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D A Prince

Publications and source records attributed to D A Prince.

At least 55 records · Page 3Linked to original sources
PubMed1995

Cholecystokinin depolarizes rat thalamic reticular neurons by suppressing a K+ conductance.

1. The thalamic reticular nucleus (nRt) is innervated by cholecystokinin (CCK)-containing neurons and contains CCK binding sites. We used tight-seal, whole cell recording techniques with in vitro rat thalamic slices to investigate the action of CCK on neurons in nRt and ventrobasal thalamus (VB). 2. Brief applications of the CCK agonist cholecystokinin octapeptide (26-33) sulfated (CCK8S) evoked prolonged spike discharges in nRt neurons but had no direct effects on VB neuron activity. This selective excitatory action of CCK8S in nRt resulted from a long-lasting membrane depolarization (2-10 min) associated with an increased input resistance. Voltage-clamp recordings revealed that CCK8S reduced membrane conductance by 0.6-3.8 nS, which amounted to 5-54% of the resting conductance of these neurons. 3. The conductance blocked by CCK8S was linear over the range of -50 to -100 mV and reversed near the potassium equilibrium potential. Modifications of extracellular K+ concentration altered the reversal potential of the conductance as predicted by the Nernst equation. The K+ channel blocker Cs+, applied either intracellularly or combined intra- and extracellularly, blocked the response to CCK8S. 4. The CCK8S-induced depolarization persisted after suppression of synaptic transmission by either tetrodotoxin or a low-Ca2+, high-Mg2+ extracellular solution, indicating that the depolarization was primarily due to activation of postsynaptic CCK receptors and not mediated through the release of other neurotransmitters. 5. The selective CCKA antagonists L364,718 and Cam-1481 attenuated the CCK8S-induced depolarization, whereas the CCKB antagonist L365,260 had little or no effect on the depolarization. 6. Our findings indicate that CCK8S, acting via CCKA-type receptors, reduces a K+ leak current, resulting in a long-lasting membrane depolarization that can presumably modify the firing mode of nRt neurons. Through this effect, CCK actions in nRt may strongly influence thalamocortical function.

Action Potentials↗
PubMed1995

Axonal sprouting in layer V pyramidal neurons of chronically injured cerebral cortex.

We performed experiments to determine whether axonal sprouting occurs in neurons of chronic neocortical epileptogenic lesions. Partially isolated somatosensory cortical islands with intact pial blood supply were prepared in mature rats. Neocortical slices from these lesions, studied 6-39 d later, generated spontaneous and/or evoked epileptiform field potentials (Prince and Tseng, 1993) during which neurons displayed prolonged polyphasic excitatory and inhibitory synaptic potentials/currents. Single electrophysiologically characterized layer V pyramidal neurons in control and epileptogenic slices were filled with biocytin using sharp and patch-electrode techniques, their axonal arbors reconstructed and compared quantitatively. Neurons in injured cortex had a 56% increase in total axonal length, a 64% increase in the number of axonal collaterals and more than a doubling (115% increase) of the number of axonal swellings. The presumed boutons were smaller and more closely spaced than those of control cells. In some neurons the main descending axon had hypertrophic segments from which branches arose. These highly significant changes were most marked in the perisomatic region of layer V. The axonal sprouting was associated with a decrease in somatic area but no significant change in dendritic arbors. Results suggest that a significant degree of axonal reorganization takes place in the chronically injured cortex where it might be an adaptive mechanism for recovery of function after injury, or might be maladaptive and play an important role in the generation of epileptiform events by increasing the numbers and density of synaptic contacts between neurons.

Animals↗
PubMed1994

Chronic neocortical epileptogenesis in vitro.

1. We used an in vitro model to explore critical aspects of chronic epileptogenesis. Partial neocortical isolations having intact blood supply were made in rat and guinea pig from postnatal day 7 to 34 and then examined 1 to 150 days later in standard brain slice preparations. 2. The epileptogenic potential of several different types of lesions was assessed. Slices containing transcortical (i.e., gray matter) lesions, with or without a contiguous white matter injury (i.e., "undercut"), developed chronic epileptogenesis after a latency of approximately 1-2 wk, manifested by evoked and spontaneous "interictal" discharges and evoked "ictal" events. The region of hyperexcitability did not extend beyond approximately 2 mm from the chronic transcortical lesion and was rarely observed in slices having only an apparent white matter injury. 3. Multiple recordings and current source density (CSD) analysis identified layer V as the source of the interictal discharge. 4. Significant differences in CSD profiles of the evoked interictal discharge occurred between chronically epileptogenic slices and control (noninjured) slices bathed in the convulsant, bicuculline methiodide, suggesting that mechanisms other than disinhibition must be involved in posttraumatic epileptogenesis. 5. Interictal events were blocked in most but not all chronically injured slices by application of the N-methyl-D-aspartate (NMDA) receptor antagonist D-2-amino-5-phosphonovalerate (D-AP5), suggesting that non-NMDA receptors were predominantly involved in some preparations. 6. This model of chronic epileptogenesis in vitro will be useful in studies relevant to mechanisms of posttraumatic epilepsy in man.

Animals↗
PubMed1994

Clonazepam suppresses GABAB-mediated inhibition in thalamic relay neurons through effects in nucleus reticularis.

1. Experiments were carried out using patch-clamp techniques in rat thalamic slices, maintained in vitro, to examine the effects of the benzodiazepine compound, clonazepam (CZP), on intrathalamic inhibition. Bath-applied CZP reduced the gamma-aminobutyric acid-B (GABAB) component of inhibitory postsynaptic potentials and currents (IPSPs and IPSCs, respectively) evoked in rat thalamic somatosensory relay neurons by stimulation of nucleus reticularis thalami (nRt), without consistently affecting the GABAA IPSP. Secondary IPSPs, which occur as a result of intrathalamic oscillations, were dramatically reduced. 2. Voltage-clamp experiments combined with local or bath perfusion of the GABAA antagonist bicuculline methiodide (BMI), demonstrated that nRt is a site of GABAA-mediated postsynaptic inhibition that affects inhibitory output onto relay neurons. BMI enhanced both GABAA and GABAB postsynaptic inhibition in relay neurons when applied to nRt. Focal applications in the ventrobasal relay nucleus near the recording electrode blocked the GABAA-mediated IPSP but had no effects on GABAB inhibitory potentials. 3. Results suggest that CZP acts to facilitate recurrent inhibition in nRt and decrease its inhibitory output onto relay neurons. Intra-nRt GABAA-mediated inhibition thus has an important role in controlling thalamic excitability and in the anti-absence actions of CZP.

Animals↗
PubMed1994

Intrathalamic rhythmicity studied in vitro: nominal T-current modulation causes robust antioscillatory effects.

Thalamocortical oscillations mediate both physiological and pathophysiological behaviors including sleep and generalized absence epilepsy (GA). Reciprocal intrathalamic circuitry and robust burst firing, dependent on underlying transient Ca current (IT) in thalamic neurons, support generation of such rhythms. In order to study the regulation of intrathalamic rhythm generation and the effects of GA anticonvulsants previously shown to reduce IT in acutely isolated thalamic neurons, we developed an in vitro rat thalamic slice preparation that retains sufficient intrathalamic circuitry to support evoked oscillations (range = 2.0-4.6 Hz, average = 2.7, n = 38), associated with burst firing in the thalamic reticular nucleus (nRt) and thalamic relay neurons. Extracellular stimulation of nRt evoked in relay neurons a biphasic inhibitory response with prominent GABAA and GABAB receptor-mediated components. The GABAA component was picrotoxin sensitive, outwardly rectifying and Cl- dependent, with a very negative reversal potential (-94 mV), indicating that an active extrusion mechanism exists in these cells to keep [Cl-]i < 5 mM. The GABAB component had a linear conductance, a reversal potential of -103 mV, and was quite long lasting (about 300 msec) so that rebound bursts often were generated on its decay phase, presumably leading to reexcitation of nRt through known excitatory connections. GABAB-mediated responses thus provide a timing mechanism for promoting slow intrathalamic oscillations. Reduction of IT (30-40%) by succinimides slightly increased the threshold for burst generation in relay and nRt cells, but there was little effect on either number of spikes/burst or intraburst frequency, and there were no other direct effects on other measures of cellular excitability. Intrathalamic oscillations were significantly reduced by these agents through a slight decrease in burst probability of thalamic neurons. We conclude that interactions between the intrinsic properties of thalamic neurons and intrathalamic circuitry lead to generation of slow oscillations. A similar mechanism may underlie the pathophysiological 3 Hz spike and wave EEG activity that characterizes GA. Furthermore, anti-GA drugs such as ethosuximide probably exert their action by reducing the burst-firing probability of neurons within populations of reciprocally interconnected relay and nRt neurons, thus producing a desynchronization of the thalamic circuit that prevents spike/wave generation.

Animals↗
PubMed1993

Heterogeneity of rat corticospinal neurons.

In order to examine the degree of diversity within a population of cortical projection neurons, rat corticospinal cells were retrogradely labeled in vivo by injecting rhodamine-tagged microspheres into the cervical spinal cord, and subsequently studied electrophysiologically and anatomically in neocortical slices maintained in vitro, by use of standard current clamp techniques and a double-labeling protocol (Tseng et al., J. Neurosci. Meth. 37:121-131, 1991). Three different subgroups were distinguished on the basis of their spiking behavior: (1) Adapting cells had a marked fast (50 ms) and slow phase (200 ms) of spike frequency adaptation; (2) regular spiking (RS) cells had only a period of fast adaptation; (3) some regular spiking neurons had prominent depolarizing afterpotentials (DAPs) and could generate bursts of spikes, often in repetitive fashion (RSDAP cells). Subgroups of RSDAP cells had different patterns of burst responses to depolarizing current pulses, suggesting differences in the types and/or sites of underlying ionic conductances. Adapting cells had a slightly higher membrane input resistance and more prominent slow hyperpolarizing afterpotentials than RS and RSDAP neurons; however, the activation of presumed anomalous rectifier current by intracellular hyperpolarizations was less prominent in adapting neurons. Orthodromic stimulation in layer I evoked presumed excitatory and inhibitory postsynaptic potentials (EPSPs and IPSPs)in all three types of cells, but prominent short-latency IPSPs were found in a higher percentage of adapting neurons. The morphology of electrophysiologically characterized corticospinal neurons was studied following intracellular injection of biocytin. All three spiking types were typical layer V pyramids with apical dendrites reaching layer 1, basal dendrites in infragranular layers, and deep-directed axons that had a moderate density of local collaterals in lower cortical layers. The profuseness of dendrites, examined by Sholl's analysis of two-dimensional, camera lucida-reconstructed neurons was comparable in the three neuronal subgroups, although a smaller somatic area and more slender apical dendritic trunk were found in adapting neurons. Our results suggest that corticospinal cells in rats are a heterogeneous population of projection neurons with respect to their spiking behavior, membrane properties, synaptic connections, and, to a lesser extent, their morphology. This diversity revealed in vitro adds new complexity to the classification of corticospinal neurons.

Action Potentials↗
PubMed1993

Postnatal development of cholinergic presynaptic inhibition in rat hippocampus.

Muscarinic depression of field potential excitatory postsynaptic potentials (fEPSPs) in striatum radiatum of area CA1 was compared in hippocampal slices from rats of different ages. Bath application of 4 microM muscarine reversibly depressed the fEPSP slope by 68.4% in slices from adult animals (P43-P60), but caused only a 32.2% depression in slices from P5-P7 animals. The magnitude of the depression increased with age during the first postnatal month. Reduced sensitivity of excitatory synaptic transmission to cholinergic depression during postnatal development could be one factor contributing to the hyperexcitability of immature hippocampus.

Animals↗
PubMed1993

Epileptogenesis in chronically injured cortex: in vitro studies.

1. Field potentials and intracellular activities were examined in neocortical slices obtained through areas of chronic cortical injury produced by cortical undercutting and transcortical lesions made in vivo 7-122 days before the terminal in vitro slice experiment. 2. Abnormal field potentials characterized by long- and variable-latency multiphasic events could be evoked by layer VI-white matter or subpial stimulation in 9 of 15 animals that had adequate partial cortical isolations. These "epileptiform" field potentials were recorded in layers II-V and propagated across the cortex. They appeared at threshold in an all-or-none fashion and, in most slices, could be blocked by increasing stimulus intensity. In one slice, spontaneous epileptiform events occurred that were similar to those evoked by extracellular stimulation. 3. Intracellular activities during the epileptiform field potentials consisted of polyphasic synaptic events that were predominantly depolarizing and that could last < or = 400-500 ms, synchronous with the field potential activities. A variety of observations suggested that the neuronal activities underlying epileptiform field potentials were relatively asynchronous and much less intense than those previously found in chemically induced epileptogenesis within the neocortex. 4. Inhibitory postsynaptic potentials (IPSPs) were not prominent in neurons when threshold stimuli evoked epileptiform events; however, suprathreshold stimuli could elicit biphasic IPSPs and block the long-latency polysynaptic activity and abnormal field potential in most slices. Depolarizing components of the polysynaptic activity had the appearance of excitatory postsynaptic potentials in terms of their responses to alterations in membrane potential. 5. Comparison of spike parameters in layer V neurons of epileptogenic slices with those in control layer V neurons showed no significant differences in spike height, threshold, duration, or rise time. Resting membrane potentials were also not significantly different. 6. There was a highly significant difference in input resistance (RN) between layer V neurons in control and injured slices; the mean value for neurons in lesioned cortex was 68.1 M omega, whereas that in control cells was 30.5 M omega. There was also a significant prolongation of the slow membrane time constant in neurons of injured cortex (19.4 ms) as opposed to that in control cells (12.2 ms), suggesting that a change in specific resistivity or capacitance contributed to the higher RNS. 7. The relationship between adapted spike frequency and applied current (f-I slope) was steeper in layer V neurons from injured cortical slices (44.3 Hz/nA) than in normal layer V cells (28.2 Hz/nA).(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1993

Transient Ca2+ currents in neurons isolated from rat lateral habenula.

1. The properties of the low-voltage-activated transient Ca2+ current (LVA, IT) that underlies rhythmic burst firing in neurons of the lateral habenula (LHb) were examined to further our understanding of mechanisms that promote rhythmogenesis in the CNS. We compared these properties with those of IT in thalamic ventrobasal relay neurons (IVB) and of the more slowly inactivating ITs of thalamic reticular neurons (InRt). 2. Patch-clamp techniques were used to record whole cell Ca2+ currents in LHb cells acutely isolated from rats ranging in age from postnatal days 6 to 34 (P6-P34). The LVA current in LHb (ILHb) had a number of properties similar to those of IVB, including activation threshold (near -65 mV) and voltage-dependent steady-state activation [half-activation voltage (V1/2) = -58.5 mV, slope = 3.4 mV-1] and inactivation (V1/2 = -83.5 mV, slope = 5.0 mV-1) functions. 3. ILHb was characterized by biphasic inactivation, with a fast, voltage-dependent time constant (20-50 ms) similar to that of IVB and a slower, voltage-independent decay phase (time constant approximately 120 ms) that was much more prominent than in IVB. Recovery of ILHb from inactivation was monophasic (time constant, 507 ms at -90 mV), and was slower than for IVB and about the same as for InRt. 4. ILHb was relatively insensitive to equimolar substitution of Ba2+ for Ca2+, in contrast to IVB, which was decreased, and InRt, which was enhanced. 5. In computer simulations, these results could not be accounted for by a mixture of the two previously described IT types (IVB and InRt) in individual LHb cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Transient enhancement of low-threshold calcium current in thalamic relay neurons after corticectomy.

1. The alterations of voltage-sensitive calcium currents produced in thalamic cells by injury were investigated under voltage clamp using patch-clamp recordings in the whole-cell configuration. 2. One day after unilateral cortical ablation in immature rats (postnatal day 7), low-threshold transient calcium (T) currents in acutely isolated thalamic relay neurons (RNs) were increased by 68% compared with contralateral controls (P < 0.001). Three days after the operation, T currents in injured neurons were at 44% of control levels (P < 0.001). On the other hand, high-threshold (L) calcium currents in RNs did not change over the same interval. 3. To investigate the mechanism for the increase of T current, both kinetics and voltage dependency of activation and inactivation were examined. At a test voltage of -40 mV, the activation time constant decreased from 4.1 to 3.2 ms (P < 0.05); however, this small change was insufficient to explain the large increase in T current. Time constants for both fast and slow inactivation did not change significantly, nor did voltage dependence of activation or inactivation of thalamic T currents. 4. Methyl-phenyl-succinimide (MPS, 1 mM), a compound known to block T currents, was used to examine possible alterations in the pharmacological properties of T channels after injury. MPS was more effective in reducing T currents in normal versus injured RNs (24 and 20% reductions, respectively; P < 0.05), suggesting that pharmacological properties of T channels in the injured RNs may be different from those of the normal RNs.(ABSTRACT TRUNCATED AT 250 WORDS)

Afferent Pathways↗
PubMed1993

Differential ontogenesis of presynaptic and postsynaptic GABAB inhibition in rat somatosensory cortex.

1. The postnatal maturation of gamma-aminobutyric acid (GABA)B receptor-mediated presynaptic inhibition was studied in brain slices of rat somatosensory cortex maintained in vitro. Patchclamp techniques were used to record whole-cell inhibitory post-synaptic currents from layer II-III neurons in animals from postnatal days (P) 7-24. Monosynaptic inhibitory postsynaptic currents (IPSCs) were evoked after N-methyl-D-aspartate (NMDA) and non-NMDA type glutamate receptors had been blocked by D-amino-phosphonovaleric acid (D-AP5, 20 microM) and 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 10 microM), respectively. These IPSCs were solely mediated by postsynaptic GABAA receptors because they were abolished by bicuculline (10 microM), reversed polarity near the chloride equilibrium potential, and were recorded with electrodes that contained Cs+ to block postsynaptic GABAB responses. 2. When pairs of stimuli separated by intervals of 0.1-10 s were used to evoke IPSCs, the second response was depressed, an effect that was maximal at 300 ms. Evoked IPSCs were also depressed by baclofen (10 microM). The paired pulse depression (PPD) of monosynaptic IPSCs was decreased or eliminated by 2-OH-saclofen (200 microM). These findings indicate that PPD of monosynaptic IPSCs was due to presynaptic GABAB receptor-mediated inhibition of GABA release. 3. There were no significant differences in the amounts of PPD in neurons from different age groups (P7-10, P12-17, P22-24) at any interstimulus interval tested (0.1-10 s).(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗
PubMed1992

Adenosine decreases neurotransmitter release at central synapses.

Adenosine, at concentrations ranging from 5 to 100 microM, decreases the efficacy of transmission at the perforant path synapses on dentate granule cells. We have used whole cell recording from these cells in slices to determine the mechanism of the reduced synaptic strength. We find that size of miniature excitatory postsynaptic currents (mepscs) is unaffected by adenosine at concentrations up to 100 microM, an observation that indicates adenosine's mode of action is not through a decreased postsynaptic sensitivity to neurotransmitter. A quantal analysis indicates, however, that the quantity of neurotransmitter released is sufficiently diminished by adenosine to account entirely for the adenosine-produced decrease in synaptic strength. Application of 3-isobutyl-1-methylxanthine (IBMX), a drug that antagonizes the effects of endogenous adenosine, produces an increase in synaptic strength. This observation suggests that the resting level of adenosine in our slices is appreciable, and an analysis of the adenosine dose-response relation is consistent with endogenous adenosine levels of about 10 microM. IBMX application produces only slight changes in the amplitude of mepscs, whereas a quantal analysis demonstrates that the drug significantly increases the amount of neurotransmitter released. Thus IBMX acts as an "anti-adenosine" in our experiments. In some experiments we have been able to record excitatory and inhibitory synaptic currents produced by the same perforant path stimulus. In these instances we find that inhibitory transmission is unaffected by concentrations of adenosine that produce a marked decrease in the strength of excitatory synapses.

1-Methyl-3-isobutylxanthine↗
PubMed1992

Postnatal development of electrogenic sodium pump activity in rat hippocampal pyramidal neurons.

We assessed the development of electrogenic sodium pump (Na+ pump) activity in CA1 pyramidal neurons of rat hippocampal slices by studying the prolonged hyperpolarization which follows glutamate-induced depolarization (postglutamate hyperpolarization or PGH) at different postnatal ages. We also examined the development of membrane-bound enzyme in the hippocampal CA1 subfield with light microscopic immunocytochemistry and an antiserum against Na+,K(+)-ATPase. The PGH, which has previously been shown to be due to activation of an electrogenic Na+ pump in adult hippocampal CA1 neurons, was eliminated by strophanthidin, a Na+,K(+)-ATPase inhibitor, at all ages. It was unaffected by several potassium channel blockers, an intracellular calcium chelator, intracellular Cl- injection or tetrodotoxin (TTX) perfusion. The PGH thus appeared to be independent of K+ and Cl- conductances and produced by an electrogenic Na+ pump in adult and immature animals activated in large part by entry of Na+ through the glutamate receptor-channel complex. The size (integrated area) of the PGH was directly proportional to the area of preceding glutamate-induced depolarization (GD) and relatively voltage independent. Similar GDs could be elicited from postnatal day (P) 7 to P greater than or equal to 35, however, only very small PGHs were produced in neurons from P7-11 animals. A ratio of PGH area to GD area (PGH ratio) was calculated for each neuron and used to compare Na+ pump activity at different ages. There was a significant increase in the mean PGH ratio with age when P7-11, P21-25 and P35-39 groups were compared. Na+ pump activity estimated from the PGH ratio is very low in the first postnatal week but develops gradually over the first 5 weeks of life. Immunostaining for Na+,K(+)-ATPase in adult rat hippocampi revealed a punctate reaction product surrounding pyramidal cell bodies, whereas the staining was uniform along plasmalemma of dendrites in stratum radiatum and stratum oriens. By contrast, only minimum staining was present surrounding cell bodies and dendrites of P7 hippocampi and staining in stratum pyramidale was not punctate at this age. Na+,K(+)-ATPase activity estimated grossly from immunocytochemical staining is very low in the first postnatal week, increases during the first 5 weeks and develops a characteristic focal localization.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1992

Excessive intracellular Ca2+ inhibits glutamate-induced Na(+)-K+ pump activation in rat hippocampal neurons.

1. The effects of increased intracellular Ca2+ concentration ([Ca2+]i) on Na(+)-K+ pump activity in CA1 pyramidal neurons of rat hippocampal slices were investigated. The postglutamate hyperpolarization (PGH), which follows glutamate (GLU)-induced depolarization (GD), was used as an index of Na(+)-K+ pump activity, as was a ratio of PGH area to the preceding GD area (PGH ratio). 2. Perfusion of slices with saline containing Ca2+ ionophore (A23187, 10 microM) inhibited the PGH without producing apparent signs of cell deterioration. A 60-100% (85 +/- 15%, mean +/- SD) reduction in the PGH ratio occurred after 20-50 min of A23187 superfusion in 12 of 18 neurons tested. Complete abolition of the PGH occurred in 8 of these 12 cells exposed to A23187 for 30-120 min. 3. Application of A23187 in Ca(2+)-free/high-Mg2+ solution did not abolish the PGH, although small (less than 50%; 37 +/- 10%) reductions in the PGH ratio were observed after perfusion of 50 min or longer in five neurons tested. 4. Intracellular injection of the Ca2+ chelator bis-(o-amino-phenoxy)-N,N,N',N'-tetraacetic acid (BAPTA, 300-400 mM) blocked inhibition of the PGH by A23187. After 50 min of perfusion with Ca2+ ionophore, no reduction of the PGH ratio was observed in five neurons tested. 5. Rundown of the PGH without apparent change in membrane properties was observed in three neurons that were stable for greater than 2-3 h, allowing repetitive GLU applications. 6. Block of the PGH produced by a Na(+)-K(+)-adenosinetriphosphatase (ATPase) inhibitor (strophanthidin) prolonged the duration of GDs because of a delay in repolarization.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

A novel T-type current underlies prolonged Ca(2+)-dependent burst firing in GABAergic neurons of rat thalamic reticular nucleus.

The inhibitory GABAergic projection of thalamic nucleus reticularis (nRt) neurons onto thalamocortical relay cells (TCs) is important in generating the normal thalamocortical rhythmicity of slow wave sleep, and may be a key element in the production of abnormal rhythms associated with absence epilepsy. Both TCs and nRt cells can generate prominent Ca(2+)-dependent low-threshold spikes, which evoke bursts of Na(+)-dependent fast spikes, and are influential in rhythm generation. Substantial differences in the pattern of burst firing in TCs versus nRt neurons led us to hypothesize that there are distinct forms of transient Ca2+ current (I(T)) underlying burst discharges in these two cell types. Using whole-cell voltage-clamp recordings, we analyzed I(T) in acutely isolated TCs and nRt neurons and found three key differences in biophysical properties. (1) The transient Ca2+ current in nRt neurons inactivated much more slowly than I(T) in TCs. This slow current is thus termed I(Ts). (2) The rate of inactivation for I(Ts) was nearly voltage independent. (3) Whole-cell I(Ts) amplitude was increased when Ba2+ was substituted for Ca2+ as the charge carrier. In addition, activation kinetics were slower for I(Ts) and the activation range was depolarized compared to that for I(T). Other properties of I(Ts) and I(T) were similar, including steady-state inactivation and sensitivities to blockade by divalent cations, amiloride, and antiepileptic drugs. Our findings demonstrate that subtypes of transient Ca2+ current are present in two different classes of thalamic neurons. The properties of I(Ts) lead to generation of long-duration calcium-dependent spike bursts in nRt cells. The resultant prolonged periods of GABA release onto TCs would play a critical role in maintaining rhythmicity by inducing TC hyperpolarization and promoting generation of low-threshold calcium spikes within relay nuclei.

Action Potentials↗
PubMed1991

Double-labelling with rhodamine beads and biocytin: a technique for studying corticospinal and other projection neurons in vitro.

Corticospinal neurons retrogradely labelled with rhodamine-labelled latex microspheres (RLMs) in vivo were studied intracellularly in a slice preparation up to 13 months later with electrodes containing biocytin. The physiological properties of these double-labelled corticospinal neurons were indistinguishable from those of comparable neurons which were impaled with biocytin-containing electrodes without prior RLM-labelling, and neurons studied with potassium acetate-filled electrodes in similar areas. Thus, neither labelling with RLMs nor injection of biocytin affected neuronal properties. This important advantage of RLMs makes them suitable for prelabelling projection neurons in vivo for subsequent studies that take advantage of the versatility of a brain slice preparation. In addition to its lack of effects on neuronal properties, intracellular labelling with biocytin also provides high-quality morphological details ideal for anatomical analysis. The compatibility of retrograde labelling with RLMs and intracellular staining with biocytin make this a useful combined technique for tracking electrophysiological and anatomical changes in identified projection neurons over time.

Animals↗
PubMed1991

Postnatal maturation of the GABAergic system in rat neocortex.

1. The postnatal maturation of intracortical inhibitory circuitry and the development of responses to applied gamma-aminobutyric acid (GABA) and baclofen were studied in pyramidal and nonpyramidal neurons from layers II and III of the rat primary somatosensory and primary visual cortex, in vitro. 2. Depolarizing spontaneous inhibitory postsynaptic potentials (IPSPs) could be recorded in approximately 70% of the young (postnatal day 4-10; P4-10), juvenile (P11-16), and adult cells (P28-41), respectively, when they were loaded with nitrate. At all ages these spontaneous events could be blocked by application of the GABAA receptor antagonist bicuculline methiodide (BMI), indicating that they were mediated by activation of GABAA receptors. 3. In 122 of the 130 adult cells tested, standardized electrical stimulation of the white matter or layer VI evoked a brief excitatory postsynaptic potential (EPSP), followed by both a fast (f-) and a long-latency (l-)IPSP. Similar stimuli evoked a biphasic IPSP in only 51 of the 98 juvenile and in only 1 of the 56 young neurons studied. The mean peak conductance of the f-IPSP and the l-IPSP increased significantly from 50.2 and 7.5 nS, respectively, in juvenile cells to 84.2 and 18.0 nS, respectively, in adult neurons. 4. Application of the N-methyl-D-aspartate (NMDA) receptor antagonist D-amino-phosphonovaleric acid (D-APV) to juvenile cells induced a significant negative shift in the reversal potential of both the f-IPSP and l-IPSP. This effect was accompanied by a reduction in the peak conductance during these events by 31 and 48%, respectively, indicating that a prominent long-lasting NMDA receptor-mediated EPSP occurs concurrent with the early and late IPSP in immature neurons. In adult neurons, D-APV had no significant effect on the reversal potential of the f- and l-IPSP, although the peak conductance decreased by 20 and 5%, respectively, suggesting that there was a smaller concurrent activation of NMDA receptors in this age group. 5. The functional maturation of GABAA and GABAB receptors was studied using focal applications of GABA to the soma and the apical dendrite. Somatic GABA applications to adult neurons held at depolarized membrane potentials evoked a triphasic response, consisting of 1) a GABAA-mediated hyperpolarizing fast component (GABAhf; reversal potential, -76 mV), 2) a GABAA-mediated depolarizing phase (GABAd; -54 mV), and 3) a hyperpolarizing late response (GABAhl; -80 mV). The GABAd response could be demonstrated at all ages in almost every neuron.(ABSTRACT TRUNCATED AT 400 WORDS)

2-Amino-5-phosphonovalerate↗