Arcuate nucleus projections to brainstem regions which modulate nociception

Administration of IL-1beta to the 4th ventricle causes anorexia that is blocked by agouti-related peptide and that coincides with activation of tyrosine-hydroxylase neurons in the nucleus of the solitary tract

Inflammation-associated cachexia is associated with multiple chronic diseases and involves activation of appetite regulating centers in the arcuate nucleus of the hypothalamus (ARH). The nucleus of the solitary tract (NTS) in the brainstem has also been implicated as an important nucleus involved in appetite regulation. We set out to determine whether the NTS may be involved in inflammation-associated anorexia by injecting IL-1 beta into the 4th ventricle and assessing food intake and NTS neuronal activation. Injection of IL-1 beta produced a decrease in food intake at 3 and 12h after injection which was ameliorated at the 12h time point by a sub-threshold dose of agouti-related peptide (AgRP). Investigation into neuron types in the NTS revealed that IL-1 beta injection was associated with an increase in c-Fos activity in NTS neurons expressing tyrosine hydroxylase (TH). Additionally, injection of IL-1 beta into the 4th ventricle did not produce c-Fos activation of neurons expressing pro-opiomelanocortin (POMC) in the ARH, cells known to be involved in producing anorexia in response to systemic inflammation. Double-label in situ hybridization revealed that TH neurons did not express IL-1 receptor I (IL1-RI) transcript, demonstrating that c-Fos activation of TH neurons in this setting was not via direct stimulation of IL-1 beta on TH neurons themselves. We conclude that IL-1 beta injection into the 4th ventricle produces anorexia and is accompanied by an increase in activation in TH neurons in the NTS. This provides evidence that the brainstem may be an important mediator of anorexia in the setting of inflammation.

Long-loop pathways in cardiovascular electroacupuncture responses

We have shown that electroacupuncture (EA) at P 5-6 (overlying median nerves) activates arcuate (ARC) neurons, which excite the ventrolateral periaqueductal gray (vlPAG) and inhibit cardiovascular sympathoexcitatory neurons in the rostral ventrolateral medulla (rVLM). To investigate whether the ARC inhibits rVLM activity directly or indirectly, we stimulated the splanchnic nerve to activate rVLM neurons. Micropipettes were inserted in the rVLM, vlPAG, and ARC for neural recording or injection. Microinjection of kainic acid (KA; 1 mM, 50 nl) in the ARC blocked EA inhibition of the splanchnic nerve stimulation-induced reflex increases in rVLM neuronal activity. Microinjection of d,l-homocysteic acid (4 nM, 50 nl) in the ARC, like EA, inhibited reflex increases in the rVLM neuronal discharge. The vlPAG neurons receive convergent input from the ARC, splanchnic nerve, P 5-6, and other acupoints. Microinjection of KA bilaterally into the rostral vlPAG partially reversed rVLM neuronal responses and cardiovascular inhibition during d,l-homocysteic acid stimulation of the ARC. On the other hand, injection of KA into the caudal vlPAG completely reversed these responses. We also observed that ARC neurons could be antidromically activated by stimulating the rVLM, and that ARC perikarya was labeled with retrograde tracer that had been microinjected into the rVLM. These neurons frequently contained beta-endorphin and c-Fos, activated by EA stimulation. Therefore, the vlPAG, particularly, the caudal vlPAG, is required for ARC inhibition of rVLM neuronal activation and subsequent EA-related cardiovascular activation. Direct projections from the ARC to the rVLM, which serve as an important source of beta-endorphin, appear also to exist.

Blood pressure regulation and cardiac autonomic control in mice overexpressing alpha- and gamma-melanocyte stimulating hormone

Melanocyte stimulating hormones (MSH) derived from pro-opiomelanocortin have been demonstrated to participate in the central regulation of cardiovascular functions. The aim of the present study was to elucidate the chronic effects of increased melanocortin activation on blood pressure regulation and autonomic nervous system function. We adapted telemetry to transgenic mice overexpressing alpha- and gamma-MSH and measured blood pressure, heart rate and locomotor activity, and analyzed heart rate variability (HRV) in the frequency-domain as well as baroreflex function by the sequence technique. Transgenic (MSH-OE) mice had increased systolic blood pressure but their heart rate was similar to wild-type (WT) controls. The 24-h mean of systolic blood pressure was 132+/-7mmHg in MSH-OE and 113+/-4mmHg in WT mice. Locomotor activity was decreased in the MSH-OE mice. Furthermore, MSH-OE mice showed slower adaptation to mild environmental stress in terms of blood pressure changes. The low frequency (LF) power of HRV tended to be higher in MSH-OE mice compared to WT mice, without a difference in overall variability. The assessment of baroreflex function indicated enhanced baroreflex effectiveness and more frequent baroreflex operations in MSH-OE mice. Baseline heart rate, increased LF power of HRV and increased baroreflex activity may all reflect maintenance of baroreflex integrity and an increase in cardiac vagal activity to counteract the increased blood pressure. These results provide new evidence that long-term activation of the melanocortin system elevates blood pressure without increasing heart rate.

5-HT1A, but not 5-HT2 and 5-HT7, receptors in the nucleus raphe magnus modulate hypoxia-induced hyperpnoea

AIM

In the present study, we assessed the role of 5-hydroxytryptamine (5-HT) receptors (5-HT(1A), 5-HT(2) and 5-HT(7)) in the nucleus raphe magnus (NRM) on the ventilatory and thermoregulatory responses to hypoxia.

METHODS

To this end, pulmonary ventilation (V(E)) and body temperature (T(b)) of male Wistar rats were measured in conscious rats, before and after a 0.1 microL microinjection of WAY-100635 (5-HT(1A) receptor antagonist, 3 microg 0.1 microL(-1), 56 mm), ketanserin (5-HT(2) receptor antagonist, 2 microg 0.1 microL(-1), 36 mm) and SB269970 (5-HT(7) receptor antagonist, 4 microg 0.1 microL(-1), 103 mm) into the NRM, followed by 60 min of severe hypoxia exposure (7% O(2)).

RESULTS

Intra-NMR microinjection of vehicle (control rats) or 5-HT antagonists did not affect V(E) or T(b) during normoxic conditions. Exposure of rats to 7% O(2) evoked a typical hypoxia-induced anapyrexia after vehicle microinjections, which was not affected by microinjection of WAY-100635, SB269970 or ketanserin. The hypoxia-induced hyperpnoea was not affected by SB269970 and ketanserin intra-NMR. However, the treatment with WAY-100635 intra-NRM attenuated the hypoxia-induced hyperpnoea.

CONCLUSION

These data suggest that 5-HT acting on 5-HT(1A) receptors in the NRM increases the hypoxic ventilatory response.

The neural pathway of galanin in the hypothalamic arcuate nucleus of rats: activation of beta-endorphinergic neurons projecting to periaqueductal gray matter

We have previously shown that microinjection of galanin into the arcuate nucleus of hypothalamus (ARC) produced antinociceptive effects in rats (Sun et al., 2003a). In this study, the neural pathway of galanin from ARC to midbrain periaqueductal gray (PAG) in nociceptive modulation was investigated. The hindpaw withdrawal latencies (HWLs) with noxious thermal and mechanical stimulation were assessed by the hotplate and the Randall Selitto tests. Intra-ARC administration of 0.1, 0.5, or 1 nmol of galanin induced significant increases in HWLs of rats. The galanin-induced increases in HWLs were inhibited by injection of 10 microg of the opioid receptor antagonist naloxone or 1 nmol of the mu-opioid receptor antagonist beta-funaltrexamine (beta-FNA) into PAG, suggesting that the antinociceptive effects induced by intra-ARC injection of galanin occur via the neural pathway from ARC to PAG. Furthermore, our results demonstrate that the galaninergic fibers directly innervated the beta-endorphinergic neurons in ARC by immunofluorescent methods. Taken together, our results suggest that galanin produces antinociceptive effects in the ARC of rats by activating the beta-endorphinergic pathway from ARC to PAG.

Mapping brain c-Fos immunoreactivity after insulin-induced voluntary lard intake: insulin- and lard-associated patterns

In addition to the inhibitory role of central insulin on food intake, insulin also acts to promote lard intake. We investigated the neural pathways involved in this facet of insulin action. Insulin or saline was infused into either the superior mesenteric or right external jugular veins of streptozotocin-diabetic rodents with elevated steady-state circulating corticosterone concentrations. After postsurgical recovery, rats were offered the choice of chow or lard to eat. Irrespective of the site of venous infusion, insulin increased lard and decreased chow intake. After 4 days, lard was removed for 8 h. On return for 1 h, only insulin infused into the superior mesenteric vein resulted in lard intake. This facilitated distinction between the effects of circulating insulin concentrations (similar in the two insulin-infused groups) and lard ingestion on the patterns of c-Fos(+) cells in the brain, termed insulin- and lard-associated patterns, respectively. Insulin-associated changes in c-Fos(+) cell numbers were evident in the arcuate nucleus, bed nucleus of the stria terminalis and substantia nigra pars compacta, concomitant with elevated leptin levels and reduced chow intake. Lard-associated changes in c-Fos(+) cell numbers were observed in the nucleus of the tractus solitarius, lateral parabrachial nucleus, central nucleus of the amygdala, ventral tegmental area, nucleus accumbens shell and the prefrontal cortex, and were associated with lower levels of triglycerides and free fatty acids. The anterior paraventricular thalamic nucleus exhibited both patterns. These data collectively fit into a framework for food intake and reward and provide targets for pharmacological manipulation to influence the choice of food intake.

Chronic fasting-induced changes of neuropeptide Y immunoreactivity in the lateral septum of intact and ovariectomized female rats

The effect of 40% food deprivation for 1 week on the immunohistochemically detectable amount of neuropeptide Y (NPY) was studied in the lateral septum (LS) of intact and ovariectomized (OVX) female rats. Animals were either fed ad libitum or 40% food-deprived. Densitometric analysis of immunostained material showed a significant decrease in NPY-immunoreactivity (NPY-IR) in OVX rats compared to the control group. Food deprivation increased the density of punctate NPY-IR profiles in both intact and OVX animals, however, the density in food-deprived OVX animals was increased compared to baseline but remained reduced compared to intact rats. Our study indicates that the lack of gonadal hormones - most likely estrogen - results in a decrease in the density of NPY-IR axonal fibers within the LS, while food deprivation induced considerable elevation in NPY density. Food restriction-induced changes in the density of NPY-containing neural elements suggest that the LS may play a crucial role in the regulation of food intake and energy balance, in concert with the relevant hypothalamic areas.

Up-regulation of galanin and corticotropin-releasing hormone mRNAs in the key hypothalamic and amygdaloid nuclei in a mouse model of visceral pain

Cyclophosphamide (CP)-induced cystitis is often used as an animal model of visceral pain. Various neuropeptides in the hypothalamic and amygdaloid nuclei are implicated in pain-induced responses. However, little information is available regarding the regulation of the neuropeptides in response to visceral pain. In the present study, we examined the effects of CP-induced cystitis on the levels of mRNAs encoding galanin, corticotropin-releasing hormone (CRH), substance P, and enkephalins in the hypothalamic and limbic nuclei using in situ hybridization histochemistry in mouse. Galanin mRNA levels in CP-treated group increased significantly in the arcuate nucleus and the paraventricular nucleus (PVN) but not in the medial preoptic area after the intraperitoneal administration of CP (200 mg/kg body weight) in comparison to those in saline-treated group. CRH mRNA levels in CP-treated group also increased significantly in the central amygdala as well as the PVN after the CP administration. In contrast, CP-induced cystitis failed to upregulate the preprotachykinin-A and preproenkephalin genes which encode substance P and enkephalins, respectively in the hypothalamic and limbic nuclei at any of the time points examined. These results suggest that visceral nociception may upregulate both galanin and CRH gene expression in the hypothalamic and limbic nuclei.

A conductor hidden in the orchestra? Role of the habenular complex in monoamine transmission and cognition

Influences of the habenular complex on electrophysiological and neurochemical aspects of brain functioning are well known. However, its role in cognition has been sparsely investigated until recently. The habenular complex, composed of medial and lateral subdivisions, is a node linking the forebrain with midbrain and hindbrain structures. The lateral habenula is the principal actor in this direct dialogue, while the medial habenula mostly conveys information to the interpeduncular nucleus before this modulates further regions. Here we describe neuroanatomical and physiological aspects of the habenular complex, and its role in cognitive processes, including new behavioral, electrophysiological and imaging findings. Habenular complex lesions result in deficits in learning, memory and attention, some of which decline during repeated testing, while others become worse, consistent with multiple roles in cognition. The habenular complex is particularly responsive to feedback about errors. Electrophysiological studies indicate a role in metaplasticity, the modulation of neuroplasticity. These studies thus reveal important roles of the habenular complex in learning, memory and attention.

Anatomy of hypothalamic CART neurons

Over the past 25 years the continuous discovery of novel neuropeptides has been a great aid in our understanding of central nervous system function. The neuropeptide CART was discovered in 1995 in a search for cocaine and amphetamine regulated transcripts in the striatum, but subsequently found to be expressed at much higher levels in the hypothalamus. Further studies on the distribution of both CART mRNA and CART immunoreactivity has added CART to the long list of neuropeptides expressed at high levels in several parts of the hypothalamus playing key roles in homeostasis and reproduction. Our extensive knowledge of hypothalamic function is due in great part to the high number of neuropeptides expressed in distinct hypothalamic cell groups, and naturally the discovery of CART led to myriad of papers examining possible roles played by CART peptides in different aspects of hypothalamic integration and reviewed elsewhere in this issue of Peptides. However, the rather widespread distribution of CART peptides in the brain certainly complicates the understanding of the role(s) played by this neurotransmitter and calls for careful interpretation of physiological/behavioral data. The aim of the present review is to focus attention on the rather complicated anatomy of the hypothalamic CART neurons, bearing in mind that a thorough understanding of brain function should be built on a solid anatomical foundation.

Cachexia: lessons from melanocortin antagonism

It is well established that disruptions in melanocortin signaling in the CNS result in morbid obesity, but only recently has evidence linked the activation of this system with the production of cachexia, also known as disease-associated wasting. Pro-opiomelanocortin-producing neurons, which express cytokine receptors, show increased activation in the presence of several cytokines that are increased in diseases that are associated with cachexia. Recent experiments show that blockade of melanocortin signaling using antagonists to the melanocortin MC(4) receptor attenuates disease-associated anorexia and wasting in rodent models of cancer and renal failure. This successful inhibition of cachexia is important because loss of appetite and lean body mass worsen the prognosis of many the diseases with which cachexia is associated.

Alternation of galanin in nociceptive modulation in the central nervous system of rats during morphine tolerance: A behavioral and immunohistochemical study

The present study was performed to investigate the alternation of galanin in nociceptive modulation and galanin-like immunoreactivity in the central nervous system of rats after morphine tolerance. The hindpaw withdrawal latencies to both thermal and mechanical stimulation increased significantly after intracerebroventricular injection of 3 nmol of galanin in opioid-naive rats. The antinociceptive effect induced by galanin was attenuated remarkably at the same dose in morphine-tolerant rats. Furthermore, an up-regulation of galanin-like immunoreactivity in the arcuate nucleus of hypothalamus of morphine-tolerant rat was observed by immunohistochemical methods, whereas no significant changes were detected in periaqueductal gray. The present study demonstrated that there are alternations in both galanin-induced antinociception and galanin-like immunoreactivity in the brain of rat after morphine tolerance. The results suggest an involvement of galanin in the central nervous system in morphine tolerance.

Preoperative concentration of beta-lipotropin immunoreactive material in cerebrospinal fluid: a predictor of postoperative pain?

Levels of beta-endorphin immunoreactive material (IRM) in cerebrospinal fluid (CSF) have been reported to correlate inversely with postoperative morphine requirement. Considering proopiomelanocortin (POMC) derivatives as predictors for sensitivity to postoperative pain, we determined authentic beta-endorphin (beta-endorphin(1-31)), beta-lipotropin IRM, N-acetyl-beta-endorphin IRM and ACTH in CSF of 17 patients undergoing hip or knee arthroplasty, before surgery (t(A)), immediately after termination of propofol infusion and still under spinal anesthesia (t(B)), under postoperative pain (t(C)) and one day after surgery (t(D)); patients rated their severity of pain on a visual analogue scale (VAS) at those four times. In all patients CSF concentrations of N-acetyl-beta-endorphin IRM and beta-lipotropin IRM were found to be increased after terminating the propofol infusion with spinal anesthesia still effective at t(B). Patients did not feel pain at times t(A), t(B) or t(D); however, they reported moderate to considerable pain at t(C). There were no correlations of postoperative pain severity at t(C) with ACTH, beta-endorphin(1-31) or N-acetyl-beta-endorphin IRM concentrations in CSF. In contrast, we observed significant inverse correlations (Spearman's rank correlation coefficients between -0.83 and -0.85, p<0.01) for postoperative pain severity with beta-lipotropin IRM concentrations in CSF at t(C), and, in addition, at t(A), t(B) and t(D); thus, postoperative pain severity appeared to be dependent on a central system controlling sensitivity to pain, linked to a POMC system releasing beta-lipotropin IRM into CSF and already active at times t(A) and t(B). We conclude that beta-lipotropin IRM in CSF might be considered to serve as a predictor of sensitivity to postoperative pain.

Ventromedial arcuate nucleus communicates peripheral metabolic information to the suprachiasmatic nucleus

The arcuate nucleus (ARC) is crucial for the maintenance of energy homeostasis as an integrator of long- and short-term hunger and satiety signals. The expression of receptors for metabolic hormones, such as insulin, leptin, and ghrelin, allows ARC to sense information from the periphery and signal it to the central nervous system. The ventromedial ARC (vmARC) mainly comprises orexigenic neuropeptide agouti-related peptide and neuropeptide Y neurons, which are sensitive to circulating signals. To investigate neural connections of vmARC within the central nervous system, we injected the neuronal tracer cholera toxin B into vmARC. Due to variation of injection sites, tracer was also injected into the subependymal layer of the median eminence (seME), which showed similar projection patterns as the vmARC. We propose that the vmARC forms a complex with the seME, their reciprocal connections with viscerosensory areas in brain stem, and other circumventricular organs, suggesting the exchange of metabolic and circulating information. For the first time, the vmARC-seME was shown to have reciprocal interaction with the suprachiasmatic nucleus (SCN). Activation of vmARC neurons by systemic administration of the ghrelin mimetic GH-releasing peptide-6 combined with SCN tracing showed vmARC neurons to transmit feeding related signals to the SCN. The functionality of this pathway was demonstrated by systemic injection of GH-releasing peptide-6, which induced Fos in the vmARC and resulted in a reduction of about 40% of early daytime Fos immunoreactivity in the SCN. This observation suggests an anatomical and functional pathway for peripheral hormonal feedback to the hypothalamus, which may serve to modulate the activity of the SCN.

The reciprocal connections of endomorphin 1- and endomorphin 2-containing neurons between the hypothalamus and nucleus tractus solitarii in the rat

In the CNS, endomorphin 1- and endomorphin 2-immunoreactive neuronal cell bodies have been principally found both in the hypothalamus and nucleus tractus solitarii. Functionally, the hypothalamus and nucleus tractus solitarii are closely related in many aspects, especially in visceral functions. On the other hand, there are also many endomorphin-immunoreactive fibers and terminals in the two regions. In the present study, to investigate whether endomorphin 1-immunoreactive and endomorphin 2-immunoreactive neurons in the hypothalamus and nucleus tractus solitarii project reciprocally between these two regions, fluorescent retrograde labeling combined with immunofluorescence histochemical staining for endomorphin 1 and endomorphin 2 was used. After injection of Fluoro-Gold into the nucleus tractus solitarii of rats, endomorphin 1/Fluoro-Gold or endomorphin 2/Fluoro-Gold double-labeled neuronal cell bodies were predominantly observed in the arcuate nucleus of the hypothalamus, a few of which were also observed in the posterior hypothalamic area and periventricular hypothalamic nucleus. After injection of Fluoro-Gold into the medial zone of hypothalamic tuberal region and the lateral hypothalamic area, respectively, endomorphin 1/Fluoro-Gold or endomorphin 2/Fluoro-Gold double-labeled neuronal cell bodies were found chiefly in the medial, commissural, lateral and gelatinous parts of the nucleus tractus solitarii. These results provide morphological evidence that there exist reciprocal endomorphinergic connections between the hypothalamus and nucleus tractus solitarii.

Functional and ultrastructural neuroanatomy of interactive intratectal/tectonigral mesencephalic opioid inhibitory links and nigrotectal GABAergic pathways: Involvement of GABAA and μ1-opioid receptors in the modulation of panic-like reactions elicited by electrical stimulation of the dorsal midbrain

In the present study, the functional neuroanatomy of nigrotectal-tectonigral pathways as well as the effects of central administration of opioid antagonists on aversive stimuli-induced responses elicited by electrical stimulation of the midbrain tectum were determined. Central microinjections of naloxonazine, a selective mu(1)-opiod receptor antagonist, in the mesencephalic tectum (MT) caused a significant increase in the escape thresholds elicited by local electrical stimulation. Furthermore, either naltrexone or naloxonazine microinjected in the substantia nigra, pars reticulata (SNpr), caused a significant increase in the defensive thresholds elicited by electrical stimulation of the continuum comprised by dorsolateral aspects of the periaqueductal gray matter (dlPAG) and deep layers of the superior colliculus (dlSC), as compared with controls. These findings suggest an opioid modulation of GABAergic inhibitory inputs controlling the defensive behavior elicited by MT stimulation, in cranial aspects. In fact, iontophoretic microinjections of the neurotracer biodextran into the SNpr, a mesencephalic structure rich in GABA-containing neurons, show outputs to neural substrate of the dlSC/dlPAG involved with the generation and organization of fear- and panic-like reactions. Neurochemical lesion of the nigrotectal pathways increased the sensitivity of the MT to electrical (at alertness, freezing and escape thresholds) and chemical (blockade of GABA(A) receptors) stimulation, suggesting a tonic modulatory effect of the nigrotectal GABAergic outputs on the neural networks of the MT involved with the organization of the defensive behavior and panic-like reactions. Labeled neurons of the midbrain tectum send inputs with varicosities to ipsi and contralateral dlSC/dlPAG and ipsilateral substantia nigra, pars reticulata and compacta, in which the anterograde and retrograde tracing from a single injection indicates that the substantia nigra has reciprocal connections with the dlSC/dlPAG featuring close axo-somatic and axo-dendritic appositions in both locations. In addition, ultrastructural approaches show inhibitory axo-axonic synapses in MT and inhibitory axo-somatic/axo-axonic synapses in the SNpr. These findings, in addition to the psychopharmacological evidence for the interaction between opioid and GABAergic mechanisms in the cranial aspects of the MT as well as in the mesencephalic tegmentum, offer a neuroanatomical basis of a pre-synaptic opioid inhibition of GABAergic nigrotectal neurons modulating fear in defensive behavior-related structures of the cranial mesencephalon, in a short link, and through a major neural circuit, also in GABA-containing perikarya and axons of nigrotectal neurons.

Involvement of neuropeptide Y and Y1 receptor in antinociception in the arcuate nucleus of hypothalamus, an immunohistochemical and pharmacological study in intact rats and rats with inflammation

Neuropeptide Y (NPY) plays an important role in pain modulation at different levels in the central nervous system. In the brain, NPY and NPY receptors distribute abundantly in the arcuate nucleus of hypothalamus (ARC), a structure involved in pain processing. The present study was undertaken to investigate the role of NPY in nociceptive modulation in the ARC of intact rats and rats with carrageenan-induced inflammation. Intra-ARC administration of NPY induced dose-dependent increases in hindpaw withdrawal latencies (HWLs) to thermal and mechanical stimulation in intact rats, which was attenuated by the Y1 receptor antagonist NPY28-36. Intra-ARC administration of NPY also induced dose-dependent increases in HWLs to noxious stimulation in rats with inflammation. Furthermore, intra-ARC injection of either the antiserum against NPY or NPY28-36 induced decreases in HWLs in rats with inflammation, while both of them produced no effects in intact ones. Additionally, there were marked increases of Y1 receptor in the bilateral ARC of rats with inflammation tested by immunohistochemistry, while no significant changes of NPY were observed, implicating that the increased Y1 receptor has an important effect in the NPY-induced antinociception. We also found that intra-ARC injection of Y2 receptor agonist NPY3-36 produced no significant antinociception in either intact rats or rats with inflammation. Together, we demonstrate that NPY exerts an antinociceptive effect in the ARC of intact rats and rats with inflammation. Both Y1 receptor and endogenous released NPY in the ARC are involved in the nociceptive modulation during inflammation.

Brain regulation of food intake and appetite: molecules and networks

In the clinic, obesity and anorexia constitute prevalent problems whose manifestations are encountered in virtually every field of medicine. However, as the command centre for regulating food intake and energy metabolism is located in the brain, the basic neuroscientist sees in the same disorders malfunctions of a model network for how integration of diverse sensory inputs leads to a coordinated behavioural, endocrine and autonomic response. The two approaches are not mutually exclusive; rather, much can be gained by combining both perspectives to understand the pathophysiology of over- and underweight. The present review summarizes recent advances in this field including the characterization of peripheral metabolic signals to the brain such as leptin, insulin, peptide YY, ghrelin and lipid mediators as well as the vagus nerve; signalling of the metabolic sensors in the brainstem and hypothalamus via, e.g. neuropeptide Y and melanocortin peptides; integration and coordination of brain-mediated responses to nutritional challenges; the organization of food intake in simple model organisms; the mechanisms underlying food reward and processing of the sensory and metabolic properties of food in the cerebral cortex; and the development of the central metabolic system, as well as its pathological regulation in cancer and infections. Finally, recent findings on the genetics of human obesity are summarized, as well as the potential for novel treatments of body weight disorders.

Post-hypoxic myoclonus induces Fos expression in the reticular thalamic nucleus and neurons in the brainstem

Post-hypoxic myoclonus is a movement disorder characterized by brief, sudden involuntary muscle jerks. Although the mechanism underlying this disorder remains unclear, earlier pharmacological studies indicated that aberrant activity of specific neuronal circuitry in the central nervous system causes this disorder. In the present study, Fos protein, an immediate-early gene product, was used as a marker of neuronal activity to identify the brain nuclei possibly involved in post-hypoxic myoclonus. We found that Fos protein was immunologically detected in the reticular thalamic nucleus (RT), the medial longitudinal fasciculus (MLF) as well as in the locus coeruleus (LC) and the periventricular gray substance (PVG) in post-hypoxic rats that developed myoclonus in response to auditory stimuli. Fos was not detected in these nuclei from rats that underwent 4 min of cardiac arrest without myoclonus. Electrolytic lesions of the RT or MLF but not the LC/PVG significantly reduced auditory stimulated myoclonus in the post-hypoxic rats. The results suggest that neuronal activity in the RT and the MLF plays a contributing role in post-hypoxic myoclonus.

Body weight is regulated by the brain: a link between feeding and emotion

Regulated energy homeostasis is fundamental for maintaining life. Unfortunately, this critical process is affected in a high number of mentally ill patients. Eating disorders such as anorexia nervosa are prevalent in modern societies. Impaired appetite and weight loss are common in patients with depression. In addition, the use of neuroleptics frequently produces obesity and diabetes mellitus. However, the neural mechanisms underlying the pathophysiology of these behavioral and metabolic conditions are largely unknown. In this review, we first concentrate on the established brain machinery of food intake and body weight, especially on the melanocortin and neuropeptide Y (NPY) systems as illustration. These systems play a critical role in receiving and processing critical peripheral metabolic cues such as leptin and ghrelin. It is also notable that both systems modulate emotion and motivated behavior as well. Secondly, we discuss the significance and potential promise of multidisciplinary molecular and neuroanatomic techniques that will likely increase the understanding of brain circuitries coordinating energy homeostasis and emotion. Finally, we introduce several lines of evidence suggesting a link between the melanocortin/NPY systems and several neurotransmitter systems on which many of the psychotropic agents exert their influence.

Electroacupuncture induces c-Fos expression in the rostral ventrolateral medulla and periaqueductal gray in cats: relation to opioid containing neurons

Our previous studies have shown that electroacupuncture (EA) at the Neiguan-Jianshi (P5-P6) acupoints inhibits sympathetic outflow and attenuates excitatory visceral cardiovascular reflexes through enkephalin- or beta-endorphin-related opioid receptors in the rostral ventrolateral medulla (rVLM). It is not known whether EA at these acupoints activates neurons containing enkephalin or beta-endorphin in the rVLM as well as in the periaqueductal gray (PAG) that are involved in EA-mediated central neural regulation of sympathetic activity. The present study evaluated activated neurons in the rVLM and PAG by detecting c-Fos immunoreactivity, and identified the relationship between c-Fos nuclei and neuronal structures containing enkephalin or beta-endorphin in these regions. To enhance the detection of cell bodies containing enkephalin or beta-endorphin, colchicine (90-100 microg/kg) was injected into the subarachnoid space in anesthetized cats 28-30 h prior to EA or the sham-operated control for EA. Following bilateral barodenervation and cervical vagotomy, EA (1-4 mA, 2 Hz, 0.5 ms) was performed at the P5-P6 acupoints (overlying median nerve; n=7) for 30 min. Identical procedures, with the exception of electrical stimulation, were carried out in five control animals. EA decreased blood pressure (BP) in four of seven cats (5-15 mm Hg) while the sham procedure for EA produced no responses. Perikarya containing enkephalin were found in the rVLM and rarely in the PAG, while no cell bodies labeled with beta-endorphin were identified in either region. Compared to animals in the control group, more c-Fos immunoreactivity, located principally in close proximity to fibers containing enkephalin or beta-endorphin, was observed in the rVLM and ventrolateral PAG (vlPAG) in EA-treated cats. Moreover, neurons double-labeled with c-Fos and enkephalin in the rVLM were significantly increased in cats following EA stimulation (P<0.05). These data indicate that EA at the P5-P6 acupoints activates neurons in the rVLM and vlPAG. These activated neurons contain enkephalin in the rVLM, and most likely interact with nerve fibers containing enkephalin or beta-endorphin in both the rVLM and vlPAG. The results from this study provide the first anatomical evidence showing that EA at the P5-P6 acupoints has the potential to influence neuronal structures (perikarya, axons and/or dendrites) containing enkephalin or beta-endorphin in specific regions of the brain stem. These neurons likely form the substrate for EA's influence on sympathoexcitatory cardiovascular reflexes.

Innate differences in neuropeptide Y (NPY) mRNA expression in discrete brain regions between alcohol-preferring (P) and -nonpreferring (NP) rats: a significantly low level of NPY mRNA in dentate gyrus of the hippocampus and absence of NPY mRNA in the medial habenular nucleus of P rats

The neuropeptide Y (NPY) gene in rat chromosome 4 has been shown to play an important role in alcohol-seeking behavior. NPY knockout mice drink more alcohol than wild-type mice, implicating a link between NPY deficiency and high alcohol intake. This is supported by recent studies showing that intracerebroventricular injections of NPY reduce alcohol intake in both alcohol-preferring (P) and high alcohol-drinking rats. However, it is unknown which anatomical NPY systems are involved in alcohol preference. This study was designed to investigate whether there are innate differences in NPY mRNA in cerebral cortical areas, dentate gyrus (DG) of the hippocampus and medial habenular nucleus (MHb) between P and alcohol-nonpreferring (NP) rats, as these discrete brain regions are rich in NPY mRNA. [(33)P]-labeled 28-mer oligodeoxynucleotide probe was applied for the in situ hybridization study to detect the NPY mRNA, measured using quantitative autoradiography. This study revealed an absence of NPY mRNA in the MHb of P rats. We found that NPY mRNA was significantly lower in the DG of P rats than NP rats. This innate difference of NPY mRNA expression in the DG between P and NP rats is region specific. For example, in most of the cerebral cortical areas examined, an innate difference was not seen. Our study suggests that lower NPY gene expression in the DG and MHb of P rats may be factors contributing to some of the phenotypic differences observed between the P and NP lines of rats.

Nitric oxide pathway in the nucleus raphe magnus modulates hypoxic ventilatory response but not anapyrexia in rats

Nucleus raphe magnus (NRM) is one of the cellular groups of the brainstem that is involved in the physiologic responses to hypoxia and contains nitric oxide (NO) synthase. In the present study, we assessed the role of NO pathway in the NRM on the hypoxic ventilatory response (HVR) and anapyrexia (a regulated decrease in body temperature). To this end, pulmonary ventilation (VE) and body temperature (Tb) of male Wistar rats were measured before and after microinjection of N-monomethyl-L-arginine (L-NMMA, a nonselective nitric oxide synthase inhibitor, 12.5 microg/0.1 microl) into the NRM, followed by hypoxia. Control rats received microinjection of saline. Under resting conditions, L-NMMA treatment did not affect pulmonary VE or Tb. Typical hypoxia-induced hyperventilation and anapyrexia were observed after saline treatment. L-NMMA into the NRM reduced the HVR but did not affect hypoxia-induced anapyrexia. In conclusion, the present study indicates that NO in the NRM is involved in HVR, exerts an inhibitory modulation on the NRM neurons but does not mediate hypoxia-induced anapyrexia.

Chemical anatomy of the human paraventricular thalamic nucleus

The paraventricular thalamic nucleus (Pa) lies in the most medial aspect of the thalamus and is considered one of the midline thalamic nuclei. In the present study, we carried out histochemical and immunohistochemical procedures in the Pa of normal individuals to visualize the pattern of distribution of acetylcholinesterase (AChE), calbindin D-28k (CB), parvalbumin (PV), calretinin (CR), limbic system-associated membrane protein (LAMP), substance P (SP), and enkephalin (ENK). Other cytoarchitectural and myeloarchitectural techniques, such as Nissl and Gallyas, were also employed to delineate the boundaries of the Pa. The main findings of this study are: 1) AChE staining in the Pa was heterogeneously distributed along its anteroposterior and mediolateral axes; 2) the Pa harbored numerous CB- and CR-immunoreactive (ir) cells and neuropil, but this nucleus was largely devoid of PV; 3) the Pa was highly enriched in LAMP and this protein appeared uniformly distributed through its whole extent; and, 4) the SP and ENK immunoreactivities in the Pa revealed numerous highly varicose fibers scattered throughout this nucleus, but no stained cells. This morphological study demonstrates that the Pa is a heterogeneous chemical structure in humans. The functional significance of these results is discussed in the light of similar data gathered in several mammalian species.

An antinociceptive role of galanin in the arcuate nucleus of hypothalamus in intact rats and rats with inflammation

In the arcuate nucleus of hypothalamus (ARC), galaninergic fibers form synaptic contacts with proopiomelanocortin neurons, which are involved in pain modulation. The present study assessed the role of exogenous and endogenous galanin in the modulation of nociception in the ARC of rats. The hindpaw withdrawal latency (HWL) to thermal and mechanical stimulation was assessed by the hot-plate test and the Randall Selitto Test. Intra-ARC injection of galanin dose-dependently increased the HWLs in intact rats, indicating an antinociceptive role of exogenous galanin in the ARC. The antinociceptive effect of galanin was blocked by following intra-ARC injection of galantide, a putative galanin receptor antagonist, suggesting that the antinociceptive effect of galanin is mediated by galanin receptors. Moreover, intra-ARC injection of galanin increased the HWL in rats with inflammation. Intra-ARC administration of galantide alone reduced the HWLs in rats with inflammation, while there were no influences of galantide on the HWL in intact rats. Taken together, the results show that galanin has an antinociceptive role in the ARC of intact rats and rats with inflammation.

Restricted daily consumption of a highly palatable food (chocolate EnsureR) alters striatal enkephalin gene expression

Brain opioid peptide systems are known to play an important role in motivation, emotion, attachment behaviour, the response to stress and pain, and the control of food intake. Opioid peptides within the ventral striatum are thought to play a key role in the latter function, regulating the affective response to highly palatable, energy-dense foods such as those containing fat and sugar. It has been shown previously that stimulation of mu opiate receptors within the ventral striatum increases intake of palatable food. In the present study, we examined enkephalin peptide gene expression within the striatum in rats that had been given restricted daily access to an energy-dense, palatable liquid food, chocolate Ensure(R). Rats maintained on an ad libitum diet of rat chow and water were given 3-h access to Ensure(R) daily for two weeks. One day following the end of this period, preproenkephalin gene expression was measured with quantitative in situ hybridization. Compared with control animals, rats that had been exposed to Ensure(R) had significantly reduced enkephalin gene expression in several striatal regions including the ventral striatum (nucleus accumbens), a finding that was confirmed in a different group with Northern blot analysis. Rats fed this regimen of Ensure(R) did not differ in weight from controls. In contrast to chronic Ensure(R), acute ingestion of Ensure(R) did not appear to affect enkephalin peptide gene expression. These results suggest that repeated consumption of a highly rewarding, energy-dense food induces neuroadaptations in cognitive-motivational circuits.

The nucleus raphe magnus modulates hypoxia-induced hyperventilation but not anapyrexia in rats

The nucleus raphe magnus (NRM) is one of the brainstem cell groups involved in physiological responses to hypoxia. Thus, we tested the hypothesis that the NRM modulates hypoxia-induced hyperventilation and anapyrexia. To this end, we assessed the participation of NRM in the respiratory and thermoregulatory responses to hypoxia using ibotenic acid lesions produced in the NRM of rats. Our results demonstrated that, under resting breathing, NRM plays no role in ventilation or body temperature. Hypoxia caused hyperventilation and anapyrexia in all groups. NMR lesions elicited an increased ventilatory response to hypoxia due to a higher tidal volume (V(T)) but did not affect hypoxia-induced anapyrexia. Therefore, we conclude that NRM exerts an inhibitory modulation of breathing during hypoxia, acting on V(T), but plays no role in the hypoxia-induced anapyrexia.

Involvement of endogenous beta-endorphin in antinociception in the arcuate nucleus of hypothalamus in rats with inflammation

Although exogenous administration of beta-endorphin to the arcuate nucleus of hypothalamus (ARC) had been shown to produce antinociception, the role of endogenous beta-endorphin of the ARC in nociceptive processing has not been studied directly. The aim of the present study was to investigate the effect of endogenous beta-endorphin in the ARC on nociception in rats with carrageenan-induced inflammation. The hindpaw withdrawal latency (HWL) to noxious thermal and mechanical stimulation was assessed by the hot-plate test and the Randall Selitto Test. Intra-ARC injection of naloxone had no significant influence on the HWL to thermal and mechanical stimulation in intact rats. The HWL decreased significantly after intra-ARC injection of 1 or 10 microg of naloxone in rats with inflammation, but not with 0.1 microg of naloxone. Furthermore, intra-ARC administration of the selective mu-opioid receptor antagonist beta-funaltrexamine (beta-FNA) decreased the nociceptive response latencies to both stimulation in a dose-dependent manner in rats with inflammation, while intra-ARC administration of the selective delta-opioid receptor antagonist naltrindole or the selective kappa-opioid receptor antagonist nor-binaltorphimine (nor-BNI) showed no influences on the nociceptive response latency. The antiserum against beta-endorphin, administered to the ARC, also dose-dependently reduced the HWL in rats with inflammation. The results indicate that endogenous beta-endorphin in the ARC plays an important role in the endogenous antinociceptive system in rats with inflammation, and that its effect is predominantly mediated by the mu-opioid receptor.

Fear and power-dominance motivation: proposed contributions of peptide hormones present in cerebrospinal fluid and plasma

We propose that fear and power-dominance drive motivation are generated by the presence of elevated plasma and cerebrospinal fluid (CSF) levels of certain peptide hormones. For the fear drive, the controlling hormone is corticotropin releasing factor, and we argue that elevated CSF and plasma levels of this peptide which occur as a result of fear-evoking and other stressful experiences in the recent past are detected and transduced into neuronal activities by neurons in the vicinity of the third ventricle, primarily in the periventricular and arcuate hypothalamic nuclei. For the power-dominance drive, we propose that the primary signal is the CSF concentration of vasopressin, which is detected in two circumventricular organs, the subfornical organ and organum vasculosum of the lamina terminalis. We suggest that the peptide-generated signals detected in periventricular structures are transmitted to four areas in which neuronal activities represent fear and power-dominance: one in the medial hypothalamus, one in the dorsolateral quadrant of the periaqueductal gray matter, a third in the midline thalamic nuclei, and the fourth within medial prefrontal cortex. The probable purpose of this system is to maintain a state of fear or anger and consequent vigilant or aggressive behavior after the initial fear- or anger-inducing stimulus is no longer perceptible. We further propose that all the motivational drives, including thirst, hunger and sexual desire are generated in part by non-steroidal hormonal signals, and that the unstimulated motivational status of an individual is determined by the relative CSF and plasma levels of several peptide hormones.

Glutamatergic afferent projections to the dorsal raphe nucleus of the rat

Based on WGA-apo-HRP-gold (WG) retrograde tracing, the present study revealed that different subdivisions of the dorsal raphe (DR) such as dorsomedial, ventromedial, lateral wing, and caudal regions receive unique, topographically organized afferent inputs, that are more restricted than previously reported. Phaseolus vulgaris leucoagglutinin anterograde tracing studies confirmed that the medial prefrontal cortex provides the major afferent input to each subdivision of the DR. Double-labeling studies combining WG tracing and glutamate immunostaining indicated that the medial prefrontal cortex, various hypothalamic nuclei including perifornical, lateral, and arcuate nuclei, and several medullary regions such as lateral and medial parabrachial nuclei, and laterodorsal tegmental nucleus provide the major glutamatergic input to each subregion of the DR. It should be noted that the degree of glutamatergic input from these afferent sites was specific for each DR subdivision. The present findings indicated that dorsomedial, ventromedial, lateral wing, and caudal subdivisions of the DR receive excitatory inputs from both cortical and subcortical sites which might be involved in regulation or modulation of a broad range of systems, including sensory and motor functions, arousal and sleep-wake cycle, biorhythmic, cognitive, and affective behaviors.

Neurons containing tuberoinfundibular peptide of 39 residues project to limbic, endocrine, auditory and spinal areas in rat

Accumulating evidence suggests that tuberoinfundibular peptide of 39 residues (TIP39) may be the endogenous ligand of the parathyroid hormone 2 receptor. The vast majority of TIP39-containing neurons are localized in two regions, the subparafascicular area at the thalamic-midbrain junction, and the medial paralemniscal nucleus in the rostral pons. In contrast to the restricted localization of TIP39-containing cell bodies, TIP39-containing fibers have a widespread distribution. TIP39 neurons were lesioned electrolytically to determine the origin of TIP39-containing fibers within different parts of the rat CNS. Following bilateral lesions of the medial subparafascicular area including the subparafascicular nucleus, TIP39-immunoreactive fibers almost completely disappeared from forebrain regions including the anterior limbic cortical areas, the shell and cone portions of the nucleus accumbens, the lateral septum, the bed nucleus of the stria terminalis, the amygdaloid nuclei, the fundus striati, the subiculum, the thalamic paraventricular nucleus, and the hypothalamic paraventricular, dorsomedial and arcuate nuclei. Unilateral lesions of the medial and the lateral subparafascicular area demonstrated that the projections are ipsilateral and that medial lesions produce higher reductions in the density of TIP39 fibers except in the amygdala and the hypothalamus. Following lesions of the medial paralemniscal nucleus, TIP39-immunoreactive fibers disappeared from the medial geniculate body, the periaqueductal gray, the deep layers of the superior colliculus, the external cortex of the inferior colliculus, the cuneiform nucleus, the nuclei of the lateral lemniscus, the lateral parabrachial nucleus, the locus coeruleus, the subcoeruleus area, the medial nucleus of the trapezoid body, the periolivary nuclei, and the spinal cord, suggesting that these regions receive TIP39-containing fibers from the medial paralemniscal nucleus, and unilateral lesions demonstrated that the projections are ipsilateral. The projections of the TIP39-containing cells in the subparafascicular area suggest their involvement in limbic and endocrine functions, while the projections of the TIP39-containing cells in the medial paralemniscal nucleus suggest their involvement in auditory and nociceptive functions.

Hypothalamic regulation of energy homeostasis

The co-ordinated regulation of food intake and energy expenditure takes place in the hypothalamic regions of the brain. Current understanding of the systems involved in this regulation suggests that, in the hypothalamus, there are two major groups of neuropeptides involved in orexigenic and anorexic processes. The orexigenic neuropeptides are neuropeptide Y (NPY) and agouti-related peptide (AgRP) and the anorexic neuropeptides are alpha-melanocyte-stimulating hormone (alpha-MSH) and cocaine and amphetamine-related transcript (CART). Theneurons expressing these neuropeptides interact with each other and with signals from the periphery (such as leptin, insulin, ghrelin and glucocorticoids) to regulate feeding behaviour, energy expenditure and various endocrine axes. Although direct evidence is limited, there are examples of genetic obesity in humans which suggest that the balance between orexigenic and anorexic pathways in the hypothalamus is also pivotally important in the maintenance of energy homeostasis in humans.

Neuroanatomical and psychopharmacological evidence for interaction between opioid and GABAergic neural pathways in the modulation of fear and defense elicited by electrical and chemical stimulation of the deep layers of the superior colliculus and dorsal periaqueductal gray matter

The effects of central administration of opioid antagonists on the aversive responses elicited by electrical (at the freezing and escape thresholds) or chemical stimulation (crossings, rearings, turnings and jumps, induced by microinjections of bicuculline) of the midbrain tectum were determined. Central microinjections of naloxone and naltrexone in the mesencephalic tectum caused a significant increase in the freezing and escape thresholds elicited by electrical midbrain tectum stimulation. Furthermore, both opioid antagonists caused a significant decrease in the mean incidence of aversive behavioral responses induced by microinjections of bicuculline in the deep layers of the superior colliculus (DLSC) and in dorsal aspects of the periaqueductal gray matter (DPAG), as compared with controls. These findings suggest an opioid modulation of the GABAergic inhibitory inputs controlling the aversive behavior elicited by midbrain tectum stimulation. In fact, immunohistochemical evidence suggests that the dorsal mesencephalon is rich in beta-endorphin-containing neurons and fibers with varicosities. Iontophoretical microinjections of the neurotracer biodextran in the substantia nigra, pars reticulata (SNpr), show nigro-tectal pathways connecting SNpr with the same neural substrate of the DPAG rich in neuronal cells immunoreactive for opioid peptides. Labeled neurons of the DLSC and periaqueductal gray matter send inputs with varsicosities to ipsi- and contralateral DPAG and ipsilateral SNpr. These findings, in addition to the psychopharmacological evidence for the interaction between opioid and GABAergic mechanisms, offer a neuroanatomical basis of a possible presynaptic opioid inhibition of GABAergic nigro-tectal neurons modulating the fear in aversive structures of the cranial mesencephalon, in a short link, and maybe through a major neural circuit, also in GABA-containing perikarya of nigro-tectal neurons.

Hypothalamic and vagal neuropeptide circuitries regulating food intake

It has been recognized for some time that a number of different neuropeptides exert powerful effects on food intake. During the last few years, the neurocircuitry within which these peptides operate has also begun to be elucidated. Peptidergic feeding-regulatory neurones are found both in the hypothalamus and the brainstem, where they act as input stations for hormonal and gastrointestinal information, respectively. These cell populations both project to several other brain regions and interconnect extensively. The present review summarizes the neuroanatomy and connectivity of some prominent peptides involved in food intake control, including neuropeptide Y, melanocortin peptides, agouti gene-related protein, cocaine- and amphetamine-regulated transcript, orexin/hypocretin, melanin-concentrating hormone and cholecystokinin. Disturbances in the hypothalamic neuropeptide systems have been implicated in the phenotype of a genetic model of fatal hypophagia, the mouse anorexia (anx) mutation, which is also discussed.

Substance P

Substance P is considered to be an important neuropeptide in nociceptive processes. Although substance P was described more than 60 years ago, there is still controversy about its exact role in nociception. This article reviews the current knowledge about the function of substance P in pain. Special emphasis is put on how to use this knowledge in the development of new ways to treat pain.

Norepinephrine modulates single hypothalamic arcuate neurons via alpha(1)and beta adrenergic receptors

The effects of norepinephrine (NE) on the electrophysiological activities of single hypothalamic arcuate neurons were studied using extracellular recording of 385 neurons from 169 brain slices in rats. The results showed that: (1) of 236 neurons selected randomly and tested with NE application, 137 (58.0%) were excited, 67 (28.4%) were inhibited, and 32 (13.6%) failed to respond; (2) substitution of low Ca(2+)-high Mg(2+) artificial cerebrospinal fluid (ACSF) for normal ACSF abolished the NE-induced inhibitory effect but failed to abolish the excitatory effect; (3) both the NE-induced excitatory and inhibitory effects were antagonized partly by phentolamine, prazosin, and propranolol but not by yohimbine; (4) naloxone and glibenclamide, a blocker of adenosine triphosphate-sensitive (K(ATP)) channels, blocked the NE-induced inhibitory effect; and (5) neurons that were inhibited by NE were also inhibited by morphine and cromakalim, an agonist of K(ATP) channels, and moreover, the morphine-induced inhibitory effect could be blocked by glibenclamide, while the cromakalim-induced inhibitory effect was not blocked by naloxone. These results imply that: (a) NE excites arcuate neurons through a mechanism that is insensitive to lowering the extracellular Ca(2+) suggesting a direct postsynaptic response through alpha(1)- and beta-adrenergic receptors, while NE inhibits cells through at least an inhibitory interneuron in arcuate and so is dependent on a Ca(2+)-sensitive presynaptic release mechanism; and (b) the inhibitory interneuron may be opioidergic, being excited first through alpha(1)- and beta-adrenergic receptors, after which the released opioids inhibit the neurons being recorded with an involvement of activation of K(ATP) channels. This possibility needs to be substantiated in much more detail.

Interconnections between the neuroendocrine hypothalamus and the central autonomic system. Geoffrey Harris Memorial Lecture, Kitakyushu, Japan, October 1998

Tract-tracing techniques in combination with immunohistochemistry and in situ hybridization were used in intact and operated rats (hypothalamic lesions, transections of neuronal pathways) to localize and characterize neuronal connections between the hypothalamus and autonomic centers. Viscerosensory and somatosensory signals which relay in the spinal cord and the medulla oblongata reach the hypothalamus through various catecholaminergic and noncatecholaminergic neuronal pathways. Vice versa, the hypothalamus influences autonomic activities through humoral and neurohumoral pathways. Descending hypothalamic efferents carry feedback signals to viscerosensory and brainstem catecholaminergic neurons and regulatory inputs to parasympathetic (dorsal vagal nucleus) and sympathetic (thoracolumbar intermediolateral cell column) preganglionic neurons. These fibers arise mainly from neurons of the paraventricular, arcuate, perifornical, and dorsomedial nuclei and the lateral hypothalamus. The major neuroanatomical observations are the following: (1) pathways between the hypothalamus and autonomic centers are bidirectional: the ascending and descending fibers may use the same avenues; (2) the descending axons are mainly peptidergic (CRF, vasopressin, oxytocin, somatostatin, enkephalin, POMC, and cANP), while the ascending fibers are both peptidergic (enkephalin, NPY, neurotensin, dynorphins) and catecholaminergic; (3) descending hypothalamic axons terminate directly on the sensory, preganglionic, and catecholaminergic neurons in the medulla and the spinal cord; (4) hypothalamic projections to the autonomic centers are always bilateral; (5) while medullary autonomic and catecholaminergic fibers innervate hypothalamic neurons directly, spinohypothalamic axons are relayed on neurons in the lateral hypothalamus.

Pain-induced analgesia mediated by mesolimbic reward circuits

We tested the hypothesis that noxious stimuli induce pain modulation by activation of supraspinal structures. We found that intense noxious stimuli (i.e., subdermal injection of capsaicin or paw immersion in hot water) induced profound attenuation of the jaw-opening reflex in the anesthetized rat; forepaw subdermal capsaicin also elevated the mechanical hindpaw-withdrawal threshold in the awake rat. These antinociceptive effects were blocked by previous injection of either a dopamine antagonist (flupentixol) or an opioid antagonist (naloxone) into the nucleus accumbens. Additional experiments in anesthetized animals showed that the antinociceptive effect of noxious stimulation by either capsaicin (>/=100 micrograms) or hindpaw immersion in hot water (>/=45 degrees C for 4 min) correlated with the intensity of the stimulus. The maximal antinociceptive effect of capsaicin was similar in magnitude to that of a high dose of morphine (10 mg/kg) injected subcutaneously. Injection of the GABA(A)-receptor agonist muscimol, but not naloxone, into the rostroventral medulla, a major component of descending pain modulation systems, blocked capsaicin-induced antinociception. Although it is widely thought that painful stimuli may induce analgesia by activating forebrain structures, this is the first demonstration that such a mechanism exists. Furthermore, this mechanism can be engaged by naturalistic stimuli in awake animals. These observations imply that painful stimuli might under certain conditions be rewarding.

Gender-specific effects of CNQX administered into the arcuate nucleus on ventilatory patterns in rats

This study evaluated the effect of microinjection of the non-N-methyl-D-aspartate (NMDA) receptor antagonist, cyano, 3-dihydro-7-nitrogluinoxaline-2, 3-dione (CNQX), into the arcuate nucleus of the hypothalamus on ventilation in male and female rats. Conscious rats received saline or 50, 100, or 200 pmol concentrations of CNQX on separate days. Significant interactions between dose and gender were observed on frequency, inspiratory (TI) and expiratory (TE) time, and tidal volume. CNQX depressed frequency, but increased tidal volume in female rats. Effects of CNQX in males on these ventilatory parameters were considerably less. In CNQX-treated females the decrease in frequency of breathing was primarily due to an increase in TI. Exposure of CNQX-treated female rats to hypercapnia, but not to hypoxia transiently decreased TI. No effect of CNQX was noted on oxygen consumption or body temperature. Thus, non-NMDA receptors in the arcuate nucleus are involved in modulating ventilatory patterns in a gender-specific manner independent of its effects on oxygen consumption or body temperature.

The neuropeptide Y/agouti gene-related protein (AGRP) brain circuitry in normal, anorectic, and monosodium glutamate-treated mice

Neuropeptide Y (NPY) and the endogenous melanocortin receptor antagonist, agouti gene-related protein (AGRP), coexist in the arcuate nucleus, and both exert orexigenic effects. The present study aimed primarily at determining the brain distribution of AGRP. AGRP mRNA-expressing cells were limited to the arcuate nucleus, representing a major subpopulation (95%) of the NPY neurons, which also was confirmed with immunohistochemistry. AGRP-immunoreactive (-ir) terminals all contained NPY and were observed in many brain regions extending from the rostral telencephalon to the pons, including the parabrachial nucleus. NPY-positive, AGRP-negative terminals were observed in many areas. AGRP-ir terminals were reduced dramatically in all brain regions of mice treated neonatally with monosodium glutamate as well as of mice homozygous for the anorexia mutation. Terminals immunoreactive for the melanocortin peptide alpha-melanocyte-stimulating hormone formed a population separate from, but parallel to, the AGRP-ir terminals. Our results show that arcuate NPY neurons, identified by the presence of AGRP, project more extensively in the brain than previously known and indicate that the feeding regulatory actions of NPY may extend beyond the hypothalamus.

Aspartic acid in the arcuate nucleus attenuates the depressive effects of naloxone on ventilation

Ventilation, oxygen consumption, the ventilatory equivalent for oxygen, and ventilatory responses to hypoxia and to hypercapnia were evaluated in conscious male rats who received each of four treatments: (1) microinjection of artificial cerebrospinal fluid (aCSF) into the arcuate nucleus and subcutaneously saline (CS); (2) aspartic acid into the arcuate nucleus and saline subcutaneously (AS); (3) aCSF into the arcuate nucleus and naloxone subcutaneously (CN); and (4) aspartic acid into the arcuate nucleus and naloxone subcutaneously (AN). Rats treated with CN exhibited a depression of ventilation, ventilatory equivalent, ventilatory response to hypercapnia, and tidal volume response to hypoxia and to hypercapnia. AS had no effect on any parameters. Administration of both aspartic acid and naloxone attenuated all the effects of CN except the depression of minute ventilation in response to hypercapnia. Therefore the naloxone (a mu opioid receptor antagonist) induced a depression of ventilation that was attenuated by aspartic acid acting on N-methyl-D-aspartic acid receptors in the arcuate nucleus.

Immunocytochemical localization of substance P receptor in rat periaqueductal gray matter: a light and electron microscopic study

The distribution of substance P receptor (SPR) protein in the rat periaqueductal gray matter (PAG) was investigated with a polyclonal antibody in the four subdivisions obtained by cytochrome-oxidase histochemistry (Co-hi). At light microscopic analysis, immunoreactivity appeared particularly dense in the dorsal subdivision of the PAG, was less intense in the other subdivisions, and formed several longitudinally organized columns. SPR-like immunoreactivity (SP(R-i)) was localized mostly to cell bodies and dendrites of small and medium-sized neurons, which constituted about 6% of the total neuronal population of the PAG. At the electron microscopic level, SP(R-i) could be observed on postsynaptic as well as on nonsynaptic regions of both cell bodies and dendrites. A small proportion of axons (4.2%) and axon terminals (5.3%) showed SP(R-i), the majority of labeled axon terminals, amounting to about 70% of synapsing elements, formed asymmetric synapses with dendrites. Rare astroglial processes displaying SP(R-i) were also observed scattered throughout the neuropil of all PAG subdivisions. Our observations suggest that 1) also in the PAG, SP may act in a diffuse, nonsynaptic manner, probably on targets that are distant from its sites of release; and 2) SP may modulate excitatory neurotransmission acting presynaptically on those labeled axons that form asymmetric synapses.

Forebrain afferents to the rat dorsal raphe nucleus demonstrated by retrograde and anterograde tracing methods

The dorsal raphe nucleus through its extensive efferents has been implicated in a great variety of physiological and behavioural functions. However, little is know about its afferents. Therefore, to identify the systems likely to influence the activity of serotonergic neurons of the dorsal raphe nucleus, we re-examined the forebrain afferents to the dorsal raphe nucleus using cholera toxin b subunit and Phaseolus vulgaris-leucoagglutinin as retrograde or anterograde tracers. With small cholera toxin b subunit injection sites, we further determined the specific afferents to the ventral and dorsal parts of the central dorsal raphe nucleus, the rostral dorsal raphe nucleus and the lateral wings. In agreement with previous studies, we observed a large number of retrogradely-labelled cells in the lateral habenula following injections in all subdivisions of the dorsal raphe nucleus. In addition, depending on the subdivision of the dorsal raphe nucleus injected, we observed a small to large number of retrogradely-labelled cells in the orbital, cingulate, infralimbic, dorsal peduncular, and insular cortice, a moderate or substantial number in the ventral pallidum and a small to substantial number in the claustrum. In addition, we observed a substantial to large number of cells in the medial and lateral preoptic areas and the medial preoptic nucleus after cholera toxin b subunit injections in the dorsal raphe nucleus excepting for those located in the ventral part of the central dorsal raphe nucleus, after which we found a moderate number of retrogradely-labelled cells. Following cholera toxin b subunit injections in the dorsal part of the central dorsal raphe nucleus, a large number of retrogradely-labelled cells was seen in the lateral, ventral and medial parts of the bed nucleus of the stria terminalis whereas only a small to moderate number was visualized after injections in the other dorsal raphe nucleus subdivisions. In addition, respectively, a substantial and a moderate number of retrogradely-labelled cells was distributed in the zona incerta and the subincertal nucleus following all tracer injections in the dorsal raphe nucleus. A large number of retrogradely-labelled cells was also visualized in the lateral, dorsal and posterior hypothalamic areas and the perifornical nucleus after cholera toxin b subunit injections in the dorsal part of the central raphe nucleus and to a lesser extent following injections in the other subdivisions. We further observed a substantial to large number of retrogradely-labelled cells in the tuber cinereum and the medial tuberal nucleus following cholera toxin b subunit injections in the dorsal part of the central dorsal raphe nucleus or the lateral wings and a small to moderate number after injections in the two other dorsal raphe nucleus subdivisions. A moderate or substantial number of labelled cells was also seen in the ventromedial hypothalamic area and the arcuate nucleus following cholera toxin injections in the dorsal part of the central dorsal raphe nucleus and the lateral wings and an occasional or small number with injection sites located in the other subdivisions. Finally, we observed, respectively, a moderate and a substantial number of retrogradely-labelled cells in the central nucleus of the amygdala following tracer injections in the ventral or dorsal parts of the central dorsal raphe nucleus and a small number after injections in the other subnuclei. In agreement with these retrograde data, we visualized anterogradely-labelled fibres heterogeneously distributed in the dorsal raphe nucleus following Phaseolus vulgaris-leucoagglutinin injections in the lateral orbital or infralimbic cortice, the lateral preoptic area, the perifornical nucleus, the lateral or posterior hypothalamic areas, the zona incerta, the subincertal nucleus or the medial tuberal nucleus. (ABSTRACT TRUNCATED)

Afferent projections to the rat nuclei raphe magnus, raphe pallidus and reticularis gigantocellularis pars alpha demonstrated by iontophoretic application of choleratoxin (subunit b)

The aim of the present study was to identify the specific afferent projections to the rostral and caudal nucleus raphe magnus, the gigantocellular reticular nucleus pars alpha and the rostral nucleus raphe pallidus. For this purpose, small iontophoretic injections of the sensitive retrograde tracer choleratoxin (subunit b) were made in each of these structures. In agreement with previous retrograde studies, after all injection sites, a substantial to large number of labeled neurons were observed in the dorsal hypothalamic area and dorsolateral and ventrolateral parts of the periaqueductal gray, and a small to moderate number were found in the lateral preoptic area, bed nucleus of the stria terminalis, paraventricular hypothalamic nucleus, central nucleus of the amygdala, lateral hypothalamic area, parafascicular area, parabrachial nuclei, subcoeruleus area and parvocellular reticular nucleus. In addition, depending on the nucleus injected, we observed a variable number of retrogradely labeled cells in other regions. After injections in the rostral nucleus raphe magnus, a large number of labeled cells were seen in the prelimbic, infralimbic, medial and lateral precentral cortices and the dorsal part of the periaqueductal gray. In contrast, after injections in the other nuclei, fewer cells were localized in these structures. Following raphe pallidus injections, a substantial to large number of labeled cells were observed in the medial preoptic area, median preoptic nucleus, ventromedial part of the periaqueductal gray, Kölliker-Fuse and lateral paragigantocellular reticular nuclei. Following injections in the other areas, a small to moderate number of cells appeared. After gigantocellular reticular pars alpha injections, a very large and substantial number of labeled neurons were found in the deep mesencephalic reticular formation and oral pontine reticular nucleus, respectively. After the other injections, fewer cells were seen. Following rostral raphe magnus or raphe pallidus injections, a substantial number of labeled cells were observed in the insular and perirhinal cortices. Following caudal raphe magnus or gigantocellular reticular pars alpha injections, fewer cells were found. After raphe magnus or gigantocellular reticular pars alpha injections, a moderate to substantial number of cells were localized in the fields of Forel, lateral habenular nucleus and ventral caudal pontine reticular nucleus. Following raphe pallidus injections, only a small number of cells were seen. Our data indicate that the rostral and caudal parts of the nucleus raphe magnus, the gigantocellular reticular nucleus pars alpha and the nucleus raphe pallidus receive afferents of comparable strength from a large number of structures. In addition, a number of other afferents give rise to stronger inputs to one or two of the four nuclei studied. Such differential inputs might be directed to populations of neurons with different physiological roles previously recorded specifically in these nuclei.

Beta-endorphin in the brain. A role in nociception

We have known the endogenous opioid peptide beta-endorphin for 20 years. Surprisingly, our knowledge of the physiological role of this peptide and its receptors in modulation of pain perception is still fragmentary. Whereas most studies have tried to elucidate the physiological role of beta-endorphin by reversing evoked responses by the opioid antagonist naloxone, this review focuses on quantification of release of beta-endorphin in the brain as the approach to define physiological and pathophysiological roles of beta-endorphin in relation to nociception. Using a lateral ventricle-cisterna magna perfusion model in the anesthetized rat, it was shown that depolarization of neurons in the arcuate nucleus of the hypothalamus, where beta-endorphin in produced, was followed by release of beta-endorphin to the cerebrospinal fluid compartment. Intense activation of spinal nociceptive pathways by intrathecal capsaicin injections also led to beta-endorphin release. It is concluded that there may still be good reason to quantify beta-endorphin in human cerebrospinal fluid to elucidate the role of beta-endorphin in pain perception.

Melanocortin antagonists define two distinct pathways of cardiovascular control by alpha- and gamma-melanocyte-stimulating hormones

Melanocortin peptides and at least two subtypes of melanocortin receptors (MC3-R and MC4-R) are present in brain regions involved in cardiovascular regulation. In urethane-anesthetized rats, unilateral microinjection of alpha-melanocyte-stimulating hormone (MSH) into the medullary dorsal-vagal complex (DVC) causes dose-dependent (125-250 pmol) hypotension and bradycardia, whereas gamma-MSH is less effective. The effects of alpha-MSH are inhibited by microinjection to the same site of the novel MG4-R/MC3-R antagonist SHU9119 (2-100 pmol) but not naloxone (270 pmol), whereas the similar effects of intra-DVC injection of beta-endorphin (1 pmol) are inhibited by naloxone and not by SHU9119. Hypotensive and bradycardic responses to electrical stimulation of the arcuate nucleus also are inhibited by ipsilateral intra-DVC microinjection of SHU9119. gamma-MSH and ACTH(4-10), but not alpha-MSH, elicit dose-dependent (0.1-12.5 nmol) pressor and tachycardic effects, which are much more pronounced after intracarotid than after intravenous administration. The effects of gamma-MSH (1.25 nmol) are not inhibited by the intracarotid injection of SHU9119 (1.25-12.5 nmol) or the novel MC3-R antagonist SHU9005 (1.25-12.5 nmol). We conclude that the hypotension and bradycardia elicited by the release of alpha-MSH from arcuate neurons is mediated by neural melanocortin receptors (MC4-R/MC3-R) located in the DVC, whereas the similar effects of beta-endorphin, a peptide derived from the same precursor, are mediated by opiate receptors at the same site. In contrast, neither MC3-R nor MC4-R is involved in the centrally mediated pressor and tachycardic actions of gamma-MSH, which, likely, are mediated by an as yet unidentified receptor.