Journal of Neurophysiology

Hicks, T. P.; Benedek, G.; Thurlow, G. A.

doi: N/Apmid: 3171635

Abstract 1. Extracellular recordings from 304 neurons were obtained with carbon fiber-containing multibarrel micropipettes. The cells were isolated in the insula in cats anesthetized with barbiturate and immobilized with gallamine triethiodide. Cells were tested with visual stimuli in the form of bars of light, moving edges, and square-wave, drifting grating patterns. 2. The spatial extent of the visually responsive region of insular cortex was assessed and was found to be limited to a surface area of approximately 6-8 mm2, the perimeter being delimited caudally by visually unresponsive cortex of the anterior sylvian gyrus, rostrally by the cortex surrounding the posterior third of the orbital sulcus (ventral bank), dorsally by the rostral extension of the dorsal bank of the anterior ectosylvian sulcus, and ventrally by a visually unresponsive zone bounded by a region about 2 mm2 ventrolateral from the anterior ectosylvian sulcal infolding. Furthermore, a group of unimodal, visually responsive cells often was found in the upper bank of the anterior rhinal sulcus. 3. The possibility of there being a visuotopic organization of insular neurons was examined by analyzing the distribution of receptive-field representation of neurons in sequential penetrations, as well as by searching for spatial progressions in the locations of visually responsive areas within the region. No such clear-cut organization was found among the cells of the insula. 4. Visually responsive neurons were encountered in groups, within electrode penetrations. These groupings were roughly segregated into three distinct levels within the depth of the cortex: the first between the pial surface and 600 micron, the second between 1,100 micron and 1,800 micron, and the third between 2,000 micron and 2,500 micron. 5. Neurons were classified according to their velocity sensitivity, directional preference, orientation sensitivity, length preference, modality specificity, response to electrical stimulation of extrageniculostriate regions, and response to light stimulation in the presence of microiontophoretically administered bicuculline methiodide (BMI). 6. Cells of superficial layers tended to exhibit a preference for high-velocity movements of light bars (600 degrees s-1), whereas those of deeper laminae generally preferred relatively lower velocity movements (60 degrees s-1). The clear preferences of many cells for certain directions of movement within the 360 degrees arc suggested the presence of a dynamic orientation sensitivity. 7. Proportionately more cells preferred moving bars (57%) to small moving spots (43%).(ABSTRACT TRUNCATED AT 400 WORDS) Copyright © 1988 the American Physiological Society

Mayer, M. L.; Westbrook, G. L.; Vyklicky, L.

doi: N/Apmid: 2902200

Abstract 1. Mouse hippocampal neurons in dissociated culture were grown at low density on previously plated hippocampal glial cell cultures and voltage clamped using the tight seal whole-cell patch-clamp technique. Flow pipes were used to rapidly exchange the extracellular solution, and to apply N-methyl-D-aspartic acid (NMDA) and some NMDA antagonists. Fluctuation analysis was used to estimate changes in the behavior of NMDA-activated ion channels during application of antagonists. In the presence of NMDA control spectra were well fit by single Lorentzian functions consistent with mean open times of 5-6 ms. 2. Two antagonists thought to act at the NMDA receptor agonist recognition site, 2-amino-5-phosphonovaleric acid (AP5) and kynurenic acid, did not produce changes in the mean open time or single channel conductance, consistent with their action as competitive antagonists. Onset of antagonism and recovery from the action of both AP5 and kynurenic acid was rapid and complete within 1 s. However, raising the extra-cellular glycine concentration, from 1 microM to 1 mM, reduced the potency of 100 microM kynurenic acid as an NMDA antagonist, suggesting that kynurenate has an additional action as a competitive antagonist at the glycine modulatory site on NMDA receptor channels. 3. In the presence of 150 microM magnesium NMDA spectra recorded at -60 mV were fit by double Lorentzian functions, consistent with single-channel events consisting of bursts of openings lasting 3.3 ms in duration, interrupted by blocking and unblocking events of average duration 0.18 ms. The onset and recovery from magnesium antagonism was rapid, and complete within 1 s, but was highly voltage dependent and at +40 mV magnesium (150 microM) failed to produce NMDA antagonism. These results are consistent with a voltage-dependent channel block of NMDA receptor channels produced by binding of magnesium to a site within the ion channel. 4. Zinc (30 microM) was a potent NMDA antagonist at both -60 and +40 mV, and at either potential appeared to reduce the mean open time of NMDA-activated ion channels from about 5 ms to approximately 3 ms. Over the frequency range measured, 1-1,000 Hz, NMDA spectra were well fit by single Lorentzians during zinc antagonism, in contrast to results obtained with magnesium. The mean single channel conductance also decreased in the presence of zinc to approximately 75% of control. Onset of antagonism and recovery from the action of zinc was rapid and complete within 1 s.(ABSTRACT TRUNCATED AT 400 WORDS) Copyright © 1988 the American Physiological Society

Lamour, Y.; Dutar, P.; Jobert, A.; Dykes, R. W.

doi: N/Apmid: 2902201

Abstract 1. Glutamate, acetylcholine (ACh), and bicuculline were delivered by iontophoretic pipettes to the 545 neurons described in the preceding paper. Their response properties were examined to determine the effect of these compounds on the behavior of neurons in rat somatosensory cortex. 2. The responses to glutamate covered a broad range. Some cells were completely depolarized by small amounts of this excitatory amino acid, whereas others were extremely insensitive requiring in excess of 100 nA to be excited. This range of sensitivities was seen throughout all cortical layers. 3. Glutamate was most effective in uncovering new receptive fields or in enhancing preexisting somatic responses in the bottom of layer II/III and in layer IV. Receptive fields uncovered by glutamate had properties comparable to receptive fields observed without drugs. Overall, glutamate enhanced the ability of afferent inputs to drive 39% of the neurons tested. 4. In 61% of the cells tested with glutamate there was no evidence of somatic input even during excitation with glutamate. Of 50 cells displaying receptive fields, only two were enlarged by treatment with glutamate. For 36 other cells receptive fields of normal dimensions were uncovered during glutamate administration. 5. Bicuculline uncovered more somatic inputs than either glutamate or ACh, leaving only 37% of 86 cells tested without evidence of excitatory inputs from the skin. Bicuculline produced an average receptive-field enlargement of 8.7 times in 11 of 56 cells tested. This drug acted uniformly throughout the cortical layers. 6. ACh excited 36.9% of the 360 cells tested. Those excited tended to be located in laminae Vb and VIb. The effects of ACh on afferent response properties could not be predicted from its ability to excite a cell. The magnitude of the response to 100 nA of ACh varied with the laminar position of the cell being tested, being weakest in layer II/III and greatest in layer Vb. 7. Overall, 34.2% of 263 cells showed changes in afferent drive during ACh treatment. ACh enhanced the responses to somatic stimulation most frequently in laminae IV and V. 8. Of the 90 neurons tested for long-term effects, 27% displayed effects of ACh that significantly outlasted the duration of the ACh administration. In 18% of these, changes lasted for greater than 5 min, sometimes remaining altered for the duration of the time that the cell was studied. These long-term changes in excitability were generally produced by administration of ACh during the time that the cell was excited by glutamate or by somatic stimulation. Copyright © 1988 the American Physiological Society

Komatsu, H.; Wurtz, R. H.

doi: N/Apmid: 3171645

Abstract 1. Pursuit eye movements are usually made against a visual background that is moved across the retina by the pursuit movement. We have investigated the effect of this visual stimulation on the response of pursuit cells that lie within the superior temporal sulcus (STS) of the monkey. 2. We assigned these pursuit cells to one of two groups depending on the nature of their preferred visual stimulus. One group of cells, comprising all cells located in the dorsal-medial region of the medial superior temporal area (MSTd) and some cells in lateral-anterior MST (MST1), responded to the motion of a large patterned field but showed little or no response to small spots or slits. The other group, consisting of all foveal middle temporal area (MTf) cells and many MST1 cells, responded preferentially to small spot motion or equally well to small spot motion or large field. 3. For many pursuit cells that preferred large-field stimuli, the visual response showed a reversal of the preferred direction of motion as the size of the stimulus field increased. The reversal usually occurred as the size of the moving random-dot field used as a stimulus increased in size from 20 x 20 degrees to 30 x 30 degrees for motion at approximately 10 degrees/s. The size of the filed stimulus leading to reversal of preferred direction depended on the speed of stimulus motion. Higher speeds of motion required larger stimulus fields to produce a reversal of preferred direction. This reversal (of preferred direction) did not reflect a center-surround organization of the receptive field but seemed to reflect the spatial summation properties of these cells. 4. For three-quarters of the cells that preferred large-field stimulation, the preferred direction of motion for the large field was opposite to the preferred direction of the pursuit response. The remaining cells showed either the same preferred directions for large-field visual stimulation and the pursuit response or had bidirectional visual responses. If we consider only the cells that show a reversal of preferred direction for large- and small-field stimuli, the preferred direction for the large field was always the opposite to that of pursuit, and the preferred direction for the small field was always the same. 5. During pursuit against a lighted background, the cells that showed opposite preferred directions for large-field stimulation and pursuit had synergistic responses--a facilitation of the pursuit response over the response during pursuit in the dark. Slow pursuit speeds (less than 20 degrees/s) produced the greatest facilitation.(ABSTRACT TRUNCATED AT 400 WORDS) Copyright © 1988 the American Physiological Society

Theriault, E.; Diamond, J.

doi: N/Apmid: 3171637

Abstract 1. The cutaneus trunci muscle (CTM) is a thin broad sheet of skeletal muscle that originates bilaterally on the humerus and inserts beneath the dermis of back and flank skin. A nociceptive stimulus applied to the skin elicits a localized reflex contraction in that region of the CTM underlying the site of sensory stimulation. While this "local sign" character of the CTM reflex corresponds to the segmental distribution of the afferent nerves (the dorsal cutaneous nerves, or DCNs) that enter the spinal cord in the lower thoracic and the lumbar levels, the motor output originates entirely from a circumscribed region of the cervical spinal cord. 2. Electrophysiological analysis of EMG activity in the muscle reflexly evoked by direct electrical stimulation of individual DCNs revealed a distinct topographic relationship, in that the shortest latency response of EMG activity in the muscle was consistently located approximately 1.0 cm rostral to the dermatome of the stimulated DCN. 3. Histochemical studies of the CTM show that individual muscle fibers run rostrocaudally, are focally innervated, and in adult rats, are approximately 3.0 cm in length. The major motor nerves exit from the brachial plexus, and functionally they divide the muscle into longitudinal (rostrocaudal) territories, which thus lie orthogonal to the dermatomal pattern of sensory innervation. The localized reflex responses to focal sensory stimuli indicate that the major longitudinal muscle fields contain many "reflex compartments." 4. The compartmentalized nature of the reflex response in the CTM suggests that nociceptive input from any one sensory dermatome has a preferred access to that fraction of the motoneuron pool that supplies the area of muscle underlying that specific region of skin, i.e., there is a sort of "matching" between groups of primary sensory neurons, interneurons, and motoneurons, which relates to the peripheral location of the stimulated nerve endings and of the muscle fibers that are reflexly activated. Although the partitioning of sensory input to motor nuclei has been shown most clearly for monosynaptic Ia connections, the CTM reflex suggests that sensory partitioning may also be demonstrated in a polysynaptic circuit. Copyright © 1988 the American Physiological Society

Rajan, R.

doi: N/Apmid: 3171642

Abstract 1. This report presents a more detailed examination of crossed olivocochlear bundle (COCB) effects on temporary threshold shifts (TTS). The principal aim was to establish the details of the relationship between the effects of continuous COCB stimulation and the TTS caused by various exposures. Initially, in various groups, different intensities of a 1-min exposure were presented with or without COCB stimulation. Stimulation at any particular rate caused greatest reductions in TTS to occur for the higher intensity exposures than for the lower intensity ones. Thus COCB stimulation at 140 pulses/s reduced maximum threshold losses by the following amounts: 13.33 106 dB sound pressure level (SPL) exposure, 13.29 (103 dB SPL exposure), 8.9 (101 dB SPL exposure), and 0.77 dB (97 dB SPL exposure). 2. The effect of COCB stimulation was also examined on a shorter duration (30 s) exposure causing TTS intermediate between that due to 1-min exposure at 97 dB SPL and that at 101 dB SPL. Reductions in TTS to the shorter duration exposure were not obtained with COCB stimulation at 140 pulses/s but only when the rate was increased to 260/s. 3. Thus COCB stimulation at any particular rate caused greatest reductions in TTS when the exposure would have caused a large amount of TTS, regardless of the intensity or duration of exposure. These two parameters of the exposure could be traded to provide a level of TTS that would be affected by a standard COCB stimulus. Low-level exposures that caused only small amounts of TTS were not affected by the standard COCB stimulus. As the level of the exposure, and therefore, the ensuing TTS, increased (with increased duration or intensity of exposure), the standard stimulus had greater effects. Increasing the rate of pulses in the COCB stimulus resulted in the low-level exposures now being affected. Even at the higher rate, greatest reductions in TTS were obtained when the exposure would have resulted in high levels of TTS. 4. In an attempt to determine the site of action of the continuous COCB stimulus the endocochlear potential (EP) and the summating potential (SP) were recorded from scala media of the basal turn while applying COCB stimuli similar to those used in the TTS experiments. Although the continuous COCB stimulus caused the traditional changes in the EP and SP associated with COCB stimulation with pulsed short electrical trains, these changes adapted quite rapidly and did not persist for the amount of time shown to be necessary for full reductions in TTS to be obtained.(ABSTRACT TRUNCATED AT 400 WORDS) Copyright © 1988 the American Physiological Society

Newsome, W. T.; Wurtz, R. H.; Komatsu, H.

doi: N/Apmid: 3171644

Abstract 1. We investigated cells in the middle temporal visual area (MT) and the medial superior temporal area (MST) that discharged during smooth pursuit of a dim target in an otherwise dark room. For each of these pursuit cells we determined whether the response during pursuit originated from visual stimulation of the retina by the pursuit target or from an extraretinal input related to the pursuit movement itself. We distinguished between these alternatives by removing the visual motion stimulus during pursuit either by blinking off the visual target briefly or by stabilizing the target on the retina. 2. In the foveal representation of MT (MTf), we found that pursuit cells usually decreased their rate of discharge during a blink or during stabilization of the visual target. The pursuit response of these cells depends on visual stimulation of the retina by the pursuit target. 3. In a dorsal-medial region of MST (MSTd), cells continued to respond during pursuit despite a blink or stabilization of the pursuit target. The pursuit response of these cells is dependent on an extraretinal input. 4. In a lateral-anterior region of MST (MST1), we found both types of pursuit cells; some, like those in MTf, were dependent on visual inputs whereas others, like those in MSTd, received an extraretinal input. 5. We observed a relationship between pursuit responses and passive visual responses. MST cells whose pursuit responses were attributable to extraretinal inputs tended to respond preferentially to large-field random-dot patterns. Some cells that preferred small spots also had an extraretinal input. 6. For 92% of the pursuit cells we studied, the pursuit response began after onset of the pursuit eye movement. A visual response preceding onset of the eye movement could be observed in many of these cells if the initial motion of the target occurred within the visual receptive field of the cell and in its preferred direction. In contrast to the pursuit response, however, this visual response was not dependent on execution of the pursuit movement. 7. For the remaining 8% of the pursuit cells, the pursuit discharge began before initiation of the pursuit eye movement. This occurred even though the initial motion of the target was outside the receptive field as mapped during fixation trials. Our data suggest, however, that such responses may be attributable to an expansion of the receptive field that accompanies enhanced visual responses.(ABSTRACT TRUNCATED AT 400 WORDS) Copyright © 1988 the American Physiological Society

Dykes, R. W.; Lamour, Y.

doi: N/Apmid: 3171648

Abstract 1. Recordings were made from 545 neurons in somatosensory granular cortex of anesthetized Sprague-Dawley rats. Of this sample, 32% were active spontaneously. Active neurons were not distributed uniformly throughout cortex but were most common in layer V. The highest mean spontaneous discharge frequency also was found in this layer. Cells with the lowest rates of spontaneous activity were located immediately above and below. One subset of spontaneously active neurons was characterized by an unusually high discharge frequency modulated by somatic stimulation. 2. Only 25.8% of the 534 neurons tested in granular cortex could be activated by somatic stimuli. Only 9.4% had cutaneous receptive fields, and 2.4% received deep inputs. The remainder (14.0%) were driven by higher intensity stimuli and could not be classified unequivocally as either cutaneous or deep. The 50 neurons with cutaneous receptive fields were located in the middle third of the cortex, and those with the largest receptive fields were found most superficially. Neurons driven by somatic stimuli were found most frequently in layer Vb, where 44.5% of the sample confirmed histologically to be in layer Vb could be excited. 3. The large proportion of neurons lacking demonstrable somatic inputs was attributed to the use of iontophoretically administered glutamate, which allowed the detection of many unresponsive neurons. This proportion was not reduced by the use of nitrous oxide and halothane as an anesthetic. 4. Neurons activated only by deep inputs were found on the medial and rostral edge of the hindlimb granular cortex, suggesting that deep and cutaneous inputs may be segregated in this species. 5. Electrical stimuli applied to the foot pads activated a sample of neurons differing from those driven by natural somatic stimuli in terms of depth, spontaneous activity, probability of somatic input, and probability of activation by the pyramidal tract. 6. Pyramidal tract neurons tended to be located in layer Vb, were active spontaneously, and had evidence of somatic inputs, although most required relatively intense stimuli to be excited. Other neurons activated synaptically from the pyramidal tract were located in the layers immediately above and below the pyramidal tract neurons. These cells were divided into two groups on the basis of action-potential latency, action-potential shape, and sensitivity to acetylcholine. Copyright © 1988 the American Physiological Society

Jiang, L. H.; Oomura, Y.

doi: N/Apmid: 2845014

Abstract 1. Neuronal activity in the central amygdaloid nucleus (ACE) was recorded during a visually guided bar-press feeding task, and the modulatory effects of catecholaminergic blockers were investigated. 2. The feeding task had the following four phases: 1) a cue light to signal the start of bar press, 2) bar press, 3) a short cue tone followed by food delivery, and 4) ingestion reward. Of 278 cells observed, 176 (63%) increased or decreased their discharge rates in one or more phases of the feeding task. Of these, 60 (34%) responded to the cue light, 81 (46%) to the bar press, 66 (37%) to the cue tone, and 176 (100%) during the reward period. In the ingestion reward phase, firing of 128 (73%) increased and firing of 48 (27%) decreased. The reward-related response depended on the nature of food. In the trials with aversion food, some neurons increased firing (n = 6), whereas others showed opposite firing changes (n = 10). 3. The decreased firing rate during the reward period was greatly attenuated in the no-reward tasks (n = 29) and was blocked by electrophoretic application of a beta-adrenoceptive antagonist sotalol (SOT), n = 26. Noradrenaline (NA) application mimicked the inhibitory effect on the reward-related activity during extinction trial (n = 4). These results suggest that the decreased firing rate observed during the reward period was modulated by beta-adrenoreceptors. 4. Of 32 neurons tested, the activity of 8 (25%) and 14 (44%) were enhanced by the cue light or bar press, respectively. These effects were attenuated by electrophoretic application of a dopamine (DA) antagonist spiperone (SPP) but not by SOT. This indicates that dopaminergic inputs may be related to recognition of visual signals and to motor initiation during the monkey feeding paradigm. Copyright © 1988 the American Physiological Society

Ishida, A. T.; Cohen, B. N.

doi: N/Apmid: 3171634

Abstract 1. We have begun to analyze neurotransmitter-activated conductances in retinal ganglion cells by measuring the response of single voltage-clamped adult goldfish ganglion cells to gamma-aminobutyric acid (GABA). Here we describe 1) our method of identifying ganglion cells in vitro after their dissociation from papain-treated retinas, and 2) the response of these cells to GABA in the tight-seal whole cell configuration of the patch-clamp method (cf. 41) after 1-4 days of primary cell culture. 2. Ganglion cell somata were backfilled in situ by injections of horseradish peroxidase (HRP) into the optic nerve. After dissociation of the retinas containing these cells, HRP reaction product was localized to cells that retained the size, shape, and an intracellular organelle characteristic of ganglion cells in situ. These features enabled us thereafter to identify ganglion cells in vitro without retrograde marker transport. 3. GABA (3-10 microM) elicited inward currents and substantial noise increases in almost all ganglion cells at negative holding potentials. Reversal potential measurements in salines containing different chloride concentrations indicated that GABA produces a chloride-selective conductance increase in ganglion cells. Bicuculline (10 microM) reversibly inhibited ganglion cell GABA responses. Baclofen (10 microM) alone elicited no responses in ganglion cells. 4. Noise analysis of GABA-activated whole cell currents yielded elementary conductance estimates of 16 pS, with a slow time constant of 30 ms plus a faster component of 1-2 ms. No significant voltage dependence of these values was observed between -20 and -80 mV. 5. We have thus devised a means of identifying ganglion cells dissociated from adult retinas, identified GABAA receptors (cf. 16) on these cells, and found that the responses mediated by these receptors resemble those found in other regions of central nervous system (CNS). These results are consistent with the notion that GABA may function as an inhibitory transmitter at synapses on ganglion cells. Copyright © 1988 the American Physiological Society