Variation in the spatial relationship between parvalbumin immunoreactive interneurones and pyramidal neurones in rat somatosensory cortex.

The morphology of pyramidal neurones was revealed by intracellular injection of Lucifer Yellow (LY) in fixed tangential cortical slices taken from rat primary somatosensory cortex. Slices were processed with a combination of antibodies to allow visualization of both the LY-injected neurones and parvalbumin immunoreactive (PV-ir) cell bodies, by confocal microscopy. Basal dendritic fields of pyramidal neurones in layer V were larger and more complex than those of layer III. Furthermore, the number of PV-ir cell bodies contained within the basal dendritic territories of pyramidal neurones in layer V was significantly greater than in layer III (mean +/- s.e.m., 36.3 +/- 3.0 and 20.9 +/- 1.6, respectively). These findings have functional implications both in terms of physiological characteristics, and inhibitory modulation of receptive field properties, of cortical neurones.     

Interconnected cortical networks between primary somatosensory cortex septal columns and posterior parietal cortex in rat

Visual and somesthetic cues are used for spatial processing in the posterior parietal cortex (PPC) of the mammalian brain. In rats, somatic information collected by the mystacial whiskers is critically involved in constructing a neural representation of the external space. Here, we delineated the topography of the cortical pathway from the primary somatosensory cortex (SI) that may deliver vibrissal cues to PPC for spatial processing. For anterograde tracing, we made small injections of biotinylated dextran amine (BDA) into SI barrel cortex. The injections in the regions directly above the septal compartments produced dense terminals in PPC, whereas injections above the center of the barrels resulted in sparse terminals. For retrograde tracing, we made large injections of cholera toxin subunit B (CtB) in PPC. Retrogradely labeled neurons within SI barrel cortex formed multiple, parallel strips. In layer IV, these strips of labeled neurons were confined within the septal rows, extending from barrel arc position 0 to 5. In the extragranular layers, labeled neurons were clustered primarily within the vertical extensions of the septal rows and extended to the edges of neighboring barrel columns. Based on these findings, in which SI projections to PPC arise mainly from the septal columns, we hypothesize that septal columns may form interconnected cortical networks that engage in spatial information processing contingent on somestheic cues.     

The synaptic relationship between vasoactive intestinal polypeptide (VIP)-like immunoreactive neurons and their axon terminals in the rat small intestine: light and electron microscopic study

The present study demonstrates synaptic contacts between vasoactive intestinal polypeptide (VIP)-like immunoreactive neurons and immunoreactive axon terminals in the submucous and myenteric plexuses of the rat small intestine. Our observations suggest that VIP afferents directly affect the VIP neurons in the small intestine via synapses.     

No relationship between vasoactive intestinal polypeptide expression and headache in pituitary tumours

BACKGROUND: Clinical studies have noted the common presentation of pituitary tumours with significant headache. This has been considered to be one, or a combination of, increased cranial pressure, tumour size with dural stretch, or cavernous sinus invasion. Newer hypotheses suggest an association between the presence of pituitary tumour-associated headaches and the expression and release of nociceptive substances. Vasoactive intestinal polypeptide (VIP), a marker of the cranial parasympathetic system, is increased during acute attacks of some primary headaches, and with its expression in the pituitary may link some pituitary tumours to their headache presentations. METHODS: Using immunohistochemical techniques, VIP expression in pituitary tumour specimens was examined to determine if there was a relationship between the presence or absence of pituitary-associated headache and the expression of VIP immunoreactivity (VIP-IR). A qualitative analysis of the VIP-IR in pituitary cells was performed by observers blinded to the headache status of each patient. The presence of VIP-IR and headache were treated as binary variables and associations tested with chi-square tests. RESULTS: Forty-five per cent of specimens positive for VIP were from patients presenting with headache. There was no statistically significant association between the presence of VIP-IR and headache (chi(2) = 0.077, P = 0.781). CONCLUSION: Although the significance of VIP positivity in pituitary tumour-associated headache is unknown it seems unrelated to headache. It remains possible that the mechanism of these headaches relates to the production of either an as yet unidentified peptide, or a combination of nociceptive peptides.     

A morphological analysis of vasoactive intestinal polypeptide (VIP)-like immunoreactive neurons in the area dentata of the rat brain

The general distribution and morphology of vasoactive intestinal polypeptide-like immunoreactive (VIP-LI) neurons in the area dentata (AD) have been studied using immunohistochemical methods on thick (70-120 micron) sections from the rat brain. The long (greater than or equal to 72 hours) incubation of free-floating sections in combination with a sensitive immunoperoxidase method resulted in extensive labeling of VIP-positive cell bodies, along with their dendritic and axonal processes in the hippocampal formation, including the area dentata. The VIP-positive cells are found in all parts of the area dentata, and plots of the distribution of individual cells showed that there is a preferential clustering of these neurons within, or in close proximity to, the granule cell layer, while the deep zones in the hilus are almost completely devoid of VIP-LI immunoreactive neurons. Throughout the long axis of the AD the number and relative position of the VIP-LI neurons remains rather constant. Analysis of the size and shape of the VIP-positive neurons in the AD shows a remarkable morphological heterogeneity, with the soma ranging from small (long axis: approximately 10 micron) ovoid or round, to large (long axis: approximately 25 micron) stellate or multipolar; of these the small to medium sized cells predominate. Comparisons between the morphology of neurons visualized with the VIP antibody and sections stained by the rapid Golgi method allow a rather conclusive classification of some of the VIP-stained neurons, while the classification of a majority of the VIP neurons remains tentative, perhaps because of the selective visualization by the rapid Golgi method of only certain cell types in the AD. On the basis of this comparison, several displaced granule cells in the molecular layer, as well as granule cells, small ovoid cells, and pyramidal basket cells in the granule cell layer have been identified as VIP-positive as determined by their somatic shape, dendritic branching pattern, and axonal projections. In addition, several VIP-positive neurons have been identified with less certainty. These include the dentate basket cell of Cajal, certain small cells in the molecular layer, and fusiform cells in the polymorph layer. Taken together the present results demonstrate the usefulness of "Golgi-like" immunoperoxidase staining for detailed classification of chemically defined neurons.(ABSTRACT TRUNCATED AT 400 WORDS)     

Age-related changes in vasoactive intestinal polypeptide levels and distribution in the rat lung

Summary Vasoactive intestinal polypeptide (VIP) levels and distribution were studied in the lung of young-adult (3-month-old) and aged (28-month-old) male Wistar rats by radioimmunoassay and immunofluorescence. VIP concentrations were reduced approximately by 60% as the animal ages. The density of VIP-immunoreactive nerve fibres was remarkably reduced within bronchial smooth muscle and bronchial glands. Moreover, the number of VIP-immunoreactive nerve cell bodies located in intraparenchymal ganglia was decreased in old rats. The density of VIP-containing perivascular plexuses was slightly reduced in senescence.The present data are indicative that VIP neuronal system is impaired in the lung of old rats. In view of the significant age-dependent loss of VIP-immunoreactive nerve fibres that supply the bronchial tree and bronchial glands it cannot be excluded that the relaxant action exerted by peptide on airway smooth muscle and the control of bronchial secretion exerted by VIP are impaired in old age.     

Development of binding sites for vasoactive intestinal polypeptide in mouse cerebral cortex and cultured cortical neurons

Binding sites for vasoactive intestinal polypeptide (VIP) and the content of immunoreactive VIP were measured in the foetal and neonatal mouse brain cortex and primary cultures of foetal murine brain-cortical neurons and astrocytes. The amount of cortical VIP binding sites and the concentration of immunoreactive VIP were low before birth, but increased postnatally reaching adult level at about 3 weeks of age. In cultures, a similar rise in neuronal binding sites occurred after 10 days, whereas the VIP concentration remained lower than in adult brain cortex. No binding sites or immunoreactive VIP could be detected in cultured astrocytes. The VIP binding sites were heterogeneous both in developing brain cortex and cultured neurons, and consisted of two classes of binding sites. The high affinity constants (2.5–2.9 nM) as well as low affinity constants (50–76 nM) were unchanged during the development, whereas the number of binding sites increased. In cultured neurons the binding constants were similar to those found in the adult mouse brain cortex. The peptide specificity for the VIP binding was similar in brain cortex and neuronal culture. In conclusion, the maturation of murine brain cortical neurons is accompanied by the development of synaptosomal VIP receptors in support of the neurotransmitter function of VIP.     

Origin of cholinergic nerves to the rat major cerebral arteries: Coexistence with vasoactive intestinal polypeptide

The distribution and density of vasoactive intestinal polypeptide (VIP) immunoreactive and acetylcholinesterase (AChE)-containing nerves around the cerebral arteries was studied by using whole mounts with or without lesioning the sphenopalatine ganglia. Abundant VIP immunoreactive and AChE-containing nerves were observed around the cerebral blood vessels in normal rats especially in the anterior circulation of the cerebral arteries. VIP-immunoreactivity and AChE-staining was also demonstrated in neurons within the sphenopalatine ganglia. Lesions of the sphenopalatine ganglia resulted in a marked reduction of both VIP-immunoreactivity and AChE activity. In many neurons, coexistence of both VIP and AChE was revealed. These results demonstrate that cholinergic neurons from the sphenopalatine ganglia innervate the cerebral vasculature at the base of the brain, and that VIP and AChE coexists within the same fibers.     

Individual axon morphology and thalamocortical topography in developing rat somatosensory cortex

The morphology of individual thalamocortical axons in developing rat primary somatosensory cortex was studied using lipophilic tracers. Anterograde labeling with lipophilic dyes demonstrated a topographical organization of thalamocortical projections exiting the thalamus as early as embryonic day (E)16; retrograde labeling studies demonstrated topography of these projections as they reached the cortex as early as E18. At E17, axons course tangentially within the intermediate zone and turn or branch near the deepest layer of cortex (layer VIb), suggesting the presence of guidance cues in this region. Axons appear to grow and branch progressively within layers VIb and VIa during the following days; axons in the intermediate zone may give rise to radially directed branches. Individual axons appear to grow steadily and progressively into the cortex, with the leading front of axons at the transition zone between the cortical plate (CP) and the differentiating cortical layers. At birth (PO), thalamocortical axons extend radially through layers VIa and V and emit branches within these layers; some axons reach the CP. By P1, layer IV has begun to differentiate and axons begin to form a few simple branches in the vicinity of the layer IV cells. Over the ensuing week, axons generate more branches within layer IV, but the tangential extent of individual axon arbors does not exceed the width of a barrel. By P7, individual axons overlap within barrel clusters, and individual axons span the width of a cluster. These observations indicate that thalamic afferents develop by progressive growth of arbors that remain spatially restricted, rather than by overbranching and retracting arbors. © 1996 Wiley-Liss, Inc.     

Corticocortical connections within the primary somatosensory cortex of the rat

Corticocortical connections within the primary somatosensory (SI) cortex of rat were investigated by using discrete injections of retro- and orthogradely transported neuroanatomical tracers (including HRP, WGA, PHA-L, and 3H-leucine). Tangential and vertical connections were defined with respect to the cytoarchitectonic divisions within the rat SI, specifically: (1) the "granular zones" (GZs), characterized by their dense layer IV granular aggregates, which receive the majority of direct ventroposterior (VP) thalamocortical terminations, (2) the "perigranular zones" (PGZs), the less-granular cortical matrix just surrounding the GZs, and (3) the "dysgranular zones" (DZs), the larger dysgranular regions lying centrally within and just lateral to the SI. Receptive fields recorded in the granular zones are small and discrete, whereas in the perigranular zones and especially in dysgranular zones they exhibit complex sensory convergence. A major aim of this study was to determine whether the pattern of intracortical connectivity within the SI is compatible with these observed physiological differences. In general, the perigranular and dysgranular zones contained more profuse systems of corticocortical connections than did the granular zones. For example, discrete tracer injections in the perigranular zones produced "walls" of labelling throughout the adjacent perigranular zones, while adjacent granular zones were relatively empty. Nevertheless, the granular zones were filled with dendritic branches of neurons in adjacent perigranular zones. Since these dendrites could presumably receive direct VP thalamocortical contacts, they represent one path through which this thalamic sensory information might be transmitted to the perigranular zones. Further transmission to the dysgranular zones might be subserved by a topographically organized system of reciprocal interconnections that was found between the perigranular zones and dysgranular zones. In coronal sections, labelling produced by relatively distant injections of either retro or orthograde tracers generally appeared in a columnar distribution, and was localized in perigranular zones and dysgranular zones. Within these zones, orthograde labelling consisted of vertically oriented axons emitting collateral sprays of terminals in all layers. Retrograde neuronal labelling (composed almost exclusively of pyramidal cells) was greatest in supragranular layers. Proximal to the injection site, labelling tended to spread out from these columns into supra- and infragranular layers in adjacent granular zones.(ABSTRACT TRUNCATED AT 400 WORDS)     

Convergence of projections from various thalamic nuclei on the rat somatosensory cortex columns

The method of primuline fluorochrome retrograde transport was used to study sources of thalamo-cortical projections on a separate somatic cortical neuronal column connected with C3 vibrissae of albino rat. Labeled cells were found in 8 thalamic nuclei: tv, tvd, tpo, pf, rh, tvm, tvl, tr. The intensity of neuron staining and cell quantity and density varied in different nuclei. Hence their axon branching in the rat cortex was also different. The majority of intensively stained and densely packed cells have been observed in tv nucleus. The observed convergence of different thalamo-cortical inputs on single somatic cortex column explains heterogeneity in functional properties of the same column neurons and makes it possible for the column to form several neuronal assemblies with different functions.     

Selective attention regulates spatial and intensity information processing in the human primary somatosensory cortex

Attention-related cognitive processes in the primary somatosensory cortex (SI) were studied by measuring somatosensory evoked magnetic fields (SEFs). Twenty-one normal adult human subjects participated in this study for investigating effects of attention and stimulus intensity on cortical finger representation in the SI cortex. Electric stimuli at low and high intensity were delivered to the index or middle finger in finger discrimination and non-discrimination task. For the low intensity stimulation at 1.25 times sensory threshold, an early component (M50) showed clear segregation of the sources for the two fingers and an increase of the amplitude specific to the finger discrimination task. Such an attentional effect on the SI cortex was masked by the high intensity stimulation (2.5 times sensory threshold); the M50 source separation by the fingers was induced irrespective of the discrimination or non-discrimination task. The results suggest that a conscious regulation of stimulus intensity coding in the SI cortex underlies the attention-dependent enhancement of spatial finger information processing.     

Development of vasoactive intestinal polypeptide (VIP) containing neurones in the rat brain

The development of VIP-containing neurones in the rat CNS and duodenum has been studied using a specific radioimmunoassay and immunohistochemistry. In the brain, VIP immunoreactivity appears entirely postnatally, while VIP in peripheral neurones in the duodenum was present before birth. The developmental changes observed in cerebral cortex appear to represent the maturation of a population of intrinsic cortical interneurones which contain VIP. These neurones develop entirely after birth. They are first seen in deep cortical layers, but later spread out into all cortical layers, particularly layers II--IV. Changes in the intensity of VIP cell body fluorescence can be correlated with changes in VIP content in the cortex measured by radioimmunoassay. Thus VIP forms a unique chemical marker for studying the maturation of a cortical neurone.     

Effects of vasoactive intestinal polypeptide on neurones of the rat suprachiasmatic nuclei in vitro

The suprachiasmatic nuclei (SCN) of the hypothalamus house the main circadian pacemaker in mammals. Vasoactive intestinal polypeptide (VIP) is the most abundant neuropeptide in the SCN and has been shown to phase-shift the electrical activity rhythm of SCN cells in vitro. However, the effects of VIP on the cellular activity of rat SCN neurones are unknown. In this study, we examined the acute effects of VIP on the extracellularly recorded spontaneous firing rate of SCN neurones in an in-vitro hypothalamic slice preparation. Furthermore, with the use of receptor-selective agonists and antagonists, we determined which receptors might mediate the effects of VIP in the SCN. Approximately 50% of cells responded to VIP; the main type of response was suppression in firing rate, although a few cells were activated. Suppression responses to VIP were mimicked by the VPAC(2) receptor agonist Ro 25-1553 and blocked by the selective VPAC(2) receptor antagonist PG 99-465. The PAC(1) receptor agonist maxadilan evoked responses from 40% of SCN cells, and activations to this agonist were not altered by PG 99-465. Responses to VIP were not blocked by antagonists to ionotropic glutamate receptors, but the duration of suppression was modulated by the GABA(A) receptor antagonist bicuculline. Our data indicate that VIP alters the electrical activity of rat SCN neurones in vitro, via both VPAC(2) and PAC(1) receptors.     

Distribution of vasoactive intestinal polypeptide (VIP) in the rat brain stem nuclei

The distribution of vasoactive intestinal polypeptide (VIP) in the individual nuclei of the rat brain stem was examined. Highest VIP concentrations in brain stem (> 1 ng/mg protein) are confined to dorsal regions, including periaqueductal gray and structures under the fourth ventricle. VIP concentrations are moderately high (0.8–1 ng/mg protein) in gracile nucleus, area postrema, nucleus of the solitary tract, motor nucleus of the XIIth, locus ceruleus and dorsal tegmental nucleus. Cerebellum and pontine nuclei contained only very low levels (< 0.2 ng/mg protein) of VIP.     

Detection psychophysics of intracortical microstimulation in rat primary somatosensory cortex

A problem of purposeful intracortical microstimulation is the long duration of neuronal integration time and the associated complex temporal interactions of effects to individual pulses in trains. Here we investigated the effects of repetitive stimuli on perception. We trained head-restraint rats to indicate the detection of cortical microstimulation in infragranular layers of barrel cortex. Three stimulus parameters: stimulus intensity, number of pulses and frequency were varied, and psychometric detection curves were assessed using the method of constant stimuli. The average psychophysical threshold of single pulses was 2.0 nC--a measure very close to what has been found earlier for the evocation of short-latency action potentials in neurons near the stimulation electrode. Detection of single-pulse stimulation always saturated at probabilities of about 0.8. In contrast, repetitive stimuli gave rise to lower thresholds (by a factor of two at 15 pulses, 320 Hz), and to saturation at probabilities close to 1. Interestingly, a large fraction of these perceptual benefits was observed already with double pulses. Moreover, the perceptual efficacy of individual pulses was higher using double pulses compared with longer sequences, i.e. double pulses were detected better than expected from the assumption of independence of single-pulse effects, while trains of 15 pulses fell well short of this expectation. The present results thus point to double-pulse stimulation as an optimal choice when trading economic stimulation against optimizing of the percept.     

Contribution of acetylcholine,vasoactive intestinal polypeptide and nitric oxide to CNS-evoked vagal gastric relaxation in the rat

Abstract Several in vitro models of gastric relaxation have elucidated a role of nitric oxide (NO) and vasoactive intestinal polypeptide (VIP) in non-adrenergic, non-cholinergic (NANC) vagally mediated gastric relaxation. However, these models do not necessarily mimic the events leading to gastric relaxation in the whole animal. We have recently described a vagally mediated gastric relaxation evoked by micro-injection of substance P (SP) into the nucleus raphe obscurus (NRO). The present study was performed to elucidate whether this CNS-stimulated in vivo gastric relaxation involved acetylcholine, NO and VIP. Atropine (1 mg kg^?1 i.v.), reduces both the rapid nadir and sustained gastric relaxation evoked by SP in the NRO, and the residual responses are abolished by N^G-Nitro-L-arginine methyl ester hydrochloride (L-NAME, 10 mg kg^?1 i.v.), an NO synthase inhibitor. Blockade of NO synthase alone is not sufficient to abolish the effect of SP into the NRO on intragastric pressure. A VIP antagonist, [p-chloro-D-Phe⁶, Leu¹⁷]VIP (32 μg i.v.) alone, or with the addition of L-NAME, does not affect the nadir of the gastric relaxation in response to SP microinjected into the NRO; however, both antagonists reduce the CNS-evoked sustained intragastric pressure relaxation. We conclude that, in CNS-evoked gastric relaxation, inhibition of cholinergic pathways is potentially important for both the rapid nadir and sustained gastric relaxation, and both NO and VIP contribute to sustained gastric relaxation.     

Characterization of the gene and messages for vasoactive intestinal polypeptide (VIP) in rat and mouse.

We have studied the structure and expression of the gene for vasoactive intestinal polypeptide (VIP) in rodents. We used a human cDNA to identify and clone a fragment of the rat VIP gene. This genomic fragment contained two separate exons, one encoding VIP itself and the other encoding a closely related neuropeptide, peptide histidine-isoleucine (PHI-27). Probes containing either exon, or both, hybridized to two messages: a prominent 1700-base (b) mRNA and a rare 1000-b species. These messages are expressed together in a tissue-specific manner, with highest levels in polyadenylated RNA from cerebral cortex and from small intestine, paralleling the reported levels of the neuropeptides themselves in these tissues. Using the rat genomic fragment as a probe, we isolated the mouse VIP gene in its entirety. The mouse gene is similar in organization to its human counterpart, with a total of 7 exons spanning 8 kilobases (kb). The 7th and largest exon, which is transcribed into the bulk of the 3' untranslated region of the messages, bears two potential polyadenylation sites 700 basepairs (bp) apart. S-1 nuclease protection with a fragment of this exon indicated that the two identifiable VIP messages differ in the extent of their 3' untranslated regions. Conversely, we found no evidence for differential splicing to produce messages encoding only one of the neuropeptides. Instead, specific oligonucleotide-directed digestion with RNase H demonstrated that all of the detectable mRNA from this gene contains both VIP and PHI coding sequences.