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)     

An N-methyl-D-aspartate receptor mediated excitatory postsynaptic potential evoked in subthalamic neurons in an in vitro slice preparation of the rat

Subthalamic (STH) neurons with slow EPSPs mediated by an N-methyl-D-aspartate (NMDA) receptor were studied in rat brain slice preparation. When STH neurons were intracellularly recorded with KCl-filled electrodes, stimulation of the internal capsule (IC) evoked a short duration depolarization followed by a slow excitatory postsynaptic potential (EPSP) lasting 100-200 ms. The amplitude of the slow EPSP was increased when the neuron was hyperpolarized by a low intensity current injection but was blocked when it was hyperpolarized with strong current. The slow EPSP was reversibly suppressed by application of 30-50 microM DL-2-amino-5-phosphonovareric acid (APV). STH neurons also were recorded, with potassium methylsulfate filled electrodes, in the slice preparation obtained from rats that received chronic knife cuts of the IC at the level of the entopeduncular nucleus. Stimulation of the IC immediately rostral to the STH evoked a fast EPSP followed by a slow EPSP, and IPSPs were largely eliminated in this preparation. The slow EPSP was augmented in MG-free medium and suppressed by 50 microM APV. These results suggest that NMDA receptor mediating slow EPSPs may regulate activities of STH neurons.     

Hyperpolarizing and depolarizing GABAA receptor-mediated dendritic inhibition in area CA1 of the rat hippocampus.

1. gamma-Aminobutyric acidA (GABAA) receptor-mediated inhibition of pyramidal neuron dendrites was studied in area CA1 of the rat hippocampal slice preparation with the use of intracellular and extracellular recording and one-dimensional current source-density (CSD) analysis. 2. Electrical stimulation of Schaffer collateral/commissural fibers evoked monosynaptic excitatory postsynaptic potentials (EPSPs) and population EPSPs, which were followed by biphasic inhibitory postsynaptic potentials (IPSPs). In the presence of the excitatory amino acid receptor antagonists 6,7-dinitroquinoxaline-2,3-dione (DNQX) and D,L-2-amino-5-phosphonovalerate (APV), stimulation in stratum radiatum evoked monosynaptic fast, GABAA and late, GABAB receptor-mediated IPSPs and fast and late positive field potentials recorded in s. radiatum. 3. Fast monosynaptic IPSPs and fast positive field potentials evoked in the presence of DNQX and APV were reversibly abolished by the GABAA receptor antagonist bicuculline methiodide (BMI; 30 microM) and were not changed by the GABAB receptor antagonist P-[3-aminopropyl]-P-diethoxymethylphosphinic acid (CGP 35,348; 0.1-1.0 mM). CGP 35,348 (0.1 mM) reversibly blocked late monosynaptic IPSPs and late positive field potentials. These results suggest that fast field potentials are GABAA receptor-mediated population IPSPs (GABAA, fast pIPSPs) and that late field potentials are GABAB receptor-mediated population IPSPs (GABAB, late pIPSPs). 4. Fast pIPSPs were reversibly abolished when the extracellular Cl- concentration [( Cl-]o) was reduced from 132 to 26 mM in parallel with a depolarizing shift in the reversal potential of fast IPSPs. Paired or repetitive stimulation in s. radiatum reversibly depressed fast pIPSPs and fast IPSPs. Paired-pulse depression of fast pIPSPs was reversibly antagonized by CGP 35,348 (0.4-0.8 mM). 5. Laminar analysis of s. radiatum-evoked fast pIPSPs and one-dimensional CSD analysis revealed active current sources in s. radiatum and passive current sinks in s. oriens and s. lacunosum moleculare. S. radiatum sources were abolished by pressure application of BMI in s. radiatum but not in s. oriens. Stimulation in s. oriens, s. pyramidale, or s. lacunosum moleculare evoked GABAA current sources horizontal to the stimulation site. Changes in the dendritic location of inhibitory current with changes in stimulus location paralleled changes in the distribution of excitatory current. 6. In the presence of 4-aminopyridine (50-100 microM), DNQX and APV long-lasting depolarizing GABAA receptor-mediated responses (LLDs) occurred spontaneously or could be evoked. Current sinks associated with s. radiatum-evoked LLDs were located in the same dendritic area as sources associated with hyperpolarizing fast IPSPs.(ABSTRACT TRUNCATED AT 400 WORDS)     

Excitatory postsynaptic potentials in rat neocortical neurons in vitro. III. Effects of a quinoxalinedione non-NMDA receptor antagonist

1. Intracellular microelectrodes were used to obtain recordings from neurons in layer II/III of rat frontal cortex. A bipolar electrode positioned in layer IV of the neocortex was used to evoke postsynaptic potentials. Graded series of stimulation were employed to selectively activate different classes of postsynaptic responses. The sensitivity of postsynaptic potentials and iontophoretically applied neurotransmitters to the non-N-methyl-D-asparate (NMDA) antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) was examined. 2. As reported previously, low-intensity electrical stimulation of cortical layer IV evoked short-latency early excitatory postsynaptic potentials (eEPSPs) in layer II/III neurons. CNQX reversibly antagonized eEPSPs in a dose-dependent manner. Stimulation at intensities just subthreshold for activation of inhibitory postsynaptic potentials (IPSPs) produced long-latency (10 to 40-ms) EPSPs (late EPSPs or 1EPSPs). CNQX was effective in blocking 1EPSPs. 3. With the use of stimulus intensities at or just below threshold for evoking an action potential, complex synaptic potentials consisting of EPSP-IPSP sequences were observed. Both early, Cl(-)-dependent and late, K(+)-dependent IPSPs were reduced by CNQX. This effect was reversible on washing. This disinhibition could lead to enhanced excitability in the presence of CNQX. 4. Iontophoretic application of quisqualate produced a membrane depolarization with superimposed action potentials, whereas NMDA depolarized the membrane potential and evoked bursts of action potentials. At concentrations up to 5 microM, CNQX selectively antagonized quisqualate responses. NMDA responses were reduced by 10 microM CNQX. D-Serine (0.5-2 mM), an agonist at the glycine regulatory site on the NMDA receptor, reversed the CNQX depression of NMDA responses.(ABSTRACT TRUNCATED AT 250 WORDS)     

Excitatory inputs to cerebellar dentate nucleus neurons from the cerebral cortex in the cat

Summary 1. In anesthetized cats, we investigated excitatory and inhibitory inputs from the cerebral cortex to dentate nucleus neurons (DNNs) and determined the pathways responsible for mediating these inputs to DNNs. 2. Intracellular recordings were made from 201 DNNs whose locations were histologically determined. These neurons were identified as efferent DNNs by their antidromic responses to stimulation of the contralateral red nucleus (RN). Stimulation of the contralateral pericruciate cortex produced excitatory postsynaptic potentials (EPSPs) followed by long-lasting inhibitory postsynaptic potentials (IPSPs) in DNNs. The most effective stimulating sites for inducing these responses were observed in the medial portion (area 6) and its adjacent middle portion (area 4) of the precruciate gyrus. Convergence of cerebral inputs from area 4 and area 6 to single DNNs was rare. 3. To determine the precerebellar nuclei responsible for mediation of the cerebral inputs to the dentate nucleus (DN), we examined the effects of stimulation of the pontine nucleus (PN), the nucleus reticularis tegmenti pontis (NRTP) and the inferior olive (IO). Systematic mapping was made in the NRTP and the PN to find effective low-threshold stimulating sites for evoking monosynaptic EPSPs in DNNs. Stimulation of either the PN or the NRTP produced monosynaptic EPSPs and polysynaptic IPSPs in DNNs. Using a conditioning-testing paradigm (a conditioning stimulus to the cerebral peduncle (CP) and a test stimulus to the PN or the NRTP) and intracellular recordings from DNNs, we tested cerebral effects on neurons in the PN and the NRTP making a monosynaptic connection with DNNs. Conditioning stimulation of the CP facilitated PN- and NRTP-induced monosynaptic EPSPs in DNNs. This spatial facilitation indicated that the excitatory inputs from the cerebral cortex to DNNs are at least partly relayed via the PN and the NRTP. 4. Stimulation of the contralateral IO produced monosynaptic EPSPs and polysynaptic IPSPs in DNNs. These monosynaptic EPSPs were facilitated by conditioning stimulation of the CP, strongly suggesting that the IO is partly responsible for mediating excitatory inputs from the cerebral cortex to the DN. A comparison was made between the latencies of IO-evoked IPSPs in DNNs and the latencies of IO-evoked complex spikes in Purkinje cells. Such a comparison indicated that the shortest-latency IPSPs evoked from the IO were not mediated via the Purkinje cells and suggested the pathway mediated by inhibitory interneurons in the DN. 5. The functional significance of the excitatory inputs from the PN and the NRTP to the DN is discussed in relation to the motor control mechanisms of the cerebellum.     

Excitatory amino acid receptors involved in primary afferent-evoked polysynaptic EPSPs of substantia gelatinosa neurons in the adult rat spinal cord slice.

Intracellular recordings were made from substantia gelatinosa (SG) neurons in spinal cord slices to determine a subclass of excitatory amino acid receptors involved in polysynaptic excitatory postsynaptic potentials (EPSPs). In the majority of neurons, polysynaptic EPSPs evoked by A delta fiber were not affected by 2-amino-5-phosphonovaleric acid (APV), while all EPSPs including monosynaptic EPSPs were depressed by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX). All spontaneous EPSPs were blocked by CNQX, while spontaneous EPSPs in a few SG neurons were attenuated by APV. These observations suggest that polysynaptic EPSPs evoked through A delta fibers are predominantly mediated by activation of the non-N-methyl-D-aspartate (non-NMDA) receptor subclass.     

Actions of excitatory amino acid antagonists on synaptic potentials of layer II/III neurons of the cat's visual cortex

Summary Actions of excitatory amino acid (EAA) antagonists on the responses of cells in layers II/III and IV of the cat's visual cortex to stimulation of layer VI and the underlying white matter were studied in slice preparations. Antagonists used were 2-amino-5-phosphonovalerate (APV), a selective antagonist for the N-methyl-D-aspartate (NMDA) type of EAA receptors, and kynurenate, a broadspectrum antagonist for the three types of EAA receptors. In extracellular recordings it was demonstrated that most of the layer II/III cells were sensitive to APV, while the great majority of the layer IV cells were not, By contrast, kynurenate suppressed the responses completely in both layers. Excitatory post-synaptic potentials (EPSPs) evoked by stimulation of layer VI and the while matter were recorded intracellularly from layer II/III neurons. To determine whether the EPSPs were elicited mono- or polysynaptically, the synaptic delay for each EPSP was calculated from a pair of onset latencies of EPSPs evoked by stimulation of the two sites. Forty-two percent of the layer II/III cells were classified as having monosynaptic EPSPs. In 60% of these monosynaptic cells, the rising slope of the EPSPs was reduced by APV while in the other 40%, it was not. In the former (APV-sensitive cells), subtraction of the APV-sensitive component from the total EPSP indicated that the onset latency of the NMDA receptor-mediated component was roughly equal to that of the non-NMDA component. In the latter (APV-resistant cells), only the slowly-decaying component was in part mediated by NMDA receptors. The conduction velocities of the afferent fibers innervating APV-resistant cells were slower than those of the APV-sensitive cells, suggesting that both types of cells are innervated by different types of afferents. The polysynaptic EPSPs of almost all layer II/III cells were sensitive to APV. The subtraction method indicated that the NMDA component had about the same magnitude as the non-NMDA components. When the slices were superfused by a Mg²⁺-free solution, the EPSPs were potentiated dramatically, but this potentiation was reduced to the control level during the administration of APV. Similarly, APV-sensitive components were potentiated during the administration of bicuculline, a selective antagonist for gamma-aminobutyric acid receptors of A type. These results suggest that NMDA receptors participate, at varying degrees, in excitatory synaptic transmission at most layer II/III cells in the cat's visual cortex, and their actions appear to be regulated by intracortical inhibition.     

Modulation of synaptic transmission in hippocampal CA1 neurons by a novel neurotoxin (beta-pompilidotoxin) derived from wasp venom.

We examined the effects of beta-pompilidotoxin (beta-PMTX), a neurotoxin derived from wasp venom, on synaptic transmission in the mammalian central nervous system (CNS). Using hippocampal slice preparations of rodents, we made both extracellular and intracellular recordings from the CA1 pyramidal neurons in response to stimulation of the Schaffer collateral/commissural fibers. Application of 5-10 microM beta-PMTX enhanced excitatory postsynaptic potentials (EPSPs) but suppressed the fast component of the inhibitory postsynaptic potentials (IPSPs). In the presence of 10 microM bicuculline, beta-PMTX potentiated EPSPs that were composed of both non-NMDA and NMDA receptor-mediated potentials. Potentiation of EPSPs was originated by repetitive firings of the presynaptic axons, causing summation of EPSPs. In the presence of 10 microM CNQX and 50 microM APV, beta-PMTX suppressed GABA(A) receptor-mediated fast IPSPs but retained GABA(B) receptor-mediated slow IPSPs. Our results suggest that beta-PMTX facilitates excitatory synaptic transmission by a presynaptic mechanism and that it causes overexcitation followed by block of the activity of some population of interneurons which regulate the activity of GABA(A) receptors.     

Synaptic responses of neurons controlling the parotid and von Ebner salivary glands in rats to stimulation of the solitary nucleus and tract

Salivary secretion results from reflex stimulation of autonomic neurons via afferent sensory information relayed to neurons in the rostral nucleus of the solitary tract (rNST), which synapse with autonomic neurons of the salivatory nuclei. We investigated the synaptic properties of the afferent sensory connection to neurons in the inferior salivatory nucleus (ISN) controlling the parotid and von Ebner salivary glands. Mean synaptic latency recorded from parotid gland neurons was significantly shorter than von Ebner gland neurons. Superfusion of GABA and glycine resulted in a concentration-dependent membrane hyperpolarization. Use of glutamate receptor antagonists indicated that both AMPA and N-methyl-D-aspartate (NMDA) receptors are involved in the evoked excitatory postsynaptic potentials (EPSPs). Inhibitory postsynaptic potential (IPSP) amplitude increased with higher intensity ST stimulation. Addition of the glycine antagonist strychnine did not affect the amplitude of the IPSPs significantly. The GABA(A) receptor antagonist, bicuculline (BMI) or mixture of strychnine and BMI abolished the IPSPs in all neurons. IPSP latency was longer than EPSP latency, suggesting that more than one synapse is involved in the inhibitory pathway. Results show that ISN neurons receive both excitatory and inhibitory afferent input mediated by glutamate and GABA respectively. The ISN neuron response to glycine probably derives from descending connections. Difference in the synaptic characteristics of ISN neurons controlling the parotid and von Ebner glands may relate to the different function of these two glands.     

post-synaptic excitation and inhibition from primary afferents in neurones of the spinocervical tract

1. Intra- and extracellular recordings were made from cells of the spinocervical tract in the lumbosacral spinal cord. A convergence of monosynaptic excitatory post-synaptic potentials (EPSPs) and disynaptic inhibitory post-synaptic potentials (IPSPs) was a general pattern of effects from the low threshold cutaneous fibres. Unitary IPSPs, probably mediated via the same disynaptic path, were evoked by light touch of hairs, which was also the adequate stimulus for exciting the cells. The receptive field for unitary IPSPs was closely related to the excitatory receptive field but was eccentric, not of a surround type.

2. EPSPs, IPSPs, or both, were evoked from the flexor reflex afferents in the great majority of neurones. Disynaptic IPSPs may be evoked from the interosseous nerve. No effects were produced by volleys in group I muscle afferents.

3. It is suggested, on the basis of the spatial organization of the excitatory and inhibitory receptive skin fields, that the spinocervical tract may give information regarding the direction of tactile stimuli.

     

Synaptic mechanisms of inspiratory off-switching evoked by pontine pneumotaxic stimulation in cats

To elucidate synaptic mechanisms and the involvement of N-methyl-D-aspartate (NMDA) receptors in inspiratory off-switching (IOS) evoked by the stimulation of the nucleus parabrachialis medialis (NPBM), excitatory and inhibitory postsynaptic potentials (EPSPs and IPSPs) were recorded from bulbar augmenting inspiratory (aug-I) and postinspiratory (PI) neurons in vagotomized cats. Stimulation of NPBM produced either transient inhibition or premature termination of inspiration (reversible or irreversible IOS), depending on the stimulus intensity. Each neuron displayed four-phasic postsynaptic responses during the reversible IOS, i.e. Phase 1 EPSPs, Phase 2 IPSPs, Phase 3 EPSPs and Phase 4 IPSPs in aug-I neurons, and Phase 1 plus 2 EPSPs, Phase 3 IPSPs and Phase 4 EPSPs in PI neurons. During the irreversible IOS, Phase 4 responses were replaced by sustained hyperpolarization in aug-I neurons and decrementing depolarization in PI neurons. Blockade of NMDA receptors by dizocilpine (0.3 mg kg(-1) i.v.) selectively increased Phase 4 potentials in both types of neurons and decreased the thresholds for evoking the irreversible IOS. The NPBM-induced responses had a pattern and time-course similar to those induced by vagal stimulation. The present results suggest that pneumotaxic and vagal inputs converge on the common IOS circuit, and the effectiveness of both inputs is modulated by NMDA receptors.     

Electrophysiological properties of cortical synaptic inputs of rubro-spinal neurons

Excitatory postsynaptic potentials (EPSPs) of the red nucleus neurons evoked by stimulation of the cerebellar nucleus interpositus as well as the sensorimotor and association parietal regions of the cerebral cortex were studies in acute cats. As for the first two structures, a monosynaptic connection of the association cortex with rubro-spinal neurons was shown to exist. The analyses of the time characteristics of the unitary EPSPs suggested a localization of synapses of fibers from the association cortex closer to the soma when compared with those which originated from axons of the sensorimotor cortical cells.     

The vestibulo-ocular reflex arc in the newborn kitten

Summary Field potentials and postsynaptic potentials were recorded in the vestibular and abducens nuclei and neurons following vestibular nerve stimulation in anesthetized newborn kittens (within 72 h after birth). Stimulation of the ipsilateral vestibular nerve evoked an initial P wave and an N₁ field potential in the vestibular nuclei. No N₂ potential was evoked. Latencies of the peak of the P wave, the onset and the peak of the N₁ potential were 0.99±0.16 ms, 1.66±0.18 ms, and 2.51±0.23 ms, respectively. Ipsilateral vestibular nerve stimulation evoked monosynaptic excitatory postsynaptic potentials (EPSPs) and polysynaptic inhibitory postsynaptic potentials (IPSPs) in vestibular nuclear neurons. Stimulation of the contralateral vestibular nerve evoked polysynaptic IPSPs in vestibular nuclear neurons. In abducens motoneurons, ipsilateral vestibular nerve stimulation evoked monosynaptic EPSPs and disynaptic IPSPs; contralateral vestibular nerve stimulation produced disynaptic EPSPs. We conclude that short circuit pathways of the vestibul-ovestibular and vestibulo-ocular reflex arc are present in the kitten already at birth.Supported by the Japanese Ministry of Education, Science, and Culture Grants-in-Aid for Scientific Research nos. 572 140 30 and 575 700 53     

Excitatory synaptic transmission in cultures of rat olfactory bulb

1. Olfactory bulb neurons were dissociated from neonatal rats and plated at low density on a confluent layer of olfactory bulb astrocytes. Intracellular stimulation of presumptive mitral/tufted (M/T) cells evoked monosynaptic excitatory postsynaptic potentials (EPSPs) in adjacent neurons. Whole-cell recording techniques and a flow-pipe drug delivery system were used to compare EPSPs with voltage-clamp recordings of currents evoked by excitatory amino acids (EAA) including N-acetylaspartylglutamate (NAAG), a putative mitral cell transmitter. 2. Cultured olfactory bulb neurons were morphologically and physiologically distinct. Large pyramidal-shaped neurons were present, which were NAAG immunoreactive; stimulation of these neurons invariably evoked EPSPs, suggesting that they were M/T cells. The majority of small bipolar neurons were glutamic acid decarboxylase (GAD) immunoreactive consistent with granule or periglomerular gamma-aminobutyric acid (GABA)ergic interneurons. 3. Monosynaptic EPSPs between M/T cells could be separated into fast and slow components by the use of EAA receptor antagonists. A fast component with a time-to-peak of 7.7 +/- 1.0 (SE) ms and half-width of 31.8 +/- 7.4 ms was blocked by the non-NMDA receptor antagonist 6-cyano-2,3-dihydroxy-7-nitro-quinoxaline (CNQX, 2.5 microM). The slow component (time-to-peak = 41.4 +/- 7.2 ms; half-width = 218.9 +/- 40.4 ms) was blocked by the N-methyl-D-aspartate (NMDA) receptor antagonist DL-2-amino-5-phosphonovaleric acid (AP5, 100 microM). 4. Under voltage clamp, flow-pipe applications of NAAG (10-1,000 microM) evoked inward currents at a holding potential of -60 mV in Mg-free solutions.(ABSTRACT TRUNCATED AT 250 WORDS)     

Induction of long-term potentiation without participation of N-methyl-D-aspartate receptors in kitten visual cortex.

1. Intracellular recording was made from layer II-III cells in slice preparations of kitten (30-40 days old) visual cortex. Low-frequency (0.1 Hz) stimulation of white matter (WM) usually evoked an excitatory postsynaptic potential (EPSP) followed by an inhibitory postsynaptic potential (IPSP). The postsynaptic potentials (PSPs) showed strong dependence on stimulus frequency. Early component of EPSP and IPSP evoked by weak stimulation both decreased monotonically at frequencies greater than 0.5-1 Hz. Strong stimulation similarly depressed the early EPSP at higher frequencies (greater than 2 Hz) and replaced the IPSP with a late EPSP, which had a maximum amplitude in the stimulus frequency range of 2-5 Hz. 2. Very weak WM stimulation sometimes evoked EPSPs in isolation from IPSPs. The falling phase of the EPSP revealed voltage dependence characteristic to the responses mediated by N-methyl-D-aspartate (NMDA) receptors and was depressed by application of an NMDA antagonist DL-2-amino-5-phosphonovalerate (APV), whereas the rising phase of the EPSP was insensitive to APV. 3. The early EPSPs followed by IPSPs were insensitive to APV but were replaced with a slow depolarizing potential by application of a non-NMDA antagonist 6,7-dinitro-quinoxaline-2,3-dione (DNQX), indicating that the early EPSP is mediated by non-NMDA receptors. The slow depolarization was mediated by NMDA receptors because it was depressed by membrane hyperpolarization or addition of APV. 4. The late EPSP evoked by higher-frequency stimulation was abolished by APV, indicating that it is mediated by NMDA receptors, which are located either on the recorded cell or on presynaptic cells to the recorded cells. 5. Long-term potentiation (LTP) of EPSPs was examined in cells perfused with solutions containing 1 microM bicuculline methiodide (BIM), a gamma-aminobutyric acid (GABA) antagonist. WM was stimulated at 2 Hz for 15 min as a conditioning stimulus to induce LTP, and the resultant changes were tested by low-frequency (0.1 Hz) stimulation of WM. 6. LTP of early EPSPs occurred in more than one-half of the cells (8/13) after strong conditioning stimulation. The rising slope of the EPSP was increased 1.6 times on average. 7. To test involvement of NMDA receptors in the induction of LTP in the early EPSP, the effect of conditioning stimulation was studied in a solution containing 100 microM APV, which was sufficient to block completely synaptic transmission mediated by NMDA receptors. LTP occurred in the same frequency and magnitude as in control solution.     

Electrophysiological properties of nucleus reticularis tegmenti pontis cells: Antidromic and synaptic activation

Summary Antidromically and synaptically activated spike and synaptic potentials in the nucleus reticularis tegmenti pontis (NRTP) of the cat were recorded intracellularly. The antidromic firing of the NRTP neurone is composed of IS-SD spikes with short duration and short spike-after-hyperpolarization. Membrane resistance and firing patterns were studied by applying depolarizing and hyperpolarizing current through the recording electrode. Findings indicate that the NRTP neurone has a relatively high membrane resistance and is capable of firing at a high frequency.Single shock stimulation of the interpositus (IP) and lateral nucleus (LN) of the cerebellum, brachium conjunctivum (BC), red nucleus (RN) and cerebral peduncle (CP) induced monosynaptic EPSPs in the NRTP neurones. Superior vestibular nucleus (SVN) stimulation induced monosynaptic IPSPs. Collision tests showed that (1) NRTP neurones are activated by the axons of IP and LN neurones which travel through BC, (2) these axons also send collaterals to RN, and (3) there is convergence of cerebellar, cerebral and brain stem inputs to a single NRTP neurone.     

Physiology and pharmacology of epileptiform activity induced by 4-aminopyridine in rat hippocampal slices.

1. Conventional intracellular and extracellular recording techniques were used to investigate the physiology and pharmacology of epileptiform bursts induced by 4-aminopyridine (4-AP, 50 microM) in the CA3 area of rat hippocampal slices maintained in vitro. 2. 4-AP-induced epileptiform bursts, consisting of a 25-to 80-ms depolarizing shift of the neuronal membrane associated with three to six fast action potentials, occurred at the frequency of 0.61 +/- 0.29 (SD)/s. The bursts were generated synchronously by CA3 neurons and were triggered by giant excitatory postsynaptic potentials (EPSPs). A second type of spontaneous activity consisting of a slow depolarization also occurred but at a lower rate (0.04 +/- 0.2/s). 3. The effects of 4-AP on EPSPs and inhibitory postsynaptic potentials (IPSPs) evoked by mossy fiber stimulation were studied on neurons impaled with a mixture of K acetate and 2(triethyl-amino)-N-(2,6-dimethylphenyl) acetamide (QX-314)-filled microelectrodes. After the addition of 4-AP, the EPSP became potentiated and was followed by the appearance of a giant EPSP. This giant EPSP completely obscured the early IPSP recorded under control conditions and inverted at -32 +/- 3.9 mV (n = 4), suggesting that both inhibitory and excitatory conductances were involved in its generation. IPSPs evoked by Schaffer collateral stimulation increased in amplitude and duration after 4-AP application. 4. The spontaneous field bursts and the stimulus-induced giant EPSP induced by 4-AP were not affected by N-methyl-D-aspartate (NMDA) receptor antagonists 3-3 (2-carboxy piperazine-4-yl) propyl-1-phosphonate (CPP) and DL-2-amino-5-phosphonovalerate (APV) but were blocked by quisqualate/kainate receptor antagonists 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) and 6,7-dinitroquinoxaline-2,3-dione (DNQX). CNQX also abolished the presence of small spontaneously occurring EPSPs, thereby disclosing the presence of bicuculline-sensitive (BMI, 20 microM) IPSPs. 5. Small, nonsynchronous EPSPs played an important role in the generation of 4-AP-induced epileptiform activity. 1) After the addition of 4-AP, small EPSPs appeared randomly on the baseline and then became clustered to produce a depolarizing envelope of irregular shape that progressively formed an epileptiform burst, 2) These small EPSPs were more numerous in the 100 ms period that preceded burst onset. 3) The frequency of occurrence of small EPSPs was positively correlated with the frequency of occurrence of synchronous bursts. 4) Small EPSPs and bursts were similarly decreased after the addition of different concentrations of CNQX (IC50 in both cases of approximately 1.2 microM).(ABSTRACT TRUNCATED AT 400 WORDS)     

The lateral reticular nucleus in the cat

The afferent paths from the spinal cord and from trigeminal afferents to the lateral reticular nucleus (LRN) were investigated by intracellular recording from 204 LRN neurones in preparations with a spinal cord lesion at C3 that spared only the ipsilateral ventral quadrant. Stimulation of nerves in the limbs evoked EPSPs and JPSPs in 201 of 204 tested LRN neurones. The strongest input was from the ipsilateral forelimb (iF) which evoked EPSPs in 49% and IPSPs in 73% of the LRN neurones. Each of the other limbs evoked EPSPs in approximately 20% and IPSPs in approximately 25% of the neurones. Stimulation of the ipsilateral trigeminal nerve (iTrig) evoked EPSPs in 32% and IPSPs in 46% of the neurones. The shortest latencies of the EPSPs and IPSPs indicated a disynaptic connection between primary afferents in the iF and iTrig and the LRN. The most direct pathways for excitatory and inhibitory responses from the other limbs were trisynaptic. Stimulation of the ventral part of the ipsilateral funiculus (iVLF) at C3 (C3iVLF) evoked monosynaptic responses in 189 of 201 tested LRN neurones. Monosynaptic EPSPs were recorded in 104 neurones and monosynaptic IPSPs in 126 neurones. Monosynaptic EPSPs and IPSPs were encountered in all parts of the LRN. Stimulation of the iVLF at L1 (L1iVLF) evoked monosynaptic EPSPs and IPSPs in the ventrolateral part of the LRN. The termination areas of excitatory and inhibitory fibres appeared to be the same. LRN neurones without monosynaptic EPSPs or IPSPs from the L1iVLF were located mainly in the dorsal part of the magnocellular division. Stimulation of the dorsal funiculi (DF) at C2 and the ipsilateral trigeminal nerve (iTrig) evoked excitatory and inhibitory responses in the LRN. The shortest latencies of EPSPs and IPSPs indicated disynaptic connections.     

Inhibitory role of dentate hilus neurons in guinea pig hippocampal slice

1. Current and voltage-clamp recording of CA3/CA4 pyramidal neurons, hilar neurons, and granule cells or pairs of these neurons were used to study the generation of Cl-dependent and K-dependent inhibitory postsynaptic potentials (IPSPs) in the guinea pig hippocampal slice preparation. 2. A sequence of an early Cl-dependent and a late K-dependent IPSP was evoked in CA3 neurons by electrical stimulation from the stratum moleculare of the dentate gyrus, the hilus, and the stratum oriens/alveus. Blockade of glutamatergic excitation by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 10 microM) and D(-)-2-amino-5-phosphonovaleric acid (APV, 30 microM) abolished IPSPs evoked from the stratum moleculare of the dentate gyrus, but IPSPs could still be evoked from the hilus and the stratum oriens/alveus. 3. Repetitive giant IPSPs, which consisted of Cl-dependent and K-dependent components, were evoked by bath application of 4-aminopyridine (4-AP, 10-50 microM) in CA3 neurons and in granule cells. Giant IPSPs were blocked by bath-applied tetrodotoxin (TTX). In addition, 4-AP hyperpolarized CA3 neurons in a Cl-dependent and picrotoxin-sensitive way. 4. Focal application of TTX to the dentate gyrus or the hilus considerably reduced the amplitude of giant IPSPs evoked by 4-AP in CA3 neurons. In hilar neurons, 4-AP evoked repetitive bursts, eventually, but not necessarily intermingled with giant IPSPs. Bursts were observed in hilar neurons in presence as well as absence of CNQX and APV. 5. In paired recordings, bursts in hilar neurons induced by 4-AP occurred simultaneously to giant IPSPs in granule cells and CA3 neurons, and giant IPSPs in granule cells occurred simultaneously to giant IPSPs in CA3 neurons. Blockade of glutamatergic excitation by CNQX and APV did not abolish this synchrony. 6. 4-AP-evoked Cl- and K-dependent IPSPs were, unlike electrically evoked IPSPs, not strictly coupled: some 20% of large IPSPs and up to 90% of small IPSPs were either Cl or K dependent. In granule cells K-dependent components either preceded or followed Cl-dependent components. 7. K-dependent IPSPs only could be evoked in CA3 neurons by focal application of 4-AP (1 mM) to the hilus, the stratum lacunosum moleculare or the stratum pyramidale. Wash out of Ca for 15-20 min blocked the Cl-dependent but not the K-dependent component of giant IPSPs evoked by bath-applied 4-AP.(ABSTRACT TRUNCATED AT 400 WORDS)     

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)