Autonomic Preganglionic Neurons Research Articles

Modulation of dopamine's effect at dopamine 2 receptors (D2R) mediated by association with the ghrelin receptor, GHSR

The typical action of dopamine at the dopamine 2 receptor (D2R) on CNS neurons is inhibition, an effect mediated via Gαi/o through GIRK channels. However, at two sites, autonomic preganglionic neurons in the lumbosacral spinal cord, and in the lateral hypothalamus, dopamine causes neuronal excitation through D2R. At both sites, dopamine neurons that are excited by dopamine express the ghrelin receptor, GHSR. Ghrelin is absent from the lateral hypothalamus and spinal cord, and it has been proposed that GHSR may modulate D2R signaling by the formation of heterodimers.In lumbrosacral spinal cord neurons of the defecation centre, D2R and GHSR agonists applied successively were both excitatory. Antagonism of GHSR at these neurons blocked the excitatory effect of DR2 stimulation, which was also blocked by depletion of intracellular calcium (iCa2+). We further investigated this interaction in recombinant cultured cells. In CHO cells expressing D2R, dopamine agonists had almost no effect on iCa2+, whereas in the presence of GHSR, D2R coupling to iCa2+ was observed in response to nanomolar dopamine. The elevation of iCa2+ by dopamine in D2R/GHSR cells was reduced by either D2R or GHSR antagonism, but the effect of a GHSR agonist was reduced only by GHSR antagonism. D2R coupling to iCa2+ in the presence of GHSR was dependent on both Gαq and Gαi/o, whereas ghrelin agonist coupling was dependent only on Gαq. D2R mediated effects on cAMP were dependent only on Gαi/o and were not effected by GHSR antagonism. D2R and GHSR in the membranes of CHO cells, revealed by fluorescent ligands, moved independently when tracked at high resolution in real time and, using fluorescent lifetime imaging, individual labelled DR2 sites were not in close enough proximity to detect resonance energy transfer (no detectable FRET). Consistent with coupling being via downstream crosstalk, no detectable DR2 dependent iCa2+ was evident in cells expressing the GHSR – A204E mutant, which lacks constitutive activity. The DR2-dependent iCa2+ increase was restored in these cells using subthreshold pre-stimulation with ghrelin. In native neurons of the defecation center, inward currents in response to D2R agonism were blocked by U73122, an inhibitor of PLCβ. Together this data indicates that dopamine-mediated excitation was dependent on GHSR, PLCβ and iCa2+, in both native and recombinant cells. We conclude that co-expression of GHSR causes augmentation of agonist-induced, D2R-mediated PLCβ activation and store Ca2+ release in recombinant cells and in a population of autonomic preganglionic neurons. D2R mediated excitation in D2R/GHSR cells is both Gαi/o and Gαq/11 dependent, but does not require receptor dimerisation. Our findings reveal a novel interaction between GPCRs, in a physiologically relevant system, that does not require direct receptor interaction and has broad implications for recoding of metabotropic neurotransmitter responses via modulation through other GPCRs. NHMRC grant, APP2012657, to SGBF This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Stress and central autonomic network.

The central autonomic network (CAN) plays a critical role in the stress response, which is triggered by challenges on the homeostasis (physiological stressors) or unpleasant social or environmental situations. This review focuses on the role of areas of the CAN including the insular and anterior cingulate cortices, extended amygdala, hypothalamus, periaqueductal gray and locus coeruleus in the stress response. These areas are interconnected and affect sympathetic or parasympathetic output via their influence on premotor or preganglionic autonomic neurons in the lower brainstem and spinal cord. The insula integrates multiple inputs to create a sense of the physiological state of the body, whereas the anterior cingulate initiates predictive visceromotor commands. The amygdala and bed nucleus of the stria terminalis provide automatic emotional tagging and trigger automatic survival responses to threat via their outputs to the hypothalamus, periaqueductal gray, and lower brainstem. Several regions of the hypothalamus, including the paraventricular nucleus, dorsomedial nucleus and lateral hypothalamic area participate in different patterns of stress response according to the type of stimulus and projections to premotor and preganglionic autonomic neurons. The periaqueductal gray initiates different patterns of autonomic, pain modulatory, and motor responses, including the "fight or flight" or "playing dead" responses. The locus coeruleus promotes emotional learning in the amygdala associated with states of anxiety. Neurons of the C1 area of the rostral ventrolateral medulla elicit sympathoexcitatory responses to internal stressors such as hypoxia and inflammation. The ventromedial medulla, including the nucleus raphe pallidus, initiates sympathoexcitatory responses to social and other external stressors.

Dopamine and ghrelin receptor co-expression and interaction in the spinal defecation centers.

Dopamine receptor 2 (DRD2) and ghrelin receptor (GHSR1a) agonists both stimulate defecation by actions at the lumbosacral defecation center. Dopamine is in nerve terminals surrounding autonomic neurons of the defecation center, whereas ghrelin is not present in the spinal cord. Dopamine at D2 receptors generally inhibits neurons, but at the defecation center, its effect is excitatory. In vivo recording of defecation and colorectal propulsion was used to investigate interaction between DRD2 and GHSR1a. Localization studies were used to determine sites of receptor expression in rat and human spinal cord. Dopamine, and the DRD2 agonist, quinpirole, directly applied to the lumbosacral cord, caused defecation. The effect of intrathecal dopamine was inhibited by the GHSR1a antagonist, YIL781, given systemically, but YIL781 was not an antagonist at DRD2. The DRD2 agonist, pramipexole, administered systemically caused colorectal propulsion that was prevented when the pelvic nerves were cut. Drd2 and Ghsr were expressed together in autonomic preganglionic neurons at the level of the defecation centers in rat and human. Behaviorally induced defecation (caused by water avoidance stress) was reduced by the DRD2 antagonist, sulpiride. We had previously shown it is reduced by YIL781. Our observations imply that dopamine is a transmitter of the defecation pathways whose actions are exerted through interacting dopamine (D2) and ghrelin receptors on lumbosacral autonomic neurons that project to the colorectum. The results explain the excitation by dopamine agonists and the conservation of GHSR1a in the absence of ghrelin.

Axonal Injury Induces ATF3 in Specific Populations of Sacral Preganglionic Neurons in Male Rats.

Compared to other neurons of the central nervous system, autonomic preganglionic neurons are unusual because most of their axon lies in the periphery. These axons are vulnerable to injury during surgical procedures, yet in comparison to peripheral neurons and somatic motor neurons, the impact of injury on preganglionic neurons is poorly understood. Here, we have investigated the impact of axotomy on sacral preganglionic neurons, a functionally diverse group of neurons required for micturition, defecation, and sexual function. We have previously observed that after axotomy, the injury-related transcription factor activating transcription factor-3 (ATF3) is upregulated in only half of these neurons (Peddie and Keast, 2011: PMID: 21283532). In the current study, we have investigated if this response is constrained to particular subclasses of preganglionic neurons that have specific functions or signaling properties. Seven days after unilateral pelvic nerve transection, we quantified sacral preganglionic neurons expressing ATF3, many but not all of which co-expressed c-Jun. This response was independent of soma size. Subclasses of sacral preganglionic neurons expressed combinations of somatostatin, calbindin, and neurokinin-1 receptor, each of which showed a similar response to injury. We also found that in contrast to thoracolumbar preganglionic neurons, the heat shock protein-25 (Hsp25) was not detected in naive sacral preganglionic neurons but was upregulated in many of these neurons after axotomy; the majority of these Hsp25 neurons expressed ATF3. Together, these studies reveal the molecular complexity of sacral preganglionic neurons and their responses to injury. The simultaneous upregulation of Hsp25 and ATF3 may indicate a distinct mechanism of regenerative capacity after injury.

Neural pathways for colorectal control, relevance to spinal cord injury and treatment: a narrative review.

Narrative review. The purpose is to review the organisation of the nerve pathways that control defecation and to relate this knowledge to the deficits in colorectal function after SCI. A literature review was conducted to identify salient features of defecation control pathways and the functional consequences of damage to these pathways in SCI. The control pathways for defecation have separate pontine centres under cortical control that influence defecation. The pontine centres connect, separately, with autonomic preganglionic neurons of the spinal defecation centres and somatic motor neurons of Onuf's nucleus in the sacral spinal cord. Organised propulsive motor patterns can be generated by stimulation of the spinal defecation centres. Activation of the somatic neurons contracts the external sphincter. The analysis aids in interpreting the consequences of SCI and predicts therapeutic strategies. Analysis of the bowel control circuits identifies sites at which bowel function may be modulated after SCI. Colokinetic drugs that elicit propulsive contractions of the colorectum may provide valuable augmentation of non-pharmacological bowel management procedures.

Calbindin-Immunoreactive Interneurons in the Intermediate Zone and Ventral Horn of the Gray Matter of the SC in White Rats

The aim of the present work was to study the topography and structure of 28-kDa calbindin (CB)-containing interneurons in the ventral horn and intermediate zone of the gray matter at levels TII and LIV of the spinal cord (SC). Experiments were performed in adult female Wistar rats (n = 4) using immunohistochemical and morphometric methods. Cryostat transverse sections of the SC of thickness 14 μm were studied. The intermediate zone of the SC was found to contain two subpopulations of CB-immunoreactive (IR) interneurons in lamina VII in both segments: sympathetic preganglionic neurons and “partition” cells. The ventral horn also contained two subpopulations of CB-IR interneurons: Renshaw cells in lamina IX in TII and lamina VII in LIV and large interneurons in lamina VIII in TII and lamina VII in LIV. The only differences between segments were in the larger numbers of Renshaw cells and partition cells in LIV. The mean cross-sectional areas of CB-IR Renshaw cells and autonomic preganglionic neurons were greater in TII, while large interneurons of the ventral horn and partition cells were larger in LIV.

Endocrine-Autonomic Linkages.

Interaction between the autonomic nervous system and the neuroendocrine system is critical for maintenance of homeostasis in a wide variety of physiological parameters such as body temperature, fluid and electrolyte balance, and blood pressure and volume. The anatomical and physiological mechanisms underlying integration of the neuroendocrine and autonomic mechanisms responsible for eliciting integrated autonomic and neuroendocrine actions are the focus of this article. This includes a focus on the hypothalamic paraventricular nucleus, because it includes both neuroendocrine neurons and preganglionic autonomic neurons that regulate sympathetic and parasympathetic outflow. The "wired" and "nonwired" mechanisms within PVN that facilitate communication between these neuronal populations are described. The impact of peripheral hormones, specifically the adrenal and gonadal steroids, on the neuroendocrine and autonomic systems is discussed, and exercise is used as a specific example of a physiological challenge/stress that requires precise integration of neuroendocrine and autonomic responses to maintain cardiovascular, fluid, and energy homeostasis.

Melanocortin 4 receptors in autonomic neurons regulate thermogenesis and glycemia.

SUMMARYMelanocortin 4 receptors (Mc4rs) are expressed by extra-hypothalamic neurons including cholinergic autonomic pre-ganglionic neurons. However, whether Mc4rs in these neurons are required to control energy and glucose homeostasis is unclear. Here we report that Mc4rs in sympathetic, but not parasympathetic, pre-ganglionic neurons are required to regulate energy expenditure and body weight including brown and white adipose tissue thermogenic responses to diet and cold exposure. In addition, deletion of Mc4rs in both sympathetic and parasympathetic cholinergic neurons impairs glucose homeostasis.

Expression of the ghrelin receptor gene in neurons of the medulla oblongata of the rat

There is ambiguity concerning the distribution of neurons that express the ghrelin receptor (GHSR) in the medulla oblongata. In the current study we used a sensitive nonradioactive method to investigate GHSR mRNA distribution by in situ hybridization. Strong expression of the GHSR gene was confirmed in neurons of the facial nucleus (FacN, 7), the dorsal vagal complex (DVC), and the semicompact (but not compact) nucleus ambiguus (AmbSC and AmbC). In addition, expression of GHSR was found in other regions, where it had not been described before. GHSR-positive neurons were observed in the gustatory rostral nucleus tractus solitarius and in areas involved in vestibulo-ocular processing (such as the medial vestibular nucleus and the nucleus abducens). GHSR expression was also noted in ventral areas associated with cardiorespiratory control, including the gigantocellular reticular nucleus, the lateral paragigantocellular nucleus, the rostral and caudal ventrolateral medulla, the (pre)-Bötzinger complex, and the rostral and caudal ventrolateral respiratory group. However, GHSR-positive neurons in ventrolateral areas did not express markers for cardiovascular presympathetic vasomotor neurons, respiratory propriobulbar rhythmogenic neurons, or sensory interneurons. GHSR-positive cells were intermingled with catecholamine neurons in the dorsal vagal complex but these populations did not overlap. Thus, the ghrelin receptor occurs in the medulla oblongata in 1) second-order sensory neurons processing gustatory, vestibulo-ocular, and visceral sensation; 2) cholinergic somatomotor neurons of the FacN and autonomic preganglionic neurons of the DMNX and AmbSC; 3) cardiovascular neurons in the DVC, Gi, and LPGi; 4) neurons of as yet unknown function in the ventrolateral medulla.

Identification of neurons that express ghrelin receptors in autonomic pathways originating from the spinal cord

Functional studies have shown that subsets of autonomic preganglionic neurons respond to ghrelin and ghrelin mimetics and in situ hybridisation has revealed receptor gene expression in the cell bodies of some preganglionic neurons. Our present goal has been to determine which preganglionic neurons express ghrelin receptors by using mice expressing enhanced green fluorescent protein (EGFP) under the control of the promoter for the ghrelin receptor (also called growth hormone secretagogue receptor). The retrograde tracer Fast Blue was injected into target organs of reporter mice under anaesthesia to identify specific functional subsets of postganglionic sympathetic neurons. Cryo-sections were immunohistochemically stained by using anti-EGFP and antibodies to neuronal markers. EGFP was detected in nerve terminal varicosities in all sympathetic chain, prevertebral and pelvic ganglia and in the adrenal medulla. Non-varicose fibres associated with the ganglia were also immunoreactive. No postganglionic cell bodies contained EGFP. In sympathetic chain ganglia, most neurons were surrounded by EGFP-positive terminals. In the stellate ganglion, neurons with choline acetyltransferase immunoreactivity, some being sudomotor neurons, lacked surrounding ghrelin-receptor-expressing terminals, although these terminals were found around other neurons. In the superior cervical ganglion, the ghrelin receptor terminals innervated subgroups of neurons including neuropeptide Y (NPY)-immunoreactive neurons that projected to the anterior chamber of the eye. However, large NPY-negative neurons projecting to the acini of the submaxillary gland were not innervated by EGFP-positive varicosities. In the celiaco-superior mesenteric ganglion, almost all neurons were surrounded by positive terminals but the VIP-immunoreactive terminals of intestinofugal neurons were EGFP-negative. The pelvic ganglia contained groups of neurons without ghrelin receptor terminal innervation and other groups with positive terminals around them. Ghrelin receptors are therefore expressed by subgroups of preganglionic neurons, including those of vasoconstrictor pathways and of pathways controlling gut function, but are absent from some other neurons, including those innervating sweat glands and the secretomotor neurons that supply the submaxillary salivary glands.

Distribution and identity of neurons expressing the oxytocin receptor in the mouse spinal cord

Oxytocin can influence various spinal functions. However, little is known about the spinal neuronal networks responsible for oxytocin effects. The aim of this study was to localize and characterize spinal neurons expressing oxytocin receptors. We used an oxytocin receptor-reporter mouse in which the fluorescent protein Venus is expressed under the control of the oxytocin receptor gene promoter. At all segmental levels, Venus-expressing neurons were most numerous in the substantia gelatinosa, mingled with protein kinase Cγ interneurons in the innermost layer of the inner lamina II, which, in contrast to the outer two thirds of this layer, does not receive nociceptive input. Venus-expressing neurons were also observed in the intermediolateral and sacral parasympathetic nuclei, where they represented about 5% of presumed preganglionic neurons identified by choline acetyltransferase immunoreactivity. Finally, Venus immunoreactivity was detected in lumbar and sacral dorsal gray commissures as well as in isolated neurons scattered in different regions of the dorsal horn. Altogether, our results establish the location of neurons putatively involved in oxytocin modulation of spinal functions, in particular of sexual functioning and nociception.

Evidence for functional ghrelin receptors on parasympathetic preganglionic neurons of micturition control pathways in the rat

1. Previous work indicates that agonists of ghrelin receptors can act within the spinal cord to stimulate autonomic outputs to the colorectum and to blood vessels. Because of the close relationship between colorectal and urinary bladder control, we have investigated whether ghrelin receptor agonists also stimulate spinal centres that influence the bladder. 2. The ghrelin receptor agonist capromorelin (10 mg/kg), injected intravenously in anaesthetized male rats, disrupted the ongoing cycle of micturition reflexes and caused phasic oscillations in pressure that averaged approximately 20 mmHg. Fluid output from the bladder was diminished. The effects of capromorelin were inhibited by hexamethonium (10 mg/kg bolus followed by 4 mg/kg per h infusion, i.v.) and were further reduced by atropine (5 mg/kg bolus followed by 2.5 mg/kg per h infusion, i.v.). Capromorelin (250 microg) injected directly into the spinal cord at the lumbosacral level also increased contractile activity of the bladder. However, capromorelin, up to 0.1 mmol/L, had no effect on the tension of isolated muscle strips from the bladder. Effects of intravenous capromorelin (10 mg/kg) on bladder pressure were still observed after the descending pathways in the spinal cord were disrupted at the thoracic level. 3. In situ hybridization studies revealed ghrelin receptor gene expression in neurons of the autonomic intermediolateral (IML) cell columns. Following a series of micturition reflexes elicited by infusion of saline into the bladder, the immediate early gene product c-Fos was observed in neurons of the lumbosacral IML and approximately 20% of these also expressed ghrelin receptor gene transcripts. 4. It is concluded that ghrelin receptors are expressed by lumbosacral autonomic preganglionic neurons of the micturition reflex pathways and that ghrelin receptor agonists stimulate these neurons.

Functional and in situ hybridization evidence that preganglionic sympathetic vasoconstrictor neurons express ghrelin receptors

Agonists of ghrelin receptors can lower or elevate blood pressure, and it has been suggested that the increases in blood pressure are caused by actions at receptors in the spinal cord. However, this has not been adequately investigated, and the locations of neurons in the spinal cord that express ghrelin receptors, through which blood pressure increases may be exerted, are not known. We investigated the effects within the spinal cord of two non-peptide ghrelin receptor agonists, GSK894490 and CP464709, and two peptide receptor agonists, ghrelin and des-acyl ghrelin, and we used polymerase chain reaction (PCR) and in situ hybridization to examine ghrelin receptor expression. I.v. application of the non-peptide ghrelin receptor agonists caused biphasic changes in blood pressure, a brief drop followed by a blood pressure increase that lasted several minutes. The blood pressure rise, but not the fall, was antagonized by i.v. hexamethonium. Application of these agonists or ghrelin peptide directly to the spinal cord caused only a blood pressure increase. Des-acyl ghrelin had no significant action. The maximum pressor effects of agonists occurred with application at spinal cord levels T9 to T12. Neither i.v. nor spinal cord application of the agonists had significant effect on heart rate or the electrocardiogram. Ghrelin receptor gene expression was detected by PCR and in situ hybridization. In situ hybridization localized expression to neurons, including autonomic preganglionic neurons of the intermediolateral cell columns at all levels from T3 to S2. The numbers of ghrelin receptor expressing neurons in the intermediolateral cell columns were similar to the numbers of nitric oxide synthase positive neurons, but there was little overlap between these two populations. We conclude that activation of excitatory ghrelin receptors on sympathetic preganglionic neurons increases blood pressure, and that decreases in blood pressure caused by ghrelin agonists are mediated through receptors on blood vessels.

Comparative analysis of NADPH-diaphorase positive neurons in the rat, rabbit and pheasant thoracic spinal cord. A histochemical study

The distribution of NADPH-diaphorase (NADPH-d) activity was investigated and compared in the rat, rabbit and pheasant thoracic spinal cord. The investigation of all spinal cord regions (laminae) in three experimental species revealed marked differences in the distribution of NADPH-d activity. Cross sectional analysis of the spinal cord of the rat, rabbit and pheasant confirmed differences in the shape of the gray matter in all examined species. More detailed investigation of Rexed's laminas showed similar distribution of NADPH-d activity in the spinal cord of the rat and rabbit, which were different when compared with the spinal cord of the pheasant. Ventral horn of the rat and rabbit showed no labelling whereas in pheasant this area possessed a number of scattered, intensively stained neurons. In the location of autonomic preganglionic neurons, differences were found as well. In the rat there was seen a number of densely packed, clearly dark blue coloured neurons. Similarly, these neurons were present in the rabbit spinal cord but they were less numerous. No staining was found in this region of pheasant. Pericentral area (lamina X) and intermediate zone (laminaVII) revealed the presence of NADPH-d positive neurons in all examined species although they differed in number and shape of their bodies. The dorsal horn showed the presence of NADPH-d staining in all three animals but its distribution was different in medio-lateral direction. It can be suggested that observed differencies in the presence and distribution of NADPH-d activity across the examined species may reflect different fylogenetic development.

Differential Islet-1 expression among lumbosacral spinal motor neurons in prenatal mouse

Onuf's nucleus in the lumbosacral spinal cord, comprising somatic motoneurons that innervate the pelvic floor muscles via the pudendal nerve, shares some characteristics with the autonomic preganglionic neurons and functions in coordination with the autonomic nervous system. In mouse, neurons projecting to the urethral sphincter and ischiocavernosus muscles form the dorsolateral (DL) nucleus at the caudal lumbar levels, whereas neurons projecting to the limb and hip joint muscles comprise the retrodorsolateral and ventral nucleus, as well as the DL nucleus at the rostral lumbar levels. The results of the present study in mouse revealed that the expression pattern of a LIM homeodomein protein Islet-1, an embryonic marker for motoneurons in the spinal cord, was different among motoneuronal groups at the prenatal stage (embryonic days 13.5–15.5); the highest expression was observed in the DL at the caudal lumbar cord, whereas there was little expression in the lateral part of the rostral DL. Islet-1 expression was also observed in the parasympathetic preganglionic neurons at the sacral spinal cord. These findings provide evidence that the DL neurons at the caudal lumbar cord, corresponding to Onuf's nucleus, are chemically distinct among the motoneuronal groups at the prenatal stages. This differential Islet-1 expression among the motoneuronal groups suggests that Islet-1 not only leads to a motoneuronal lineage, but also to the differentiation of motoneuronal subsets in the lumbosacral spinal cord.

Evidence that activation of ghrelin receptors of autonomic preganglionic neurons stimulates autonomic outflows

Evidence that activation of ghrelin receptors of autonomic preganglionic neurons stimulates autonomic outflows

Phosphorylation of neuronal nitric oxide synthase at Ser847 in the nucleus intermediolateralis after spinal cord injury in mice

We previously demonstrated that Ca2+/calmodulin (CaM)-dependent protein kinase IIα (CaM-KIIα) can phosphorylate neuronal nitric oxide synthase (nNOS) at Ser847 and attenuate NOS activity in neuronal cells. In the present study we focused on chronological alteration in levels and cellular location of nNOS, phosphorylated (p)-Ser847-nNOS (NP847), CaM-KII and p-Thr286-CaM-KIIα following spinal cord injury (SCI) in mice. Western blot analysis showed nNOS to be significantly phosphorylated at Ser847 from 3 h after SCI, peaking at 24 h and gradually decreasing thereafter, and CaM-KII to be colocalized with nNOS after SCI. Immunohistochemical analysis revealed that SCI causes an increase in both NP847 and p-Thr286-CaM-KIIα in the nucleus intermediolateralis. These findings suggest that SCI induces p-Thr286-CaM-KIIα, which phosphorylates the nNOS at Ser847 in the nucleus intermediolateralis where NO is thought to play a role as a neurotransmitter in autonomic preganglionic neurons. Thus, the NP847 signaling pathway might be involved in the autonomic failure which occurs immediately after SCI.

Prenatal development of transient receptor potential vanilloid 1-expressing primary sensory projections to sacral autonomic preganglionic neurons

The visceral reflexes of the pelvic organs are mediated by connections between primary afferents innervating the pelvic organs and parasympathetic preganglionic neurons in the intermediolateral column of the sacral spinal cord. The present immunohistochemical study revealed many varicosities expressing transient receptor potential vanilloid 1 (TRPV1) that were closely apposed to the preganglionic neuronal perikarya at embryonic day 16 in mice. Many, but not all, varicosities expressing TRPV1 in the intermediolateral column were also immunopositive for calcitonin gene-related peptide. In contrast, no nerve fibers expressing TRPV1 projected to the sympathetic preganglionic cell column in the lumbar spinal cord in prenatal stages. The results of the present study raised the possibility that the primary afferents transmit signals elicited by the activation of TRPV1 receptors to the sacral parasympathetic preganglionic neurons. Thus, the functional circuit for pelvic spinal reflexes, such as micturition induced by urine influx, might develop in the prenatal stages in mice.

Hypothalamus: Central Regulator of the Autonomic Nervous System

Autonomic motor neurons, like somatic motor neurons, are controlled both by reflex connections and by descending projections from hierarchically organized CNS structures. The hypothalamus is a nodal point in this hierarchy. It receives a wide array of sensory inputs relevant to homeostatic needs. Some are delivered by hypothalamic neurons directly sensitive to temperature, osmolality, and other parameters; others arrive from brainstem nuclei, prominently including the nucleus of the solitary tract and the parabrachial nuclei, and still others from the spinal cord. The hypothalamus then integrates this information with inputs from limbic structures such as the amygdala and insular and orbitofrontal cortex, finally producing output signals that descend to the brainstem and spinal cord, reaching autonomic pattern generators and preganglionic autonomic neurons.

HCN1 ion channel immunoreactivity in spinal cord and medulla oblongata

Hyperpolarization-activated cyclic nucleotide-gated (HCN) non-selective cation channels in neurons carry currents proposed to perform diverse functions, including the hyperpolarization activated I h current. The 4 HCN subunits have unique but overlapping patterns of expression in the CNS. Here, we examined the distribution of HCN1 channel subunits in the brainstem and spinal cord using immunohistochemistry. At all levels of the spinal cord dorsal horn, HCN1 immunoreactivity (HCN1-IR) was predominantly absent from laminae I and II, while a dense band of punctate labeling was visible in lamina III. Labeled neurons were identified in close vicinity to the central canal, in the lateral spinal nucleus, in the ventral horn and occasionally in lamina II and III. Those in the ventral horn were identified as α motor neurons using retrograde tracing and/or double or triple immunostaining with neuronal markers neurofilament 200 (NF200) and choline acetyltransferase. HCN1-IR neurons in the brainstem included neurons in sensory pathways such as the dorsal column nuclei, the area postrema, the spinal trigeminal nucleus as well as identified motor neurons in motor nuclei. In the nucleus ambiguus, a mixed visceral/motor nucleus, HCN1-IR was present only in NF200-IR cells, suggesting that it is expressed in motor but not autonomic preganglionic neurons. HCN1-IR motor neurons in the nucleus ambiguus also expressed the neurokinin 1 receptor and were labeled retrogradely from the larnyx. At the light microscopic level, the NTS and inferior olive contained punctate labeling, which ultrastructural examination revealed to be present in predominantly synaptic terminals or dendrites respectively. These data therefore described the first localization of the HCN1 subunit in the spinal cord and extend previous reports from the brainstem.