High Frequency Spikes Research Articles

Inhibitory synchronization of bursting in biological neurons: dependence on synaptic time constant.

Using the dynamic clamp technique, we investigated the effects of varying the time constant of mutual synaptic inhibition on the synchronization of bursting biological neurons. For this purpose, we constructed artificial half-center circuits by inserting simulated reciprocal inhibitory synapses between identified neurons of the pyloric circuit in the lobster stomatogastric ganglion. With natural synaptic interactions blocked (but modulatory inputs retained), these neurons generated independent, repetitive bursts of spikes with cycle period durations of approximately 1 s. After coupling the neurons with simulated reciprocal inhibition, we selectively varied the time constant governing the rate of synaptic activation and deactivation. At time constants <or=100 ms, bursting was coordinated in an alternating (anti-phase) rhythm. At longer time constants (>400 ms), bursts became phase-locked in a fully overlapping pattern with little or no phase lag and a shorter period. During the in-phase bursting, the higher-frequency spiking activity was not synchronized. If the circuit lacked a robust periodic burster, increasing the time constant evoked a sharp transition from out-of-phase oscillations to in-phase oscillations with associated intermittent phase-jumping. When a coupled periodic burster neuron was present (on one side of the half-center circuit), the transition was more gradual. We conclude that the magnitude and stability of phase differences between mutually inhibitory neurons varies with the ratio of burst cycle period duration to synaptic time constant and that cellular bursting (whether periodic or irregular) can adopt in-phase coordination when inhibitory synaptic currents are sufficiently slow.

Whole-cell recordings from preoptic/hypothalamic slices reveal burst firing in gonadotropin-releasing hormone neurons identified with green fluorescent protein in transgenic mice.

Central control of reproduction is governed by a neuronal pulse generator that underlies the activity of hypothalamic neuroendocrine cells that secrete GnRH. Bursts and prolonged episodes of repetitive action potentials have been associated with hormone secretion in this and other neuroendocrine systems. To begin to investigate the cellular mechanisms responsible for the GnRH pulse generator, we used transgenic mice in which green fluorescent protein was genetically targeted to GnRH neurons. Whole-cell recordings were obtained from 21 GnRH neurons, visually identified in 200-microm preoptic/hypothalamic slices, to determine whether they exhibit high frequency bursts of action potentials and are electrically coupled at or near the somata. All GnRH neurons fired spontaneous action potentials, and in 15 of 21 GnRH neurons, the action potentials occurred in single bursts or episodes of repetitive bursts of high frequency spikes (9.77 +/- 0.87 Hz) lasting 3-120 sec. Extended periods of quiescence of up to 30 min preceded and followed these periods of repetitive firing. Examination of 92 GnRH neurons (including 32 neurons that were located near another green fluorescent protein-positive neuron) revealed evidence for coupling in only 1 pair of GnRH neurons. The evidence for minimal coupling between these neuroendocrine cells suggests that direct soma to soma transfer of information, through either cytoplasmic bridges or gap junctions, has a minor role in synchronization of GnRH neurons. The pattern of electrical activity observed in single GnRH neurons within slices is temporally consistent with observations of GnRH release and multiple unit electrophysiological correlates of LH release. Episodes of burst firing of individual GnRH neurons may represent a component of the GnRH pulse generator.

Cardiac responses to sensory stimulation in the adult tobacco budworm moth, Heliothis virescens

Electrocardiogram recordings were performed on intact Heliothis virescens moths using Ag-AgCl electrodes positioned on the body cuticular surface. Regular heart activity and its changes in response to mechanical and olfactory stimulations were analysed. Moths were also tested in their anemotactic orientation in response to olfactory stimulation. Results show that regular cardiac activity in Heliothis is cyclical and consists of the alternation of a high and a low spike-frequency period. This activity pattern is strongly influenced by sensory stimulation. Both mechanical stimulations at various intensities and olfactory stimulations with sex pheromone and 1-hexanol evoked tachycardiac effects when applied during low spike-frequency cardiac activity. In contrast, they did not affect high spike-frequency cardiac activity. It is concluded that the cardiac response in Heliothis is an effective indicator of sensory reception. It would therefore appear to represent a valid tool for testing insect reactivity.

Amiloride high- and low-sensitivity, as well as insensitive sites in the blowfly: implications for sugar, water and anion taste reception mechanisms

Among chemoreceptor cells of the blowfly ( Protophormia terraenovae , the so-called 'sugar' and 'water' cells respond to bovine serum albumin (BSA) and L -alanine (the C-terminal amino acid of the BSA molecule) with the highest spike frequency. In both cell types the response to either BSA or L -alanine was unaffected by 0.1 mM amiloride. However, 0.5 mM amiloride decreased the response of the 'water' cell to both BSA and L-alanine significantly, and similarly inhibited the response of the 'sugar' cell to L -alanine, but in contrast to the 'water' cell, 0.5 mM amiloride did not affect the 'sugar' cell response to BSA. The 'sugar' cell responses to both BSA and L-alanine were unaffected by the putative cell second messengers, cAMP and cGMP. The so-called 'anion' cell unexpectedly gave responses to BSA and L-alanine that were enhanced by amiloride at both concentrations. However, like the 'sugar' cell, the 'anion' cell was also unaffected by cAMP and cGMP.We conclude that the 'sugar' cell must have at least three types of receptor sites: the previously described 'F' (amiloride sensitive) and the 'P' (amiloride insensitive) sites, and a low-sensitivity 'T' site that mediates, at least in part, the response to BSA and L -alanine. The effects of amiloride on the responses of the 'water' and 'anion' cells are more difficult to interpret because fundamental information on their chemoreception mechanisms is still lacking.

Activity-dependent properties of synaptic transmission at two classes of connections made by rat neocortical pyramidal axons in vitro.

1. To compare the dynamics of synaptic transmission at different types of connection, dual intracellular recordings were made from pairs of neurones in slices of adult rat neocortex. Excitatory postsynaptic potentials (EPSPs) were elicited by single spikes, spike pairs and brief spike trains in presynaptic pyramidal cells and responses recorded in postsynaptic pyramidal cells and in interneurones. 2. Pyramid-pyramid EPSPs were strongly voltage dependent and this resulted in a range of paired pulse effects. At thirty-two of sixty-nine pyramid-pyramid connections, the 2nd EPSP was the same shape as the 1st, indicating minimal interaction between active synapses. In these thirty-two connections, paired pulse depression (PPD) was apparent (2nd EPSP integral 46 +/- 21% of the 1st, at 5-20 ms), which recovered within 60-70 ms. 3. In eleven additional pyramid-pyramid pairs, the 2nd EPSP was also the same shape as the 1st, but paired pulse facilitation (PPF, 149 +/- 32%) decaying within 50-60 ms was apparent. Even these connections displayed frequency-dependent depression, however, as 3rd EPSPs were smaller than 1st EPSPs at intervals < 100 ms. 4. At twenty-five pyramid-pyramid connections, 2nd EPSPs were broader than 1st EPSPs and in sixteen of these, voltage- and NMDA receptor-dependent enhancement was large enough to obscure the underlying PPD. PPD was revealed by postsynaptic hyperpolarization (4 pairs), N-methyl-D-aspartate (NMDA) receptor blockade (3 paris), or if Mg2+ was removed (in the one case studied). If synapse location allowed significant depolarization of one active site by another, voltage-dependent enhancement could produce supralinear EPSP summation and overcome PPD. Third EPSPs were, however, consistently smaller than 1st EPSPs. 5. In striking contrast, profound frequency-dependent facilitation, independent of voltage or NMDA receptors was seen at fifteen connections involving two classes of postsynaptic interneurones. 6. At these pyramid-interneurone connections, facilitation of the 2nd EPSP (655 +/- 380% at 5-20 ms) decayed rapidly, within 50-60 ms. Third and fourth EPSPs showed additional facilitation which decayed more slowly, within 90 ms and 2 s, respectively. Facilitation due to five to six spike trains was still apparent at 3 s. Therefore, once initiated by a brief high frequency spike train, facilitation was maintained at lower frequencies.

システムニューロサイエンス教教育講座 ８． 垂直眼球運動の神経機構 垂直性バーストニューロンとその局在

A paramedian area of the mesodiencephalic junction, referred to as the rostral interstitial nucleus of the medial longitudinal fasciculus (riMLF) or Forel's field H, is important in the genesis of vertical saccadic eye movements. Vertical medium-lead burst neuron (MLBN) exhibits a high frequency burst of spikes that are induced 5-15 msec prior to vertical saccades. These MLBNs are located in the dorsomedial part of the Forel's field H. These MLBNs directly project to the oculomotor nucleus, forming direct synaptic connections with vertical eye movement-related motoneurons in the oculomotor nucleus. Omnipause neurons (OPNs) in the paramedian pontine reticular formation form direct inhibitory connections with vertical MLBNs. Based on these results, we postulated that vertical saccades are generated when the disynaptic excitatory input from the superior colliculus reaches the vertical MLBNs, which form direct connections with vertical motoneurons. The high frequency spike burst of the MLBNs during vertical saccades is presumed to be created by this excitatory input when the MLBNs are released from tonic inhibition caused by OPN activity.

Respiratory challenge induces high frequency spiking on the static charge sensitive bed (SCSB).

The static charge sensitive bed (SCSB) is a simple and noninvasive device used for the detection of sleep apnoea. In addition to episodes of apnoea or hypopnoea, heavy snorers commonly present with episodes of high frequency spiking on the SCSB. These spiking episodes have been claimed to represent partial upper airway obstruction during sleep, but the mechanism of their appearance is not known. We studied the SCSB spiking phenomenon in awake subjects during experimental respiratory challenge. One female and five male volunteers were studied whilst breathing freely, during hypoxia, hypercapnia and inspiratory and expiratory loading. Oxygen saturation, end-tidal carbon dioxide tension, minute ventilation, oesophageal pressure, electrocardiographic activity (ECG), blood pressure and the SCSB signals were monitored. During free breathing, the SCSB high frequency signal consisted of low amplitude complexes with close time relationship to the cardiac cycle. During respiratory challenge, spiking occurred. These spikes showed no time relationship to the cardiac cycle, but were time-linked to the onset of inspiration or expiration. Spike amplitude correlated with breathing frequency (r2 = 0.59; p < 0.005) and variation in oesophageal pressure (r2 = 0.57; p < 0.005). We conclude that during quiet, unobstructed breathing the static charge sensitive bed high frequency signal represents cardiac activity (ballistocardiogram), whereas during high-drive breathing high frequency spikes are produced. These spikes are respiratory in origin and are likely to represent fast components of respiratory movements. Our results support the use of static charge sensitive bed spiking as a noninvasive measure of breathing stimulation.

Bursts of high-frequency plasma waves at an electric double layer

The high-frequency (HF) oscillations, which are driven by the electron beam on the high-potential side of an electric double layer, are investigated in a laboratory experiment. A new HF probe design has made it possible to achieve a combination of absolute amplitude calibration and spatial resolution which, for such high frequencies, has not been achieved before. The HF waves convert about 20% of the beam energy to oscillations within a region extending from 100 to 400 Debye lengths on the high-potential side of the double layer. This makes the HF waves the dominant mechanism of local tapping of the beam energy, and the modified energy and particle balance is investigated. The HF waves propagate with an approximately constant phase velocity which is slightly smaller than the beam velocity. Time-averaged measurements locate them to a HF region, extending approximately from 5 to 15 cm from the double layer, with a typical half width of 10 cm for the time-averaged electric field amplitude. Time-resolved measurements show, however, a much more narrow structure. The envelope of the electric field amplitude has a single maximum within the HF region and a typical half width of 1 - 2 cm (about one wavelength) along the beam. We call this envelope `the HF spike'. The position of the HF spike changes in an apparently irregular fashion within the HF region and it moves with velocities in the range . The spatial increase and decrease in amplitude of the wave is exponential over nearly two orders of magnitudes, with electron-folding distances of only about 5 mm, so the maximum of the envelope is very sharp. The amplitude increase agrees approximately with the growth rate from linear beam-plasma theory and the maximum amplitude observed agrees with saturation by beam trapping. The strong spatial decrease in the wave amplitude is not understood. It is proposed that the motion of the HF spike is caused by fluctuations, on the ion acoustic time scale, both in the growth length and in the starting point for wave growth at the double layer, which moves back and forth. This motion is shown to be strongly correlated to the motion of the HF spike in a particular case. Amplitude modulations, as observed by a stationary probe, are found on two time scales. On a slower time scale of typically , the motion of the HF spike, together with its limited spatial extent, gives rise to a temporal burst. Within these bursts the waves are also modulated on a much faster time scale of 10 - 30 ns (the wave period is 3 ns). The HF spike cannot be interpreted as a linear superposition of waves with the constant phase velocity measured, because this wave packet would have a spatial extention at least ten times larger than the width of the HF spike.

Point Source Distribution Affects Pheromone Spike Frequency and Communication Disruption of Epiphyas postvittana (Lepidoptera: Tortricidae)

To determine impact of point source distribution on communication disruption in Epiphyas postvittana (Walker), 100 dispensers releasing pheromone and inhibitor were deployed in replicated 0.5-ha New Zealand apple orchard blocks at 3 point source densities (1, 9, or 100 points), along with untreated control. Weekly inspections of pheromone-baited sticky traps were compared with field electroantennogram (EAG) recordings, of 3-min duration, which were made at 2 locations in the 4 treatments with the same antenna. EAG recordings were later normalized to the calibration pulses, and the mean squared error of the signal (MSE) was calculated. Assessment of spike size and frequency was also made. Significantly increased disruption of trap catches resulted from increased number of point sources. In pheromone-treated plots, 4 inner traps were more disrupted than were 12 outer traps. EAG signals in treated plots showed significantly higher numbers of spikes that exceeded a given signal-to-noise ratio (as defined from untreated sites). Spike size and spike frequency both increased with increasing numbers of point sources. The MSE signal from the EAG was also higher in the more dense of the pheromone treatments. The inverse relationship between spike frequency and catch suggests that aerial environments with higher spike frequencies are more effective at communication disruption. There appears to be value in using both the MSE and spike frequency recorded by EAG to characterize fluctuations in pheromone concentrations in treated orchards.

Strontium isotope stratigraphy of the Middle Devonian: Brachiopods and conodonts

A set of 145 strontium isotope ratios, based on skeletal components of Emsian to Frasnian age, reveals a detailed structure of the seawater 87Sr/ 86Sr curve that can ultimately serve as a tool for “high resolution isotope stratigraphy” in the Devonian. Brachiopod and conodont samples were collected in the Eifel region of Germany, the area around the global stratotype for the Middle Devonian, with an apparent average temporal resolution in the 10 5 y range. Preservation of the brachiopod shell material has been assessed by optical microscopy, SEM, and cathodoluminescence and only the better preserved internal (“secondary”) layer of the shell has been utilized for strontium isotope measurements. The 87Sr/ 86Sr curve shows a short decline from 0.7081 to 0.7078 through the late Emsian, followed by short-term fluctuations with an amplitude of up to 10 −4 around a mean of ~0.7078 during the Eifelian and Givetian, and a rise from late Givetian into the Late Devonian. The above high frequency oscillations and spikes are likely a reflection of condensed sedimentary records, due to erosional and nondepositional events, but a direct confirmation for such a scenario can be claimed only for the latest Eifelian otomari-event. Insufficient stratigraphic resolution precludes testing for the other events and isotopic spikes. Conodont skeletal elements, even if well preserved at CAI < 2.5, yielded results that are mostly enriched in radiogenic 87Sr, if compared to coeval brachiopods. Although this enrichment is usually within the 10 −5 range, conodonts, despite their superior stratigraphic resolution, should be utilized only as a material of second choice in cases where brachiopods are rare or absent.

A minimal, compartmental model for a dendritic origin of bistability of motoneuron firing patterns.

Various nonlinear regenerative responses, including plateau potentials and bistable repetitive firing modes, have been observed in motoneurons under certain conditions. Our simulation results support the hypothesis that these responses are due to plateau-generating currents in the dendrites, consistent with a major role for a noninactivating calcium L-type current as suggested by experiments. Bistability as observed in the soma of low- and higher-frequency spiking or, under TTX, of near resting and depolarized plateau potentials, occurs because the dendrites can be in a near resting or depolarized stable steady state. We formulate and study a two-compartment minimal model of a motoneuron that segregates currents for fast spiking into a soma-like compartment and currents responsible for plateau potentials into a dendrite-like compartment. Current flows between compartments through a coupling conductance, mimicking electrotonic spread. We use bifurcation techniques to illuminate how the coupling strength affects somatic behavior. We look closely at the case of weak coupling strength to gain insight into the development of bistable patterns. Robust somatic bistability depends on the electrical separation since it occurs only for weak to moderate coupling conductance. We also illustrate that hysteresis of the two spiking states is a natural consequence of the plateau behavior in the dendrite compartment.

Consequences and mechanisms of spike broadening of R20 cells in Aplysia californica

We studied frequency-dependent spike broadening in the two electrically coupled R20 neurons in the abdominal ganglion of Aplysia. The peptidergic R20 cells excite the R25/L25 interneurons (which trigger respiratory pumping) and inhibit the RB cells. When fired at 1-10 Hz, the duration of the falling phase of the action potential in R20 neurons increases 2-10 fold during a spike train. Spike broadening recorded from the somata of the R20 cells affected synaptic transmission to nearby follower cells. Chemically mediated synaptic output was reduced by approximately 50% when recorded trains of nonbroadened action potentials were used as command signals for a voltage-clamped R20 cell. Electrotonic EPSPs between the R20 cells, which normally facilitated by two- to fourfold during a high frequency spike train, showed no facilitation when spike broadening was prevented under voltage-clamp control. To examine the mechanism of frequency-dependent spike broadening, we applied two-electrode voltage-clamp and pharmacological techniques to the somata of R20 cells. Several voltage-gated ionic currents were isolated, including INa, a multicomponent ICa, and three K+ currents--a high threshold, fast transient A-type K+ current (IAdepol), a delayed rectifier K+ current (IK-V), and a Ca(2+)-sensitive K+ current (IK-Ca), made up of two components. The influences of different currents on spike broadening were determined by using the recorded train of gradually broadening action potentials as the command for the voltage clamp. We found the following. (1) IAdepol is the major outward current that contributes to repolarization of nonbroadened spikes. It undergoes pronounced cumulative inactivation that is a critical determinant of spike broadening. (2) Activity-dependent changes in IK-V, IK-Ca, and ICa have complex effects on the kinetics and extent of broadening. (3) The time integral of ICa during individual action potentials increases approximately threefold during spike broadening.

Genetic epilepsy model derived from common inbred mouse strains.

The recombinant inbred mouse strain, SWXL-4, exhibits tonic-clonic and generalized seizures similar to the commonest epilepsies in humans. In SWXL-4 animals, seizures are observed following routine handling at about 80 days of age and may be induced as early as 55 days by rhythmic gentle tossing. Seizures are accompanied by rapid, bilateral high frequency spike cortical discharges and followed by a quiescent post-ictal phase. Immunohistochemistry of the immediate early gene products c-Fos and c-Jun revealed abnormal activation within cortical and limbic structures. The seizure phenotype of SWXL-4 can be explained and replicated fully by the inheritance of susceptibility alleles from its progenitor strains, SWR/J and C57L/J. Outcrosses of SWXL-4 with most other common inbred strains result in F1 hybrids that have seizure at least as frequently as SWXL-4 itself. Quantitative trait locus mapping reveals a seizure frequency determinant, Szf1, near the pink-eyed dilution locus on chromosome 7, accounting for up to 32% of the genetic variance in an F2 intercross between SWXL-4 and the linkage testing strain ABP/Le. These studies demonstrate that common strains of mice such as SWR and C57L contain latent epilepsy susceptibility alleles. Although the inheritance of susceptibility may be complex, these results imply that a number of potentially important and practical, noninvasive models for this disorder can be constructed and studied in crosses between common mouse strains.

The pattern of agonist-evoked cytosolic Ca2+ oscillations depends on the resting intracellular Ca2+ concentration.

The agonists acetylcholine (ACh) and cholecystokinin (CCK) have been shown to evoke markedly different patterns of cytosolic Ca2+ oscillations in the same isolated pancreatic acinar cells. ACh induces high frequency sinusoidal oscillations (spiking) associated with activation of Ca2+ influx. CCK evokes longer lasting discrete transients separated by long intervals, and these low frequency transients persist for many minutes in the absence of extracellular Ca2+. Using digital imaging of fura-2 fluorescence, we have now monitored the free cytoplasmic Ca2+ concentration ([Ca2+]i) simultaneously in many individual cells from the same population. In the resting condition [Ca2+]i ranged from about 50 to 300 nM. When the resting [Ca2+]i was below 150 nM, ACh (50-100 nM) invariably evoked typical high frequency spiking. In the majority of cells which had a resting [Ca2+]i higher than 150 nM, ACh also evoked low frequency transients. Although initiated by ACh, these transients displayed the temporal and functional characteristics of the CCK-evoked transients. Removal of extracellular Ca2+ for a few minutes had no effect on this type of oscillation, whereas such a procedure reversibly abolished the ACh-evoked high frequency response. For the response evoked by 10-30 pM Ca2+ signal amplitude and the resting [Ca2+]i. Because the Ca2+ signal amplitude and the resting [Ca2+]i. Because CCK could never induce high frequency spiking there is some receptor specificity in dictating the time course of Ca2+ oscillations, but the resting [Ca2+]i is a major determinant of the Ca2+ signal pattern.

Kinetic properties of NMDA receptor‐mediated synaptic currents in rat hippocampal pyramidal cells versus interneurones.

1. Whole-cell tight-seal recordings were obtained from visually identified pyramidal cells (PCs) and interneurones (INs) in the CA1 field of thin hippocampal slices from 13- to 23-day-old rats. The INs sampled were classified according to their location either in the molecular layer (M-INs) or in the oriens layer and alveus (OA-INs). PCs and INs differed in their mode of firing when depolarized by a prolonged current pulse. Whereas PCs fired a single action potential, most INs responded with non-accommodating high frequency spike firing. 2. In the presence of 1 microM tetrodotoxin (TTX), bath application of either 50 microM L-glutamate with 10 microM 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) or 2.5 microM N-methyl-D-aspartate (NMDA), induced a similar conductance increase in PCs and INs that was completely blocked by 200 microM DL-2-amino-5-phosphonovaleric acid (APV). The NMDA receptor-mediated currents reversed around 4 mV and exhibited an area of negative slope conductance at potentials more negative than -20 to -30 mV in the presence of 1-2 mM Mg2+. 3. Dual-component excitatory postsynaptic currents (EPSCs) were evoked in PCs and INs by stimulating afferent fibres close to the neurone. The NMDA receptor-mediated component of the EPSCs (NMDA EPSC) was isolated by adding 10 microM CNQX to block non-NMDA receptors. The NMDA EPSCs in all cell types reversed around 1.5 mV and were abolished by 50 microM APV. 4. In saline containing 1 mM Mg2+, the peak current-voltage (I-V) relationship of NMDA EPSCs in PCs and INs showed an area of negative slope conductance at voltages more negative than -20 to -30 mV. In nominally Mg(2+)-free saline, the peak I-V relation was linear over a much wider voltage range in both cell types. 5. The 10-90% rise times of NMDA EPSCs at -60 mV ranged from 4.5 to 16 ms in PCs (mean 8.7 ms; n = 25) and in M-INs (mean 9.1 ms; n = 10). Their decay could be best fitted with the sum of two exponentials. The decay of NMDA EPSCs in PCs was significantly slower than that recorded in INs. The average fast (tau f) and slow (tau s) time constants of decay were, respectively, 66.5 and 353.9 ms in PCs, and 34.4 and 212.5 ms in M-INs.(ABSTRACT TRUNCATED AT 400 WORDS)

Electrical activity of neurons in the ventrolateral septum and bed nuclei of the stria terminalis in suckled rats: Statistical analysis gives evidence for sensitivity to oxytocin and for relation to the milk-ejection reflex

Our previous results obtained by lesioning or stimulating the ventrolateral part of the lateral septum and the bed nuclei of the stria terminalis suggested that this area is involved in the control of milk ejection pattern in rats. The present study was undertaken with the aim of testing ventrolateral part of the lateral septum-bed nuclei of the stria terminalis neurons as a putative link of the neuronal network controlling the bursting activity of oxytocin neurons in suckled lactating rats (anaesthetized with urethane). Ventrolateral part of the lateral septum-bed nuclei of the stria terminalis neurons were recorded simultaneously with hypothalamic oxytocin neurons in either the paraventricular or supraoptic nucleus in rats with ( N = 26) or without ( N = 29) periodic milk ejections. Analysis of their firing pattern enabled differentiation of two subgroups: type I, characterized by numerous high frequency spikes, often grouped in clusters; and type II with very few or no high frequency clusters of spikes. The probability density function of the interspike intervals of both patterns could be modelled using a mixture of two log-normal distributions, the parameters of which differed significantly. The presence or absence of milk ejections did not influence the overall mean level of activity (2.0 ± 0.5 and 1.9 ± 0.4 spikes/s, respectively). However, the characteristics of the type I firing pattern were affected by the presence of the milk-ejection reflex. The average level of activity was not always constant and 16/55 ventrolateral part of the lateral septum-bed nuclei of the stria terminalis neurons displayed cyclical activity (from 0.6 ± 0.2 to 4.0 ± 0.5 spikes/s) both in the presence ( N = 8) and absence ( N = 8) of the milk-ejection reflex. In five of eight neurons recorded during milk-ejection reflex, the cycles in firing were clearly correlated with the bursting of oxytocin neurons. These five neurons exhibited the type I firing pattern. The three remaining neurons and the eight neurons recorded in the absence of milk-ejection reflex displayed the type II firing pattern. Oxytocin (1–2 ng = 0.45−0.9 mU) was injected into the third ventricle (i.c.v.) in order to examine the possible involvement of ventrolateral part of the lateral septum-bed nuclei of the stria terminalis neurons in the facilitatory effect of oxytocin on the reflex. Oxytocin caused an excitation of 13/47 ventrolateral part of the lateral septum-bed nuclei of the stria terminalis neurons independent of whether the reflex was facilitated by oxytocin ( N = 6) or not ( N = 7). In the former case, the increase in firing rate occurred before facilitation of the reflex. Most of the oxytocin-sensitive neurons (10/13) had the type I firing pattern, the characteristics of which were variably affected by oxytocin. The positions of 18 neurons were histologically localized in the ventrolateral part of the lateral septum-bed nuclei of the stria terminalis by iontophoretic deposition of a dye. The location of 10 of these neurons was further correlated with oxytocin-binding sites using autoradiography. The majority of these neurons (including both oxytocin-sensitive and -insensitive neurons) were located in regions expressing oxytocin-binding sites. In conclusion, there exists a population of ventrolateral part of the lateral septum-bed nuclei of the stria terminalis neurons displaying numerous high frequency spikes (type I firing pattern) which exhibits a strong correlation with milk ejection-related bursting activity of hypothalamic oxytocin neurons, and/or which are sensitive to oxytocin. It is suggested that these neurons might be involved as an element of a neuronal network mediating the central effects of oxytocin on the milk-ejection reflex.

Electroencephalographic changes in experimental autoimmune myasthenia gravis

A number of reports have suggested that central disturbances of cholinergic function may occur in patients with myasthenia gravis. The present study was designed in order to examine cortical electroencephalographic (EEG) activity in Lewis rats with experimental autoimmune myasthenia gravis (EAMG). Experiments were performed on conscious rats with clinical EAMG and demonstrable antibodies against the acetylcholine receptor. The animals showed no gross changes in cortical EEG discharge in terms of cycles and durations of wake, desynchronized sleep, and synchronized sleep, as compared with control rats. However, abnormalities characterized by single spikes or waves, and by spike and wave complexes, were observed, most commonly during synchronization of the EEG. Use of computerized frequency analysis of the EEG records revealed the presence of three basic differences in EEG discharge in myasthenic animals: (1) additional high-amplitude, low frequency (< 4 Hz) activity was recorded, especially during synchronized sleep; (2) decreases in mid-range (4–7 Hz) activity were recorded, particularly during periods of wakefulness; and, (3) increases in high frequency (> 8 Hz) spike discharge were observed at all times, although this was most evident during periods of synchronized sleep. The data provide further evidence for alterations in central cholinergic function in myasthenia gravis.

Differential responses of galeal gustatory sensilla of the adult Colorado potato beetle, Leptinotarsa decemlineata (Say), to leaf saps from host and non‐host plants

ABSTRACT Responses of galeal sensilla of the Colorado potato beetle, Leptinotarsa decemlineata Say (Coleoptera: Chrysomelidae), to leaf sap from Solanum tuberosum and a number of other solanaceous and non‐solanaceous plants are described. A single cell responds vigorously to expressed sap from S.tuberosum, ‐and even to ten‐fold dilutions of expressed sap. The response is characterized by a high spike frequency, low phasic activity and a tonic phase which can last for tens of seconds. At 8 s following stimulus application the primary response is typically 50% of its original activity, indicating slow adaptation to the sap stimulus. The primary response varies little among multiple stimulations of single sensilla and among sensilla on the same animal. There is a secondary response to potato leaf sap from one or more cells which have low spike amplitudes. This is usually of much lower frequency than the response from the primary cell, and it is highly variable.The prominent and reproducible single cell response to potato sap may be an important component in signalling the presence of a host plant. This hypothesis is tested using saps from two other species of Solanum which are hosts, and several solanaceous and non‐solanaceous non‐hosts. Responses of galeal sensilla to the three host‐plants tested were qualitatively similar and reproducible while responses to the non‐hosts were highly variable and qualitatively different from responses to host saps. These results are interpreted and discussed in the context of a possible mechanism for chemosensory coding of complex stimuli in the insect/plant relationship.Analysis of the raw electrophysiological data required extensive use of a microcomputer and several programs were developed during the course of this study. The computer analyses are briefly described in the paper and additional information and copies of the programs are available from the authors.

Behavioural, electroencephalographic and neuropathological effects of the intrahippocampal injection of the venom of the South American rattlesnake ( Crotalus durissus terrificus)

L. E. A. M. Mello and E. A. Cavalheiro. Behavioural, electroencephalographic and neuropathological effects of the intrahippocampal injection of the venom of the South American rattlesnake ( Crotalus durissus terrificus). Toxicon 27, 189–199, 1989.—Venom was microinjected into the dorsal hippocampus of rats and electroencephalographic recordings were obtained from the hippocampus and occipital cortex. Behavioural alterations consisted of circling, wet shaking and scratching that evolved to head and body jerks and isolated clonic episodes and then to wild running followed by tonic-clonic generalized seizures and status epilepticus. Electroencephalographic alterations consisted of high frequency and high voltage spikes together with epileptiform seizures beginning in the hippocampus and evolving to the cortex. However there was only a poor electrographic-behavioural correlation between the generalized tonic-clonic seizures preceded by wild running and the electrical recordings from hippocampus and occipital cortex. Histology revealed lesions at the site of injection as well as at distant sites. Severity of neuronal damage was associated with seizure intensity. Damaged areas were almost the same as found within other models of epilepsy. Nevertheless a remarkable difference was the highly lesioned hypothalamus seen in this experiment. We discuss our results in relation to results obtained with other methods of inducing epilepsy. This venom may be a useful tool for studying the nervous system.

Morphological and physiological properties of rat cerebellar neurons in mature and developing cultures

Immunohistochemical techniques and antibodies to γ-aminobutyric acid (GABA), parvalbumin, and cyclic guanosine monophosphate-dependent protein kinase were used to identify populations of cerebellar neurons in culture that exhibit morphological features and immunoreactivity characteristic of neuronal types present in the cortical region of the cerebellum in vivo. The cultures were examined at 3 culture ages: 6–9, 12–15 and >15 days in vitro, reflecting early, intermediate and late periods in cerebellar development. Neurons identified as Purkinje neurons (PNs), granule cells or inhibitory interneurons (stellate, basket, Golgi and Lugaro cells) were present at all culture ages. The granule cells (GCs) and inhibitory interneurons (INs) were morphologically well developed at the youngest culture age studied; morphological features did not change dramatically during the culture period. In contrast, the PNs were morphologically immature at 6–9 DIV (DIV = days in vitro) and exhibited dramatic changes in morphological structure with culture age. Extracellular recordings from PNs, GCs and INs in living cultures revealed that all classes of neurons exhibited spontaneous activity, but that only a portion of the GCs and INs were spontaneously active. The spontaneously active GCs and INs exhibited variable patterns of activity and low firing rates (∼ 2–6 Hz) at all culture ages studied. At 6 DIV, PNs exhibited firing rates and patterns similar to that of the interneurons. At older culture ages, the firing rate and pattern of PNs was significantly different from the GCs and INs and was characterized by high frequency (>10 Hz) spike activity usually in a regular pattern. All cerebellar neurons were excited by the transmitter glutamate (Glu). The Glu response in the GCs and INs consisted of a brief burst of single spikes; in PNs, the response to Glu was prolonged and multiphasic. These data indicate that the cerebellar GCs and INs express morphological, physiological and developmental properties that are significantly different from the PN.