Negative-going Potential Research Articles

On the synchronous activity induced by 4-aminopyridine in the CA3 subfield of juvenile rat hippocampus

1. Extracellular field potential and intracellular recordings were made in the CA3 subfield of hippocampal slices obtained from 10- to 24-day-old rats during perfusion with artificial cerebrospinal fluid (ACSF) containing the convulsant 4-aminopyridine (4-AP, 50 microM). 2. Three types of spontaneous, synchronous activity were recorded in the presence of 4-AP by employing extracellular microelectrodes positioned in the CA3 stratum (s.) radiatum: first, inter-ictal-like discharges that lasted 0.2-1.2 s and had an occurrence rate of 0.3-1.3 Hz; second, ictal-like events (duration: 3-40 s) that occurred at 4-38 x 10(-3) Hz; and third, large-amplitude (up to 8 mV) negative-going potentials that preceded the onset of the ictal-like events and thus appeared to initiate them. 3. None of these synchronous activities was consistently modified by addition of antagonists of the N-methyl-D-aspartate (NMDA) receptor to the ACSF. In contrast, the non-NMDA receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 2-10 microM) reversibly blocked interictal- and ictallike discharges. The only synchronous, spontaneous activity recorded in this type of medium consisted of the negative-going potentials that were abolished by the GABAA receptor antagonists bicuculline methiodide (5-20 microM) or picrotoxin (50 microM). Hence they were mediated through the activation of the GABAA receptor. 4. Profile analysis of the 4-AP-induced synchronous activity revealed that the gamma-aminobutyric acid (GABA)-mediated field potential had maximal negative amplitude in s. lacunosum-moleculare, attained equipotentiality at the border between s. radiatum and s. pyramidale, and became positive-going in s. oriens. These findings indicated that the GABA-mediated field potential presumably represented a depolarization occurring in the dendrites of CA3 pyramidal cells. 5. This conclusion was supported by intracellular analysis of the 4-AP-induced activity. The GABA-mediated potential was reflected by a depolarization of the membrane of CA3 pyramidal cells that triggered a few variable-amplitude, fractionated spikes or fast action potentials. By contrast, the ictal-like discharge was associated with a prolonged depolarization during which repetitive bursts of action potentials occurred. Short-lasting depolarizations with bursts of action potentials occurred during each interictal-like discharge. 6. The GABA-mediated potential recorded intracellularly in the presence of CNQX consisted of a prolonged depolarization (up to 12 s) that was still capable of triggering a few fast action potentials and/or fractionated spikes.(ABSTRACT TRUNCATED AT 400 WORDS)

Light-evoked increases in [K+]o in proximal portion of the dark-adapted cat retina.

1. The scotopic threshold response (STR) and slow negative response are negative-going potentials in the dark-adapted electroretinogram (ERG) of the cat eye that originate proximal to the photoreceptors and are present at threshold and with dim illuminations. The present paper examines the hypothesis that these events are associated with Müller cell responses to potassium released by proximal retinal neurons by measuring light-dependent changes in extracellular K+ concentration [( K+]o, in proximal retina. 2. Extracellular field potentials and changes in [K+]o, evoked in response to diffuse illumination of the dark-adapted retina, were recorded with a double-barreled K+-sensitive microelectrode placed in the retina at different depths. The vitreal ERG was recorded at the same time. 3. The dynamic range of the light-evoked increases in [K+]o, recorded in proximal retina from threshold to saturation, was strikingly similar to that of the STR and slow negative response. The threshold for the [K+]o increase was near that of the most sensitive ganglion cells, and the response saturated approximately 2.4 log units below rod saturation. Also, onset latencies and rates of rise for the increases in [K+]o and the field potentials in proximal retina followed similar functions of intensity. 4. The depth distribution of the light-evoked [K+]o increases resembled that of the STR. The increases in [K+]o were largest and fastest in proximal retina where the STR was largest. This was true both for very low intensity stimuli, below the threshold for PII (DC-component and b-wave) in distal retina, and for stimulus intensities near STR saturation, where PII (DC-component) was present. For stimuli of intensities near rod saturation, when the b-wave was present in distal retina, there was a small fast increase in [K+]o at light onset in distal retina and a slower increase in proximal retina. Both increases were truncated by spread of the large light-evoked decrease in [K+]o in subretinal space that is known to cause the c-wave in the ERG and slow PIII in neural retina. 5. The duration of the increases in [K+]o in proximal retina was more sustained than the proximal field potentials. In response to stimuli of 2-4 s, the field potential began to recover toward base line after about 300 ms, whereas the increases in [K+]o remained at maximal levels until stimulus offset.(ABSTRACT TRUNCATED AT 400 WORDS)

Contributions to the electroretinogram of currents originating in proximal retina.

We have investigated responses in proximal retina of the cat that contribute to two kinds of electroretinogram (ERG) recordings: (1) the pattern ERG, a light-adapted response and (2) the threshold and near threshold ERG, a dark-adapted response (Sieving et al., 1986a, 1986b; Sieving & Steinberg, 1985). In intraretinal, extracellular recordings, two negative-going responses were identified that are maximal around the inner plexiform layer, and distinct from PII, which is maximal in distal retina: under light-adapted conditions, a spatially tuned response at light and light offset, the "M-wave" (previously described in cold-blooded animals by Karwoski & Proenza (1977, 1980)), and under dark-adapted conditions, the scotopic threshold response, or "STR," a response at light onset. The results under dark-adapted conditions are examined in more detail here. The STR is a very sensitive response whose threshold is 1.5-2.0 log units below that of the dc-component of PII and therefore well below the threshold of the a-, b-, and c-waves. It saturates about 2.4 log units below rod saturation. The STR contributes a negative-going potential to the dark-adapted ERG that is dominant near threshold; while PII (dc-component and b-wave) contributes a positive-going potential that is dominant at higher intensities (Sieving et al., 1986b). Investigation of the mechanism of the proximal retinal responses that contribute to the ERG supports of K(+)-Müller cell hypothesis of their origin.

Event-related potentials, semantic processes, and expectancy factors in word recognition

Electrophysiological activity was recorded at 16 scalp locations during a word recognition task in order to investigate the effect of expectency factors on ERPs. In each of 160 trials two stimuli (S1 and S2) were presented with a stimulus onset asynchrony (SOA) of 1500 msec. There were four experimental conditions. In the word-antonym (W-A) and the word-nonantonym (W-NA) conditions, both S1 and S2 were words. The subjects' task was to think of the antonym to S1 and respond as fast as possible after the presentation of S2 by pressing a “YES” button if S2 was an antonym to S1 (in the W-A trials), or a “NO” button if S2 was not an antonym to S1 (in the W-NA trials). In the nonword-word (NW-W) and nonword-nonword (NW-NW) conditions S1 was a nonword, while S2 was either a word (in NW-W trials) or a nonword (in NW-NW trials). If S1 was not a word, the subjects were instructed to wait for S2, and respond as fast as possible by pressing the “YES” button if it was a word an the “NO” button if it was not a word. EEG was sampled during a time epoch that started 100 msec before the onset of S1 and continued for another 2560 msec. The ERPs were analyzed separately for each experimental condition and for time epochs related to S1, to S2, and to the SOA. Expected antonyms were recognized significantly faster than any other words or nonwords. The RTs to words in the W-NA and NW-W condition, and to nonwords in the NW-NW condition did not differ significantly from each other. The ERP difference between the four conditions following S2 was interpreted in terms of a negative-going potential which appeared prior to the P300, during a time period which started 200 msec and ended 550 msec from stimulus onset. The negativity related to nonwords was significantly larger than the negativity related to words. The negativity related to the expected antonym was almost nonexistent. It is speculated that this negativity has the same origin as N400, and that it might be related to the process of lexical access.

M-wave of proximal retina in cat.

There has been relatively little known about responses from proximal retina in mammals that could contribute to the electroretinogram (ERG). Recently, there has been evidence that the proximal retina is involved in generating the pattern electroretinogram (PERG). In the present work we investigated proximal retinal activity in the intact cat eye during light adaptation. Extracellular potentials evoked in response to circular spots of light, flashed on steady backgrounds, were recorded with microelectrodes placed intraretinally at different depths. Prominent negative responses were found in proximal retina that could be identified as the M-wave previously observed only in cold-blooded retinas. Like the cold-blooded responses, the cat's M-wave consisted of negative-going potentials at stimulus onset and offset that were maximum in amplitude with small spots. By analogy to the cold-blooded data, the cat M-wave is presumed to be the extracellular voltage arising from Müller cell responses to K+ released by proximal retinal neurons. In addition, the cat M-wave only appeared with backgrounds at and above rod saturation and had short latencies (30 ms) at stimulus onset and offset, indicating that it is a cone-driven response. The M-wave could be clearly distinguished from PII (b-wave and DC component) on the basis of its form, depth distribution, and stimulus-response characteristics. For example, photopic PII had its maximum voltage in the distal retinal at 55% retinal depth, whereas the M-wave was maximal in the proximal retina at 25% retinal depth. Also, PII simply increased in amplitude as stimulus spots were enlarged, whereas the M-wave exhibited spatial tuning. Under light-adapted conditions and with small-spot stimuli the M-wave is the largest extracellular voltage in cat retina. By recording the vitreal ERG near the retinal surface with the microelectrode referenced to a silver wire in the vitreous, we found that the M-wave in response to a small spot always had a negative polarity in the vitreous. Thus, unlike PII, the M-wave does not reverse polarity at the vitreo-retinal border. Because of stray-light effects, however, we were not able to assess the amplitude of the M-wave's contribution to the ERG obtained with diffuse retinal illumination. We conclude that the M-wave is present in the cat as a prominent cone-driven response of proximal retina that is separate from the b-wave, and whose significance for electroretinographic recordings remains to be determined.

Unitary and field potential responses in the pigeon optic tectum evoked by luminous stimuli.

Receptive fields of retinotectal axons and of tectal cells were plotted, and the magnification factor at the tectal surface was measured. In the SGFS, receptive fields were often below 6 degrees in size and are probably derived from radially disposed pyriform cells. In the SGC, receptive fields were up to 40 degrees in size and are probably derived from the multipolar cells. Spike discharge in the retino-recipient layers was accompanied by a phasic negative-going slow potential, occurring at on and off to flashed spot stimuli.

Voltage-clamp analysis of the potassium current that produces a negative-going action potential in Ascaris muscle.

1. A voltage clamp has been developed for the pharyngeal muscle of the nematode Ascaris lumbricoides and has been used to analyse the potassium current that produces a negative-going, regenerative action potential in this muscle. 2. Depolarizing voltage steps elicit a sustained inward current; returning the membrane voltage to the resting level evokes a strong, transient, outward current. This outward current reverses direction at the same voltage as that reached by the negative-going spike and is identified as the negative spike current. 3. The negative spike current decays with a time constant of 30 msec at voltages more negative than -30mV. This inactivation of the negative spike conductance is removed by holding the membrane at potentials more positive than -15mV. The time constant for removal of inactivation decreases from more than 300 msec at -15 mV to about 30 msec at +10 mV. 4. When inactivation has been removed, the negative spike conductance is turned on by stepping to potentials more negative than -15 mV. 5. Although the reversal potential for this current depends strongly on [K+]o (42 mV/decade), the potential at which the conductance is turned on is independent of [K+]o. 6. External Na+ seems to facilitate the negative spike current. Reduction of [Na+]o reduces its conductance and shifts the reversal potential to more positive values. 7. External Rb+ and Cs+ show voltage-dependent blocking of this current. 8. This K current is different from all the K currents which have been studied previously; however, it is analogous to the classical Na current of nerve and muscle, except for an inversion of the voltage dependencies.