Search PubMed⌕ Search

Biomedical subjects

G Alonso

Publications and source records attributed to G Alonso.

At least 109 records · Page 6Linked to original sources
PubMed1990

Adrenergic innervation of the dorsal vagal motor nucleus: possible involvement in inhibitory control of gastric acid and pancreatic insulin secretion.

Morphological and physiological approaches were used to investigate the possible role of an adrenergic innervation of the dorsal vagal complex in the control of basal gastric acid and pancreatic insulin secretion in the rat. The use of retrograde-tracing methods with injections of True Blue or of wheat-germ agglutinin into the stomach or pancreas first confirmed that most vagal preganglionic neurons innervating these two viscera are localized in the dorsal motor nucleus of the vagus, a number of them connected to both viscera. Light- and electron-microscopic investigation of the organization of adrenergic neuronal structures immunoreactive to phenylethanolamine-N-methyltransferase within this medullary nucleus further revealed: (i) that adrenergic axons establish profuse synaptic connections of the symmetrical type with perikarya and dendrites of this nucleus, and (ii) that several of these adrenergic fibers are connected with retrogradely labeled neurons innervating the stomach and/or pancreas. Lastly, measurements of basal gastric acid output and plasma insulin clearly indicated that both visceral secretions are rapidly and conspicuously decreased by local infusion of 2 nM adrenaline within the dorsal vagal complex. Taken together, these data strongly suggest that the adrenergic innervation of the dorsal medulla oblongata is involved in direct synaptic inhibition of the parasympathetic preganglionic neurons of the vagus that control secretion of gastric acid and pancreatic insulin.

Adrenergic Fibers↗
PubMed1990

Some aspects of metabolic adaptations in lipid metabolism during starvation are mimicked by epinephrine in rat adipocytes.

1. The effects of fasting on the neutral lipid synthesis to insulin and/or epinephrine in isolated fat cells have been examined using [1-14C]glucose. 2. The ability of adipocytes from starved rats to synthesize fatty acids from both labeled substrates was markedly diminished compared to adipocytes from control rats. 3. The response of lipogenic stimulation to insulin at all concentrations tested was greatly diminished in adipocytes from 24 hr starved rats. 4. [1-14C]glucose utilization rates in the absence or in the presence of insulin were not significantly different in adipocytes from 24 hr starved rats as compared with control adipocytes, although basal and insulin stimulated glyceride-glycerol synthesis were significantly higher in starved adipocytes. 5. Epinephrine acutely inhibited [1-14C]acetate incorporation into fatty acids for insulin-stimulated lipogenesis in control adipocytes, in contrast, this lipolytic agent strongly increased [1-14C]glucose conversion to triacylglycerols. 6. In both cases, the differences in lipid synthesis capacities found in both nutritional states were abolished by epinephrine.

Acetates↗
PubMed1989

Comparative immunocytochemical study of the catecholaminergic and peptidergic afferent innervation to the dorsal vagal complex in rat and guinea pig.

Light and electron microscopic immunocytochemistry was used to study the fine structural organization of the catecholaminergic and hypothalamic peptidergic innervation of the dorsal vagal complex of the medulla oblongata in the rat and guinea pig, the latter of which is known to lack central adrenergic neurons. In the rat, adrenergic fibers immunoreactive to phenylethanolamine-N-methyltransferase were concentrated in the dorsal motor nucleus of the vagus, where they established frequent symmetric synapses with dendrites and perikarya. On the other hand, the density of both oxytocin- and corticotropin-immunoreactive fibers appeared far lower in this nucleus than in the dorsal regions of the nucleus of the tractus solitarius, where they formed asymmetric synapses with small dendrites. In tissue treated for the dual labeling of two neuronal antigens, oxytocin- or corticotropin-reactive fibers were in close contact with adrenergic neurons in this dorsal medullary region. In the guinea pig, unlike the rat, the dorsal motor nucleus of the vagus contained large amounts of oxytocin- and corticotropin-reactive fibers, which formed many symmetric synapses with perikarya and dendrites. Taken together, these data suggest that the control of vagal preganglionic neurons by hypothalamic peptidergic neurons involves a bisynaptic neuronal pathway including adrenergic medullary neurons in the rat, whereas it is direct in the guinea pig, which lacks this adrenergic relay.

Adrenergic Fibers↗
PubMed1989

The organization of prolactin-like-immunoreactive neurons in the rat central nervous system. Light- and electron-microscopic immunocytochemical studies.

The localization and distribution of prolactin-like-immunoreactive perikarya and nerve fibers in the rat central nervous system have been studied by a preembedding immunoperoxidase method using well-characterized specific immunsera to rat prolactin. Although the localization of labeled neuronal structures in a number of brain areas correlates with the data of previous immunocytochemical studies, we found prolactin-immunoreactive neurons in various regions not previously reported. In untreated animals, the highest concentrations of prolactin-fibers were observed: (i) in the external layers of the median eminence where they exhibited close contact with blood vessels, and (ii) in the bed nucleus of the stria terminalis and in the central nucleus of the amygdala where they closely surrounded unlabeled perikarya. Dense networks of finely varicose prolactin fibers were also observed in the organum vasculosum of the lamina terminalis, in the subfornical organ, and in the dorsolateral regions of the medulla oblongata and the spinal cord. Lastly, a number of large, varicose, intensely immunoreactive fibers were found in the olfactory bulb, the cingulum, and the periventricular regions of the hypothalamus and central gray, whereas isolated fibers could be detected in the caudate nucleus and in the cerebral cortex. In animals treated with colchicine, prolactin-immunoreactive perikarya were essentially located within the periventricular and perifornical regions of the hypothalamus, and within the bed nucleus of the stria terminalis. Although corticotropin (ACTH 17-39)-immunoreactive fibers could be detected in several regions found to contain prolactin fibers, the distribution and organization of both fiber types clearly differed in numerous brain regions, and the regions containing the corresponding perikarya did not overlap.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenocorticotropic Hormone↗
PubMed1989

Combined use of immunoperoxidase and radioimmunocytochemistry for double immunocytochemical labeling of neurons at light and electron microscopic level.

Complexes formed by binding 125I- or 3H-labeled neuropeptides to one of the two binding sites of their specific antibodies allowed specific and sensitive labeling of various peptidergic neurons, which could be detected by classical autoradiographic methods. To visualize two neuronal antigens on the same material at both light and electron microscopic level, we used a new technique of double immunocytochemical labeling, combining immunoperoxidase and radioimmunocytochemistry. The main steps of the process included: (a) indirect labeling of the first antigen by its specific antibody and by a peroxidase-labeled Fab immunoglobulin fragment directed against the primary antibody; (b) direct labeling of the second antigen by a radiolabeled peptide-antibody complex; (c) revealing of the first label in the presence of peroxidase substrate; and (d) revealing of the second label by autoradiographic treatment of tissue sections. Compared with other known techniques of double immunostaining, this technique offers major advantages for combined visualization of two neuronal antigens at the electron microscopic level: (a) two neuron types can be labeled by a pre-embedding approach, allowing highly sensitive detection of neuronal antigens throughout the 50-microns thickness of vibratome sections; (b) two primary antibodies obtained in the same species can be used to label the two antigens without any risk of crossreactions between the two successive labelings; and (c) the two labels can easily be differentiated, even when they are co-localized within the same neuron structures. Application of this double immunostaining technique is illustrated by data obtained in rat hypothalamus concerning the relationships among a variety of identified neurons and the co-localization of different neuropeptides within the same neuron system.

Animals↗
PubMed1988

Effects of colchicine on the intraneuronal transport of secretory material prior to the axon: a morphofunctional study in hypothalamic neurosecretory neurons of the rat.

The effects of colchicine on neurosecretory neurons of the rat hypothalamus were studied by immunocytochemistry, high-resolution radioautography, and conventional electron microscopy. In control rats, intraneuronal immunocytochemical labeling of vasopressin, oxytocin and somatostatin occurred essentially in the Golgi apparatus, the neurosecretory granules and to a lesser extent, the endoplasmic reticulum. These immunostaining patterns were dramatically modified 24 h after the administration of colchicine: immunoreactive peptides were located in granular or tubular structures accumulated at the periphery of the perikarya, but the Golgi stacks were not immunostained. Two h after the administration of tritiated leucine, quantitative analysis of radioautographic labeling of supraoptic perikarya revealed large amounts of radioactive protein in the Golgi saccules of neurosecretory neurons in control rats, but in the neurons of colchicine-treated rats, radioautographic labeling was mainly located in granular structures accumulated at the periphery of the perikarya, with no significant labeling on the Golgi stacks. Lastly, 3 noteworthy effects of colchicine on the ultrastructural morphological features of these neurosecretory neurons consisted in: (1) a dramatic disorganization of the Golgi complexes, (2) an accumulation of electron-dense proteic material within the lumen of cisternae of both the rough and smooth endoplasmic reticulum and, (3) a marked depolymerization of perikaryal microtubules, specifically those associated with the Golgi stacks. Taken together, these data do not fit the prevailing concept that the colchicine-induced accumulation of secretory material within the perikarya of neurosecretory neurons essentially results from the blockade of axoplasmic transport mechanisms. Instead, they support the idea that the effects of colchicine are related to the inhibition of the intraneuronal transport of newly synthesized secretory material from the endoplasmic reticulum to the Golgi apparatus, suggesting that the microtubules associated with the Golgi stacks are possible sites of colchicine action.

Animals↗
PubMed1988

Peptidergic neurohormonal systems in the basal hypothalamus of the ferret and the mink: immunocytochemical study of variations during the annual reproductive cycle.

The hypothalamic systems secreting corticotropin-releasing hormone (CRF), somatostatin, oxytocin, vasopressin and luteinizing hormone-releasing hormone (LHRH) were characterized using immunochemistry, and variations were studied in relation to the recrudescence of testicular activity in the ferret and the mink, two species with opposite photoregulation of their annual reproductive cycles. Under the present conditions of study, the immunoreactivity of the CRF, somatostatin, and oxytocin systems showed no significant variation in either species. In contrast, in these two species, the immunoreactivity of the LHRH system varied considerably depending on the date of observation. The increase in the number and immunoreactivity of the LHRH-secreting neurons that occurred in November in the mink and in January in the ferret, is in agreement with previous results showing that the photoperiod plays an essential role in regulating the annual activity of the testis and that the photoperiodic environmental conditions required for the activation of the LHRH system differ between the species. Similarly, correlations could be found between an increase in immunoreactivity of the vasopressinergic axons projecting to the external median eminence and the recrudescence of testicular activity.

Animals↗
PubMed1988

Immunocytochemical ultrastructural study of hypothalamic neurons containing corticotropin-releasing factor in normal and adrenalectomized rats.

The neurons of the rat hypothalamus which secrete corticotropin-releasing factor were studied by using a pre-embedding immunocytochemical staining technique that improves both the penetration of immunoreagents within the tissue and the preservation of the ultrastructural morphology of labeled structures. Comparison was made between the subcellular location of corticotropin-releasing factor-41 in perikarya of the paraventricular nucleus and axons of the median eminence, both in intact and adrenalectomized animals either untreated or 24 h after the intracerebral injection of colchicine. Morphometric analysis of the numerical density and of the diameter of corticotropin-releasing factor immunoreactive neurosecretory granules in axons of the median eminence of rats not treated with colchicine, indicated that the main modifications induced by adrenalectomy concerned (1) the differential repartition of labeled granules within the preterminal and terminal axonal portions of the median eminence, and (2) the enlargement of the diameter of labeled granules contained in these axons (from 98 nm to 165 nm). In the hypothalamus of intact and adrenalectomized rats, colchicine treatment increased the number of corticotropin-releasing factor-immunoreactive granules in the neuronal perikarya and reduced their number in the axons, but both these variations were much more marked in adrenalectomized rats. Although the corticotropin-releasing factor immunoreactive granules that accumulated in the perikarya after colchicine treatment were slightly smaller than those in the corresponding axons, the diameter of perikaryal-labeled granules was larger in adrenalectomized than in intact animals (129 nm vs 93 nm). These findings fit the idea that adrenalectomy markedly stimulates both the synthesis and axonal excretion of secretory granules in the hypothalamic neurons secreting corticotropin-releasing factor. They also indicate that suppression of circulating corticosteroids induces qualitative modifications in these neurons leading to the visualization of larger neurosecretory granules, which may reflect differential synthesis and granular packing of synergistic peptides other than corticotropin-releasing factor and/or changes in the process of intragranular maturation of hormonal material.

Adrenalectomy↗
PubMed1988

Central catecholaminergic system stimulates secretion of CRH at different sites.

To explore a possible differential role of distinct catecholamine (CA) innervation sites in corticotropin-releasing hormone (CRH) secretion, especially under stress conditions, we compared the effects in adult female rats of selective CA denervation of either the whole hypothalamus, by a discrete pharmacological lesion of the ventral noradrenergic ascending bundle [VNAB; 3 micrograms of 6-hydroxydopamine (6-OHDA) in 0.2 microliter of vehicle, bilaterally] or of the paraventricular nuclei (PVN) alone (1 microgram of 6-OHDA in 0.2 microliter of vehicle, bilaterally). Although both procedures induced a similar dramatic fall in norepinephrine and epinephrine concentrations (-55 to -65%) measured by high-performance liquid chromatography in PVN punches, the VNAB lesion, unlike PVN denervation, depleted the median eminence (ME) of both amines (-80%). Concomitantly, the VNAB lesion led to a 97% reduction of the immunoreactive (ir) CRH-41 concentration in the hypophysial portal vessels, associated with a 64% fall in plasma adrenocorticotropic hormone (ACTH), and, in another group, with an 80% inhibition of ether stress-induced ACTH surge. The deletion of CA innervation of the PVN alone reduced irCRH-41 levels in the portal vessels by only 57% and plasma ACTH by 35%. This lesion did not significantly impair stress-induced ACTH release. These results suggest that the CA innervation of the hypothalamus exerts a stimulatory control on CRH-41-secreting neurons not only directly at the perikaryal level but also at other hypothalamic sites of VNAB innervation including peripheral contacts between the terminals of CA and CRH nerves in the external ME.

Adrenocorticotropic Hormone↗
PubMed1988

Axons containing a prolactin-like peptide project into the perivascular layer of the median eminence: an immunocytochemical light and electron microscope study in adult and infant rats.

A light and electron microscopic immunocytochemical study was undertaken to explore the fine structural organization of prolactin-immunoreactive axons in the rat median eminence. In adult intact males and females and in hypophysectomized females, light microscopic immunocytochemical labeling of the mediobasal hypothalamus revealed a marked concentration of prolactin-like immunoreactive fibers in the perivascular layer throughout the median eminence and the hypophysial stalk. At the electron microscopic level, immunostaining was associated with typical neurosecretory axons located either in the palisade layer where they displayed numerous contacts with tanycyte processes, or in the perivascular layer where they frequently contacted the perivascular space. Within the labeled axonal profiles, immunostaining was essentially located on secretory granules, 90-120 nm in diameter, whereas the microvesicles accumulated in some perivascular profiles constantly remained unlabeled. These data strongly suggest that most prolactin-immunoreactive axons of the median eminence release their content into the hypophysial portal vessels. In 1-day-old infant rats, intensely prolactin-like immunoreactive fibers were similarly localized in the most external layer of the median eminence, in which, contrary to adult animals, very slight if any tyrosine-hydroxylase-immunoreactive fibers were detected. Since earlier studies have provided evidence for a nondopaminergic prolactin-release-inhibiting factor in the hypothalamus of infant rats, and for an inhibitory effect of prolactin on pituitary mammotrophs, we propose that hypothalamic prolactin may contribute, as an additional prolactin-release-inhibiting factor, to the multifactorial control of pituitary mammotrophs.

Aging↗
PubMed1988

Decrease of hypothalamic TRH levels but not plasmatic TSH levels after ablation of submandibular salivary glands in the rat.

Indirect relationships are thought to exist between submandibular salivary glands (SSG) and the central nervous system (CNS) via superior cervical ganglia (SCG). To study this topic, the concentrations of thyrotropin releasing hormone (THR) and somatostatin (SRIF) were measured in both whole and specific areas of the hypothalamus, as well as plasmatic thyrotropin stimulating hormone (TSH) levels following ablation of SSG. Twenty, forty and fifty days after ablation of SSG, groups of operated and sham-operated animals weighing 230-260 g at the beginning of experimentation, were killed by cervical dislocation. Plasma was taken, frozen and stored for TSH-radioimmunoassay (RIA) and the hypothalami were removed and homogenized in either 0.1 N HCl (for TRH-RIA) or 0.2 N acetic acid (for SRIF-RIA). Twenty days after ablation of SSG in another group, TRH concentrations were measured in both the median eminence (ME) and the paraventricular nucleus (PVN), dissected by the micropunch technique. The results show that twenty days after SSG ablation, the hypothalamic TRH concentrations was significantly lower in operated than in sham-operated animals (295.2 +/- 24.8 vs 226 +/- 11.15 pg/mg hypothalamus respectively p less than 0.01, n = 9). No differences were observed at later intervals. This finding seems to be specific for this peptide since the SRIF level was not modified twenty days after SSG removal. Among the discrete hypothalamic areas examined, only the ME exhibited a significant decrease in TRH content (25.43 +/- 3.02 ng/mg prot. VS. 41.24 +/- 1.33 ng/mg prot., respectively). Despite these results on TRH levels, no modifications in plasmatic TSH levels were observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

The effects of smoking and silica exposure on pulmonary epithelial permeability: a radioaerosol study with 99mTc-DTPA.

1. Pulmonary epithelial permeability (PEP) as evaluated by the clearance rate (K, %/min) of 99mTc-DTPA from lung to blood was measured in 4 groups of individuals: 10 normal controls; 10 smokers; 15 silica dust-exposed ceramic workers, 7 without chest X-ray alternations; and 8 with mild radiographic alterations, consistent with silicosis (small opacities of up to 1.5 mm diameter). 2. All subjects had normal pulmonary function tests. The mean clearance rates of smokers (3.0 %/min) and silica-exposed workers with X-ray changes (2.9 %/min) were accelerated compared to controls (1.2%/min) (P less than 0.05). Ceramic workers with normal X-rays had mean clearance rates (2.0 %/min) similar to controls. However, 3 of 7 (43%) had K values higher than the upper limit of the 95% confidence interval for the control mean. 3. Comparison of regional K (%/min) values with controls indicated faster clearance of 99mTc-DTPA in the upper lung regions of smokers. There was also increased clearance in the silicotic workers although of more uniform distribution over the lung regions analyzed. 4. Both smokers and ceramic workers exposed to a silica dust environment, with or without chest X-ray alterations, may show increased PEP compared to controls. As measurement of this parameter appears to be a sensitive index of lung injury, follow-up studies involving workers exposed to noxious dust are proposed to relate alterations in PEP to early silicosis and to the extent of lung injury.

Capillary Permeability↗
PubMed1987

Increase of thyrotropin-releasing hormone immunoreactivity in the nucleus of the solitary tract following bilateral lesions of the hypothalamic paraventricular nuclei.

The effects of bilateral electrolytic lesions of hypothalamic paraventricular nucleus on thyrotropin-releasing hormone (TRH)-immunoreactive fibers of the nucleus of the solitary tract were studied by both immunocytochemistry and radioimmunoassay. Contrasting with a near disappearance of TRH immunoreactivity in the median eminence, both morphological and biochemical approaches demonstrate that such hypothalamic lesions induced significant increase of TRH immunoreactivity in the nucleus of solitary tract. These results confirm that TRH fibers of the nucleus of the solitary tract do not originate in the hypothalamic paraventricular nucleus (PVN). They further indicate that these TRH neurons projecting to the nucleus of the solitary tract are strongly influenced by neurons located within the PVN area.

Animals↗
PubMed1987

The corticotropin-releasing factor release in rat hypophysial portal blood is mediated by brain catecholamines.

In order to study the involvement of the hypothalamic corticotropin-releasing factor (CRF) in catecholamine-induced adrenocorticotropin (ACTH) secretion, we have measured CRF levels in rat hypophysial portal blood (HPB) after the pharmacological destruction of the ventral noradrenergic bundle (VNAB), using 6-hydroxydopamine (6-OHDA) stereotaxically injected into the VNAB. CRF levels in HPB were measured by radioimmunoassay, and the effects of 6-OHDA injection were controlled by the determination of catecholamine concentrations in the total hypothalamus. VNAB lesions induced a dramatic decrease in norepinephrine and epinephrine hypothalamic concentration. The CRF levels in HPB were also significantly reduced. These results suggest that central catecholamines exert a direct stimulatory control on the CRF release and play a major role in stress-induced ACTH secretion.

Adrenocorticotropic Hormone↗
PubMed1986

Immunocytochemical evidence for stimulatory control by the ventral noradrenergic bundle of parvocellular neurons of the paraventricular nucleus secreting corticotropin releasing hormone and vasopressin in rats.

The regulation, by catecholaminergic innervation, of parvocellular neurons of the paraventricular nuclei (PVN) secreting corticotropin releasing hormone (CRH) and vasopressin (Vp) was studied by immunocytochemical visualization of both neurohormones in control rats and in rats given discrete injections of 6-hydroxydopamine in the ventral noradrenergic ascending bundle (VNAB). In both groups, the changes in immunostaining intensities observed in axon terminals of the external median eminence and in PVN perikarya 48 h after a blockade of axoplasmic transport by intraventricular injections of colchicine, served as an index for hormonal release and synthesis. In controls, this treatment induced a strong decrease in CRH and Vp immunoreactivity within the terminals, together with intense labeling of PVN perikarya containing CRH. By contrast, bilateral VNAB lesions strikingly inhibited both the colchicine-induced reduction of the CRH and Vp immunoreactivity in axons and the accumulation of CRH in the perikarya. Unilateral VNAB lesions induced similar alterations but these were restricted to the ipsilateral PVN and median eminence. Comparison of these immunocytochemical data with earlier physiological observations on the effects of VNAB lesions on ACTH secretion indicates that the catecholaminergic afferents to the PVN conveyed by the VNAB stimulate the release and the synthesis of CRH and Vp by parvocellular neurons projecting into the external median eminence.

Afferent Pathways↗
PubMed1986

Radioautographic evidence that axons from the area of supraoptic nuclei in the rat project to extrahypothalamic brain regions.

The axonal efferents of neurons of the supraoptic nucleus area were studied by radioautography in the rat after discrete stereotaxic injections of [3H]leucine into this nucleus. Beside a densely labeled pathway running from the nucleus to the posterior pituitary through the internal median eminence, several of the visualized labeled axonal bundles were found to project into various extrahypothalamic regions, including the olfactory bulb, the cortex, the lateral habenula, the subcommissural organ, the amygdala, the mammillary bodies and the locus coeruleus. These results suggest that part of the vasopressin- or oxytocin-containing perikarya located in the supraoptic nucleus constitute the cells of origin of axons which also contain these peptides and which have already been shown to be present in the above extrahypothalamic areas. This also implies that, like the paraventricular nucleus, the supraoptic nucleus is also involved in central extrahypothalamic regulations.

Animals↗
PubMed1986

Immunoreactivity of hypothalamo-neurohypophysial neurons which secrete corticotropin-releasing hormone (CRH) and vasopressin (Vp): immunocytochemical evidence for a correlation with their functional state in colchicine-treated rats.

The specific immunoreactivity of neurons containing corticotropin-releasing hormone (CRH) or vasopressin (Vp) was studied both centrally, in the parvocellular division of the paraventricular nucleus, and distally, in the external median eminence. Control rats were compared with adrenalectomized rats and with animals supplemented with corticosterone or dexamethasone, either without additional treatment, or 24, and 48 h after an intraventricular injection of colchicine. In all groups of animals, colchicine induced a progressive and parallel decrease in both CRH and Vp immunoreactivity within the axons of the external median eminence. A semi-quantitative estimation of this axonal immunostaining showed that the decrease was clearly correlated with the axons' releasing activity according to the different functional states of the adrenocorticotropic system. Increased rates of hormonal release induced by adrenalectomy could be seen in the accelerated depletion of axonal immunoreactivity whereas corticosteroid supplementation had the opposite effect. Correspondingly, the progressive intensification of the CRH and Vp immunoreactivity within the perikarya following colchicine treatment was further markedly enhanced in adrenalectomized rats and diminished after corticosteroid supplementation. Taken together, these data suggest that in these neurons, perikaryal hormone synthesis may be closely related to the releasing activity of the axon terminals. They further point to appropriate colchicine treatment as useful tool for evaluating the functional state of CRH and Vp neurons of the parvocellular paraventricular nucleus under various experimental conditions.

Animals↗