Neurons In Anterior Hypothalamus Research Articles

Anterior hypothalamic parvalbumin neurons are glutamatergic and promote escape behavior

The anterior hypothalamic area (AHA) is a critical structure for defensive responding. Here, we identified a cluster of parvalbumin-expressing neurons in the AHA (AHAPV) that are glutamatergic with fast-spiking properties and send axonal projections to the dorsal premammillary nucleus (PMD). Using invivo functional imaging, optogenetics, and behavioral assays, we determined the role of these AHAPV neurons in regulating behaviors essential for survival. We observed that AHAPV neuronal activity significantly increases when mice are exposed to a predator, and in a real-time place preference assay, we found that AHAPV neuron photoactivation is aversive. Moreover, activation of both AHAPV neurons and the AHAPV → PMD pathway triggers escape responding during a predator-looming test. Furthermore, escape responding is impaired after AHAPV neuron ablation, and anxiety-like behavior as measured by the open field and elevated plus maze assays does not seem to be affected by AHAPV neuron ablation. Finally, whole-brain metabolic mapping using positron emission tomography combined with AHAPV neuron photoactivation revealed discrete activation of downstream areas involved in arousal, affective, and defensive behaviors including the amygdala and the substantia nigra. Our results indicate that AHAPV neurons are a functional glutamatergic circuit element mediating defensive behaviors, thus expanding the identity of genetically defined neurons orchestrating fight-or-flight responses. Together, our work will serve as a foundation for understanding neuropsychiatric disorders triggered by escape such as post-traumatic stress disorder (PTSD).

Unravelling the dorsal periaqueductal grey matter NMDA receptors relevance in the nitric oxide-mediated panic‑like behaviour and defensive antinociception organised by the anterior hypothalamus of male mice.

Previous studies suggested that the dorsal column of the periaqueductal grey matter (dPAG) can be a target of neural pathways from hypothalamic nuclei involved in triggering fear-related defensive responses. In turn, evidence is provided suggesting that microinjection of the nitric oxide (NO) donor SIN-1 into the anterior hypothalamus (AH) of mice evokes panic-like behaviours and fear-induced antinociception. However, it is unknown whether the dPAG of mice mediates these latter defensive responses organised by AH neurons. This study was designed to examine the role of dPAG in mediating SIN-1-evoked fear-induced defensive behavioural and antinociceptive responses organised in the AH of mice. First, neural tract tracing was performed to characterise the AH-dPAG pathways. Then, using neuropharmacological approaches, we evaluated the effects of dPAG pretreatment with either the non-selective synaptic blocker cobalt chloride (CoCl2; 1mM/0.1 μL) or the competitive N-methyl-D-aspartate (NMDA) receptor antagonist LY235959 (0.1nmol/0.1 μL) on defensive behaviours and antinociception induced by microinjections of SIN-1 in the AH of male C57BL/6 mice. AlexaFluor488-conjugated dextran-labelled axonal fibres from AH neurons were identified in both dorsomedial and dorsolateral PAG columns. Furthermore, we showed that pre-treatment of the dPAG with either CoCl2 or LY235959 inhibited freezing and impaired oriented escape and antinociception induced by infusions of SIN-1 into the AH. These findings suggest that the panic-like freezing and oriented escape defensive behaviours, and fear-induced antinociception elicited by intra-AH microinjections of SIN-1 depend on the activation of dPAG NMDA receptors.

Synaptic Innervation of the GnRH Neuron Distal Dendron in Female Mice.

GnRH neuron cell bodies are scattered throughout the basal forebrain but funnel their projections to the median eminence to release GnRH into the pituitary portal system to control fertility. Prior studies have shown that GnRH neurons located in the anterior hypothalamus send projections to the median eminence that have characteristics of both dendrites and axons. These unusual structures have been termed "dendrons." To address whether the dendron is unique to anterior hypothalamic GnRH neurons or is also a characteristic of more rostral GnRH neurons, we used viral vector‒mediated GnRH neuron‒specific tract-tracing coupled with CLARITY optical clearing. Individual rostral preoptic area GnRH neurons in female mice were identified to elaborate processes up to 4 mm in length that exhibited spines and projected all the way to the median eminence before branching into multiple short axons. The synaptic innervation patterns of distal GnRH neuron dendrons and their short axons in the vicinity of the median eminence were examined using electron microscopy. This revealed the presence of a high density of synaptic inputs to distal dendrons at the border of the median eminence. In contrast, no synapses were detected on any GnRH neuron axons. These studies demonstrate that GnRH neurons in the rostral preoptic area project dendrons to the edge of the median eminence, whereupon they branch into multiple short axons responsible for GnRH secretion. The dense synaptic innervation of these distal dendrons likely represents an efficient mechanism for controlling GnRH secretion required for fertility.

Classical and membrane-initiated estrogen signaling in an in vitro model of anterior hypothalamic kisspeptin neurons.

The neuropeptide kisspeptin is essential for sexual maturation and reproductive function. In particular, kisspeptin-expressing neurons in the anterior rostral periventricular area of the third ventricle are generally recognized as mediators of estrogen positive feedback for the surge release of LH, which stimulates ovulation. Estradiol induces kisspeptin expression in the neurons of the rostral periventricular area of the third ventricle but suppresses kisspeptin expression in neurons of the arcuate nucleus that regulate estrogen-negative feedback. To focus on the intracellular signaling and response to estradiol underlying positive feedback, we used mHypoA51 cells, an immortalized line of kisspeptin neurons derived from adult female mouse hypothalamus. mHypoA51 neurons express estrogen receptor (ER)-α, classical progesterone receptor (PR), and kisspeptin, all key elements of estrogen-positive feedback. As with kisspeptin neurons in vivo, 17β-estradiol (E2) induced kisspeptin and PR in mHypoA51s. The ERα agonist, 1,3,5-Tris(4-hydroxyphenyl)-4-propyl-1H-pyrazole, produced similar increases in expression, indicating that these events were mediated by ERα. However, E2-induced PR up-regulation required an intracellular ER, whereas kisspeptin expression was stimulated through a membrane ER activated by E2 coupled to BSA. These data suggest that anterior hypothalamic kisspeptin neurons integrate both membrane-initiated and classical nuclear estrogen signaling to up-regulate kisspeptin and PR, which are essential for the LH surge.

Physiology of the Hypothalamic-Pituitary-Testicular Complex: A View by Stages in the Light of Recent Advances

The male gonadotropic axis consists of the hypothalamus, pituitary gland and testes. Testosterone is produced by the Leydig cells in the presence of pituitary luteinizing hormone (LH). LH and FSH (follicle stimulating hormone) are themselves regulated by gonadotropin-releasing hormone or GnRH, released in pulses by the anterior hypothalamic neurons. The embryonic migration of GnRH neurons, which is a critical step in this process, is now better understood thanks to the identification of new genes that are involved. The regulation of the gonadotropic function has itself been illuminated by the identification of new peptide regulatory factors which include kisspeptins. This review traces the physiology of male gonadotrope axis based on new knowledge relating to its establishment, its operation and its regulation, allowing a better understanding of the congenital hypogonadotropic hypogonadism.

Single unit activity of the suprachiasmatic nucleus and surrounding neurons during the wake–sleep cycle in mice

The suprachiasmatic nucleus (SCN) of the mammalian hypothalamus contains a circadian clock for timing of diverse neuronal, endocrine, and behavioral rhythms, such as the cycle of sleep and wakefulness. Using extracellular single unit recordings, we have determined, for the first time, the discharge activity of individual SCN neurons during the complete wake–sleep cycle in non-anesthetized, head restrained mice. SCN neurons (n=79) were divided into three types according to their regular (type I; n=38) or irregular (type II; n=19) discharge activity throughout the wake–sleep cycle or their quiescent activity during waking and irregular discharge activity during sleep (type III; n=22). The type I and II neurons displayed a long-duration action potential, while the type III neurons displayed either a short-duration or long-duration action potential. The type I neurons discharged exclusively as single isolated spikes, whereas the type II and III neurons fired as single isolated spikes, clusters, or bursts. The type I and II neurons showed wake-active, wake/paradoxical (or rapid eye movement) sleep-active, or state-unrelated activity profiles and were, respectively, mainly located in the ventral or dorsal region of the SCN. In contrast, the type III neurons displayed sleep-active discharge profiles and were mainly located in the lateral region of the SCN. The majority of type I and II neurons tested showed an increase in discharge rate following application of light to the animal’s eyes. Of the 289 extra-SCN neurons recorded, those displaying sleep-active discharge profiles were mainly located dorsal to the SCN, whereas those displaying wake-active discharge profiles were mainly located lateral or dorsolateral to the SCN. This study shows heterogeneity of mouse SCN and surrounding anterior hypothalamic neurons and suggests differences in their topographic organization and roles in mammalian circadian rhythms and the regulation of sleep and wakefulness.

An aggression-specific cell type in the anterior hypothalamus of finches

The anterior hypothalamus (AH) is a major integrator of neural processes related to aggression and defense, but cell types in the AH that selectively promote aggression are unknown. We here show that aggression is promoted in a very selective and potent manner by dorsal AH neurons that produce vasoactive intestinal polypeptide (VIP). Fos activity in a territorial finch, the violet-eared waxbill (Estrildidae: Uraeginthus granatina) is positively related to aggression in the dorsal AH, overlapping a population of VIP-producing neurons. VIP is known to promote territorial aggression in songbirds, and thus we used antisense oligonucleotides to selectively block AH VIP production in male and female waxbills. This manipulation virtually abolishes aggression, reducing the median number of displacements in a 3-min resident-intruder test from 38 in control subjects to 0 in antisense subjects. Notably, most antisense and control waxbills exhibit an agonistic response such as a threat or agonistic call within 2 s of intrusion. Thus, antisense subjects clearly classify intruders as offensive, but fail to attack. Other social and anxiety-like behaviors are not affected and VIP cell numbers correlate positively with aggression, suggesting that these cells selectively titrate aggression. Additional experiments in the gregarious zebra finch (Estrildidae: Taeniopygia guttata) underscore this functional specificity. Colony-housed finches exhibit significant reductions in aggression (primarily nest defense) following AH VIP knockdown, but no effects are observed for social preferences, pair bonding, courtship, maintenance behaviors, or anxiety-like behaviors. To our knowledge, these findings represent a unique identification of an aggression-specific cell type in the brain.

The effects of the alpha‐2 adrenoreceptor agonist clonidine on the activity of thermally classified neurons in anterior hypothalamus of the rat

In response to infection, noradrenergic vagal afferents to the hypothalamus may be responsible for a rapid biphasic shift in thermoregulatory control. An initial hypothermic shift may result from the activation of alpha-2 adrenoreceptors, which is followed by an enduring hyperthermic response that is initiated by activation of alpha-1 andrenoreceptors and prolonged by the presence of prostaglandin E2 (PGE2). While previous studies from our lab have characterized the effects of PGE2 (Ranels & Griffin, 2003) and the alpha-1 agonist Cirazoline (Imbery et al., 2007), this study recorded the in vitro single-unit activity of thermally classified anterior hypothalamic neurons in response to the alpha-2 adrenoreceptor agonist Clonidine (100 μM). Based on their responses to temperature, warm sensitive neurons (m > 0.8 impulses.s-1.oC-1) showed significant increases in firing rate while temperature insensitive neurons showed significant decreases in firing rate. These changes would result in a hypothermic response according to Hammel's model, demonstrating the role of this adrenoreceptor subtype in temperature regulation. This research was supported by grants from the NIH (NS053794, NS065461 & NS053794-S1) and in part by a Howard Hughes Medical Institute grant through the Undergraduate Science Program to the College of William and Mary.

The Effects of leptin on thermosensitive neurons in the anterior hypothalamus of the rat

The hormone leptin is thought to play a role in regulating body fat and metabolism in mammals through its ability to alter the activity of anterior hypothalamus (AH) neurons that play a role in homeostatic control. Recent studies have shown that when leptin is injected either intravenously or into the ventricles in rodents, an increase in body temperature is detected, which may be a possible through which leptin inhibits feeding behavior. On the basis of current models for thermoregulation, we hypothesized that warm sensitive neurons in the AH would exhibit a decrease in firing rate in response to leptin while temperature insensitive neurons would respond with an increase in firing rate. Using a tissue slice preparation, the extracellular activity of AH neurons was recorded to classify their responses to temperature and to leptin (100 μM). The majority of warm sensitive neurons decreased their firing rates. While nearly 50% of the temperature insensitive neurons responded with an increase in firing rate, the majority of the remaining temperature insensitive neurons showed decreases in firing rate. This contrast in responses may relate to the specific efferent connections of these thermoregulatory neurons which will be characterized in a future study. This research was supported by grants from the NIH (NS053794, NS065461 & NS053794-01S1) and a Howard Hughes Medical Institute grant to the College of William and Mary.

The effects of Cirazoline, an alpha-1 adrenoreceptor agonist, on the firing rates of thermally classified anterior hypothalamic neurons in rat brain slices

Peripheral exposure to LPS induces a biphasic fever thought to be initiated via vagal afferents to the preoptic area of the anterior hypothalamus (POAH), an important thermoregulatory control center in the brain. Previous studies have shown that norepinephrine synaptically mediates this Prostaglandin E 2 (PGE 2)-dependent change in temperature through the selective activation of alpha-2 adrenoreceptors (AR). However, there is clear evidence that alpha-1 AR activation of thermoregulatory hypothalamic neurons will result in a rapid hyperthermia that is not dependent on PGE 2. This direct action of norepinephrine in the POAH was tested in the present study by recording the single-unit activity of POAH neurons in a tissue slice preparation from the adult male rat, in response to temperature and the selective alpha-1 AR agonist Cirazoline (1–100 μM). Neurons were classified as either warm sensitive or temperature insensitive. Warm sensitive neurons responded to Cirazoline with a decrease in firing rate, while temperature insensitive neurons showed a firing rate increase. These responses are similar to those reported for PGE 2 and suggest that both warm sensitive and temperature insensitive neurons in the POAH are important in mediating this alpha-1 AR-dependent hyperthermic shift in body temperature.

Laminar organization of the early developing anterior hypothalamus

The bHLH-PAS transcription factor SIM1 is required for the development of neurons of the anterior hypothalamus (AH). In order to dissect this developmental program, we compared gene expression in the AH of E12.5 Sim1 +/+ and Sim1 − /− littermates using an oligonucleotide-based microarray. Our analysis identified 48 genes that were downregulated and 8 genes that were upregulated. We examined the expression pattern of 10 of the identified genes – Cart, Cbln1, Alcam, Unc-13c, Rgs4, Lnx4, Irx3, Sax1, Ldb2 and Neurod6 – by in situ hybridization in E12.5 embryos. All of these genes are expressed in domains that are contained within that of Sim1 and their expression is changed in Sim1 − /− embryos as predicted by the microarray analysis. Classical dating studies have established that the hypothalamus follows an “outside–in” pattern of neurogenesis, with neurons of the lateral hypothalamus being born before the medial ones. Analysis of the genes identified in this microarray study showed that the developing AH is characterized by different layers of gene expression that most likely correspond to distinct waves of neurogenesis. In addition, our analysis suggests that Sim1 function is required for the production or the survival of postmitotic neurons as well as for correct positioning of AH neurons.

IL‐1β induces a MyD88‐dependent and ceramide‐mediated activation of Src in anterior hypothalamic neurons

The proinflammatory cytokine interleukin 1beta (IL-1beta), acting at IL-1R1 receptors, affects neuronal signaling under both physiological and pathophysiological conditions. The molecular mechanism of the rapid synaptic actions of IL-1beta in neurons is not known. We show here that within minutes of IL-1beta exposure, the firing rate of anterior hypothalamic (AH) neurons in culture was inhibited. This effect was prevented by pre-exposure of the cells to the Src family inhibitor, PP2, suggesting the involvement of Src in the hyperpolarizing effects of IL-1beta. The IL-1beta stimulation of neurons induced a rapid increase in the phosphorylation of the tyrosine kinase Src and kinase suppressor of Ras (ceramide activated protein kinase (CAPK)/KSR) in neurons grown on glia from IL-1RI(-/-) mice. These effects of IL-1beta were dependent on the association of the cytosolic adaptor protein, MyD88, to the IL-1 receptor, and on the activation of the neutral sphingomyelinase, leading to production of ceramide. A cell-permeable analog of ceramide mimicked the effects of IL-1beta on the cultured AH neurons. These results suggest that ceramide may be the second messenger of the fast IL-1beta actions in AH neurons, and that this IL-1beta/ceramide pathway may underlie the fast non-transcription-dependent, electrophysiological effects of IL-1beta observed in AH neurons in vivo.

Point-Counterpoint: Heat-induced membrane depolarization of hypothalamic neurons: a putative/an unlikely mechanism of central thermosensitivity

heating and cooling various sites of the preoptic area and anterior hypothalamus (PO/AH) of mammals with fine thermodes reflexively evoke thermoregulatory responses, indicating that many central thermostats regulate temperature (T) of the brain ([16][1]). In PO/AH, heating- and cooling-activated

Evidence suggesting that angiotensins released not via synaptic inputs are involved in the basal activity of anterior hypothalamic neurons in rats

Previously, we have demonstrated that angiotensin II-sensitive neurons exist in the anterior hypothalamic area (AHA) and that these neurons are tonically activated by endogenous angiotensins in rats. Chemical stimulation of the lateral septal area (LSV) and medial amygdaloid nucleus (MeA), and intracerebroventricular injection of hypertonic saline, activated AHA angiotensin II-sensitive neurons. To investigate mechanisms of the basal activity of AHA angiotensin II-sensitive neurons, we examined the effect of N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide hydrochloride (W7), a calmodulin inhibitor, applied onto AHA neurons on the basal activity and the stimulus-evoked activation of these neurons. Male Wistar rats were anesthetized and artificially ventilated. Extracellular potentials were recorded from single neurons in the AHA. Microinjections of carbachol into the LSV and corticotropin-releasing factor into the MeA, and intracerebroventricular injection of hypertonic saline, activated AHA angiotensin II-sensitive neurons. These three kinds of injection-induced activations of AHA neurons were abolished by pressure application of W7 onto the same neurons, while the calmodulin inhibitor did not affect the increase in firing of AHA neurons induced by pressure application of angiotensin II onto the same neurons. The pressure application of W7 did not affect the basal activity of AHA angiotensin II-sensitive neurons, whereas the angiotensin AT1 receptor antagonist losartan similarly applied inhibited it. These findings suggest that the basal activity of AHA angiotensin II-sensitive neurons is mediated by angiotensins released not via synaptic inputs.

MyD88-dependent and -independent signaling by IL-1 in neurons probed by bifunctional Toll/IL-1 receptor domain/BB-loop mimetics

Interleukin (IL)-1beta is a pluripotent proinflammatory cytokine that signals through the type-I IL-1 receptor (IL-1RI), a member of the Toll-like receptor family. In hypothalamic neurons, binding of IL-1beta to IL-1RI mediates transcription-dependent changes that depend on the recruitment of the cytosolic adaptor protein myeloid differentiation primary-response protein 88 (MyD88) to the IL-1RI/IL-1 receptor accessory protein (IL-1RAcP) complex through homomeric Toll/IL-1 receptor (TIR)-TIR interactions. Through design and synthesis of bifunctional TIR mimetics that disrupt the interaction of MyD88 with the IL-1RI/IL-1RAcP complex, we analyzed the involvement of MyD88 in the signaling of IL-1beta in anterior hypothalamic neurons. We show here that IL-1beta-mediated activation of the protein tyrosine kinase Src depended on a MyD88 interaction with the IL-1RI/IL-1RAcP complex. The activation of the protein kinase Akt/PKB depended on the recruitment of the p85 subunit of PI3K to IL-1RI and independent of MyD88 association with the IL-1RI/IL-1RAcP complex. These bifunctional TIR-TIR mimetics represent a class of low-molecular-weight compounds with both an antiinflammatory and neuroprotective potential. These compounds have the potential to inhibit the MyD88-dependent proinflammatory actions of IL-1beta, while permitting the potential neuronal survival supporting actions mediated by the MyD88-independent activation of the protein kinase Akt.

Angiotensin II sensitivity of anterior hypothalamic area neurons is enhanced in both spontaneously hypertensive rats and Dahl salt-sensitive rats

We have previously demonstrated that some neurons in the anterior hypothalamic area (AHA) are tonically activated by endogenous angiotensins. Furthermore, we have demonstrated that intracerebroventricular injection of hypertonic saline increases the firing rate of AHA angiotensin II-sensitive neurons via angiotensins and that the central sodium-induced activation of AHA neurons is enhanced in spontaneously hypertensive rats (SHR) and Dahl salt-sensitive (Dahl S) rats. In this study, we examined whether sensitivities of AHA angiotensin II-sensitive neurons to angiotensin II are enhanced in SHR and Dahl S rats as compared with their respective controls. Male 15- to 16-week-old SHR and age-matched Wistar Kyoto rats (WKY), and male 15- to 16-week-old Dahl S rats and Dahl R rats were anesthetized and artificially ventilated. Extracellular potentials were recorded from single neurons in the AHA. In SHR, pressure application of angiotensin II (3 × 10 −9 to 3 × 10 −8 M) onto AHA angiotensin II-sensitive neurons increased their firing rate in a concentration-dependent manner. In WKY, only the highest concentration of angiotensin II increased the firing rate, while the lower concentrations of angiotensin II did not affect it. In Dahl S rats, pressure application of angiotensin II (10 −8 and 3 × 10 −8 M) onto AHA neurons increased their firing rate, while angiotensin II (3 × 10 −9 M) did not affect it. In Dahl R rats, the highest concentration of angiotensin II increased the firing rate, while the lower concentrations of angiotensin II did not affect it. These findings indicate that the sensitivity of AHA neurons to angiotenisn II is enhanced in SHR and Dahl S rats as compared with their respective controls.

Modulation of spiking of neurons of the cat anterior hypothalamus induced by experimental shifts in the osmolarity of the blood plasma

We examined changes in the impulse activity (IA) generated by neurons of the anterior hypothalamus (including the preoptic region) resulting from infusions of hyper-and hypotonic NaCl solutions (3.0 and 0.2%, respectively; hyper-and hypoosmotic stimulations, respectively); the infused volumes did not exceed 200 µl. The effects of hyper-and hypoosmotic stimulations were studied in detail in 83 and 88 neurons, respectively. In 31.2% (26 cells) and 29.6% (26 cells) of the neurons of the above groups, these stimulations evoked changes in the IA frequency greater than +40 or −40% of the mean background IA frequency. In approximately 50% of the responding neurons in each group, such shifts in the IA frequency were observed in the course of infusions of test solutions (5 sec long) and within the subsequent 5 min after termination of the infusion. In another 50% of the neurons, changes in the IA frequency occurred within the afterperiod (30 sec long); these shifts could develop exclusively within the latter interval, or these changes accompanied an initial early reaction. In general, activating responses dominated (they were observed in 65% of the cases where test stimulations of both modalities were used). The possible aspects of the involvement of neurons of the anterior hypothalamus in the control of the water/salt balance in the organism are discussed.

Posterior hypothalamus cholinergic stimulation-induced activation of anterior hypothalamic area neurons is enhanced in spontaneously hypertensive rats

We have previously demonstrated that some neurons in the anterior hypothalamic area (AHA) are tonically activated by endogenous angiotensins in rats and that activities of these AHA neurons are enhanced in spontaneously hypertensive rats (SHR). In addition, we have demonstrated that cholinergic mechanisms in the posterior hypothalamic nucleus (PHN) are involved in the activation of AHA angiotensin-II-sensitive neurons. It has been suggested that cholinergic function in the posterior hypothalamus is enhanced in SHR and that this hyperactivity plays a role in hypertension in SHR. In the present study, we examined whether the PHN cholinergic stimulation-induced activation of AHA angiotensin-II-sensitive neurons is altered in SHR. Male 15- to 16-week-old SHR and age-matched Wistar Kyoto rats (WKY) were anesthetized and artificially ventilated. Extracellular potentials were recorded from single neurons in the AHA. Microinjection of the cholinoceptor agonist carbachol, the cholinesterase inhibitor physostigmine and the excitatory amino acid glutamate into the PHN caused increases in firing rate of AHA angiotensin-II-sensitive neurons in anesthetized WKY and SHR. The increase in firing rate of AHA neurons induced by these drugs was enhanced in SHR as compared to WKY. The enhancement of the physostigmine-induced activation of AHA neurons in SHR was similar to that of the carbachol-induced activation of AHA neurons in SHR. The enhancement of the glutamate-induced activation of AHA neurons in SHR was similar to that of the carbachol-induced activation of AHA neurons in SHR. Microinjection of scopolamine, a cholinoceptor antagonist, into the PHN caused a small but significant decrease of firing rate of AHA angiotensin-II-sensitive neurons in SHR but not in WKY. These findings indicate that the PHN cholinergic stimulation-induced activation of AHA angiotensin-II-sensitive neurons is enhanced in SHR and that PHN cholinergic mechanisms are involved in tonic activation of angiotensin-II-sensitive neurons in the AHA of SHR. It appears that the enhancement of the PHN cholinergic stimulation-induced activation of AHA neurons in SHR results mainly from the enhanced neural reactivity to angiotensins in AHA neurons of SHR.

Cholinergic systems in the posterior hypothalamic nucleus are involved in blood pressure decrease-induced excitation of anterior hypothalamic area neurons in rats

Previously, we have demonstrated that decreases in blood pressure induced by intravenous nitroprusside increase the firing rate of angiotensin II-sensitive neurons in the anterior hypothalamic area (AHA) of rats and that this increase of neural firing rate is blocked by the pressure application of losartan onto the same neurons. It has been suggested that acetylcholine in the posterior hypothalamic nucleus (PHN) serves as a neurotransmitter in a pathway which can modulate baroreceptor reflexes. In the present study, we examined whether acetylcholine in the PHN is involved in the nitroprusside-induced increase of the firing of angiotensin II-sensitive neurons in the AHA of rats. Male Wistar rats were anesthetized and artificially ventilated. Extracellular potentials were recorded from single neurons in the AHA. Decreases in blood pressure induced by intravenous nitroprusside (100 ug/kg) increased the firing rate of AHA angiotensin II-sensitive neurons. The nitroprusside-induced increase of firing rate of AHA neurons was inhibited by PHN microinjection of the cholinoceptor antagonist scopolamine and potentiated by PHN microinjection of the cholinesterase inhibitor physostigmine. Microinjections of carbachol and glutamate into the PHN caused increases of firing rate of AHA neurons. The carbachol-induced but not glutamate-induced increase of unit firing was abolished by the pre-microinjection of scopolamine into the same sites of the PHN. These findings suggest that the nitroprusside-induced increase of firing of AHA neurons is mediated via acetylcholine at the level of the PHN.

Electrophysiological properties and thermosensitivity of mouse preoptic and anterior hypothalamic neurons in culture

Responses of mouse preoptic and anterior hypothalamic neurons to variations of temperature are key elements in regulating the setpoint of homeotherms. The goal of the present work was to assess the relevance of culture preparations for investigating the cellular mechanisms underlying thermosensitivity in hypothalamic cells. Our working hypothesis was that some of the main properties of preoptic/anterior hypothalamic neurons in culture are similar to those reported by other authors in slice preparations. Indeed, cultured preoptic/anterior hypothalamic neurons share many of the physiological and morphological properties of neurons in hypothalamic slices. They display heterogenous dendritic arbors and somatic shapes. Most of them are GABAergic and their activity is synaptically driven by the activation of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid/kainate receptors. Active membrane properties include a depolarizing “sag” in response to hyperpolarization, and a low threshold spike, which is present in a majority of cells and is generated by T-type Ca 2+ channels. In a fraction of the cells, the low threshold spike repeats rhythmically, either spontaneously, or in response to depolarization. The background synaptic noise in cultured neurons is characterized by the presence of numerous postsynaptic potentials which can be easily distinguished from the baseline, thus providing an opportunity for assessing their possible roles in thermosensitivity. An unexpected finding was that GABA-A receptors can generate both hyper- and depolarizing postsynaptic potentials in the same neuron. About 20% of the spontaneously firing preoptic/anterior hypothalamic neurons are warm-sensitive. Warming (32–41°C) depolarizes some cells, a phenomenon which is Na +-dependent and tetrodotoxin-insensitive. The increased firing rate of warm-sensitive cells in response to warming can be prepotential and/or synaptically driven. Overall, our data suggest that a warm-sensitive phenotype is already developed in cultured cells. Therefore, and despite obvious differences in their networks, cultured and slice preparations of hypothalamic neurons can complement each other for further studies of warm-sensitivity at the cellular and molecular level.