Biomedical subjects

K Inenaga

Publications and source records attributed to K Inenaga.

At least 55 records · Page 3Linked to original sources

PubMed1987

gamma-Aminobutyric acid antagonist blocks baroreceptor-activated inhibition of neurosecretory cells in the hypothalamic paraventricular nucleus of rats.

The effects of gamma-aminobutyric acid (GABA) antagonists on baroreceptor-activated inhibition of neurosecretory cells in the paraventricular nucleus (PVN) were examined in urethane-chloralose anesthetized rats. In 11 neurosecretory cells which were inhibited by baroreceptor activation induced by intravenous application of phenylephrine, microiontophoretically applied bicuculline and/or picrotoxin blocked the inhibition (n = 9) completely or partially, whereas strychnine (n = 4) did not. The results suggest that GABA is, at least in part, involved in the baroreceptor-activated inhibition of PVN neurosecretory cells.

Action Potentials↗

PubMed1987

Thermosensitivity of neurons in the paraventricular nucleus of the rat slice preparation.

The thermosensitivity of 65 spontaneously active neurons in the paraventricular nucleus (PVN) was investigated by extracellular recording in the rat hypothalamic slice preparation. The firing rate of these cells was comparatively low, ranging from 0.03 to 10.0 (mean 2.46) impulses/s at 37 degrees C, and only a minority showed a phasic firing pattern. Of 65 neurons tested, 23 (35%) increased their firing rate when the slice was warmed (warm-sensitive neurons) and 9 (14%) showed the opposite response (cold-sensitive neurons). Thermosensitivity was also tested in solutions with reduced [Ca2+] and high [Mg2+]. Eight out of 10 warm-sensitive neurons and 5 of 7 cold-sensitive neurons retained thermosensitivity after synaptic blockade. Out of 6 phasic firing neurons tested, one showed warm-sensitivity and another one showed cold-sensitivity. The thermosensitive neurons were diffusely distributed throughout the PVN and were not located in particular areas of the nucleus. Thus a group of cells in the PVN, including probably both magno- and parvocellular neurons, showed an inherent thermosensitivity, which suggests an important role for the PVN in thermoregulation.

Animals↗

PubMed1987

Inhibitory effects of 2-deoxytetronic acid, a putative endogenous satiety factor, on paraventricular neurons of rats, in vitro.

The endogenous sugar acid, 2-deoxytetronic acid (2-DTA) was investigated for its effects on activity of paraventricular nucleus (PVN) neurons in slice preparations from rats. 2-DTA dose-responsively inhibited the spontaneous activity of 23 of the 53 PVN neurons tested at concentrations of 10(-5) to 10(-2) M, and 2 were excited. The inhibitory responses were not due to osmotic changes by 2-DTA administration. The high concentration of 2-DTA needed to produce responses suggests that it acts as substrate for oxidative metabolism rather than as a neurotransmitter or neuromodulator in the suppression of feeding behavior.

Action Potentials↗

PubMed1987

Oxytocin predominantly excites putative oxytocin neurons in the rat supraoptic nucleus in vitro.

To determine the oxytocin (OXT) sensitivity of neurons in the supraoptic nucleus (SON), extracellular recordings were made from the rat hypothalamic slice preparation. OXT added to the bathing medium (3 X 10(-7) M) excited 13 (93%) of 14 cells which fired continuously (average 4.9 +/- 0.7 spikes/s) and 26 (81%) of 32 cells which fired slowly and irregularly (average 1.4 +/- 0.4 spikes/s). By contrast, only 2 (8%) of 26 phasically firing neurons were excited and none of the SON cells tested were inhibited. The excitation was reversibly antagonized by a synthetic OXT analogue, 1-deamino-[2-(O-methyltyrosine), 4-valine, 8-D-arginine]vasopressin. The results suggest that OXT exerts predominantly excitatory effects in the SON and that putative OXT cells are more likely to be affected than putative vasopressin cells.

Action Potentials↗

PubMed1987

Depolarizing effect of noradrenaline on neurons of the rat supraoptic nucleus in vitro.

Noradrenaline (NA) (1-100 microM) was applied to 41 neurons recorded intracellularly from the supraoptic nucleus (SON) of the rat hypothalamic slice preparation; 34 (83%) neurons showed membrane depolarization which was dose-dependent. The depolarization was frequently accompanied by decreased membrane resistance, increased firing rate and increased fluctuations in membrane potential. Following the application of the alpha-agonist, phenylephrine, 10 out of 11 neurons tested showed similar responses, while the beta-agonist, isoproterenol, caused no changes in 6 out of 7 SON cells. We found no difference in responsiveness between neurons having a 'phasic' or a 'non-phasic' pattern of firing. We conclude that NA depolarized and increased the firing rate of both vasopressin- and oxytocin-containing neurons through an action on alpha-adrenergic receptors.

Animals↗

PubMed1987

Chloride channels activated by gamma-aminobutyric acid in normal bovine lactotrophs.

The effect of gamma-aminobutyric acid (GABA) on normal bovine lactotrophs was investigated using the patch clamp technique. GABA application (1-10 microM) induced fluctuations of membrane current, accompanied by an increase in inward current. The mean conductance of GABA-activated channels was estimated to be 19 pS from statistical analysis of these fluctuations whereas the mean conductance for GABA-activated single ion channels was 16 pS. The reversal potential of the current was near to the equilibrium potential for chloride ions. These results indicate that the one possible mechanism for inhibition of prolactin release induced by GABA is probably mediated by activation of chloride channels.

Animals↗

PubMed1987

Angiotensin II sensitive neurons in the supraoptic nucleus, subfornical organ and anteroventral third ventricle of rats in vitro.

The angiotensin II (AII) sensitivity of neurons in the supraoptic nucleus (SON), subfornical organ (SFO) and the region near the anteroventral part of the third ventricle (AV3V) was investigated using extracellular recording in the rat brain slice preparation by adding AII (10(-10)-10(-6) M) to the perfusion medium. Forty seven (44%) of 106 SON neurons, 62 (66%) of 94 SFO neurons and 28 (33%) of 86 AV3V neurons were excited by AII. One cell was inhibited by AII in the SON and one in the SFO. The threshold concentration to evoke responses in the SON neurons was approximately 10(-9) M, but neurons in the SFO and AV3V showed clear excitatory responses to AII at 10(-10) M. In the SON, 18 (40%) of 45 phasic firing neurons (putative vasopressin neurons) and 29 (48%) of 61 nonphasic firing neurons (including putative oxytocin neurons) were excited by AII. The excitatory effect of AII was reversibly antagonized by a specific antagonist saralasin and persisted after synaptic blockade in medium with low [Ca2+] and high [Mg2+]. We conclude that AII can stimulate both vasopressin and oxytocin release, acting directly upon SON neurons and also that both the SFO and AV3V are important receptive sites for AII (although the SFO is relatively more sensitive) which contributes SON input and modulates release of these hormones.

Angiotensin II↗

PubMed1987

Gamma-aminobutyric acid modulates chloride channel activity in cultured primary bovine lactotrophs.

The effects of GABA, the analogues muscimol and baclofen, and the antagonist bicuculline were investigated on cultured primary bovine lactotrophs using the patch clamp technique. Under voltage clamp in the whole cell mode using solutions containing chloride as the only permeable ion, GABA application increased the amplitude of mean membrane current and fluctuations of current about this mean. Statistical analysis of current fluctuations induced by GABA showed that the power density spectra in 8 of 12 cells were best fitted to double Lorentzian functions and the variance was smallest around the estimated equilibrium potential of chloride ions. The underlying channel open time estimated from noise analysis was only weakly voltage-dependent. The variance of current noise increased with GABA concentration within the range of 1-30 microM, although a slight decrease of variance in one cell could be observed at 30 microM, suggesting that desensitization to GABA might occur. Muscimol mimicked the effect of GABA but baclofen was without effect under these conditions. Bicuculline reduced the GABA-activated membrane current fluctuations. GABA- or muscimol-activated channels recorded in isolated outside-out patches had a slope conductance of about 20 pS. Mean open times of the channel were characterized by two exponential decay functions. We conclude that bovine lactotrophs have GABA-activated chloride channels, which appear to be voltage-independent. In addition, the action of GABA appears to be mediated through the GABAA receptor subtype.

Animals↗

PubMed1986

Characterization of hypothalamic noradrenaline receptors in the supraoptic nucleus and periventricular region of the paraventricular nucleus of mice in vitro.

In an attempt to determine the basis for apparently conflicting reports of the effects of noradrenaline (NA) on the neurohypophyseal system and its effects on the parvocellular periventricular region of the paraventricular nucleus (PVN), recordings were made from the neurons in the supraoptic nucleus (SON) and the periventricular region in the mouse hypothalamic slice preparation. Of 47 SON neurons, 43 (91%) were excited and two (4%) were inhibited by NA. Seven SON neurons increased the firing rate with increase of NA concentration (10(-7)-10(-4) M). Both the alpha 1-agonists phenylephrine and methoxamine also increased the activity of all SON neurons tested whereas application of the alpha 2-agonist clonidine and the beta-agonist isoproterenol had weak and inconsistent effects. While the alpha 2-antagonist yohimbine had no consistent influence, the alpha 1-antagonist prazosin blocked or reversed the effects of NA. Another group of 37 neurons in the periventricular region of the PVN was also tested; 13 (35%) were excited and 22 (59%) inhibited by application of NA (10(-5) M). When tested with phenylephrine or methoxamine, 6 of the 7 neurons were excited and one inhibited but all the 4 neurons tested were excited by isoproterenol. Clonidine strongly depressed the activity of all 12 neurons tested. The NA-induced excitatory effects were suppressed or reversed by pre-application of prazosin and the beta-antagonist propranolol while the inhibitory ones were suppressed or reversed by yohimbine. Synaptic blockade did not affect the excitatory responses of SON cells to NA nor the inhibitory responses of periventricular neurons to NA or clonidine. We conclude that SON neurons receive adrenergic excitatory effects mainly through alpha 1-receptors. The periventricular neurons receive the excitatory effects through alpha 1- or beta-receptors and receive the inhibitory effects through alpha 2-receptors.

Animals↗

PubMed1986

[Electrophysiological studies on the central control of feeding and drinking under hyperbaric environment].

Increased urinary output, decreased fluid intake and reduction in body weight have been reported in divers exposed to hyperbaric environments. Single unit activity of hypothalamic neurons in the lateral hypothalamic area and paraventricular nucleus which control energy and body fluid balance was recorded with chronically implanted electrodes in rats. Neurons in the prefrontal cortex and central medical thalamus were also recorded for comparison. Out of 33 hypothalamic neurons, 19 reversibly decreased their firing rate to 67%, in average, under high pressure (7 atmospheres absolute) of air compared with precompression control. On the other hand, the remaining 14 neurons and all prefrontal and thalamic neurons tested were unaffected. Decreased hypothalamic unit activity was also found under normobaric hyperoxic environment and normoxic hyperbaric environment. The results suggest that hyperbaric air specifically affected the hypothalamic neurons by means of increased partial pressure of both oxygen and nitrogen.

Animals↗

PubMed1986

Excitation of neurones in the rat paraventricular nucleus in vitro by vasopressin and oxytocin.

Extracellular recordings were made from ninety-seven spontaneously firing cells in the paraventricular nucleus (p.v.n.) of the rat hypothalamic slice preparation. The spontaneously firing cells tested fired at 0.1-8 spikes/s but the majority showed a slow irregular firing pattern. The average firing rate of all ninety-seven cells was 2.2 +/- 0.2 spikes/s (mean +/- S.E. of mean). Six cells showed a phasic firing pattern. Following bath application of arginine-vasopressin (AVP) 10(-7) M, sixty-four (66%) of ninety-seven p.v.n. cells showed excitatory responses and three (3%) cells inhibitory responses. Bath application of oxytocin (OXT) 10(-7) M excited thirty-nine (57%) of sixty-eight p.v.n. cells and inhibited two (3%) cells. Individual p.v.n. cells responded to application of both AVP and OXT, but the magnitude and threshold of the responses varied from cell to cell. Of the sixty-six cells tested with both peptides at 10(-7) M, sixteen showed similar responses to both and fifteen showed no response to either: twenty cells showed a greater response to AVP and fifteen a greater response to OXT. Of six phasic firing cells, two showed excitatory responses to AVP and all four cells tested did not show any response to OXT. The dose-dependence of the response to AVP and OXT was tested in six p.v.n. cells. There was a direct relationship between peptide concentration and increased firing rate. The threshold concentration of the peptides ranged from 10(-8) to 10(-10) M. The cells responsive to the peptides were not located in particular areas of the p.v.n. but were diffusely distributed throughout the nucleus. After blocking synaptic transmission with a low Ca2+ and high Mg2+ medium, all tested cells (AVP, n = 15; OXT, n = 14) which had responded to applications of AVP or OXT in normal medium still showed responses to the peptides, although the effect was less marked in half the cells. However, in the absence of synaptic transmission two cells showed unimpaired responses to one of the peptides but greatly depressed responses to the other. The V1-receptor antagonist [1-(beta-mercapto-, beta-cyclopentamethylenepropionic acid)], 8-D-arginine-vasopressin (d(CH2)5DAVP) or V1/V2-receptor antagonist [1-(beta-mercapto-, beta-cyclopentamethylenepropionic acid), 2-D-tyrosine,4-valine]arginine-vasopressin (d(CH2)5D-TyrVAVP) completely or partly blocked the AVP-induced responses, while the V2-receptor agonist 1-deamino-8-D-arginine-vasopressin (dDAVP) did not influence the spontaneous discharges of the cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗

PubMed1984

Possible projections from regions of paraventricular and supraoptic nuclei to the spinal cord: electrophysiological studies.

The existence of monosynaptic connections between neurons in the paraventricular nucleus (PVN) of the hypothalamus and the intermediolateral cell column (ILC) of the spinal cord was studied by electrophysiological techniques in chloralose-anesthetized cats. Sympathetic preganglionic discharges (recorded from the 2nd or 3rd thoracic white ramus) were evoked by microstimulation of certain regions in or near the PVN with short train of pulses and below 50 microA current. By recording responses of 'identified' and 'non-identified' neurosecretory cells in the PVN and supraoptic nucleus (SON) to stimulation of the ILC of the thoracic cord, it was possible to identify antidromically evoked action potentials in 9 out of 297 neurons tested. Among them, 2 neurons were also antidromically excited by the pituitary stalk stimulation, 5 were orthodromically excited by the same stimulus and the remaining 2 were not excited by the stalk stimulation. Our results indicate that some PVN neurons, though small in number, send axons directly to the ILC of the cord, and that a very few neurons among these also send their axons to the pituitary gland.

Afferent Pathways↗

PubMed1983

Phasically firing neurons in the supraoptic nucleus of the rat hypothalamus: immunocytochemical and electrophysiological studies.

Relations between firing patterns and peptides in supraoptic neurons of rat hypothalamic slice preparations were studied by electrophysiology, intracellular fluorescent dye-marking and immunocytochemistry. Seven out of 10 magnocellular neurons which showed phasically firing patterns were identified by injections of Lucifer Yellow-CH (LY); these were also stained with an anti-vasopressin serum. This report presents direct evidence that most of the phasically firing neurosecretory neurons in the supraoptic nucleus contain vasopressin. This study demonstrates the feasibility of combining immunocytochemical and electrophysiological techniques to study the peptides contents of single mammalian neurons.

Animals↗

PubMed1983

Immunohistochemical identification of Lucifer Yellow-labeled neurons in the rat supraoptic nucleus.

An attempt was made to identify Lucifer Yellow-labeled neurons in the rat supraoptic nucleus as vasopressin-containing neurons, by means of a combination of immunoperoxidase histochemistry and iontophoretic single cell-injection. We came to the conclusion that the fluorescent dye does not diminish the immunoreactivity of vasopressin in the magnocellular neurons. This newly developed method, along with its modifications, should prove to be quite useful for electrophysiological and morphological studies on the neuropeptide-releasing neurons in the mammalian neuroendocrine system.

Animals↗

PubMed1983