Efferents of the opiocortin-containing region of the commissural nucleus tractus solitarius

Electroacupuncture modulates the activity of the hippocampus-nucleus tractus solitarius-vagus nerve pathway to reduce myocardial ischemic injury

The hippocampus is involved in the regulation of the autonomic nervous system, together with the hypothalamus and brainstem nuclei, such as the paraventricular nucleus and nucleus tractus solitarius. The vagus nerve-nucleus tractus solitarius pathway has an important role in cardiovascular reflex regulation. Myocardial ischemia has been shown to cause changes in the autonomic nervous system, affecting the dynamic equilibrium of the sympathetic and vagal nerves. However, it remains poorly understood how the hippocampus communicates with brainstem nuclei to regulate the autonomic nervous system and alleviate myocardial ischemic tissue damage. A rat model of acute myocardial ischemia (AMI) was made by ligating the left anterior descending branch of the coronary artery. Three days before ischemia, the hippocampal CA1 region was damaged. Then, 3 days after ischemia, electroacupuncture (EA) at Shenmen (HT7)-Tongli (HT5) was performed (continuous wave, 1 mA, 2 Hz, duration of 30 minutes). Cluster analysis of firing patterns showed that one type of neuron was found in rats in the sham and AMI groups. Three types of neurons were observed in the AMI + EA group. Six types of neurons were found in the AMI + EA + Lesion group. Correlation analysis showed that the frequency of vagus nerve discharge in each group was negatively correlated with heart rate (HR) (P < 0.05, r = −0.424), and positively correlated with mean arterial pressure (MAP) (P < 0.05, r = 0.40987) and the rate-pressure product (RPP) (P < 0.05, r = 0.4252). The total frequency of the nucleus tractus solitarius discharge in each group was positively correlated with vagus nerve discharge (P < 0.01, r = 0.7021), but not with hemodynamic index (HR: P > 0.05, r = −0.03263; MAP: P > 0.05, r = −0.08993; RPP: P > 0.05, r = −0.03263). Some neurons (Neuron C) were negatively correlated with vagus nerve discharge, HR, MAP and RPP in the AMI + EA group (vagus nerve discharge: P < 0.05, r = −0.87749; HR: P < 0.01, r = −0.91902; MAP: P < 0.05, r = −0.85691; RPP: P < 0.01, r = −0.91902). Some neurons (Neurons C, D and E) were positively correlated with vagus nerve discharge, HR, MAP and RPP in the AMI + EA + Lesion group (vagus nerve discharge: P < 0.01, r = 0.8905, P < 0.01, r = 0.9725, P < 0.01, r = 0.9054; HR: P < 0.01, r = 0.9347, P < 0.01, r = 0.9089, P < 0.05, r = 0.8247; MAP: P < 0.05, r = 0.8474, P < 0.01, r = 0.9691, P < 0.01, r = 0.9027; RPP: P < 0.05, r = 0.8637, P < 0.01, r = 0.9407, P < 0.01, r = 0.9027). These findings show that the hippocampus-nucleus tractus solitarius-vagus nerve pathway is involved in the cardioprotective effect of EA at the heart meridian. Some interneurons in the nucleus tractus solitarius may play a particularly important role in the cardiomodulatory process.

Hypothalamic and hindbrain melanocortin receptors contribute to the feeding, thermogenic, and cardiovascular action of melanocortins

Forebrain ventricular delivery of melanocortin receptor (MC3/4R) agonist increases energy expenditure and decreases food intake (FI). Because forebrain ventricular delivery provides ligand to various anatomically distributed MC3/4R-bearing nuclei, it is unclear which of the receptor subpopulations contributes to the feeding suppression and the sympathetic-thermogenic effects observed. The literature indicates that reexpression of MC4R in the paraventricular nucleus (PVH) affects the feeding but not the energetic phenotype of the MC4R knockout, suggesting that divergent MC4R populations mediate energy expenditure (hindbrain) and FI (hypothalamus) effects of stimulation. Not consistent with this view are data indicating that PVH sympathetic projection neurons express MC4Rs and that feeding effects are induced from hindbrain MC4R sites. Therefore, we hypothesize an opposing perspective: that stimulation of anatomically diverse MC3/4R-bearing nuclei triggers energetic as well as feeding effects. To test this hypothesis, ventricle subthreshold doses of MC3/4R agonist (5 and 10 pmol) were applied in separate experiments to six hindbrain and hypothalamic sites; core temperature (Tc), heart rate (HR), spontaneous activity (SPA), and FI were measured in behaving rats. Nucleus tractus solitarius and PVH stimulation increased Tc, HR, and SPA and decreased FI. Rostral ventrolateral medulla, parabrachial nucleus, and retrochiasmatic area stimulation increased Tc, HR, but not SPA, and decreased FI. The response profile differed to some extent for each nucleus tested, suggesting differential output circuitries for the measured parameters. Data are consistent with the view that energetic and feeding responses are not controlled by regionally divergent MC3/4Rs and can be elicited from multiple, anatomically distributed MC3/4R populations.

Regulation of thermogenesis by the central melanocortin system

Adaptive thermogenesis represents one of the important homeostatic mechanisms by which the body maintains appropriate levels of stored energy and its core temperature. Dysregulation of adaptive thermogenesis promotes obesity. The central melanocortin system, in particular the melanocortin 4 receptor (MC4R) signaling pathway, influences the regulation of every aspect of energy balance, including thermogenesis, and plays a critical role in energy homeostasis in both rodent and man. This review will outline our current understanding of adaptive thermogenesis, focusing on the role of the central melanocortin pathway in the regulation of thermogenesis.

Inhibition of the central extended amygdala by loud noise and restraint stress

It is well established that the central nucleus of the amygdala (CEA) is involved in responses to stress, fear and anxiety. Many studies have used c-fos expression to map the brain's response to processive stress, but curiously the CEA generally is not highly activated. We have previously shown that exposure to a novel vs. home environment reduces amphetamine-induced activation of the lateral CEA (CEAl) and the oval nucleus of the bed nucleus of the stria terminalis (BSTov). This is consistent with the idea that processive stress inhibits neurons in these nuclei. We have tested this hypothesis by exposing rats to noise, at a range of intensities from non-stressful to stressful, or to restraint conditions, immediately after a remote injection of amphetamine, 2 mg/kg i.p., or interleukin-1beta (IL-1beta) 0.5 microg/kg i.p. (used to obtain a level of c-fos mRNA against which to measure inhibition). In keeping with our hypothesis, amphetamine- or IL-1beta-induced c-fos and zif-268 mRNA were significantly decreased in the CEAl and BSTov under conditions of loud noise or restraint stress compared with control conditions. This inhibition does not require a stress-induced rise in corticosterone because data were similar in animals that had been adrenalectomized with a low-dose corticosterone replacement. As both the CEAl and BSTov are highly gamma-aminobutyric acid (GABA) -ergic and project to the medial CEA (CEAm), their inhibition potentially causes an increased input to the CEAm. As the CEAm is a major output nucleus of the amygdala, this could have important consequences within the neural circuitry controlling responses to processive stress.

Anatomy and neurochemistry of the pair bond

Studies in monogamous rodents have begun to elucidate the neural circuitry underlying the formation and maintenance of selective pair bonds between mates. This research suggests that at least three distinct, yet interconnected, neural pathways interact in the establishment of the pair bond. These include circuits involved in conveying somatosensory information from the genitalia to the brain during sexual activity, the mesolimbic dopamine circuits of reward and reinforcement, and neuropeptidergic circuits involved specifically in the processing of socially salient cues. Here we present an integrated description of the interaction of these circuits in a model of pair bond formation in rodents with a discussion of the implications of these findings for evolution, individual variation, and human bonding.

Distribution of ACTH immunoreactivity in the diencephalon and the brainstem of the dog

The present work describes for the first time the anatomical distribution of adrenocorticotropic hormone (ACTH) in the diencephalon and the brainstem of the dog by means of the indirect immunoperoxidase technique. The distribution found in this species agrees well with the pattern found in other mammals and particularly confirms much of the findings reported in the cat. An exception to that concordance is the presence of ACTH perikarya in the nucleus of the solitary tract of the dog, a population that has been described in the rat but not in the cat, and in the ventral mesencephalon. This last population spread across the ventral tegmental area from the raphe to the cerebral peduncle and appeared to be a specific feature of the canine brain. On the other hand, we can not see ACTH fibers in the substantia nigra of the dog which could be a characteristic of the domestic carnivores, opposite to rodents, since these fibers appeared to be also lacking in the cat. Nevertheless, the widespread distribution of ACTH fibers in the brain of the dog included many other nuclei containing monoaminergic neurons which supported a possible role for ACTH in the regulation of these neurotransmitter systems.

Anterograde transneuronal viral tracing of central viscerosensory pathways in rats

Previous studies demonstrated that strain H129 of herpes simplex virus-1 undergoes anterograde transneuronal transport in mice and primates after peripheral or central injection. In this study, H129 was used in rats to identify CNS regions that receive relayed viscero-sensory inputs from the stomach wall. We also examined whether transneuronal viral transport in this model is exclusively anterograde. H129 or an established retrograde transneuronal viral tracer, pseudorabies virus (PRV), was injected into the ventral stomach wall in intact rats or in rats with previous subdiaphragmatic vagal sensory deafferentation. Rats were perfused with fixative 3-5 d later, and tissues were processed for immunocytochemical detection of transported virus. In intact rats, H129 was transported transneuronally via vagal and spinal viscerosensory neurons to postsynaptic target cells in the medullary dorsal vagal complex and thoracic dorsal horn, respectively, with subsequent transport to discrete regions of the medullary and pontine reticular formation, cerebellum, parabrachial nucleus, periaqueductal gray, thalamus, hypothalamus, amygdala, bed nucleus of the stria terminalis, and other central sites. Comparison of labeling patterns in intact and vagal deafferented rats indicated that H129 also produced first-order retrograde infection of autonomic neurons that project directly to virus injection sites, similar to PRV. Unlike PRV, however, H129 was not transported transneuronally in the retrograde direction from infected neurons to central sources of presynaptic input. We conclude that transneuronal transport of H129 occurs exclusively in the anterograde direction to reveal CNS regions that receive direct and relayed viscerosensory signals.

Neuronal activation in the caudal brainstem associated with mating by voles

The expression of c-fos, a marker of neuronal activation, was examined in the gracile nucleus (GN) and nucleus of the solitary tract (NTS) after social interactions, including mating, between male and female prairie voles. In GN, mating, but not non-sexual interactions, induced similar significant increases in c-fos immunoreactivity in both males and females. The increased immunoreactivity was concentrated in medial and dorsal GN suggesting that expression was driven by stimulation of reproductive organs. In contrast, in NTS, mating-induced increases in c-fos expression occurred only in males. These results suggest that both GN and NTS comprise different functional components of mating circuitry and may contribute to pair bonding in monogamous voles.

Is there tonic activity in the endogenous opioid systems? A c-Fos study in the rat central nervous system after intravenous injection of naloxone or naloxone-methiodide

This study examined the possibility that a tonic activity in the endogenous opioid systems (EO systems) exists in animals under normal conditions. In a first set of experiments, concurrent changes in behavioral responses and in the numbers of c-Fos-like immunoreactive (Fos-LI) neurons in 58 structures of the brain and lumbosacral spinal cord were analyzed in rats after systemic administration of the opioid antagonist naloxone (NAL; 2 mg/kg). Possible roles of the EO systems were inferred from changes in the numbers of Fos-LI neurons between normal rats that received either NAL or the same volume of saline. Free-floating sections were processed immunohistochemically for c-Fos protein using standard avidin-biotin complex methods. After NAL, the numbers of Fos-LI neurons were significantly increased in the area postrema; in the caudal, intermediate, and rostral parts of the nucleus tractus solitarii; in the rostral ventrolateral medulla; in the Kölliker-Fuse nucleus; in the supramammillary nucleus; and in the central nucleus of the amygdala. In a second set of experiments examining changes in c-Fos expression in the latter structures, similar increases were found after NAL but not after an equimolar dose of NAL-methiodide, a preferential, peripherally acting opioid receptor antagonist. Therefore, Fos-LI was likely triggered after blockade of central opioid receptors, but not peripheral opioid receptors, releasing neurons from EO system-mediated inhibition. The results of this study suggest the existence of a tonic activity of the EO systems exerted on a restricted number of brain regions in normal rats. This tonic activity of the EO systems may control part of the neural networks involved in cardiorespiratory functions and in emotional and learning processes.

Long-term effects on feeding and body weight after stimulation of forebrain or hindbrain CRH receptors with urocortin

Research on the contribution of CRH receptor stimulation to energy homeostasis has focused on forebrain substrates. In this study, we explored the effects of caudal brainstem administration of the CRH receptor agonist, urocortin, on food intake and body weight, and on plasma glucose and corticosterone (CORT) in non-deprived rats. Urocortin (0, 0.3, 1, 3 microg) delivered, respectively, to the fourth and lateral ventricles yielded substantial suppression of food intake measured 2, 4 and 24 h later. A significant but more modest anorexia was observed between 24 and 48 h after injection. Intake responses did not differ between the injection sites, but body weight loss measured 24 h after lateral-i.c.v. injection was substantially greater than that after fourth-i.c.v. injection. Fourth-i.c.v. urocortin administration (3 microg) produced substantial elevations in plasma glucose and CORT that were not distinguishable in magnitude and duration from responses to lateral-i.c.v. delivery. Unilateral microinjection of urocortin into the dorsal vagal complex significantly reduced 24-h food intake at a dose (0.1 microg) that was subthreshold for the response to ventricular administration, suggesting that fourth-i.c.v. effects are mediated in part by stimulation of CRH receptors in this region of the caudal brainstem. The results indicate that similar effects can be obtained from stimulation of anatomically disparate populations of CRH receptors, and that interactions between forebrain and hindbrain structures should be considered in the evaluation of CRH contributions to food intake and body weight control.

Anatomical distribution of sodium-dependent [(3)H]naloxone binding sites in rat brain

The sulfhydryl alkylating reagent N-ethylmaleimide (NEM) blocks opioid receptor binding and receptor/G-protein coupling. Sodium partially restores [(3)H]naloxone binding after inhibition by NEM to reveal sodium-dependent [(3)H]naloxone sites, defined as binding in the presence of 50-100 mM NaCl after treatment of membranes or sections with 750 microM NEM. In the present study, receptor autoradiography of [(3)H]naloxone binding in control and NEM-treated tissue was used to examine the anatomical distribution of sodium-dependent [(3)H]naloxone sites in rat brain. In brain membranes, the pharmacology of sodium-dependent [(3)H]naloxone sites was consistent with that of mu opioid receptors. Relatively high IC(50) values for agonists and lack of effect of Gpp(NH)p on DAMGO displacement of [(3)H]naloxone binding in NEM-treated membranes indicated that the sodium-dependent sites were low affinity sites, presumably uncoupled from G-proteins. Autoradiograms revealed that NEM treatment dramatically reduced [(3)H]naloxone binding in all brain regions. However, [(3)H]naloxone binding was increased in specific regions in NEM-treated sections in the presence of sodium, including bed nucleus of the stria terminalis, interpeduncular nucleus, periaqueductal gray, parabrachial nucleus, locus coeruleus, and commissural nucleus tractus solitarius. Sodium-dependent [(3)H]naloxone binding sites were not found in other areas that exhibited [(3)H]naloxone binding in control tissue, including the striatum and thalamus. These studies revealed the presence of a subpopulation of [(3)H]naloxone binding sites which are sodium-dependent and have a unique regional distribution in the rat brain.

The effects on the central nervous system of nitroglycerin--putative mechanisms and mediators

Nitroglycerin is an organic nitrate that has been used as a vasodilator in the treatment of cardiac diseases for over a century. Only recently it has been demonstrated that the vasodilator effect of this drug depends upon the formation of nitric oxide in the blood vessel wall. However, clinical and research data gathered during the last decades have suggested that nitroglycerin possesses, besides its peripheral vasodilator effect, additional, puzzling biological activities. This organic nitrate compound provokes reflex cardiovascular activities via its interaction with the central sympathetic system. Its cerebrovascular effect, on the other hand, is probably mediated by the local release of neuropeptides. The direct application of nitroglycerin onto brain nuclei causes a prompt increase in the neuronal discharge rate. From a neurological point of view, nitroglycerin consistently induces a specific headache attack in patients suffering from migraine. Because of its temporal pattern and clinical characteristics, nitroglycerin-induced headache cannot be solely ascribed to the a drug-induced vasorelaxation. The demonstration that systemic nitroglycerin administration activates a widespread set of vegetative, nociceptive and neuroendocrine structures in the central nervous system seems to further support the occurrence of central mechanisms in the biological activity of nitroglycerin. Double labeling immunocytochemical and neuropharmacological studies have provided information on the putative neurotransmitters and neurochemical mechanisms involved in nitroglycerin-induced neuronal activation.

Intrinsic connections of the rat amygdaloid complex: projections originating in the central nucleus

Inputs from the amygdaloid and extraamygdaloid areas terminate in various divisions of the central nucleus. To elucidate the interconnections between the different regions of the central nucleus and its connectivity with the other amygdaloid areas, we injected the anterograde tracer, Phaseolus vulgaris-leucoagglutinin (PHA-L) into the capsular, lateral, intermediate, and medial divisions of the central nucleus in rat. There were a number of labeled terminals near the injection site within each division. The intrinsic connections between the various divisions of the central nucleus were organized topographically and originated primarily in the lateral division, which projected to the capsular and medial divisions. Most of the connections were unidirectional, except in the capsular division, which received a light reciprocal projection from its efferent target, the medial division. The intermediate division did not project to any of the other divisions of the central nucleus. Extrinsic projections from the central nucleus to the other amygdaloid nuclei were meager. Light projections were observed in the parvicellular division of the basal nucleus, the anterior cortical nucleus, the amygdalohippocampal area, and the anterior amygdaloid area. No projections to the contralateral amygdala were found. These data show that the central nucleus has a dense network of topographically organized intradivisional and interdivisional connections that may integrate the intraamygdaloid and extraamygdaloid information entering the different regions of the central nucleus. The sparse reciprocal connections to the other amygdaloid nuclei suggest that the central nucleus does not regulate the other amygdaloid regions but, rather, executes the responses evoked by the other amygdaloid nuclei that innervate the central nucleus.