Short-latency Action Potentials Research Articles

Cortical Control of Striatal Dopamine Transmission via Striatal Cholinergic Interneurons

Corticostriatal regulation of striatal dopamine (DA) transmission has long been postulated, but ionotropic glutamate receptors have not been localized directly to DA axons. Striatal cholinergic interneurons (ChIs) are emerging as major players in striatal function, and can govern DA transmission by activating nicotinic receptors (nAChRs) on DA axons. Cortical inputs to ChIs have historically been perceived as sparse, but recent evidence indicates that they strongly activate ChIs. We explored whether activation of M1/M2 corticostriatal inputs can consequently gate DA transmission, via ChIs. We reveal that optogenetic activation of channelrhodopsin-expressing corticostriatal axons can drive striatal DA release detected with fast-scan cyclic voltammetry and requires activation of nAChRs on DA axons and AMPA receptors on ChIs that promote short-latency action potentials. By contrast, DA release driven by optogenetic activation of intralaminar thalamostriatal inputs involves additional activation of NMDA receptors on ChIs and action potential generation over longer timescales. Therefore, cortical and thalamic glutamate inputs can modulate DA transmission by regulating ChIs as gatekeepers, through ionotropic glutamate receptors. The different use of AMPA and NMDA receptors by cortical versus thalamic inputs might lead to distinct input integration strategies by ChIs and distinct modulation of the function of DA and striatum.

Neuronal Mechanisms Underlying the Laryngeal Adductor Reflex

Electromyographic studies of the laryngeal adductor reflex, glottal closure occurring in response to laryngeal stimulation, have demonstrated an early ipsilateral response (R1) and a late bilateral response (R2). To better define the physiologic properties of these responses, we recorded responses from expiratory laryngeal motoneurons (ELMs) in rats during stimulation of the superior laryngeal nerve (SLN). Single unit extracellular recordings were obtained from 5 ELMs, identified by their antidromic responses to recurrent laryngeal nerve stimulation and postinspiratory firing pattern, in 4 Sprague-Dawley rats. Unilateral stimulation of the SLN (at 20 Hz) stopped both phrenic nerve inspiratory activity and ELM postinspiratory activity. However, the ELMs displayed robust tonic firing, consisting of non-respiratory burst activity and single action potentials. The single action potentials were identified as short-latency ones (5 to 10 ms) activated by ipsilateral SLN stimulation, with an occurrence rate of 90%, and long-latency ones (20 to 50 ms) activated by bilateral SLN stimulation, with occurrence rates of 47% on the ipsilateral side and 58% on the contralateral side. The R1 response appears to be the result of the short-latency action potentials, orthodromically activated by ipsilateral stimulation of the SLN. The R2 response is likely to be a result of the long-latency action potentials that can be recorded from ELMs on both sides.

Frequency-Dependent Recruitment of Fast Amino Acid and Slow Neuropeptide Neurotransmitter Release Controls Gonadotropin-Releasing Hormone Neuron Excitability

The anteroventral periventricular nucleus (AVPV) is thought to play a key role in regulating the excitability of gonadotropin-releasing hormone (GnRH) neurons that control fertility. Using an angled, parahorizontal brain slice preparation we have undertaken a series of electrophysiological experiments to examine how the AVPV controls GnRH neurons in adult male and female mice. More than half (59%) of GnRH neurons located in the rostral preoptic area were found to receive monosynaptic inputs from the AVPV in a sex-dependent manner. AVPV stimulation frequencies <1 Hz generated short-latency action potentials in GnRH neurons with GABA and glutamate mediating >90% of the evoked fast synaptic currents. The AVPV GABA input was dominant and found to excite or inhibit GnRH neurons in a cell-dependent manner. Increasing the AVPV stimulation frequency to 5-10 Hz resulted in the appearance of additional poststimulus inhibitory as well as delayed excitatory responses in GnRH neurons that were independent of ionotropic amino acid receptors. The inhibition observed immediately following the end of the stimulation period was mediated partly by GABA(B) receptors, while the delayed activation was mediated by the neuropeptide kisspeptin. The latter response was essentially absent in Gpr54 knock-out mice and abolished by a Gpr54 antagonist. Together, these studies show that AVPV neurons provide direct amino acid and neuropeptidergic inputs to GnRH neurons. Low-frequency activation generates predominant GABA/glutamate release with higher frequency activation recruiting release of kisspeptin. This frequency-dependent release of amino acid and neuropeptide neurotransmitters greatly expands the range of AVPV control of GnRH neuron excitability.

A low-cost multielectrode system for data acquisition enabling real-time closed-loop processing with rapid recovery from stimulation artifacts

Commercially available data acquisition systems for multielectrode recording from freely moving animals are expensive, often rely on proprietary software, and do not provide detailed, modifiable circuit schematics. When used in conjunction with electrical stimulation, they are prone to prolonged, saturating stimulation artifacts that prevent the recording of short-latency evoked responses. Yet electrical stimulation is integral to many experimental designs, and critical for emerging brain-computer interfacing and neuroprosthetic applications. To address these issues, we developed an easy-to-use, modifiable, and inexpensive system for multielectrode neural recording and stimulation. Setup costs are less than US$10,000 for 64 channels, an order of magnitude lower than comparable commercial systems. Unlike commercial equipment, the system recovers rapidly from stimulation and allows short-latency action potentials (<1 ms post-stimulus) to be detected, facilitating closed-loop applications and exposing neural activity that would otherwise remain hidden. To illustrate this capability, evoked activity from microstimulation of the rodent hippocampus is presented. System noise levels are similar to existing platforms, and extracellular action potentials and local field potentials can be recorded simultaneously. The system is modular, in banks of 16 channels, and flexible in usage: while primarily designed for in vivo use, it can be combined with commercial preamplifiers to record from in vitro multielectrode arrays. The system's open-source control software, NeuroRighter, is implemented in C#, with an easy-to-use graphical interface. As C# functions in a managed code environment, which may impact performance, analysis was conducted to ensure comparable speed to C++ for this application. Hardware schematics, layout files, and software are freely available. Since maintaining wired headstage connections with freely moving animals is difficult, we describe a new method of electrode-headstage coupling using neodymium magnets.

Motor Cortex Gates Vibrissal Responses in a Thalamocortical Projection Pathway

Higher-order thalamic nuclei receive input from both the cerebral cortex and prethalamic sensory pathways. However, at rest these nuclei appear silent due to inhibitory input from extrathalamic regions, and it has therefore remained unclear how sensory gating of these nuclei takes place. In the rodent, the ventral division of the zona incerta (ZIv) serves as a relay station within the paralemniscal thalamocortical projection pathway for whisker-driven motor activity. Most, perhaps all, ZIv neurons are GABAergic, and recent studies have shown that these cells participate in a feedforward inhibitory circuit that blocks sensory transmission in the thalamus. The present study provides evidence that the stimulation of the vibrissa motor cortex suppresses vibrissal responses in ZIv via an intra-incertal GABAergic circuit. These results provide support for the proposal that sensory transmission operates via a top-down disinhibitory mechanism that is contingent on motor activity.

Detection psychophysics of intracortical microstimulation in rat primary somatosensory cortex

A problem of purposeful intracortical microstimulation is the long duration of neuronal integration time and the associated complex temporal interactions of effects to individual pulses in trains. Here we investigated the effects of repetitive stimuli on perception. We trained head-restraint rats to indicate the detection of cortical microstimulation in infragranular layers of barrel cortex. Three stimulus parameters: stimulus intensity, number of pulses and frequency were varied, and psychometric detection curves were assessed using the method of constant stimuli. The average psychophysical threshold of single pulses was 2.0 nC--a measure very close to what has been found earlier for the evocation of short-latency action potentials in neurons near the stimulation electrode. Detection of single-pulse stimulation always saturated at probabilities of about 0.8. In contrast, repetitive stimuli gave rise to lower thresholds (by a factor of two at 15 pulses, 320 Hz), and to saturation at probabilities close to 1. Interestingly, a large fraction of these perceptual benefits was observed already with double pulses. Moreover, the perceptual efficacy of individual pulses was higher using double pulses compared with longer sequences, i.e. double pulses were detected better than expected from the assumption of independence of single-pulse effects, while trains of 15 pulses fell well short of this expectation. The present results thus point to double-pulse stimulation as an optimal choice when trading economic stimulation against optimizing of the percept.

Voltage-gated and background K + channel subunits expressed by the bushy cells of the rat cochlear nucleus

Bushy cells of the ventral cochlear nucleus produce a single, short latency action potential at the beginning of long depolarisations. In the present work an immunochemical survey was performed to detect the presence of K + channel subunits which may contribute to the specific membrane properties of the bushy cells. The immunocytochemical experiments conducted on enzymatically isolated bushy cells indicated positive immunolabelling for several subunits known to be responsible for the genesis of rapidly inactivating K + currents. Bushy cells showed strong expression of Kv3.4, 4.2 and 4.3 subunits, with the lack of Kv1.4 specific immunoreaction. The Kv3.4-specific immunoreaction had a specific, patchy appearance. Bushy cells also expressed various members of the Kv1 subunit family, most notably Kv1.1, 1.2, 1.3 and 1.6. Weak positivity could be observed for Kv3.2 subunits. The positive immunolabelling for Kv3.4, Kv4.2 and Kv4.3 was confirmed in free-floating tissue slices. Voltage-clamp experiments performed on positively identified bushy cells in brain slices corroborated the presence and activity of Kv3.4 and Kv4.2/4.3 containing K + channels. Bushy cell showed strong immunopositivity for TASK-1 channels too. The results presented in this work indicate that bushy cells possess several types of voltage-gated K + channel subunits whose activity may contribute to the membrane properties and firing characteristics of these neurones.

Subthreshold oscillations generated by TTX-sensitive sodium currents in dorsal cochlear nucleus pyramidal cells.

During intracellular recordings in rodent brainstem slice preparations, dorsal cochlear nucleus (DCN) pyramidal cells (PCs) exhibit characteristic discharge patterns to depolarizing current injection that depend on the membrane potential from which the responses are evoked. When depolarized from hyperpolarized potentials, PCs can respond with a short-latency action potential followed by a long silent interval (pauser) or a train of action potentials with a long latency (buildup). During the silent intervals in a pauser or a buildup response, the membrane potential slowly depolarizes towards spike threshold, often exhibiting distinct voltage oscillations of 1-2 mV before the first spike. The subthreshold voltage oscillations were investigated using whole cell recordings from DCN PCs in rat pup (P10-14) brainstem slices. The oscillations were unaffected by excitatory and inhibitory neurotransmitter antagonists, and were not temporally locked to the onset of the depolarization. The oscillations typically became larger as spike threshold was approached, and had a characteristic frequency between 40 and 100 Hz. In the presence of tetrodotoxin (TTX, 500 nM), the oscillations were significantly suppressed, and could not be evoked at any voltage below or above spike threshold. The oscillations were not blocked by phenytoin or Cd2+, but they were affected by prior activity in the neuron for approximately 1 s. We conclude that voltage-gated Na+ channels are required to generate membrane oscillations during the buildup phase. We suggest that the subthreshold oscillations play a role in controlling spike timing in PCs when the membrane potential slowly approaches, or hovers near, spike threshold.

Brainstem stimulation during sleep evokes abnormal rhythmic activity in thalamic neurons in feline penicillin epilepsy

Some periods in the sleep-waking cycle are more seizure prone than others. In absence epilepsy, transition periods between nonrapid-eye-movement (nonREM) sleep and waking or REM sleep can be more seizure prone that stable states. One feature of transition periods that is hypothesized to promote seizure activity is the presence of coincident activity in ascending brainstem reticular formation (RF) arousal systems with synchronized thalamo-cortical activity. To evaluate this hypothesis we examined the state-dependent effects of low intensity RF stimulation on thalamic single unit activity in control conditions and following systemic penicillin-G administration to adult cats. In control conditions, RF stimulation during waking and REM sleep typically evoked a short-latency action potential in thalamic neurons. The same stimulation during nonREM sleep commonly evoked a high frequency burst of action potentials followed by a period of suppressed discharge. In 16 26 neurons, a second rebound burst of action potentials followed the period of discharge suppression. The average interval between the initial and rebound bursts was 75.1 ± 6.0 ms, which was similar to the interburst interval recorded in these same cells during spontaneous EEG spindles. Following administration of penicillin-G, RF stimulation during nonREM sleep evoked high frequency burst firing, followed by 1–2 rebound bursts in 21 22 thalamic neurons. The average evoked interburst interval was 152.5 ± 7.3 ms, a value comparable to the interburst interval displayed by these same cells during spontaneous spike-wave seizure activity (157.8 ± 8.7 ms). RF-evoked rhythmic discharges were dependent upon the presence of thalamocortical synchronization, as responses evoked during waking and REM sleep in penicillin treated cats were similar to those observed in control conditions.

Membrane properties and discharge characteristics of guinea pig dorsal cochlear nucleus neurons studied in vitro

Intracellular recordings were made from neurons of the guinea pig dorsal cochlear nucleus in an in vitro brain slice preparation. The membrane properties of the cells were studied, and the membrane potentials were manipulated by current injection to determine how intrinsic conductances might alter the cell discharge patterns. Eleven cells were marked with Lucifer yellow. Ten of these cells were identified as the large pyramidal cells of layer 2 of this nucleus, and 1 cell was identified as a "vertical" cell in layer 3. Two kinds of action potentials were observed: simple spikes and complex spikes. This report discusses only cells with simple spikes. Simple spiking cells (60/72 recorded cells; all stained cells were simple spiking cells) discharged in a regular fashion with depolarization, and had linear frequency-current relationships up to 2 nA with a mean slope of 116 Hz/nA. The discharge rate was approximately constant throughout the current pulse. Responses of simple spiking cells to depolarizing current steps superimposed on a steady-state membrane hyperpolarization were studied. When the membrane has been held hyperpolarized, small current pulses produce a long-latency regular train of action potentials. Larger current pulses superimposed on membrane hyperpolarization can produce a short-latency action potential followed by a long silent interval (i.e., a long first interspike interval), and finally a regular train of spikes. It is concluded that the membrane conductances of DCN pyramidal cells are capable of generating at least 3 discharge patterns (regular firing, long first spike latency, and long first interspike interval) depending on the state of the membrane potential prior to a depolarizing current step. These responses are similar to the "chopper," "buildup," and "pauser" discharge patterns reported for these cells in vivo in response to tone bursts. The modulation of the intrinsic membrane conductances by membrane polarization and the possible contribution of these conductances to the generation of DCN discharge patterns provide new insights into the mechanisms underlying the responses of DCN cells to acoustic stimuli.

Electrotonic coupling between cercal afferents and giant interneurons in the American cockroach

Stimulation of the cercal nerve of the female American cockroach evokes a short-latency action potential in one giant axon in the ipsilateral connective of the ventral nerve cord. Neither procion yellow nor cobalt passes from the nerve cord into the cercal nerve, and the short-latency response disappears several weeks after removal of the cercus. Therefore, the short-latency spike is not due to a branch of the giant interneuron extending into the cercal nerve, but is presumably due to electrotonic coupling of cercal afferents to the giant. Responses of the presumed electrotonic junction to drugs, varied ionic concentrations and tonicity, and to cold are described. These responses and the impermeability of the junction to procion yellow suggest that the coupling is not by means of a gap junction. There is evidence for electrotonic coupling to another giant axon in the female, but this junction does not ordinarily transmit a spike. Electrotonic coupling is rare in males. In some females action potentials in giant interneurons excite cercal afferents electrically, and the afferents then re-excite the giants chemically. Electrotonic coupling may reduce fatigue and habituation of chemical synapses by depolarizing presynaptic terminals whenever the giants are active.

Effects of acetylcholine and atropine upon reticular excitation of cortical neurons : R. Spehlmann (Chicago, Ill., U.S.A.)

Some periods in the sleep-waking cycle are more seizure prone than others. In absence epilepsy, transition periods between nonrapid-eye-movement (nonREM) sleep and waking or REM sleep can be more seizure prone that stable states. One feature of transition periods that is hypothesized to promote seizure activity is the presence of coincident activity in ascending brainstem reticular formation (RF) arousal systems with synchronized thalamo-cortical activity. To evaluate this hypothesis we examined the state-dependent effects of low intensity RF stimulation on thalamic single unit activity in control conditions and following systemic penicillin-G administration to adult cats. In control conditions, RF stimulation during waking and REM sleep typically evoked a short-latency action potential in thalamic neurons. The same stimulation during nonREM sleep commonly evoked a high frequency burst of action potentials followed by a period of suppressed discharge. In 1626 neurons, a second rebound burst of action potentials followed the period of discharge suppression. The average interval between the initial and rebound bursts was 75.1 ± 6.0 ms, which was similar to the interburst interval recorded in these same cells during spontaneous EEG spindles. Following administration of penicillin-G, RF stimulation during nonREM sleep evoked high frequency burst firing, followed by 1–2 rebound bursts in 2122 thalamic neurons. The average evoked interburst interval was 152.5 ± 7.3 ms, a value comparable to the interburst interval displayed by these same cells during spontaneous spike-wave seizure activity (157.8 ± 8.7 ms). RF-evoked rhythmic discharges were dependent upon the presence of thalamocortical synchronization, as responses evoked during waking and REM sleep in penicillin treated cats were similar to those observed in control conditions.