bluuebunny/crossref_metadata_2025 huggingface dataset:
Visible Evidence for Differences in Synaptic Effectiveness With Activity-Dependent Vesicular Uptake and Release of FM1-43
Authors: Quigley P. A. , Msghina M. , Govind C. K. , Atwood H. L.
Published: December 2017

Quigley, P. A., M. Msghina, C. K. Govind, and H. L. Atwood. Visible evidence for differences in synaptic effectiveness with activity-dependent vesicular uptake and release of FM1-43. J. Neurophysiol. 81: 356–370, 1999. Activity-dependent uptake and release of the fluorescent probe FM1-43 were used to compare synaptic performance (rates of transmitter release and synaptic vesicle turnover) at different frequencies in phasic and tonic motor neurons innervating the crayfish leg extensor muscle and in the tonic motor neuron of the opener muscle. The phasic extensor motor neuron, which has a high quantal content of transmitter release, accumulated and released FM1-43 more rapidly than the tonic motor neuron, especially at low frequencies of stimulation. Individual bright spots appeared on the varicosities of the junctional terminals during stimulation in FM1-43; these spots corresponded to zones of immunostaining for the synaptic vesicle associated protein synaptotagmin, but they were larger and less numerous than synapses identified by electron microscopy and appear to represent one to several synapses with their associated clusters of synaptic vesicles. The number of bright spots observed on varicosities of the tonic terminal after stimulation at ≥20 Hz is generally similar to values for responding units ( n) calculated from binomial distributions derived from quantal analysis. At frequencies of ≤10 Hz, bright spots did not usually appear on tonic extensor varicosities, and the quantal release patterns were best fitted with Poisson distributions. Another tonic motor neuron, the excitor of the opener muscle, showed individual bright spots at lower frequencies of stimulation, consistent with its higher quantal output at these frequencies and corresponding with the binomial fits for quantal release distributions. In this axon, the number of distinctive bright spots increased with frequency in the 2- to 20-Hz range, indicating increased participation of synapses during frequency facilitation. In the tonic extensor neuron terminals, the brightness and the size of the individual spots increased with frequency, and new foci of dye uptake appeared at the edges of preexisting spots. Relative intensity change varied considerably among individual spots during dye loading at different frequencies. Similarly, individual spots on a single tonic terminal destained at different rates when stimulated after previous loading with FM1-43. These results suggest differential performance of individual synapses or small groups of synapses, some being more effective in transmitter release than others, as inferred from previous ultrastructural and quantal analysis studies. The large overall differences between phasic and tonic synapses suggest differential regulation of transmitter release at individual synapses in the two neurons.
Reduction of Zolpidem Sensitivity in a Freeze Lesion Model of Neocortical Dysgenesis
Authors: Defazio R. Anthony , Hablitz John J.
Published: December 2017

DeFazio, R. Anthony and John J. Hablitz. Reduction of zolpidem sensitivity in a freeze lesion model of neocortical dysgenesis. J. Neurophysiol. 81: 404–407, 1999. Early postnatal freeze lesions in rat neocortex produce anatomic abnormalities resembling those observed in human patients with seizure disorders. Although in vitro brain slices containing the lesion are hyperexcitable, the mechanisms of this alteration have yet to be elucidated. To test the hypothesis that changes in postsynaptic inhibitory receptors may underlie this hyperexcitability, we examined properties of γ-aminobutyric acid type A receptor (GABAAR)–mediated miniature inhibitory postsynaptic currents (mIPSCs). Recordings were obtained in layer II/III pyramidal cells located 1–2 mm lateral to the lesion. mIPSC peak amplitude and rate of rise were increased relative to nonlesioned animals, whereas decay time constant and interevent interval were unaltered. Bath application of zolpidem at a concentration (20 nM) specific for activation of the type 1 benzodiazepine receptor had no significant effect on decay time constant in six of nine cells. Exposure to higher concentrations (100 nM) enhanced the decay time constant of all cells tested ( n = 7). Because mIPSCs from unlesioned animals were sensitive to both concentrations of zolpidem, these results suggest that freeze lesions may decrease the affinity of pyramidal cell GABAARs for zolpidem. This could be mediated via a change in α-subunit composition of the GABAAR, which eliminates the type 1 benzodiazepine receptor.
Retention of Hindlimb Stepping Ability in Adult Spinal Cats After the Cessation of Step Training
Authors: De Leon R. D. , Hodgson J. A. , Roy R. R. , Edgerton V. R.
Published: December 2017

de Leon, R. D., J. A. Hodgson, R. R. Roy, and V. R. Edgerton. Retention of hindlimb stepping ability in adult spinal cats after the cessation of step training. J. Neurophysiol. 81: 85–94, 1999. Adult spinal cats were trained to perform bipedal hindlimb locomotion on a treadmill for 6–12 wk. After each animal acquired the ability to step, locomotor training was withheld, and stepping was reexamined 6 and 12 wk after training ended. The performance characteristics, hindlimb muscle electromyographic activity patterns, and kinematic characteristics of the step cycle that were acquired with training were largely maintained when training was withheld for 6 wk. However, after 12 wk without training, locomotor performance declined, i.e., stumbling was more frequent, and the ability to consistently execute full weight-bearing steps at any treadmill speed decreased. In addition, the height that the paw was lifted during the swing phase decreased, and a smaller range of extension in the hindlimbs occurred during the E3 phase of stance. When three of the spinal cats underwent 1 wk of retraining, stepping ability was regained more rapidly than when trained initially. The finding that stepping ability in trained adult spinal cats can persist for 6 wk without training provides further evidence that training-induced enhancement of stepping is learned in the spinal cats and that a memory of the enhanced stepping is stored in the spinal networks. However, it appears that the spinal cord can forget how to consistently execute stepping if that task is not practiced for 12 wk. The more rapid learning that occurred with retraining is also consistent with a learning phenomenon. These results in conjunction with our earlier findings suggest that the efficacy of the neural pathways that execute a motor task is highly dependent on the periodic activation of those pathways in a sequence compatible with that motor task.
Potassium Currents in Precursor Cells Isolated From the Anterior Subventricular Zone of the Neonatal Rat Forebrain
Authors: Stewart R. R. , Zigova T. , Luskin M. B.
Published: December 2017

Stewart, R. R., T. Zigova, and M. B. Luskin. Potassium currents in precursor cells isolated from the anterior subventricular zone of the neonatal rat forebrain. J. Neurophysiol. 81: 95–102, 1999. The progenitor cells from the anterior part of the neonatal subventricular zone, the SVZa, are unusual in that, although they undergo division, they have a neuronal phenotype. To characterize the electrophysiological properties of the SVZa precursor cells, recordings were made of potassium and sodium currents from SVZa cells that were removed from postnatal day 0–1 rats and cultured for 1 day. The properties of the delayed rectifier and A-type potassium currents were described by classical Hodgkin and Huxley analyses of activation and inactivation. In addition, cells were assessed under current clamp for their ability to generate action potentials. The A-type potassium current ( I K(A)) was completely inactivated at a holding potential of −50 mV. The remaining potassium current resembled the delayed rectifier current ( I K(DR)) in that it was blocked by tetraethylammonium (TEA; IC50 4.1 mM) and activated and inactivated slowly compared with I K(A). The conductance-voltage ( G- V) curve revealed that G increased continuously from 0.2 nS at −40 mV to a peak of 2.6 nS at +10 or +20 mV, and then decreased for voltages above +30 mV. Activation time constants were largest at −40 mV (∼11 ms) and smallest at 100 mV (∼1.5 ms). The properties of I K(A) were studied in the presence of 20 mM TEA, to block I K(DR), and from a holding potential of −15 mV, to inactivate both I K(DR) and I K(A). I K(A) was then allowed to recover from inactivation to negative potentials during 200- to 800-ms pulses. Recovery from inactivation was fastest at −130 mV (∼21 ms) and slowest at −90 mV (∼135 ms). Inactivation was voltage independent from −60 to +60 mV with a time constant of ∼15 ms. At steady state, I K(A) was half inactivated at −90 mV. G K(A) increased from 0.2 nS at −60 mV to a peak of 2.4 nS at +40 mV. Finally, the activation time constants ranged from ∼1.9 ms at −50 mV to 0.7 ms at +60 mV. The properties of I K(A) resembled those of I K(A) found in differentiating cerebellar granule neurons. Most SVZa cells had sodium currents (28/32 cells). However, in current clamp 11 of 12 cells were incapable of generating action potentials from voltages of −30 to −100 mV, suggesting that the available current densities were too low to support excitability.
N-Type Voltage-Dependent Calcium Channels Mediate the Nicotinic Enhancement of GABA Release in Chick Brain
Authors: Tredway Trevor L. , Guo Jian-Zhong , Chiappinelli Vincent A.
Published: December 2017

N-type voltage-dependent calcium channels mediate the nicotinic enhancement of GABA release in chick brain. The role of voltage-dependent calcium channels (VDCCs) in the nicotinic acetylcholine receptor (nAChR)-mediated enhancement of spontaneous GABAergic inhibitory postsynaptic currents (IPSCs) was investigated in chick brain slices. Whole cell recordings of neurons in the lateral spiriform (SpL) and ventral lateral geniculate (LGNv) nuclei showed that cadmium chloride (CdCl2) blocked the carbachol-induced increase of spontaneous GABAergic IPSCs, indicating that VDCCs might be involved. To conclusively show a role for VDCCs, the presynaptic effect of carbachol on SpL and LGNv neurons was examined in the presence of selective blockers of VDCC subtypes. ω-Conotoxin GVIA, a selective antagonist of N-type channels, significantly reduced the nAChR-mediated enhancement of γ-aminobutyric acid (GABA) release in the SpL by 78% compared with control responses. Nifedipine, an L-type channel blocker, and ω-Agatoxin-TK, a P/Q-type channel blocker, did not inhibit the enhancement of GABAergic IPSCs. In the LGNv, ω-Conotoxin GVIA also significantly reduced the nAChR-mediated enhancement of GABA release by 71% from control values. Although ω-Agatoxin-TK did not block the nicotinic enhancement, L-type channel blockers showed complex effects on the nAChR-mediated enhancement. These results indicate that the nAChR-mediated enhancement of spontaneous GABAergic IPSCs requires activation of N-type channels in both the SpL and LGNv.
Cardiovascular and Neuronal Responses to Head Stimulation Reflect Central Sensitization and Cutaneous Allodynia in a Rat Model of Migraine
Authors: Yamamura Hiroyoshi , Malick Amy , Chamberlin Nancy L. , Burstein Rami
Published: December 2017

Reduction of the threshold of cardiovascular and neuronal responses to facial and intracranial stimulation reflects central sensitization and cutaneous allodynia in a rat model of migraine. Current theories propose that migraine pain is caused by chemical activation of meningeal perivascular fibers. We previously found that chemical irritation of the dura causes trigeminovascular fibers innervating the dura and central trigeminal neurons receiving convergent input from the dura and skin to respond to low-intensity mechanical and thermal stimuli that previously induced minimal or no responses. One conclusion of these studies was that when low- and high-intensity stimuli induce responses of similar magnitude in nociceptive neurons, low-intensity stimuli must be as painful as the high-intensity stimuli. The present study investigates in anesthetized rats the significance of the changes in the responses of central trigeminal neurons (i.e., in nucleus caudalis) by correlating them with the occurrence and type of the simultaneously recorded cardiovascular responses. Before chemical stimulation of the dura, simultaneous increases in neuronal firing rates and blood pressure were induced by dural indentation with forces ≥2.35 g and by noxious cutaneous stimuli such as pinching the skin and warming >46°C. After chemical stimulation, similar neuronal responses and blood pressure increases were evoked by much smaller forces for dural indentation and by innocuous cutaneous stimuli such as brushing the skin and warming it to ≥43°C. The onsets of neuronal responses preceded the onsets of depressor responses by 1.7 s and pressor responses by 4.0 s. The duration of neuronal responses was 15 s, whereas the duration of depressor responses was shorter (5.8 s) and pressor responses longer (22.7 s) than the neuronal responses. We conclude that the facilitated cardiovascular and central trigeminal neuronal responses to innocuous stimulation of the skin indicate that when dural stimulation induces central sensitization, innocuous stimuli are as nociceptive as noxious stimuli had been before dural stimulation and that a similar process might occur during the development of cutaneous allodynia during migraine.
NMDA-Dependent Currents in Granule Cells of the Dentate Gyrus Contribute to Induction but Not Permanence of Kindling
Authors: Sayin Ümit , Rutecki Paul , Sutula Thomas
Published: December 2017

NMDA-dependent currents in granule cells of the dentate gyrus contribute to induction but not permanence of kindling. Single-electrode voltage-clamp techniques and bath application of the N-methyl-d-aspartate (NMDA) receptor antagonist 2-amino-5-phosphonovaleric acid (APV) were used to study the time course of seizure-induced alterations in NMDA-dependent synaptic currents in granule cells of the dentate gyrus in hippocampal slices from kindled and normal rats. In agreement with previous studies, granule cells from kindled rats examined within 1 wk after the last of 3 or 30–35 generalized tonic-clonic (class V) seizures demonstrated an increase in the NMDA receptor–dependent component of the perforant path–evoked synaptic current. Within 1 wk of the last kindled seizure, NMDA-dependent charge transfer underlying the perforant path–evoked current was increased by 63–111% at a holding potential of −30 mV. In contrast, the NMDA-dependent component of the perforant-evoked current in granule cells examined at 2.5–3 mo after the last of 3 or 90–120 class V seizures did not differ from age-matched controls. Because the seizure-induced increases in NMDA-dependent synaptic currents declined toward control values during a time course of 2.5–3 mo, increases in NMDA-dependent synaptic transmission cannot account for the permanent susceptibility to evoked and spontaneous seizures induced by kindling. The increase in NMDA receptor–dependent transmission was associated with the induction of kindling but was not responsible for the maintenance of the kindled state. The time course of alterations in NMDA-dependent synaptic current and the dependence of the progression of kindling and kindling-induced mossy fiber sprouting on repeated NMDA receptor activation are consistent with the possibility that the NMDA receptor is part of a transmembrane signaling pathway that induces long-term cellular alterations and circuit remodeling in response to repeated seizures, but is not required for permanent seizure susceptibility in circuitry altered by kindling.
RINm5f Cells Express Inactivating BK Channels Whereas HIT Cells Express Noninactivating BK Channels
Authors: Li Zi-Wei , Ding Jiu Ping , Kalyanaraman Vani , Lingle Christopher J.
Published: December 2017

RINm5f cells express inactivating BK channels whereas HIT cells express noninactivating BK channels. Large-conductance Ca2+- and voltage-activated BK-type K+channels are expressed abundantly in normal rat pancreatic islet cells and in the clonal rat insulinoma tumor (RINm5f) and hamster insulinoma tumor (HIT) beta cell lines. Previous work has suggested that the Ca2+sensitivity of BK channels in RIN cells is substantially less than that in HIT cells, perhaps contributing to differences between the cell lines in responsiveness to glucose in mediating insulin secretion. In both RIN cells and normal pancreatic beta cells, BK channels are thought to play a limited role in responses of beta cells to secretagogues and in the electrical activity of beta cells. Here we examine in detail the properties of BK channels in RIN and HIT cells using inside-out patches and whole cell recordings. BK channels in RIN cells exhibit rapid inactivation that results in an anomalous steady-state Ca2+dependence of activation. In contrast, BK channels in HIT cells exhibit the more usual noninactivating behavior. When BK inactivation is taken into account, the Ca2+and voltage dependence of activation of BK channels in RIN and HIT cells is essentially indistinguishable. The properties of BK channel inactivation in RIN cells are similar to those of inactivating BK channels (termed BKichannels) previously identified in rat chromaffin cells. Inactivation involves multiple, trypsin-sensitive cytosolic domains and exhibits a dependence on Ca2+and voltage that appears to arise from coupling to channel activation. In addition, the rates of inactivation onset and recovery are similar to that of BKichannels in chromaffin cells. The charybdotoxin (CTX) sensitivity of BKicurrents is somewhat less than that of the noninactivating BK variant. Action potential voltage-clamp waveforms indicate that BK current is activated only weakly by Ca2+influx in RIN cells but more strongly activated in HIT cells even when Ca2+current magnitude is comparable. Concentrations of CTX sufficient to block BKicurrent in RIN cells have no effect on action potential activity initiated by glucose or DC injection. Despite its abundant expression in RIN cells, BKicurrent appears to play little role in action potential activity initiated by glucose or DC injection in RIN cells, but BK current may play an important role in action potential repolarization in HIT cells.
Central Pattern Generator for Escape Swimming in the Notaspid Sea SlugPleurobranchaea californica
Authors: Jing Jian , Gillette Rhanor
Published: December 2017

Central pattern generator for escape swimming in the notaspid sea slug Pleurobranchaea californica. Escape swimming in the notaspid opisthobranch Pleurobranchaea is an episode of alternating dorsal and ventral body flexions that overrides all other behaviors. We have explored the structure of the central pattern generator (CPG) in the cerebropleural ganglion as part of a study of neural network interactions underlying decision making in normal behavior. The CPG comprises at least eight bilaterally paired interneurons, each of which contributes and is phase-locked to the swim rhythm. Dorsal flexion is mediated by hemiganglion ensembles of four serotonin-immunoreactive neurons, the As1, As2, As3, and As4, and an electrically coupled pair, the A1 and A10 cells. When stimulated, A10 commands fictive swimming in the isolated CNS and actual swimming behavior in whole animals. As1–4 provide prolonged, neuromodulatory excitation enhancing dorsal flexion bursts and swim cycle number. Ventral flexion is mediated by the A3 cell and a ventral swim interneuron, IVS, the soma of which is yet unlocated. Initiation of a swim episode begins with persistent firing in A10, followed by recruitment of As1–4 and A1 into dorsal flexion. Recurrent excitation within the As1–4 ensemble and with A1/A10 may reinforce coactivity. Synchrony among swim interneuron partners and bilateral coordination is promoted by electrical coupling among the A1/A10 and As4 pairs, and among unilateral As2–4, and reciprocal chemical excitation between contralateral As1–4 groups. The switch from dorsal to ventral flexion coincides with delayed recruitment of A3, which is coupled electrically to A1, and with recurrent inhibition from A3/IVSto A1/A10. The alternating phase relation may be reinforced by reciprocal inhibition between As1–4 and IVS. Pleurobranchaea’s swim resembles that of the nudibranch Tritonia; we find that the CPGs are similar in many details, suggesting that the behavior and network are primitive characters derived from a common pleurobranchid ancestor.
In Vivo Intracellular Analysis of Granule Cell Axon Reorganization in Epileptic Rats
Authors: Buckmaster Paul S. , Dudek F. Edward
Published: December 2017

In vivo intracellular analysis of granule cell axon reorganization in epileptic rats. In vivo intracellular recording and labeling in kainate-induced epileptic rats was used to address questions about granule cell axon reorganization in temporal lobe epilepsy. Individually labeled granule cells were reconstructed three dimensionally and in their entirety. Compared with controls, granule cells in epileptic rats had longer average axon length per cell; the difference was significant in all strata of the dentate gyrus including the hilus. In epileptic rats, at least one-third of the granule cells extended an aberrant axon collateral into the molecular layer. Axon projections into the molecular layer had an average summed length of 1 mm per cell and spanned 600 μm of the septotemporal axis of the hippocampus—a distance within the normal span of granule cell axon collaterals. These findings in vivo confirm results from previous in vitro studies. Surprisingly, 12% of the granule cells in epileptic rats, and none in controls, extended a basal dendrite into the hilus, providing another route for recurrent excitation. Consistent with recurrent excitation, many granule cells (56%) in epileptic rats displayed a long-latency depolarization superimposed on a normal inhibitory postsynaptic potential. These findings demonstrate changes, occurring at the single-cell level after an epileptogenic hippocampal injury, that could result in novel, local, recurrent circuits.
17β-Estradiol Enhances NMDA Receptor-Mediated EPSPs and Long-Term Potentiation
Authors: Foy M. R. , Xu J. , Xie X. , Brinton R. D. , Thompson R. F. , Berger T. W.
Published: December 2017

17β-estradiol enhances NMDA receptor-mediated EPSPs and long-term potentiation. Gonadal steroid hormones influence CNS functioning through a variety of different mechanisms. To test the hypothesis that estrogen modulates synaptic plasticity in the hippocampus, in vitro hippocampal slices from 2-mo-old Sprague-Dawley male rats were used to determine the effect of 17β-estradiol on both N-methyl-d-aspartate (NMDA) receptor-mediated excitatory postsynaptic potentials (EPSPs) through intracellular recordings and long-term potentiation (LTP) through extracellular recordings. Intracellular EPSPs and extracellular field EPSPs (fEPSPs) were recorded from CA1 pyramidal cells by stimulating Schaffer collateral fibers. In intracellular experiments, slices were perfused with medium containing bicuculline (5 μM) and low Mg2+(0.1 mM) to enhance the NMDA receptor-mediated currents and 6,7-dinitroquinoxaline-2,3-dione (DNQX) (10 μM) to block the α-amino-3-hydroxy-5-methyl-4-isoxazoleproprianate (AMPA) receptor-mediated component. The effects of 17β-estradiol on NMDA receptor-mediated activity were excitatory; concentrations >10 nM induced seizure activity, and lower concentrations (1 nM) markedly increased the amplitude of NMDA-mediated EPSPs (both the first and second responses increased during paired pulse stimulation by 180 and 197%, respectively). In extracellular experiments, slices perfused with 17β-estradiol (100 pM) exhibited a pronounced, persisting, and significant enhancement of LTP of both the fEPSP slope (192%) and fEPSP amplitude (177%) compared with control slices (fEPSP slope = 155%; fEPSP amplitude = 156%) 30 min after high-frequency stimulation. These data demonstrate that estrogen enhances NMDA receptor-mediated currents and promotes an enhancement of LTP magnitude.
Properties of Conditioned Abducens Nerve Responses in a Highly Reduced In Vitro Brain Stem Preparation From the Turtle
Authors: Anderson Curtis W. , Keifer Joyce
Published: December 2017

Properties of conditioned abducens nerve responses in a highly reduced in vitro brain stem preparation from the turtle. Previous work suggested that the cerebellum and red nucleus are not necessary for the acquisition, extinction, and reacquistion of the in vitro classically conditioned abducens nerve response in the turtle. These findings are extended in the present study by obtaining conditioned responses (CRs) in preparations that received a partial ablation of the brain stem circuitry. In addition to removing all tissue rostral to and including the midbrain and cerebellum, a transection was made just caudal to the emergence of the IXth nerve. Such ablations result in a 4-mm-thick section of brain stem tissue that functionally eliminates the sustained component of the unconditioned response (UR) while leaving only a phasic component. We refer to this region of brain stem tissue caudal to the IXth nerve as the “caudal premotor blink region.” Neural discharge was recorded from the abducens nerve following a single shock unconditioned stimulus (US) applied to the ipsilateral trigeminal nerve. When the US was paired with a conditioned stimulus (CS) applied to the posterior eighth, or auditory, nerve using a delay conditioning paradigm, a positive slope of CR acquisition was recorded in the abducens nerve, and CR extinction was recorded when the stimuli were alternated. Resumption of paired stimuli resulted in reacquisition. Quantitative analysis of the CRs in preparations in which the caudal premotor blink region had been removed and those with cerebellar/red nucleus lesions showed that both types of preparations had abnormally short latency CR onsets compared with preparations in which these regions were intact. Preparations with brain stem transections had significantly earlier CR offsets as more CRs terminated as short bursts when compared with intact or cerebellar lesioned preparations. These data suggest that a highly reduced in vitro brain stem preparation from the turtle can be classically conditioned. Furthermore, the caudal brain stem is not a site of acquisition in this reduced preparation, but it contributes to the sustained activity of both the UR and CR. Finally, the unusually short CR onset latencies following lesions to the cerebellum are not further exacerbated by removal of the caudal brain stem. These studies suggest that convergence of CS and US synaptic inputs onto the abducens nerve reflex circuitry may underlie acquisition in this reduced preparation, but that mechanisms that control learned CR timing arise from the cerebellorubral system.
Characterization of theAplysia californicaCerebral Ganglion F Cluster
Authors: Rubakhin Stanislav S. , Li Lingjun , Moroz Tatiana P. , Sweedler Jonathan V.
Published: December 2017

Characterization of the Aplysia californica cerebral ganglion F cluster. The cerebral ganglia neurons of Aplysia californica are involved in the development and modulation of many behaviors. The medially located F cluster has been characterized using morphological, electrophysiological and biochemical techniques and contains at least three previously uncharacterized neuronal population. As the three subtypes are located in three distinct layers, they are designated as top, middle, and bottom layer F-cluster neurons (CFT, CFM, and CFB). The CFTcells are large (92 ± 25 μm), white, nonuniformly shaped, and located partially in the sheath surrounding the ganglion. These neurons exhibit weak electrical coupling, the presence of synchronized spontaneous changes in membrane potential, and a generalized inhibitory input upon electrical stimulation of the anterior tentacular (AT) nerve. Similar to the CFTneurons, the CFMneurons (46 ± 12 μm) are mainly silent but do not show electrical coupling or synchronized changes in membrane potential. Unlike the CFTneurons, the CFMneurons exhibit weak action potential broadening during constant current injection. Comparison of the peptide profiles of CFT, CFM, and CFB(10–30 μm) neurons using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry demonstrates distinct peptide molecular weights for each neuronal subtype with the masses of these peptides not matching any previously characterized peptides from A. californica. The mass spectra obtained from the AT nerve are similar to the CFTneuron mass spectra, while upper labial nerve contains many peptides observed in the CFMneurons located in nongranular neuron region.
Bursting in Inhibitory Interneuronal Networks: A Role for Gap-Junctional Coupling
Authors: Skinner F. K. , Zhang L. , Velazquez J. L. Perez , Carlen P. L.
Published: December 2017

Bursting in inhibitory interneuronal networks: a role for gap-junctional coupling. Much work now emphasizes the concept that interneuronal networks play critical roles in generating synchronized, oscillatory behavior. Experimental work has shown that functional inhibitory networks alone can produce synchronized activity, and theoretical work has demonstrated how synchrony could occur in mutually inhibitory networks. Even though gap junctions are known to exist between interneurons, their role is far from clear. We present a mechanism by which synchronized bursting can be produced in a minimal network of mutually inhibitory and gap-junctionally coupled neurons. The bursting relies on the presence of persistent sodium and slowly inactivating potassium currents in the individual neurons. Both GABAA inhibitory currents and gap-junctional coupling are required for stable bursting behavior to be obtained. Typically, the role of gap-junctional coupling is focused on synchronization mechanisms. However, these results suggest that a possible role of gap-junctional coupling may lie in the generation and stabilization of bursting oscillatory behavior.
Primary Afferent Fibers That Contribute to Increased Substance P Receptor Internalization in the Spinal Cord After Injury
Authors: Allen Brian J. , Li Jun , Menning Patrick M. , Rogers Scott D. , Ghilardi Joseph , Mantyh Patrick W. , Simone Donald A.
Published: December 2017

Primary afferent fibers that contribute to increased substance P receptor internalization in the spinal cord after injury. Upon noxious stimulation, substance P (SP) is released from primary afferent fibers into the spinal cord where it interacts with the SP receptor (SPR). The SPR is located throughout the dorsal horn and undergoes endocytosis after agonist binding, which provides a spatial image of SPR-containing neurons that undergo agonist interaction. Under normal conditions, SPR internalization occurs only in SPR+ cell bodies and dendrites in the superficial dorsal horn after noxious stimulation. After nerve transection and inflammation, SPR immunoreactivity increases, and both noxious as well as nonnoxious stimulation produces SPR internalization in the superficial and deep dorsal horn. We investigated the primary afferent fibers that contribute to enhanced SPR internalization in the spinal cord after nerve transection and inflammation. Internalization evoked by electrical stimulation of the sciatic nerve was examined in untreated animals, at 14 days after sciatic nerve transection or sham surgery and at 3 days after hindpaw inflammation. Electrical stimulation was delivered at intensities to excite Aβ fibers only, Aβ and Aδ fibers or A and C fibers as determined by the compound action potential recorded from the tibial nerve. Electrical stimuli were delivered at a constant rate of 10 Hz for a duration of 5 min. Transection of the sciatic nerve and inflammation produced a 33.7 and 32.5% increase in SPR and immunoreactivity in lamina I, respectively. Under normal conditions, stimulation of Aδ or C fibers evoked internalization that was confined to the superficial dorsal horn. After transection or inflammation, there was a 20–24% increase in the proportion of SPR+ lamina I neurons that exhibited internalization evoked by stimulation of Aδ fibers. The proportion of lamina I SPR+ neurons that exhibited internalization after stimulation of C-fibers was not altered by transection or inflammation because this was nearly maximal under normal conditions. Moreover, electrical stimulation sufficient to excite C fibers evoked SPR internalization in 22% of SPR+ lamina III neurons after nerve transection and in 32–36% of SPR+ neurons in lamina III and IV after inflammation. Stimulation of Aβ fibers alone never evoked internalization in the superficial or deep dorsal horn. These results indicate that activation of small-caliber afferent fibers contributes to the enhanced SPR internalization in the spinal cord after nerve transection and inflammation and suggest that recruitment of neurons that possess the SPR contributes to hyperalgesia.
Muscarinic Receptors Differentially Modulate the Persistent Potassium Current in Striatal Spiny Projection Neurons
Authors: Gabel Lisa A. , Nisenbaum Eric S.
Published: December 2017

Muscarinic receptors differentially modulate the persistent potassium current in striatal spiny projection neurons. Cholinergic regulation of striatal spiny projection neuron activity is predominantly mediated through muscarinic receptor modulation of several subclasses of ion channels. Because of its critical role in governing the recurring episodes of hyperpolarization and depolarization characteristic of spiny neurons in vivo, the 4-aminopyridine–resistant, persistent potassium (K+) current, I Krp, would be a strategic target for modulation. The present results show that I Krp can be either suppressed or enhanced by muscarinic receptor stimulation. Biophysical analysis demonstrated that the depression of I Krp was associated with a hyperpolarizing shift in the voltage dependence of inactivation and a reduction in maximal conductance. By contrast, the enhancement of I Krp was linked to hyperpolarizing shifts in both activation and inactivation voltage dependencies. Viewed in the context of the natural activity of spiny neurons, muscarinic depression of I Krp should uniformly increase excitability in both hyperpolarized and depolarized states. In the hyperpolarized state, the reduction in maximal conductance should bolster the efficacy of impending excitatory input. Likewise, in the depolarized state, the decreased availability of I Krp produced by the shift in inactivation should enhance ongoing synaptic input. The alterations associated with enhancement of I Krpare predicted to have a more dynamic influence on spiny cell excitability. In the hyperpolarized state, the negative shift in activation should increase the flow of I Krp and attenuate subsequent excitatory synpatic input; whereas once the cell has traversed into the depolarized state, the negative shift in inactivation should reduce the availability of this current and diminish its influence on the existing excitatory barrage.
Local Excitatory Circuits in the Intermediate Gray Layer of the Superior Colliculus
Authors: Pettit Diana L. , Helms Matthew C. , Lee Psyche , Augustine George J. , Hall William C.
Published: December 2017

Local excitatory circuits in the intermediate gray layer of the superior colliculus. We have used photostimulation and whole cell patch-clamp recording techniques to examine local synaptic interactions in slices from the superior colliculus of the tree shrew. Uncaging glutamate 10–75 μm from the somata of neurons in the intermediate gray layer elicited a long-lasting inward current, due to direct activation of glutamate receptors on these neurons, and brief inward currents caused by activation of presynaptic neurons. The synaptic responses occurred as individual currents or as clusters that lasted up to several hundred milliseconds. Excitatory synaptic responses, which reversed at membrane potentials near 0 mV, could be evoked by uncaging glutamate anywhere within 75 μm of an intermediate layer neuron. Our results indicate the presence of extensive local excitatory circuits in the intermediate layer of the superior colliculus and support the hypothesis that such intrinsic circuitry contributes to the development of presaccadic command bursts.
Blockade of SK-Type Ca2+-Activated K+Channels Uncovers a Ca2+-Dependent Slow Afterdepolarization in Nigral Dopamine Neurons
Authors: Ping Han Xian , Shepard Paul D.
Published: December 2017

Blockade of SK-type Ca2+-activated K+ channels uncovers a Ca2+-dependent slow afterdepolarization in nigral dopamine neurons. Sharp electrode current-clamp recording techniques were used to characterize the response of nigral dopamine (DA)-containing neurons in rat brain slices to injected current pulses applied in the presence of TTX (2 μM) and under conditions in which apamin-sensitive Ca2+-activated K+ channels were blocked. Addition of apamin (100–300 nM) to perfusion solutions containing TTX blocked the pacemaker oscillation in membrane voltage evoked by depolarizing current pulses and revealed an afterdepolarization (ADP) that appeared as a shoulder on the falling phase of the voltage response. ADP were preceded by a ramp-shaped slow depolarization and followed by an apamin-insensitive hyperpolarizing afterpotential (HAP). Although ADPs were observed in all apamin-treated cells, the duration of the response varied considerably between individual neurons and was strongly potentiated by the addition of TEA (2–3 mM). In the presence of TTX, TEA, and apamin, optimal stimulus parameters (0.1 nA, 200-ms duration at −55 to −68 mV) evoked ADP ranging from 80 to 1,020 ms in duration (355.3 ± 56.5 ms, n = 16). Both the ramp-shaped slow depolarization and the ensuing ADP were markedly voltage dependent but appeared to be mediated by separate conductance mechanisms. Thus, although bath application of nifedipine (10–30 μM) or low Ca2+, high Mg2+ Ringer blocked the ADP without affecting the ramp potential, equimolar substitution of Co2+ for Ca2+ blocked both components of the voltage response. Nominal Ca2+ Ringer containing Co2+ also blocked the HAP evoked between −55 and −68 mV. We conclude that the ADP elicited in DA neurons after blockade of apamin-sensitive Ca2+-activated K+ channels is mediated by a voltage-dependent, L-type Ca2+ channel and represents a transient form of the regenerative plateau oscillation in membrane potential previously shown to underlie apamin-induced bursting activity. These data provide further support for the notion that modulation of apamin-sensitive Ca2+-activated K+ channels in DA neurons exerts a permissive effect on the conductances that are involved in the expression of phasic activity.
Nitric Oxide Inhibits L-Type Ca2+Current in Glomus Cells of the Rabbit Carotid Body Via a cGMP-Independent Mechanism
Authors: Summers Beth A. , Overholt Jeffrey L. , Prabhakar Nanduri R.
Published: December 2017

Nitric oxide inhibits L-type Ca2+current in glomus cells of the rabbit carotid body via a cGMP-independent mechanism. Previous studies have shown that nitric oxide (NO) inhibits carotid body sensory activity. To begin to understand the cellular mechanisms associated with the actions of NO in the carotid body, we monitored the effects of NO donors on the macroscopic Ca2+current in glomus cells isolated from rabbit carotid bodies. Experiments were performed on freshly dissociated glomus cells from adult rabbit carotid bodies using the whole cell configuration of the patch-clamp technique. The NO donors sodium nitroprusside (SNP; 600 μM, n = 7) and spermine nitric oxide (SNO; 100 μM, n = 7) inhibited the Ca2+current in glomus cells in a voltage-independent manner. These effects of NO donors were rapid in onset and peaked within 1 or 2 min. In contrast, the outward K+current was unaffected by SNP (600 μM, n = 6), indicating that the inhibition by SNP was not a nonspecific membrane effect. 2-(4-carboxyphenyl)-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide (carboxy-PTIO; 500 μM), an NO scavenger, prevented inhibition of the Ca2+current by SNP ( n = 7), whereas neither superoxide dismutase (SOD; 2,000 U/ml, n = 4), a superoxide scavenger, nor sodium hydrosulfite (SHS; 1 mM, n = 7), a reducing agent, prevented inhibition of the Ca2+current by SNP. However, SNP inhibition of the Ca2+current was reversible in the presence of either SOD or SHS. These results suggest that NO itself inhibits Ca2+current in a reversible manner and that subsequent formation of peroxynitrites results in irreversible inhibition. SNP inhibition of the Ca2+current was not affected by 30 μM LY 83,583 ( n = 7) nor was it mimicked by 600 μM 8-bromoguanosine 3′:5′-cyclic monophosphate (8-Br-cGMP; n = 6), suggesting that the effects of NO on the Ca2+current are mediated, in part, via a cGMP-independent mechanism. N-ethylmaleimide (NEM; 2.5 mM, n= 6) prevented the inhibition of the Ca2+current by SNP, indicating that SNP is acting via a modification of sulfhydryl groups on Ca2+channel proteins. Norepinephrine (NE; 10 μM) further inhibited the Ca2+current in the presence of NEM ( n = 7), implying that NEM did not nonspecifically eliminate Ca2+current modulation. Nisoldipine, an L-type Ca2+channel blocker (2 μM, n = 6), prevented the inhibition of Ca2+current by SNP, whereas ω-conotoxin GVIA, an N-type Ca2+channel blocker (1 μM, n = 9), did not prevent the inhibition of Ca2+current by SNP. These results demonstrate that NO inhibits L-type Ca2+channels in adult rabbit glomus cells, in part, due to a modification of calcium channel proteins. The inhibition might provide one plausible mechanism for efferent inhibition of carotid body activity by NO.
In Vivo Assessment of the Midbrain Raphe Nuclear Regulation of Serotonin Release in the Hamster Suprachiasmatic Nucleus
Authors: Dudley Thomas E. , Dinardo Lisa A. , Glass J. David
Published: December 2017

In vivo assessment of the midbrain raphe nuclear regulation of serotonin release in the hamster suprachiasmatic nucleus. Serotonin (5-HT) plays important regulatory roles in mammalian circadian timekeeping; however, little is known concerning the regulation of serotonergic activity in the circadian clock located in the suprachiasmatic nuclei (SCN). By using in vivo microdialysis to measure 5-HT release we demonstrated that electrical or pharmacological stimulations of the dorsal or median raphe nuclei (DRN and MRN, respectively) can alter basal release of 5-HT in the hamster SCN. There were similar increases in SCN 5-HT release after electrical stimulation of either the MRN or DRN, indicating that both could contribute to the serotonergic activity in the SCN. Systemic pretreatment with the 5-HT antagonist metergoline abolished DRN-induced SCN 5-HT release but had little effect on MRN-induced SCN 5-HT release, suggesting different pathways for these nuclei in regulating 5-HT output in the SCN. Microinjections of the 5-HT1A autoreceptor agonist 8-OH-DPAT or antagonist WAY 100635 into the MRN caused significant inhibition and stimulation of SCN 5-HT release, respectively. Both drugs had substantially less effect in the DRN. These differential drug actions indicate that somatodendritic 5-HT1A autoreceptors on MRN neurons provide the prominent raphe autoregulation of 5-HT output in the SCN. Collectively the current results are evidence that DRN as well as MRN neurons can contribute to the regulation of 5-HT release in the hamster SCN. On the basis of the current observations and those from recent anatomic tracing studies of serotonergic projections to SCN it is hypothesized that DRN input to the SCN could be mediated by a DRN → MRN → SCN pathway involving a 5-HT–sensitive multisynaptic interaction between the DRN and MRN neurons.
Impact of Network Activity on the Integrative Properties of Neocortical Pyramidal Neurons In Vivo
Authors: Destexhe Alain , Paré Denis
Published: December 2017

Impact of network activity on the integrative properties of neocortical pyramidal neurons in vivo. During wakefulness, neocortical neurons are subjected to an intense synaptic bombardment. To assess the consequences of this background activity for the integrative properties of pyramidal neurons, we constrained biophysical models with in vivo intracellular data obtained in anesthetized cats during periods of intense network activity similar to that observed in the waking state. In pyramidal cells of the parietal cortex (area 5–7), synaptic activity was responsible for an approximately fivefold decrease in input resistance ( R in), a more depolarized membrane potential ( V m), and a marked increase in the amplitude of V m fluctuations, as determined by comparing the same cells before and after microperfusion of tetrodotoxin (TTX). The model was constrained by measurements of R in, by the average value and standard deviation of the V m measured from epochs of intense synaptic activity recorded with KAc or KCl-filled pipettes as well as the values measured in the same cells after TTX. To reproduce all experimental results, the simulated synaptic activity had to be of relatively high frequency (1–5 Hz) at excitatory and inhibitory synapses. In addition, synaptic inputs had to be significantly correlated (correlation coefficient ∼0.1) to reproduce the amplitude of V m fluctuations recorded experimentally. The presence of voltage-dependent K+ currents, estimated from current-voltage relations after TTX, affected these parameters by <10%. The model predicts that the conductance due to synaptic activity is 7–30 times larger than the somatic leak conductance to be consistent with the approximately fivefold change in R in. The impact of this massive increase in conductance on dendritic attenuation was investigated for passive neurons and neurons with voltage-dependent Na+/K+ currents in soma and dendrites. In passive neurons, correlated synaptic bombardment had a major influence on dendritic attenuation. The electrotonic attenuation of simulated synaptic inputs was enhanced greatly in the presence of synaptic bombardment, with distal synapses having minimal effects at the soma. Similarly, in the presence of dendritic voltage-dependent currents, the convergence of hundreds of synaptic inputs was required to evoke action potentials reliably. In this case, however, dendritic voltage-dependent currents minimized the variability due to input location, with distal apical synapses being as effective as synapses on basal dendrites. In conclusion, this combination of intracellular and computational data suggests that, during low-amplitude fast electroencephalographic activity, neocortical neurons are bombarded continuously by correlated synaptic inputs at high frequency, which significantly affect their integrative properties. A series of predictions are suggested to test this model.