Somatostatinergic neurons in the insular cortex project to the spinal cord: combined retrograde axonal transport and immunohistochemical study

Neurons in and near insular cortex are responsive to muscular contraction and have sympathetic and/or cardiac-related discharge

Insular cortex (IC) is recognized as a potential site for "central command" of cardiorespiratory responses during exercise. Muscular contraction (MC) decreased the discharge rate of most IC neurons. Activity of most contraction sensitive neurons was either not altered by elevating blood pressure or showed a response converse to that of MC. IC may thus have a role in central command but the area is clearly modulated by MC.

The palliative effects of octreotide in cancer patients

Octreotide is an extremely useful compound for palliative care physicians. It appears to be active in a number of different pain states and may be given by the spinal and intraventricular route. Its actions in reducing gut motility and secretions make it a valuable adjunct in the management of inoperable bowel obstruction. The same actions make it a potent antidiarrheal agent. Octreotide will often succeed where other antidiarrheal agents fail. Its ability to reduce gut secretions has led to its use in the treatment of fistulae. It has also been proposed as a useful drug in the management of cachexia and ascites. Most of the existing evidence is based on small numbers of case reports and further larger trials are necessary.

Effects of octreotide and morphine on the clearance rate of indium-111-pentetreotide from the epidural space

In this study we aimed to evaluate the possible mechanisms by which somatostatin acts when given epidurally. Twenty male New Zealand rabbits were randomly separated into four groups and various drugs were administered via a caudal epidural catheter. Group 1 received a bolus of 3.7 MBq indium-111 ((111)In)-pentetreotide, group 2 received 200 microg octreotide and after 15 min a bolus of 3.7 MBq (111)In-pentetreotide, group 3 received 0.1 mg morphine and after 15 min a bolus of 3.7 MBq (111)In-pentetreotide, and group 4 received a bolus of 3.7 MBq technetium-99m (99Tc(m))-diethylene triamine pentaacetic acid (DTPA). Dynamic images of 60 min' duration were obtained from the posterior projection. T(1/2), fast and T(1/2) total clearance half-times were calculated. When unlabelled octreotide was given to block somatostatin receptors, clearance of (111)In-pentetreotide was found to be faster. Epidural morphine administration did not change the clearance rate of (111)In-pentetreotide. All these findings are in favour of octreotide binding to its probable own specific receptors present in the epidural space.

Physiological influence of lateral proisocortex on the midbrain periaqueductal gray: evidence for a role of an excitatory amino acid in synaptic activation

Recent anatomical studies in this laboratory have demonstrated that the proisocortex cortex adjacent and dorsal to the rhinal sulcus is one of the major forebrain afferent inputs to the midbrain periaqueductal gray matter in the rat. The physiological influence(s) of this projection has not been examined. The present studies investigated the responses of periaqueductal gray neurons to chemical and electrical stimulation of proisocortex in chloral hydrate-anesthetized rats. In addition, the role of glutamate as a possible transmitter in excitatory proisocortex-periaqueductal gray synaptic responses was tested. Microinjection of D,L-homocysteate into proisocortex excited 44% (19/43), inhibited 37% (16/43) and had no effect on 19% of periaqueductal gray cells. The onset of D,L-homocystic acid-evoked responses ranged from 2 to 60 s; the duration of responses ranged from 1 to 18 min. Low-frequency, single-pulse electrical stimulation of proisocortex robustly altered neuronal discharge in 25% of periaqueductal gray neurons sampled; 10% (74/724) of neurons were excited and 15% (107/724) were inhibited. Insular cortex-evoked excitatory responses had a mean onset latency of 19.5 +/- 4.2 ms and a mean duration of 38.5 +/- 26.9 ms. Inhibitory responses had a mean onset latency of 26.2 +/- 15.6 ms and mean duration of 108.0 +/- 84.9 ms. Trains of high-frequency electrical stimulation of proisocortex excited 22% (13/59) and inhibited 25% (15/59) of periaqueductal gray cells tested. In separate experiments, stimulation electrodes were placed in periaqueductal gray to antidromically activate proisocortex neurons that project to periaqueductal gray.(ABSTRACT TRUNCATED AT 250 WORDS)

Distribution of cortical neurons projecting to dorsal column nuclear complex and spinal cord in the hedgehog tenrec, Echinops telfairi

Using retrograde axonal flow and wheatgerm agglutinin conjugated to horseradish peroxidase, we studied the distribution of cortical neurons giving rise to spinal and dorsal column nuclear projections, and correlated the regions involved in the projections with the cytoarchitectonic areas recently identified in the lesser hedgehog tenrec, Echinops telfairi (Insectivora). Labeled cortical neurons were most numerous following injections of tracer into higher cervical segments, whereas almost none were found following thoracic injections. The cortical labeling appeared more prominent ipsilaterally than contralaterally after spinal injections, although it was more prominent on the contralateral side after injection into the dorsal column nuclear complex. The majority of labeled neurons found in lamina V occupied the neocortex adjacent to the interhemispheric fissure along the rostrocaudal extent of the small corpus callosum. This location corresponded to an intermediate rostrocaudal portion of the hemisphere, and particularly to area 2 of Rehkämper. In some cases, adjacent portions of areas 1 and 3 were also involved, as well as neocortical regions of the lateral hemisphere. The present data did not suggest a somatotopic organization of the projections; likewise, evidence for the presence of more than one somatosensorimotor representation was sparse.

Subpopulations of somatostatin 28-immunoreactive neurons display different vulnerability in senile dementia of the Alzheimer type

We tested whether the vulnerability of somatostatin (SST) neurons in senile dementia of the Alzheimer type (SDAT) depended upon their co-localization with neuropeptide Y (NPY). Density estimates of SST28- and NPY-immunoreactive neurons and percentage of double-labeled SST-NPY neurons were obtained in the cortex (areas 9 and 25) and the bed nucleus of stria terminalis (BST), in 6 SDAT and 5 control cases. Counts of senile plaques (SP) and neurofibrillary tangles (NFT) were done on thioflavin S stains. In both cortical areas, a decrease in the density of SST28-IR neurons was found in SDAT cases (-60% in area 25 and -80% in area 9), whereas density of NPY-IR neurons was unchanged. Accordingly, the proportion of single-labeled SST neurons decreased; this decrease was significantly correlated with SP (r = -0.89, P less than 0.001). We conclude that single SST-IR neurons, in cortical layers II-III, and V, are preferentially lost relative to co-localized SST-NPY neurons. In the BST, no significant reduction of SST-IR, NPY-IR neurons nor of the percentage of single labeled SST neurons was found, despite the presence of SP. Thus one subpopulation of SST neurons, defined by associated neurochemical characters (not co-localized with NPY nor with NADPH diaphorase) and by topography (cortical layers III and V) appears to be particularly vulnerable in SDAT. The potential importance of their position in neural circuitry is emphasized.

Immunohistochemical localization of seven different peptides in the human spinal cord

It is necessary to study the normal chemical contents in the human spinal cord in order to understand neurochemical changes that might occur under pathological conditions. In the present study, the comparative distribution of seven peptides was examined immunohistochemically in four levels (cervical, C; thoracic, T; lumbar, L; sacral, S) of the human spinal cord by means of the peroxidase-antiperoxidase technique. The peptides examined included bombesin (BOM), substance P (SP), cholecystokinin (CCK), somatostatin (SOM), methionine-enkephalin (M-ENK), vasoactive intestinal polypeptide (VIP), and thyrotropin releasing hormone (TRH). Among the seven peptides examined, four (BOM, CCK, SOM, and TRH) have never been described in the human spinal cord and the present work clearly demonstrates their existence in specific patterns. The terminals that were immunostained for BOM and CCK were localized in high concentration in the superficial dorsal horn (laminae I-II), in moderate amounts in the lateral part of laminae V and VII, and lesser amounts in the intermediate gray (lamina VII) and the dorsal part of the central gray (lamina X). Whereas BOM showed a similar distribution pattern at all spinal levels, CCK was mainly found in thoracic and lumbar levels. The SOM terminals were localized in the superficial dorsal horn (the highest density in lamina II but very few in lamina I), the intermediolateral cell column, intermediate gray, and central gray. This peptide was more widely distributed in the sacral cord with its terminal field extending into the ventral horn. The TRH terminals were mainly located in the ventral horn. Frequently, TRH terminals were seen adjacent to large ventral horn neurons. Furthermore, many neurons in the ventral and intermediate gray and Clarke's column demonstrated TRH immunoreactivity. The other three peptides (SP, M-ENK, and VIP) have been previously demonstrated in the human spinal cord and the present study confirmed their general spinal distribution with minor differences.

An electron microscopic study of somatostatin immunoreactive structures in lamina II of the rat spinal cord

We are reporting the results of a light and electron microscopic study of somatostatin (SOM) immunoreactive (I) structures in lamina II of the lumbar spinal cord of the rat. At the light microscopic level, the observed distribution and morphology of SOM-I cell bodies and fibers confirmed published studies. At the electron microscopic level, SOM immunostaining in perikarya was localized to the golgi region. Immunostaining in cell bodies could be enhanced by colchicine treatment and after such treatment, it was noticeably increased in the cytoplasm. Synaptic contacts on SOM-I cell bodies were rare and SOM-I axons contacted unlabeled somata in lamina II. Some SOM-I dendrites participate in glomerular arrangements and they exhibited postsynaptic densities adjacent to the central profile of the glomerulus. Nonglomerular SOM-I dendrites and spines were postsynaptic to vesicles containing axons. Vesicle containing SOM-I axons presynaptic to larger dendrites were also observed in the outer portion of lamina II. Somatostatin has been implicated in nociception and some of the SOM-I structures reported here may be the anatomical substrates for SOM-induced analgesia.

Neural associations of the substantia innominata in the rat: afferent connections

The afferent connections of the substantia innominata (SI) in the rat were determined employing the anterograde axonal transport of Phaseolus vulgaris leucoagglutinin (PHA-L) and the retrograde transport of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP), in combination with histochemical procedures to characterize the neuropil of the SI and identify cholinergic cells. Both neurochemical and connectional data establish that the SI is organized into a dorsal and a ventral division. Each of these divisions is strongly affiliated with a different region of the amygdala, and, together with its amygdalar affiliate, forms part of one of two largely distinct constellations of interconnected forebrain and brainstem cell groups. The dorsal SI receives selective innervation from the lateral part of the bed nucleus of the stria terminalis, the central and basolateral nuclei of the amygdala, the fundus of the striatum, distinctive perifornical and caudolateral zones of the lateral hypothalamus, and caudal brainstem structures including the dorsal raphe nucleus, parabrachial nucleus, and nucleus of the solitary tract. Projections preferentially directed to the ventral SI arise from the medial part of the bed nucleus of the stria terminalis, the rostral two-thirds of the medial nucleus of the amygdala, a large region of the rat amygdala that lies ventral to the central nucleus, the medial preoptic area, anterior hypothalamus, medialmost lateral hypothalamus, and the ventromedial hypothalamus. Both SI divisions appear to receive afferents from the dorsomedial and posterior hypothalamus, supramammillary region, ventral tegmental area, and the peripeduncular area of the midbrain. Projections to the SI whose selectivity was not determined originate from medial prefrontal, insular, perirhinal, and entorhinal cortex and from midline thalamic nuclei. Findings from both PHA-L and WGA-HRP experiments additionally indicate that cell groups preferentially innervating a single SI division maintain numerous projections to one another, thus forming a tightly linked assembly of structures. In the rat, cholinergic neurons that are scattered throughout the SI and in parts of the globus pallidus make up a cell population equivalent to the primate basal nucleus of Meynert (Mesulam et al.: Neuroscience 10:1185-1201, '83). PHA-L-filled axons, labelled from lectin deposits in the dorsal raphe nucleus, peripeduncular area, ventral tegmental area, or caudomedial hypothalamus were occasionally seen to approach individual cholinergic neurons int he SI, and to contact the surface of such cells with axonal varicosities (putative synaptic boutons.(ABSTRACT TRUNCATED AT 400 WORDS)

Somatostatin immunoreactive structures in the developing rat spinal cord

Somatostatin immunoreactive (SOM-I) perikarya were first observed in the ventral horn at E12, in the presumptive intermediate gray area at E14, and in the alar plate of the rostral spinal cord at E14. In general, after their initial appearance, their density increased and then decreased during development. A moderate density of SOM-I varicosities became obvious in the superficial laminae of the E20 dorsal horn. By E12 a few SOM-I perikarya, interpreted to be dorsal root ganglia, were observed lateral to the spinal cord, and by E13, SOM immunoreactivity was visualized within the central and peripheral processes of dorsal root ganglion axons. In the marginal zone, SOM-I fibers were first demonstrable in the ventral funiculus at E14, and in the lateral funiculus at E15. After their initial appearance, their density increased and then decreased with age, with the exception of the dorsal part of the lateral funiculus where it increased at the early stages of development to an apparently stable level. The early detection of SOM immunoreactivity in specific spinal regions corresponds well with the birth dates of cells in those regions. This indicates that the SOM-I cells are capable of synthesizing the substance at least as early as they have entered their final cell division.

A role of insular cortex in cardiovascular function

We sought to determine whether the insular cortex contributes to the regulation of arterial blood pressure (AP). Responses to electrical and chemical stimulation of the cortex were studied in the anesthetized, paralyzed, and artificially ventilated Sprague-Dawley rat. The insular cortex was initially defined, anatomically, by the distributions of retrogradely labeled perikarya following injections of wheat germ agglutinin-horseradish peroxidase (WGA-HRP) into the nucleus tractus solitarii (NTS). Injections of WGA-HRP into the insular cortex anterogradely labeled terminals in cardiopulmonary and other divisions of the NTS and confirmed projections revealed by retrograde tracing experiments. Electrical stimulation of the insular cortex elicited elevations of AP (less than or equal to 50 mm Hg) and cardioacceleration (less than or equal to 40 bpm). The locations of the most active pressor sites corresponded closely to the locations of retrogradely labeled cells in layer V of granular and posterior agranular areas of the insular cortex (areas 14 and 13) and the extreme capsule. Maximal pressor responses were obtained at a stimulus intensity of three to five times threshold current of 20-30 microA. Responses elicited mostly with higher-threshold currents were also mapped in areas 2a and 5lb and the claustrum and within the corpus callosum. Unilateral injections into the insular pressor area of the excitatory amino acid monosodium glutamate (L-Glu; 0.05 nmol to 10 nmol) or the rigid structural analogue of L-Glu, kainic acid (KA) (0.4 nmol) (which specifically excite perikarya), caused topographically specific elevations in AP and tachycardia. During the course of the anatomical transport studies, new findings were obtained on the organization and characteristics of the cortical innervation of the NTS and the nucleus reticularis parvocellularis. Topographic relationships between the cortex and the NTS were organized in a more complex manner than previously thought. Cells projecting to caudal cardiopulmonary segments of the NTS were fewer and generally located ventrally and caudally and in a more restricted area than cells projecting rostrally or to the parvicellular reticular formation. Anterograde transport data revealed new presumptive terminal fields in dorsolateral, ventral, periventricular, and commissural regions of the NTS, including an area overlapping the terminal field of the aortic baroreceptor nerve. We conclude that neurons within an area of the insular cortex projecting to multiple brainstem autonomic nuclei, including a region of the NTS innervated by baroreceptor afferents, increase arterial blood pressure and heart rate.(ABSTRACT TRUNCATED AT 400 WORDS)

Changes in plasma catecholamine levels after insula damage in experimental stroke

The effect of permanent occlusion of the left middle cerebral artery (MCA) on plasma catecholamine levels was investigated in chloralose-anesthetized cats. Two-5 h after occlusion of the MCA the plasma levels of norepinephrine, epinephrine and dopamine were significantly elevated (33%, 44% and 28%, respectively) compared to preocclusion levels only in animals in which the cerebral infarction involved the insular cortex. No significant changes were observed in plasma catecholamine levels in animals in which either the infarction did not involve the insula or in sham-stroked animals. These data suggest that withdrawal of inhibitory inputs from the insula on central cardiovascular regulating centers after stroke results in an increase in the activity of the sympathoadrenal system.

Sensitive double-labeling technique of retrograde biotinized tracer (biotin-WGA) and immunocytochemistry: light and electron microscopic analysis

We developed a simple method to identify fiber projections that contain bioactive substances using biotinized wheat-germ agglutinin. Tracer that accumulated retrogradely in the soma was made visible under the light microscope by linking it with streptavidin-Texas red, which has a red fluorescence, while antigen was demonstrated in the same section by indirect immunofluorescence using fluorescein isothiocyanate with green fluorescence as a marker. Under the electron microscope, the tracer was identified using streptavidin-colloidal gold particles, while the antigen was demonstrated in the same ultrathin section using the peroxidase-antiperoxidase technique. This method makes it possible to demonstrate the locations of both the biotinized retrograde tracer and the antigen in the soma of the same neuron at both light and electron microscopic levels.