Increase In Firing Frequency Research Articles

Long-term recovery from fire by a population of honey possums (Tarsipes rostratus) in the extreme south-west of Western Australia

The impact of two fires, six years apart, on the long-term recovery of a population of honey possums (Tarsipes rostratus) in the extreme south-west of Western Australia was documented over a 23-year period. Recovery was relatively rapid after the first fire, with catch rates reaching 78% of precatch levels within six years, but was much slower following the second fire in April 1999. Regression analysis estimates that full recovery to prefire catch rates and densities would take 25.6 years. The spread of Phytophthora cinnamomi (dieback) throughout the study area has severely impacted Banksia ilicifolia trees, which are the honey possums’ primary food source, and the impact has been greater in the burnt than unburnt areas. Analysis of catch-per-unit-effort and density of individual honey possums over the whole 29-year period of the study shows that numbers have not declined in the long-unburnt southern area of the study site, despite the spread of dieback and loss of banksia trees. The data are discussed in relation to the impact of fire on other vertebrate species that have specific habitat requirements. Given predictions of increasing fire frequencies due to climate change and an increased utilisation of prescribed burning to protect human life and property, it is imperative that management of areas harbouring honey possums be protected from too-frequent fire if this iconic species is to persist.

Effects of wind and tree density on forest fire patterns in a mixed-tree species forest

ABSTRACTIt is well known that global climate change causes an increase in forest fire frequency and severity. Thus, understanding fire dynamics is necessary to comprehend the mitigation of the negative effects of forest fires. Our objective was to inform how fire spreads in a simulated two-species forest with varying wind strengths. The forest in this study was comprised of two different tree species with varying probabilities of transferring fire that was randomly distributed in space at densities (Ctot) ranging from 0.0 (low) to 1.0 (high). We studied the distribution pattern of burnt trees by using local rules of the two-dimensional model. This model incorporated wind blowing from south to north with strength (Pw) ranging from 0.0 (low) to 1.0 (high). Simulation results showed that when Ctot > 0.45 the fire covered the entire forest, but when Ctot ≤ 0.45 the fire did not spread. The wind effect on the variation of the amount of the burnt tree was maximized at the critical density and dramatically decreased with increasing Ctot. Additionally, we found that the term of Ctot and Pw plays an important role in determining the distribution.

Determinants of patchiness of woody vegetation in an African savanna

AbstractQuestionsHow is woody vegetation patchiness affected by rainfall, fire and large herbivore biomass? Can we predict woody patchiness and cover over large‐scale environmental gradients?LocationHluhluwe‐iMfolozi Park, South Africa.MethodsWe quantified variation in local patchiness as the lacunarity of woody cover on satellite‐derived images. Using Random Forest regression we analysed how both average woody cover and its patchiness depend on annual rainfall, fire frequency and grazer and browser metabolic biomass densities.ResultsFire frequency and rainfall were the clearest predictors, whereas effects of large herbivores on woody vegetation were smaller and more complex. Under low rainfall conditions (500 mm·yr−1) trees had less total cover and were more regularly spaced across the landscape (lower patchiness). Woody cover and vegetation patchiness increased with rainfall whereas fire frequency decreased woody cover and further increased patchiness.ConclusionThese results suggest a switch from competition between neighbouring trees under low rainfall conditions towards benefits among neighbours with increasing fire frequencies. Whereas overall woody cover and its patchiness are two independent aspects of savanna woody vegetation patterns, both need to be investigated to obtain a good understanding of the functioning and diversity of savanna ecosystems.

Cumulative patterns of logging and fire (1940–2009): consequences on the structure of the eastern Canadian boreal forest

Although logging has affected circumboreal forest dynamics for nearly a century, very few studies have reconstructed its influence on landscape structure at the subcontinental scale. This study aims to document spatiotemporal patterns of logging and fire since the introduction of logging in the early twentieth-century, and to evaluate the effects of these disturbances on landscape structure. We used historical (1940–2009) logging and fire maps to document disturbance patterns across a 195,000-km2 boreal forest landscape of eastern Canada. We produced multitemporal (1970s–2010s) mosaics providing land cover status using Landsat imagery. Logging significantly increased the rate of disturbance (+74 %) in the study area. The area affected by logging increased linearly with time resulting in a significant rejuvenation of the landscape along the harvesting pattern (south–north progression). From 1940 to 2009, fire was the dominant disturbance and showed a more random spatial distribution than logging. The recent increase of fire influence and the expansion of the proportion of area classified as unproductive terrestrial land suggest that regeneration failures occurred. This study reveals how logging has modified the disturbances dynamics, following the progression of the logging frontier. Future management practices should aim for a dispersed spatial distribution of harvests to generate landscape structures that are closer to natural conditions, in line with ecosystem-based management. The challenges of defining sustainable practices will remain complex with the predicted increase in fire frequency, since this factor, in combination with logging, can alter both the structure and potentially the resilience of boreal forest.

Gondwanan conifer clones imperilled by bushfire.

Global increases in fire frequency driven by anthropogenic greenhouse emissions and land use change could threaten unique and ancient species by creeping into long-term fire refugia. The perhumid and mountainous western half of Tasmania is a globally important refugium for palaeo-endemic, fire intolerant lineages, especially conifers. Reproductive strategy will be crucial to the resilience of these organisms under warmer, dryer and more fire prone climates. This study analysed clonal versus sexual reproduction in old growth plots dominated by the palaeo-endemic conifer Athrotaxis cupressoides (Cupressaceae), a species that lacks any traits to tolerate frequent landscape fire. Across most of the seven plots the amount of sexually derived individuals was lower than clonally derived with, on average, 60% of all stems belonging to the same multi-locus lineage (MLL) (i.e. were clonal). Some MLLs were large spanning over 10 s of metres and consisted of up to 62 stems. The high mortality after fire and the rarity of sexual regeneration means that the range of this fire-intolerant species is likely to contract under enhanced fire regimes and has a limited capacity to disperse via seed to available fire refugia in the landscape.

Low-intensity repetitive magnetic stimulation lowers action potential threshold and increases spike firing in layer 5 pyramidal neurons in vitro

Repetitive transcranial magnetic stimulation (rTMS) has become a popular method of modulating neural plasticity in humans. Clinically, rTMS is delivered at high intensities to modulate neuronal excitability. While the high-intensity magnetic field can be targeted to stimulate specific cortical regions, areas adjacent to the targeted area receive stimulation at a lower intensity and may contribute to the overall plasticity induced by rTMS. We have previously shown that low-intensity rTMS induces molecular and structural plasticity in vivo, but the effects on membrane properties and neural excitability have not been investigated. Here we investigated the acute effect of low-intensity repetitive magnetic stimulation (LI-rMS) on neuronal excitability and potential changes on the passive and active electrophysiological properties of layer 5 pyramidal neurons in vitro. Whole-cell current clamp recordings were made at baseline prior to subthreshold LI-rMS (600 pulses of iTBS, n=9 cells from 7 animals) or sham (n=10 cells from 9 animals), immediately after stimulation, as well as 10 and 20min post-stimulation. Our results show that LI-rMS does not alter passive membrane properties (resting membrane potential and input resistance) but hyperpolarises action potential threshold and increases evoked spike-firing frequency. Increases in spike firing frequency were present throughout the 20min post-stimulation whereas action potential (AP) threshold hyperpolarization was present immediately after stimulation and at 20min post-stimulation. These results provide evidence that LI-rMS alters neuronal excitability of excitatory neurons. We suggest that regions outside the targeted region of high-intensity rTMS are susceptible to neuromodulation and may contribute to rTMS-induced plasticity.

Effects of aging and coronary artery disease on sympathetic neural recruitment strategies during end-inspiratory and end-expiratory apnea.

In response to acute physiological stress, the sympathetic nervous system modifies neural outflow through increased firing frequency of lower-threshold axons, recruitment of latent subpopulations of higher-threshold axons, and/or acute modifications of synaptic delays. Aging and coronary artery disease (CAD) often modify efferent muscle sympathetic nerve activity (MSNA). Therefore, we investigated whether CAD (n = 14; 61 ± 10 yr) and/or healthy aging without CAD (OH; n = 14; 59 ± 9 yr) modified these recruitment strategies that normally are observed in young healthy (YH; n = 14; 25 ± 3 yr) individuals. MSNA (microneurography) was measured at baseline and during maximal voluntary end-inspiratory (EI) and end-expiratory (EE) apneas. Action potential (AP) patterns were studied using a novel AP analysis technique. AP frequency increased in all groups during both EI- and EE-apnea (all P < 0.05). The mean AP content per integrated burst increased during EI- and EE-apnea in YH (EI: Δ6 ± 4 APs/burst; EE: Δ10 ± 6 APs/burst; both P < 0.01) and OH (EI: Δ3 ± 3 APs/burst; EE: Δ4 ± 5 APs/burst; both P < 0.01), but not in CAD (EI: Δ1 ± 3 APs/burst; EE: Δ2 ± 3 APs/burst; both P = NS). When APs were binned into "clusters" according to peak-to-peak amplitude, total clusters increased during EI- and EE-apnea in YH (EI: Δ5 ± 2; EE: Δ6 ± 4; both P < 0.01), during EI-apnea only in OH (EI: Δ1 ± 2; P < 0.01; EE: Δ1 ± 2; P = NS), and neither apnea in CAD (EI: Δ -2 ± 2; EE: Δ -1 ± 2; both P = NS). In all groups, the AP cluster size-latency profile was shifted downwards for every corresponding cluster during EI- and EE-apnea (all P < 0.01). As such, inherent dysregulation exists within the central features of apnea-related sympathetic outflow in aging and CAD.

13,000 years of fire history derived from soil charcoal in a British Columbia coastal temperate rain forest

AbstractLittle is known regarding the fire history of high‐latitude coastal temperate rain forests in the Pacific Northwest (PNW) of North America. While reconstructing historical fire regimes typically requires dendrochronological records from fire‐scarred trees or stratigraphically preserved lake sediment data, this type of information is virtually non‐existent in this region. To describe the long‐term fire history of a site on the central coast of British Columbia, Canada, we radiocarbon‐dated 52 pieces of charcoal. Charcoal ages ranged from 12,670 to 70 yr BP. Fires occurred regularly since 12,670 yr BP, with the exception of a distinct fire‐free period at 7500–5500 yr BP. Time since fire (TSF) estimates from soil charcoal and fire‐scarred trees ranged from 12,670 to 100 yr BP (median = 327 yr), and 70% of the sites examined had burned within the past 1000 yr. An increase in fire frequency in the late Holocene is consistent with the widely held hypothesis that anthropogenic fires were common across the PNW. We evaluate TSF distributions and discuss the difficulties in assigning actual fire dates from charcoal fragments with large inbuilt ages in a coastal temperate rain forest setting. We determine that a comprehensive approach using soil charcoal and fire scar analyses is necessary to reconstruct general trends in fire activity throughout the Holocene in this region.

Climate adaption and post‐fire restoration of a foundational perennial in cold desert: insights from intraspecific variation in response to weather

Summary The loss of foundational but fire‐intolerant perennials such as sagebrush due to increases in fire size and frequency in semi‐arid regions has motivated efforts to restore them, often with mixed or even no success. Seeds of sagebrush Artemisia tridentata and related species must be moved considerable distances from seed source to planting sites, but such transfers have not been guided by an understanding of local climate adaptation. Initial seedling establishment and its response to weather are a key demographic bottleneck that likely varies among subspecies and populations of sagebrush. We assessed differences in survival, growth and physiological responses of sagebrush seedlings to weather among eleven seed sources that varied in subspecies, cytotype and climates‐of‐origin over 18 months following outplanting. Diploid or polyploid populations of mountain, Wyoming and basin big sagebrush (A. tridentata ssp. vaseyana, A. tridentata ssp. wyomingensis and A. tridentata ssp. tridentata, respectively) were planted onto five burned sites that normally support A.t. wyomingensis with some A.t. tridentata. A.t. wyomingensis had the most growth and survival, and tetraploid populations had greater survival and height than diploids. Seasonal timing of mortality varied among the subspecies/cytotypes and was more closely related to minimum temperatures than water deficit. Temperatures required to induce ice formation were up to 6 °C more negative in 4n‐A.t. tridentata and A.t. wyomingensis than in other subspecies/cytotypes, indicating greater freezing avoidance. In contrast, freezing resistance of photosynthesis varied only 1 °C among subspecies/cytotypes, being greatest in A.t. wyomingensis and least in the subspecies normally considered most cold‐adapted, A.t. vaseyana. A large spectrum of reliance on freezing avoidance vs. freezing tolerance was observed and corresponded to differences in post‐fire survivorship among subspecies/cytotypes. Differences in water deficit responses among subspecies/cytotypes were not as strong and did not relate to survival patterns. Synthesis and applications. Low‐temperature responses are a key axis defining climate adaptation in young sagebrush seedlings and vary more with cytotype than with subspecies, which contrasts with the traditional emphases on (i) water limitations to explain establishment in these deserts, and (ii) subspecies in selecting restoration seedings. These important and novel insights on climate adaptation are critical for seed selection and parameterizing seed transfer zones, and were made possible by incorporating weather data with survival statistics. The survival/weather statistics used here could be applied to any restoration planting or seeding to help elucidate factors contributing to success and enable adaptive management.

Excitability and Burst Generation of AVPV Kisspeptin Neurons Are Regulated by the Estrous Cycle Via Multiple Conductances Modulated by Estradiol Action.

The preovulatory secretory surge of gonadotropin-releasing hormone (GnRH) is crucial for fertility and is regulated by a switch of estradiol feedback action from negative to positive. GnRH neurons likely receive estradiol feedback signals via ERα-expressing afferents. Kisspeptin neurons in anteroventral periventricular nucleus (AVPV) are thought to be critical for estradiol-positive feedback induction of the GnRH surge. We examined the electrophysiological properties of GFP-identified AVPV kisspeptin neurons in brain slices from mice on the afternoon of diestrus (negative feedback) and proestrus (positive feedback, time of surge). Extracellular recordings revealed increased firing frequency and action potential bursts on proestrus versus diestrus. Whole-cell recordings were used to study the intrinsic mechanisms of bursting. Upon depolarization, AVPV kisspeptin neurons exhibited tonic firing or depolarization-induced bursts (DIB). Both tonic and DIB cells exhibited bursts induced by rebound from hyperpolarization. DIB occurred similarly on both cycle stages, but rebound bursts were observed more often on proestrus. DIB and rebound bursts were both sensitive to Ni2+, suggesting that T-type Ca2+ currents (ITs) are involved. IT current density was greater on proestrus versus diestrus. In addition to IT, persistent sodium current (INaP) facilitated rebound bursting. On diestrus, 4-aminopyridine-sensitive potassium currents contributed to reduced rebound bursts in both tonic and DIB cells. Manipulation of specific sex steroids suggests that estradiol induces the changes that enhance AVPV kisspeptin neuron excitability on proestrus. These observations indicate cycle-driven changes in circulating estradiol increased overall action potential generation and burst firing in AVPV kisspeptin neurons on proestrus versus diestrus by regulating multiple intrinsic currents.

Floristic implications of two contemporaneous inland upper Neogene sites in the eastern US: Pipe Creek Sinkhole, Indiana, and the Gray Fossil Site, Tennessee (USA)

Late Neogene floras of North America are mainly represented by sites located along the east coast Piedmont and the Great Plains. To date, there are only two upper Neogene inland localities in the eastern half of North America, the Pipe Creek Sinkhole (Indiana) and the Gray Fossil Site (Tennessee). At both sites, a lacustrine environment was formed from sinkholes that preserve fossil assemblages including invertebrates, vertebrates, and plant remains. We reviewed the floristic record (micro and macrofossils) of each site to determine the late Neogene composition of the flora, its vertical stratification, and to provide insight into the changes associated with warmer and drier conditions in the eastern deciduous forest. The Pipe Creek Sinkhole flora when compared to extant pollen floras of the eastern US is nested within the Beach-Maple-Basswood forest type of Dyer; however, the Miocene forest is dominated by a pine-hickory or pine-hickory-cottonwood association. The Gray Fossil Site flora when compared to extant pollen floras of the eastern US is nested within the Mesophytic Forest and is dominated by an oak-hickory-pine assemblage. The Pipe Creek Flora and the Gray Fossil Site Flora lack the common sub story and understory taxa and are dominated by specific woody taxa and an array of herbaceous taxa that have high light requirements and indicate some disturbance. The lack of vertical forest structure indicates that at both sites, woodland to woodland savanna to prairie-like habitats may have prevailed. The common occurrence of charcoals in the lacustrine sediments indicates that fire was a frequent disturbance factor, which may have suppressed the development of a structured forest with a closed canopy at both localities. This was further exacerbated by the impact of large herbivores. Both fossil floras, despite changes in the vegetation composition and vertical stratification when compared to the extant indigenous deciduous forest, include the major elements from their respective extant mesophytic C3 floristic associations that currently exist at these locations, i.e. the Beech-Maple-Basswood (Pipe Creek Sinkhole) and the Hickory-Oak-Pine Mesophytic Forest (Gray Fossil Site). The Miocene-Pliocene climate, in comparison to the extant climate, affected the vegetation in eastern North America by the selective elimination of those taxa that could not tolerate the warmer and drier conditions; the concomitant increase in fire frequency and the impact of large herbivores further contributed to maintaining woodland/savanna communities at both localities.

Effects of Morphology Constraint on Electrophysiological Properties of Cortical Neurons.

There is growing interest in engineering nerve cells in vitro to control architecture and connectivity of cultured neuronal networks or to build neuronal networks with predictable computational function. Pattern technologies, such as micro-contact printing, have been developed to design ordered neuronal networks. However, electrophysiological characteristics of the single patterned neuron haven’t been reported. Here, micro-contact printing, using polyolefine polymer (POP) stamps with high resolution, was employed to grow cortical neurons in a designed structure. The results demonstrated that the morphology of patterned neurons was well constrained, and the number of dendrites was decreased to be about 2. Our electrophysiological results showed that alterations of dendritic morphology affected firing patterns of neurons and neural excitability. When stimulated by current, though both patterned and un-patterned neurons presented regular spiking, the dynamics and strength of the response were different. The un-patterned neurons exhibited a monotonically increasing firing frequency in response to injected current, while the patterned neurons first exhibited frequency increase and then a slow decrease. Our findings indicate that the decrease in dendritic complexity of cortical neurons will influence their electrophysiological characteristics and alter their information processing activity, which could be considered when designing neuronal circuitries.

Post-fire soil functionality and microbial community structure in a Mediterranean shrubland subjected to experimental drought

Fire may cause significant alterations in soil properties. Post-fire soil dynamics can vary depending, among other factors, on rainfall patterns. However, little is known regarding variations in response to post-fire drought. This is relevant in arid and semiarid areas with poor soils, like much of the western Mediterranean. Furthermore, climate change projections in such areas anticipate reduced precipitation and longer annual drought periods, together with an increase in fire severity and frequency. This research evaluates the effects of experimental drought after fire on soil dynamics of a Cistus-Erica shrubland (Central Spain). A replicated (n=4) field experiment was conducted in which the total rainfall and its patterns were manipulated by means of a rain-out shelters and irrigation system. The treatments were: environmental control (natural rainfall), historical control (average rainfall, 2months drought), moderate drought (25% reduction of historical control, 5months drought) and severe drought (45% reduction, 7months drought). After one growing season under these rainfall treatments, the plots were burned. One set of unburned plots under natural rainfall served as an additional control. Soils were collected seasonally. Fire increased soil P and N availability. Post-fire drought treatments reduced available soil P but increased N concentration (mainly nitrate). Fire reduced available K irrespective of drought treatments. Fire reduced enzyme activities and carbon mineralization rate, a reduction that was higher in post-fire drought-treated soils. Fire decreased soil microbial biomass and the proportion of fungi, while that of actinomycetes increased. Post-fire drought decreased soil total microbial biomass and fungi, with bacteria becoming more abundant. Our results support that increasing drought after fire could compromise the resilience of Mediterranean ecosystems to fire.

Transient potassium channels augment degeneracy in hippocampal active dendritic spectral tuning.

Hippocampal pyramidal neurons express an intraneuronal map of spectral tuning mediated by hyperpolarization-activated cyclic-nucleotide-gated nonspecific-cation channels. Modeling studies have predicted a critical regulatory role for A-type potassium (KA) channels towards augmenting functional robustness of this map. To test this, we performed patch-clamp recordings from soma and dendrites of rat hippocampal pyramidal neurons, and measured spectral tuning before and after blocking KA channels using two structurally distinct pharmacological agents. Consistent with computational predictions, we found that blocking KA channels resulted in a significant reduction in resonance frequency and significant increases in input resistance, impedance amplitude and action-potential firing frequency across the somato-apical trunk. Furthermore, across all measured locations, blocking KA channels enhanced temporal summation of postsynaptic potentials and critically altered the impedance phase profile, resulting in a significant reduction in total inductive phase. Finally, pair-wise correlations between intraneuronal percentage changes (after blocking KA channels) in different measurements were mostly weak, suggesting differential regulation of different physiological properties by KA channels. Our results unveil a pivotal role for fast transient channels in regulating theta-frequency spectral tuning and intrinsic phase response, and suggest that degeneracy with reference to several coexisting functional maps is mediated by cross-channel interactions across the active dendritic arbor.

KCNQ Potassium Channels Modulate Sensitivity of Skin Down-hair (D-hair) Mechanoreceptors

M-current-mediating KCNQ (Kv7) channels play an important role in regulating the excitability of neuronal cells, as highlighted by mutations in Kcnq2 and Kcnq3 that underlie certain forms of epilepsy. In addition to their expression in brain, KCNQ2 and -3 are also found in the somatosensory system. We have now detected both KCNQ2 and KCNQ3 in a subset of dorsal root ganglia neurons that correspond to D-hair Aδ-fibers and demonstrate KCNQ3 expression in peripheral nerve endings of cutaneous D-hair follicles. Electrophysiological recordings from single D-hair afferents from Kcnq3(-/-) mice showed increased firing frequencies in response to mechanical ramp-and-hold stimuli. This effect was particularly pronounced at slow indentation velocities. Additional reduction of KCNQ2 expression further increased D-hair sensitivity. Together with previous work on the specific role of KCNQ4 in rapidly adapting skin mechanoreceptors, our results show that different KCNQ isoforms are specifically expressed in particular subsets of mechanosensory neurons and modulate their sensitivity directly in sensory nerve endings.

D-Neuron: Is it Ligand-Producing Neuron of Taar1? From Schizophrenia Research

Recent pharmacological studies has been shown the importance of trace amine-associated receptor, type 1 (TAAR1), a subtype of trace amine receptors, as a prospective target receptor for novel neuroleptics. In the present article, the author shows D-neuron research in psychiatric field. Although dopamine (DA) dysfunction is a well-known hypothesis of etiology of schizophrenia, its molecular basis has not yet been clarified. To explain this, modulating function of trace amines on DA neurotransmission was considered. The TAAR1 has a large number of ligands, including tyramine, β-phenylethylamine and methamphetamine that influence on human mental state. Reduced stimulation of TAAR1 on DA neurons in the midbrain ventral tegmental area (VTA) has been revealed to increase firing frequency of VTA DA neurons. Previously, the author and her colleagues reported D-neuron decrease in the striatum including nucleus accumbens of postmortem brains of patients with schizophrenia. This implies the decrease of trace amine synthesis and consequent reduction of TAAR1 stimulation on terminals of midbrain VTA DA neurons, and may lead to mesolimbic DA hyperactivity in schizophrenia. Striatal D-neuron decrease of postmortem brains, due to neural stem cell dysfunction in the subventricular zone of lateral ventricle, might be pivotal in etiology of schizophrenia. The new “D-cell hypothesis”, in which D-neurons and TAAR1 are involved, is concordant with recent reports showing effectiveness of TAAR1 ligands for schizophrenia model animals.

Period-adding bifurcation of neural firings induced by inhibitory autapses with time-delay

Neural firing rhythm plays an important role in achieving the function of a nervous system. Neurons with autapse, which starts and ends in the same cell, are widespread in the nervous system. Previous results of both experimental and theoretical studies have shown that autaptic connection plays a role in influencing dynamics of neural firing patterns and has a significant physiological function. In the present study, the dynamics of a neuronal model, i.e., Rulkov model with inhibitory autapse and time delay, is investigated, and compared with the dynamics of neurons without autapse. The bifurcations with respect to time-delay and the coupling strength are extensively studied, and the time series of membrane potentials is also calculated to confirm the bifurcation analysis. It can be found that with the increase of time-delay and/or the coupling strength, the period-adding bifurcation of neural firing patterns can be induced in the Rulkov neuron model. With the increase of the period number of the firing rhythm, the average firing frequency increases. When time-delay and/or coupling strength are/is greater than their/its corresponding certain thresholds/threshold, the average firing frequency is higher than that of the neuron without autapse. Furthermore, new bursting patterns, which appear at suitable time delays and coupling strengths, can be well interpreted with the dynamic responses of an isolated single neuron to a negative square current whose action time, duration, and strength are similar to those of the inhibitory coupling current modulated by the coupling strength and time delay. The bursts of neurons with autapse show the same pattern as the square negative current-induced burst of the isolated single neuron when the time delay corresponds to the phase. The bifurcation structure of the neural firing rhythm of the neuron without autapse can be obtained with the fast-slow dissection method. The dynamic responses of the isolated bursting neuron to the negative square current are acquired by using the fast-slow variable dissection method, which can help to recognize the new rhythms induced by the external negative pulse current applied at different phases. The new rhythm patterns are consistent with those lying in the period-adding bifurcations. The results not only reveal that the inhibitory autapse can induce typical nonlinear phenomena such as the period-adding bifurcations, but also provide the new phenomenon that the inhibitory autapse can enhance the firing frequency, which is different from previous viewpoint that inhibitory effect often reduces the firing frequency. These findings further enrich the understanding of the nonlinear phenomena induced by inhibitory autapse.

A role of local VTA GABAergic neurons in mediating dopamine neuron response to nicotine

The local circuitry of the tegmental area (VTA) consists primarily of dopamine (DA) and GABA neurons. Interactions between DA and GABA neurons are critical for regulating DA neuron activity, and thus DA efflux throughout the brain. One striking example that demonstrates the significance of local interactions between DA and GABA neurons is related to nicotine reinforcement. Experimentally, it was shown that activation of nicotinic acetylcholine (nAch) receptors on GABA neurons by Ach leads to an increase in both firing and bursting of the DA neuron, while nicotine produces an opposite effect [1]. In order to investigate the mechanism of this GABA-mediated effect, we created a biologically plausible model of local VTA microcircuitry. The model network consists of a population of GABA neurons innervating one DA neuron. DA neuron dynamics are described by a conductance based model; which includes intrinsic and synaptic currents conducted by NMDA, AMPA, GABA, and nAch receptors. GABA neurons that are described by Wang-Buszaki equations provide inhibitory drive to the DA neuron. Excitatory inputs (Glu and Ach) to DA and GABA neurons are modeled as Poisson-distributed spike trains. Ach pulses act as synchronizing inputs to a population of GABA neurons, due to a transient activation of GABA nAch receptors, while nicotine persistently activates nAch receptor, causing an increase in firing frequency of GABA neurons. Modeling revealed that synchronization of GABA neurons by cholinergic input could provide a mechanism for the elevation of DA neuron firing frequency and bursting. Synchronized GABA inputs act via phasic disinhibition that promotes rebound spikes, but is conditioned on the presence of depolarizing currents to the DA neuron. The opposite effects of nicotine applied to the GABA neuron only (decrease in firing and bursting of DA neuron), could be the result of desynchronization in population of GABA neurons, produced by tonic activation of nAch receptor. A desynchronized GABA population provides constant inhibition to the DA neuron that suppresses firing (see Figure ​Figure1).1). These data highlight the important and powerful role local circuit dynamics VTA. Furthermore, synchrony amongst GABA neurons seems to be a critical intermediary that regulates DA neuron activity and, by extension, DA release throughout the brain. Figure 1 A) Quantification of Ach mediated firing of DA neuron (firing rate and %SWB) B) Nicotine-elicited modifications in firing rate of DA neuron. Vertical black lines indicate nicotine injection. Horizontal dashed lines indicate the baseline firing rate. ...

Characteristics of renal sympathetic nerve single units in rabbits with angiotensin‐induced hypertension

We examined the effect of chronic angiotensin (Ang II)-induced hypertension on activity of postganglionic renal sympathetic units to determine whether altered whole renal nerve activity is due to recruitment or changes in firing frequency. Rabbits were treated with a low (20 ng kg(-1) min(-1), 8 weeks) or high dose (50 ng kg(-1) min(-1), 4 weeks) of Ang II before the experiment under chloralose-urethane anaesthesia. Spontaneously active units were detected from multiunit recordings using an algorithm that separated units by action potential shape using templates that matched spikes within a prescribed standard deviation. Multiunit sympathetic nerve activity was 40% higher in rabbits treated with low-dose Ang II than in sham (P = 0.012) but not different in high-dose Ang II. Resting firing frequency was similar in sham rabbits (1.00 ± 0.09 spikes s(-1), n = 144) and in those treated with high-dose Ang II (1.10 ± 0.08 spikes s(-1), n = 112) but was lower with low-dose Ang II (0.65 ± 0.08 spikes s(-1), n = 149, P < 0.05). Unit firing rhythmicity was linked to the cardiac cycle and was similar in sham and low-dose Ang II groups but 29-32% lower in rabbits treated with high-dose Ang II (P < 0.001). Cardiac linkage followed a similar pattern during hypoxia. All units showed baroreceptor dependency. Baroreflex gain and range were reduced and curves shifted to the right in Ang II groups. Firing frequency during hypoxia increased by +39% in low-dose Ang II and +82% in shams, but the greatest increase was in the high-dose Ang II group (+103%, P(dose) = 0.001). Responses to hypercapnia were similar in all groups. Increases in sympathetic outflow in hypertension caused by low-dose chronic Ang II administration are due to recruitment of neurons, but high-dose Ang II increases firing frequency in response to chemoreceptor stimuli independently of the arterial baroreceptors.

Tachykinin acts upstream of autocrine Hedgehog signaling during nociceptive sensitization in Drosophila.

Pain signaling in vertebrates is modulated by neuropeptides like Substance P (SP). To determine whether such modulation is conserved and potentially uncover novel interactions between nociceptive signaling pathways we examined SP/Tachykinin signaling in a Drosophila model of tissue damage-induced nociceptive hypersensitivity. Tissue-specific knockdowns and genetic mutant analyses revealed that both Tachykinin and Tachykinin-like receptor (DTKR99D) are required for damage-induced thermal nociceptive sensitization. Electrophysiological recording showed that DTKR99D is required in nociceptive sensory neurons for temperature-dependent increases in firing frequency upon tissue damage. DTKR overexpression caused both behavioral and electrophysiological thermal nociceptive hypersensitivity. Hedgehog, another key regulator of nociceptive sensitization, was produced by nociceptive sensory neurons following tissue damage. Surprisingly, genetic epistasis analysis revealed that DTKR function was upstream of Hedgehog-dependent sensitization in nociceptive sensory neurons. Our results highlight a conserved role for Tachykinin signaling in regulating nociception and the power of Drosophila for genetic dissection of nociception.