Journal of Neurophysiology

Carp, J. S.; Wolpaw, J. R.

doi: N/Apmid: 7965025

Abstract 1. Monkeys can gradually increase or decrease the size of the triceps surae H-reflex in response to an operant conditioning task. This conditioning modifies the spinal cord. To determine the location and nature of the spinal cord plasticity and define its role in the behavioral change (i.e., H-reflex increase or decrease) we have recorded intracellularly from triceps surae motoneurons in conditioned animals and compared the results with data from naive (i.e., unconditioned) animals. 2. Eleven monkeys (Macaca nemestrina, male) were exposed to the HRdown conditioning mode, in which reward occurred when H-reflex size in one leg (i.e., the trained leg) was below a criterion value. In six animals (5.1–8.2 kg) H-reflex size in the trained leg fell to 24–58% of its initial value, whereas in the other five animals (4.0–5.5 kg) it remained at 92–114% of its initial value. This outcome, which was in accord with recent data indicating that success in HRdown conditioning is age dependent, allowed comparison of intracellular data from successful HRdown animals with data from unsuccessful animals as well as with data from naive (i.e., unconditioned) animals. 3. Intracellular recordings were obtained from 221 triceps surae motoneurons on trained and control sides of successful and unsuccessful HRdown animals. Measurements included axonal conduction velocity, input resistance, time constant, electrotonic length, rheobase, firing threshold, afterhyperpolarization duration and amplitude, and composite homonymous and heteronymous excitatory postsynaptic potentials to peripheral nerve stimulation. Results were compared with data from 109 triceps surae motoneurons in naive animals. 4. Motoneurons from the trained side of successful HRdown animals had a significantly more positive average firing threshold (-52 vs. -55 mV) and a significantly lower average conduction velocity (67 vs. 71 m/s) than those from naive animals. In contrast, motoneurons from the trained side of unsuccessful HRdown animals were not significantly different from naive motoneurons. 5. These data are consistent with the hypothesis that operantly conditioned decrease in H-reflex size is due to a positive shift in motoneuron firing threshold and a consequent increase in the depolarization needed to reach that threshold. 6. The more positive firing threshold, if present in the axon as well as in the soma, could also account for the decreased conduction velocity observed in motoneurons from the trained side of successful animals. Copyright © 1994 the American Physiological Society

Bianchi, R.; Wong, R. K.

doi: N/Apmid: 7964998

Abstract 1. Carbachol effects on CA3 hippocampal cells were studied in the absence of ionotropic glutamatergic and GABAergic transmission with intracellular and extracellular recordings from guinea pig septohippocampal slices. 2. In all experiments the perfusing solution contained ionotropic glutamate and gamma-aminobutyric acid (GABA) receptor blockers 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 10–20 microM), 3-((+/-)-2-carboxypiperazin-4-il)propyl-1-phosphonic acid (CPP, 10–20 microM), and picrotoxin (50 microM), respectively. Under these conditions, the excitatory and early inhibitory postsynaptic potentials, evoked in CA3 pyramidal cells by mossy fiber stimulation before the addition of the blockers, were completely suppressed. 3. Carbachol (50 microM) introduced via bath perfusion or pulse application elicited a series of rhythmic bursts with overriding action potentials. Each rhythmic burst lasted up to 30 s and repeated at intervals of 0.7–6 min. Rhythmic bursts were blocked by atropine (1 microM). 4. At membrane potentials more depolarized than -70 mV, carbachol also elicited a sustained depolarization associated with an increase in membrane input resistance and action-potential firing. This response was blocked by atropine (1 microM). 5. Carbachol can induce both rhythmic bursts and sustained depolarizations in the same cell. Rhythmic bursts were elicited when the membrane potential of the cell was more hyperpolarized than -70 mV; sustained depolarizing responses were activated by carbachol when the cell membrane potential was more depolarized than -70 mV. 6. Extracellular field potential responses in the CA3 region occurred simultaneously with rhythmic bursts, indicating the synchronization of the event in the CA3 field. Dual intracellular recordings confirmed that rhythmic bursts occurred simultaneously in CA3 hippocampal pyramidal cells.(ABSTRACT TRUNCATED AT 250 WORDS) Copyright © 1994 the American Physiological Society

Mooney, R. D.; Shi, M. Y.; Rhoades, R. W.

doi: N/Apmid: 7965014

Abstract 1. Radioligand binding with 125I -cyanopindolol in the presence of isoproterenol was used to define the distribution of 5 -HT1B receptors in the superior colliculus (SC) of adult hamsters. There was a high density of these receptors in the stratum griseum superficiale (SGS), and they were much less dense in other SC laminae. Enucleation of one eye produced a marked reduction in the density of these receptors in the contralateral SGS, suggesting that they are located primarily on retinotectal axon terminals. 2. Intracellular recording techniques were used to evaluate the effects of serotonin (5 -HT) on the excitatory postsynaptic potentials (EPSPs) evoked in SC cells of adult hamsters by stimulation of the optic tract (OT) in vitro. Application of 5 -HT produced a reduction of > or = 50% in OT -evoked EPSPs in 79% of the 67 cells tested. The average EPSP amplitude was 7.8 +/- 2.1 (SD) mV under control conditions and 2.7 +/- 1.9 mV in the presence of 5 -HT (P < 0.01). For most of these neurons, application of 5 -HT had little effect on their membrane potential or input resistance. The average percent change in membrane potential for cells tested with 5 -HT was 0.5 +/- 6.0% and the average percent change in input resistance was 0.6 +/- 22.9%. 3. For four of six cells tested, application of 5 -HT had no significant effects on the responses evoked by application of glutamate, either under normal bathing conditions or when the medium included low Ca2+ and high Mg2+. 4. Pharmacologic experiments indicated that the effects of 5 -HT on retinotectal transmission were mimicked by the 5 -HT1B agonists 1 -3 -(trifluoromethyl)phenyl -piperazine and 7 -trifluoromethyl -4(4 -methyl -1 -piperazinyl) 1,2 -a -quinoxaline maleate and antagonized by the 5 -HT1A/1B antagonists ( -) -pindolol and methiothepin. The effects of 5 -HT on the OT -evoked EPSP were not antagonized by either spiperone, ketanserin, 1 -(2 -methoxyphenyl) -4 -4 -(2 -phthalimido)butyl -piperazine HBr, or 1 -H -3 alpha -5 alpha -tropan -3 -yl -3,5 -dichlorobenzoate. 5. Both the anatomic and physiological results are consistent with the conclusion that 5 -HT presynaptically inhibits retinotectal transmission and that this effect is mediated by the 5 -HT1B receptor Copyright © 1994 the American Physiological Society

Sato, H.; Katsuyama, N.; Tamura, H.; Hata, Y.; Tsumoto, T.

doi: N/Apmid: 7965002

Abstract 1. Input mechanisms of 21 color-selective cells in cytochrome oxidase-rich blobs in layer II/III of the anesthetized and paralyzed monkey primary visual cortex were studied by an iontophoretic administration of the GABAergic receptor antagonist bicuculline methiodide (BMI). 2. Color-selective blob cells become responsive to originally nonresponsive colors of stimuli or brightness contrast stimuli during removal of intracortical inhibition. 3. The magnitudes of the cells' responses to color stimuli during BMI administration were larger than the expected value of response calculated from the previously reported color tuning of color-selective geniculate cells and emission spectra of color stimulus. 4. These results suggest that color-selective blob cells receive a convergence of different types of chromatic inputs and that intracortical inhibition confers selectivity for a given color on them. Copyright © 1994 the American Physiological Society

Masetto, S.; Russo, G.; Prigioni, I.

doi: N/Apmid: 7965026

Abstract 1. Electrical responses in hair cells located in the peripheral regions and in the central region of the frog crista ampullaris were investigated in thin slice preparations by using the whole-cell configuration of the patch-clamp technique. 2. Hair cells from the peripheral regions exhibited mostly a club-like shape and had an average resting potential of -46 mV, whereas cells from the central region had mostly a cylindrical shape and a more negative resting potential (-57 mV). 3. Voltage-clamp recordings revealed that ionic conductances differed in the two epithelial regions. Cells from the peripheral regions exhibited a transient K+ current of A-type (IA) in conjunction with a slow rectifier outward K+ current (IK). Cells from the central region showed little or no IA and generated an IK together with an inward rectifier K+ current (IIR). In both regions, hair cells showed a rapidly activating Ca(2+)-dependent outward K+ current (IK(Ca)) that rapidly inactivated to reach a steady-state level during 150-ms test pulses. 4. IA activated close to -60 mV and was inhibited by 12 mM 4-aminopyridine (4-AP). The time course of this current showed time to peak values of 3-4 ms at 0 mV. Inactivation was fast and almost voltage-independent. The decay time constant was approximately 35 ms at 0 mV. 5. IK was recruited close to -60 mV and activated slowly, reaching peak values in approximately 100 ms at 0 mV. It showed no evidence of inactivation during 150-ms test pulses and it was insensitive to 4-AP. 6. IIR activated at membrane potentials more negative than -90 mV and was blocked by exposure to 6 mM Cs+ or to a K(+)-free medium. This current showed an outward relaxation at potentials more negative than -140 mV, an effect that disappeared after exposure to a Na(+)-free medium. 7. IK(Ca) was recruited close to -40 mV and was inhibited by exposure to a Ca(2+)-free external medium or to 0.5 mM Cd2+. The time to peak of this current was approximately 3 ms at 0 mV and inactivation was very fast and almost independent from the membrane potential. The decay time constant was approximately 4 ms at 0 mV. 8. IK and IA were prominent in hair cells from the peripheral regions, whereas IK accounted for most of the membrane conductance in cells from the central region. The contribution of IK(Ca) was comparable in cells from both epithelial regions.(ABSTRACT TRUNCATED AT 400 WORDS) Copyright © 1994 the American Physiological Society

Medina, I.; Filippova, N.; Barbin, G.; Ben-Ari, Y.; Bregestovski, P.

doi: N/Apmid: 7965027

Abstract 1. Ionic currents and the cytosolic free calcium concentration (Ca2+i) were recorded in rat hippocampal neurons in culture using the whole-cell configuration of the patch-clamp technique and confocal laser scanning microscopy with the fluorescent Ca2+ indicator Fluo-3 or dual-emission microspectrofluorimetry with the fluorescent Ca2+ indicator Indo-1. The excitatory amino acids, kainate and N-methyl-D-aspartate (NMDA), were repeatedly applied to the neurons using either a fast perfusion system or pressure-ejection from micropipettes. 2. Conditioning (1–10 s) applications of NMDA induced desensitization of NMDA currents. Recovery from desensitization, estimated from analysis of the amplitudes of short (20–50 ms) test NMDA currents, was double exponential. The time constant of the first phase was < 2 s and for the second phase it was in the range 10–50 s. 3. Conditioning applications of kainate decreased the amplitude of NMDA currents. Recovery of NMDA currents from kainate-induced inactivation was slow and could be fitted with a single exponential. The time constant of recovery was in the range 10–50 s and increased with prolongation of the conditioning pulse of kainate. 6-Cyano-7-nitroquinoxaline-2,3-dione (CNQX; 20 microM) prevented kainate-induced inactivation of NMDA currents. 4. Depolarizing voltage pulses (1–10 s) also induced an inactivation of NMDA currents with a slow recovery. The time course of the recovery increased with prolongation of depolarizing pulses and with an elevation of external calcium. Cadmium, a blocker of voltage-gated channels, prevented development of the depolarization-induced inactivation of NMDA currents. 5. Simultaneous recording of ionic currents and fluorescence of Ca(2+)-sensitive dyes showed that application of kainate, NMDA, or depolarizing pulses resulted in a rise of Ca2+i. Cadmium (100 microM) reversibly blocked Ca2+i transients induced by depolarizing pulses without modification of kainate-induced rise in fluorescence intensity. 6. For equal inward currents the elevation of Ca2+i was approximately 3.5-fold higher for applications of NMDA than for kainate. 7. Strong buffering of Ca2+i prevented the inactivation of NMDA currents induced by kainate or by depolarization. 8. Our results suggest that in the hippocampal neurons kainate produces inactivation of NMDA currents via an elevation of Ca2+i. Copyright © 1994 the American Physiological Society

Matzner, O.; Devor, M.

doi: N/Apmid: 7965019

Abstract 1. We used the tested fiber method to record from single myelinated afferents axons ending in a chronic nerve injury site (neuroma) in the rat sciatic nerve or L4,5 dorsal root. Axons were chosen for study that fired spontaneously with a stable tonic or interrupted (bursty) autorhythmic firing pattern. 2. Agents that block voltage-sensitive Na+ channels tetrodotoxin (TTX), lidocaine, voltage-sensitive Ca2+ channels (Cd2+, Co2+, Ni2+, verapamil, D600, nifedipine, and fluarizine), volt-age-sensitive K+ channels tetraethylammonium (TEA), 4-aminopyridine (4-AP), and Ca(2+)-activated K+ channels (gK+Ca2+;quinidine, apamine) were applied topically to the neuroma. Effects on baseline rhythmogenesis and on the duty cycle of bursting were documented. Spike pattern analysis was used to determine whether changes in firing frequency were associated with changes in impulse initiation (electrogenesis), or resulted from (partial) block of impulse propagation downstream from the site of electrogenesis. Effects of veratridine were also noted. 3. Na+ channel blockers consistently quenched neuroma firing, and they did so by suppressing the process of impulse initiation. Only rarely was propagation block the dominant process. In bursty fibers the duration of on-periods shortened as the duration of off-periods lengthened, without a significant change in the baseline interspike interval (ISI). Veratridine accelerated firing, also via the impulse generating process. 4. Ca2+ channel blockers had essentially no effect on baseline firing rate (i.e., ISI). 5. Ca2+ channel blockers, as well as blockers of gK+Ca2+, had substantial, but inconsistent effects on burst pattern. It is not clear whether this reflects variability in the experimental conditions, or heterogeneity among the fibers sampled. 6. Blockade of K+ channels failed to evoke rhythmogenesis in acutely cut axons as it does in chronically injured axons, even in the presence of veratridine. This is consistent with other evidence that ectopic neuroma firing depends on postinjury remodeling of membrane electrical properties. 7. The data indicate that, in chronically injured axons, the inward currents that underly electrogenicity, enable ectopic discharge, and, together with outward K+ currents, set the fundamental firing rhythm (ISI), operate primarily with the use of voltage-sensitive Na+ rather than Ca2+ channels. 8. The on-off duty cycle in bursty fibers was affected by Na+ channel ligands and also, although less so, and less consistently by, Ca2+ channel ligands. This indicates that both may play a role in the slow modulations of membrane potential that presumably underly interrupted autorhythmicity. Copyright © 1994 the American Physiological Society

Wall, M. J.; Dale, N.

doi: N/Apmid: 7965018

Abstract 1. To assess the role that K+ currents play in the production of the swimming motor pattern in the Xenopus embryo, we have used low doses of the K+ channel blockers, 3,4-diaminopyridine (3,4-DAP; 25–100 microM) and tetraethylammonium (TEA; 500 microM), to reduce K+ currents and investigated the effects on motor output. 2. To confirm that 3,4 -DAP and TEA block K+ currents and characterize their actions, we made whole -cell voltage -clamp recordings from acutely isolated spinal neurons. Both 25–100 microM 3,4 -DAP and 100–500 microM TEA blocked the sustained K+ current in a dose -dependent manner. 3. Because TEA can block acetylcholine nicotinic receptors on autonomic ganglia, and nicotinic acetylcholine receptors have recently been shown to be present on Xenopus spinal neurons, we have tested both 3,4 -DAP and TEA for antagonist action against the nicotinic agonist 1,1-dimethyl-4-phenylpiperazinium (DMPP). Although 500 microM TEA blocked the DMPP -induced depolarization, 25 microM 3,4-DAP did not. 4. In the intact embryo, application of 25–100 microM 3,4 -DAP or 500 microM TEA disrupted both the left and right alternation of ventral root discharge and the motor pattern recorded intracellularly from spinal neurons during swimming. Both blockers allowed the firing of an extra action potential at midcycle, which led to a number of different patterns. These patterns were categorized as follows: type A, cycles with midcycle action potentials; type B, the simultaneous firing of neurons on both sides of the cord; and type C, in which one side was active, whereas the other side was inhibited. In both 3,4-DAP and TEA these abnormalities tended to occur at the beginning of swimming episodes. Both blockers also caused a significant increase in the cycle period. Because both 3,4-DAP and TEA produced very similar affects to the motor pattern, we conclude that the perturbations are probably a result of reducing K+ current amplitude. 5. To investigate whether 3,4-DAP and TEA were producing disruptions in the motor pattern by increasing synaptic drive through the broadening of action potentials, we made measurements of spike width, tonic depolarization, and midcycle inhibitory postsynaptic potential (IPSP) amplitude during swimming. Both 3,4-DAP and TEA caused significant but modest spike broadening (20.8 and 29.8%, respectively); however, their effects on tonic depolarization were inconsistent although both blockers increased midcycle IPSP amplitude. 6. To test whether a reduction in K+ currents could plausibly produce the specific motor pattern perturbations that were seen, we have made computer simulations of simplified spinal networks.(ABSTRACT TRUNCATED AT 400 WORDS) Copyright © 1994 the American Physiological Society

Staley, K.

doi: N/Apmid: 7965011

Abstract 1. The relationship of the activation of a voltage-sensitive chloride conductance GCl(V) to the chloride transmembrane equilibrium potential (ECl) and the consequent role of this conductance in determining the effect of the gamma-aminobutyric acid-A (GABAA) receptor-mediated transmembrane chloride (Cl-) flux were investigated with the use of whole-cell recordings in the CA1 and dentate gyrus regions of adult rat hippocampal slice preparations. 2. GCl(V) was inwardly rectifying, with significant conductance only at membrane potentials more negative than ECl. For all tested neuronal Cl- concentrations, the activation of GCl(V) could be described by a Boltzman equation with an average half-activation voltage 15 mV negative to ECl, a slope factor of 14 mV, and a maximum conductance of 5 microS. There was no time-dependent inactivation of GCl(V). 3. GCl(V) was modulated by intracellular divalent cations. When magnesium was omitted from the electrode solution, the inward rectification of GCl(V) was unchanged, but the maximum amplitude of GCl(V) increased by a factor of 1.7. GCl(V) was blocked by bath application of 100 microM zinc (Zn2+), but not when 1–6 mM ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) or bis-(o-aminophenoxy)-N,N,N',N'-tetraacetic acid (BAPTA) were present in the electrode solution. 4. GCl(V) was increased by 10 microM norepinephrine, and by activation of protein kinase A (PKA) with 1 mM 8-bromoadenosine cyclic monophosphate (8-Br cAMP). GCl(V) was blocked by activation of protein kinase C (PKC) with 10 microM phorbol 12,13-dibutyrate (PdBu) or 1-oleoyl-2-acetyl-sn-glycerol (OAG). 5. GCl(V) was present in all tested CA1 pyramidal neurons but no dentate gyrus neurons. In standard extracellular solution, the amplitude of GCl(V) was initially negligible but increased with recording time, suggesting that under normal conditions GCl(V) is blocked by an endogenous divalent cation or downregulated by PKC. 6. In current-clamp recordings, the steady-state resting membrane potential (RMP) diminished with Cl- loading, from -73 mV (4 mM electrode Cl-) to -27 mV (131 mM electrode Cl-). When GCl(V) was blocked with PdBu, there was no change in the RMP with Cl- loading. When electroneutral Cl- transport was blocked, voltage-clamp experiments using electrode Cl- concentrations of 4–131 mM demonstrated that ECl changed in parallel with the holding potential, but not when GCl(V) was blocked by PdBu.(ABSTRACT TRUNCATED AT 400 WORDS) Copyright © 1994 the American Physiological Society

Kao, C. Q.; McHaffie, J. G.; Meredith, M. A.; Stein, B. E.

doi: N/Apmid: 7965010

Abstract 1. The onset of visual activity in the superficial layers of the cat superior colliculus begins abruptly at about 6 days postnatal (DPN), just before natural eye opening. Despite the presence of many inactive sites at this time, the systematic nature of the superior colliculus visuotopy is already evident. The number of inactive sites across the horizontal dimension of the superficial layers decreases rapidly so that by 9–10 DPN most sites are visually responsive. 2. Initially, visual activity is restricted to the topmost portion of the superficial gray layer, where W-cell terminals predominate, but rapidly extends down to include Y-cell territory at 10 DPN. 3. In contrast to what might have been expected based on earlier behavioral observations, there was no physiological evidence for a central-to-peripheral gradient in the development of the superior colliculus visuotopy. Rather, the entire visual field is well represented long before the expression of any visually initiated behaviors. 4. In contrast to the rapidity of the appearance and organization of the visual representation in superficial layers, deep layers remain refractory to visual stimuli for weeks. Copyright © 1994 the American Physiological Society