey brain as a suitable animal model for translational studies.

Neural Correlates of a Trance Process and Alternative States of Consciousness in a Traditional Healer

Trance processes are a form of altered states of consciousness (ASC) widely reported across cultures. Entering these states is often linked to auditory stimuli such as singing, chanting, or rhythmic drumming. While scientific research into this phenomenon is relatively nascent, there is emerging interest in investigating the neural correlates of altered states of consciousness such as trance. This report aims to add to this field of ASC through exploring how the perception of an experienced Sangoma (traditional South African healer) entering a trance process correlates to blood-oxygen-level-dependent (BOLD) signal modulation with auditory stimuli. Functional Magnetic Resonance Imaging (fMRI) data were analyzed using a General Linear Model comparing music versus no music condition multiplied by the percept of experiencing trance (High or Low). Positive BOLD activation was shown in the auditory cortex in both hemispheres during a trance process. Other brain regions tightly correlated to trance perception were the right parietal, right frontal, and area prostriata (p < 0.05, Bonferroni corrected). The orbitofrontal cortex (part of the Default Mode Network) was negatively activated and most correlated with music when trance was high, showing the largest differential between high and low trance perception. This is the first study to directly correlate BOLD signal variations in an expert subject’s percept of trance onset and intensity, providing insight into the neural signature and dynamics of this unique form of ASC. Future studies should examine in greater detail the perception of trance processes in expert subjects, adding other neuroimaging modalities to further investigate how these brain regions are modulated by trance expertise.

Broad characterization of endogenous peptides in the tree shrew visual system

Endogenous neuropeptides, acting as neurotransmitters or hormones in the brain, carry out important functions including neural plasticity, metabolism and angiogenesis. Previous neuropeptide studies have focused on peptide-rich brain regions such as the striatum or hypothalamus. Here we present an investigation of peptides in the visual system, composed of brain regions that are generally less rich in peptides, with the aim of providing the first broad overview of peptides involved in mammalian visual functions. We target three important parts of the visual system: the primary visual cortex (V1), lateral geniculate nucleus (LGN) and superior colliculus (SC). Our study is performed in the tree shrew, a close relative of primates. Using a combination of data dependent acquisition and targeted LC-MS/MS based neuropeptidomics; we identified a total of 52 peptides from the tree shrew visual system. A total of 26 peptides, for example GAV and neuropeptide K were identified in the visual system for the first time. Out of the total 52 peptides, 27 peptides with high signal-to-noise-ratio (>10) in extracted ion chromatograms (EIC) were subjected to label-free quantitation. We observed generally lower abundance of peptides in the LGN compared to V1 and SC. Consistently, a number of individual peptides showed high abundance in V1 (such as neuropeptide Y or somatostatin 28) and in SC (such as somatostatin 28 AA1-12). This study provides the first in-depth characterization of peptides in the mammalian visual system. These findings now permit the investigation of neuropeptide-regulated mechanisms of visual perception.

Chronic exposure to either somatostatin (SS) or octreotide, a long-lasting SS analogue, affects SS expression in the postnatal visual cortex of the rat

The peptide somatostatin (SS) is widely distributed in the mammalian brain where it modulates neuronal activity through interactions with specific membrane-bound receptor subtypes (ssts). Five different ssts were characterized so far (sst1-5) and their selective agonists were developed on the basis of their binding specificity. SS and ssts are transiently expressed in the developing brain, suggesting a functional role of somatostatinergic systems in neuronal maturation. In the present study, we investigated the effects of chronic exposure to either the SS synthetic analogue, SS-14 or octreotide (a long-acting sst2-preferring analogue) on the maturation of SS-immunoreactivity (-ir) in the primary visual cortex of the rat. SS-ir maturation was investigated both by an evaluation of the number of SS-immunoreactive cells and by radioimmunoassay (RIA) to measure the levels of SS in the postnatal visual cortex. In the visual cortex of normal rats, the number of SS-positive cells markedly increased during the second postnatal week and then significantly decreased until the adult value was reached at the third week. Early and repeated intracerebroventricular (i.c.v.) injections of either SS-14 or octreotide prevented the increase in the number of SS-positive cells, with adult values reached at the end of the first postnatal week. Similarly, administration of either SS-14 or octreotide significantly decreased the SS content of the visual cortex, measured at the end of the second postnatal week. These results show that high local concentrations of either SS-14 or octreotide interfere with SS expression in developing cortical neurons in a restricted postnatal period.

Somatostatin receptors in the rhesus monkey brain: localization and pharmacological characterization

To characterize the nature and distribution of somatostatin (SRIF) receptors, radioligand binding studies and in vitro receptor autoradiography were performed in Rhesus monkey brain using either [125I]LTT-SRIF-28 ([Leu8, D-Trp22, 125I-Tyr25]SRIF-28) alone or in the presence of 3 nM seglitide (to block sst2 sites), [125I]Tyr3-octreotide or [125I]CGP 23996 (c[Asu-Lys-Asn-Phe-Trp-Lys-Thr-Tyr-Thr-Ser]) in buffer containing either 120 mM Na+ or 5 mM Mg2+. [125I]Tyr3 -octreotide labelled an apparently homogeneous population of sites in cerebral and cerebellar cortex (Bmax = 27.3 +/- 2.8 fmol/mg protein and 52.6 +/- 8.6 fmol/mg protein, PKd = 9.46 +/- 0.03 and] 9.93 +/- 0.03, respectively). The pharmacological profile of these sites correlated highly significantly with that of human recombinant sst2 receptors (r = 0.996), but not or much less with that of human recombinant sst3 and sst5 receptors (r = 0.12 and 0.45, respectively). [125I]CGP 23996 (in Na(+)-buffer) also labelled an apparently homogeneous population of sites in Rhesus monkey cerebral cortex membranes (Bmax = 3.1 +/- 0.3 fmol/mg protein, pKd = 10.57 +/- 0.08), the pharmacological profile of which was highly significantly correlated with the profiles of human recombinant sst1 and sst4 receptors (r = 0.98 and 0.96, respectively). Using receptor autoradiography, high levels of [125I]LTT-SRIF-28 and [125I]Tyr3 -octreotide recognition sites were found in basal ganglia, molecular and granular layers of the cerebellum and layers III, V and VI of entorhinal cortex. In these regions, the addition of 3 nM seglitide produced a marked decrease of [125I]LTT-SRIF-28 binding. Low levels of [125I]LTT-SRIF-28 binding were observed in subiculum, pituitary and choroid plexus. By contrast, [125I]CGP 23996 labelling in the presence of Mg2+ as well as Na+ ions was highest in pituitary and choroid plexus. However, [125I]CGP 23996 binding was diversely affected by these ionic conditions in several regions of hippocampus and cerebral cortex. Displacement of [125I]CGP 23996 (in Mg(2+)-buffer) with seglitide in the molecular layer of the cerebellum, deep layers of the entorhinal cortex, layers I, II and V of the insular cortex and frontal pole yielded complex competition curves suggesting the presence of two populations of SRIF receptors. By contrast, [125I]CGP 23996 binding (in Mg(2+)-buffer) in the choroid plexus, hilus of the dentate gyrus and stratum oriens and radiatum of the CA3 field of hippocampus was not affected by seglitide up to 10 microM, suggesting only sst1 and/or sst4 sites which have a negligible affinity for seglitide to be present in these structures. Taken together, these results suggest that [125I]CGP 23996 (in the presence of Na+) labels exclusively SRIF-2 receptors (sst1 and/or sst4), whereas in the presence of Mg2+ ions, [125I]CGP 23996 labels both SRIF-2 and SRIF-1 receptors (sst2, sst3 and sst5). The present study also demonstrates the presence and differential distribution of sst2 and sst1/sst4 receptors in the Rhesus monkey brain.

Effect of sensory deafferentation on immunoreactivity of GABAergic cells and on GABA receptors in the adult cat visual cortex

To investigate the effects of sensory deafferentation on the cortical GABAergic circuitry in adult cats, glutamic acid decarboxylase (GAD) and gamma-aminobutyric acid (GABA) immunoreactivity and GABA receptor binding were studied in the visual cortex of normal cats and compared with cats that had received restricted binocular central lesions of the retina and had survived for 2 weeks postlesion in a normal visual environment. In the visual cortex of lesioned cats, two changes were observed in the number of GAD-immunoreactive elements in the regions affected by the retinal lesions: the number of GAD-positive puncta decreased, whereas that of GAD-immunoreactive somata increased. In contrast, no detectable changes were measured in the number of GABA-immunopositive somata or puncta. At the receptor level, we observed no differences in either the laminar distribution or the affinity of cortical GABAA and GABAB receptors labeled with [3H]-muscimol and [3H]-baclofen, respectively, in the lesioned versus normal cats. We present the hypothesis that sensory deafferentation in these adult cats (1) leads to a reduction of cortical GABAergic inhibition in the deafferented region, and (2) that this decreased inhibition may permit changes in efficiency of synapses and (3) that these changes may represent a first stage of events underlying the retinotopic reorganization preceeding the structural changes.

Localization of the two protein kinase C beta-mRNA subtypes in cat visual system

Protein kinase C (PKC) consists of a family of different subtypes encoded by different PKC genes. We investigated the distribution of PKC beta 1 and PKC beta 2 in the visual system of the adult cat by in situ hybridization using oligonucleotide probes complementary to the PKC beta 1 and PKC beta 2 mRNAs, two splicing variants of the same gene transcript. In the primary visual cortex PKC beta 1 and PKC beta 2 were both present. The laminar distribution patterns found for the two PKC subtypes were identical. A remarkable finding was the difference between the laminar distribution of the PKC beta s in areas 17 and 18 when compared with area 19. In all three areas the highest expression levels were found in layer VI, moderately high levels were found in layers II, III and V, while layer I was devoid of signal. In area 17 and 18 layer IV stood out by its low PKC beta signal. In sharp contrast, layer IV of area 19 was indiscernible from the superficial layers because of an evenly high signal. In the dLGN of the adult cat PKC beta 1 and PKC beta 2 mRNAs were distributed rather homogeneously over the different layers, but the expression levels for PKC beta 1 were clearly higher than those for PKC beta 2.

Partial colocalization of the GABAA receptor with parvalbumin and calbindin D-28K in neurons of the visual cortex and the dorsal lateral geniculate nucleus of the cat

Monoclonal antibodies to a synthetic peptide fragment of the beta 1-subunit of the bovine central GABAA/benzodiazepine receptor were used to investigate immunocytochemically the distribution of this receptor in the visual system of the cat. Labeled neurons were observed in all layers of the visual cortex and the dorsal lateral geniculate nucleus. About half of the total cortical or geniculate neuronal population was found to be positive. To further identify immunocytochemically these GABAA receptor expressing cells, double stainings were undertaken with, on one hand, the monoclonal antibodies directed against the receptor complex, and on the other hand polyclonal antisera directed against cat muscle parvalbumin or chicken calbindin D-28K. A high degree of colocalization between either of the two calcium binding proteins and the GABAA receptor was found in the upper layers (I, II and III) of the visual cortex and in the A and C laminae of the dorsal lateral geniculate nucleus; all calbindin D-28K-positive cells were immunoreactive for the GABAA receptor. The parvalbumin-positive cells, scattered throughout all layers of the dorsal lateral geniculate nucleus and the visual cortex, except cortical layer I, were also all positive for the GABAA receptor. However, a large proportion of all GABAA receptor bearing cells were negative for one of the calcium binding proteins.

Distribution of immediate early gene zif-268, c-fos, c-jun and jun-D mRNAs in the adult cat with special references to brain region related to vision

The distribution of immediate early gene zif-268, c-fos, c-jun and jun-D mRNAs was investigated in the visual cortex, dorsal lateral geniculate nucleus and hippocampus of the adult cat brain with in situ hybridization. In area 17, zif-268, c-jun and jun-D were found predominantly in layers II-III and VI, while c-fos mRNA was abundant in layer VI. In area 18, the zif-268, c-fos and c-jun labelling pattern was identical to that of area 17, this was not true for jun-D. In area 19, only c-jun retained the lamination pattern of areas 17 and 18, while zif-268, c-fos and jun-D were homogeneously distributed. In the dorsal lateral geniculate nucleus, only c-fos and jun-D resulted in labelling. In the pyramidal layer of hippocampus, zif-268 was found in CA1-4, c-jun in CA1-3, and jun-D in CA2-4. In the dentate gyrus, c-jun was abundant, jun-D moderate and zif-268 faint. C-fos labelling was absent in the hippocampal formation.

Decrease of somatostatin receptor binding in the rat cerebral cortex after ibotenic acid lesion of the nucleus basalis magnocellularis: a quantitative autoradiographic study

The specific binding of 125I-Tyr11-somatostatin-14 (125I-Tyr11-SS-14) was measured in different cortical regions after unilateral ibotenic acid lesion of the rat nucleus basalis magnocellularis (NBM). A marked loss of acetylcholinesterase-positive fibers was observed in the frontal, parietal, temporal and occipital cortices ipsilateral to the lesion. The loss of cholinergic cell bodies in the NBM was further investigated with choline-acetyltransferase (ChAT) immunohistochemistry which indeed demonstrated a loss of ChAT-positive magnocellular perikarya. Autoradiographic analyses of specific binding of 125I-Tyr11-SS-14 demonstrated a significant reduction in binding density in the denervated parts of the neocortex. The decrease in specific binding was most pronounced (40-50%) in the superficial layers (I-III) of the frontal, parietal and temporal cortices 2 and 4 weeks after lesion. A significant loss in 125I-Tyr11-SS-14 binding in the deeper layers was only observed in the frontal cortex after 2 and 4 weeks. In the occipital cortex a significant decrease was measured in the superficial layers only after 4 weeks. The specific binding in all cortical regions returned to normal after 6 weeks. The results suggested that 125I-Tyr11-SS-14 binding sites are localized on cholinergic afferents in the rat neocortex and that an up-regulation of number of binding sites, alternatively an increased binding affinity occurred with time after lesion.

Laminar distribution of NMDA receptors in cat and monkey visual cortex visualized by [3H]-MK-801 binding

Glutamate is the major excitatory neurotransmitter of the mammalian central nervous system. Two major classes of glutamate receptors have been reported. The actions of glutamate on its N-methyl-D-aspartate (NMDA)-type receptor may underlie developmental and adult plasticity as well as neurotoxicity. The NMDA-type of glutamate receptor in cat and monkey visual cortex was visualized by means of in vitro receptor autoradiography with the noncompetitive NMDA-receptor antagonist [3H]-MK-801. The kinetics, performed on tissue sections, revealed an apparently single, saturable site with an approximate dissociation constant (KD) of 18.5 nM in cat and 15.9 nM in monkey visual cortex. Autoradiography, performed on frontal sections of cat and monkey visual cortex, revealed a heterogeneous laminar distribution of NMDA receptors. Cat areas 17, 18, 19, and the lateral suprasylvian areas exhibited a similar NMDA-receptor distribution. In these areas, NMDA receptors were most prominent in layer II and the upper part of layer III. In monkey striate cortex, NMDA receptors were primarily concentrated in layers II, upper III, IVc, V, and VI. In monkey secondary visual cortex, [3H]-MK-801 labeling was most prominent in layers II, V, and VI; whereas in the temporal visual areas included in this study layer II displayed the heaviest receptor labeling. In neither cat nor monkey could we observe significant differences in NMDA-receptor distribution between different retinotopic subdivisions within a single visual area. Neither did we detect any periodic changes in NMDA-receptor distribution that would correspond to the compartments defined by cytochrome-oxidase in monkey V1 and V2.

Somatostatin-like immunoreactivity in the pigeon visual system: developmental expression and effects of retina removal

The distribution of somatostatin (SS)-containing neurons was investigated by immunocytochemical methods in the central visual system of adult, developing, and retina-ablated pigeons. In normal adult brains, SS-positive cells and processes were present in the optic tectum, the nucleus of the basal optic root, the visual Wulst, and the ectostriatum. During development, progressive increase or decrease in the numerical density and the total number of SS-containing neurons occurred as determined by quantitative analysis. Changes in SS immunoreactivity also occurred as a consequence of unilateral and bilateral retina removal immediately after hatching, i.e. before retinofugal connections have been established. In spite of the segregation of visual inputs due to the almost completely crossed retinal projections, unilateral and bilateral deafferentation differentially affected SS-containing visual regions. In addition, different effects were observed on the relative packing density of labeled cells as compared to their total number. A possible role of retinal axons in regulating the distribution of SS immunoreactivity was suggested by its altered expression induced by retinal deafferentation. In addition, parallels with the distribution of SS immunoreactivity in the pigeon's visual system were used to suggest possible equivalence between cell populations in the avian and the mammalian brains.

Postnatal development of somatostatin-containing neurons in the visual cortex of normal and dark-reared rats

The distribution of somatostatin (SRIF)-immunoreactive neurons in the visual cortical areas 17, 18 and 18a of Wistar rats from birth to adulthood was followed in both normal and dark-reared animals. The SRIF neurons show difference in distribution amongst the three cortical areas studied as early as the first postnatal week. Area 17 was distinguished by fewer SRIF cells in the upper layers (I-III), which results in a lower overall density. The SRIF neurons in all areas appeared to increase in numbers up to about 3 weeks and then decline dramatically to adult levels, which were 14-19% of the peak levels. Although this decline was still obvious, it moderated to 25-31% in dark-reared animals. The greatest effect was seen in area 18 where, at 60 days of age, there were twice as many SRIF cells in dark-reared as in normal controls. It is suggested that, under conditions of dark rearing, the overall pattern of development of SRIF neurons, being uninfluenced by extrinsic factors, reveals the cells' genetic potential.