Preoptic Neurons Research Articles

Perchance to sleep…

Why and how do we sleep? The history of sleep research is full of stories of dedicated human researchers living in caves, and experiments on animal brainstems, but we still do not really know the answers to the fundamental questions of how and why (and therefore also why not). The latest research, however, is beginning to confirm the answer to how.From the results of in vivo animal experiments, neurons that induce the onset of sleep are thought to reside in the ventrolateral preoptic nucleus (VLPO) at the base of the forebrain1xActivation of ventrolateral preoptic neurons during sleep. Sherin, J.E. et al. Science. 1996; 271: 216–219Crossref | PubMedSee all

Effect of bicuculline on K+ currents in rat medial preoptic neurons

Effect of bicuculline on K+ currents in rat medial preoptic neurons

Sympathetic‐related neurons in the preoptic region of the rat identified by viral transneuronal labeling

The viral transneuronal labeling method was used to localize sympathetic-related neurons in the preoptic region following pseudorabies virus (PRV) injections into either the superior cervical ganglion, stellate ganglion, celiac ganglion, or adrenal gland of rats. A general pattern of infection was detected. First, neuronal labeling was found in the medial preoptic area, medial preoptic nucleus, median preoptic nucleus, and lateral preoptic area, and then it spread to the anteroventral periventricular, anteroventral preoptic, and parastrial nuclei. Finally, the forebrain circumventricular organs: organum vasculosum of the lamina terminalis (OVLT) and subfornical organ (SFO) became infected. Neuropeptide-containing preoptic neurons were analyzed following PRV injections in the stellate ganglion. Some thyrotropin-releasing hormone and neurotensin neurons were labeled, but none of the calcitonin gene-related peptide, cholecystokinin, corticotropin-releasing factor, galanin, luteinizing hormone-releasing hormone, enkephalin, substance P, or tyrosine hydroxylase neurons were PRV infected. Two major sympathetic networks appear to be represented in the preoptic region. One is linked to the OVLT, SFO, and anteroventral third ventricular (AV3V) region, sites previously implicated in fluid and electrolyte balance as well as cardiovascular control. The other descending sympathetic pathway appears to target the medial preoptic nucleus as its key nodal point, receiving inputs from infralimbic cortex and limbic regions, such as the lateral septum, medial nucleus of the amygdala, subiculum, and amygdalohippocampal area, and then, projecting caudally to the hypothalamus and brainstem. This second sympathetic network may subserve affiliative, defensive and sexual behaviors. J. Comp. Neurol. 414:361–378, 1999. © 1999 Wiley-Liss, Inc.

Sympathetic-related neurons in the preoptic region of the rat identified by viral transneuronal labeling

The viral transneuronal labeling method was used to localize sympathetic-related neurons in the preoptic region following pseudorabies virus (PRV) injections into either the superior cervical ganglion, stellate ganglion, celiac ganglion, or adrenal gland of rats. A general pattern of infection was detected. First, neuronal labeling was found in the medial preoptic area, medial preoptic nucleus, median preoptic nucleus, and lateral preoptic area, and then it spread to the anteroventral periventricular, anteroventral preoptic, and parastrial nuclei. Finally, the forebrain circumventricular organs: organum vasculosum of the lamina terminalis (OVLT) and subfornical organ (SFO) became infected. Neuropeptide-containing preoptic neurons were analyzed following PRV injections in the stellate ganglion. Some thyrotropin-releasing hormone and neurotensin neurons were labeled, but none of the calcitonin gene-related peptide, cholecystokinin, corticotropin-releasing factor, galanin, luteinizing hormone-releasing hormone, enkephalin, substance P, or tyrosine hydroxylase neurons were PRV infected. Two major sympathetic networks appear to be represented in the preoptic region. One is linked to the OVLT, SFO, and anteroventral third ventricular (AV3V) region, sites previously implicated in fluid and electrolyte balance as well as cardiovascular control. The other descending sympathetic pathway appears to target the medial preoptic nucleus as its key nodal point, receiving inputs from infralimbic cortex and limbic regions, such as the lateral septum, medial nucleus of the amygdala, subiculum, and amygdalohippocampal area, and then, projecting caudally to the hypothalamus and brainstem. This second sympathetic network may subserve affiliative, defensive and sexual behaviors.

Bicuculline-sensitive potassium currents in rat medial preoptic neurons

Bicuculline-sensitive potassium currents in rat medial preoptic neurons

The Possible Role of c-fos Protein in Hypothalamus in Sleep Disturbance in Chronic Uremic Rats

Sleep disturbance is very common in patients with chronic renal failure, but its mechanism is not clear. The activity of c-fos protein (FOS) in ventrolateral preoptic neurons (VLPO) is associated with the sleep pattern. The purpose of this study was to evaluate the relationship between sleep disturbance and the expression of FOS in VLPO of chronic uremic rats. Chronic uremia was induced by the 5/6 nephrectomized model. The movements of the rats were measured with infrared monitoring during the daytime (8.00–20.00) and nighttime (20.00–8.00). Rats were killed at 10.00 or 16.00 h for the daytime (uremic rats 7, control 8) and at 22.00 h for the nighttime (uremic rats 7, control 9). The expression of FOS in VLPO was examined with the immunohistochemical method. The number of recorded daytime movements in uremic rats was significantly higher than in control rats (458 ± 185 vs. 222 ± 41, p < 0.001), but the number of recorded nighttime movements in uremic rats was lower than in control rats (949 ± 430 vs. 1,618 ± 261, p < 0.001). In the daytime, the number of FOS immunoreactive cells in uremic rats was lower than in control rats (18.4 ± 5.3 vs. 42.8 ± 6.3, p < 0.001), but there was no difference between two groups in the nighttime (10.8 ± 8.4 vs. 12.5 ± 5.1, p = 0.62). There was a strong negative correlation between the number of recorded movements and the number of FOS immunoreactive cells in VLPO (r = –0.700, p < 0.001). This finding suggests that sleep disturbances in chronic uremic rats might be related to the decreased expression of FOS in VLPO.

Synaptic contacts between nerve terminals originating from the ventrolateral medullary catecholaminergic area and median preoptic neurons projecting to the paraventricular hypothalamic nucleus

A significant role of catecholaminergic projection to the median preoptic nucleus (POMe) which activates vasopressin-producing cells of the paraventricular hypothalamic nucleus (PVN) has been suggested. We investigated the existence of the synaptic contacts between catecholaminergic fibers from the ventrolateral medulla and the POMe neurons projecting to the PVN. Rats received a retrograde tracer in the PVN and subsequently an anterograde tracer into the catecholaminergic area of the ventrolateral medulla at the level of the area postrema. In the POMe, anterogradely labeled nerve terminals were found to make axo-somatic and axo-dendritic synaptic contacts onto retrogradely labeled neurons. Additional studies in which a retrograde tracer was injected into the POMe revealed that almost all retrogradely labeled neurons in the ventrolateral medulla at the level of the area postrema were immunoreactive to tyrosine hydroxylase, suggesting that projection to the POMe from the ventrolateral medulla is largely limited to catecholamine neurons. These results provide, for the first time, direct evidence that catecholaminergic inputs from the ventrolateral medulla affect POMe neurons projecting to the PVN by way of direct synaptic contact.

Spontaneous Activity of Preoptic Neurons in Slice Preparations of the Hypothalamus of European Hamsters (Cricetus cricetus) and Wistar Rats under Different States of Hypothermia

Hypothermia was induced in European hamsters (hibernators) and Wistar rats (nonhibernators), and changes in the firing rate and spike duration of extracellularly recorded action potentials were investigated in hypothalamic slicesin vitro.At slice temperatures close to normal body temperature (37 ± 3°C), 32 and 57% of spontaneously active neurons in the medial preoptic area were classified as warm-sensitive in rats and hamsters, respectively. With decreasing slice temperature, the number of active neurons decreased progressively without a significant difference between rats and hamsters. At a slice temperature of 10°C, 57% of all hypothalamic neurons in rats and 42% in hamsters were still spontaneously active. The average temperature at which activity ceased completely when the temperature was decreased further (the cut-off temperature) was 7.9 ± 0.3°C (n= 14) in rats but was significantly lower at 4.9 ± 0.4°C (n= 8) in hamsters (P< 0.001). Firing rates and temperature coefficients did not differ in their temperature dependence between rats and hamsters. Action potential duration increased with decreasing slice temperature in both species, but the increase in duration was significantly greater in rats.

Changes of characteristics of preoptic neurons and NA metabolism in hypothalamus of ground squirrel (Citelleus Dautieus) in different seasons and hibernating phases

The unit firing activities of neurons in the preoptic area (POA) of ground squirrel hypothalamic tissue slices were recorded and the metabolism of NA in hypothalamus was measured with high performance liquid chromatography (HPLC). Thermosensitivity, proportions, the critical temperature (Tc) and the lowest temperature (TL) of firing activity of the above-mentioned neurons, and NA metabolism in hypothalamus were compared in different seasons and hibernating phases. In comparison with that in summer euthermar, it was shown that (i) the percentage and thermosensitivity of the POA neurons varied respectively in the hibernating phases; (ii) TL and Tc of the POA neurons in winter, both euthermar and hibernation, were markedly decreased; (iii) the POA neurons in hibernation became much more sensitive to NA, and the response of cold-sensitive neurons to NA changed from inhibiting pattern in summer to exciting one in hibernation; (iv) the contents and metabolism of NA in hypothalamus decreased significantly in the entering phase and deep hibernation phase, while the metabolism of NA increased remarkably in the arousal phase. These changes might explain the regulatory mechanism how ground squirrel actively decreases body temperature (Tb) in entering into hibernation and quickly recovers body temperature in arousal phase.

ANG II AT1 receptors induce depolarization and inward current in rat median preoptic neurons in vitro

To examine ANG II receptors in rat median preoptic (MnPO) neurons, we used patch-clamp whole cell recordings in a parasagittal brain slice preparation. Lucifer yellow-filled neurons displayed a simple morphology with two to three aspiny dendrites. Bath-applied ANG II (1-2,000 nM for 30 s) induced a response in 37 of 70 cells. In current-clamp recordings, cells displayed a prolonged (10- to 30-min) depolarizing plateau with action potential discharges and an associated reduction in postburst afterhyperpolarization and spike frequency adaptation. In voltage-clamp recordings (holding potential -65 mV), cells displayed tetrodotoxin-resistant inward currents of 7. 6 +/- 1.9 (n = 5), 9.9 +/- 1.9 (n = 9), and 9.2 +/- 2.2 pA (n = 6) at 10, 200, and 2,000 nM, respectively. Responses were blockable by pretreatment with losartan (2 microM; n = 6) but not by PD-123177 (20 microM; n = 3). Net ANG II-induced current revealed a 7.8 +/- 0. 9% reduction in membrane conductance, decreasing but not reversing at hyperpolarized levels. Neurons expressing a strong hyperpolarization-activated, time-independent inward rectification were more likely to respond to ANG II. There was no correlation between the response of a neuron to ANG II and its response to norepinephrine.

Heterogeneous presynaptic Ca2+ channel types triggering GABA release onto medial preoptic neurons from rat

1. Voltage-dependent Ca2+ channels triggering GABA release onto neurons from the medial preoptic nucleus of rat were investigated. Acutely dissociated neurons with adherent functional synaptic terminals were investigated by tight-seal whole-cell recordings from the postsynaptic cells. 2. Spontaneous current events similar to miniature postsynaptic currents were recorded. They were blocked by bicuculline (100 microM), showed a roughly unimodal amplitude distribution and a reversal potential consistent with a Cl- current, and were therefore attributed to GABAA receptors activated by synaptically released GABA. 3. Application of 140 mM KCl, expected to depolarize presynaptic terminals, evoked currents that were ascribed to a more massive release of GABA. The KCl-induced synaptic currents were abolished in Ca2+-free solutions and showed a roughly hyperbolic relation to external Ca2+ concentration with half-saturation at 0.15 mM. They further depended on the concentration of applied KCl in a way expected for high-threshold Ca2+ channels. 4. The KCl-evoked synaptic currents were completely blocked by 200 microM Cd2+, but only partially blocked by 200 microM Ni2+. The KCl-evoked synaptic currents were insensitive to the L-type Ca2+ channel blocker nifedipine (10 microM). However, the synaptic currents were sensitive to either 1 microM omega-conotoxin GVIA, 25 nM omega-agatoxin IVA or 1 microM omega-conotoxin MVIIC. 6. It was concluded that, in many presynaptic terminals, the Ca2+ influx triggering GABA release onto medial preoptic neurons is mainly mediated by one predominant type of high- threshold Ca2+ channel that may be either of N-, P- or Q-type. 7. It was further concluded that terminals with similar predominant channel types often were clustered on the same postsynaptic cell.

Studies on the sleep-promoting mechanisms mediated by adenosine A 2A receptors

Daily cycles of wakefulness and sleep are regulated by coordinated interactions between wakefulness- and sleep-regulating neural circuitry. Wakefulness is associated with neuronal activity in cholinergic neurons in the brainstem and basal forebrain, monoaminergic neurons in the brainstem and posterior hypothalamus, and hypocretin (orexin) neurons in the lateral hypothalamus that act in a coordinated manner to stimulate cortical activation on the one hand and behavioral arousal on the other hand. Each of these neuronal groups subserves distinct aspects of wakefulness-related functions of the brain. Normal transitions from wakefulness to sleep involve sleep-related inhibition and/or disfacilitation of the multiple arousal systems. The cell groups that shut off the network of arousal systems, at sleep onset, occur with high density in the ventral lateral preoptic area (VLPO) and the median preoptic nucleus (MnPN) of the hypothalamus. Preoptic neurons are activated during sleep and exhibit sleep--wake state-dependent discharge patterns that are reciprocal of that observed in several arousal systems. Neurons in the VLPO contain the inhibitory neuromodulator, galanin, and the inhibitory neurotransmitter, gamma-aminobutyric acid (GABA). The majority of MnPN sleep-active neurons synthesize GABA. VLPO and MnPN neurons are sources of projections to arousal-regulatory systems in the posterior and lateral hypothalamus and the rostral brainstem. Mechanisms of sleep induction by these nuclei are hypothesized to involve GABA-mediated inhibition of multiple arousal systems. Normal cycling between discrete behavioral states is mediated by the combined influence of a sleep need that increases with continued wakefulness and an intrinsic circadian oscillation. This chapter will review anatomical and functional properties of populations of sleep- /wake-regulating neurons, focusing on recent findings supporting functional significance of the VLPO and MnPN in the regulation of sleep--wake homeostasis. Evidence indicating that MnPN and VLPO neurons have different, but complementary sleep regulatory functions will be summarized. Potential mechanisms that function to couple activity in these two sleep-regulatory neurons will be discussed.

Median preoptic nucleus neurons: an in vitro patch-clamp analysis of their intrinsic properties and noradrenergic receptors in the rat

The median preoptic nucleus is recognized as an important forebrain site involved in hydromineral and cardiovascular homeostasis. In the present study, whole cell patch-clamp recordings in parasagittal slices of adult rat brain were used to obtain information on the properties of median preoptic neurons. Lucifer Yellow-labelled cells demonstrated small ovoid somata with two to three aspiny main dendrites and axons that branched sparingly. Median preoptic neurons displayed varying degrees of hyperpolarization-activated time-dependent and/or time-independent inward rectification, and 86% of cells demonstrated low threshold spikes. Median preoptic nucleus is known to receive a prominent noradrenergic innervation from the medulla, and 59% of 156 tested neurons were found to respond to bath applied noradrenaline (1–100 μM). In the majority ( n=62) of cells, the response was an α 2 adrenoreceptor-mediated, tetrodotoxin-resistant, membrane hyperpolarization that was associated with a 43±6% increase in membrane conductance. The net noradrenaline-induced current (5–45 pA) was inwardly rectifying, cesium-resistant but barium sensitive. Current reversal at −102±4 mV in 3.1 mM [K] o and −62±3 mV in 10 mM [K] o implied opening of potassium channels. By contrast, a minority ( n=27) of cells responded to noradrenaline with an α 1-mediated, tetrodotoxin-resistant membrane depolarization. These observations imply a functional diversity among median preoptic neurons, and the prevalence of hyperpolarizing α 2 and, to a lesser extent, depolarizing α 1 adrenoreceptors on median preoptic neurons suggests that noradrenergic inputs can exert a prominent influence on their cellular excitability.

Innervations of median preoptic neurons projecting to the paraventricular hypothalamic nucleus by nerve terminals immunoreactive to β-endorphin

Innervations of median preoptic neurons projecting to the paraventricular hypothalamic nucleus by nerve terminals immunoreactive to β-endorphin

Synaptic connections between substance P-containing axons and estrogen receptor-synthesizing neurons in the medial preoptic area of the rat brain

Dual-label immunocytochemical procedures were employed to provide ultrastructural evidence for the presence of substance P (SP) in afferents to estrogen-receptive neurons in the medial preoptic area (MPO) of the female rat. SP-immunoreactive axon terminals were observed to innervate the periventricular (PvPO) and medial (MPN) preoptic nuclei of the MPO densely, and to form synaptic connections at these sites with neurons which contain estrogen receptors in their nucleus. These results indicate that estrogen-receptive preoptic neurons may be regulated by SP-containing neuronal pathways via synaptic mechanisms.

Currents evoked by GABA and glycine in acutely dissociated neurons from the rat medial preoptic nucleus

The responses of acutely dissociated medial preoptic neurons to application of GABA and glycine were studied using the perforated-patch whole-cell recording technique under voltage-clamp conditions. GABA, at a concentration of 1 mM, evoked outward currents in all cells ( n=33) when studied at potentials positive to −80 mV. The I– V relation was roughly linear. The currents evoked by GABA were partially blocked by 25–75 μM picrotoxin and were also partially or completely blocked by 100–200 μM bicuculline. Glycine, at a concentration of 1 mM, did also evoke outward currents in all cells ( n=12) when studied at potentials positive to −75 mV. The I– V relation was roughly linear. The currents evoked by glycine were largely blocked by 1 μM strychnine. In conclusion, the present work demonstrates that neurons from the medial preoptic nucleus of rat directly respond to the inhibitory transmitters GABA and glycine with currents that can be attributed to GABA A receptors and glycine receptors respectively.

Intracellular recording of magnocellular preoptic neuron responses to olfactory brain

The magnocellular preoptic nucleus of the rat supplies centrifugal input to the olfactory bulb as well as projecting to other olfactory-related areas. The extent to which the piriform and entorhinal cortices can influence the activity of magnocellular preoptic neurons and hence that of the olfactory bulb were examined using intracellular in vivo recording. Stable recordings were obtained in 58 neurons impaled in the magnocellular preoptic nucleus. Antidromic responses occurred on stimulating olfactory bulb (15), piriform cortex (14), or entorhinal area (eight). Monosynaptic excitation was evoked by piriform (27 of 37 tested) and entorhinal cortex (15 of 32 tested) stimulation with polysynaptic inhibition occurring in seven and five neurons, respectively. Polysynaptic as well as antidromic excitation by olfactory bulb stimulation occurred in four; a further 28 tested responded polysynaptically. No response to olfactory bulb stimulation was monosynaptic. In stable impalements, 29 neurons discharged spontaneously in the absence of applied current. Lucifer Yellow and Neurobiotin were used to label 16 cells. All but one had smooth dendrites with soma diameters ranging from 8 to 24 μm. These results provide a framework in which magnocellular preoptic neurons can influence olfactory processing by direct action on the olfactory bulb, which action can be boosted by positive feedback from the bulb through the olfactory piriform and entorhinal cortices.

Regulation of forebrain and midbrain GnRH neurons in juvenile teleosts

Three molecular species of gonadotropin releasing hormone (GnRH) mRNA-containing neuronal populations (terminal nerve: salmon-GnRH; preoptic area: seabream-GnRH; midbrain: chic- ken-GnRH-II) have been localized in teleosts. While the termi- nal nerve GnRH neurons originate from the olfactory placode, a separate intracerebral source of origin for preoptic and midbrain neurons is possible. The preoptic GnRH neurons are regulated by gonadal steroids and gonadal maturation, however, the regulation and role of terminal nerve and midbrain GnRH neurons in teleosts reproduction is speculative and debatable.

The maturation of the salmon GnRH system and its regulation by gonadal steroids in masu salmon

Pituitary gonadotropin (GTH) secreting cells and brain gonadotropin-releasing hormone (GnRH) secreting neurons are known to be subjected to feedback control by gonadal steroid in teleosts. In masu salmon, Oncorhynchus masou, salmon GnRH (sGnRH) neurons in the ventral telencephalon (VT) and the preoptic area (POA) are involved in the control of GTH cells because sGnRH synthesis in these areas is activated with gonadal maturation. In this study, we attempted to clarify mechanisms of feedback control of sGnRH neurons by gonadal steroids. We examined the effects of 17α-methyltestosterone (MT) on sGnRH synthesis in yearling and 2-year-old female fish (which were immature during experimentation in May), and the effects of castration on sGnRH synthesis in underyearling precocious male fish in August. sGnRH synthesis in the POA, but not in the VT, was increased by MT administration in 2-year-old females only, indicating higher sensitivity to MT in the preoptic sGnRH neurons. Castration increased sGnRH synthesis in the VT but not in the POA. These results suggest that sGnRH neurons in the VT and those in the POA are differentially regulated by gonadal steroids.

2425 Median preoptic neurons projecting to the CVLM catecholaminergic area receive synaptic inputs of the nerve terminals

Currently, it is not possible to prevent essential hypertension and this presents a challenge to the clinician, pharmacologist, and medicinal chemist to discover adequate therapies. This chapter discusses the beneficial effects of drug therapy in the management of hypertension, the significance of catecholamine levels in hypertension, role of the sympathoadrenal axis in hypertension, and the need for intact vascular endothelium for vascular responses to a number of agents. A cautionary note offered that the levels in mixed venous blood are unreliable indicators of sympathetic neural activity in hypertension. Current evidence supports the hypothesis that converting enzyme (CEI) exerts their hypotensive effects primarily by inhibition of circulating and tissue-bound converting enzyme. A summary of the pharmacology of enalapril (MK-421) has appeared along with an account of the clinical studies done with lisinopril (MK-521) that suggest this drug will be suitable for once-a-day anti-hypertensive therapy. Analogs of enalapril that have appeared include the perhydroindole derivative. New evidence suggests certain calcium entry blockers (CEB) affect neural regulation of blood vessels at several sites. Studies in anesthetized dogs indicate that nifedipine increases and verapamil decreases the sensitivity of carotidsinus baroreceptors apparently by interference with a calcium-dependent and a sodium-dependent mechanism, respectively. New studies have examined the interaction of various CEB with α-adrenoceptors and their effect on the processes mediated by a-adrenoceptors. The (+) and (-) antipodes of verapamil, nicardipine, and (+) D-600 showed similar inhibition of radioligand binding to al-adrenoceptors, whereas diltiazem and nifedipine showed a very low level of activity.