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P Shinnick-Gallagher

Publications and source records attributed to P Shinnick-Gallagher.

At least 19 recordsLinked to original sources
PubMed1995

Agonist action of (RS)-alpha-methyl-4-carboxyphenylglycine (MCPG) in the amygdala.

Glutamatergic excitatory postsynaptic potentials (EPSPs) in the basolateral amygdala (BLA) are reduced in amplitude following agonist activation of presynaptic metabotropic glutamate receptors (mGluR). In this study, the effect of a presumed mGluR antagonist, (RS)-alpha-methyl-4-carboxyphenylglycine (MCPG), was investigated on the EPSP recorded intracellularly in BLA neurons. Superfusion of MCPG (500 microM) significantly reduced the amplitude of evoked EPSPs. In the presence of MCPG, postsynaptic responses to alpha-amino-3-hydroxy-5-methyl-4-isoxazoleproprionic acid (AMPA, 1 microM) were unaltered while responses to N-methyl-D-aspartate (NMDA, 3-5 microM) were potentiated. These data suggest that the MCPG-induced reduction of EPSP amplitude is due to a mGluR agonist action at a presynaptic mGluR 'autoreceptor'.

Amygdala↗
PubMed1995

The functional role of metabotropic glutamate receptors in epileptiform activity induced by 4-aminopyridine in the rat amygdala slice.

The metabotropic glutamate receptor (mGluR) antagonist, (RS)-alpha-methyl-4-carboxyphenylglycine (MCPG; 500 microM), was tested on intracellularly recorded epileptiform activity induced by 4-aminopyridine (4-AP) in amygdala neurons. Superfusing 4-AP (1 mM) produced interictal spiking followed by ictal bursting. MCPG prevented the progressive transition from interictal spiking to ictal bursting but affected neither induction of interictal spiking nor maintenance of ongoing ictal bursting. These data suggest that mGluRs may be involved in the induction of ictal seizure events.

4-Aminopyridine↗
PubMed1994

Interleukin-1 beta inhibits synaptic transmission and induces membrane hyperpolarization in amygdala neurons.

Interleukin-1 beta (IL-1 beta), a mediator of immune response, is found in the brain and IL-1 binding sites are located in the basolateral amygdala (BLA). Superfusion of IL-1 beta (118 pM) hyperpolarized the membrane and decreased input resistance in most BLA neurons in brain slice preparations. The hyperpolarization was dose dependent, reversible, persisted in tetrodotoxin and had an estimated EC50 of 15.3 pM. Reversal potentials for the hyperpolarization recorded with potassium acetate and KCl electrodes were -74 and -40 mV, respectively. These data suggest involvement of a chloride conductance. The hyperpolarization was not observed in bicuculline or in acutely dissociated BLA neurons, which implicates an indirect mediation through enhancement of endogenous gamma-aminobutyric acid (GABA). Superfusion of IL-1 beta (118 pM) inhibited excitatory and fast and slow inhibitory postsynaptic potentials evoked by stimulating either the stria terminalis or the lateral amygdala. Fast and slow inhibitory postsynaptic potentials elicited by direct stimulation of GABA interneurons in the lateral amygdala were also depressed by IL-1 beta. IL-1 beta did not depress responses to GABA or glutamate receptor agonists in slices or currents induced by glutamate agonists in acutely dissociated BLA neurons. These findings indicate that inhibition of synaptic transmission is presynaptic. The results show that IL-1 beta inhibits excitatory and inhibitory transmission at a presynaptic site and hyperpolarizes the membrane through an indirect action, possibly by enhancing the action of endogenous GABA in the BLA nucleus. The inhibitory effect of IL-1 beta suggests that factors in the immune system play a role in modulating neuronal function in the BLA.

Amino Acid Sequence↗
PubMed1994

Activation of postsynaptic metabotropic glutamate receptors by trans-ACPD hyperpolarizes neurons of the basolateral amygdala.

Glutamate has traditionally been regarded as an excitatory neurotransmitter. Synaptic activation of ionotropic glutamate receptors mediates fast EPSPs in the CNS. Moreover, activation of metabotropic glutamate receptors (mGluRs), which are coupled to second messenger effector systems via GTP-binding proteins (G-proteins), results in the expression of slow EPSPs. We have now examined the response of basolateral amygdala (BLA) neurons to activation of postsynaptic mGluRs. In approximately 78% of BLA neurons examined, activation of postsynaptic mGluRs results in membrane hyperpolarization and an associated decrease in membrane input resistance or a hyperpolarization followed by a depolarization associated with an increase in input resistance. The purpose of this study was to address the mechanisms underlying the membrane hyperpolarization. Here, we report that the ACPD-induced hyperpolarization is insensitive to TTX, is dependent on extracellular K+ concentrations, and has a reversal potential (-84 mV) close to that estimated from the Nernst equation for an increase in a K+ conductance. In addition, the ACPD response is resistant to (1) intracellular chloride loading, (2) the GABAB receptor antagonist CGP55845A, (3) the ACh receptor antagonist atropine, and (4) the ionotropic glutamate receptor antagonists CNQX and APV. These data suggest that the hyperpolarization results from a direct activation of postsynaptic mGluRs on neurons of the BLA. Furthermore, we performed studies that suggest that the hyperpolarization is G-protein mediated and results from activation of a TEA-sensitive, calcium-dependent potassium conductance. The sensitivity of this conductance to thapsigargin further suggests that this response requires the release of calcium from intracellular stores. In summary, these data suggest a role for glutamate as an inhibitory transmitter in the BLA during periods of metabotropic glutamate receptor activation. In nuclei such as the BLA that are exquisitely sensitive to seizure induction, an inhibitory response to glutamate may act to delay the onset of epileptogenesis.

Action Potentials↗
PubMed1993

The central nucleus of the rat amygdala: in vitro intracellular recordings.

Membrane properties of neurons from the central nucleus of the rat amygdala (ACe) were analyzed using intracellular current-clamp recordings from in vitro coronal slices of adult rat amygdala. Two types of neurons were identified and classified according to their accommodation characteristics and the nature of their afterhyperpolarizations (AHP). Type A neurons represented 74% of the population and were identified by a lack of accommodation and a medium-AHP (m-AHP) in response to transient (100 ms) depolarizing current injection. The m-AHP was defined by a fast decay time constant with a mean tau AHP = 113.6 ms. In both Type A and Type B ACe cells the m-AHP can be reduced with cadmium and rubidium. Type B neurons represented 26% of the population and were identified by the presence of accommodation and a long duration slow-AHP (s-AHP) following the m-AHP. The s-AHP was defined by a slow decay time constant with a mean tau AHP = 1.7 s. The s-AHP was similar to the AHP mediated by IAHP, a long duration calcium-dependent, noradrenaline-sensitive current present in hippocampal neurons. In Type B cells, the s-AHP was reduced by cadmium and noradrenaline. There was no significant difference between Type A and B ACe neurons in passive electrical properties such as the membrane input resistance (RiA = 113 M omega, RiB = M omega), and the membrane time constant (tau A = 15 ms, tau B = 16 ms). However, there was a statistically significant difference in the resting membrane potentials of Type A and B ACe neurons (RMPA = -67 mV; RMPB = -63 mV). These data suggest that the characteristic active membrane properties displayed by Type A and Type B neurons will determine the ability of each type to integrate and encode neuronal information.

Action Potentials↗
PubMed1993

Intracellular recordings from morphologically identified neurons of the basolateral amygdala.

1. Intracellular current-clamp recordings were made from neurons of the basolateral nucleus of the amygdala (BLA) of the rat in the in vitro slice preparation. Neurons were identified morphologically after intracellular injection of biocytin, and the electrophysiological properties and morphological characteristics were correlated. 2. Three distinct morphological subtypes were identified: Class I pyramidal neurons, Class I stellate neurons, and Class II neurons. Each morphological subtype could also be distinguished according to its characteristic electrophysiological properties. 3. Class I pyramidal neurons typically had pyramidal perikarya (cross-sectional area = 245 microns2) with spine-laden apical and basal dendrites. The axon originated from the largest basal dendrite and produced several collaterals that ramified throughout the dendritic arborization of the parent cell. These neurons were characterized electrophysiologically by their higher input resistance (65.6 M omega), long time constant of membrane charging tau 0 (27.8 ms), long duration action potential (half-width = 0.85 ms), and regular firing pattern [1st interspike interval ISI) = 91 ms]. 4. Class I stellate neurons differed morphologically from Class I pyramidal neurons only in the size (cross sectional area = 330 microns 2) and stellate appearance of their perikarya. These neurons had characteristic lower input resistance (40.1 M omega), shorter time constant of membrane charging tau 0 (14.5 ms), shorter duration action potential (half-width = 0.7 ms), and a burst firing pattern (1st ISI = 6.0 ms), all of which were statistically different from Class I pyramidal neurons. 5. Class II neurons were multipolar (cross sectional area = 235 microns 2) and were distinguishable from Class I neurons by the almost complete absence of dendritic spines. Class II neurons were characterized electrophysiologically by a midrange input resistance (58 M omega), intermediate time constant of membrane charging tau 0 (19 ms), intermediate action-potential duration (half-width = 0.77 ms), and a burst firing pattern (1st ISI = 6.0 ms). In contrast to Class I neurons, action-potential firing of Class II neurons did not accommodate in response to prolonged depolarizing current injection. 6. In conclusion, BLA neurons may be characterized by their specific electrophysiological properties as well as by their morphological traits. Therefore, permitting assessment of signal transduction in identified populations of neurons within this nucleus.

Action Potentials↗
PubMed1992

In vivo kindling does not alter afterhyperpolarizations (AHPs) following action potential firing in vitro in basolateral amygdala neurons.

Kindling in vivo results in enhanced glutamatergic synaptic transmission and epileptiform bursting in vitro in neurons of the basolateral amygdala (BLA). We tested the hypothesis that reduction of intrinsic inhibitory mechanisms, such as the slow- and medium-afterhyperpolarizations (s-AHPs, m-AHPs), contributes to the enhanced neuronal excitability observed in kindling-induced epileptogenesis using intracellular recording methodology. In these studies, neurons were recorded from the BLA contralateral to the kindling site. AHPs following depolarizing current-induced (100 ms, 1 nA) action potentials were recorded from BLA neurons of control and kindled animals. We found no difference in the amplitude of the s-AHP and m-AHP, or the duration of the s-AHP between control and kindled neurons. In addition, kindling did not alter the distribution of accommodating/non-accommodating BLA neurons (as assessed from neuronal responses during long (500 ms) depolarizing current injection). It is concluded that an alteration in the neuronal network within the BLA rather than a blockade of an intrinsic inhibitory mechanism underlies the enhanced excitability recorded in BLA neurons following kindling.

Action Potentials↗
PubMed1992

Trans-ACPD and L-APB presynaptically inhibit excitatory glutamatergic transmission in the basolateral amygdala (BLA).

Intracellular recordings were obtained from neurones of the basolateral nucleus of the amygdala (BLA) and glutamate-mediated EPSPs evoked by stimulation of the stria terminalis (ST). The conformationally restricted analogue of glutamate trans-1-aminocyclopentane-1,3-dicarboxylic acid (trans-ACPD) caused a dose-dependent reduction in EPSP amplitude, EC50 approximately 50 microM. This effect was mimicked by the glutamate autoreceptor agonist, L-aminophosphonobutyric acid (L-APB, 50 microM). Furthermore, the effects of submaximal concentrations (50 microM) of trans-ACPD and L-APB were additive. The reduction in EPSP amplitude is observed with concentrations of both drugs that have no effect on either the resting membrane potential or the input resistance of BLA neurones. In addition, these compounds can reduce EPSP amplitude but not the response to exogenous application of alpha-amino-3-hydroxy-5-methyl-4-isoxazole-proprionate (AMPA) suggesting activation of presynaptic receptors. These findings suggest that both trans-ACPD and L-APB act at presynaptic glutamate receptors on glutamatergic afferents to reduce excitatory transmission in the BLA.

Aminobutyrates↗
PubMed1992

Kindling-induced long-lasting changes in synaptic transmission in the basolateral amygdala.

1. Intracellular current-clamp recordings were obtained from neurons of the basolateral amygdala (BLA) in an in vitro slice preparation from control and kindled animals. Postsynaptic potentials, elicited by stimulation of the stria terminalis (ST) or lateral amygdaloid nucleus (LA), were used to investigate the role of excitatory and inhibitory amino acid transmission in kindling-induced epileptiform activity. The contributions of glutamatergic and GABAergic receptor subtypes were analyzed by use of the non-N-methyl-D-aspartate (non-NMDA) antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), the NMDA antagonist DL-2-amino-5-phosphonovaleric acid (APV), and the GABAA antagonist bicuculline methiodide (BMI). 2. The synaptic waveform evoked in control neurons consisted of an excitatory postsynaptic potential (EPSP), a fast inhibitory postsynaptic potential (f-IPSP), and a slow inhibitory postsynaptic potential (s-IPSP). Stimulation of the ST or LA pathways evoked a burst-firing response in BLA neurons contralateral from the site of stimulation of kindled animals. 3. APV (50 microM) reduced, but CNQX (10 microM) completely blocked, the burst-firing response in BLA neurons from kindled animals and bicuculline-induced bursting in control neurons. 4. Kindling significantly increased the amplitude of both the slow NMDA- and the fast non-NMDA-receptor-mediated components of synaptic transmission (s- and f-EPSPs, respectively). Furthermore, the stimulus intensities required to evoke EPSPs just subthreshold for action potential generation were significantly lower in slices from kindled animals. 5. In kindled neurons no significant change was observed in the membrane input resistance and resting membrane potential or in the number of action potentials elicited in response to depolarizating current injection. 6. Kindling resulted in a pathway-specific loss of ST- and LA-evoked feedforward GABAergic synaptic transmission and of spontaneous IPSPs. In the same BLA neurons, direct GABAergic inhibition via stimulation of the LA was not affected by kindling. 7. The enhanced glutamatergic transmission was not due to disinhibition, because, in the presence of BMI (and CNQX to prevent BMI-induced bursting), the s-EPSP amplitude was still greater in kindled than in control neurons. 8. These results provide evidence that the epileptiform activity observed in BLA neurons after kindling results from an increase in excitatory NMDA- and non-NMDA-receptor-mediated glutamatergic transmission and a decrease in inhibitory gamma-aminobutyric acid (GABA)-receptor-mediated transmission; the enhanced excitatory transmission cannot be accounted for by reduced inhibition.(ABSTRACT TRUNCATED AT 400 WORDS)

2-Amino-5-phosphonovalerate↗
PubMed1992

Epileptogenesis reduces the sensitivity of presynaptic gamma-aminobutyric acidB receptors on glutamatergic afferents in the amygdala.

Intracellular recordings were obtained from the basolateral amygdala in in vitro rat brain slice preparations to examine whether gamma-aminobutyric acid (GABA)B receptors are altered after in vivo kindling-induced epileptogenesis. Stimulating the stria terminalis evoked excitatory (EPSPs) and inhibitory (IPSPs) postsynaptic potentials in control neurons, and epileptiform bursting or enhanced EPSPs, but no IPSPs, in neurons from animals, 4 to 8 weeks after the last kindled seizure. Baclofen (0.1 nM-100 microM) depressed EPSPs in control and kindled basolateral amygdala neurons, but the EC50 appeared to be shifted 100-fold from 5 nM in control to 500 nM in kindled neurons. Further analysis suggested a high-affinity component may be affected in kind led neurons. The absence of IPSPs in kindled neurons could not account for this shift, because effects of baclofen on EPSP amplitude were reduced in kindled animals even when GABAA receptors were blocked with bicuculline methiodide (30 microM) and postsynpatic GABAB receptors with intracellular guanosine 5'-O-3-thiotriphosphate (10 mM); 6-cyano-2,3-dihydroxy-7-nitroquinoxaline (10 microM) was also present to block bicuculline methiodide-induced bursting. Membrane responses to exogenously applied N-methyl-D-aspartate and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid were not affected by baclofen. Baclofen also hyperpolarized basolateral amygdala neurons and reduced membrane input resistance with an EC50 of 1 microM in control and kindled neurons. Post- but not presynaptic effects of baclofen were blocked by 2-hydroxy-saclofen (100 microM) and pertussis toxin pretreatment. In conclusion, kindling-induced epileptogenesis reduces the sensitivity of presynaptic GABAB receptors, an effect which may contribute to the enhancement of excitatory transmission in kindled animals. Furthermore, different pharmacological properties of pre- and postsynaptic receptors in the amygdala suggest two distinct populations of GABAB receptors whose long-lasting responses to kindling-induced seizures are different.

Animals↗
PubMed1992

Differential actions of corticotropin releasing factor on basolateral and central amygdaloid neurones, in vitro.

Intracellular current- and voltage-clamp recordings were obtained from basolateral (BLA) and central (ACe) neurones of the rat amygdala in vitro. The effect of superfusion of rat corticotropin releasing factor (rCRF) was examined on the ACe and BLA, nuclei with a high density of CRF-immunoreactive cell bodies and CRF receptors, respectively. rCRF (12.5-250 nM) had no effect on either resting membrane potential or input resistance in BLA neurones. In contrast, at low nanomolar concentrations rCRF (10-50 nM) caused hyperpolarisation and decreased membrane input resistance in the majority of ACe neurones. The equilibrium potential for this effect was -84 mV in the presence of tetrodotoxin (0.5 microM), suggesting that this response may be mediated by a postsynaptic increase in K+ conductance. Furthermore, rCRF consistently reduced the amplitude of, and the current mediating, the slow after hyperpolarisation following evoked action potential firing in both nuclei. This effect was concentration-dependent with an EC50 of 40 nM in BLA neurones and was insensitive to tetrodotoxin and noradrenergic antagonists. In addition, the putative CRF antagonist alpha-helical CRF9-41 (5 microM) blocked the effect of rCRF and showed partial agonist action on slow after hyperpolarisations. In BLA neurones, rCRF (50 nM) prolonged the Ca(2+)-spike evoked in the presence of tetrodotoxin and tetraethylammonium (2 mM), suggesting that the blockade of the slow after hyperpolarisation occurs subsequent to Ca2+ entry. These results suggest that rCRF has a differential effect on the membrane properties of BLA and ACe neurones possibly by activation of a heterogeneous population of CRF receptors.

Amygdala↗
PubMed1991

Decrease of GABA-immunoreactive neurons in the amygdala after electrical kindling in the rat.

The present study was designed to investigate the effects of electrical kindling in vivo on GABA immunoreactivity (GABA-IR) of the lateral and basolateral amygdaloid nuclei 2-6 months post-stimulation. Male Sprague-Dawley rats were implanted with bipolar electrodes in the basolateral nucleus and stimulated once per day until 3-5 stage 5 seizures were observed. Coronal sections containing the amygdala were processed for GABA-IR using the contralateral side of the brain. Results indicate that, in comparison to controls, fully kindled animals showed a significant decrease in total number of GABA-IR amygdala neurons. Decreases in GABA-positive punctate structures surrounding unlabeled pyramidal cells were also observed, but not quantified. The present data suggest that epileptogenesis of the amygdala is associated with a significant reduction of GABA-IR in the lateral and basolateral areas throughout the contralateral amygdaloid nucleus.

3,3'-Diaminobenzidine↗
PubMed1991

Excitatory transmission in the basolateral amygdala.

1. Intracellular current-clamp recordings obtained from neurons of the basolateral nucleus of the amygdala (BLA) were used to characterize postsynaptic potentials elicited through stimulation of the stria terminalis (ST) or the lateral amygdala (LA). The contribution of glutamatergic receptor subtypes to excitatory postsynaptic potentials (EPSPs) were analyzed by the use of the non N-methyl-D-aspartate (non-NMDA) antagonist, 6-cyano-7-nitro-quinoxaline-2,3-dione (CNQX), and the NMDA antagonist, (DL)-2-amino-5-phosphonovaleric acid (APV). 2. Basic membrane properties of BLA neurons determined from membrane responses to transient current injection showed that at the mean resting membrane potential (RMP; -67.2 mV) the input resistance (RN) and time constant for membrane charging (tau) were near maximal, and that both values were reduced with membrane hyperpolarization, suggesting an intrinsic regulation of synaptic efficacy. 3. Responses to stimulation of the ST or LA consisted of an EPSP followed by either a fast inhibitory postsynaptic potential (f-IPSP) only, or by a fast- and subsequent slow-IPSP (s-IPSP). The EPSP was graded in nature, increasing in amplitude with increased stimulus intensity, and with membrane hyperpolarization after DC current injection. Spontaneous EPSPs were also observed either as discrete events or as EPSP/IPSP waveforms. 4. In physiological Mg2+ concentrations (1.2 mM), at the mean RMP, the EPSP consisted of dual, fast and slow, glutamatergic components. The fast-EPSP (f-EPSP) possessed characteristics of kainate/quisqualate receptor activation, namely, the EPSP increased in amplitude with membrane hyperpolarization, was insensitive to the NMDA receptor antagonist, APV (50 microM), and was blocked by the non-NMDA receptor antagonist, CNQX (10 microM). In contrast, the slow-EPSP (s-EPSP) decreased in amplitude with membrane hyperpolarization, was insensitive to CNQX (10 microM), and was blocked by APV (50 microM), indicating mediation by NMDA receptor activation. 5. In the presence of CNQX (10 microM), ST stimulation evoked an APV-sensitive s-EPSP. In contrast, LA stimulation evoked a f-IPSP, which when blocked by subsequent addition of bicuculline methiodide (BMI; 30 microM) revealed a temporally overlapping APV-sensitive s-EPSP. These data suggest that EPSP amplitude and duration are determined, in part, by the shunting of membrane conductance caused by a concomitant IPSP. 6. Superfusion of either CNQX or APV in BLA neurons caused membrane hyperpolarization and blockade of spontaneous EPSPs and IPSPs, suggesting that these compounds may act to block tonic excitatory amino acid (EAA) release within the nucleus, and that a degree of feed-forward inhibition occurs within the nucleus.(ABSTRACT TRUNCATED AT 400 WORDS)

2-Amino-5-phosphonovalerate↗
PubMed1991

Inhibitory transmission in the basolateral amygdala.

1. Intracellular recording techniques were used to characterize synaptic inhibitory postsynaptic potentials (IPSPs) recorded from neurons of the basolateral nucleus of the amygdala (BLA). Bipolar electrodes positioned in the stria terminalis (ST) or lateral amygdala (LA) were used to evoke synaptic responses at a frequency of 0.25 Hz. 2. Two synaptic waveforms having IPSP components could be evoked by electrical stimulation of either pathway: a biphasic, excitatory postsynaptic potential (EPSP), fast-IPSP (f-IPSP) waveform, and a multiphasic, EPSP, f-IPSP, and subsequent slow-IPSP (s-IPSP) waveform. Expression of either waveform was dependent on the site of stimulation. ST stimulation evoked a similar number of biphasic (45%) and multiphasic (50%) synaptic responses. In contrast, stimulation of the LA pathway evoked mainly (80%) multiphasic synaptic responses. 3. Both the f- and s-IPSP elicited by ST stimulation could be reduced in amplitude in the presence of the glutamatergic, N-methyl-D-aspartate (NMDA) antagonist, (DL)-2-amino-5-phosphonovaleric acid (APV, 50 microM), and were abolished by the glutamatergic, non-NMDA antagonist, 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 10 microM). In contrast, a CNQX-resistant f-IPSP was evoked with LA stimulation and abolished by subsequent addition of bicuculline methiodide (BMI), a gamma-aminobutyric acid (GABAA) receptor antagonist, suggesting direct inhibition of BLA neurons by GABAergic LA interneurons. The sensitivity of the s-IPSPs and the f-IPSPs to glutamatergic antagonists suggests the presence of feed-forward inhibition onto BLA neurons. 4. The f-IPSP possessed characteristics of potentials mediated by GABAA receptors linked to Cl- channels, namely, a reversal potential of -70 mV, a decrease in membrane resistance (13.5 M omega) recorded at -60 mV, a block by BMI, and potentiation by sodium pentobarbital (NaPB). 5. The s-IPSP was associated with a resistance decrease of 4.5 M omega, a reversal potential of -95 mV, and was reversibly depressed (approximately 66%) by 2-hydroxy-saclofen (100 microM), suggesting activation of GABAB receptors. 6. The large resistance change associated with the f-IPSP, its temporal overlap with evoked EPSPs, and the development of both spontaneous and evoked burst firing in the presence of BMI suggests that the f-IPSP determines the primary state of excitability in BLA neurons.(ABSTRACT TRUNCATED AT 400 WORDS)

2-Amino-5-phosphonovalerate↗
PubMed1990

Slow inward and late slow outward currents induced by hyperpolarizing pre-pulses in cat bladder parasympathetic neurones.

Single-electrode voltage-clamp techniques were used to examine membrane currents recorded as a result of hyperpolarizing pre-pulses in cat bladder parasympathetic neurones. In 84 ganglion cells examined, two types of current were observed in response to hyperpolarizing pre-pulses of 10 ms to 1 s duration from holding potentials of -30 to -60 mV to test potentials of -90 to -130 mV. In 46 cells, a short-duration pulse induced a slow inward current (SIC); with longer pulse durations, an outward current was superimposed on the SIC, resulting in a late slow outward current (LSOC). In the remaining cells, either a SIC (n = 12) or an LSOC (n = 26) was recorded over a range of hyperpolarizing pre-pulse durations. The more depolarized the holding potential, the more hyperpolarized the test potential and the longer the pulse duration, the larger the amplitude of the SIC and LSOC. The SIC and LSOC were associated with an increase in input conductance. The extrapolated reversal potential (Vrev) for the LSOC obtained at a holding potential of -60 mV (where the LSOC seemed to be less contaminated with the SIC) was -89 +/- 4 mV (mean +/- standard error of the mean; n = 5), which is close to the equilibrium potential for the K ion. The LSOC was depressed by a high-K (10-20 mM) solution and potentiated by a low-K (0.47 mM) solution. The SIC was depressed by a low-Na (26.2 mM) solution, but was not affected significantly by a low-Cl (12.2 mM) solution. A low-Ca (0.1 mM)/high-Mg (5 mM) solution depressed the LSOC, while a high-Ca (5 mM) solution potentiated it. Cd (0.5 mM) blocked the SIC almost completely, and suppressed the LSOC. The LSOC but not the SIC was suppressed by tetraethylammonium chloride (10 mM). Superfusing Cs (3 mM) did not affect either the LSOC or the SIC. 4-Aminopyridine (1 mM) and muscarine (10 microM) depressed or replaced the SIC with an outward current, while potentiating the LSOC. These results suggest that a hyperpolarizing pre-pulse induces slow inward Na- and late slow outward Ca-dependent K currents, which are inactivated at depolarized potentials and are de-inactivated by hyperpolarizing pulses in a time-dependent manner.

4-Aminopyridine↗
PubMed1990

Action of an irreversible acetylcholine esterase inhibitor, soman, on muscarinic hyperpolarization in cat bladder parasympathetic ganglia.

1. Intracellular recording techniques were used to examine the action of an irreversible acetylcholine esterase (AChE) inhibitor, soman, on the hyperpolarizations mediated through muscarinic cholinoceptors in cat bladder parasympathetic neurones. 2. Soman (0.1-10 microM) depressed the amplitude and prolonged the duration of the muscarinic slow inhibitory postsynaptic potential (s-i.p.s.p.) elicited by a preganglionic tetanus (40 Hz for 1 s) in the presence of mecamylamine (20 microM), phentolamine (1 microM) and caffeine (1 mM), in a dose-dependent manner. The effect of soman on the amplitude of the s-i.p.s.p. was partially reversible, while the effect on the duration was irreversible. 3. Soman hyperpolarized the membrane and decreased input resistance, but this effect could not account for soman-induced inhibition of the s-i.p.s.p. 4. Soman depressed the amplitude and prolonged the duration of a muscarinic hyperpolarization induced by pressure application of acetylcholine (ACh) in the presence of mecamylamine, phentolamine and caffeine. The time course of this effect paralleled that on the synaptically-evoked muscarinic s-i.p.s.p. 5. A reversible AChE inhibitor, pyridostigmine (10-100 microM), also depressed the amplitude and prolonged the duration of a muscarinic hyperpolarization induced by either preganglionic stimulation or ACh pressure application. These actions were reversible, and not accompanied by a significant change in membrane potential or input resistance. 6. The inhibitory action of soman (1 microM) on the muscarinic hyperpolarization was prevented by pyridostigmine (10 microM), but not by atropine (1 microM). 7. These results demonstrate that soman prolongs not only the muscarinic hyperpolarization, but also inhibits its amplitude through a postsynaptic action, probably through AChE inhibition, in cat bladder parasympathetic neurones.

Acetylcholine↗