bluuebunny/crossref_metadata_2025 huggingface dataset:
Cholinergic and GABAergic receptors on fly tangential cells and their role in visual motion detection
Authors: Brotz T. M. , Borst A.
Published: December 2017

1. To identify some of the neurotransmitters involved in the processing of visual motion information the pharmacology of transmitter receptors on motion-sensitive visual interneurons (VS and HS cells) was investigated in an in vitro preparation of the blowfly (Calliphora erythrocephala) brain. Cholinergic and GABAergic drugs were applied in the bath and iontophoretically while recording intracellularly from HS and VS cells. 2. Bath-applied carbachol (10 and 100 microM) leads to a depolarization in HS and VS cells. One micromolar nicotine also has a depolarizing effect. Both agonists are effective in 0 Ca2+/high Mg(2+)-saline, too, which isolates the cells synaptically. The muscarinic agonists pilocarpine and oxotremorine have no effects on the membrane potential. 3. Iontophoretic application of acetylcholine, carbachol, and nicotine depolarizes VS and HS cells. The iontophoretic carbachol response is antagonized by alpha-bungarotoxin (EC50 = 0.19 microM), mecamylamine (EC50 = 0.32 microM), d-tubocurarine (EC50 = 9.5 microM), and bicuculline but not by decamethonium and scopolamine. 4. Bath application of muscimol strongly hyperpolarizes VS cells in normal fly saline. The gamma-aminobutyric acid-C (GABAC)-receptor agonist cis-4-aminocrotonic acid (CACA) has no effects. The hyperpolarizing response to iontophoretic applied muscimol is present in 0 Ca2+/high Mg2+ saline as well as in Co(2+)-containing saline. The muscimol response is reduced in low chloride saline and thus chloride sensitive. The muscimol response is blocked by picrotoxinin (EC50 = 3.4 microM) but not by the GABAA receptor antagonist bicuculline. 5. Taken together the primary responses of the lobula plate tangential cells appear to be nicotinic cholinergic and GABAergic. 6. The pharmacology of natural synaptic input to VS cells was investigated by extracellular electrical stimulation of the medulla. Such evoked excitatory postsynaptic potentials (EPSPs) are blocked reversibly in 0 Ca2+/high Mg2+ saline. The nicotinic antagonists mecamylamine (1 microM) and d-tubocurarine (50-100 microM) abolish or diminish the EPSPs, respectively. 7. The pharmacological data are incorporated into a semicellular model of a visual motion detector favoring a role of lobula plate tangential cells in certain steps of visual motion processing. Cholinergic and GABAergic inputs are an ideal cellular implementation of a linear subtraction of the signals arising from local motion-sensitive elements with opposite preferred direction. Such a mechanism enhances direction-selectivity and, together with dendritic integration, increases the sensitivity of the tangential cells for wide-field motion.
Neuronal activity in the claustrum of the monkey during performance of multiple movements
Authors: Shima K. , Hoshi E. , Tanji J.
Published: December 2017

1. We studied neuronal activity in the claustrum of monkeys during performance of three different arm movements. We verified recording sites of claustral neurons by histological confirmation of microlesions. For the sake of comparison, we also recorded from the arm area of the precentral motor cortex (MI). Selection of the movements was either visually guided or determined by memorized information. 2. A striking property of claustral neurons is their nonselective relation to the three movements (push, pull, and turn a manipulandum). A vast majority (70%) of movement-related neurons exhibited increase of discharge in relation to all three movements, whereas only 16% were active in relation to one of the three movements. By contrast, about one-half of neurons in the MI were active in relation to a single movement. In both areas, the movement-related activity was similar regardless of whether the movements were selected by visual signals or by memory. 3. The study is the first to reveal involvement of claustral neurons in motor execution, and their activity property suggests that the way they are involved is different from that of MI neurons.
Visceral nociceptive input into the ventral posterolateral nucleus of the thalamus: a new function for the dorsal column pathway
Authors: Al-Chaer E. D. , Lawand N. B. , Westlund K. N. , Willis W. D.
Published: December 2017

1. Extracellular recordings were made from single neurons in the ventral posterolateral (VPL) nucleus of the thalamus in anesthetized male rats. VPL cells that responded to colorectal distension (CRD) were further tested with cutaneous and visceral stimuli before and after sequential lesions of the dorsal column (DC) and of the ventrolateral column (VLC). 2. A total of 105 VPL viscerosensitive cells was isolated. In this study, we report results from 27 cells that were tested for visceral responses before and after lesions of the DC and the VLC. 3. Ten VPL cells, isolated in 10 different rats, that responded to CRD and to activation of their cutaneous receptive fields with innocuous and noxious stimuli were tested before and after a lesion of the DC and again after a lesion of the VLC. Ten other VPL cells were isolated in 10 different rats. These were also tested for responses to CRD and to cutaneous stimuli spanning the innocuous and the noxious range before and after a lesion of the VLC and again after a lesion of the DC. 4. A lesion of the DC dramatically reduced the responses of VPL cells to CRD as well as to innocuous cutaneous stimuli. A lesion of the VLC reduced and sometimes abolished the responses of VPL cells to noxious cutaneous stimuli; however, its effect on the responses to visceral or innocuous cutaneous stimuli was minor when compared with that of a DC lesion. 5. The activity of seven VPL cells that responded to CRD and to cutaneous stimuli was observed after an injection of a chemical irritant, mustard oil (MO), into the colon. These cells showed an increase in background activity that started approximately 25-30 min after the MO injection. A lesion of the DC reduced the background activity of the cells to levels near initial values. 6. We conclude that the DC in the rat contains a pathway that is more important for transmitting visceral nociceptive signals to the VPL nucleus than are pathways in the VLC, including the spinothalamic tract. Conversely, the VLC is more important for transmitting nociceptive information of cutaneous origin.
Prostaglandins Suppress an Outward Potassium Current in Embryonic Rat Sensory Neurons
Authors: Nicol G. D. , Vasko M. R. , Evans A. R.
Published: December 2017

Nicol, G. D., M. R. Vasko, and A. R. Evans. Prostaglandins suppress an outward potassium current in embryonic rat sensory neurons. J. Neurophysiol. 77: 167–176, 1997. The cellular mechanisms giving rise to the enhanced excitability induced by prostaglandin E2 (PGE2) and carba prostacyclin (CPGI2) in embryonic rat sensory neurons were investigated using the whole cell patch-clamp recording technique. Exposing sensory neurons to 1 μM PGE2 produced a twofold increase in the number of action potentials elicited by a ramp of depolarizing current, but this eicosanoid had no effect on the resting membrane potential or the amplitude of the slow afterhyperpolarization. Characterization of the outward potassium currents in the embryonic sensory neurons indicated that the composition of the total current was variable among these neurons. A steady-state inactivation protocol was used to determine the extent of residual noninactivating current. A conditioning prepulse to +20 mV demonstrated that some of these neurons exhibited only a sustained potassium current with little steady-state inactivation whereas others exhibited some combination of a sustained as well as a rapidly inactivating I A-type current. Treatment with 1 μM PGE2 or 1 μM CPGI2, but not 1 μM prostaglandin F2α (PGF2α) produced a time-dependent suppression of the total potassium current. After a 20-min exposure, PGE2 and CPGI2 inhibited the maximal current obtained at +60 mV by 48 and 40%, respectively. The prostaglandin-induced suppression of the potassium current was not associated with a shift in the voltage dependence for activation. Subtraction of the currents remaining after PGE2 or CPGI2 treatment from their respective control recordings revealed that the prostaglandin-sensitive current had characteristics that were consistent with a sustained-type of potassium current. This idea is supported by the following observation. The steady-state inactivation protocol revealed that for prepulse voltages activating both rapidly inactivating and sustained currents, the relaxation of the current was accelerated after treatment with PGE2 or CPGI2 suggesting the removal of a slower component. This effect was not observed in neurons exhibiting only the sustained type current. These results suggest that pro-inflammatory prostaglandins enhance the excitability of rat sensory neurons, in part, through the suppression of an outward potassium current that may modulate the firing threshold for generation of the action potential.
Regulation of Excitatory Input to Inhibitory Interneurons of the Dentate Gyrus During Hypoxia
Authors: Doherty James , Dingledine Raymond
Published: December 2017

Doherty, J. and R. Dingledine. Regulation of excitatory input to inhibitory interneurons of the dentate gyrus during hypoxia. J. Neurophysiol. 77: 393–404, 1997. The role of metabotropic glutamate receptors (mGluRs) and adenosine receptors in hypoxia-induced suppression of excitatory synaptic input to interneurons residing at the granule cell–hilus border in the dentate gyrus was investigated with the use of whole cell electrophysiological recording techniques in thin (250 μm) slices of immature rat hippocampus. Minimal stimulation evoked glutamatergic excitatory postsynaptic currents (EPSCs) in dentate interneurons in 68 ± 4% (mean ± SE) of trials during stimulation in the dentate granule cell layer (GCL) and 48 ± 3% of trials during stimulation in CA3. Hypoxic episodes, produced by switching the perfusing solution from 95% O2-5% CO2 to a solution containing 95% N2-5% CO2 for 3–5 min, rapidly and reversibly decreased the synaptic reliability, or probability of evoking an EPSC, from either input without reducing EPSC amplitude, consistent with a presynaptic suppression of transmitter release. The mGluR antagonist (+)-α-methyl-4-carboxyphenylglycine [(+)MCPG; 500 μM] did not alter synaptic reliability or mean EPSC amplitude in either pathway. However, (+)MCPG significantly attenuated hypoxic suppression of input from both pathways, suggesting that mGluRs activated by release of glutamate partially mediate hypoxic suppression of EPSCs to dentate interneurons. The mGluR agonist (1S,3R)-1-aminocyclopentane-1,3-dicarboxylic acid (ACPD; 100 μM) rapidly decreased the reliability of excitatory transmission from both the GCL (19 ± 5% of control) and CA3 (39 ± 15% of control). ACPD also increased the frequency of spontaneous EPSCs and evoked a slow inward current in dentate interneurons. Exogenous adenosine (10–300 μM) decreased synaptic reliability for both pathways and reduced the frequency of spontaneous EPSCs, but did not cause a decrease in the mean amplitude of evoked EPSCs, consistent with a presynaptic suppression of excitatory input to dentate interneurons. Conversely, the selective adenosine A1 receptor antagonists 8-cyclopentyl-1,3-dipropylxanthine (200 nM to 1 μM) and N6-cyclopentyl-9-methyladenine (1 μM) enhanced excitatory input to dentate interneurons by increasing synaptic reliability for both the GCL and CA3 inputs. Adenosine A1 receptor antagonists did not, however, reduce hypoxic suppression of excitatory input to dentate interneurons. These results indicate that hypoxia induces a presynaptic inhibition of excitatory input to dentate interneurons mediated in part by activation of mGluRs, but not adenosine A1 receptors, whereas both mGluRs and adenosine A1 receptors can depress excitatory input to dentate interneurons during normoxic stimulation. Regulation of excitatory input to dentate interneurons provides a mechanism to shape excitatory input to the hippocampus under both normal and pathological conditions.
Simulated Optic Flow and Extrastriate Cortex. II. Responses to Bar Versus Large-Field Stimuli
Authors: Mulligan Kathleen , Kim Jong-Nam , Sherk Helen
Published: December 2017

Mulligan, Kathleen, Jong-Nam Kim, and Helen Sherk. Simulated optic flow and extrastriate cortex. II. Responses to bar versus large-field stimuli. J. Neurophysiol. 77: 562–570, 1997. In the preceding paper we described the responses of cells in the cat's lateral suprasylvian visual area (LS) to large-field optic flow and texture movies. To assess response properties such as direction selectivity, cells were also tested with moving bar stimuli. We expected that there would be good agreement between response properties elicited with optic flow movies and those revealed with bar stimuli. We first asked how well bar response properties predicted responsiveness to optic flow movies. There was no correlation between responsiveness to movies and the degree of end-stopping, length summation, or preference for bars that accelerated and expanded. We then considered only the 322 cells that responded to both bars and optic flow or texture movies and asked how well the strength of their response to movies could be predicted from the direction-tuning curves generated with bar stimuli. One-third of these cells responded much more strongly to movies than could be predicted from their direction-tuning curves. Generally, such cells were rather well tuned for the direction of bar motion and preferred a direction substantially different from what they saw in optic flow movies. Optic flow movies shown in the forward direction were the most effective variety of movie for two-thirds of these cells. To see whether this outcome stemmed from differential direction tuning for bars and large multielement displays, in a second series of experiments we compared direction tuning for bars and large-field texture movies. Many cells showed substantially different direction tuning for the two kinds of stimulus: almost [Formula: see text] of 409 cells had tuning curves that overlapped each other by <50%. But only a small number of cells (<10%) responded much better to texture movies than to bars in the predominant direction of image motion in optic flow movies. This result, like that reported in the preceding paper, suggests that cells in LS respond differently to optic flow than to texture displays lacking optic flow motion cues.
Responses of Rat Sacral Spinal Neurons to Mechanical and Noxious Thermal Stimulation of the Tail
Authors: Douglass Diana K. , Carstens E.
Published: December 2017

Douglass, Diana K. and E. Carstens. Responses of rat sacral spinal neurons to mechanical and noxious thermal stimulation of the tail. J. Neurophysiol. 77: 611–620, 1997. In this study we investigated the receptive field properties, responses to mechanical and thermal stimuli, and sensitivity to systemic administration of pentobarbital sodium and morphine of single neurons recorded in the sacral spinal cords of pentobarbital-anesthetized rats. Fifty-three neurons responded to innocuous mechanical stimulation of the tail. Of 45 neurons that were additionally tested with noxious thermal stimulation, 62% responded and were classified as wide-dynamic-range or multireceptive neurons. Recording sites were located mainly in the middle layers of the S2–S4 dorsal horn. Mechanosensitive receptive fields on the tail varied widely in size (range 0.14–35 cm2, mean 10.33 cm2) and form, and were in nearly all cases bilateral. Most neurons responded with a high-frequency discharge followed by a more slowly adapting response to pressure stimuli delivered with von Frey hairs. Responses (maximal frequency and total number of impulses) increased in a graded manner to pressure stimuli ranging from 1.2 to 447 g. For neurons responsive to noxious heating of the tail, responses increased in a linear manner over the range of 38–54°C and often leveled off at higher temperatures. Of nine neurons tested with both graded von Frey and noxious heat stimuli, mean responses (maximal frequency and total number of impulses) evoked by the strongest pressure stimuli were larger than those evoked by the most intense heat stimuli, but the difference was not statistically significant. Responses to repeated 48°C stimuli were significantly attenuated within 8 min after systemic administration of morphine (1 or 2 mg/kg ip), reaching maximal suppression (to 37.3%; N = 13) after 18 min, with recovery following systemic naloxone. After morphine (1 and 2 mg/kg ip), the slope of the population stimulus-response function for noxious heat was reduced (51.8%), and the threshold was increased (by 4°C). Responses to noxious heat were significantly depressed (to a mean of 54%; N = 10) by supplemental administration of pentobarbital (mean 17 mg/kg over 5 min). On the basis of similarities between the present data and previous behavioral measures of tail flick stimulus-response functions and their modulation, it is suggested that some of the present neurons might function as interneurons in the tail flick reflex arc.
Characteristics of Electrically Evoked Somatodendritic Dopamine Release in Substantia Nigra and Ventral Tegmental Area In Vitro
Authors: Rice M. E. , Cragg S. J. , Greenfield S. A.
Published: December 2017

Rice, M. E., S. J. Cragg, and S. A. Greenfield. Characteristics of electrically evoked somatodendritic dopamine release in substantia nigra and ventral tegmental area in vitro. J. Neurophysiol. 77: 853–862, 1997. Somatodendritic dopamine (DA) release from neurons of the midbrain represents a nonclassical form of neuronal signaling. We assessed characteristics of DA release during electrical stimulation of the substantia nigra pars compacta (SNc) in guinea pig midbrain slices. With the use of parameters optimized for this region, we compared stimulus-induced increases in extracellular DA concentration ([DA]o) in medial and lateral SNc, ventral tegmental area (VTA), and dorsal striatum in vitro. DA release was monitored directly with carbon-fiber microelectrodes and fast-scan cyclic voltammetry. Detection of DA in SNc was confirmed by electrochemical, pharmacological, and anatomic criteria. Voltammograms of the released substance had the same peak potentials as those of DA obtained during in vitro calibration, but different from those of the indoleamine 5-hydroxytryptamine. Similar voltammograms were also obtained in the DA-rich striatum during local electrical stimulation. Contribution from the DA metabolite 3,4-dihydroxyphenylacetic acid to somatodendritic release was negligible, as indicated by the lack of effect of the monoamine oxidase inhibitor pargyline (20 μM) on the signal. Lastly, DA voltammograms could only be elicited in regions that were subsequently determined to be positive for tyrosine hydroxylase immunoreactivity (TH-ir). The frequency dependence of stimulated DA release in SNc was determined over a range of 1–50 Hz, with a constant duration of 10 s. Release was frequency dependent up to 10 Hz, with no further increase at higher frequencies. Stimulation at 10 Hz was used in all subsequent experiments. With this paradigm, DA release in SNc was tetrodotoxin insensitive, but strongly Ca2+ dependent. Stimulated [DA]o in the midbrain was also site specific. At the midcaudal level examined, DA efflux was significantly greater in VTA (1.04 ± 0.05 μM, mean ± SE) than in medial SNc (0.52 ± 0.05 μM), which in turn was higher than in lateral SNc (0.35 ± 0.03 μM). This pattern followed the apparent density of TH-ir, which was also VTA > medial SNc > lateral SNc. This report has introduced a new paradigm for the study of somatodendritic DA release. Voltammetric recording with electrodes of 2–4 μm tip diameter permitted highly localized, direct detection of endogenous DA. The Ca2+ dependence of stimulated release indicated that the process was physiologically relevant. Moreover, the findings that somatodendritic release was frequency dependent across a range characteristic of DA cell firing rates and that stimulated [DA]o varied markedly among DA cell body regions have important implications for how dendritically released DA may function in the physiology and pathophysiology of substantia nigra and VTA.
Large Amplitude Miniature Excitatory Postsynaptic Currents in Hippocampal CA3 Pyramidal Neurons Are of Mossy Fiber Origin
Authors: Henze Darrell A. , Card J. Patrick , Barrionuevo German , Ben-Ari Yezekiel
Published: December 2017

Henze, Darrell A., J. Patrick Card, German Barrionuevo, and Yezekiel Ben-Ari. Large amplitude miniature excitatory postsynaptic currents in hippocampal CA3 pyramidal neurons are of mossy fiber origin. J. Neurophysiol. 77: 1075–1086, 1997. Neonatal (P0) γ-irradiation was used to lesion selectively the mossy fiber (MF) synaptic input to CA3 pyramidal cells. This lesion caused a >85% reduction in the MF input as determined by quantitative assessment of the number of dynorphin immunoreactive MF boutons. Theγ-irradiation lesion caused a reduction in the mean number of miniature excitatory postsynaptic currents (mEPSCs) recorded from CA3 pyramidal cells (2,292 vs. 1,429/3-min period; n = 10). The lesion also caused a reduction in the mean mEPSC peak amplitude from 19.1 ± 0.45 to 14.6 ± 0.49 pA (mean ± SE; peak conductance 238.8 ± 5.6 to 182.0 ± 6.1 pS). Similarly, there was a reduction in the mean 10–85% rise time from 1.72 ± 0.02 ms to 1.42 ± 0.04 ms. The effects of the γ-irradiation on both mEPSC amplitude and 10–85% rise time were significant at P < 0.002 and P < 0.005 (2-tailed Kolmogorov-Smirnov test). Based on the selectivity of the γ-irradiation, MF and non-MF mEPSC amplitude and 10–85% rise-time distributions were calculated. Both the amplitude and 10–85% rise-time distributions showed extensive overlap between the MF and non-MF mediated mEPSCs. The MF mEPSC distributions had a mean peak amplitude of 24.6 pA (307.5 pS) and a mean 10–85% rise time of 2.16 ms. The non-MF mEPSC distributions had a mean peak amplitude of 12.2 pA (152.5 pS) and 10–85% rise time of 1.26 ms. The modes of the amplitude distributions were the same at 5 pA (62 pS). The MF and non-MF mEPSC amplitude and 10–85% rise-time distributions were significantly different at P ≪ 0.001 (1-tailed, large sample Kolmogorov-Smirnov test). The data demonstrate that the removal of the MF synaptic input to CA3 pyramidal cells leads to the absence of the large amplitude mEPSCs that are present in control recordings.
Two Types of Identified Ascending Interneurons With Distinct GABA Receptors in the Crayfish Terminal Abdominal Ganglion
Authors: Miyata Hiroki , Nagayama Toshiki , Takahata Masakazu
Published: December 2017

Miyata, Hiroki, Toshiki Nagayama, and Masakazu Takahata. Two types of identified ascending interneurons with distinct GABA receptors in the crayfish terminal abdominal ganglion. J. Neurophysiol. 77: 1213–1223, 1997. More than half of the identified ascending interneurons originating in the terminal abdominal ganglion of the crayfish received inhibitory sensory inputs from hair afferents innervating the tailfan on the side contralateral to their main branches. Biochemical aspects of this transverse lateral inhibition of ascending interneurons were examined by the use of neurophysiological and pharmacological techniques. Local application of γ-aminobutyric acid (GABA) and its agonist muscimol into the neuropil induced membrane hyperpolarization of identified ascending interneurons with an increase in membrane conductance. Because the reversal potential of inhibitory postsynaptic potentials (IPSPs) in ascending interneurons elicited by the sensory stimulation and GABA injection was similar, and the sensory-stimulated IPSPs of the interneurons were blocked by GABA and muscimol application, this study strongly suggests a GABAergic nature for transverse lateral inhibition of ascending interneurons. According to the response to the GABAAantagonists bicuculline and picrotoxin, ascending interneurons were classified into two types, picrotoxin-sensitive and picrotoxin-insensitive interneurons. Identified ascending interneurons VE-1 and RO-4 showed a pharmacological profile similar to that of the classical GABAAreceptor of the vertebrates. Bath application of both bicuculline and picrotoxin reversibly reduced the amplitudes of IPSPs. The other identified ascending interneurons CA-1, RO-1, and RO-2 were not affected significantly by the bath application of GABAAand GABABantagonists, although bath application of low-chloride saline reversed the sensory-stimulated IPSPs. IPSPs of the picrotoxin-sensitive interneurons had a rather faster time course and shorter duration in comparison with those of the picrotoxin-insensitive interneurons.
Central Modifications of Reflex Parameters May Underlie the Fastest Arm Movements
Authors: Adamovich Serge V. , Levin Mindy F. , Feldman Anatol G.
Published: December 2017

Adamovich, Serge V., Mindy F. Levin, and Anatol G. Feldman. Central modifications of reflex parameters may underlie the fastest arm movements. J. Neurophysiol. 77: 1460–1469, 1997. Descending and reflex pathways usually converge on common interneurons and motoneurons. This implies that active movements may result from changes in reflex parameters produced by control signals conveyed by descending systems. Specifically, according to the λ-model, a fast change in limb position is produced by a rapid change in the threshold of the stretch reflex. Consequently, external perturbations may be ineffective in eliciting additional reflex modifications of electromyographic (EMG) patterns unless the perturbations are relatively strong. In this way, the model accounts for the relatively weak effects of perturbations on the initial agonist EMG burst (Ag1) usually observed in fast movements. On the other hand, the same model permits robust reflex modifications of the timing and shape of the Ag1 in response to strong perturbations even in the fastest movements. To test the model, we verified the suggestion that the onset time of the Ag1, even in the fastest movements, depends on proprioceptive feedback in a manner consistent with a stretch reflex. In control trials, subjects ( n = 6) made fast unopposed elbow flexion movements of ∼60° (peak velocity 500–700°/s) in response to an auditory signal. In random test trials, a brief (50 ms) torque of 8–15 Nm either assisting or opposing the movement was applied 50 ms after this signal. Subjects had no visual feedback and were instructed not to correct arm deflections in case of perturbations. In all subjects, the onset time of the Ag1 depended on the direction of perturbation: it was 25–60 ms less in opposing compared with assisting load conditions. Assisting torques caused, at a short latency of 37 ms, an additional antagonist EMG burst preceding the Ag1. The direction-dependent effects of the perturbation persisted when cutaneous feedback was suppressed. It was concluded that the direction-dependent changes in the onset time and duration of the Ag1 as well as the antagonist activation preceding the Ag1 resulted from stretch reflex activity elicited by the perturbations rather than from a change in the control strategy or cutaneous reflexes. The results support the hypothesis on the hierarchical scheme of sensorimotor integration in which EMG patterns and movement emerge from the modification of the thresholds and other parameters of proprioceptive reflexes by control systems.
Effects of Opioids on Mechanosensitive Pelvic Nerve Afferent Fibers Innervating the Urinary Bladder of the Rat
Authors: Su X. , Sengupta J. N. , Gebhart G. F.
Published: December 2017

Su, X., J. N. Sengupta, and G. F. Gebhart. Effects of opioids on mechanosensitive pelvic nerve afferent fibers innervating the urinary bladder of the rat. J. Neurophysiol. 77: 1566–1580, 1997. A total of 443 pelvic nerve afferent fibers in the L6 dorsal root of the rat were identified by electrical stimulation of the pelvic nerve; 319 (72%) were myelinated Aδ fibers with a mean conduction velocity (CV) of 11.8 m/s and 124 (28%) were unmyelinated C fibers with mean CV of 1.9 m/s. Two hundred fifty-two fibers (57%) responded to noxious urinary bladder distension (UBD; 80 mmHg); 108 were C fibers (mean CV: 1.9 m/s) and 144 were Aδ fibers (mean CV: 8.2 m/s). Forty-nine UBD-sensitive fibers were further characterized; all gave monotonic increases in firing to increasing distending pressures. Thirty-six fibers (73%) had a low-threshold (LT) for response (mean: 6 mmHg) and 13 fibers (27%) had high-thresholds (HT) for response (mean: 32 mmHg). Responses of 15 fibers to graded UBD (11 LT and 4 HT) were tested before and after instillation of 0.5 ml of 30% xylenes ( n = 11) or 5% mustard oil ( n = 4) into the bladder. The mean resting activity of 13 fibers significantly increased, and 7 fibers exhibited sensitization of responses to graded UBD 30 min after xylenes or mustard oil instillation. All 4 HT fibers were sensitized; 3 of the 11 LT fibers were sensitized (i.e., gave increased responses to UBD). The effects of opioid receptor agonists were tested on responses to noxious UBD (80 mmHg). Cumulative intraaterial doses of μ-opioid receptor agonists (morphine, 8 mg/kg, and fentanyl, 300 μg/kg) and of δ-opioid receptor agonists (DPDPE, 300 μg/kg, and SNC-80, 300 μg/kg) did not affect responses to noxious UBD. In contrast, cumulative 16 mg/kg intraarterial doses of the κ-opioid receptor agonists U50,488H, U69,593 and U62,066 dose-dependently attenuated responses to noxious UBD. There were no differences in the dose-response relationships of these drugs on afferent fibers from untreated and xylenes- or mustard oil-treated urinary bladder. These results reveal that there is a greater proportion of UBD-sensitive fibers in the L6 dorsal root (57%) than in the S1 dorsal root of the rat (38%; a previous study). The attenuation of responses to UBD by κ, but not μ or δ opioid receptor agonists suggests a potential use for peripherally acting κ opioid receptor agonists in the control of urinary bladder pain.
Selective Modulation of GABAA Receptors by Aluminum
Authors: Trombley Paul Q.
Published: December 2017

Trombley, Paul Q. Selective modulation of GABAA receptors by aluminum. J. Neurophysiol. 80: 755–761, 1998. Aluminum has been implicated in several neurodegenerative conditions including Alzheimer's disease. Because the mammalian olfactory system has an unusual capacity for the uptake and transneuronal spread of inhaled substances such as aluminum, whole cell recording techniques were used to examine the actions of aluminum on basic membrane properties and amino acid receptors on rat olfactory bulb mitral/tufted (M/T) neurons in culture. Aluminum had little direct effects on M/T neurons. Aluminum (100 μM) did not evoke a membrane current or alter action-potential shape or duration. Aluminum also had no marked effects on the family of voltage-gated membrane currents evoked by a series of 10-mV, 50-ms depolarizing steps. However, aluminum dramatically potentiated the current evoked by 30 μM γ-aminobutyric acid (GABA) at concentrations <100 μM. Conversely, higher concentrations of aluminum blocked the GABA-evoked current. The effects of aluminum on GABA-evoked currents were not voltage dependent. Aluminum (100 μM) equally potentiated both inward currents at −30 mV and outward currents at + 30 mV. At 300 μM, aluminum blocked both inward and outward currents to a similar extent. In some neurons, aluminum only blocked the current and potentiation was not observed. The biphasic action of aluminum on GABA-evoked currents suggests separate binding sites: a high-affinity potentiating site and a low-affinity inhibiting site. Despite its effects on GABA-evoked currents, aluminum did not alter membrane currents evoked by glutamate, N-methyl-d-aspartate, kainate, or glycine. Aluminum also did not reduce spontaneous excitatory synaptic activity, suggesting little, if any, effect on glutamate release. Although a causal role for aluminum in Alzheimer's disease and other neuropathological conditions remains controversial, it is clear that elevated aluminum concentrations in the brain are associated with a variety of cognitive impairments. The present results indicate that aluminum can alter the function of GABAA receptors and may suggest that aluminum can contribute to cognitive impairment through disruption of inhibitory circuits.
Hand Dominance and Motor Unit Firing Behavior
Authors: Adam Alexander , Luca Carlo J. De , Erim Zeynep
Published: December 2017

Adam, Alexander, Carlo J. De Luca, and Zeynep Erim. Hand dominance and motor unit firing behavior. J. Neurophysiol. 80: 1373–1382, 1998. Daily preferential use was shown to alter physiological and mechanical properties of skeletal muscle. This study was aimed at revealing differences in the control strategy of muscle pairs in humans who show a clear preference for one hand. We compared the motor unit (MU) recruitment and firing behavior in the first dorsal interosseous (FDI) muscle of both hands in eight male volunteers whose hand preference was evaluated with the use of a standard questionnaire. Myoelectric signals were recorded while subjects isometrically abducted the index finger at 30% of the maximal voluntary contraction (MVC) force. A myoelectric signal decomposition technique was used to accurately identify MU firing times from the myoelectric signal. In MUs of the dominant hand, mean values for recruitment threshold, initial firing rate, average firing rate at target force, and discharge variability were lower when compared with the nondominant hand. Analysis of the cross-correlation between mean firing rate and muscle force revealed cross-correlation peaks of longer latency in the dominant hand than in the nondominant side. This lag of the force output with respect to fluctuations in the firing behavior of MUs is indicative of a greater mechanical delay in the dominant FDI muscle. MVC force was not significantly different across muscle pairs, but the variability of force at the submaximal target level was higher in the nondominant side. The presence of lower average firing rates, lower recruitment thresholds, and greater firing rate/force delay in the dominant hand is consistent with the notion of an increased percentage of slow twitch fibers in the preferentially used muscle, allowing twitch fusion and force buildup to occur at lower firing rates. It is suggested that a lifetime of preferred use may cause adaptations in the fiber composition of the dominant muscle such that the mechanical effectiveness of its MUs increased.
Compensation for Gaze Perturbation During Inactivation of the Caudal Fastigial Nucleus in the Head-Unrestrained Cat
Authors: Goffart Laurent , Guillaume Alain , Pélisson Denis
Published: December 2017

Goffart, Laurent, Alain Guillaume, and Denis Pélisson. Compensation for gaze perturbation during inactivation of the caudal fastigial nucleus in the head-unrestrained cat. J. Neurophysiol. 80: 1552–1557, 1998. Muscimol injection in the caudal part of the fastigial nucleus (cFN) leads, in the head-unrestrained cat, to a characteristic dysmetria of saccadic gaze shifts toward visual targets. The goal of the current study was to test whether this pharmacological cFN inactivation impaired the ability to compensate for unexpected perturbations in gaze position during the latency period of the saccadic response. Such perturbations consisted of moving gaze away from the target by a transient electrical microstimulation in the deep layers of the superior colliculus simultaneously with extinction of the visual target. After injection of muscimol in the cFN, targets located in the contralesional hemifield elicited gaze shifts that fell short of the target in both “perturbed” and “unperturbed” trials. The amplitude of the compensatory contraversive gaze shifts in perturbed trials coincided with the predicted amplitude of unperturbed responses starting from the same position. Targets located in the opposite hemifield elicited hypermetric gaze shifts in both trial types, and the error of compensatory responses was not statistically different from that of unperturbed gaze shifts. These results indicate that inactivation of the cFN does not interfere with the ability of the head-unrestrained cat to compensate for ipsiversive or contraversive perturbations in gaze position. Thus the gaze-related feedback signals that are used to compute a reference signal of desired gaze displacement are not impaired by cFN inactivation.
Role of the Oculomotor Vermis in Generating Pursuit and Saccades: Effects of Microstimulation
Authors: Krauzlis R. J. , Miles F. A.
Published: December 2017

Krauzlis, R. J. and F. A. Miles. Role of the oculomotor vermis in generating pursuit and saccades: effects of microstimulation. J. Neurophysiol. 80: 2046–2062, 1998. We studied the eye movements evoked by applying small amounts of current (2–50 μA) within the oculomotor vermis of two monkeys. We first compared the eye movements evoked by microstimulation applied either during maintained pursuit or during fixation. Smooth, pursuitlike changes in eye velocity caused by the microstimulation were directed toward the ipsilateral side and occurred at short latencies (10–20 ms). The amplitudes of these pursuitlike changes were larger during visually guided pursuit toward the contralateral side than during either fixation or visually guided pursuit toward the ipsilateral side. At these same sites, microstimulation also often produced abrupt, saccadelike changes in eye velocity. In contrast to the smooth changes in eye velocity, these saccadelike effects were more prevalent during fixation and during pursuit toward the ipsilateral side. The amplitude and type of evoked eye movements could also be manipulated at single sites by changing the frequency of microstimulation. Increasing the frequency of microstimulation produced increases in the amplitude of pursuitlike changes, but only up to a certain point. Beyond this point, the value of which depended on the site and whether the monkey was fixating or pursuing, further increases in stimulation frequency produced saccadelike changes of increasing amplitude. To quantify these effects, we introduced a novel method for classifying eye movements as pursuitlike or saccadelike. The results of this analysis showed that the eye movements evoked by microstimulation exhibit a distinct transition point between pursuit and saccadelike effects and that the amplitude of eye movement that corresponds to this transition point depends on the eye movement behavior of the monkey. These results are consistent with accumulating evidence that the oculomotor vermis and its associated deep cerebellar nucleus, the caudal fastigial, are involved in the control of both pursuit and saccadic eye movements. We suggest that the oculomotor vermis might accomplish this role by altering the amplitude of a motor error signal that is common to both saccades and pursuit.
Focal Epileptogenesis in a Rat Model of Polymicrogyria
Authors: Jacobs Kimberle M. , Hwang Bryan J. , Prince David A.
Published: December 2017

Jacobs, Kimberle M., Bryan J. Hwang, and David A. Prince. Focal epileptogenesis in a rat model of polymicrogyria. J. Neurophysiol. 81: 159–173, 1999. Polymicrogyria, a developmental cortical malformation associated with epilepsy, can be modeled in rats with a transcortical freeze lesion on the day of birth (P0) or P1. We have used field potential recordings to characterize the incidence, propagation patterns, and distribution of epileptiform activity in slices from rats with experimental microgyri. Interictal-like epileptiform activity was evoked in slices from 85% of freeze-lesioned rats aged P12–P118. These data show age-specific properties of epileptogenesis, including: a delay in onset, a decrease in the incidence of epileptiform activity in rats >P40 that was specific to those lesioned on P0 as opposed to P1, and a shift in the likely site of initiation to areas further from the microgyrus in mature animals. Several observations suggest that the area adjacent to the microgyrus, which appears histologically normal in Nissl stains, contains the necessary epileptogenic neuronal circuits: 1) in 78% of slices, epileptiform activity could be evoked only from a focal zone adjacent to the microgyrus (paramicrogyral zone) and not within the microgyrus proper; 2) epileptiform activity consistently originated from a particular site within this paramicrogyral zone, independent of the location of the stimulating electrode, suggesting that the generator is outside of the microgyrus; 3) evoked epileptiform activities in the paramicrogyral cortex were unaltered after separation of this zone from the microgyrus with a transcortical cut; and 4) the short-latency graded field potential evoked in the paramicrogyral zone contained an additional negativity not seen in control slices. The epileptiform activity was blocked reversibly by N-methyl-d-aspartate receptor antagonists in slices from mature as well as immature freeze-lesioned rats. These results suggest that aberrant synaptic connectivity develops in rat cortex surrounding the microgyrus and produces a focal epileptogenic zone whose capacity to generate epileptiform activities does not depend on connections with the malformation itself. We hypothesize that afferents, originating from cortical and extracortical sites, lose their targets in the region of the malformation and make appropriate laminar contacts in the cortex adjacent to the malformation, creating an overabundance of excitatory input to this cortical zone. Increased excitatory feedback onto specific cortical elements may be one factor involved in epileptogenesis in this model of a cortical malformation.
Physiological Properties of Raphe Magnus Neurons During Sleep and Waking
Authors: Leung Cynthia G. , Mason Peggy
Published: December 2017

Physiological properties of raphe magnus neurons during sleep and waking. Neurons in the medullary raphe magnus (RM) that are important in the descending modulation of nociceptive transmission are classified by their response to noxious tail heat as on,off, or neutral cells. Experiments in anesthetized animals demonstrate that RM on cells facilitate and off cells inhibit nociceptive transmission. Yet little is known of the physiology of these cells in the unanesthetized animal. The first aim of the present experiments was to determine whether cells with on- and off-like responses to noxious heat exist in the unanesthetized rat. Second, to determine if RM cells have state-dependent discharge, the activity of RM neurons was recorded during waking and sleeping states. Noxious heat applied during waking and slow wave sleep excited one group of cells (on-u) in unanesthetized rats. Other cells were inhibited by noxious heat (off-u) applied during waking and slow wave sleep states in unanesthetized rats. Neutral-u cells did not respond to noxious thermal stimulation applied during either slow wave sleep or waking. On-u and off-u cells were more likely to respond to noxious heat during slow wave sleep than during waking and were least likely to respond when the animal was eating or drinking. Although RM cells rarely respond to innocuous stimulation applied during anesthesia, on-u andoff-u cells were excited and inhibited, respectively, by innocuous somatosensory stimulation in the unanesthetized rat. The spontaneous activity of >90% of the RM neurons recorded in the unanesthetized rat was influenced by behavioral state. Off-u cells discharged sporadically during waking but were continuously active during slow wave sleep. By contrast,on-u and neutral-u cells discharged in bursts during waking and either ceased to discharge entirely or discharged at a low rate during slow wave sleep. We suggest that off cell discharge functions to suppress pain-evoked reactions during sleep, whereas on cell discharge facilitates pain-evoked responses during waking.
MST Neuronal Responses to Heading Direction During Pursuit Eye Movements
Authors: Page William K. , Duffy Charles J.
Published: December 2017

MST neuronal responses to heading direction during pursuit eye movements. As you move through the environment, you see a radial pattern of visual motion with a focus of expansion (FOE) that indicates your heading direction. When self-movement is combined with smooth pursuit eye movements, the turning of the eye distorts the retinal image of the FOE but somehow you still can perceive heading. We studied neurons in the medial superior temporal area (MST) of monkey visual cortex, recording responses to FOE stimuli presented during fixation and smooth pursuit eye movements. Almost all neurons showed significant changes in their FOE selective responses during pursuit eye movements. However, the vector average of all the neuronal responses indicated the direction of the FOE during both fixation and pursuit. Furthermore, the amplitude of the net vector increased with increasing FOE eccentricity. We conclude that neuronal population encoding in MST might contribute to pursuit-tolerant heading perception.
An Intrinsic Oscillation in Interneurons of the Rat Lateral Geniculate Nucleus
Authors: Zhu J. Julius , Lytton William W. , Xue Jin-Tang , Uhlrich Daniel J.
Published: December 2017

Intrinsic oscillation in interneurons of the rat lateral geniculate nucleus. By using the whole cell patch recording technique in vitro, we examined the voltage-dependent firing patterns of 69 interneurons in the rat dorsal lateral geniculate nucleus (LGN). When held at a hyperpolarized membrane potential, all interneurons responded with a burst of action potentials. In 48 interneurons, larger current pulses produced a bursting oscillation. When relatively depolarized, some interneurons produced a tonic train of action potentials in response to a depolarizing current pulse. However, most interneurons produced only oscillations, regardless of polarization level. The oscillation was insensitive to the bath application of a combination of blockers to excitatory and inhibitory synaptic transmission, including 30 μM 6,7-dinitroquinoxaline-2,3-dione, 100 μM (±)-2-amino-5-phosphonopentanoic acid, 20 μM bicuculline, and 2 mM saclofen, suggesting an intrinsic event. The frequency of the oscillation in interneurons was dependent on the intensity of the injection current. Increasing current intensity increased the oscillation frequency. The maximal frequency of the oscillation was 5–15 Hz for most cells, with some ambiguity caused by the difficulty of precisely defining a transition from oscillatory to regular firing behavior. In contrast, the interneuron oscillation was little affected by preceding depolarizing and hyperpolarizing pulses. In addition to being elicited by depolarizing current injections, the oscillation could also be initiated by electrical stimulation of the optic tract when the interneurons were held at a depolarized membrane potential. This suggests that interneurons may be recruited into thalamic oscillations by synaptic inputs. These results indicate that interneurons may play a larger role in thalamic oscillations than was previously thought.
Reorganization of the Somatosensory Cerebral CortexAfter Peripheral Damage
Authors: Verley R
Published: December 2017

If a sensory nerve is sectioned, it is expected that the centrally deprived projection area should be reduced to silence and atrophy. However, in recent years the capacity of the central nervous system for reorganization has received increasing attention. This article concerns elimination of input from the tactile system on the head of rodents, which has two components, the long vibrissae and the common fur. After early destruction of the vibrissae in newborn rats, the deprived cortex unexpectedly was not significantly reduced because substitution occurred. If only the vibrissae were destroyed, small fur hairs substituted for them. If both vibrissae and small hairs on the muzzle were destroyed, fur hairs of other head regions took over. This shows that early deprivation leads to reorganization in the somatosensory cortex that reveals greater than expected plasticity. Thus the principle of specificity of neural connections, a basic principle of neurology, must be reappraised.