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Pathophysiological responses to peripheral nerve injury include alterations in the activity, intrinsic membrane properties and excitability of spinal neurons. The intrinsic excitability of α-motoneurons is controlled in part by the expression, regulation, and distribution of membrane-bound ion channels. Ion channels, such as Kv2.1 and SK, which underlie delayed rectifier potassium currents and afterhyperpolarization respectively, are localized in high-density clusters at specific postsynaptic sites ( Deardorff et al., 2013 , Muennich and Fyffe, 2004 ). Previous work has indicated that Kv2.1 channel clustering and kinetics are regulated by a variety of stimuli including ischemia, hypoxia, neuromodulator action and increased activity. Regulation occurs via channel dephosphorylation leading to both declustering and alterations in channel kinetics, thus normalizing activity ( Misonou et al., 2004 , Misonou et al., 2005 , Misonou et al., 2008 , Mohapatra et al., 2009 , Park et al., 2006 ). Here we demonstrate using immunohistochemistry that peripheral nerve injury is also sufficient to alter the surface distribution of Kv2.1 channels on motoneurons. The dynamic changes in channel localization include a rapid progressive decline in cluster size, beginning immediately after axotomy, and reaching maximum within one week. With reinnervation, the organization and size of Kv2.1 clusters do not fully recover. However, in the absence of reinnervation Kv2.1 cluster sizes fully recover. Moreover, unilateral peripheral nerve injury evokes parallel, but smaller effects bilaterally. These results suggest that homeostatic regulation of motoneuron Kv2.1 membrane distribution after axon injury is largely independent of axon reinnervation.

Neuronal intrinsic properties control action potential firing rates and serve to define particular neuronal subtypes. Changes in intrinsic properties have previously been shown to contribute to hyperexcitability in a number of epilepsy models. Here we examined whether a developmental insult producing the cortical malformation of microgyria altered the identity or firing properties of layer V pyramidal neurons and two interneuron subtypes. Trains of action potentials were elicited with a series of current injection steps during whole cell patch clamp recordings. Cells in malformed cortex identified as having an apical dendrite had firing patterns similar to control pyramidal neurons. The duration of the second action potential in the train was increased in paramicrogyral (PMG) pyramidal cells, suggesting that these cells may be in an immature state, as was previously found for layer II/III pyramidal neurons. Based on stereotypical firing patterns and other intrinsic properties, fast-spiking (FS) and low threshold-spiking (LTS) interneuron subpopulations were clearly identified in both control and malformed cortex. Most intrinsic properties measured in malformed cortex were unchanged, suggesting that subtype identity is maintained. However, LTS interneurons in lesioned cortex had increased maximum firing frequency, decreased initial afterhyperpolarization duration, and increased total adaptation ratio compared to control LTS cells. FS interneurons demonstrated decreased maximum firing frequencies in malformed cortex compared to control FS cells. These changes may increase the efficacy of LTS while decreasing the effectiveness of FS interneurons. These data indicate that differential alterations of individual neuronal subpopulations may endow them with specific characteristics that promote epileptogenesis.

Apamin-sensitive small conductance Ca(2+)-dependent K(+)(SK) channels are generally accepted as responsible for the medium afterhyperpolarization (mAHP) after single or train of action potentials. Here, we examined the functional involvement of these channels in the firing precision, post train AHP and spike frequency adaptation (SFA) in neurons of snail Caucasotachea atrolabiata. Apamin, a selective SK channel antagonist, reduced the duration of single-spike AHP and disrupted the spontaneous rhythmic activity. High frequency trains of evoked action potentials showed a time-dependent decrease in the action potential discharge rate (spike frequency adaptation) and followed by a prominent post stimulus inhibitory period (PSIP) as a marker of slow AHP (sAHP). Neither sAHP nor SFA was attenuated by apamin, suggesting that apamin-sensitive SK channels can strongly affect the rhythmicity, but are probably not involved in the SFA and sAHP. Nifedipine, antagonist of L-type Ca(2+) channels, decreased the firing frequency and neuronal rhythmicity. When PSIP was normalized to the background interspike interval, a suppressing effect of nifedipine on PSIP was also observed. Intracellular iontophoretic injection of BAPTA, a potent Ca(2+) chelator, dramatically suppressed PSIP that confirms the intracellular Ca(2+) dependence of the sAHP, but had no discernable effect on the SFA. During train-evoked activity a reduction in the action potential overshoot and maximum depolarization rate was also observed, along with a decrease in the firing frequency, while the action potential threshold increased, which indicated that Na(+) channels, rather than Ca(2+)-dependent K(+) channels, are involved in the SFA.

Previous research indicates that an age-related increase in the amplitude of the Ca2+-dependent, K+-mediated afterhyperpolarization (AHP) is related to cognitive decline. However, because the AHP is measured following completion of training, it is unclear whether the AHP amplitude is strictly dependent on biological aging or is modified by the training procedure. To address this distinction we examined the effect of environmental enrichment on the AHP amplitude. Young (5–8 months) and aged (22–24 months) male Fischer 344 rats were exposed to environmental enrichment conditions (EC) or maintained in individual cages (IC). Following 8–10 weeks of differential experience, sharp microelectrode current-clamp recordings were obtained in CA1 pyramidal neurons in hippocampal slices. Examination of the AHP demonstrated that the amplitude was significantly reduced in aged animals exposed to enriched conditions. The results indicate that the amplitude of the AHP in hippocampal pyramidal cells from aged animals is dependent on the history of experience and hippocampal activity.

In anesthetized, artificially ventilated rats with one vagus nerve section, the purposes of the present study were to investigate whether release from phasic consecutive hyperinflations (inflation volume=3 tidal volumes) results in the afterhyperpolarization (AHP) of the slowly adapting pulmonary stretch receptor (SAR) activity and whether the effect of ouabain, a Na+-K+ ATPase inhibitor, alters AHP of the SAR activity seen after release from maintained inflations. Release from 10 consecutive phasic hyperinflations did not cause any significant inhibition of SAR activity. Release from maintained inflations (for approximately 10 and 15 cmH2O) for 5 s produced the induction of disappearance of SAR activity, corresponding with the AHP. Intravenous administration of ouabain (20 and 40 microg/kg) had no significant effects on the responses of SAR activity and SAR adaptation index (AI) to maintained inflations, but ouabain treatment with at 40 microg/kg resulted in a significant increase in the SAR activity after stopping the respirator and significantly attenuated the AHP of the SAR activity. In the immunohistochemical study, we found Na+-K+ ATPase alpha3-subunit-isoforms-like immunoreactivity in SAR terminals, forming leaflike extensions in the intrapulmonary bronchioles at different diameters, and those terminals were buried in the smooth muscle. In the same sections, the alpha1 subunit immunoreactivity of SAR terminals was not found. These results suggest that the mechanism of generating the AHP of SARs is mainly mediated by the activation of Na+-K+ ATPase alpha3 subunit isoform.

To determine whether chronic epilepsy induces persistent cellular changes in subicular neurons intracellular recordings were used to compare membrane properties of control and kindled rats. In both, control and kindled preparations the subiculum contained regular firing cells and an extensive sub-population of bursting cells expressing amplifying membrane characteristics. Subicular cells showed a transient depression of the fast and slow AHP in the course of kindling that may contribute to the induction but not permanence of the kindled state.

Neuromodulators which influence the operation of neural networks act as a rule via several cellular and synaptic mechanisms. Activation of GABA B -receptors in the lamprey spinal cord reduce both calcium currents and the peak amplitude of the post-spike afterhyperpolarization (AHP). Activation of GABA B -receptors reduce the segmental alternation rate and modifies the intersegmental coordination when the spinal locomotor circuits are activated by NMDA. Using physiological experiments we find that a reduced AHP is not sufficient to account for the observed reduction of the burst rate. Computer simulations revealed that either a reduced AHP or calcium current could alter the phase coordination between the segments similar to earlier experiments.

The effects of a newly synthesized cognitive enhancer, (-)-R-alpha-[[2-(diethylamino) ethoxy] methyl] benzo [b] thiophene-5-methanol hydrochloride (T-588), on the membrane properties of hippocampal CA1 neurons were investigated in a rat brain slice preparation. T-588 produced a slow and long-lasting depolarization of CA1 neurons with an increase in membrane resistance; this action showed close similarity to that of acetylcholine (ACh). However, the action of T-588 was not affected by atropine, tetrodotoxin or DL-2-amino-5-phosphonovalerate, while the action of ACh was blocked by atropine. The estimated reversal potential of this T-588 effect was near -90 mV which is the reversal potential of potassium ions in CA1 neurons. In the whole-cell voltage-clamp study, T-588 produced a reversible block of the outward potassium current in CA1 neurons. T-588 did not block the afterhyperpolarization evoked by an intracellular current injection, while ACh suppressed it. These results suggest that T-588 has a direct effect on CA1 neurons independent of its cholinergic activity, resulting from blockade of a conductance carried predominantly by potassium ions.

Intracellular recordings are made from distal apical dendrites of CA1 pyramidal neurones in the rat hippocampal slice preparation. Injection of a threshold current evoked two predominant firing patterns: fast spiking and compound spiking. Suprathreshold current injection evoked high frequency dendritic spiking followed by a pronounced slow afterhyperpolarization (sAHP(dend)) lasting for several hundred milliseconds, during which spiking was inhibited for a variable period. In fast spiking dendrites, the size of the sAHP(dend) depended on the number and frequency of preceding spikes, whereas, in compound spiking dendrites, it was more closely related to the size and duration of preceding Ca(2+)-spikes. During the peak of the sAHP(dend), the membrane conductance was increased by 56%. The sAHP(dend) was blocked by perfusion with Ca2+ and by intradendritic injection of ethyleneglycol-bis-(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA; 0.01 or 0.2 M), indicating that the activation of the sAHP(dend) depends on a rise in intradendritic Ca2+. The sAHP(dend) was also blocked by low concentrations (0.5-1 microM) of carbachol. The data presented here therefore, provide strong evidence that the sAHP(dend) is due to the activation of a local Ca(2+)-dependent K(+)-conductance. Possible implications of a dendritic Ca(2+)-dependent K(+)-conductance for the integration of synaptic potentials are discussed.

Mollusc neurons, including those from Helix aspersa, have been extensely used for studies on synaptic plasticity and for pharmacological experiments. Synaptic interactions in H. aspersa are less well documented. In this work, I describe the identification and electrophysiological characteristics of a chemical synapse which is modulated by Met-Enkephalin (ME) and GABA. Low frequency repetitive presynaptic stimulation leads to a progressive amplitude reduction of the EPSPs (homosynaptic depression) of 45% after 20 stimuli and up to 80% after long-lasting repetitive stimulation (150-200 stimuli). The values of the smallest detectable EPSP after profound depression under normal neurotransmitter release levels corresponded to those obtained under high Mg(2+)-low Ca2+ conditions (0.33 +/- 0.045 mV) and to the spontaneous EPSPs (0.4 mV, sigma 2 = 0.02). Recovery after homosynaptic depression could occur by withdrawing the stimulation during 25 s after 15-20 stimuli or 2 min after 150-200 stimuli. Both, ME and GABA reduced the amplitude of the evoked EPSPs and augmented homosynaptic depression although this inhibition was independent of the homosynaptic depression trend. The amplitude of the spontaneous EPSPs was not affected. Naloxone alone did not produce any effect, making it unlikely that the enkephalinergic system could be recruited during homosynaptic depression. ME also shortened the duration of the presynaptic action potential and enhanced its afterhyperpolarization. These results suggest that ME and GABA exert a presynaptic modulation.

Febrile seizures (FS), or fever-induced seizures, are the most common form of seizures during childhood. Although simple FS are usually considered benign, prolonged or recurrent FS are proposed to increase the risk for developing subsequent temporal lobe epilepsy (TLE) in adults. The pathophysiology of FS is still largely unknown. In this study, by using whole-cell patch-clamp recording techniques, we demonstrated that hyperthermia (39-40°C) induced a "febrile seizure-like event" expressed as spontaneous, recurrent, epileptiform discharges (SREDs) followed by a series of sustained depolarizations (SDs) in cultured rat cortical neurons (7-14DIV). The SREDs were characterized by abruptly developing, paroxysmal depolarizing shifts (PDS) of membrane potential with high-frequency spike firing characteristic of electrographic seizures. Furthermore, we also found that hyperthermia induced persistent neuronal hyperexcitability as assessed by their intrinsic electrogenic characteristics which include: 1) depolarized resting potential (RP); 2) decreased input resistance (R(in)); 3) a marked decrease in amplitude, duration and afterhyperpolarization (AHP) of spontaneous action potentials; 4) a prominent reduction in action potential (AP) current threshold (I(th)) and potential threshold (TP); and 5) a dramatic shortened duration, decreased inter-spike intervals (ISI), and increased firing frequency of evoked action potentials. Additionally, our present study also revealed that baclofen (100μM), a specific GABA(B) receptor agonist, significantly repressed the hyperthermia-induced neuronal hyperexcitability and epileptiform discharges in cultured cortical neurons. The results suggest that hyperthermia may induce epileptiform activities in cultured cortical neurons by suppression of the GABA(B) receptor-mediated inhibition, in turn leading to the development of persistent neuronal hyperexcitability when the cells suffered from heating insult. This study provides a novel cellular model for studying the pathogenetic mechanisms of febrile seizures in vitro.

Short-term sleep deprivation (SD) has been shown to enhance cortical activity. However, alterations in the cellular excitability of cortical neurons following SD are not yet fully understood. The present study investigated the effects of 4-hour SD on pyramidal neurons in the prefrontal cortex (PFC) of rats using whole-cell patch-clamp recording. SD led to an increase in the initial slope of firing frequency–current curve and a decrease in frequency adaptation, which were reversed by recovery sleep (RS). Correspondingly, the total afterhyperpolarization (AHP) was reduced in the SD group and returned in the RS group. Furthermore, the component of AHP changed after SD seemed to be sensitive to Ca2+. These observations indicate an enhancement in intrinsic excitability due to short-term SD, and suggest a role for Ca2+-dependent AHP in this change. The findings of the present study may provide a possible explanation for the SD-induced increase in cortical activity.

The excitability level of pyramidal neurons in the basolateral amygdala (BLA) is greatly increased following muscarinic receptor activation, an effect associated with an increased rate of action potential firing and reduction of the afterhyperpolarization (AHP). We impaled BLA pyramidal neurons in slices of rat ventral forebrain with a single microelectrode to examine the currents underlying the AHP and spike frequency accommodation and determine their sensitivities to muscarinic modulation. In voltage-clamp, depolarizing steps were followed by biphasic outward tail currents, consisting of rapidly decaying (IFast) and slowly decaying (ISlow) current components. These corresponded temporally with the medium and slow portions of the AHP, respectively. The reversal potential for the IFast component of the AHP tail current shifted in the depolarizing direction with increases in the extracellular K+ concentration. The amplitude of IFast was reduced during perfusion of 0-Ca2+ medium or by superfusion of TEA (1-5 mM) or carbachol (10-40 microM). It is suggested that IFast was produced by the rapidly decaying Ca(2+)-activated K+ current (IC) and the muscarinic-sensitive M-current (IM). The ISlow tail current component reversed at the estimated values for EK in medium containing either normal or elevated K+ levels. This component was eliminated by perfusion of 0-Ca2+ medium or inclusion of cyclic-AMP in the recording electrode. It was not blocked by TEA (5 mM) or apamin (50-500 nM), but was reduced by carbachol in a dose-dependent manner (IC50 = 0.5 microM). Electrical stimulation of cholinergic afferent pathways to the BLA produced inhibition of ISlow, an effect which was enhanced by eserine and prevented by atropine. Loss of the ISlow component was always accompanied by similar reductions in accommodation and the slow AHP. It was concluded that this tail current component resulted from the slowly decaying Ca(2+)-activated K+ current, IAHP. Thus, the muscarinic inhibition of IAHP contributes to the enhanced excitability exhibited by BLA pyramidal neurons following cholinergic stimulation.

The present in vitro study was performed to characterize neurons within dorsal regions of the nucleus tractus solitarii (NTS), principally at the level of area postrema, and known to receive inputs predominantly from cardiovascular and respiratory afferents (i.e. cardiorespiratory NTS). This report describes 4 classes of neurons (S1-S4) that were silent at their resting membrane potential and received relatively short (< 3.6 ms) and consistent latency synaptic inputs (+/- 0.4 ms) comprising either an EPSP or EPSP/IPSP sequence following low intensity electrical stimulation of the solitary tract (ts). Intracellular recording with sharp electrodes were used to characterize neuron types based on their different firing response patterns to injection of depolarizing current. S1 cells showed a single action potential; S2 fired repetitively; S3 produced a 2-5 spike burst coincident with the start of the current pulse and S4 neurons showed delayed excitation. Accommodation of firing frequency was seen in S2, S3 and some S4 cells. The voltage dependency of the different discharge patterns of the 4 cell groups was tested by current pulse stimulation at different holding potentials. However, in the majority of cells in any one cell class the firing pattern was qualitatively similar. Based on these findings it is suggested that the different firing characteristics reflect differences in intrinsic membrane properties between neuron classes. Representative examples from each of the defined cell classes were further studied in current and voltage clamp using the whole cell patch technique to define the presence and role of certain ionic currents in the firing response patterns of the 4 cell groups. In the current clamp configuration the firing behavior of S1 neurons (single spiking) was unaltered during exposure to 4-aminopyridine (4-AP; 2 mM), cobalt chloride (Co; 5 mM), norepinephrine (NE; 20 microM) and muscarine chloride (50 microM). It is suggested that the relatively low excitability of this neuron is due a persistent outward current which occurred at -40 mV during depolarizing voltage steps in the voltage clamp configuration. A common characteristic of S2 neurons (repetitively firing) was that they showed accommodation during current injection which was greatly attenuated in the presence of Co or NE. In addition, 4-AP slowed the firing frequency, reduced the afterhyperpolarization and broadened the spike width of S2 cells. Interestingly, the amount of accommodation observed in S2 cells was variable for cells of this class and was proportional to the magnitude of a Co-sensitive inward current present during depolarizing voltage steps between -45 to -5 mV.(ABSTRACT TRUNCATED AT 400 WORDS)

The effect of caffeine on the CA1 pyramidal neurons freshly dissociated from rat hippocampus was investigated with nystatin-perforated patch technique under voltage-clamp condition. Caffeine evoked a transient outward current ( I caffeine ) in a concentration-dependent manner at a holding potential of −40 mV. The activation and inactivation of I caffeine were accelerated with increasing caffeine concentration. The reversal potential for I caffeine was close to K + equilibrium potential. The I caffeine was not blocked by apamin and 4-aminopyridine but suppressed by charybdotoxin, tetraethylammonium, quinine and Ba 2+ . Thus, the pharmacological characteristics of I caffeine were similar to those of Ca 2+ -activated K + current having a large conductance ( I C ), which generates a fast afterhyperpolarization (a.h.p.). I caffeine was depressed by pretreatment with a membrane-permeant Ca 2+ chelator (BAPTA-AM) and by depletion of the Ca 2+ -induced Ca 2+ release (CICR) pool with ryanodine. A blocker of CICR sites, procaine, potently depressed the I caffeine . In the absence of the extracellular Ca 2+ , an application of 10 mM caffeine depleted the caffeine-sensitive Ca 2+ pools. I caffeine recovered in an exponential fashion in the presence of the extracellular Ca 2+ . It was concluded that rat hippocampal pyramidal neurons have a caffeine-sensitive Ca 2+ pool. Furthermore, the Ca 2+ released from the pool evokes K + current similar to I C current and hyperpolarizes the neurons.

Acute exposure to ethanol at 22 and 44 mM concentrations altered several features of the current-evoked voltage responses of cerebellar Purkinje neurons and hippocampal neurons studied in culture model systems. Whole cell current clamp techniques were used. At 22 mM, ethanol depressed current-evoked spiking in the hippocampal neurons but enhanced the current-evoked spiking in the Purkinje neurons. In both neuronal types, 44 mM ethanol depressed spiking, the amplitude of the afterhyperpolarization generated at the termination of a current pulse and the amplitude of the off-response generated at the termination of a hyperpolarizing pulse. Ethanol had little or no effect on resting membrane potential or the passive membrane properties measured near resting level in either neuronal type. Some changes in the current-voltage curves were observed at more depolarized or hyperpolarized potentials in both neuronal types. In the Purkinje neurons, where spontaneous activity was a prominent feature of some recordings, exposure to ethanol reduced the frequency of the spontaneous events. These results indicate that acute exposure to ethanol at intoxicating doses alters the membrane excitability of these two CNS neuronal types. The ethanol induced changes in neuronal excitability presumably contribute to the changes in firing properties observed in extracellular recordings from these neuronal types in vivo and the behavioral effects observed during alcohol intoxication in animal models.

Membrane potential oscillations (MPOs) of 2-10 Hz and up to 6 mV were found in almost all stable hippocampal CA1 and CA3 neurons in the in vitro slice preparation. MPOs were prominent for pyramidal cells but less pronounced in putative interneurons. MPOs were activated at threshold depolarizations that evoked a spike and the frequency of the MPOs increased with the level of depolarization. MPOs were distinct from and seemed to regulate spiking, with a spike often riding near the top of a depolarizing MPO wave. Analysis of the periodicity of the oscillations indicate that the period of MPOs did not depend on the afterhyperpolarization (AHP) following a single spike. MPOs persisted in low (0-0.1 mM) Ca2+ medium, with or without Cd2+ (0.2 mM), when synaptic transmission was blocked. Choline-substituted low-Na+ (0-26 mM) medium, 3 microM tetrodotoxin (TTX) or intracellular injection of QX-314 reduced or abolished the fast Na(+)-spike and reduced inward anomalous rectification. About 40% of CA1 neurons had no MPOs after Na+ currents were blocked, suggesting that these MPOs were Na(+)-dependent. In about 60% of the cells, a large depolarization activated Ca(2+)-dependent MPOs and slow spikes. MPOs were not critically affected by extracellular Ba2+ or Cs2+, or by 0.2 mM 4-aminopyridine, with or without 2 mM tetraethylammonium (TEA). However, in 5-10 mM TEA medium, MPOs were mostly replaced by 0.2-3 Hz spontaneous bursts of wide-duration spikes followed by large AHPs. Low Ca2+, Cd2+ medium greatly reduced the spike width but not the spike-bursts. In conclusion, each cycle of an MPO in normal medium probably consists of a depolarization phase mediated by Na+ currents, possibly mixed with Ca2+ currents activated at a higher depolarization. The repolarization/hyperpolarization phase may be mediated by Na+/Ca2+ current inactivation and partly by TEA-sensitive, possibly the delayed rectifier, K+ currents. The presence of prominent intrinsic, low-threshold MPOs in all hippocampal pyramidal neurons suggests that MPOs may play an important role in information processing in the hippocampus.

Studies on in vivo and in vitro epilepsy models have shown that progression and maintenance of epileptiform activity can be affected by the slow Ca(2+)-dependent K(+) current (I(sAHP)). This study aimed to investigate the influence of the I(sAHP) on population activity and single cell activity during the transition from the interictal- to the ictal-like phase of an epileptiform field potential induced by Cs(+). Extracellular and intracellular recordings were performed in area CA1 on 400 microm thick hippocampal slices from adult male Wistar rats. During maintained exposure to Cs(+), the transition between the two phases underwent a slow, time-dependent change, where synchronized population activity gradually disappeared and a plateau-like prolongation of the interictal-like phase emerged. In parallel, the size of the ictal-like phase increased. These effects could be ascribed to a gradual block of the I(sAHP) and were mimicked by the I(sAHP) antagonists carbacholine (2 microM), isoproterenol (4 microM) and Ba(2+) (0.2 mM). Cessation of population activity generally occurred without a concomitant decrease in firing rate of single CA1 pyramidal neurons, but was accompanied by the disappearance of hyperpolarizing prepotentials, indicating a shift in the mechanism of action potential initiation. These findings suggest that the presence of the I(sAHP) increases the tendency of hyperexcitable neurons to fire in synchrony, but at the same time serves to dampen the ictal-like activity that follows the hyperexcitable state. Our data indicate that both effects can be attributed to the influence of this current on the steady-state membrane potential in the period of the transition from interictal- to ictal-like activity.

The effects of apamin on rat locus coeruleus (LC) neurons were studied in a brain slice preparation with intracellular recording. Bath application of apamin (2–500 nM) reduced the amplitude of an intermediate component of the afterhyperpolarization (AHP) following single spontaneous action potentials, but did not change the size or time-course of fast and slow components of the AHP, spike amplitude or duration. Apamin blocked the early component of the post-stimulus hyperpolarization (PSH) which follows a train of action potentials. The size of the late component of PSH was sometimes augmented by apamin. Apamin increased the number of spikes evoked by a depolarizing current pulse and increased the slope of the spike frequency-current intensity relation. Accommodation of firing during long depolarizing pulses showed a biexponential time-course indicating 2 distinct components. Apamin specifically reduced the contribution of the fast component of accommodation and increased its time constant. These data indicate that the apamin-sensitive conductance is functionally important in accommodation at faster firing rates such as those seen during evoked spike trains in the present experiments, and which may occur in vivo during behavioral arousal and in anxiety or drug withdrawal syndromes.

Cerebellar Purkinje cells (PCs) are the sole output neurons of the cerebellar cortex. Mature PCs discharge either tonically Na+ spikes or bursts of Na+ spikes ending to a Ca2+ spike. These cells express inactivating and non-inactivating large conductance Ca2+ -dependent K+ (BK) channels in their soma and dendrites. Somatic intracellular recording of acutely prepared brain slices was performed to examine the role of BK channels-mediated current in the tonic and burst firing of PCs. Continuous injection of a negative DC current was used to both suppress the spontaneous activity and stabilize the resting membrane potential around -70 mV. Then, the short depolarizing current injection was used to evoke spike discharge. For establishing of the burst firing, 4-aminopyridine (4-AP) was bath applied to the bath solution. Blockade of BK channels with iberiotoxin (IbTx); a specific blocker of BK channels, did not affect the Na+ spike configuration in the tonic firing but caused a remarkable change in the shape of Na+ and Ca2+ spikes in 4-AP-induced burst. Our results showed that during the burst firing, strong activation of IbTx-sensitive BK channels enhances the amplitude of fast afterhyperpolarization while decreases the duration of both Na+ and Ca2+ spikes. The current from these channels contributes to both the repolarizing of Na+ spike in the burst and setting of the amplitude of post-pulse AHP that occurs immediately after a depolarizing pulse. These data reveal an important role of IbTx-sensitive BK current in regulating of the spike configuration during the burst firing of PCs.

The effects of 5-hydroxytryptamine (5-HT), noradrenaline (NA), dopamine (DA) and the muscarinic receptor agonist carbachol (CCh) on the voltage step-induced outward currents underlying afterhyperpolarization (AHP), consisting of a medium (I(mAHP)) and slow (I(sAHP)) component, were investigated in layer V pyramidal cells of the rat medial prefrontal cortex (mPFC). Whole-cell voltage clamp recordings were performed in vitro to quantitatively measure I(mAHP) and I(sAHP) and to examine their functional link to spike-frequency adaptation in the presence of agonists. CCh, 5-HT and NA all reduced the I(sAHP) and the spike adaptation, and, in some cells, replaced the I(sAHP) by the slow inward currents (I(sADP)) underlying the slow afterdepolarization (sADP). DA, however, failed to increase the frequency despite its comparable inhibition of the I(sAHP) over a range of concentrations. In order to test the neuromodulator agonists to see if they have additive actions on the I(sAHP), the effects of co-application of two agonists that increased spike-frequency, 5-HT+NA, 5-HT+CCh and CCh+NA, all at the concentration 30 microM were examined. Specific combinations that included CCh showed additive effects on the slow afterpolarization currents, possibly via both inhibition of I(sAHP) and generation of I(sADP). These findings suggest that neuromodulators have differential effects on the link between the I(sAHP) modulation and spike-frequency adaptation, and that they could exert additive effects on the slow aftercurrents following a strong excitation and, therefore, regulate the repetitive firing properties of the output cells of the rat mPFC.

In vitro patch-clamp recordings were made to study the membrane properties and synaptic connectivity of fast-spiking interneurons in rat ventral striatum. Using a whole-cell configuration in acutely prepared slices, fast-spiking interneurons were recognized based on their firing properties and their morphological phenotype was confirmed by immunocytochemistry. Membrane properties of fast-spiking interneurons were distinguished from those of medium-sized spiny neurons by their more depolarized resting membrane potential, lower action potential amplitude and shorter half-width, short spike repolarization time and deep spike afterhyperpolarization. Firing patterns of interneurons could be subdivided in a bursting and non-bursting mode. Simultaneous dual whole-cell recordings revealed a high degree of connectivity of fast-spiking interneurons to medium-sized spiny neurons via unidirectional synapses. Burst firing in fast-spiking interneurons that were presynaptic to medium-sized spiny neurons resulted in barrages of postsynaptic potentials showing an initial amplitude increment, rapidly followed by a decrement. In conclusion, ventral striatal fast-spiking interneurons can be clearly distinguished from medium-sized spiny neurons by their membrane properties and their firing patterns can be subdivided in bursting and non-bursting modes. Their synaptic connectivity to medium-sized spiny neurons is unidirectional and characterized by frequency-dependent, dynamic changes in postsynaptic amplitude.

The firing of a train of action potentials in hippocampal pyramidal neurons is terminated by an afterhyperpolarization (AHP) that displays two main components; the medium AHP (I(mAHP)), lasting a few hundred milliseconds and the slow AHP (I(sAHP)), that has a duration of several seconds. It is unclear how much of I(mAHP) is dependent on the entry of calcium ions (Ca(2+)), whereas it is accepted that I(sAHP) is caused by activation of Ca(2+)-activated potassium channels. There has been controversy regarding the subcellular localization and mechanism of activation of these channels. Whole-cell recordings from CA1 neurons in the hippocampal slice preparation showed that inhibition of L-type, but not N-, P/Q-, T- and R-type Ca(2+) channels, reduced both I(mAHP) and I(sAHP). Inhibition of both AHP components by L-type Ca(2+) channel antagonists was not complete, with I(sAHP) being significantly more sensitive than I(mAHP). Somatic extracellular ionophoresis of BAPTA during I(sAHP) caused a transient inhibition, but had no effect on I(mAHP). Cell-attached patch recordings from the soma of CA1 neurons within a slice displayed channels that produced an ensemble waveform reminiscent of I(sAHP) when the patch was subjected to a train of action potential waveforms. The channels were Ca(2+)-activated, exhibited a limiting slope conductance of 19 pS and were not observed in dendritic membrane patches. These data demonstrate that the I(sAHP) is somatic in origin and arises from continued Ca(2+) entry through functionally co-localized L-type channels.

In the hippocampus of chronic temporal lobe epilepsy, many abnormalities in structure and function have been described but their pathophysiological relevance often is poorly understood. In this study, we asked whether there may be a link between changes in the firing pattern and the loss of the calcium binding protein calbindin-D28k in epileptic hippocampal granule cells. Using the perforated patch-clamp technique, we investigated granule cells in slices prepared from human hippocampi removed for the treatment of pharmacoresistant temporal lobe epilepsy. Granule cells in hippocampi without significant signs of structural damage (lesion group) displayed a firing pattern indistinguishable from that of rodent granule cells and were strongly labeled with anti-calbindin-D28k antibodies. In contrast, half of granule cells in sclerotic hippocampi (HS group) showed an altered firing pattern and a severe loss of calbindin-D28k. While these cells show passive membrane properties comparable to cells of the rodent and lesion group, they lack the medium afterhyperpolarization and display only a weak spike frequency adaptation. On the other hand, granule cells in the HS group have an increased action potential threshold and an enlarged fast afterhyperpolarization. Applying post-recording immunohistochemistry to individual electrophysiologically characterized granule cells, we show that the loss of calbindin-D28k is not causally related to any of the changes in firing pattern. Both alterations seem to occur during the course of temporal lobe epilepsy, with the firing pattern being affected earlier than the calbindin-D28k content. In conclusion, we propose that it is the combination of the altered intrinsic excitability of granule cells with the amplified and prolonged synaptic input from perforant path fibers previously described in the epileptic dentate area which promotes tonic, non-adapting, high frequency firing of granule cells and thereby strongly augments the excitability of the hippocampus.

Despite many studies on the biological and pharmacological properties of (-)-epigallocatechin-3-gallate (EGCG), an active component of green tea, information on neuronal modulation by EGCG is limited. This study was designed to investigate the effects of EGCG on the electrical activity of rat substantia nigra dopaminergic neurons using whole-cell patch clamp recordings. The spike frequency was increased to 6.33+/-0.23 (p

The effects of organophosphate (OP) paraoxon, active metabolite of parathion, were studied on the Ca(2+) and Ba(2+) spikes and on the excitability of the neuronal soma membranes of land snail (Caucasotachea atrolabiata). Paraoxon (0.3 muM) reversibly decreased the duration and amplitude of Ca(2+) and Ba(2+) spikes. It also reduced the duration and the amplitude of the afterhyperpolarization (AHP) that follows spikes, leading to a significant increase in the frequency of Ca(2+) spikes. Pretreatment with atropine and hexamethonium, selective blockers of muscarinic and nicotinic receptors, respectively, did not prevent the effects of paraoxon on Ca(2+) spikes. Intracellular injection of the calcium chelator BAPTA dramatically decreased the duration and amplitude of AHP and increased the duration and frequency of Ca(2+) spikes. In the presence of BAPTA, paraoxon decreased the duration of the Ca(2+) spikes without affecting their frequency. Apamin, a neurotoxin from bee venom, known to selectively block small conductance of calcium-activated potassium channels (SK), significantly decreased the duration and amplitude of the AHP, an effect that was associated with an increase in spike frequency. In the presence of apamin, bath application of paraoxon reduced the duration of Ca(2+) spike and AHP and increased the firing frequency of nerve cells. In summary, these data suggest that exposure to submicromolar concentration of paraoxon may directly affect membrane excitability. Suppression of Ca(2+) entry during the action potential would down regulate Ca(2+)-activated K(+) channels leading to a reduction of the AHP and an increase in cell firing.

This study aims to investigate whether (−)-epigallocatechin-3-gallate (EGCG) affects neuronal activity of acutely isolated rat medial vestibular nuclear neurons in whole-cell configuration patch-clamp experiments. EGCG (0.5 and 1 μM) lowered the spontaneous firing rate and hyperpolarized the membrane potential of medial vestibular nuclear neurons. However, it did not change the amplitude of afterhyperpolarization or the spike width of the action potential. A second application of EGCG with the same concentration elicited lesser responses. These results suggest that EGCG decreases neuronal activity by affecting potassium currents which are responsible for membrane potentials.

The possible involvement of protein kinase A (PKA) in the muscarinic inhibition of the slow afterhyperpolarizing current ( I AHP ) was investigated in rat hippocampal pyramidal cells. I AHP was recorded using the whole cell method in hippocampal slices, and Rp-cAMPs, a PKA antagonist, was applied intracellularly. The inhibition of I AHP by carbachol was not affected by Rp-cAMPS. In contrast, Rp-cAMPS reduced the cAMP-dependent inhibition of I AHP by norepinephrine. The results show that phosphorylation by PKA does not contribute to the muscarinic effect on I AHP .

Intracellular recordings were obtained from rat presumed jaw-closing motoneurons in slice preparations to investigate the involvement of the serotonin(7) (5-HT(7)) receptors in serotonergic inhibition of the postspike medium-duration afterhyperpolarization (mAHP) and enhancement of the afterdepolarization (ADP). 5-HT-induced suppression of the mAHP and enhancement of the ADP were mimicked by application of the 5-HT(1A/7) receptor agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) and antagonized by the 5-HT(2/6/7) receptor antagonist clozapine, whereas the 5-HT(2) receptor agonist alpha-methyl-5-hydroxytryptamine (alpha-methyl-5-HT) did not affect the mAHP and ADP. 8-OH-DPAT-induced attenuation of the mAHP and enhancement of the ADP were also antagonized by clozapine and another 5-HT(2/6/7) receptor antagonist ritanserin, whereas the 5-HT(1A) receptor antagonist pindolol failed to block the 8-OH-DPAT-induced effects on the mAHP and ADP. 8-OH-DPAT-induced suppression of the mAHP and enhancement of the ADP were also antagonized by a protein kinase A (PKA) inhibitor H89, whereas 8-OH-DPAT could inhibit the mAHP and enhance the ADP in the presence of a protein kinase C (PKC) inhibitor chelerythrine. The 8-OH-DPAT-induced suppression of the mAHP was enhanced under raised [Ca(2+)](o) and this enhancement was reduced by chelerythrine. It is suggested that the 5-HT(7) receptors are involved in 5-HT-induced attenuation of the mAHP and enhancement of the ADP through activation of PKA, and the attenuation of mAHP through the 5-HT(7) receptors is enhanced under raised [Ca(2+)](o) by PKC activation.

It has been reported previously that the neuronal excitability persistently suppresses and the amplitude of fast afterhyperpolarization (fAHP) increases in CA1 pyramidal cells of rat hippocampus following transient forebrain ischemia. To understand the conductance mechanisms underlying these post-ischemic electrophysiological alterations, we compared differences in activities of large conductance Ca(2+)-activated potassium (BK(Ca)) channels in CA1 pyramidal cells acutely dissociated from hippocampus before and after ischemia by using inside-out configuration of patch clamp techniques. (1) The unitary conductance of BK(Ca) channels in post-ischemic neurons (295 pS) was higher than that in control neurons (245 pS) in symmetrical 140/140 mM K(+) in inside-out patch; (2) the membrane depolarization for an e-fold increase in open probability (P(o)) showed no significant differences between two groups while the membrane potential required to produce one-half of the maximum P(o) was more negative after ischemia, indicating no obvious changes in channel voltage dependence; (3) the [Ca(2+)](i) required to half activate BK(Ca) channels was only 1 microM in post-ischemic whereas 2 microM in control neurons, indicating an increase in [Ca(2+)](i) sensitivity after ischemia; and (4) BK(Ca) channels had a longer open time and a shorter closed time after ischemia without significant differences in open frequency as compared to control. The present results indicate that enhanced activity of BK(Ca) channels in CA1 pyramidal neurons after ischemia may partially contribute to the post-ischemic decrease in neuronal excitability and increase in fAHP.

Whole-cell and intracellular recordings were made in coronal hypothalamic slices prepared from ovariectomized female guinea pigs. 62% of preoptic area (POA) neurons fired action potentials in a bursting manner, and exhibited a significantly greater afterhyperpolarization (AHP) than did non-bursting POA neurons. The majority (70%) of POA neurons (n=76) displayed a time-dependent inward rectification (I(h)) that was blocked by CsCl (3 mM) or by ZD 7288 (30 microM). In addition, 51% of the cells expressed a low-threshold spike (LTS) associated with a transient inward current (I(T)) that was blocked by NiCl(2) (200 microM). A smaller percentage of POA neurons (29%) expressed a transient outward, A-type K(+) current that was antagonized by a high concentration of 4-aminopyridine (3 mM). Moreover, POA neurons responded to bath application of the mu-opioid receptor agonist DAMGO (93%) or the GABA(B) receptor agonist baclofen (83%) with a membrane hyperpolarization or an outward current. These responses were accompanied by a decrease in input resistance or an increase in conductance, respectively, and were attenuated by BaCl(2) (100 microM). In addition, the reversal potential for these responses closely approximated the Nernst equilibrium potential for K(+). These results suggest that POA neurons endogenously express to varying degrees an AHP, an I(h), an I(T) and an A-type K(+) current. The vast majority of these neurons also are inhibited upon mu-opioid or GABA(B) receptor stimulation via the activation of an inwardly-rectifying K(+) conductance. Such intrinsic and transmitter-activated conductances likely serve as important determinants of the firing patterns of POA neurons.

The synaptic regulatory mechanism of resting membrane potential of layer III and V pyramidal neurons was analyzed intracellularly in the slice preparation of cat sensorimotor cortex. During the tetanic stimulation of white matter, subthreshold membrane depolarization was induced, and after that, a slowly developing hyperpolarization was induced in the normal solution. When the membrane potential showed a slow change, spike duration and input resistance did not change and evoked single synaptic response did not reveal the enhancement of slow IPSPs. However, afterhyperpolarization following action potential was enhanced. The slow hyperpolarization and the enhancement of afterhyperpolarization were not observed in the cells treated with an NMDA receptor antagonist or a calcium channel blocker Ni2+ (50–100 μM), or the cells hyperpolarized more than −80 mV before the tetanic stimulation.

Intracellular recordings were performed to study the effects of 5-HT on membrane properties and EPSP/IPSP responses of subicular neurons in rat combined hippocampal-entorhinal cortex slices. Application of 5-HT induced in 76% of the investigated subicular cells a hyperpolarization and a reduction of membrane resistance. In bursting neurons, 5-HT caused a reduction of the depolarizing envelope underlying burst discharges and attenuated the subsequent afterhyperpolarization. While 5-HT decreased isolated AMPA/kainate and NMDA receptor-mediated responses as well as slow IPSPs, we could not find a consistent effect on isolated fast IPSPs. Since in approximately 25% of subicular neurons EPSPs and slow IPSPs were reduced without any increase of membrane conductance, we conclude that 5-HT has in addition to membrane effects also effects on synaptic currents.

The effects of l -deprenyl (selegiline), a highly selective monoamine oxidase type B (MAO-B) inhibitor, on cell excitability of rat hippocampal CA1 neurons were examined in slice preparations using intracellular recording techniques. Superfusion of l -deprenyl (10 and 20 μM) reversibly limited the repetitive firing (RF) of action potentials elicited by injection of depolarizing current pulses (100 ms) into the pyramidal cells. At a concentration of 1–50 μM, l -deprenyl did not alter resting membrane potential or input resistance of the hippocampal CA1 neurons. The limitation of RF by l -deprenyl (20 μM) was accompanied by the reduction of the maximal rate of rise (Vmax) of the action potentials in a non-voltage-dependent manner. In 80% of recorded cells, application of l -deprenyl (20 μM) produced an increase in the amplitude and duration of afterhyperpolarization (AHP). The limitation of l -deprenyl on RF was mimicked by other MAO-B inhibitors, pargyline and 4-phenylpyridine. In addition, the ability of l -deprenyl to limit RF was not observed in the hippocampal CA1 neurons taken from dopamine (DA)-depleted rats. Moreover, we also observed that the l -deprenyl-induced limitation of RF was specifically antagonized by (±)-7-bromo-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine (SKF-83566, 5 μM), a selective D1 dopaminergic receptor antagonist. However, the D2 dopaminergic receptor antagonist, sulpiride (5 μM), had no effect on l -deprenyl's action. These results indicate that the MAO-B inhibitory ability leading to an increase of the dopaminergic tone in the hippocampus is involved, at least in part, in the l -deprenyl-induced reduction of neuronal excitability in the CA1 region of rat hippocampus and that the D1 dopaminergic receptor is involved in l -deprenyl's action. © 1997 Elsevier Science B.V. All rights reserved.

Opioids have an excitatory effect on CA1 pyramidal neurons in the hippocampus due to the inhibition of γ-aminobutyric acid (GABA) release from interneurons. Electrophysiologically, this pyramidal cell excitation is manifest as an increase in extracellularly recorded population spikes, while the reduction in synaptic GABA release is manifest as a decrease in the amplitude of intracellularly recorded inhibitory postsynaptic potentials (IPSPs). Recent studies suggest that some of the behavioral effects of opioids, such as antinociception, can be inhibited antiopioid peptides such as neuropeptide FF (NPFF). In the present study, we have used the hippocampal response to opioids to examine the potential interactions between morphine and NPFF in vitro. Morphine alone (20–200 μM) caused reversible concentration-dependent increases in population spikes and decreases in IPSPs. In extracellular experiments, NPFF (1 μM) alone had no effect on population spikes, but significantly and concentration-dependently inhibited the morphine-induced increases in these responses. Intracellular experiments indicated that while NPFF had no effect on IPSP amplitude, or other pyramidal neurons membrane properties (membrane potential, input resistance, afterhyperpolarization, action potential frequency), it significantly reduced the decrease in IPSP amplitude caused by morphine. These results demonstrate that NPFF can attenuate the effects of morphine on population spikes and IPSPs in the hippocampus, and suggest that this effect occurs at a presynaptic site, possibly involving GABAergic interneurons.

Electrophysiological properties of guinea pig ambiguus (AMB) neurons were studied in a brainstem slice preparation. During subthreshold depolarization AMB neurons displayed an early slow depolarization and a late outward rectification both of which were blocked by replacing Ca2+ with Co2+ in the extracellular solution. AMB neurons showed hyperpolarizing inward rectification which was blocked by extracellular Cs+ and is likely caused by the activation of Ih: In 58% (n = 49) of AMB neurons spike firing was restricted to the early phase of a long-lasting depolarizing current injection (phasic firing). The remaining AMB neurons showed repetitive firing throughout the depolarization (tonic firing). A Ca(2+)-mediated K+ current (IK(Ca)) caused an afterhyperpolarization that followed both single and repetitive spike firing. IK(Ca) also controlled the firing pattern in both types of firing, especially in the phasic firing. Norepinephrine (NE) blocked both the hyperpolarizing inward rectification and the Ca(2+)-dependent AHP. These effects of NE were antagonized by propranolol. It is proposed that the blockade of IK(Ca) and Ih contribute to the improvement of the 'signal-to-noise ratio' by NE in AMB neurons.

The membrane potential of neuropile glial cells and Retzius neurones in the central nervous system of the leech Hirudo medicinalis was measured using electrolyte-filled single-barreled microelectrodes. Intracellular Na+ activity (aNai) was recorded with Na(+)-sensitive double-barreled microelectrodes. Bath-application of kainate, quisqualate and L-glutamate elicited concentration-dependent membrane depolarizations in both cell types as demonstrated by dose-response curves. The competitive quinoxalinedione antagonists 6,7-dinitroquinoxaline-2,3-dione (DNQX) or 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) to the non-NMDA glutamate receptor inhibited the membrane depolarizations in neuropile glial cells completely, but in Retzius neurones only partially. These results confirm that leech neuropile glial cells have a kainate- and quisqualate-preferring non-NMDA glutamate receptor similar to that in the Retzius neurones. The initial decrease in aNai in neuropile glial cells in kainate- or quisqualate-containing solutions and the afterhyperpolarization in these glial cells and the Retzius neurones following the removal of both glutamate antagonists, were blocked in the presence of the cardiac glycoside ouabain (10(-4) M). In saline solutions containing 42.5 mM Li+ instead of Na+ the afterhyperpolarizations were blocked in neuropile glial cells and Retzius neurones. We conclude that the initial aNai changes and the afterhyperpolarization could be due to the stimulation of the electrogenic Na+/K+ pump in the glial and neuronal membranes.

Pyramidal neurons in the rat CA1 hippocampal area contain membrane receptors for acetylcholine but also intracellular receptors for the adrenal corticosteroid hormone corticosterone, i.e., mineralocorticol receptors (MRs) and glucocorticoid receptors (GRs). In this in vitro study we investigated if occupation of MRs or GRs affects the responsiveness of CA1 pyramidal neurons to the cholinergic analogue carbachol. In slices from adrenally intact rats, where probably most of the MRs and a considerable degree of the GRs were occupied, carbachol (0.1–30 μM) induced a dose-dependent: (i) depolarization; (ii) reduction of the afterhyperpolarization and spike frequency accomodation associated with depolarizing current pulses; and (iii) reduction of the synaptically evoked EPSP, slow IPSP and (with higher doses) the fast IPSP. The carbachol responses in slices from adrenalectomized (ADX) rats, where both MRs and GRs are unoccupied, were generally similar to the responses in the adrenally intact controls. However, neurons recorded in slices from ADX rats 1–4 h after a brief (20 min) applications of 3 nM aldosterone, thus predominantly occupying MRs, showed a significant reduction of the carbachol (1 μM) induced depolarization, when compared to the adrenally intact group. By contrast, neurons recorded in ADX slices treated with 30 nM corticosterone, inducing simultaneous activation of MRs and GRs, displayed significantly larger carbachol-evoked depolarizations (1 and 3 μM) than neurons in the three previous experimental groups. Carbachol-induced actions on the afterhyperpolarization, accomodation and synaptically evoked responses did not consistently depend on steroid receptor occupation. The data suggest that under conditions of low adrenocorical activity, i.e., with predominant MR occupation, carbachol induced depolarization will be small, while a gradual increase of the adrenocortical activity, resulting in additional GR occupation, will enhance the carbachol responsiveness in CA1 neurons.

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.

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 accomodating/non-accomodating 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 inhibnitory mechanism underlies the enhanced excitability recorded in BLA neurons following kindling.

Acetate is the primary breakdown product of ethanol metabolism in the liver and has been found in the brain following ethanol ingestion in rats. Systemically administered acetate has been shown to cause motor impairment, an effect which is blocked by the adenosine receptor blocker, 8-phenyltheophylline (8-PT). The effects of sodium acetate were investigated in this study using intracellular recording techniques in rat hippocampal dentate granule cells, and were compared to the actions of ethanol and adenosine individually and in conjunction with 8-PT. Acetate hyperpolarized the membrane at 0.4-0.8 mM. The amplitude and duration of the postspike train afterhyperpolarization (AHP) were increased by acetate when the cell was repolarized to the control resting membrane potential. Comparable results were seen in voltage clamp. Acetate also decreased spike frequency adaptation. The effects of acetate were mimicked by adenosine (50 microM) and ethanol (20 mM). The ethanol effects occluded those produced by acetate. All of the effects of acetate, adenosine and ethanol could be inhibited with prior perfusion of 8-PT (1-10 microM). These data suggest that the actions of the major metabolite of ethanol, acetate, may be mediated by adenosine receptor activation.

Intracellular recordings were made from 52 lateral horn neurones in thin slices of neonatal rat thoracolumbar spinal cord. Of these neurones 12 were spontaneously active and the remainder silent. A number of these cells could be activated antidromically by stimulation of ventral roots. The conduction velocity of the antidromic potential was estimated to be 0.9-2 m/s which is within the range reported for axons of sympathetic preganglionic neurones (SPNs). The membrane properties of antidromically identified SPNs were similar to other lateral horn neurones included in this study and comparable to those reported for SPNs by others. Spontaneous burst firing was recorded in 3 neurones and activity in a further 5 neurones was characterized by the discharge of an action potential followed by an afterhyperpolarization potential (AHP) of peak amplitude 3-13 mV and duration 0.5-4 s. The AHP had an initial fast component (fAHP) which was sensitive to the potassium channel blocker tetraethylammonium (TEA), and a second slower component (sAHP) which was both sensitive to extracellular calcium and TEA. The effects of the selective excitatory amino acid receptor agonists N-methyl-D-aspartate (NMDA), kainate and quisqualate were investigated by superfusion of the agonists, at known concentrations (100 nM to 100 microM). These agonists induced concentration-dependent depolarizations which were primarily associated with a reduction in neuronal input resistance. NMDA-induced depolarizations were potentiated in the absence of magnesium.(ABSTRACT TRUNCATED AT 250 WORDS)

The post-tetanic sequelae of trains of synaptic stimuli (50 pulses at 5 or 10 Hz) were studied with intracellular recordings from rat hippocampal neurons in vitro. In a large proportion of CA1 neurons, stimulation of afferent fibers was followed by a prolonged membrane hyperpolarization (peak amplitude approximately 6 mV) that was associated with a decrease in neuronal input resistance (approximately 33%) that lasted from tens of seconds to over 1 min. Antidromic stimulation or activation of cells with intracellular current injection did not elicit this post-tetanic hyperpolarization (PTH). The PTH could be elicited in chloride (Cl-)-loaded cells, its null potential shifted in response to changes in extracellular potassium ([K+]o), and it was significantly reduced by 5-10 mM extracellular cesium (Cs+). The K(+)-dependent PTH may also be calcium (Ca2+) dependent as its amplitude and associated conductance increase were sensitive to changes in [Ca2+]o. The PTH was enhanced by treatments that increase Ca2+ entry into cells including perfusion with elevated [Ca2+]o, with picrotoxin or with tetraethylammonium ion (TEA). The K+ conductance blocker 4-AP had no consistent effect on the PTH. The PTH was potently blocked by the membrane-permeant forms of cAMP, dibutyryl- and 8-bromo-cAMP. However, phorbol esters that activate protein kinase C and carbachol, which usually block the same potential that is blocked by cAMP, did not depress the PTH. The cardiac glycosides dihydro-ouabain and strophanthidin had only small and variable effects on the PTH.(ABSTRACT TRUNCATED AT 250 WORDS)

We have examined the establishment of functional connectivity between hippocampal and locus coeruleus co-transplants in oculo. Co-transplants were allowed to mature in oculo for 8-54 weeks following grafting and were subsequently removed from the anterior eye chamber for in vitro electrophysiological studies. Single hippocampal transplants in oculo have been shown to exhibit prolonged synaptic responses to local electrical stimulation, and similar responses were observed in hippocampal neurons following stimulation of the hippocampal portion of hippocampus-locus coeruleus co-transplants. Electrical stimulation of the locus coeruleus attenuated the afterhyperpolarization in hippocampal neurons elicited by the injection of depolarizing current, an effect that has been described previously in hippocampal slices following direct application of norepinephrine, and this effect was antagonized by pretreatment with the beta-adrenergic antagonist timolol. Stimulation of the locus coeruleus also produced both hyperpolarizing and depolarizing changes in the resting membrane potential in hippocampal neurons in 2- and 6-month-old co-transplants. In the 2-month-old co-transplants the responses were primarily depolarizing, and appeared to be mediated by a beta-adrenergic receptor, whereas in the 6-month-old co-transplants the responses were more varied. The results suggest that functional alpha- as well as beta-adrenergic receptors develop in oculo, and that the release of norepinephrine at nerve terminals in double grafts produces effects in the hippocampal neurons which are similar to those observed during superfusion of the hippocampal slice preparation with exogenous norepinephrine.