Biomedical subjects

K Inenaga

Publications and source records attributed to K Inenaga.

At least 19 recordsLinked to original sources

PubMed2006

Galanin inhibits neural activity in the subfornical organ in rat slice preparation.

The activation of the subfornical organ (SFO), a circumventricular organ, induces water intake and vasopressin release. Since central administrations of galanin (GAL) suppress water intake and vasopressin release, GAL may inhibit the neural activity of SFO neurons. In the present study, we investigated effects of GAL on the SFO using molecular biological, electrophysiological and anatomical techniques. Reverse transcription-polymerase chain reaction analysis demonstrated the presence in the SFO of rats of the mRNAs for each of the three known GAL receptor subtypes (GalR1, GalR2 and GalR3). In extracellular recordings in SFO slice preparations, GAL dose-dependently inhibited the neural activity of cells from a number of recording sites. Many GAL-sensitive SFO neurons showed excitatory responses to angiotensin II (ANGII). The GalR1 agonist M617 inhibited the activity of SFO neurons, whereas the GalR2 and GalR3 agonist GAL(2-11) had almost no effect. In patch-clamp recordings, GAL induced an outward current in SFO neurons without influencing synaptic currents. An immunoelectron microscopic study revealed the existence of GAL-containing synaptic vesicles in the SFO. These results suggest that the SFO has neural inputs involving GAL. The response to GAL is inhibitory, mediated at least in part by GalR1 and provides a plausible explanation for the opposite effects of ANGII and GAL seen in vivo on water intake and vasopressin release.

Action Potentials↗

PubMed2006

Gender difference in unstimulated whole saliva flow rate and salivary gland sizes.

OBJECTIVE: A gender difference in the unstimulated whole saliva flow rate (UWSFR) may be due to a difference in the sizes of the salivary glands. In this study, we investigated the relationships among the UWSFR, gland sizes and body sizes of healthy young adult males and females. DESIGN: Unstimulated whole saliva was collected for 5 min by the spitting method in 50 healthy young adults, and the flow rate of the saliva was measured. Heights and weights were measured, and body mass indices (BMI) were calculated. The sizes of the salivary glands were measured by use of a magnetic resonance imaging technique. RESULTS: Parotid and submandibular gland sizes and flow rates in females were significantly smaller than those in males, as were also the weights, heights and BMI. In both males and females, there were significant positive correlations between gland sizes and the flow rates, weights and BMI. The variations of the flow rates were reduced by standardizing them with gland sizes, weights and BMI. CONCLUSIONS: These results suggest that the lower UWSFR in females as compared with males is due to the smaller gland sizes due to the smaller body sizes.

Adult↗

PubMed2006

Dynamic magnetic resonance sialography as a new diagnostic technique for patients with Sjögren's syndrome.

OBJECTIVE: To evaluate the clinical utility of dynamic magnetic resonance (MR) sialographic images as a diagnostic tool for patients with Sjögren's syndrome. METHODS: The morphological findings and various kinds of functional parameters in volunteers on dynamic MR sialographic images were compared with those in five patients with definite Sjögren's syndrome. RESULTS: On the MR sialographs of all five patients with Sjögren's syndrome, the so-called 'apple-tree appearance' was seen. The difference in two functional parameters using the dynamic MR sialographic data was elucidated between the two groups. The maximum area of the detectable ducts in the group of patients was significantly smaller (P < 0.001) than that in the group of volunteers. The ratio of change in the detectable ducts in the group of patients was significantly lower (P = 0.011) than that in the group of volunteers. CONCLUSIONS: Our study suggests that dynamic MR sialographic data in addition to MR sialographic images might be useful for the diagnosis of Sjögren's syndrome.

Adult↗

PubMed2006

Pilocarpine-induced salivation and thirst in conscious rats.

The muscarinic receptor agonist pilocarpine is widely used as a sialogogue. It has been well-established that it also induces water intake in animals. However, the mechanisms underlying the relationships between these events are unknown. To address this problem, we examined water intake and parotid salivary secretion in conscious rats. Intraperitoneally injected pilocarpine increased both water intake and salivary secretion. Intracerebroventricularly injected pilocarpine also induced water intake, but not salivary secretion. Intracerebroventricularly applied atropine, a muscarinic receptor antagonist, suppressed the water intake produced by pilocarpine applied intraperitoneally and intracerebroventricularly. However, it did not affect the salivary secretion induced by pilocarpine applied peripherally. We conclude that peripherally applied pilocarpine affects the parotid glands and the thirst center in the central nervous system, while it may induce salivary secretion mainly via peripheral responses, but water intake mainly via the central nervous system.

Animals↗

PubMed2004

DAMGO suppresses both excitatory and inhibitory synaptic transmission in supraoptic neurones of mouse hypothalamic slice preparations.

Opioid effects on synaptic transmission in the mouse supraoptic nucleus (SON) were investigated using whole-cell, patch-clamp techniques. The mu-opioid receptor agonist, [D-Ala(2), N-Me-Phe(4), Gly(5)-ol]-enkephalin (DAMGO) decreased the amplitude of both evoked excitatory postsynaptic currents (eEPSCs) and inhibitory postsynaptic currents (eIPSCs), and also decreased the frequency of both miniature EPSCs and IPSCs without effect on the amplitude. The selective mu-opioid receptor antagonist, D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Pen-Thr-NH(2), and the nonselective antagonist naloxone, antagonized these inhibitory effects. The application of DAMGO suppressed the amplitude of both the first and second evoked postsynaptic currents with a paired-pulse stimulus protocol, but increased the paired-pulse ratios (second ePSC/first ePSC). DAMGO induced neither inward nor outward currents, and had no significant changes in either glutamate- or GABA-induced currents. When compared with the relatively selective kappa- and delta-opioid receptor agonists dynorphin and [D-Pen(2), D-Pen(5)]-enkephalin, DAMGO showed the most potent inhibitory effects on evoked and miniature postsynaptic currents. Taken together, these results imply that DAMGO strongly suppresses the release of glutamate and GABA via mu-opioid receptors in the mouse SON, and support the involvement of presynaptic regulation by opioids in the control of magnocellular neurosecretory neurones.

Analgesics, Opioid↗

PubMed2003

Activation of muscarinic receptors in rat subfornical organ neurones.

Cholinergic muscarinic inputs to subfornical organ (SFO) neurones in rats were studied using histochemical, molecular-biological and electrophysiological techniques. Neurones in the medial septum and the diagonal band (MS-DBB) were retrogradely labelled by a tracer wheat germ agglutinin-conjugated horseradish peroxidase-colloidal gold complex injected into the SFO. Some in the MS-DBB were double-labelled by choline acetyltransferase (ChAT) antibody. Many ChAT-immunoreactive fibres were observed in the SFO. M3 muscarinic receptor subtype-like immunoreactivity, detected using a polyclonal antiserum, was observed in the SFO. In slice preparations, muscarine induced inward currents in a dose-related manner. The inward currents were suppressed by the relatively M3 muscarinic receptor selective antagonist 4-diphenylacetoxy-N-methylpiredine methiodide. In the whole-cell current mode, muscarine depolarized the membrane with increased frequency of action potentials. Reverse transcriptase-polymerase chain reaction showed the presence of M2-M5 receptor mRNA in the SFO tissues. These results suggest that the SFO receives cholinergic muscarinic synaptic inputs from the MS-DBB. Acetylcholine postsynaptically activates and depolarizes neurones in the SFO partly through specific muscarinic receptors, including M3 receptor subtypes.

Acetylcholine↗

PubMed2001

Spontaneously active GABAergic interneurons in the subfornical organ of rat slice preparations.

Inhibitory postsynaptic currents (IPSCs) were recorded from subfornical organ (SFO) neurons in slice preparations of rats, using whole-cell voltage clamp techniques. Some SFO neurons showed bimodal distributions in amplitude with the large and small IPSCs. The large IPSCs vanished in the tetrodotoxin perfusion medium, but the small did not. Both sizes of the IPSCs were completely abolished by application of bicuculline and picrotoxin. Further subpopulation of SFO neurons with the bimodal distributions showed intermittent bursts of the large IPSCs. Immunohistochemical approach revealed existence of gamma-aminobutyric acid (GABA)-immunoreactive neurons and axons in the SFO. These suggest that spontaneously-active and intermittently-burst-firing GABA interneurons affect other SFO neurons in slice preparations of rats.

Animals↗

PubMed2001

The effect of food consistency and dehydration on reflex parotid and submandibular salivary secretion in conscious rats.

Changes in salivary secretion with different consistency of diet and dehydration were studied in male Wistar rats under unrestricted conditions. To measure the salivary secretion, a stop-flow method was used. There was little unstimulated salivary secretion from the parotid and submandibular glands, but eating solid, powdered, and liquid diets induced parotid and submandibular saliva. There was no significant change in the volume and flow rate of saliva in bilateral parotid glands during the eating of solid diets. The solid and powdered diets induced significantly more salivary secretion from the parotid gland than did the liquid. The salivary flow rate with solid diets was significantly greater from the parotid gland than from the submandibular. On the other hand, the salivary flow rate with the liquid diet was significantly smaller from the parotid gland than from the submandibular. Appreciable amounts of submandibular saliva, but little parotid saliva were secreted during grooming. Clearly, parotid and submandibular saliva have different roles in the rat. When injected intraperitoneally with 1.5 M NaCl solution or water-deprived for 24 h, rats took longer to eat the solid diets, and had increased salivary volume and decreased flow rate from the parotid gland. These results indicate that the moisture content of the diet and the dryness of the mouth alters the volume of parotid saliva secreted in rats and show that parotid saliva plays an important part in mastication and swallowing.

Animals↗

PubMed2001

Angiotensin II induces inward currents in subfornical organ neurones of rats.

The action of angiotensin II on subfornical organ (SFO) neurones was studied using whole-cell current and voltage-clamp recordings in rat slice preparations. In the current-clamp mode, membrane depolarization in response to angiotensin II was accompanied by an increased frequency of action potentials and an increased membrane conductance. In the voltage-clamp mode, angiotensin II elicited inward currents in a dose-dependent manner. The net angiotensin II-induced inward currents were voltage-independent, with a mean reversal potential of -29.8 +/- 6.2 mV. Amplitudes of the angiotensin II-induced inward currents were decreased during perfusion with a low sodium medium. The angiotensin II-induced inward currents were blocked by the AT1 antagonist losartan, and were partially blocked by the AT2 antagonist PD-123319. Neurones which were sensitive to angiotensin II were found in the peripheral region of the SFO, whereas neurones in the central region were less sensitive to angiotensin II. These results suggest that angiotensin II induces inward currents, with opening of nonselective cation channels through mainly AT1 receptors in a subpopulation of SFO neurones of rats.

Angiotensin II↗

PubMed2001

Muscarinic modulation of GABAergic transmission to neurons in the rat subfornical organ.

Cholinergic actions on subfornical organ (SFO) neurons in rat slice preparations were studied by using whole cell voltage- and current-clamp recordings. In the voltage-clamp recordings, carbachol and muscarine decreased the frequency of GABAergic inhibitory postsynaptic currents (IPSCs) in a dose-dependent manner, with no effect on the amplitudes or the time constants of miniature IPSCs. Meanwhile, carbachol did not influence the amplitude of the outward currents induced by GABA. Furthermore, carbachol and muscarine also elicited inward currents in a TTX-containing solution. From the current-voltage relationship, the reversal potential was estimated to be -7.1 mV. These carbachol-induced responses were antagonized by atropine. In the current-clamp recordings, carbachol depolarized the membrane with increased frequency of action potentials. These observations suggest that acetylcholine suppresses GABA release through muscarinic receptors located on the presynaptic terminals. Acetylcholine also directly affects the postsynaptic membrane through muscarinic receptors, by opening nonselective cation channels. A combination of these presynaptic and postsynaptic actions may enhance activation of SFO neurons by acetylcholine.

Animals↗

PubMed2000

Glutamatergic synaptic inputs activate neurons in the subfornical organ through non-NMDA receptors.

The subfornical organ (SFO) plays an important role in central regulation of the autonomic nervous system. The synaptic transmission properties of neurons in the SFO were studied with intracellular and whole-cell patch clamp recordings in the rat slice preparations. Both the spontaneous and evoked excitatory postsynaptic potentials (EPSPs) and currents (EPSCs) were almost completely suppressed by the glutamate receptor antagonist kynurenic acid and the non-NMDA (N-methyl-D-aspartic acid) antagonist CNQX. The non-NMDA agonist kainic acid depolarized the membrane most potently, compared with NMDA and quisqualic acid. These suggest that glutamate is a main excitatory neurotransmitter in the SFO and that its action is at least partly mediated through non-NMDA receptors.

Afferent Pathways↗

PubMed2000

Disorder of salivary secretion in inbred polydipsic mouse.

To find mechanisms of an extreme polydipsia in an inbred strain of mice, STR/N, this study was undertaken using Institute of Cancer Research (ICR) mice as a control. During food deprivation, daily water intake of both strains decreased. The decrement in the STR/N mice was larger than that in the ICR mice. During dehydration, daily food intake of the STR/N mice was smaller than that of the ICR mice. These data indicate that prandial drinking was more severely affected for the STR/N mice. Under anesthesia, the stimulated salivary secretion by pilocarpine of the STR/N mice was significantly smaller than that of the ICR mice. The submandibular gland of the STR/N mice was lighter and harder than that of the ICR mice. After desalivation from the major three salivary glands, the ICR mice drank as much as the STR/N mice. Young STR/N mice with undeveloped polydipsia did not show different salivary secretion stimulated by pilocarpine from the young ICR mice. These findings indicate a dysfunction with age in the salivary glands of the STR/N mice, and they suggest that the decreased saliva induces thirst and triggers extraordinary drinking in the polydipsic mice.

Age Factors↗

PubMed1998

Glutamatergic synaptic inputs to mouse supraoptic neurons in calcium-free medium in vitro.

The effects of Ca2+-free perfusion medium on excitatory postsynaptic currents (EPSCs) and potentials (EPSPs) were studied by whole-cell recordings from neurons of the supraoptic nucleus (SON) in trimmed slice preparations of mouse hypothalamus. EPSCs evoked with either focal stimulation to the SON or perfusion of slices with high K+-medium, spontaneous EPSCs (sEPSCs) and miniature EPSCs (mEPSCs) recorded from neurons of the SON were blocked by the glutamate receptor antagonist kynurenic acid (1 mM). While EPSCs evoked by focal stimulation were abolished in the presence of Ca2+-free perfusion medium; sEPSCs and mEPSCs remained. Neither the frequency nor the amplitude of the sEPSCs and mEPSCs significantly changed during the application of Ca2+-free perfusion medium. Perfusion of slices with high K+-medium increased the mEPSC frequency compared with that recorded in normal Ca2+-containing perfusion medium. In contrast, mEPSC frequency did not change during perfusion with Ca2+-free high K+-medium. In current-clamp mode sEPSPs were observed during the perfusion with Ca2+-free medium. Some sEPSPs recorded in Ca2+-free medium were sufficiently large to evoke action potentials. These results imply that spontaneous glutamatergic synaptic inputs to the hypothalamic neurosecretory cells exist in Ca2+-free perfusion medium. Thus, the present study suggests that Ca2+-free medium does not always block the synaptic transmission in hypothalamic slice preparations.

Action Potentials↗

PubMed1997

C-type natriuretic peptide suppresses arginine-vasopressin secretion from dissociated magnocellular neurons in newborn rat supraoptic nucleus.

Central administration of C-type natriuretic peptide (CNP) affects various neuroendocrine systems. In the present study, we examined whether CNP acts directly on arginine-vasopressin (AVP) secretion from rat supraoptic nucleus (SON) neurons, using acute dissociated cell preparations. CNP inhibited the basal secretion of AVP in a dose-dependent manner (10(-11)-10(-6) M). A- type natriuretic peptide (ANP) and B-type natriuretic peptide (BNP) also suppressed the basal secretion of AVP, however, the effects were two-orders of magnitude less potent than CNP. CNP also suppressed All-induced AVP secretion, however, the inhibitory effect of CNP was less than that of ANP or BNP. These findings suggest that CNP inhibits the basal secretion of AVP through natriuretic peptide receptor (NPR)-B and has a role in the body water and electrolyte homeostasis in the central nervous system.

Animals↗

PubMed1997

Osmotic modulation in glutamatergic excitatory synaptic inputs to neurons in the supraoptic nucleus of rat hypothalamus in vitro.

To clarify influence of osmotic stimulation on the excitatory synaptic inputs to the neurosecretory cells of the supraoptic nucleus (SON), the blind patch technique was used in rat hypothalamic slice preparations. Stable whole-cell recordings were made from 22 neurons in the SON. To observe spontaneous excitatory postsynaptic currents (sEPSCs) in the SON neurons, membrane potentials were clamped between -50 and -90mV. The effects of hypertonic stimulation on the frequency of the sEPSCs were tested in 18 SON neurons. Bath application of mannitol 30 or 60 mM increased the frequency of the sEPSCs. During the application of mannitol (60 mM), the frequency of the sEPSCs increased in 12 of 15 neurons without a change in amplitude. Hypertonic stimulation with NaCl (30 mM) had similar effects to that of mannitol. The increased frequency of miniature EPSCs (mEPSCs) during mannitol application persisted in the presence of TTX in all 8 SON neurons tested with no change in amplitude. Both the non-NMDA antagonist CNQX at 10-30 microM (n = 6) and the non-selective glutamate antagonist kynurenic acid at 1 mM (n = 3) almost completely blocked the EPSCs while the NMDA antagonist AP-5 at 10 microM had no effect on the frequency of the EPSCs in the 4 neurons tested. During application of CNQX, mannitol (60 mM) was added to the perfusion medium in 3 SON neurons. Under these conditions, mannitol had no effect on the frequency of EPSCs. We conclude that hypertonic stimulation directly influences glutamatergic inputs to the neurosecretory cells of the SON by an action on the presynaptic terminals and enhances the excitatory synaptic events.

6-Cyano-7-nitroquinoxaline-2,3-dione↗

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↗