Neurochemical organization of the hypothalamic projection to the spinal cord in the rat

Paraventricular nucleus influence on renal sympathetic activity in vasopressin gene-deleted rats

In Wistar rats, an increase in renal sympathetic activity is induced by activation of presympathetic neurones in the paraventricular nucleus (PVN) and reflexly by a mild venous haemorrhage. Both stimuli are dependent on the release of vasopressin and glutamate at spinal synapses. The significance of the supraspinal pathway and the co-operative interaction of vasopressin with an excitatory amino acid is unclear. The present study examines this in Brattleboro rats, which have a natural vasopressin gene deletion. The responses were compared with Long-Evans rats, from which Brattleboro rats are derived. All rats were anaesthetized with a mixture of urethane (650 mg kg(-1) i.v.) and chloralose (50 mg kg(-1) i.v.). Recordings were made of blood pressure, heart rate and renal sympathetic nerve activity (RSNA). Microinjection of d,l-homocysteic acid (DLH, 0.2 m, 100 nl) at sites restricted to the PVN elicited significant increases in RSNA (P < 0.001) in both strains of rats. These changes were significantly reduced (P < 0.01) in Long-Evans rats by intrathecal application to the spinal cord of either a V(1a) antagonist or a glutamate antagonist (kynurenic acid), whereas in Brattleboro rats the changes were significantly reduced (P < 0.05) only by kynurenic acid. Removal of 1 ml of venous blood in Long-Evans rats increased RSNA by 28 +/- 4% (P < 0.01), which was significantly reduced (P < 0.05) by prior intrathecal application of either the V(1a) antagonist or by kynurenic acid. The same test in Brattleboro rats caused a significantly greater (P < 0.05) increase (63 +/- 14.7%) in RSNA which, in contrast to Long-Evans rats, was unchanged by intrathecal application of the V(1a) antagonist, being significantly reduced (P < 0.01) only by intrathecal kynurenic acid. Thus, in Brattleboro rats, the lack of vasopressin in the brain sympathetic pathways appears to be compensated, acutely, by glutamate-releasing pathways. This might indicate that, in normal rats, vasopressin is more important in maintaining longer term adjustments to stressors.

A spinal vasopressinergic mechanism mediates hyperosmolality-induced sympathoexcitation

An elevation in plasma osmolality elicits a complex neurohumoral response, including an activation of the sympathetic nervous system and an increase in arterial pressure. Using a combination of in vivo and in situ rat preparations, we sought to investigate whether hypothalamic vasopressinergic spinally projecting neurones are activated during increases in plasma osmolality to elicit sympathoexcitation. Hypertonic saline (HS, i.v. bolus), which produced a physiological increase in plasma osmolality to 299 +/- 1 mosmol (kg water)(-1), elicited an immediate increase in mean arterial pressure (MAP) (from 101 +/- 1 to 121 +/- 3 mmHg) in vivo. Pre-treatment with prazosin reversed the HS-induced pressor response to a hypotensive response (from 121 +/- 3 to 68 +/- 2 mmHg), indicating significant activation of the sympathetic nervous system. In an in situ arterially perfused decorticate rat preparation, hyperosmotic perfusate consisted of either 135 mm NaCl, or a non-NaCl osmolyte, mannitol (0.5%); both increased lumbar sympathetic nerve activity (LSNA) by 32 +/- 5% (NaCl) and 21 +/- 1% (mannitol), which was attenuated after precollicular transection (7 +/- 3% and 1 +/- 1%, respectively). Remaining experiments used the NaCl hyperosmotic stimulus. In separate preparations the hyperosmotic-induced sympathoexcitation (21 +/- 2%) was also significantly attenuated after transection of the circumventricular organs (2 +/- 1%). Either isoguvacine (a GABA(A) receptor agonist) or kynurenic acid (a non-selective ionotropic glutamate receptor antagonist) microinjected bilaterally into the paraventricular nucleus (PVN) attenuated the increase in LSNA induced by the hyperosmotic stimulus (control: 25 +/- 2%; after isoguvacine: 7 +/- 2%; after kynurenic: 8 +/- 3%). Intrathecal injection of a V(1a) receptor antagonist also reduced the increase in LSNA elicited by the hyperosmotic stimulus (control: 29 +/- 6%; after blocker: 4 +/- 1%). These results suggest that a physiological hyperosmotic stimulus produces sympathetically mediated hypertension in conscious rats. These data are substantiated by the in situ decorticate preparation in which sympathoexcitation was also evoked by comparable hyperosmotic stimulation. Our findings demonstrate the importance of vasopressin acting on spinal V(1a) receptors for mediating sympathoexcitatory response to acute salt loading.

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.

Activation of spinally projecting and nitrergic neurons in the PVN following heat exposure

The present study investigated the effect of acute thermal stimulation in conscious rats on the production of Fos, a marker of increased neuronal activity, in spinally projecting and nitrergic neurons in the hypothalamic paraventricular nucleus (PVN). The PVN contains a high concentration of nitrergic neurons, as well as neurons that project to the intermediolateral cell column (IML) of the spinal cord that can directly influence sympathetic nerve activity (SNA). During thermal stimulation, the PVN is activated, but it is unknown whether spinally projecting PVN neurons and the nitrergic neurons are involved. Compared with controls, rats exposed to an environmental temperature of 39 degrees C for 1 h had a 10-fold increase in the number of cells producing Fos in the PVN (133 +/- 23 vs. 1,336 +/- 43, respectively, P < 0.0001). Of the spinally projecting neurons in the PVN of heated rats (98 +/- 10), over 20% expressed Fos. Additionally, of the nitrergic neurons (NADPH-diaphorase positive) located in the parvocellular PVN (723 +/- 17), 40% also expressed Fos (P < 0.0001 compared with controls). Finally, there was a significant increase in the number of spinally projecting neurons in the PVN that were nitrergic and expressed Fos after heat exposure (12%) compared with controls (0.1%) (P < 0.0001). These results suggest that spinally projecting and nitrergic neurons in the PVN may contribute to the central pathways activated by thermal stimulation.

The role of supraspinal vasopressin and glutamate neurones in an increase in renal sympathetic activity in response to mild haemorrhage in the rat

This study investigated the importance of supraspinal vasopressin and glutamate neurones in regulating renal sympathetic activity as part of the response to an acute reduction in blood volume. Wistar rats anaesthetized with chloralose and urethane were instrumented to record arterial blood pressure, heart rate and left renal sympathetic nerve activity. Pharmacological agonists and antagonists to glutamate and vasopressin were applied to the renal outflow of the spinal cord via an intrathecal catheter inserted at the foramen magnum and with the tip at the level of T10. Both glutamate and vasopressin increased renal sympathetic activity, and these actions were shown to be selectively blocked by their respective antagonists. Removing 1 ml of venous blood from a femoral venous catheter elicited an increase of 26 +/- 2% in renal sympathetic activity. This response to mild haemorrhage was halved to 13 +/- 4% by prior intrathecal application of a selective V1a antagonist. Similarly, prior intrathecal application of kynurenic acid reduced the response to the mild haemorrhage from 28 +/- 2 to 12.6 +/- 2.8%. Intrathecal application of both antagonists together reduced the haemorrhage response even further to 8 +/- 3%. All the changes were statistically significant at P < 0.01. It is concluded that a small reduction in blood volume induces an increase in renal sympathetic activity dependent on vasopressin and glutamate release from terminals of supraspinal neurones. It is suggested that the vasopressin neurones most probably originate from the paraventricular nucleus of the hypothalamus.

Re-growth of catecholaminergic fibers and protection of cholinergic spinal cord neurons in spinal repaired rats

The extent of re-growth of catecholaminergic fibers, the survival of cholinergic neurons and the degree of autonomic dysreflexia were assessed in complete spinal cord-transected adult rats that received a repair treatment of peripheral nerve grafts and acidic fibroblast growth factor (aFGF). The rats were randomly divided into three groups: (1) sham control group (laminectomy only); (2) spinal cord transection at T8 (transected group); and (3) spinal cord transection at T8, followed by aFGF treatment and peripheral nerve graft (repaired group). The spinal cords and brains of all rats were collected at 6 months post-surgery. Immunohistochemistry for tyrosine hydroxylase (TH) and dopamine-beta-hydroxylase (DBH), and fluoro-gold (FG) retrograde tracing were used to evaluate axon growth across the damage site, and immunocytochemistry for choline acetyl transferase (ChAT) was used to evaluate cholinergic neuronal cell survival following the injury and treatment. When comparing with the transected group, the repaired group showed: (1) lower elevation of mean arterial pressure during colorectal distension; (2) retrogradely labeled neurons in the hypothalamus, zona incerta, subcoeruleus nuclei and rostral ventrolateral medulla following application of FG below the repair site; (3) the presence of TH- and DBH-labeled axons below the lesion site; (4) higher numbers of ChAT-positive neurons in ventral horn and intermediolateral column near the lesion site. We conclude that peripheral nerve graft and aFGF treatments facilitate the re-growth of catecholaminergic fibers, also protect sympathetic preganglionic neurons and spinal motor neurons, and reduce autonomic dysfunction in a T-8 spinal cord-transected rat model.

Cold stress induces metabolic activation of thyrotrophin-releasing hormone-synthesising neurones in the magnocellular division of the hypothalamic paraventricular nucleus and concomitantly changes ovarian sympathetic activity parameters

Recent studies suggest thyrotrophin-releasing hormone (TRH) serves as a neurotransmitter and thereby provides a functional vegetative connection between the brain and the ovary. In the present study, magnocellular neurones of the paraventricular nucleus (PVN) in animals subjected to cold exposure were studied to determine the hypothalamic origin of the TRH involved in this pathway. In situ hybridisation analysis of hypothalamic tissue showed that cold exposure causes a two-fold increase in the total number of neurones expressing TRH mRNA in the PVN. Immunohistochemical studies showed that TRH peptide is localised to the magnocellular PVN and that the number of TRH immunoreactive cells increases two-fold following 64 h of cold exposure. Double-immunostaining for MAP-2 and TRH revealed that TRH peptide is localised in the perikarya of the magnocellular neurones. TRH release was measured in vivo from the magnocellular portion of the PVN using push-pull perfusion. Although controls exhibited a very low level of TRH release, animals subjected to cold showed a pulsatile-like TRH release profile with two different patterns of release: (i) low basal level with small bursts of TRH release and (ii) a profile with an up to seven-fold increase in TRH release compared to controls. The colocalisation of TRH with the specific somato-dendritic marker MAP-2 in processes of the magnocellular neurones suggested a local release of TRH. Additional studies demonstrated a reduction in ovarian noradrenaline content after 48 h of cold exposure, a feature indicative of nerve activation at the terminal organ. After 64 h of cold exposure, the ovarian noradrenaline returned to control values but the noradrenaline content of the coeliac ganglia was increased, suggesting a compensatory effect originating in the cell bodies of the sympathetic neurones that innervate the ovary. The correlation between the local release of TRH from dendrites within the magnocellular PVN in conditions of cold and the activation of the sympathetic nerves supplying the ovary raises the possibility that TRH contributes to the processing regulating sympathetic outflow and may thereby impact on the functional activity of the ovary.

ANP-mediated cGMP signaling and phosphodiesterase inhibition in the rat cervical spinal cord

Natriuretic peptides (NP) and the corresponding receptors are present in the rodent spinal cord. We have studied the structures which respond to atrial natriuretic peptide, brain natriuretic peptide, or C-type natriuretic peptide with an increased synthesis of cGMP. NP-responsive cGMP-producing structures were observed in laminae I-III, and X, and in addition in ependymal cells, astrocytes and a subpopulation of dorsal root ganglion cells. As the cGMP concentration is controlled by the rate of synthesis and the rate of breakdown by phosphodiesterases, we studied NP-responsive structures in spinal cord slices incubated in the presence of different phosphodiesterase inhibitors. We studied EHNA and BAY 60-7550 as selective PDE2 inhibitors, sildenafil as a selective PDE5 inhibitors, dipyridamole as a mixed type PDE5 and PDE10 inhibitor, rolipram as a PDE4 inhibitor, and SCH 81566 as a selective PDE9 inhibitor. Double immunostainings showed that cGMP-IR colocalized partial with the vesicular acetylcholine transporter molecule in lamina X, with Substance P in a subpopulation of neuronal fibers situated dorsolateral, and with a subpopulation of CGRP-IR dorsal root ganglion neurons. Colocalization of cGMP-IR was absent with parvalbumin, synaptophysin, and the vesicular transporter molecules for GABA and glutamate. It is concluded that NPs in the spinal cord are probably involved in integrating intersegmental sensory processing in the spinal cord although the greater part of the NP-responsive cGMP-producing fibers could not be characterized. PDE2, 5, and 9 are involved in regulating NP-stimulated cGMP levels in the spinal cord. NPs may have a role in regulating cerebrospinal fluid homeostasis.

Central autonomic control of the bone marrow: multisynaptic tract tracing by recombinant pseudorabies virus

Bone marrow is the primary place of hematopoiesis, where the development, survival and release of multipotent stem cells, progenitors, precursors and mature cells are under continuous humoral and neural control. Dense network of nerve fibers, containing various neurotransmitters is found in the bone marrow, however, the central neuronal circuit that regulates the activities of the bone marrow through these fibers remained unexplored. Transsynaptically connected neurons were mapped by virus-based transneuronal tracing technique using two isogenic, genetically engineered pseudorabies viruses, Bartha-DupGreen and Ba-DupLac expressing green fluorescent protein and beta-galactosidase, respectively. Bartha-DupGreen was injected into the femoral bone marrow of male rats and the progression of infection was followed 4-7 days post-inoculation. Virus-labeled cells were revealed in ganglia of the paravertebral chain and in the intermediolateral cell column of the lower thoracic spinal cord. Neurons were retrogradely labeled in the C1, A5, A7 catecholaminergic cell groups and several other nuclei of the ventrolateral and ventromedial medulla, the periaqueductal gray matter, the paraventricular and other hypothalamic nuclei, and in the insular and piriform cortex. Nerve transections and double-virus tracing from the bone marrow and the surrounding muscles were used to confirm the specific spreading of the virus. These results provide anatomical evidence for the CNS control of the bone marrow and identify putative brain areas, which are involved in autonomic regulation of the hematopoiesis, the release of progenitor cells, the blood supply and the immune cell function in the bone marrow.

Ethanol-induced FOS immunoreactivity in the brain of mu-opioid receptor knockout mice

Using mu-opioid receptor knockout (MKO) mice, we examined ethanol-induced FOS immunoreactivity (FOSir) in the brain as an indicator of neuronal activation to assess the role of the mu-opioid receptor in modulating ethanol's actions in the central nervous system (CNS). Saline stimulated FOSir in the paraventricular thalamic nucleus (PVA) and the dorsal hypothalamic area (DA) in MKO mice, but not in wild-type (WT), suggesting that MKO homozygotes may differ responsively from WT. Treatment with ethanol (4 g/kg, i.p.) induced FOSir in the PVA, DA, supraoptic (SO), paraventricular hypothalamic (PVN), lateral parabrachial (LPB), locus coeruleus (LC) and Edinger-Westphal (EW) nuclei in both MKO and WT mice. However, ethanol stimulated modest FOSir in the lateral septal division (LSV), suprachiasmatic nucleus (SCh) and the dorsal and ventral lateral geniculate nuclei (DLG and VLG) in WT mice, but not in MKO mice. In contrast, higher levels of ethanol-induced FOSir were observed in the ventral pallidum (VP) and globus pallidus (GP) of MKO mice as compared to WT. These data suggest that ethanol continues to activate several brain regions, even without the mu-opioid receptor pathway. However, the mu-opioid receptor may be significant in mediating ethanol's effects in some restricted areas of the brain.

Paraventricular nucleus, stress response, and cardiovascular disease

The paraventricular nucleus of the hypothalamus (PVN) is a complex effector structure that initiates endocrine and autonomic responses to stress. It receives inputs from visceral receptors, circulating hormones such as angiotensin II, and limbic circuits and contains neurons that release vasopressin, activate the adrenocortical axis, and activate preganglionic sympathetic or parasympathetic outflows. The neurochemical control of the different subgroups of PVN neurons is complex. The PVN has been implicated in the pathophysiology of congestive heart failure and the metabolic syndrome.

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.

Serotonergic pathways converge upon central melanocortin systems to regulate energy balance

Multiple lines of research provide compelling support for an important role for central serotonergic (5-hydroxytryptamine, 5-HT) and melanocortin pathways in the regulation of food intake and body weight. In this brief review, we outline data supporting a model in which serotonergic pathways affect energy balance, in part, by converging upon central melanocortin systems to stimulate the release of the endogenous melanocortin agonist, alpha-melanocyte stimulating hormone (alpha-MSH). Further, we review the neuroanatomical mapping of a downstream target of alpha-MSH, the melanocortin 4 receptor (MC4R), in the rodent brain. We propose that downstream activation of MC4R-expressing neurons substantially contributes to serotonin's effects on energy homeostasis.

Leptin fragments induce Fos immunoreactivity in rat hypothalamus

Leptin presents an important role in energy balance and neuroendocrine control in mammals. In an attempt to identify regions of the leptin molecule responsible for its bioactivity, we have synthesized six peptides based on the protein three-dimensional structure. Fragments were synthesized by the solid-phase methodology, purified by reverse-phase high-performance liquid chromatography (RP-HPLC), and characterized by liquid chromatography-electrospray ionization mass spectrometry (LC/ESI-MS). They were injected intravenously and their ability to induce Fos immunoreactivity (Fos-ir) in rat hypothalamus was compared with that of the recombinant human leptin and saline. Fragment Ac-[Ser117]Lep116-140-NH2 (V) induced Fos-ir in hypothalamic nuclei that express leptin receptor long form. No similar ability was observed for the other five fragments. To investigate whether Fos-ir was induced in the same neuronal group activated by leptin, we proceeded with a dual-label immunohistochemistry for cocaine- and amphetamine-regulated transcript (CART), a neuropeptide related to leptin action in rat hypothalamus. We found that Ac-[Ser117]Lep116-140-NH2 (V) differentially activates CART neurons through the rostrocaudal extension of the arcuate nucleus. These results suggest that this fragment acts in the same group of neurons that mediate leptin response. This approach may offer the basis for the development of leptin-related compounds, having potential application in human or veterinary medicine.

Stimulation of the lateral hypothalamus produces antinociception mediated by 5-HT1A, 5-HT1B and 5-HT3 receptors in the rat spinal cord dorsal horn

The lateral hypothalamus is part of an efferent system that modifies pain at the spinal cord dorsal horn, but the mechanisms by which lateral hypothalamus-induced antinociception occur are not fully understood. Previous work has shown that antinociception produced from electrical stimulation of the lateral hypothalamus is mediated in part by spinally projecting 5-hydroxytryptamine (5-HT) neurons in the ventromedial medulla. To further examine the role of the lateral hypothalamus in antinociception, the cholinergic agonist carbamylcholine chloride (125 nmol) was microinjected into the lateral hypothalamus of female Sprague-Dawley rats and nociceptive responses measured on the tail-flick and foot-withdrawal tests. Intrathecal injections of the selective 5-HT1A, 5-HT1B, 5-HT3 receptor antagonists, WAY 100135, SB-224289, and tropisetron, respectively, and the non-specific antagonist methysergide, were given. Lateral hypothalamus stimulation with carbamylcholine chloride produced significant antinociception that was blocked by WAY 100135, tropisetron, and SB-224289 on both the tail-flick and foot-withdrawal tests. Methysergide was not different from controls on the tail flick test, but increased foot-withdrawal latencies compared with controls. These results suggest that the lateral hypothalamus modifies nociception in part by activating spinally projecting serotonin neurons that act at 5-HT1A, 5-HT1B, and 5-HT3 receptors in the dorsal horn.

Cardiac concomitants of performance monitoring: context dependence and individual differences

Feedback processing is an important aspect of cognitive control and decision-making. Several studies have shown that heart rate slows following feedback that indicates incorrect performance or loss of money. The current study was the first to investigate (1) whether this slowing reflects an evaluation of the valence of the outcome or a system that indicates that the feedback contains informative value, (2) whether the slowing is determined by the value of the outcome relative to the range of possible outcomes, and (3) whether highly anxious individuals have a hypersensitive feedback monitoring system. The results showed that heart rate only slows when the feedback is performance based. The information provided by negative feedback is processed in a context-sensitive manner, suggesting that heart rate slowing following feedback reflects a signal associated with informative value for subsequent performance adjustment. Highly anxious individuals showed larger heart rate slowing in response to feedback indicating high stakes, but they failed to respond to feedback in a context-sensitive manner. These results were interpreted to suggest that anxious individuals are generally more sensitive to performance outcomes. Heart rate changes following informative feedback proved to be a sensitive index of component processes associated with performance monitoring.

Supraspinal connections of the reproductive organs: structural and functional aspects

Gonadal functions are governed by the hypothalamo-hypophyseal system. Other organs of the reproduction tract are under the regulatory action of gonadal steroids. In the past two decades several data have been accumulated on the involvement of fine-tuning control mechanisms which include autocrine and paracrine effects of biologically active substances produced locally and the regulatory action of nerves innervating the organs of the system. Recent studies using the viral transsynaptic technique have revealed cell groups in the central nervous system that are transneuronally connected with the male and female reproductive organs. This review summarizes neuromorphological data on the supraspinal innervation of reproductive organs and the functional significance of these brain areas in the control of reproduction.

Peptidergic neuromodulation of the lumbar locomotor network in the neonatal rat spinal cord

It is now well established that a dynamic balance of neurotransmitters and neuromodulators finely influence the output of neuronal networks and subsequent behaviors. In the present study, to further understand the modulatory processes that control locomotor behavior, we investigated the action of 11 neuropeptides, chosen among the various peptide subfamilies, on the lumbar neuronal network in the in vitro neonatal rat spinal cord preparation. Peptides were bath-applied alone, in combination with N-methyl-D,L-aspartate (NMA) or with the classical 'locomotor cocktail' of NMA and serotonin. Using these different experimental paradigms, we show that each peptide can neuromodulate the lumbar locomotor network and that peptides exhibit different neuromodulatory profiles and potencies even within the same family. Only vasopressin, oxytocin, bombesin and thyrotropin releasing hormone triggered tonic or non-organized rhythmic activities when bath-applied alone. All the neuropeptides modulated NMA induced activity and/ or ongoing sequences of fictive locomotion to varying degrees. These results suggest that neuropeptides play an important role in the control of the neural network for locomotion in the neonatal rat. Their various profiles of action may account in part for the great flexibility of motor behaviors.

A role for the paraventricular nucleus of the hypothalamus in the autonomic control of heart and kidney

It is now well accepted that the sympathetic nervous system responds to specific afferent stimuli in a unique non-uniform fashion. The means by which the brain transforms the signals from a single type of receptor into an appropriate differential sympathetic output is discussed in this brief review. The detection of and response to venous filling are used for illustration. An expansion of blood volume has been shown in a number of species to increase heart rate reflexly via sympathetic nerves and this effect is primarily an action of volume receptors at the venous-atrial junctions of the heart. Stimulation of these volume receptors also leads to an inhibition of renal sympathetic nerve activity. Thus the reflex response to an increase in plasma volume consists of a distinctive unique pattern of sympathetic activity to maintain fluid balance. This reflex is dependent on neurones in the paraventricular nucleus (PVN). Neurones in the PVN show early gene activation on stimulation of atrial receptors, and a similar differential pattern of cardiac sympathetic excitation and renal inhibition can be evoked by activating PVN neurones. Cardiac atrial afferents selectively cause a PVN GABA neurone-induced inhibition within the PVN of PVN spinally projecting vasopressin-containing neurones that project to renal sympathetic neurones. A lesion of these spinally projecting neurones abolishes the reflex. With regard to the cardiac sympathetics, there is a population of PVN spinally projecting neurones that selectively increase heart rate by the release of oxytocin, a peptide pathway that has no action on renal sympathetic outflow. In heart failure the atrial reflex becomes blunted, and evidence is emerging that there is a downregulation of nitric oxide synthesis and reduced GABA activity in the PVN. How this might give rise to increased sympathetic activity associated with heart failure is briefly discussed.

The electrophysiology of feeding circuits

Obesity is quickly becoming one of the most common and debilitating disorders of the developed world. More than 60% of American adults are now overweight or obese, predisposing them to a host of chronic diseases. To understand the etiology of obesity, and to discover new therapies for obesity, we must understand the components of energy balance. In simple terms, energy intake (feeding) must equal energy expenditure (physical activity, basal metabolism and adaptive thermogenesis) for body weight homeostasis. To maintain homeostasis, neurocircuitry must sense both immediate nutritional status and the amount of energy stored in adipose tissue, and must be able to provide appropriate output to balance energy intake and energy expenditure. The brain receives various signals that carry information about nutritional and metabolic status including neuropeptide PYY(3-36), ghrelin, cholecystokinin, leptin, glucose and insulin. Circulating satiety signals access the brain either by "leakage" across circumventricular organs or transport across the blood-brain barrier. Signals can also activate sensory vagal terminals that innervate the whole gastrointestinal tract.

A comparative analysis of transcribed genes in the mouse hypothalamus and neocortex reveals chromosomal clustering

The hypothalamus and neocortex are subdivisions of the mammalian forebrain, and yet, they have vastly different evolutionary histories, cytoarchitecture, and biological functions. In an attempt to define these attributes in terms of their genetic activity, we have compared their genetic repertoires by using the Serial Analysis of Gene Expression database. From a comparison of 78,784 hypothalamus tags with 125,296 neocortical tags, we demonstrate that each structure possesses a different transcriptional profile in terms of gene ontological characteristics and expression levels. Despite its more recent evolutionary history, the neocortex has a more complex pattern of gene activity. Gene identities and levels of gene expression were mapped to their chromosomal positions by using in silico definition of GC-rich and GC-poor genome bands. This analysis shows contrasting views of gene activity on a genome scale that is unique to each brain substructure. We show that genes that are more highly expressed in one tissue tend to be clustered together on a chromosomal scale, further defining the genetic identity of either the hypothalamus or neocortex. We propose that physical proximity of coregulated genes may facilitate transcriptional access to the genetic substrates of evolutionary selection that ultimately shape the functional subdivisions of the mammalian brain.

Angiotensin II excites paraventricular nucleus neurons that innervate the rostral ventrolateral medulla: an in vitro patch-clamp study in brain slices

Neurons of the hypothalamic paraventricular nucleus (PVN) are key controllers of sympathetic nerve activity and receive input from angiotensin II (ANG II)-containing neurons in the forebrain. This study determined the effect of ANG II on PVN neurons that innervate in the rostral ventrolateral medulla (RVLM)-a brain stem site critical for maintaining sympathetic outflow and arterial pressure. Using an in vitro brain slice preparation, whole cell patch-clamp recordings were made from PVN neurons retrogradely labeled from the ipsilateral RVLM of rats. Of 71 neurons tested, 62 (87%) responded to ANG II. In current-clamp mode, bath-applied ANG II (2 muM) significantly (P < 0.05) depolarized membrane potential from -58.5 +/- 2.5 to -54.5 +/- 2.0 mV and increased the frequency of action potential discharge from 0.7 +/- 0.3 to 2.8 +/- 0.8 Hz (n = 4). Local application of ANG II by low-pressure ejection from a glass pipette (2 pmol, 0.4 nl, 5 s) also elicited rapid and reproducible excitation in 17 of 20 cells. In this group, membrane potential depolarization averaged 21.5 +/- 4.1 mV, and spike activity increased from 0.7 +/- 0.4 to 21.3 +/- 3.3 Hz. In voltage-clamp mode, 41 of 47 neurons responded to pressure-ejected ANG II with a dose-dependent inward current that averaged -54.7 +/- 3.9 pA at a maximally effective dose of 2.0 pmol. Blockade of ANG II AT1 receptors significantly reduced discharge (P < 0.001, n = 5), depolarization (P < 0.05, n = 3), and inward current (P < 0.01, n = 11) responses to locally applied ANG II. In six of six cells tested, membrane input conductance increased (P < 0.001) during local application of ANG II (2 pmol), suggesting influx of cations. The ANG II current reversed polarity at +2.2 +/- 2.2 mV (n = 9) and was blocked (P < 0.01) by bath perfusion with gadolinium (Gd(3+), 100 muM, n = 8), suggesting that ANG II activates membrane channels that are nonselectively permeable to cations. These findings indicate that ANG II excites PVN neurons that innervate the ipsilateral RVLM by a mechanism that depends on activation of AT1 receptors and gating of one or more classes of ion channels that result in a mixed cation current.

Estrogen receptor-β in oxytocin and vasopressin neurons of the rat and human hypothalamus: Immunocytochemical and in situ hybridization studies

Topographical distribution of estrogen receptor-beta (ER-beta)-synthesizing oxytocin (OT) and vasopressin (VP) neurons was studied in the hypothalamic paraventricular and supraoptic nuclei (PVH; SO) of ovariectomized rats. In distinct subregions, 45-98% of OT neurons and 88-99% of VP neurons exhibited ER-beta immunoreactivity that was confined to cell nuclei. Neuronal populations differed markedly with respect to the intensity of the ER-beta signal. Magnocellular OT neurons in the PVH, SO, and accessory cell groups typically contained low levels of the ER-beta signal; in contrast, robust receptor labeling was displayed by OT cells in the ventral subdivision of medial parvicellular subnucleus and in the caudal PVH (dorsal subdivision of medial parvicellular subnucleus and lateral parvicellular subnucleus). Estrogen receptor-beta signal was generally more intense and present in higher proportions of magnocellular and parvicellular VP vs. OT neurons of similar topography. Immunocytochemical observations were confirmed via triple-label in situ hybridization, an approach combining use of digoxigenin-, fluorescein-, and 35S-labeled cRNA hybridization probes. Further, ER-beta mRNA was also detectable in corticotropin-releasing hormone neurons in the parvicellular PVH. Finally, double-label immunocytochemical analysis of human autopsy samples showed that subsets of OT and VP neurons also express ER-beta in the human. These neuroanatomical studies provide detailed information about the topographical distribution and cellular abundance of ER-beta within subsets of hypothalamic OT and VP neurons in the rat. The variable receptor content may indicate the differential responsiveness to estrogen in distinct OT and VP neuronal populations. In addition, a relevance of these findings to the human hypothalamus is suggested.

Neuropeptide specificity of prostaglandin E2-induced activation of splenic and renal sympathetic nerves in the rat

Sympathetic activation occurs rapidly following intracerebroventricular (icv) injection of prostaglandin E2(PGE2). This study examined whether neuropeptides mediate PGE2-induced sympathetic nerve activation in urethane/chloralose-anesthetized Sprague-Dawley rats. Animals were pretreated (20.0 microg, icv) with the following receptor antagonists; CRF ([D-Phe12,Nle21,38,Calpha-MeLeu37]CRF12-41), AVP-V1 (Des-Gly-[Phaa1, D-Tyr(Et)2,Lys6,Arg8]-vasopressin), or OT (OT+V1, [d(CH2)5,Tyr(Me)2,Orn8]-vasotocin) followed 20 min later by PGE2 (2.0 microg, icv). Pretreatment with the CRF antagonist attenuated the increase in renal nerve activity induced by PGE2 when measured 10 and 30 min post-injection. PGE2-induced renal nerve activity was also inhibited at both time points by the AVP antagonist and, to a similar extent, the OT antagonist. The AVP antagonist did not effect splenic nerve responses to PGE2 whereas the CRF antagonist produced an incomplete and transient reduction in PGE2-induced activation of the splenic nerve. However, the OT antagonist completely blocked the activation of the splenic nerve after central injection of PGE2. ICV injections of AVP and OT produced immediate changes in splenic and renal nerve activity whereas CRF failed to alter the activity of either nerve in anesthetized or conscious animals. Thus, PGE2 acts through neuropeptide-specific pathways to initiate sympathetic outflow and OT is a specific component of the sympathetic pathway innervating the spleen.

Hypothalamus of the human fetus

The organization of the human hypothalamus was studied in 31 brains aged from 9 weeks of gestation (w.g.) to newborn, using immunohistochemistry for parvalbumin, calbindin, calretinin, neuropeptideY, neurophysin, growth associated protein GAP43, synaptophysin and glycoconjugate, 3-fucosyl-N-acetyl-lactosamine. Morphogenetic periods 9-10 and 11-14 w.g. are characterized by differentiating structures of the lateral hypothalamic zone, which give rise to the lateral hypothalamus (LH) and posterior hypothalamus. The perifornical nucleus differentiates at 18 w.g., from LH neurons which remain anchored in the perifornical position while most of the LH cells are displaced laterally. A transient supramamillary nucleus was apparent at 14 w.g. but not after 16 w.g. As the ventromedial nucleus differentiated at 13-16 w.g., three principal parts; the ventrolateral, the dorsomedial and the shell were revealed by distribution of calbindin, calretinin and GAP43 immunoreactivity. Morphogenetic periods 15-17, 18-23 and 24-33 w.g. are characterized by differentiation of the hypothalamic core, in which calbindin positive neurons revealed the medial preoptic nucleus at 16 w.g. abutted laterally by the intermediate nucleus. The dorsomedial nucleus was clearly defined at 10 w.g. and consisted of compact and diffuse parts, an organization that was lost after 15 w.g. Differentiation of the medial mamillary body into lateral and medial was seen at 13-16 w.g. Morphogenetic period after 34 w.g. was marked by differentiation of midline zone structures including suprachiasmatic, arcuate and paraventricular nuclei. The findings of the present study provide for a better understanding of the structural organization of the adult human hypothalamus, produce new evidence for homologies with the better studied rat hypothalamus and underpin staging system for fetal human hypothalamic development.

Cardiovascular responses evoked by leptin acting on neurons in the ventromedial and dorsomedial hypothalamus

Leptin, a circulating hormone produced by adipose tissue, is believed to act on the hypothalamus to increase sympathetic vasomotor activity, in addition to its well-known effects on appetite and energy expenditure. In this study, we determined the cardiovascular effects of direct application of leptin to specific cell groups within the hypothalamus that are known to be activated by circulating leptin. In rats anesthetized with urethane, microinjections of leptin (16 ng in 20 nL solution) were made into the ventromedial hypothalamic nucleus, dorsomedial hypothalamic nucleus, and paraventricular nucleus. Compared with vehicle solution, microinjections of leptin into the ventromedial hypothalamic nucleus evoked significant increases in arterial pressure and renal sympathetic nerve activity, but not heart rate. In contrast, microinjections of leptin into the dorsomedial hypothalamic nucleus evoked significant increases in arterial pressure and heart rate but not renal sympathetic nerve activity, whereas microinjections of leptin into the paraventricular nucleus had no significant effect on any of the measured cardiovascular variables. These results indicate that the ventromedial and dorsomedial hypothalamic regions might be important sites at which leptin activation leads to increases in sympathetic vasomotor activity and heart rate, as occurs in obesity-related hypertension.

Transgenic mice expressing green fluorescent protein under the control of the melanocortin-4 receptor promoter

The melanocortin-4 receptor (MC4-R) is an important regulator of energy homeostasis, and evidence suggests that MC4-R-expressing neurons are downstream targets of leptin action. MC4-Rs are broadly expressed in the CNS, and the distribution of MC4-R mRNA has been analyzed most extensively in the rat. However, relatively little is known concerning chemical profiles of MC4-R-expressing neurons. The extent to which central melanocortins act presynaptically or postsynaptically on MC4-Rs is also unknown. To address these issues, we have generated a transgenic mouse line expressing green fluorescent protein (GFP) under the control of the MC4-R promoter, using a modified bacterial artificial chromosome. We have confirmed that the CNS distribution of GFP-producing cells is identical to that of MC4-R mRNA in wild-type mice and that nearly all GFP-producing cells coexpress MC4-R mRNA. For example, cells coexpressing GFP and MC4-R mRNA were distributed in the paraventricular hypothalamic nucleus (PVH) and the dorsal motor nucleus of the vagus (DMV). MC4-R promotor-driven GFP expression was found in PVH cells producing thyrotropin-releasing hormone and in cholinergic DMV cells. Finally, we have observed that a synthetic MC3/4-R agonist, MT-II, depolarizes some GFP-expressing cells, suggesting that MC4-Rs function postsynaptically in some instances and may function presynaptically in others. These studies extend our knowledge of the distribution and function of the MC4-R. The transgenic mouse line should be useful for future studies on the role of melanocortin signaling in regulating feeding behavior and autonomic homeostasis.

Involvement of oxytocin in spinal antinociception in rats with inflammation

The present study was conducted on rats with inflammation induced by subcutaneous injection of carrageenan into the left hindpaw. Intrathecal administration of oxytocin produced dose-dependent increases in the hindpaw withdrawal latency (HWL) to thermal and mechanical stimulation in rats with inflammation. The antinociceptive effect of oxytocin was blocked by intrathecal administration of atosiban, a selective oxytocin antagonist, indicating that oxytocin receptor mediates oxytocin-induced antinociception in the spinal cord. The oxytocin-induced antinociceptive effect was attenuated by intrathecal administration of the opioid antagonist naloxone, suggesting an involvement of the endogenous opioid system in oxytocin-induced antinociception in the spinal cord of rats with inflammation. Furthermore, the antinociceptive effect of oxytocin was attenuated by intrathecal injections of the mu-receptor antagonist beta-funaltrexamine and the kappa-receptor antagonist nor-binaltorphimine, but not by the delta-receptor antagonist naltrindole, illustrating that mu- and kappa-receptors, but not delta-receptor, are involved in oxytocin-induced antinociception in the spinal cord of rats with inflammation. Moreover, intrathecal administration of atosiban alone induced a hyperalgesia in rats with inflammation, indicating that endogenous oxytocin is involved in the transmission and regulation of nociceptive information in the spinal cord of rats with inflammation. The present study showed that both exogenous and endogenous oxytocin displayed antinociception in the spinal cord in rats with inflammation, and mu- and kappa-receptors were involved in oxytocin-induced antinociception.

Actions of oxytocin and interactions with glutamate on spontaneous and evoked dorsal spinal cord neuronal activities

Among the numerous pain control mechanisms that have been proposed, those acting at the spinal cord have been broadly studied, but little is known about how neuropeptides originating in supraspinal structures may relate to pain and analgesic mechanisms. Oxytocin (OT), in addition to its well known hormonal action, produces neuronal effects in various regions of the central nervous system. Indeed, some parvocellular neurons in the hypothalamic paraventricular nucleus (PVN) are oxytocinergic and project to the caudal part of the brain and the spinal cord. Moreover, the rat spinal cord shows a good overlap between the oxytocinergic hypothalamo-spinal neuron projections and the distribution of OT binding sites. However, the physiological significance of these binding sites is largely unknown. Extracellular unit activity of spinal cord neurons was recorded at the T13-L1 levels in male rats anesthetized with halotane. Somatic stimulation was applied to the inner and outer thigh of the ipsilateral hindpaw, and glutamate (GLU) and OT were locally delivered by pressure using pipettes coupled to recording electrodes. Our results show that spinal cord neurons, mainly located in the dorsal horn, in the intermediolateral cell column (IML) and in the intermediomedial gray matter (IMM), respond to the application of OT (71.5%) with activation (48%) or inhibition (52%). In some cases, opposite OT effects were observed during simultaneous recordings of two cells, suggesting OT activation of an inhibitory interneuron followed by the inhibition of the second recorded neuron. Increases in neuronal firing rate produced by GLU could be blocked by prior OT application. Finally, OT could reduce or partially block the responses to tactile and nociceptive somatic stimulation. We found that spinal cord neurons are sensitive to OT indicating that OT binding sites are functionally active. OT effects suggest the activation of inhibitory interneurons acting on a second order projecting cells to modulate afferent tactile and nociceptive information.

Generation of the melatonin endocrine message in mammals: a review of the complex regulation of melatonin synthesis by norepinephrine, peptides, and other pineal transmitters

Melatonin, the major hormone produced by the pineal gland, displays characteristic daily and seasonal patterns of secretion. These robust and predictable rhythms in circulating melatonin are strong synchronizers for the expression of numerous physiological processes in photoperiodic species. In mammals, the nighttime production of melatonin is mainly driven by the circadian clock, situated in the suprachiasmatic nucleus of the hypothalamus, which controls the release of norepinephrine from the dense pineal sympathetic afferents. The pivotal role of norepinephrine in the nocturnal stimulation of melatonin synthesis has been extensively dissected at the cellular and molecular levels. Besides the noradrenergic input, the presence of numerous other transmitters originating from various sources has been reported in the pineal gland. Many of these are neuropeptides and appear to contribute to the regulation of melatonin synthesis by modulating the effects of norepinephrine on pineal biochemistry. The aim of this review is firstly to update our knowledge of the cellular and molecular events underlying the noradrenergic control of melatonin synthesis; and secondly to gather together early and recent data on the effects of the nonadrenergic transmitters on modulation of melatonin synthesis. This information reveals the variety of inputs that can be integrated by the pineal gland; what elements are crucial to deliver the very precise timing information to the organism. This also clarifies the role of these various inputs in the seasonal variation of melatonin synthesis and their subsequent physiological function.

Identification of neurones of the brain and spinal cord involved in the innervation of the ductus deferens using the viral tracing method

Using the viral transneuronal tracing technique cell groups of the spinal cord and brain transsynaptically connected with the ductus deferens were identified. Neurotropic (pseudorabies) virus was injected into the muscular coat of the ductus deferens and after survival times of 3, 4 and 5 days the spinal cord and brain were processed immunocytochemically. Virus-labelled neurones could be detected in the preganglionic sympathetic neurones and the dorsal commissural nucleus (upper lumbar segments) and in the sacral parasympathetic nucleus (L6-S1). Virus-infected perikarya were present in several brain stem nuclei including the gigantocellular and paragigantocellular nucleus, the lateral reticular nucleus, the nucleus of the solitary tract, the caudal raphe nuclei, the A1/C1, A2, A5 and A7 noradrenergic cell groups and the locus coeruleus. In the hypothalamus significant numbers of virus-infected neurones could be detected in the paraventricular nucleus. In most cases moderate numbers of virus-labelled cells were present in the lateral hypothalamic area, in the retrochiasmatic area, in the periventricular region and in the median preoptic area. Double-labelling immunofluorescence detection of virus-infected neurones and thyrosine hydroxylase (TH) showed colocalization of virus protein and TH in portion of neurones of the A1/C1, A2, A5 and A7 noradrenergic cell groups, in the locus coeruleus and in the hypothalamic paraventricular nucleus. The present results provide the first morphological data on the multisynaptic circuit of neurones innervating the ductus deferens.

Expression of melanocortin 4 receptor mRNA in the central nervous system of the rat

The melanocortin 4 receptor (MC4-R) plays a pivotal role in maintaining energy homeostasis in rodents and humans. For example, MC4-R deletion or mutation results in obesity, hyperphagia, and insulin resistance. Additionally, subsets of leptin-induced autonomic responses can be blocked by melanocortin receptor antagonism, suggesting that MC4-R-expressing neurons are downstream targets of leptin. However, the critical autonomic control sites expressing MC4-Rs are still unclear. In the present study, we systematically examined the distribution of MC4-R mRNA in the adult rat central nervous system, including the spinal cord, by using in situ hybridization histochemistry (ISHH) with a novel cRNA probe. Autonomic control sites expressing MC4-R mRNA in the hypothalamus included the anteroventral periventricular, ventromedial preoptic, median preoptic, paraventricular, dorsomedial, and arcuate nuclei. The subfornical organ, dorsal hypothalamic, perifornical, and posterior hypothalamic areas were also observed to express MC4-R mRNA. Within extrahypothalamic autonomic control sites, MC4-R-specific hybridization was evident in the infralimbic and insular cortices, bed nucleus of the stria terminalis, central nucleus of the amygdala, periaqueductal gray, lateral parabrachial nucleus, nucleus of the solitary tract, dorsal motor nucleus of the vagus (DMV), and intermediolateral nucleus of the spinal cord (IML). By using dual-label ISHH, we confirmed that the cells expressing MC4-R mRNA in the IML and DMV were autonomic preganglionic neurons as cells in both sites coexpressed choline acetyltransferase mRNA. The distribution of MC4-R mRNA is consistent with the proposed roles of central melanocortin systems in feeding and autonomic regulation.

Heterogeneous synaptic inputs from the ventrolateral periaqueductal gray matter to neurons responding to somatosensory stimuli in the rostral ventromedial medulla of rats

The ventrolateral cell column of the midbrain periaqueductal gray matter (vl-PAG) plays a major role in the attenuation of pain behaviour. It is established that this effect is exerted via modulation of neuronal activities in the rostral ventromedial medulla (RVM). Until recently it has been generally accepted that the vl-PAG exerts its modulatory effects upon RVM neurons through a direct monosynaptic pathway. However, recent data suggest that an additional indirect, di- or polysynaptic pathway may also exist. Using in vivo intracellular recordings we tested this hypothesis, by studying synaptic responses of somatosensory receptive RVM neurons evoked by electric stimulation of the vl-PAG in rats. RVM neurons were regarded as somatosensory receptive if they responded to electrical stimulation of the sciatic nerve. Most of the recorded RVM cells were excited by vl-PAG stimulation. Some of them responded with a short onset latency (3.6+/-0.9 ms) corresponding to monosynaptic excitation. All of these neurons were also excited by sciatic nerve stimulation at nociceptive intensities. In contrast to this, another proportion of the recorded RVM neurons responded with a four times longer (14.8+/-3 ms) onset latency to the vl-PAG stimulation, corresponding to polysynaptic modulation. All of these neurons were inhibited by sciatic nerve stimulation. The findings show that RVM neurons receive heterogeneous monosynaptic and polysynaptic inputs from the vl-PAG. The results also suggest that the monosynaptic and polysynaptic pathways modulate the activity of functionally distinct groups of RVM neurons.

Estrogen modulates oxytocin gene expression in regions of the rat supraoptic and paraventricular nuclei that contain estrogen receptor-beta

Oxytocin is an important modulator of female reproductive functions including parturition, lactation and maternal behavior, while vasopressin regulates water balance and acts as a neurotransmitter. For decades, it has been suggested that estrogen regulates the production and/or release of oxytocin and vasopressin in the rodent brain. Although several studies demonstrated that estrogen can modulate vasopressin mRNA levels in regions known to contain estrogen receptor (ER), such as the bed nucleus of the stria terminalis and medial amygdala, data from the paraventricular and supraoptic nuclei were inconclusive. Since early immunohistochemical and in situ hybridization studies revealed few, if any, ER containing cells in these hypothalamic nuclei, it was thought that oxytocin and vasopressin were not directly regulated by estrogen. The discovery of a second ER (ER-beta) in the late 1990s suggested that estrogen could act in many brain regions heretofore not considered targets for estrogen action. Initial in situ hybridization studies revealed a wide distribution of ER-beta mRNA in the rat brain including neurons of the supraoptic nucleus and the parvocellular and magnocellular divisions of the paraventricular nucleus. Subsequent double-label in situ hybridization/immunocytochemistry studies showed that ER-beta mRNA was present in oxytocin and vasopressin neurons, with the degree of colocalization being both neuropeptide and region specific. In an attempt to demonstrate that ER-beta mRNA was translated into a biologically active protein, a series of in vivo binding studies were conducted in rats with 125I-estrogen. These data revealed the presence of nuclear estrogen binding sites in neurons of the magnocellular system indicating that ER-beta mRNA was translated into protein. Concurrent studies in mice found that the distribution of ER-beta mRNA and 125I-estrogen binding was similar to rats, although there were some notable differences. For example, ER-beta mRNA and binding were not detected in the mouse supraoptic nucleus and although ER-beta was the principle ER in the paraventricular nucleus, ER-alpha was also present. The prevalence of ERs in the mouse paraventricular nucleus was further investigated using ER-alpha and ER-beta knockout mice for in vivo binding studies with 125I-estrogen. The results of these studies showed that ER-beta was the predominant ER in the paraventricular nucleus and confirmed the presence of ER-beta in other brain regions. Moreover, our group recently generated and characterized several polyclonal antisera raised against the C-terminus of ER-beta. Through the use of these antisera, we have confirmed the presence of ER-beta in the rat paraventricular and supraoptic nuclei and shown that ER-beta is colocalized, in part, with oxytocin and vasopressin. To assess the ability of estrogen to modulate the expression of oxytocin mRNA, ovariectomized rats were treated with vehicle or estradiol and the brains processed for in situ hybridization. The results of these studies revealed that estradiol down-regulated oxytocin mRNA in the rat paraventricular nucleus within 6 h of treatment. Together these data and the observation that some of the oxytocin and vasopressin neurons contain ER-beta suggest that estrogen, acting through ER-beta, may directly regulate oxytocin gene expression. However, since the paraventricular nucleus has many subdivisions with different projections and the degree of colocalization of ER-beta with oxytocin/vasopressin varies among subdivisions, the effects of estrogen treatment on gene expression requires further study to ascertain the role of estrogen action in this neuronal systems.

Time of genesis determines projection and neurokinin-3 expression patterns of diencephalic neurons containing melanin-concentrating hormone

Anatomical and functional evidence suggests that the diencephalic melanin-concentrating hormone- (MCH-) containing neurons do not form a homogeneous population. In this work, the expression of the neurokinin-3 receptor (NK3) has been researched in MCH neurons which have been retrogradely labelled following fast blue injections into either the spinal cord or the cerebral cortex. The birth-date of these cortically and spinally projecting cells has been determined using the bromodeoxyuridine method. The results obtained show that neurons projecting to the spinal cord are born early (E11) and most of them (78,7%) do not express NK3, but neurons that send axons to the cerebral cortex are born later (E12-E13) and most of them (84,8%) express NK3. Both neuronal types are largely intermingled in the lateral hypothalamic area proper. These results are discussed in terms of the functional organization of the MCH neuronal population.

Antinociception from lateral hypothalamic stimulation may be mediated by NK(1) receptors in the A7 catecholamine cell group in rat

Stimulation of the lateral hypothalamus (LH) produces antinociception that is modified by intrathecal alpha-adrenergic antagonists. Spinally-projecting noradrenergic neurons in the LH have not been identified, suggesting that the LH may innervate brainstem noradrenergic neurons, such as the A7 catecholamine cell group in the dorsolateral pontine tegmentum, that modify nociception at the level of the spinal cord dorsal horn. Recently we demonstrated in neuroanatomical studies that substance P-immunoreactive neurons in the LH project the A7 area. To identify a functional connection between substance P neurons in the LH and the A7 cell group, the cholinergic agonist carbachol (125 nmol) was microinjected into the LH of female Sprague-Dawley rats and antinociception was obtained on the tail flick or foot withdrawal test. Cobalt chloride (100 nM) was then microinjected near the A7 cell group to block synaptic activation of spinally-projecting A7 neurons, which were identified using tyrosine-hydroxylase immunoreactivity. Within 5 min of the cobalt chloride injection, the antinociceptive effect of carbachol stimulation was blocked. In another set of experiments, the NK(1) receptor antagonist L-703-606 (5 microg) was microinjected near the A7 cell group following LH stimulation with carbachol. L-703-606 also abolished LH-induced antinociception. These results support the conclusion that antinociception produced by activating substance P neurons in the LH is mediated in part by the subsequent activation of spinally-projecting noradrenergic neurons in the A7 cell group.

The central autonomic nervous system: conscious visceral perception and autonomic pattern generation

The overall organization of the peripheral autonomic nervous system has been known for many decades, but the mechanisms by which it is controlled by the central nervous system are just now coming to light. In particular, two major issues have seen considerable progress in the past decade. First, the pathways that provide visceral sensation to conscious perception at a cortical level have been elucidated in both animals and humans. The nociceptive system runs in parallel to the pathways carrying visceral sensation from the cranial nerves and may be considered in itself a component of visceral sensation. Second, structures in the central nervous system that generate patterns of autonomic response have been identified. These pattern generators are located at multiple levels of the central nervous system, and they can be combined in temporal and spatial patterns to subserve a wide range of behavioral needs.

Evidence for a direct projection from the paraventricular nucleus of the hypothalamus to putative serotoninergic neurons of the nucleus paragigantocellularis involved in the control of erection in rats

In the male rat, serotoninergic neurons of the ventrolateral medulla send direct projections onto spinal preganglionic neurons that innervate the penis. The role of the paraventricular nucleus of the hypothalamus in the control of penile erection is well recognized. Our aim was to demonstrate anatomical relation between paraventricular neurons and medullary serotoninergic neurons innervating the penis. In adult male rats, stereotaxic iontophoretic injections of Phaseolus vulgaris leuco-agglutinin were performed in the paraventricular nucleus. Neurons in the ventrolateral medulla were retrogradely labelled using transneuronal retrograde transport of pseudorabies virus injected in the corpus cavernosum. Sections of the ventro-lateral medulla were processed for double immunofluorescence to reveal both Phaseolus vulgaris leuco-agglutinin and pseudorabies virus using specific antibodies. Sections were also processed for the simultaneous detection of pseudorabies virus and serotonin. Pseudorabies virus-infected neurons in the ventrolateral medulla were present in the nucleus paragigantocellularis, reticular formation of the medulla, raphe pallidus and raphe magnus. In the nucleus paragigantocellularis, all pseudorabies virus-infected-neurons were immunoreactive for serotonin. Some of them received Phaseolus vulgaris leuco-agglutinin-labelled varicose fibres that ran along the soma of pseudorabies virus-infected neurons. Confocal microscopy suggested the presence of several close appositions between them, which were demonstrated using three-dimensional reconstruction of serial optical sections. Our results show that paraventricular neurons send direct projections in the nucleus paragigantocellularis onto neurons that innervate the penis. They suggest a possible role of the paraventricular nucleus in penile erection through the control of descending serotoninergic raphe-spinal neurons. The neurotransmitter used in this pathway remains to be determined.

Glucagon-like peptide-1 receptor stimulation increases blood pressure and heart rate and activates autonomic regulatory neurons

Glucagon-like peptide-1 (GLP-1) released from the gut functions as an incretin that stimulates insulin secretion. GLP-1 is also a brain neuropeptide that controls feeding and drinking behavior and gastric emptying and elicits neuroendocrine responses including development of conditioned taste aversion. Although GLP-1 receptor (GLP-1R) agonists are under development for the treatment of diabetes, GLP-1 administration may increase blood pressure and heart rate in vivo. We report here that centrally and peripherally administered GLP-1R agonists dose-dependently increased blood pressure and heart rate. GLP-1R activation induced c-fos expression in the adrenal medulla and neurons in autonomic control sites in the rat brain, including medullary catecholamine neurons providing input to sympathetic preganglionic neurons. Furthermore, GLP-1R agonists rapidly activated tyrosine hydroxylase transcription in brainstem catecholamine neurons. These findings suggest that the central GLP-1 system represents a regulator of sympathetic outflow leading to downstream activation of cardiovascular responses in vivo.

Metabolic sensors: viewing glucosensing neurons from a broader perspective

Glucose is a critical substrate for brain and organ function. Specialized glucosensing neurons, which are involved in the control of energy homeostasis and neuroendocrine function, are located in specific anatomic locations in the brain. Glucose-excited neurons increase their firing rate when ambient glucose levels rise. This glucosensing capacity appears to be regulated by a combination of glucokinase and an ATP-sensitive K(+) (K(ATP)) channel whose activity is regulated by ATP derived from glucose metabolism. Glucose inhibited neurons decrease their firing rate when glucose levels rise, although it is unclear what mechanism is used to control this function. Neuropeptide Y and proopiomelanocortin neurons in the hypothalamic arcuate nucleus are examples of neurons that are capable of sensing both glucose and a host of other peripheral metabolic signals, possibly by their actions on the K(ATP) channel. These metabolic sensing neurons are intimately involved in energy homeostasis, and it is postulated that glucose is only one of several peripheral metabolic signals involved in this process under physiologic conditions. However, when glucose supply is severely limited, glucose appears to assume primacy as a stimulant of glucosensing in order to activate the counterregulatory and ingestive processes necessary to restore the vital supply of glucose. Thus, the role of glucosensing is postulated to be a relative one that is dependent upon the supply of peripheral glucose.

Multiple neural systems controlling food intake and body weight

Discovery of the leptin receptor and its downstream peptidergic pathways has reconfirmed the crucial role of the hypothalamus in the regulation of food intake and energy balance. Strategically located in the midst of the mammalian neuraxis, the hypothalamus receives at least three distinct types of relevant information via direct or indirect neural connections as well as hormone receptors and substrate sensors bestowed on hypothalamic neurons. First, the medial and to a lesser extent the lateral hypothalamus receive a rich mix of information pertaining to the internal state of relative energy repletion/depletion. Second, specific hypothalamic nuclei receive information about the behavioral state, such as diurnal clock, physical activity-level, reproductive cycle, developmental stage, as well as imminent (e.g. fight and flight) and chronic (e.g. infection) stressors, that can potentially impact on short-term availability of fuels and long-term energy balance. Third, the hypothalamus, particularly its lateral aspects, receives information from areas in the forebrain involved in the acquisition, storage, and retrieval of sensory representations of the external food space and internal food experience, as well as from the executive forebrain involved in behavior selection and initiation. In addition, rich intrahypothalamic connections facilitate further distribution of incoming information to various hypothalamic nuclei. On the other hand, the hypothalamus has widespread neural projections to the same cortical areas it receives inputs, and many hypothalamic neurons are one synapse away from most endocrine systems and from both sympathetic and parasympathetic effector organs involved in the flux, storage, mobilization, and utilization of fuels. It is argued that processing within cortico-limbic areas and communication with hypothalamic areas are particularly important in human food intake control that is more and more guided by cognitive rather than metabolic aspects in the obesigenic environment of affluent societies. A distributed neural network for the control of food intake and energy balance consisting of a central processor and several parallel processing loops is hypothesized. Detailed neurochemical, anatomical, and functional analysis of reciprocal connections of the numerous peptidergic neuron populations in the hypothalamus with extrahypothalamic brain areas will be necessary to better understand what hypothalamus, forebrain, and brainstem tell each other and who is in charge under specific conditions of internal and external nutrient availability.

Organization of human hypothalamus in fetal development

The organization of the human hypothalamus was studied in 33 brains aged from 9 weeks of gestation (w.g.) to newborn, using immunohistochemistry for parvalbumin, calbindin, calretinin, neuropeptide Y, neurophysin, growth-associated protein (GAP)-43, synaptophysin, and the glycoconjugate 3-fucosyl- N-acetyl-lactosamine. Developmental stages are described in relation to obstetric trimesters. The first trimester (morphogenetic periods 9-10 w.g. and 11-14 w.g.) is characterized by differentiating structures of the lateral hypothalamic zone, which give rise to the lateral hypothalamus (LH) and posterior hypothalamus. The PeF differentiates at 18 w.g. from LH neurons, which remain anchored in the perifornical position, whereas most of the LH cells are displaced laterally. A transient supramamillary nucleus was apparent at 14 w.g. but not after 16 w.g. As the ventromedial nucleus differentiated at 13-16 w.g., three principal parts, the ventrolateral part, the dorsomedial part, and the shell, were revealed by distribution of calbindin, calretinin, and GAP43 immunoreactivity. The second trimester (morphogenetic periods 15-17 w.g., 18-23 w.g., and 24-33 w.g.) is characterized by differentiation of the hypothalamic core, in which calbindin- positive neurons revealed the medial preoptic nucleus at 16 w.g. abutted laterally by the intermediate nucleus. The dorsomedial nucleus was clearly defined at 10 w.g. and consisted of compact and diffuse parts, an organization that was lost after 15 w.g. Differentiation of the medial mamillary body into lateral and medial was seen at 13-16 w.g. Late second trimester was marked by differentiation of periventricular zone structures, including suprachiasmatic, arcuate, and paraventricular nuclei. The subnuclear differentiation of these nuclei extends into the third trimester. The use of chemoarchitecture in the human fetus permitted the identification of interspecies nuclei homologies, which otherwise remain concealed in the cytoarchitecture.

Oxytocin mediates stress-induced analgesia in adult mice

As a neurohormone and as a neurotransmitter, oxytocin has been implicated in the stress response. Descending oxytocin-containing fibres project to the dorsal horn of the spinal cord, an area important for processing nociceptive inputs. Here we tested the hypothesis that oxytocin plays a role in stress-induced analgesia and modulates spinal sensory transmission. Mice lacking oxytocin exhibited significantly reduced stress-induced antinociception following both cold-swim (10 degrees C, 3 min) and restraint stress (30 min). In contrast, the mice exhibited normal behavioural responses to thermal and mechanical noxious stimuli and morphine-induced antinociception. In wild-type mice, intrathecal injection of the oxytocin antagonist dOVT (200 microM in 5 microl) significantly attenuated antinociception induced by cold-swim. Immunocytochemical staining revealed that, in the mouse, oxytocin-containing neurones in the paraventricular nucleus of the hypothalamus are activated by stress. Furthermore, oxytocin-containing fibres were present in the dorsal horn of the spinal cord. To test whether descending oxytocin-containing fibres could alter nociceptive transmission, we performed intracellular recordings of dorsal horn neurones in spinal slices from adult mice. Bath application of oxytocin (1 and 10 microM) inhibited excitatory postsynaptic potentials (EPSPs) evoked by dorsal root stimulation. This effect was reversed by the oxytocin antagonist dOVT (1 microM). Whole-cell recordings of dorsal horn neurones in postnatal rat slices revealed that the effect of oxytocin could be blocked by the addition of GTP-gamma-S to the recording pipette, suggesting activation of postsynaptic oxytocin receptors. We conclude that oxytocin is important for both cold-swim and restraint stress-induced antinociception, acting by inhibiting glutamatergic spinal sensory transmission.

Ups and downs for neuropeptides in body weight homeostasis: pharmacological potential of cocaine amphetamine regulated transcript and pre-proglucagon-derived peptides

Although most humans experience an underlying upwards drift of the body-weight set-point, body weight appears tightly regulated throughout life. The present review describes the structural basis of the adipostat and hypothesise, which components may constitute available targets for pharmacotherapy of excess body weight. Hypothalamic neurones constitute the major components of the body weight homeostasis maintaining device. Together with neurones of the nucleus of the solitary tract, neurones of the hypothalamic arcuate nucleus constitute the sensory components of the adipostat. The arcuate nucleus neurones respond to circulating levels of leptin and insulin, both of which reflect the levels of energy stored as triacylglycerol in adipocytes. The arcuate nucleus projects heavily to the hypothalamic paraventricular nucleus. Neurones of the hypothalamic paraventricular nucleus are hypothesised to constitute, at least partly, the adipostat motor pattern generator, which upon stimulation activates either net anabolic or catabolic physiological responses. The overall sensitivity of the adipostat is influenced by gain setting neurones hypothesised to be located in the dorsomedial hypothalamic nucleus and lateral hypothalamic area. Cocaine amphetamine regulated transcript (CART) peptides and pre-proglucagon derived peptides, glucagon-like peptide-1 (GLP-1) and glucagon-like peptide-2 (GLP-2) are catabolic neurotransmitters synthesised in neurones of the arcuate nucleus and the nucleus of the solitary tract, respectively. The present review summarises the available evidence that both families of peptides constitute endogenous transmitters mediating satiety and touch upon potential pharmacological exploitation of this knowledge.

Descending control of pain

Upon receipt in the dorsal horn (DH) of the spinal cord, nociceptive (pain-signalling) information from the viscera, skin and other organs is subject to extensive processing by a diversity of mechanisms, certain of which enhance, and certain of which inhibit, its transfer to higher centres. In this regard, a network of descending pathways projecting from cerebral structures to the DH plays a complex and crucial role. Specific centrifugal pathways either suppress (descending inhibition) or potentiate (descending facilitation) passage of nociceptive messages to the brain. Engagement of descending inhibition by the opioid analgesic, morphine, fulfils an important role in its pain-relieving properties, while induction of analgesia by the adrenergic agonist, clonidine, reflects actions at alpha(2)-adrenoceptors (alpha(2)-ARs) in the DH normally recruited by descending pathways. However, opioids and adrenergic agents exploit but a tiny fraction of the vast panoply of mechanisms now known to be involved in the induction and/or expression of descending controls. For example, no drug interfering with descending facilitation is currently available for clinical use. The present review focuses on: (1) the organisation of descending pathways and their pathophysiological significance; (2) the role of individual transmitters and specific receptor types in the modulation and expression of mechanisms of descending inhibition and facilitation and (3) the advantages and limitations of established and innovative analgesic strategies which act by manipulation of descending controls. Knowledge of descending pathways has increased exponentially in recent years, so this is an opportune moment to survey their operation and therapeutic relevance to the improved management of pain.

Pain-autonomic interactions: a selective review

The nociceptive and the autonomic systems interact at the level of the periphery, spinal cord, brainstem, and forebrain. Spinal and visceral afferents provide converging information to spinothalamic neurons in the dorsal horn and to neurons of the nucleus tractus solitarius and parabrachial nuclei. These structures project to areas involved in reflex, homeostatic, and behavioral control of autonomic outflow, endocrine function, and nociception. These include monoaminergic cell groups of the medulla and pons, periaqueductal gray, hypothalamus, amygdala, insular cortex, and anterior cingulate gyrus. These interactions should be taken into account to understand the complex pathophysiology of chronic pain disorders.

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.

Glutamate and GABA mediate suprachiasmatic nucleus inputs to spinal-projecting paraventricular neurons

We used patch-clamp recordings in slice preparations from Sprague-Dawley rats to evaluate responses of 20 spinal-projecting neurons in the dorsal paraventricular nucleus (PVN) to electrical stimulation in suprachiasmatic nucleus (SCN). Neurons containing a retrograde label transported from the thoracic (T(1)-T(4)) intermediolateral column displayed three intrinsic properties that collectively allowed distinction from neighboring parvocellular or magnocellular cells: a low-input resistance, a hyperpolarization-activated time-dependent inward rectification, and a low-threshold calcium conductance. Twelve of fifteen cells tested responded to electrical stimulation in SCN. All of 10 cells tested in media containing 2,3,-dioxo-6-nitro-1,2,3,4-tetrahydrobenzo[f]quinoxaline-7-sulfonamide disodium (5 microM) and D(-)-2-amino-5-phosphonopentanoic acid (20 microM) responded with constant latency (11.4 +/- 0.7 ms) inhibitory postsynaptic potentials, able to follow 20- to 50-Hz stimulation and blockable with bicuculline (20 microM). By contrast, all eight cells tested in the presence of bicuculline demonstrated constant latency (9.8 +/- 0.6 ms) excitatory postsynaptic potentials that followed at 20-50 Hz and featured both non-N-methyl-D-aspartate (NMDA) and NMDA receptor-mediated components. We conclude that both GABAergic and glutamatergic neurons in SCN project directly to spinal-projecting neurons in the dorsal PVN.

The projections of the midbrain periaqueductal grey to the pons and medulla oblongata in rats

It is now established that stimulation of the ventrolateral midbrain periaqueductal grey (PAG) evokes inhibition of nociceptive spinal neurons, which results in analgesia and a powerful attenuation of pain behaviour. It is postulated that the PAG exerts this inhibitory effect on spinal nociceptive functions through the activation of descending serotonergic and noradrenergic pathways that arise from the rostral ventromedial medulla (RVM) and pontine noradrenergic nuclei. To investigate the neuroanatomical substrate of this functional link between the PAG and RVM, as well as the pontine noradrenergic nuclei in the rat, we labelled axons that project from the ventrolateral PAG to various regions of the pons and medulla oblongata using the anterograde tracing substance, Phaseolus vulgaris leucoagglutinin. We demonstrated that some of PAG efferents really do terminate in the RVM and pontine noradrenergic nuclei, but a substantial proportion of them project to the intermediate subdivision of the pontobulbar reticular formation. Combining the axonal tracing with serotonin- and tyrosine-hydroxylase-immunohistochemistry, we also found that, in contrast to previous results, PAG efferents make relatively few appositions with serotonin- and tyrosine-hydroxylase-immunoreactive neurons in the RVM and pontine noradrenergic nuclei; most of them terminate in nonimmunoreactive territories. The results suggest that the ventrolateral PAG may activate a complex pontobulbar neuronal assembly including neurons in the intermediate subdivision of the pontobulbar reticular formation, serotonin- and tyrosine-hydroxylase-immunoreactive and nonimmunoreactive neurons in the RVM and pontine noradrenergic nuclei. This pontobulbar neural circuitry, then, may mediate the PAG-evoked activities towards the spinal dorsal horn resulting in the inhibition of spinal nociceptive functions.