Ghrelin projection from the lateral hypothalamus area to the dorsal vagal complex and its regulation of gastric motility in cisplatin-treated rats

ObjectiveTo investigate ghrelin projection from the lateral hypothalamus area (LHA) to the dorsal vagal complex (DVC) and its regulation of gastric motility in cisplatin-treated rats.Materials and methodsIn the present study, the protein and mRNA expression of ghrelin and its receptor GHSR-1a were measured by Western blot and PCR, respectively. The ghrelin fiber projections arising from the LHA and projecting to the DVC were investigated by retrograde tracing combined with fluoro-immunohistochemical staining. The effects of ghrelin in the DVC, electrical stimulation of the LHA, and electrical lesion of the DVC on gastric motility were measured in cisplatin-treated rats.ResultsGhrelin fibers originating in the LHA projected to the DVC. The protein and mRNA expression of GHSR-1a was greater in cisplatin-treated rats than in saline-treated rats. Conversely, the expression of ghrelin in the LHA and DVC was reduced in cisplatin-treated rats. Cisplatin treatment also reduced gastric contractions. Ghrelin administrated into the DVC significantly promoted gastric motility, an effect completely blocked by treatment with the ghrelin receptor antagonist [D-Lys-3]-GHRP-6. In addition, electrical stimulation of the LHA promoted gastric motility, though this effect was much weaker in cisplatin-treated rats than in control rats. The excitatory effect of electrical stimulation of the LHA on gastric motility was partially blocked by pretreatment of the DVC with [D-Lys-3]-GHRP-6. Electrical lesion of the DVC diminished the excitatory effect that was induced by electrical stimulation of the LHA.ConclusionsDVC, especially AP, may have a role for gastric contraction induced by the stimulation of the LHA. This regulation on gastric motility was weaker in cisplatin-treated rats than in saline-treated rats, possibly due to reduced ghrelin expression in the LHA and ghrelin projection from the LHA to the DVC.     

The calcitonin gene-related peptide-containing fiber projection from the hypothalamus to the lateral septal area including its fine structures

The afferent source of calcitonin gene-related peptide-like immunoreactive (CGRPI) fibers in the lateral septal area of the rat was sought by using indirect immunofluorescence technique. These fibers decreased markedly on the operated side after the destruction of the area between the anterior hypothalamic nucleus and the lateral hypothalamus where a number of CGRPI cells. We also examined the fine structure of CGRPI fibers in the lateral septal area. Many CGRPI fibers forming axosomatic synapses were identified. These facts strongly suggest that CGRPI cells in the area between the anterior hypothalamic nucleus and the lateral hypothalamus project ipsilaterally to the lateral septal area and directly influence the soma there.     

Lesions of the lateral hypothalamus impair pilocarpine-induced salivation in rats

In the present study we investigated the effects of electrolytic lesions of the lateral hypothalamus (LH) in the salivation induced by intracerebroventricular (i.c.v.) or intraperitoneal (i.p.) injection of the cholinergic agonist pilocarpine. Rats with sham or LH lesions and stainless steel cannulas implanted into the lateral ventricle (LV) were used. In rats anesthetized with urethane (1.25mg/kg of body weight) saliva was collected using pre-weighed cotton balls inserted in the animal mouth during a period of 7 min following i.c.v. or i.p. injection of pilocarpine. Injection of pilocarpine (1mg/kg of body weight) i.p. in sham-operated rats (6h, 2, 7, and 15 days after the surgery) induced salivation (497+/-24, 452+/-26, 476+/-30, and 560+/-75 mg/7 min, respectively). The effects of i.p. pilocarpine was reduced 6h, 2 and 7 days after LH lesions (162+/-37, 190+/-32, and 229+/-27 mg/7 min, respectively), not 15 days after LH lesions (416+/-89 mg/7 min). Injection of pilocarpine (120 micro g/micro l) i.c.v., in sham-operated rats (6h, 2, 7, and 15 days after the surgery) also produced salivation (473+/-20, 382+/-16, 396+/-14, and 427+/-47 mg/7 min, respectively). The salivation induced by i.c.v. pilocarpine was also reduced 6h, 2 and 7 days after LH lesions (243+/-19, 278+/-24, and 295+/-27 mg/7 min, respectively), not 15 days after LH lesions (385+/-48 mg/7 min). The present results show the participation of the LH in the salivation induced by central or peripheral injection of pilocarpine in rats, reinforcing the involvement of central mechanisms on pilocarpine-induced salivation.     

Axonal connections from posterior paralaminar thalamic neurons to basomedial amygdaloid projection neurons to the lateral entorhinal cortex in rats

Stimulation of amygdaloid nuclei and emotionally relevant stimuli are known to influence the induction and maintenance of long-term potentiation in the hippocampal formation and the formation of long-term declarative memories. Because the thalamic projection from the posterior paralaminar thalamic nuclei is an important sensory afferent projection to amygdaloid nuclei mediating the fast acquisition of fear-potentiated behavior, we were interested in verifying whether this projection establishes synaptic contacts on amygdala neurons that project to the hippocampal formation. Thalamic afferents were labeled with the anterograde tracer Phaseolus vulgaris leucoagglutinin and amygdalo-hippocampal neurons were identified by injection of the retrograde tracer Fluorogold into the lateral entorhinal cortex. A massive overlap of both projection systems was observed especially in the anterior basomedial nucleus of the amygdala. Light microscopic examination revealed that single anterogradely labeled boutons were in close apposition to retrogradely labeled neurons suggesting synaptic contacts. The occurrence of such synaptic contacts was confirmed with electron microscopy. However, despite the massive overlap of anterogradely labeled axons and retrogradely labeled neurons observed at the light microscopic level, electron microscopy revealed that only 10% of all labeled profiles make direct contacts on each other; anterogradely labeled boutons predominantly contacted unlabeled profiles but synapses with direct contact between labeled profiles were rare. Altogether the findings demonstrate that the thalamic connection with the basomedial nucleus of the amygdala may represent an anatomical substrate for modulating amygdala output to the hippocampal formation.     

Tryptophan increases extracellular serotonin in the lateral hypothalamus of food-deprived rats

Although it is well established that increases in tryptophan availability can increase brain serotonin synthesis, the effect of tryptophan loads on serotonin release is not as clear. We have used in vivo microdialysis in order to monitor extracellular serotonin in the lateral hypothalamus to examine this issue. Tryptophan methyl ester (100 mg/kg IP) was administered to ad lib-fed and 48-h food-deprived rats. The results suggest that a peripheral tryptophan load can elevate extracellular serotonin in food-deprived subjects more effectively than in food-replete subjects.     

Substance P-like immunoreactive projection to the hippocampal formation from the posterior hypothalamus in the cat

Following the injection of the fluorescent tracer, 4',6-diamidino-2-phenylindol-2HCl (DAPI) or Fluoro-Gold (FG), into the hippocampal formation of the cat, retrogradely-labeled cells were seen mainly in the supramammillary nucleus and the posterior hypothalamic area. Some of these labeled cells contain substance P-like immunoreactivity (SP-LI). When wheat germ agglutinin conjugated with horseradish peroxidase (WGA-HRP) was injected into the supramammillary nucleus and its adjacent regions, anterogradely-labeled terminals were detected, for the most part, in the granular layer and the supragranular molecular layer of the dentate gyrus as well as in the pyramidal layers of the hippocampus and subiculum. All of these layers were included within the terminal areas containing the SP-like immunoreactivity.     

Increased adrenergic projection from the locus coeruleus to the lateral geniculate nucleus of rats following one-eye-removal at birth

Electrophysiological studies were made on plastic changes in the projection from the locus coeruleus (LC) to the lateral geniculate nucleus (LGN). In adult rats with one eye removed at birth it was found that the chance for encountering LC neurons activated antidromically from the LGN was significantly larger in the side of eye removal than in control. This was thought to indicate that the amount of projection from the LC to the LGN had increased in response to eye removal at birth.     

Changes in projection from locus coeruleus to lateral geniculate nucleus following ablation of visual cortex in adult rats

The visual cortex of adult rats was unilaterally ablated. A histofluorescence study revealed an increase of noradrenergic terminals in the lateral geniculate nucleus (LGN) ipsilateral to the decortication, confirming the previous report. Corresponding to this, the frequency for encountering neurons in the locus coeruleus (LC) activated antidromically from the LGN was increased. We suggest that LC neurons whose axon terminals were damaged by ablation of the visual cortex formed new axons or axon collaterals (pruning effect) in the LGN, thus contributing, at least partly, to the increase of noradrenergic terminals therein.     

Cardiovascular responses to the injection of L-glutamate in the lateral hypothalamus of unanesthetized or anesthetized rats

The present experiment was designed to compare the cardiovascular effects of injections of 0.1 M L-glutamate (50, 100 or 500 nL) into the anterior (LHa), tuberal (LHt) or posterior (LHp) regions of the lateral hypothalamus (LH) of either unanesthetized or anesthetized male Wistar rats. In unanesthetized rats, L-glutamate caused significant depressor responses without significant heart rate (HR) effects. L-Glutamate caused similar depressor responses when injected into the different LH subregions. A positive trend was observed between depressor response intensity and injected volume. In urethane-anesthetized rats, L-glutamate caused either depressor responses or biphasic responses, characterized by a significant initial depressor component followed by a secondary pressor response which was significant only after the injection of L-glutamate in 500 nL. The depressor component was accompanied by significant bradycardia only when the LHa or LHt were stimulated. Similar depressor responses were observed after L-glutamate microinjection into the different LH subregions. A positive trend was observed between depressor response intensity and injected volume. The present results suggest that: 1) lateral hypothalamic L-glutamate-sensitive neurons are involved in cardiovascular control and may have a wide and homogeneous distribution throughout the LH; 2) these neurons are mainly associated to the expression of hypotensive responses in unanesthetized rats; and 3) bradycardiac responses are evidenced when L-glutamate is microinjected into the LHa and the LHt in urethane-anesthetized rats.     

Projections of the septum to the lateral hypothalamus

Evoked potentials recorded in the lateral hypothalamus (LH) of the rat to stimulation of the septum were observed to have response components of 3–6, 10–14, and 18–23 msec. These components were elicited from different regions of the septum; the 3–6 and 10–14 msec components from dorsal and midline regions corresponding to the projection field of the precommissural fornix from the hippocampus and the 18–23 msec component from a ventrolateral region corresponding to projections of the stria terminalis. Stimulation of the hippocampus and stria terminalis evoked responses in the LH of similar configuration but with latencies longer than the 10–14 and 18–23 msec components, respectively. Lesions in the dorsal midline and ventrolateral septum attenuated these responses suggesting that the precommissural fornix and stria terminalis are the pathways mediating the septal evoked components. These data provide a neuroanatomical framework for the dual role of the septum on response patterns elicited from the hypothalamus.     

Attenuation during paradoxical sleep of signals from tooth pulp to thalamus

Quantitative evaluation of the response of thalamic neurons to tooth pulp stimulation was made in chronically prepared cats. The latency, duration and intensity of the responses were measured from the post-stimulus time histograms to estimate, from various aspects, the alteration in the responsiveness during different phases of sleep and wakefulness. During slow wave sleep, tooth pulp-evoked impulses tended to be transmitted to the thalamus in a similar or slightly higher intensity compared to wakefulness. In contrast, during paradoxical sleep the signals were often attenuated in many aspects. The results seem to be in favor of the idea that the impairment of signal to noise ratio in a variety of neuronal networks is one of the characteristics of paradoxical sleep.     

Electrolytic lesions of the lateral hypothalamus influence peripheral blood NK cytotoxicity in rats

Bilateral electrolytic lesions of the lateral hypothalamic (LH) area in Wistar rats result in a time-dependent blood NK cytotoxicity changes as measured by the ⁵¹Cr-release (for entire cell population) and agarose (for a single-cell) assays. NK activity against YAC-1 and K-562 cells shift from depression through enhancement to another depression on the 2nd, 5th and 21st post-lesion day, respectively, as compared to both LH sham-operated animals and the pre-lesion baselines. This effect is not attributable to malnutrition and dehydration resulting from ingestive impairments evoked by LH lesions. No significant change in NK cytotoxicity was found after destruction of the medial hypothalamus (MH). The results indicate that LH, under normal conditions, which may be considered as a dynamogenic and stressogenic hypothalamic area is essential for proper regulations of NK cytotoxicity at both population and single-cell level.     

Clonidine and phenylephrine injected into the lateral hypothalamus inhibits water intake in rats

It has been demonstrated that peripheral or intracerebroventricular (i.c.v.) administration of the alpha 2-adrenoceptor agonist, clonidine, blocks the water intake induced by several dipsogenic stimuli in rats. In the present investigation we studied the effect of the injection of clonidine, phenylephrine, prazosin or yohimbine into the lateral hypothalamic area (LHA) on the water intake induced by water deprivation or central angiotensin II (AII) in rats. Rats with chronic cannulas implanted into the lateral ventricle and LHA were used. Injection of clonidine or phenylephrine into the LHA reduced the water intake produced by both water deprivation and i.c.v. injection of AII. Previous injection of the alpha 1- or alpha 2-adrenoceptor antagonists, prazosin or yohimbine, into the LHA reduced the antidipsogenic effect of clonidine or phenylephrine injected into the same area. These results suggest that the alpha 1- and alpha 2-adrenergic receptors of the hypothalamus are part of the central inhibitory system for the thirst produced by dehydration or central AII.     

The organization of the retinal projection to the dorsal lateral geniculate nucleus in pigmented and albino rats

The retina maps over the dorsolateral and posterior surfaces of the contralateral dorsal lateral geniculate nucleus of albino and pigmented rats, such that the upper retina projects posteriorly and the lower retina projects over the dorsolateral surface. Nasal retina projects ventrolaterally and temporal retina dorsomedially. From the surface, lines of projection (demonstrated after either localised retinal or visual cortical lesions) tend to run deep and anteriorly within the nucleus. The area covered by the uncrossed optic pathway differs between pigmented and albino rats. In the pigmented animals it extends no more than 60° from the edge of the visual field represented in the crossed projection, while in albino animals it extends as far as 100° or more. The uncrossed projection in the albino strains tends to be deficient posteriorly (upper retinal representation) and dorsomedially, and the overall density is less than that found in the pigmented animals. Small lesions localised in the extreme peripheral temporal retina of both albino and pigmented rats have always produced degeneration in the contralateral as well as ipsilateral geniculate, even though some of the lesions map only as far as, or within the peripheral 20° on the contralateral colliculus. Most of these lesions in the albino rats give two patches of uncrossed degeneration in the geniculate with at least one focus of degeneration in the contralateral geniculate. Those made in the lower temporal retina of the albino rat give in addition to the uncrossed patches, two areas of crossed degeneration in the geniculate separated by about 50° in terms of visual field projection. These double projection aberrations do not occur in pigmented animals. The suggestion is offered that in albino rats the retina of each eye maps totally on the contralateral lateral geniculate nucleus. However, the vertical midline of the visual field is represented at about 40–50° from the medial edge of the nucleus. A normal (but sparse) uncrossed pathway maps lateral to this position, but also maps in duplicate medial to it. In addition, it appears that some crossed axons may also be abnormal in their termination, and project to both sides of the vertical meridian. If the above interpretation is correct, the anomalies of the albino rat may derive from a confusion of attempting both field and retinotopic maps on the same nucleus. The possibility exists that a comparable total crossed retinogeniculate projection exists in pigmented animals but that the retina temporal to the vertical midline projection is restricted in its connection to a small band on the medial border of the contralateral nucleus.