Frequency-domain order parameters for the burst and spike synchronization transitions of bursting neurons

We are interested in characterization of synchronization transitions of bursting neurons in the frequency domain. Instantaneous population firing rate (IPFR) R(t), which is directly obtained from the raster plot of neural spikes, is often used as a realistic collective quantity describing population activities in both the computational and the experimental neuroscience. For the case of spiking neurons, a realistic time-domain order parameter, based on R(t), was introduced in our recent work to characterize the spike synchronization transition. Unlike the case of spiking neurons, the IPFR R(t) of bursting neurons exhibits population behaviors with both the slow bursting and the fast spiking timescales. For our aim, we decompose the IPFR R(t) into the instantaneous population bursting rate R_b(t) (describing the bursting behavior) and the instantaneous population spike rate R_s(t) (describing the spiking behavior) via frequency filtering, and extend the realistic order parameter to the case of bursting neurons. Thus, we develop the frequency-domain bursting and spiking order parameters which are just the bursting and spiking “coherence factors” β_b and β_s of the bursting and spiking peaks in the power spectral densities of R_b and R_s (i.e., “signal to noise” ratio of the spectral peak height and its relative width). Through calculation of β_b and β_s, we obtain the bursting and spiking thresholds beyond which the burst and spike synchronizations break up, respectively. Consequently, it is shown in explicit examples that the frequency-domain bursting and spiking order parameters may be usefully used for characterization of the bursting and the spiking transitions, respectively.     

大鼠急性分离下丘脑神经元的自发性放电特性

目的和方法：采用电流钳技术,观察SD大鼠急性分离下丘脑神经元的自发性放电。结果：放电形式包括不放电、连续的单个放电和簇状放电等3种,但放电过程中出现一些阈下电位,这些闯下电位会明显影响神经元的放电过程,使放电表现为规则或不规则,规则放电通常由缓慢的去极化电位触发,而不规则放电常出现较多的阈下电位。结论：急性分离神经元具有与脑片和培养神经元不完全相同的放电特性,对此展开研究,有利于揭示下丘脑参与机体稳态的调控机制。     

Endogenous nature of spontaneous bursting in hippocampal pyramidal neurons

The normal spontaneous bursting behavior of hippocampal pyramidal neurons was investigated. Bursting frequency was found to be membrane potential dependent, the frequency increasing with maintained depolarization and decreasing upon hyperpolarization. Short depolarizing-current pulses would trigger bursts which outlasted the stimulus, and bursting continued when synaptic transmission had been blocked. The spontaneous bursts of these neurons, in contrast to bursts induced by convulsive agents, appear to exhibit the classical behavior of endogenous bursts as observed in invertebrate neurons. The endogenous bursts in hippocampal neurons may result, also, from an interplay of intrinsic membrane currents.     

Noise-induced burst and spike synchronizations in an inhibitory small-world network of subthreshold bursting neurons

We are interested in noise-induced firings of subthreshold neurons which may be used for encoding environmental stimuli. Noise-induced population synchronization was previously studied only for the case of global coupling, unlike the case of subthreshold spiking neurons. Hence, we investigate the effect of complex network architecture on noise-induced synchronization in an inhibitory population of subthreshold bursting Hindmarsh–Rose neurons. For modeling complex synaptic connectivity, we consider the Watts–Strogatz small-world network which interpolates between regular lattice and random network via rewiring, and investigate the effect of small-world connectivity on emergence of noise-induced population synchronization. Thus, noise-induced burst synchronization (synchrony on the slow bursting time scale) and spike synchronization (synchrony on the fast spike time scale) are found to appear in a synchronized region of the J–D plane (J: synaptic inhibition strength and D: noise intensity). As the rewiring probability p is decreased from 1 (random network) to 0 (regular lattice), the region of spike synchronization shrinks rapidly in the J–D plane, while the region of the burst synchronization decreases slowly. We separate the slow bursting and the fast spiking time scales via frequency filtering, and characterize the noise-induced burst and spike synchronizations by employing realistic order parameters and statistical-mechanical measures introduced in our recent work. Thus, the bursting and spiking thresholds for the burst and spike synchronization transitions are determined in terms of the bursting and spiking order parameters, respectively. Furthermore, we also measure the degrees of burst and spike synchronizations in terms of the statistical-mechanical bursting and spiking measures, respectively.     

Electrophysiological properties and modeling of murine vomeronasal sensory neurons in acute slice preparations

The vomeronasal system is involved in the detection of pheromones in many mammals. Vomeronasal sensory neurons encode the behaviorally relevant information into action potentials that are directly transmitted to the accessory olfactory bulb. We developed a model of the electrical activity of mouse basal vomeronasal sensory neurons, which mimics both the voltage-gated current properties and the firing behavior of these neurons in their near-native state, using a minimal number of parameters. Data were obtained by recordings with the whole-cell voltage-clamp or current-clamp techniques from mouse basal vomeronasal sensory neurons in acute slice preparations. The resting potential ranged from -50 to -70 mV, and current injections of less than 2-10 pA induced tonic firing in most neurons. The experimentally determined firing frequency as a function of injected current was well described by a Michaelis-Menten equation and was exactly reproduced by the model, which could be used in combination with future models that will include details of the mouse vomeronasal transduction cascade.     

Projection pattern of sensory neurons in the central nervous system of a homeotic mutation of the moth Manduca sexta

Octopod (Octo) is a mutation of the moth Manduca sexta, which transforms the first abdominal segment (A1) in the anterior direction. Mutant animals are characterized by the appearance of homeotic thoracic-like legs on A1. We exploited this mutation to determine what rules might be used in specifying the fates of sensory neurons located on the body surface of larval Manduca. Mechanical stimulation of homeotic leg sensilla did not cause reflexive movements of the homeotic legs, but elicited responses similar to those observed following stimulation of ventral A1 body wall hairs. Intracellular recordings demonstrated that several of the motoneurons in the A1 ganglion received inputs from the homeotic sensory hairs. The responses of these motoneurons to stimulation of homeotic sensilla resembled their responses to stimulation of ventral body wall sensilla. Cobalt fills revealed that the mutation transformed the segmental projection pattern of only the sensory neurons located on the ventral surface of A1, resulting in a greater number with intersegmental projection patterns typical of sensory neurons found on the thoracic body wall. Many of the sensory neurons on the homeotic legs had intersegmental projection patterns typical of abdominal sensory neurons: an anteriorly directed projection terminating in the third thoracic ganglion (T3). Once this projection reached T3, however, it mimicked the projections of the thoracic leg sensory neurons. These results demonstrate that the same rules are not used in the establishment of the intersegmental and leg-specific projection patterns. Segmental identity influences the intersegmental projection pattern of the sensory neurons of Manduca, whereas the leg-specific projections are consistent with a role for positional information in determining their pattern. © 1995 John Wiley & Sons, Inc.     

Differentiated pattern of sodium channel expression in dissociated Purkinje neurons maintained in long-term culture

Cerebellar Purkinje neurons in vivo exhibit high frequency and multi-spike action potentials with transient (INaT), resurgent (INaR) and persistent (INaP) Na+ currents arising from voltage-gated Na+ channels, which play important roles in shaping the action potentials and electrical activity of these cells. However, little is known about Na+ channel expression in cultured Purkinje neurons despite the use of in vitro approaches to study these cells. Therefore, GFP-expressing Purkinje neurons isolated from transgenic mice were analysed after four weeks in culture, when, coincident with distinct axonal and dendritic morphologies, cultured Purkinje neurons exhibited dendrite-specific MAP2 expression characteristic of polarized neurons. In cell-attached patch clamp recordings, Na+ currents occurred at significantly higher frequencies and amplitudes in patches from the soma and axon than from dendrites, similar to the polarized distribution observed in vivo. INaT, INaR and INaP Na+ currents with properties similar to those observed in acutely isolated Purkinje neurons were detected in nucleated outside-out patches from cultured Purkinje cells. RT-PCR analysis detected Nav1.1, Nav1.2 and Nav1.6, but not Nav1.3, Nav1.4, Nav 1.5 or Nav1.8 Na+ channel alpha subunit gene expression in cultured Purkinje neurons, as observed in vivo. Together, the results indicate that key aspects of Na+ channel expression in mature Purkinje neurons in vivo occur in vitro.     

Common general morphological pattern of peptidergic neurons in the arachnid brain: crustacean cardioactive peptide-immunoreactive neurons in the protocerebrum of seven arachnid species

A polyclonal antiserum raised against crustacean cardioactive peptide labels 14 clusters of immunoreactive neurons in the protocerebrum of the spiders Tegenaria atrica and Nephila clavipes, and the harvestman (opilionid) Rilaena triangularis. In all species, these clusters possess the same number of neurons, and share similar structural and topological characteristics. Two sets of bilateral symmetrical neurons associated with the optic lobes and the arachnid central body were analysed in detail, comparing the harvestman R. triangularis and the spiders Brachypelma albopilosa (Theraphosidae), Cupiennius salei (Lycosidae), Tegenaria atrica (Agelenidae), Meta segmentata (Metidae) and Nephila clavipes (Araneidae). Sixteen neurons have been identified that display markedly similar axonal pathways and arborization patterns in all species. These neurons are considered homologues in the opilionid and the araneid brains. We presume that these putative phylogenetically persisting neurons represent part of the general morphological pattern of the arachmid brain.     

Homeostatic regulation mechanism of spontaneous firing determines glutamate responsiveness in the midbrain dopamine neurons

Autonomous tonic firing of the midbrain dopamine neuron is essential for maintenance of ambient dopamine level in the brain, in which intracellular Ca²⁺ concentration ([Ca²⁺]c) plays a complex but pivotal role. However, little is known about Ca²⁺ signals by which dopamine neurons maintain an optimum spontaneous firing rate. In the midbrain dopamine neurons, we here show that spontaneous firing evoked [Ca²⁺]c changes in a phasic manner in the dendritic region but a tonic manner in the soma. Tonic levels of somatic [Ca²⁺]c strictly tallied with spontaneous firing rates. However, manipulatory raising or lowering of [Ca²⁺]c with caged compounds from the resting firing state proportionally suppressed or raised spontaneous firing rate, respectively, suggesting presence of the homeostatic regulation mechanism for spontaneous firing rate via tonic [Ca²⁺]c changes of the soma. More importantly, abolition of this homeostatic regulation mechanism significantly exaggerated the responses of tonic firings and high-frequency phasic discharges to glutamate. Therefore, we conclude that this Ca²⁺-dependent homeostatic regulation mechanism is responsible for not only maintaining optimum rate of spontaneous firing, but also proper responses to glutamate. Perturbation of this mechanism could cause dopamine neurons to be more vulnerable to glutamate and Ca²⁺ toxicities.     

Time-related changes in the labeling pattern of motor and sensory neurons innervating the gastrocnemius muscle,as revealed by the retrograde transport of the cholera toxin B subunit

Summary Morphological changes in the motor and sensory neurons in the lumbar spinal cord and the dorsal root ganglia were investigated at different survival times following the injection of the B subunit of cholera toxin (CTB) into the medial gastrocnemius muscle. Unconjugated CTB, visualized immunohistochemically, was found to be retrogradely transported through ventral and dorsal roots to motor neurons in the anterior horn, each lamina in the posterior horn, and ganglion cells in the dorsal root ganglia at L₃–L₆. The largest numbers of labeled motor neurons and ganglion cells were observed 72 h after the injection of CTB. Thereafter, labeled ganglion cells were significantly decreased in number, whereas the amount of labeled motor neurons showed a slight reduction. Motor neurons had extensive dendritic trees filled with CTB, reaching lamina VII and even the pia mater of the lateral funiculus. Labeling was also seen in the posterior horn, but the central and medial parts of laminae II and III had the most extensively labeled varicose fibers, the origin of which was the dorsal root ganglion cells. The results indicate that CTB is taken up by nerve terminals and can serve as a sensitive retrogradely transported marker for identifying neurons that innervate a specific muscle.     

Peptidergic neurons of the crab,Cardisoma carnifex,in defined culture maintain characteristic morphologies under a variety of conditions

Summary Peptidergic neurons dissociated from the neurosecretory cell group, the X-organ, of adult crabs (Cardisoma carnifex) show immediate outgrowth on unconditioned plastic dishes in defined medium. Most of the neurons can be categorized as small cells, branchers or veilers. A fourth type, superlarge, found occasionally, has a soma diameter greater than 40 m and multipolar outgrowth. We report here the effects on morphology that follow alterations of the standard defined culturing conditions. The three common types of neurons are present when cells are grown in crab saline or saline with l-glutamine and glucose (saline medium). Changes of pH between 7.0 to 7.9 have no effect. Osmolarity changes cause transient varicosities in small cells. In some veilers, pits rapidly appear in the veil and then disappear within 35 min. In cultures at 26° C instead of 22° C, veilers extend processes from the initial veil in a pattern similar to branchers, and the processes of adjacent veilers sometimes form appositions. Culturing in higher [K⁺]_o medium ([K⁺]_o=15–110 mM; standard=11 mM) has no long-term effect, but growth is arrested by [K⁺]_o greater than 30 mM. Cultures were also grown in media in which [Ca²⁺]_o ranged from 0.1 M to 26 mM (standard=13 mM). Outgrowth occured from all neuronal types in all [Ca²⁺]_o tested. Thus, the expression of different outgrowth morphologies occurs under a wide variety of culturing conditions.