Medial Preoptic Neurons Research Articles

Electrophysiological and neurochemical characterization of neurons of the medial preoptic area in Japanese quail ( Coturnix japonica)

Intracellular recordings of medial preoptic neurons demonstrated that most neurons show a spontaneous firing, a linear I– V relationship and low-threshold-like events suppressed by the application of Ni 2+. Some neurons had a depolarizing sag of the membrane potential in response to hyperpolarizing current pulses. The majority of the cells exhibited a robust spontaneous synaptic activity suppressed by SR95531 (100 μM), a GABA A receptor antagonist, and/or by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 10 μM), an ( RS)-α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA)/kainate (KA) glutamate receptor antagonist. Most neurons were affected by the application of AMPA (10 μM), kainate (30 μM), N-methyl- d-aspartic acid (NMDA, 10 μM), isoguvacine (a GABA A receptor agonist, 100 μM), dopamine (100 μM), and norepinephrine (100 μM). Biocytin injections coupled to aromatase immunocytochemistry identified 19 recorded neurons including 3 displaying a dense aromatase immunoreactivity. All of them responded to kainate, dopamine, and norepinephrine, while only one responded to isoguvacine and NMDA. Taken together, these results demonstrate a relative electrical and neurochemical homogeneity of the medial preoptic neurons, including a few aromatase-immunoreactive neurons that could be identified by immunocytochemistry after biocytin labeling of the recorded neurons.

Bicuculline free base blocks voltage-activated K + currents in rat medial preoptic neurons

The effects of the well-known GABA A-receptor blocker bicuculline on voltage-gated K + currents were studied in neurons from the medial preoptic nucleus (MPN) of rat. Whole-cell currents were recorded using the perforated-patch technique. Voltage steps from –54 to +6 mV resulted in tetraethylammonium-sensitive K + currents of delayed rectifier type. The total K + current (at 300 ms), including Ca 2+-dependent and Ca 2+-independent components, was reversibly reduced (17 ± 4%) by 100 μM bicuculline methiodide and (37 ± 5%) by 100 μM bicuculline as free base. The Ca 2+-independent fraction (77 ± 2%) of K + current evoked by a voltage step was, however, reduced (54 ± 6%) only by bicuculline free base, but was not affected by bicuculline methiodide. The half-saturating concentration of bicuculline free base for blocking this purely voltage-gated K + current was 113 μM, whereas for blocking a steady Ca 2+-dependent K + current it was 36 μM. The bicuculline-sensitive voltage-gated K + current was composed of 4-AP-sensitive and 4-AP-resistant components with different kinetic properties. No component of the purely voltage-gated K + current was affected neither by 100 nM α-dendrotoxin nor by 100 nM I-dendrotoxin. The possible K +-channel subtypes mediating the bicuculline-sensitive current in MPN neurons are discussed.

Norepinephrine acts via α 2 adrenergic receptors to suppress N-type calcium channels in dissociated rat median preoptic nucleus neurons

The median preoptic (MnPO) nucleus, a key CNS site for hydromineral and cardiovascular homeostasis, receives a dense norepinephrine innervation from brainstem autonomic centers. Since norepinephrine is known to influence neuronal excitability by modulating calcium channel function, we applied whole cell patch clamp techniques to study calcium currents in 116 dissociated MnPO neurons, including 30 cells identified by a retrograde label as projecting to the hypothalamic paraventricular nucleus. Norepinephrine (3–50 μM) suppressed high-voltage-activated calcium currents (HVA I Ca) in 80% of cells, selectively blockable by yohimbine and mimicked by UK14,304 and clonidine. The norepinephrine effect was relieved by strong prior depolarization, indicating a voltage-dependent component. Intracellular GTP-γ-S blocked the effect. Blockade by extracellular NEM suggested involvement of pertussis-toxin sensitive G-proteins. Based on pharmacological properties, these HVA I Cas had the following composition: 40–45% N-type (blockable by ω-conotoxin GVIA); 20–25% L-type (blockable by nimodipine); 15–20% P/Q-type (blockable by ω-agatoxin IVA). Since ∼75% of the norepinephrine effect was blockable with ω-conotoxin GVIA, we conclude that postsynaptic α 2 adrenoceptors preferentially suppress N-type calcium channels, revealing a novel mechanism whereby norepinephrine can modulate excitability in MnPO neurons.

The functional role of a bicuculline-sensitive Ca2+-activated K+ current in rat medial preoptic neurons.

A Ca2+-activated K+ current was identified in neurons from the rat medial preoptic nucleus. Its functional role for the resting potential and for impulse generation was characterised by using the reversible blocking agent bicuculline methiodide. Acutely dissociated neurons were studied by perforated-patch recordings. The effect of bicuculline methiodide was investigated under voltage-clamp conditions to clearly identify the current affected. At membrane potentials > -50 mV, bicuculline methiodide rapidly (< 1 s) and reversibly blocked a steady outward current. Half-saturating concentration was 12 microM. The current amplitude increased with potential in the range -50 to 0 mV. The bicuculline-sensitive current was identified as an apamin-sensitive, Ca2+-dependent K+ current. It was neither affected by the GABAA receptor blocker picrotoxin (100 microM) nor by a changed pipette Cl- concentration, but was affected by substitution of extracellular K+ for Na+. The current was dependent on extracellular Ca2+ and was sensitive to 1 microM apamin but not to 200 nM charybdotoxin. A role for the Ca2+-dependent K+ current in setting the resting potential and controlling spontaneous firing frequency was observed under current-clamp conditions. Bicuculline methiodide (100 microM) induced a positive shift (5 +/- 1 mV; n = 18) of resting potential in all neurons tested. In the majority of spontaneously firing neurons, the firing frequency was reversibly affected, either increased or decreased depending on the cell, by bicuculline methiodide.

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

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

Bicuculline-sensitive potassium currents in rat medial preoptic neurons

Bicuculline-sensitive potassium currents in rat medial preoptic neurons

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.

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.

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

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.

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.

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

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

2422 Responses of median preoptic neurons projecting to the hypothalamic paraventricular nucleus to osmotic stimulation in WKY and SHR

2422 Responses of median preoptic neurons projecting to the hypothalamic paraventricular nucleus to osmotic stimulation in WKY and SHR

Responses of median preoptic neurons projecting to the hypothalamic paraventricular nucleus to osmotic stimulation in Wistar-Kyoto and spontaneously hypertensive rats

Twenty-one median preoptic nucleus (MnPO) neurons in normotensive Wistar-Kyoto rats (WKY) and 18 MnPO neurons in spontaneously hypertensive rats (SHR) were antidromically activated by electrical stimulation of the hypothalamic paraventricular nucleus (PVN) under urethane anesthesia. No significant differences in the latency, conduction velocity, or threshold of antidromic activation were observed between WKY and SHR. The spontaneous discharge rate was significantly higher in SHR than in WKY. The activity of these identified MnPO units was examined for response to intracarotid injections of isotonic (0.15 M NaCl solution, 0.05 ml) or hypertonic (0.3 M NaCl solution, 0.05 ml) saline. All the units did not change their activity to the injections of isotonic saline. Of these units, 14 units in WKY and 12 units in SHR displayed an increase and 3 units in WKY and 4 units in SHR exhibited a reduction in neuronal activity following the injections of hypertonic saline, while the remaining 4 units in WKY and 2 units in SHR were unresponsive. The duration and frequency of excitatory response, but not the inhibitory response, caused by the osmotic stimulation was much greater in SHR than in WKY. These results show that MnPO neurons projecting to the PVN may carry the information from osmosensitive elements and that there is a difference between WKY and SHR in the responsivity of these MnPO neurons to the osmotic stimulation.

Diametrically opposite effects of estrogen on the excitability of female rat medial and lateral preoptic neurons with axons to the midbrain locomotor region

Electrical stimulation of the midbrain locomotor region (MLR) in 76 ovariectomized, urethan-anesthetized female rats elicited antidromic action potentials in 252 preoptic neurons. Thresholds and refractory periods for the activation ranged from 60 to 1550 μA and 1.3 to 5.0 ms, respectively. The probability distribution for the peak-to-peak amplitude (2–14 mV) or the overall duration (0.7–4.4 ms) was bell-shaped, whereas that for the latency (1.8–33.5 ms) was distinctively bimodal with a division at 12.0 ms. Two groups of preoptic neurons of a similar soma size therefore project to the MLR presumably via different routes. In 121 neurons with latencies ≤12.0 ms, estrogen lowered the antidromic activation thresholds (nested analysis of variance, P < 0.02), but 131 neurons with latencies >12.0 ms had their thresholds increased ( P < 0.005) and refractory periods prolonged ( P < 0.02) by estrogen. Even though both overlapped in part, many potentials with the shorter latencies were recorded from the medial part of the lateral preoptic area (mLPO), lateral to the recording sites of the longer-latency potentials in the medial preoptic area (MPO). The observed antagonistic effects of estrogen on the two groups of preoptic neurons with axons to the MLR may contribute to increased locomotor activity in female rats in estrus.

Whole-cell recordings of spontaneous synaptic currents in medial preoptic neurons from rat hypothalamic slices: mediation by amino acid neurotransmitters

Whole-cell recordings in hypothalamic slices from immature rats were used to test the hypothesis that inhibitory and excitatory amino acid neurotransmitters mediate fast synaptic currents in the medial preoptic area (MPOA). Bicuculline methiodide reversibly blocked spontaneous inhibitory postsynaptic currents (IPSCs), and 6-cyano-2,3-dihydroxy-7-nitroquinoxaline (CNOX) blocked spontaneous excitatory postsynaptic currents (EPSCs). These competitive antagonists act at γ-aminobutyric acid (GABA) A and non-N- methyl- d-aspartate (NMDA) glutamate receptors, respectively, thus supporting the hypothesis that these amino acid receptors activate most if not all fast synaptic currents in the MPOA.

Homogeneity of intracellular electrophysiological properties in different neuronal subtypes in medial preoptic slices containing the sexually dimorphic nucleus of the rat.

The sexually dimorphic nucleus of the preoptic area (SDN-POA) is larger in male than in female rats, the male phenotype requiring the presence of circulating androgens perinatally. These experiments investigated the intracellular electrophysiology and morphology of SDN-POA neurons and compared these properties with those of other medial preoptic area (MPOA) neurons. Biocytin-injected cells in the SDN-POA either had one or two primary dendrites, or they had multipolar dendritic arrays; dendrites were aspiny or sparsely spiny and displayed limited branching. Neurons in other parts of the MPOA were similar morphologically. Regardless of morphology, neurons situated in either the SDN-POA or surrounding MPOA had low-threshold potentials and linear or nearly linear current-voltage relations. In most (73%) cells, stimulation of the dorsal preoptic region evoked a fast excitatory postsynaptic potential followed by a fast inhibitory postsynaptic potential (IPSP). Bicuculline blocked the fast IPSPs, which reversed near the Cl2 equilibrium potential (-71 +/- 5 mV), indicating their mediation by gamma-aminobutyric acid (GABA)A receptors. Neurons in the SDN-POA have electrophysiological properties similar to those of other medial preoptic cells. When compared with the hypothalamic paraventricular nucleus, the MPOA appears relatively homogeneous electrophysiologically. This is despite the morphological variability within this population of neurons and heterogeneities that are also apparent at other levels of analysis. Finally, GABA-mediated, inhibitory synaptic contacts are widespread among medial preoptic neurons, consistent with indications from earlier reports that GABA provides a link in the feedback actions of gonadal steroids on the release of gonadotropic hormones.

In vitro sensitivity of median preoptic neurons to angiotensin II, osmotic pressure, and temperature.

In vivo experiments suggest an interaction of the mechanisms involved in the regulation of body fluid balance and body temperature. Increases in plasma osmolality initiate drinking and increase the thermal set point for sweating. The median preoptic nucleus (MnPO) has anatomical connections with brain areas important in fluid balance and cardiovascular regulation and, with the preoptic-anterior hypothalamus, a thermoregulatory region. The present experiments employed in vitro single-unit recordings to determine the sensitivity of MnPO neurons to angiotensin II (ANG II), changes in osmotic pressure, and changes in temperature. One-fifth (11 of 55) of the MnPO neurons responded with changes in firing rate during the ANG II treatment, one-fourth (19 of 75) responded to changes in perfusate osmolality, and there was a significant effect of osmolality and ANG II on the thermosensitivity of 25% of the neurons tested.