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K Inenaga

Publications and source records attributed to K Inenaga.

At least 19 recordsLinked to original sources
PubMed1995

GABAergic inhibitory inputs to subfornical organ neurons in rat slice preparations.

To investigate GABAergic inhibitory inputs to neurons of the subfornical organ (SFO), intracellular recordings were made in rat brain slice preparations. Inhibitory postsynaptic potentials, which occurred spontaneously or were evoked by focal electric stimulation, had reversal potentials of approximately -60 mV, and were almost totally abolished by the GABAA antagonists bicuculline at 3-100 microM or picrotoxin at 50 microM. Following the application of bicuculline or picrotoxin, the resting membrane potentials were decreased by 4-8 mV. GABA at 10-100 microM and the GABAA agonist muscimol at 1-100 microM decreased the membrane resistance and the firing rate in all neurons tested. The reversal potential of the response to muscimol was similar to that for inhibitory postsynaptic potentials. The actions of muscimol persisted in the presence of 1 microM tetrodotoxin, implying that muscimol must act directly on the recorded neurons. These results suggest that there is a tonic inhibitory GABAergic input to SFO neurons which are mainly mediated through GABAA receptors.

Animals↗
PubMed1995

Transient outward current in adult rat supraoptic neurones with slice patch-clamp technique: inhibition by angiotensin II.

1. Outward potassium currents were recorded from microscopically identified supraoptic neurones of adult Wistar male rats using the whole-cell patch-clamp technique in thin-slice preparations. The basic characteristics of transient outward current (IA or A-current) and the effects of angiotensin II (AII) on the currents were studied. 2. IA was isolated by subtracting outward currents elicited by stepping from two different holding potentials to a test potential or by applying 4-aminopyridine (4-AP) at 5 mM. The isolated IA had a threshold for activation between -55 and -65 mV and was characterized by fast activation and inactivation. Values of the time to peak and the inactivation time constants for current decay at different test potentials were voltage dependent. 3. Normalized currents for activation and steady-state inactivation of IA were fitted to the Boltzmann function. The mid-points and the slope factors were, respectively, -35.0 and -14.3 +/- 0.40 mV (n = 5) for the activation curve, and -72.0 and 7.0 +/- 0.68 mV (n = 5) for the inactivation curve. 4. The time course of recovery from inactivation was best fitted to a single exponential function with the time constant of 37.8 +/- 6.6 ms (n = 6). 5. The effects of AII on IA and delayed rectifier current (IK) were investigated. According to their responses to AII, cells were classified into two groups, sensitive and low-sensitive. Bolus injection of AII (10 microM, 100 microliters) decreased the IA amplitude by 25.1 +/- 2.4% in seven (53.8%) of the thirteen neurones tested (sensitive group), whereas the other six neurones (low-sensitive group) changed by only 2.2 +/- 0.8%. Perfusion of AII (0.1 microM) decreased the IA amplitude by 21.3 +/- 3.1% in six (54.5%) of eleven neurones tested (sensitive group), whereas the other five neurones (low-sensitive group) changed only by 1.7 +/- 0.8%. Bolus injection of AII (10 microM, 100 microliters) decreased the IK amplitude 9.6 +/-1.6% mV in five (45.5%) of the eleven neurones tested (sensitive group), whereas the other six neurones (low-sensitive group) changed only by 0.46 +/- 0.27%. In the sensitive groups, the reduction of IA by AII was significantly larger than that of IK (P < 0.05). 6. Application of saralasin at 1 microM, an AII antagonist, blocked the effects of AII on IA. 7. These results suggest that the excitatory action of AII on supraoptic neurosecretory cells is mediated at least in part through suppression of IA.

Angiotensin II↗
PubMed1995

Cardiovascular-related peptides influence hypothalamic neurons involved in control of body water homeostasis.

The cardiovascular-related peptides, atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP) and endothelin (ET) were originally isolated from the atrium, brain and endothelial cells, respectively. ANP and BNP have hypotensive, natriuretic, diuretic and vasodilator effects. ET has strong vasoconstrictor effects. Centrally applied ANP and BNP attenuate pressure and drinking responses and vasopressin secretion induced by angiotensin II. Similar application of ET increases blood pressure in vivo and vasopressin secretion in vitro. To clarify direct effects of these peptides on neurons in the regions involved in body water homeostasis, extracellular recordings were made from neurons in the supraoptic nucleus (SON) and regions of anteroventral third ventricle (AV3V) of rat hypothalamic slice preparations. ANP and BNP inhibited AV3V neurons, suggesting direct actions of the peptides on drinking. In the SON, these peptides inhibited selectively putative vasopressin neurons but not putative oxytocin neurons, suggesting direct actions of the peptides on vasopressin secretion. We demonstrated that the inhibitory response by ANP and BNP is mediated through a second messenger cGMP system but not cAMP. Contrary to natriuretic peptides, ET excited AV3V neurons but inhibited SON neurons. Roles of ANP, BNP and ET on the central regulatory systems of body water homeostasis, acting as neurotransmitters or neuromodulators, will be discussed.

Animals↗
PubMed1995

Cardiovascular system related peptides and hypothalamic neurons.

The hypothalamus is known to be an integrative site of cardiovascular, endocrine and autonomic functions. Our previous studies, using extracellular, intracellular and/or whole cell patch-clamp recordings in rat hypothalamic slice preparations, revealed that cardiovascular related peptides such as atrial natriuretic polypeptides (ANP), B-type polypeptides (BNP), endothelin (ET), angiotensin II (AII) and interleukin-1 beta (IL-1 beta) influence the hypothalamic neurons. ANP modulated the firing rates in the supraoptic nucleus (SON). BNP inhibited the SON neurons and these effects were mediated through cGMP and cGMP-dependent protein kinase. ET also inhibited approximately 60% of SON neurons. By using slice patch-clamp techniques, AII inhibited the transient outward potassium current in the SON neurons. IL-1 beta increased the firing rate and depolarized the membrane of the most SON neurons. A new type of transmitter, nitric oxide (NO), identified as an endothelial-derived relaxing factor (EDRF), modulated the glutaminergic inputs of the SON neurons. The results suggest that cardiovascular related peptides and NO modulate the neuronal activity of neurosecretory cells in the SON.

Angiotensin II↗
PubMed1994

Kappa-selective agonists decrease postsynaptic potentials and calcium components of action potentials in the supraoptic nucleus of rat hypothalamus in vitro.

To investigate the effects of the endogenous kappa-receptor agonists dynorphin and leumorphin on neurons of the supraoptic nucleus in the rat hypothalamus, intracellular recordings were made from 62 supraoptic neurons in slice preparations. Bath application of dynorphin and leumorphin at 10(-7) M to 3 x 10(-6) M decreased the spontaneous firing rate with slight hyperpolarization of the membrane potential (-3.8 +/- 0.5 mV, mean +/- S.E.M.) but did not detectably change input resistance. The inhibitory effects were blocked by the relatively selective kappa-antagonist MR-2266. The synthetic kappa-receptor agonist U-50,488H had similar inhibitory effects on supraoptic neurons. Postsynaptic potentials evoked by electrical stimulation dorsal or dorsolateral to the supraoptic nucleus were suppressed by dynorphin and leumorphin. Morphine and [D-Ala, D-Leu]enkephalin, which are relatively selective to mu- and delta-receptors, respectively, influenced the postsynaptic potentials less. Dynorphin and leumorphin also decreased the duration of action potentials that were prolonged by either bath application of tetraethylammonium chloride at 5-10 mM or intracellular injection of Cs ions from the recording electrodes which were filled with 3 M cesium citrate. The prolongation was blocked by 1 mM MnCl2 and 2 mM CoCl2, which suggested that the components were due to voltage-dependent Ca2+ influx. The results suggest that endogenous kappa-receptor agonists inhibit neurosecretory cells of the supraoptic nucleus to suppress synaptic events and Ca2+ components of action potentials.

3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cycloh↗
PubMed1994

Sodium nitroprusside modulates NMDA response in the rat supraoptic neurons in vitro.

The modulatory effects of NO on N-methyl-D-aspartate (NMDA)-induced response in neurons of the supraoptic nucleus (SON) were studied by intracellular recording and radioimmunoassay of cyclic nucleotides using the rat brain slice preparation. Depolarization induced by 100 microM NMDA was reduced by application of 1 to 3 mM of the NO-donors, sodium nitroprusside, and isosorbide dinitrate in all 8 neurons and in 6 of 10 neurons, respectively. The scavenger for NO, hemoglobin, and the inhibitor of NO synthase, NG-nitro-L-arginine (LNNA) enhanced the NMDA-induced depolarization in four neurons and two of three neurons, respectively. Intracellular cGMP accumulation induced by NMDA was significantly diminished by LNNA. However, NMDA-induced depolarization was not affected by either the protein kinase inhibitor, N-[2-(methylamino)ethyl]-5- isoquinolinesulfonamide dihydrochloride (H-8), or the phosphodiesterase inhibitor, 3-isobutyl-1-methylxanthine (IBMX). These results indicate that NO reduces NMDA-induced depolarization in a manner that is independent of cGMP and may control the activity of the SON neurons through NMDA receptors.

Animals↗
PubMed1993

GABAergic inputs modulate effects of interleukin-1 beta on supraoptic neurones in vitro.

We have previously reported that human recombinant interleukin (IL)-1 beta depolarizes membrane potentials in most rat hypothalamic supraoptic (SON) neurones in vitro. In the present study intracellular recordings have been made to examine contributions of local GABAergic interneurones to the effects of IL-1 beta on SON neurones in rat brain slice preparations. The results suggest that local GABAergic inputs modulate IL-induced excitatory responses, and are involved in tonic inhibition of SON neuronal activities.

Animals↗
PubMed1993

Lateral preoptic neurons inhibit thirst in the rat.

Kainic acid (KA) and muscimol were injected into the lateral preoptic area (LPO) of the rat to study their effects on drinking behavior. A low dose (5 ng) of KA, which stimulates neurons, decreased the amount of water intake induced by hypertonic saline (IP) and angiotensin II (SC). Injection of 2 ng muscimol, a potent GABAA receptor agonist that suppresses neurons, facilitated drinking responses induced by hypertonic saline, but did not affect angiotensin II-induced drinking. Rats injected with a high dose (150 ng) of KA, which destroys neurons, showed marked polydipsia accompanied by increased urination. One week after the KA lesion, drinking and urine output recovered to normal. During the polydipsia, a small volume of concentrated urine could be excreted if water intake was restricted. After recovery, excessive drinking responses followed water deprivation and hypertonic saline load. The rats normally drank water in response to angiotensin II and to polyethylene glycol solution. The results show that activation of LPO neurons inhibits water intake, and that suppression of LPO neurons facilitates osmotically induced water intake. Therefore, LPO neurons are probably involved in the inhibition of thirst.

Animals↗
PubMed1993

The actions of endothelin on single cells in the anteroventral third ventricular region and supraoptic nucleus in rat hypothalamic slices.

Endothelin (ET), a peptide consisting of 21 amino-acid residues was recently isolated from the culture supernatant of porcine aortic endothelial cells. ET has been reported to be a more potent vasoconstrictor than angiotensin II. Other studies suggest that ET is involved in central control of the autonomic nervous system and body water regulation. Extracellular recordings were made from neurons in the anteroventral third ventricle (AV3V) and supraoptic nucleus (SON) in rat hypothalamic slice preparations. ET-3 was applied at concentrations of 10(-10) M to 3 x 10(-7) M. Of 226 AV3V neurons tested, 48 (21%) were excited, 8 (4%) were inhibited, and 170 (75%) were unaffected by ET-3 at 10(-7) M. The threshold concentration to evoke the responses was approximately 10(-9) M. Of 144 SON neurons tested, 64 had a phasic firing pattern and 80 had a non-phasic firing pattern. Of 64 phasic neurons tested, 39 (61%) were inhibited by ET-3 at 10(-7) M, 25 (39%) were non-responsive and none was excited. Of 80 non-phasic neurons tested, 14 (17.5%) were inhibited by ET-3 at 10(-7) M, 66 (82.5%) were non-responsive and none was excited. The effects of ET-1 were compared with those of ET-3. The number of neurons responding to ET-1 and their responsiveness were almost the same as for ET-3. To investigate whether the ET responses are dependent on Ca2+ influx, a Ca2+ free medium and the Ca2+ antagonist, nicardipine, were used. The excitatory responses of AV3V neurons to ET were maintained in the Ca2+ free medium.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Inhibitory effects of natriuretic peptides on vasopressin neurons mediated through cGMP and cGMP-dependent protein kinase in vitro.

The effects of natriuretic peptides on electrical activity and cellular cGMP levels were studied in neurons of the supraoptic nucleus (SON) of rat hypothalamic slice preparations. Intracellular and extracellular recordings showed that bath application of A type natriuretic peptide (ANP) at 100 nM or B type natriuretic peptide (BNP) at 100 to 300 nM decreased the firing rate and hyperpolarized the membrane potential in phasically firing (putative vasopressin) neurons. Non-phasically firing (putative oxytocin) neurons did not respond to these natriuretic peptides in firing rate or membrane potential. The membrane-permeable cGMP analogue 8-bromo cGMP at 0.5 mM and the phosphodiesterase inhibitor 3/isobutyl-1-methylxanthine (IBMX) at 50 microM mimicked the inhibitory effects of ANP and BNP. The specific inhibitor of cGMP phosphodiesterase 1-(3-chloroanilino)-4-phenylphthalazine+ ++ (MY5445) at 30 microM also decreased the firing rate of SON neurons. The cGMP-dependent protein kinase inhibitor N-(2-(methylamino)ethyl)-5-isoquinoline-sulfonamide dihydrochloride (H8) at 1 microM abolished the inhibition by natriuretic peptides. We measured cGMP and cAMP contents in discrete SON regions and compared the change of contents before and after application of ANP and BNP. The increases in cellular cGMP accumulation were 430% for ANP and 120% for BNP, although they did not cause significant change of cAMP accumulation. The results suggest that the inhibitory effects of natriuretic peptides on putative vasopressin neurons are mediated through cGMP and cGMP-dependent protein kinase.

1-Methyl-3-isobutylxanthine↗
PubMed1993

Inward sodium current involvement in regenerative bursting activity of rat magnocellular supraoptic neurones in vitro.

1. The rat hypothalamic slice preparation was used to investigate the involvement of inward Na+ currents as well as inward Ca2+ currents in the generation of bursting activity by supraoptic (SON) neurones. Intracellular records were made from thirty-two SON neurones which showed regenerative bursting activity. The bursting activity consisted of spontaneous, intermittent bursts of action potentials with subsequent silent periods. During the bursts, plateau potentials on which action potentials were superimposed were frequently observed. 2. Perfusion of a low-Na+ medium, a tetrodotoxin (TTX)-containing medium or a Ca(2+)-free medium suppressed the regenerative bursting activity. 3. Addition of 3-10 microM veratridine to Ca(2+)-free medium elicited regenerative bursting activity and spontaneous plateau potentials. The veratridine-induced regenerative bursting activity and plateau potentials were blocked by 1 microM TTX. Addition of 5 mM TEA allowed regenerative bursting activity to persist in Ca(2+)-free medium. 4. These results suggest that TTX-sensitive Na+ inward currents as well as Ca2+ inward currents contribute to the generation of bursting activity in rat SON cells.

Animals↗
PubMed1992

Intracellular EGTA alters phasic firing of neurons in the rat supraoptic nucleus in vitro.

To determine the function of intracellular free Ca2+ which is important in generating the phasic firing pattern characteristic of vasopressin neurons in the supraoptic nucleus (SON), we injected the highly specific Ca(2+)-chelating agent ethyleneglycol-bis-(beta-aminoethyl ether) N,N-tetraacetic acid (EGTA) into SON cells in the rat hypothalamic slice preparation. Intracellular recordings from 29 SON neurons which showed phasic firing were analyzed. Of the 29 SON neurons, 21 were recorded with microelectrodes filled with 3 M potassium acetate and 20 of the 21 neurons retained the phasic pattern more than 1 h after penetration by the electrode. Only one neuron lost phasic firing and fired randomly. By contrast, in all 8 neurons which were recorded with microelectrodes filled with 100 mM EGTA/2 M potassium acetate, phasic firing disappeared 10-80 min after penetration of the recording electrode although the neurons still showed spontaneous activity. These neurons also lost the after hyperpolarization and plateau potentials which followed bursting discharges. Our results suggest that intracellular free Ca2+ may play an important role in generating phasic firing.

Action Potentials↗
PubMed1992

Functional neuronal binding sites for oxytocin in the ventromedial hypothalamus of the guinea pig after gonadectomy.

Castration in rats of either sex has been shown to markedly decrease hypothalamic oxytocin binding in the ventromedial hypothalamus and this can be reversed by injecting gonadal steroids. We wondered whether castration exerts similar effects on homologous oxytocin binding sites present in the guinea pig hypothalamus. Adult male guinea pigs were castrated and killed 2-90 days later. Binding sites for oxytocin in the ventromedial nucleus and neuronal responses to this peptide were little affected by gonadectomy, in contrast to what is observed in the rat under similar experimental conditions. The steroid dependency of hypothalamic oxytocin receptors appears therefore to be species dependent.

Animals↗
PubMed1991

Endothelin-3 directly affects neurons in the anteroventral third ventricle region and supraoptic nucleus of the rat hypothalamus in vitro.

Extracellular recordings were made from anteroventral third ventricle (AV3V) and supraoptic nucleus (SON) neurons of rat hypothalamus in slice preparations. ET-3 was applied at concentrations of 10(-10) to 3 x 10(-7) M. Of 119 AV3V neurons tested, 21 (18%) were excited, 8 (6%) were slightly inhibited, and 90 (76%) were unaffected. The threshold concentration to evoke responses was approximately 10(-8) M. Excitatory responses of the AV3V neurons to ET-3 remained in a Ca(2+)-free medium. Of 120 SON neurons tested, 46 were phasic (putative vasopressin neuron) and 74 were nonphasic (putative oxytocin neuron). Of 46 phasic neurons tested, 26 (56.5%) were inhibited by ET-3, 20 (43.5%) were nonresponsive, and none was excited. Of 74 nonphasic neurons tested, 14 (19%) neurons were inhibited by ET-3, 60 (81%) were nonresponsive, and none was excited. These results suggest that ET-3 has dual effects on AV3V and SON neurons and the mechanisms of the responses may be different in the AV3V and SON neurons.

Animals↗
PubMed1990

Osmotic responses of rat paraventricular neurons by pressure ejection method.

Extracellular recordings were made from 44 spontaneously active neurosecretory and 43 unidentified neurons in the paraventricular nucleus (PVN) of the hypothalamus in urethane-anesthetized rats. Physiologically hypertonic (+30 mOsm/kg, NaCl or mannitol) and hypotonic (-30 mOsm/kg) solutions were applied by pressure through multibarrel micropipettes to the immediate vicinity of neurons. Of 44 neurosecretory neurons tested, 31 (70%) were unaffected by locally applied osmotic stimulation, and the remaining 13 were excited. Of these 31 osmotically unresponsive neurosecretory neurons, 21 were further tested with very strong hypertonic (+260 mOsm/kg, NaCl) solution, and only 7 were affected. Of 43 unidentified neurons, 28 (65%) were unaffected by osmotic stimulation, and 12 were excited. Accordingly, only parts (30%) of both the neurosecretory and unidentified neurons in the PVN were found to be osmosensitive. We concluded that some neurons in the rat PVN are osmosensitive and osmosensitivity is not specific to neurosecretory neurons in the PVN.

Action Potentials↗
PubMed1989

Beta-adrenergic and opioid receptors on pituicytes cultured from adult rat neurohypophysis: regulation of cell morphology.

Explants of adult rat neurohypophysis were maintained in culture for 14 days. The majority of cells present in the outgrowth of such cultures were identified as pituicytes on the basis of immunostaining for glial fibrillary acidic protein. Pituicytes were also stained by antisera to the membrane glycoprotein antigen Thy-1 and the extracellular matrix glycoprotein fibronectin. The cultures contained naloxone sensitive binding sites for the opioid receptor ligand [3H] dynorphin A 1-8 and peripheral-type benzodiazepine binding sites. Dynorphin binding was visualised over pituicytes following autoradiography. The morphology of cultured pituicytes was regulated by beta-adrenergic receptors present on the cells which, when activated, stimulated rapid transformation from a flattened irregular morphology to a stellate, process-bearing morphology. Dynorphin was without effect on the morphology of cultured pituicytes. These findings are discussed in the context of the known morphological plasticity of pituicytes in vivo.

Animals↗
PubMed1989

Effect of brain-gut peptides upon neurons in centrally regulating sites for drinking.

The effects of angiotensin II (A II) and ANP on spontaneously active neurons in the subfornical organ (SFO), anteroventral third ventricle (AV3V) and supraoptic (SON) and paraventricular nucleus (PVN) were investigated using slice preparations and extracellular recordings. Application of A II (10(-7)M) excited the neural activity of 66% of the SFO neurons, 28% of the AV3V neurons and 44% of the SON neurons. The threshold concentration to produce responses in SFO and AV3V neuron was less than 10(-10)M, while that in SON neurons was 10(-9)M. The excitatory effects of A II were reversibly antagonized by saralasin and persisted after synaptic blockade in a low Ca2+ and high Mg2+ medium. Application of ANP (10(-7)M) inhibited the neural activity of 41% of the AV3V neurons, 22% of the PVN neurons and only 14% of the SFO neurons but had no effect on SON neurons. The threshold concentration for ANP in the AV3V was 10(-11)M. Interestingly, ANP inhibited A II induced excitation in most of the SFO neurons (87%), while ANP had little effects on their spontaneous firing rates. These results show that both peptides of A II and ANP have direct central actions on hypothalamic neurons although ANP can not directly influence magnocellular neurons, suggesting that these blood borne peptides are detected in the SFO and AV3V and that they are acting as a neurotransmitter or a neuromodulator in the central nervous system to regulate water homeostasis.

Angiotensin II↗