Modulating action of barium and other ions on the sensory activity of frog labyrinth

The effect of Ba2+, TEA, 4-AP and CoCl2 on the EPSP and spike discharges recorded from single fibres of the posterior nerve in the isolated frog labyrinth has been investigated. In Ca-free solution Ba2+ preserved, at low concentration (0.3 mM), the resting activity and at higher levels (up to 6 mM) it resulted in a pronounced facilitation of the EPSP and spike discharges. Facilitation increased on increasing Ba2+ concentration up to 4-5 mM and it was more evident in those units exhibiting a low resting spike firing. The effect of Ba2+ (1 mM) was completely antagonized by 10 mM Ca2+ X CoCl2 (3 mM) suppressed the resting rate at the normal external Ca2+ concentration; the Co2+ block was partially relieved by 1.8 mM Ba2+ X TEA (20 mM) evoked a clear-cut increase in the EPSP and spike discharges which, however, was less consistent than that produced by Ba2+. By comparing the effect of TEA on the spike frequency with that obtained at different Ba2+ levels, the Ba2+ capacity to carry the Ca2+ current was dissected. Such an effect is dose-dependent and it is more evident in low-frequency units. Conversely, 4-AP did not affect the resting discharge frequency. These results indicate that either the Ca2+ or the Ba2+ current sustain the transmitter release at the cyto-neural junction. The effect of TEA suggests that the Ca2+-dependent K+ current may play an important role in supporting the neurosecretory process by controlling the membrane potential of the hair cells.     

Spike generation by spinal neurons evoked by sinusoidal depolarization in cats

Dynamic characteristics of transformation of cell membrane depolarization by spinal neurons into spike discharge frequency were investigated in anesthetized cats. Neurons were activated by sinusoidally modulated currents passed through an intracellular microelectrode. Frequency analysis of this transformation for motoneurons was carried out within a modulation frequency range of 0.2–10 Hz. Frequency characteristics were determined with respect to parameters of the first harmonic of the evoked firing rate; the region of values of current fluctuations was chosen on the linear part of the current intensity versus firing rate characteristic curve. Changes in amplitude characteristics did not exceed 5 dB in absolute terms; at the same time the phase lead of the output signal increased with a rise of frequency. At a frequency of 0.2 Hz phase shifts were virtually absent, but at frequencies of 1, 5, and 10 Hz they amounted to 32, 50, and 83° on average respectively. Transformation of membrane depolarization by neurons into spike discharge frequency is characterized by essentially nonlinear properties, due in particular to the absence of a dynamic component of the response to a negative rate of change of depolarizing current. The frequency characteristics of spike activity of neurons of the motor system are discussed from the standpoint of possible correction of dynamic properties of the whole system at the single unit level.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Dnepropetrovsk State University. Translated from Neirofiziologiya, Vol. 14, No. 1, pp. 35–42, January–February, 1982.     

Hypothalamic Proline-Rich Polypeptide is an Oxidative Burst Regulator

The AGAPEPAEPAQPGVY proline-rich polypeptide (PRP) was isolated from neurosecretory granules of the bovine neurohypophysis; it is produced by N. supraopticus and N. paraventricularis. PRP possesses immune-modulating activity, preventing the death of Gram-negative bacteria-infected mice. Here we show that PRP does not affect human peripheral blood neutrophlis and monocytes phagocytosis but dramatically enhances spontaneous or fMLP- and PMA-induced, and also phagocytosis-dependent, oxidative burst. We demonstrated the regulatory role of PRP on the oxidative burst induction of normal and relapsing inflammatory disease (Behcets disease and familial Mediterranean fever) neutrophils and monocytes. Our results suggest a previously undescribed role for the hypothalamic peptide within primary activated neutrophils and monocytes, since we provide evidence that PRP can differentially regulate both chemotaxis- and phagocytosis-dependent oxidative burst in normal and inflammatory disease effector cells.     

Computer simulation for studying calcium dependent abnormalities in firing mechanism of molluscan neurones

Computer modelling technique is proposed to assist in physiological research on invertebrate neuronal membranes. The firing mechanism of a single patch of invertebrate neuronal membrane has been studied in dependence on maximum Ca++ conductance. The calculations are based on modification of Hodgkin-Huxley's data completed by a straight line approximation between experimental points of the kinetic parameters of Ca++ current and early transient potassium current. The time course of conductance changes is assumed to be proportional to m2h for Ca++ current. Three distinct potassium currents are involved into the model, viz. transient potassium current, delayed potassium current and Ca++-dependent potassium current. The modified Euler method run on a digital computer has been used for numerical integration of kinetic equations. Significant effects of Ca++ conductance on spike broadening, plateau development and spike afterhyperpolarization are represented. In the range of small Ca++ conductance an infinite spontaneous activity can be triggered by a short (suprathreshold) current pulse which may be considered a model of pacemaker activity. Plateau development resulting from potassium blocking or decreasing potassium equilibrium is facilitated by Ca++ conductance in the range of greater Ca++ conductance. The effects of voltage sensitivity of the coupling coefficient describing the current of Ca++-dependent K+ channels were studied and compared to the voltage independent case. The coupling coefficient seems to be a crucial factor in broadening the range of Ca++ conductance responsible for pacemaker activity. For greater values of Ca++ conductance, a decrease of the coupling coefficient leads to a transition from prolonged bursting to interruption of burst activity by burst-afterhyperpolarization. The blocking effect of 4-aminopyridine on fast outward current has been studied by the model which has a practical significance considering that aminopyridine is known as a convulsive agent. We suppose that it is reasonable to study the convulsive effects of aminopyridine by the model based on the kinetics of the isolated neuronal membrane. The model may help in understanding the ionic background underlying abnormal network activity during epileptic discharges of mammalian neurones.     

Factors affecting slow regular firing in the suprachiasmatic nucleus in vitro

In isolated slices of hypothalamus, suprachiasmatic nucleus (SCN) neurons were recorded intracellularly. Blockade of Ca++ channels increased spike duration, eliminating an early component of the afterhyperpolarization (AHP) that followed evoked spikes. The duration and reversal potential of AHPs were, however, unaffected, suggesting that only an early, fast component of the AHP was Ca(++)-dependent. Unlike other central neurons that exhibit pacemaker activity, therefore, SCN neurons do not display a pronounced, long-lasting Ca(++)-dependent AHP. Extracellular Ba++ and intracellular Cs+ both revealed slow depolarizing potentials evoked either by depolarizing current injection, or by repolarization following large hyperpolarizations. They had different effects on the shape of spikes and the AHPs that followed them, however. Cs+, which blocks almost all K+ channels, dramatically reduced resting potential, greatly increased spike duration (to tens of milliseconds), and blocked AHPs completely. In contrast, Ba++ had little effect on resting potential and produced only a small increase in spike duration, depressing an early Ca(++)-dependent component and a later Ca(++)-independent component of the AHP. The relatively weak pacemaker activity of SCN neurons appears to involve voltage-dependent activation of at least one slowly inactivating inward current, which brings the cells to firing threshold and maintains tonic firing; both Ca(++)-dependent and Ca(++)-independent K+ channels, which repolarize cells after spikes and maintain interspike intervals; and Ca++ channels, which contribute to activation of Ca(++)-activated K+ currents and may also contribute to slow depolarizing potentials. In the absence of powerful synaptic inputs, SCN neurons express a pacemaker activity that is sufficient to maintain an impressively regular firing pattern. Slow, repetitive activation of optic input, however, increases local circuit activity to such an extent that the normal pacemaker potentials are overridden and firing patterns are altered. Since SCN neurons are very small and have large input resistances, they are particularly susceptible to synaptic input.     

Pattern of response in neurosecretory cells of the rat hypothalamic supraoptic nucleus to subiculum stimulation under water deprivation

The effects of water deprivation were investigated in the pattern of response produced by subiculum stimulation in antidromically identified hypothalamic supraoptic neurosecretory cells of lactating rats. In dehydrated animals as compared with the controls, the percentage of neurons responding to subiculum stimulation with an inhibitory action (blockade of antidromic action potential) remained unchanged, although the proportion of differing inhibitory response did alter: numbers of cells with gradually developing inhibitory response increased significantly and fewer cells showed transitory development of inhibition. Inhibitory response emerging as depression of background spike activity showed a quantitative increase, moreover. Plasticity was found to be one distinguishing feature of afferent input from the subiculum to supraoptic nucleus neurosecretory cells and, in particular, a capacity for reorganization under water deprivation.A. A. Ukhtomskii Institute of Physiology, State University, Leningrad. Translated from Neirofiziologiya, Vol. 22, No. 2, pp. 243–249, March–April, 1990.     

Amplitude-dependent spike-broadening and enhanced Ca(2+) signaling in GnRH-secreting neurons

In GnRH-secreting (GT1) neurons, activation of Ca(2+)-mobilizing receptors induces a sustained membrane depolarization that shifts the profile of the action potential (AP) waveform from sharp, high-amplitude to broad, low-amplitude spikes. Here we characterize this shift in the firing pattern and its impact on Ca(2+) influx experimentally by using prerecorded sharp and broad APs as the voltage-clamp command pulse. As a quantitative test of the experimental data, a mathematical model based on the membrane and ionic current properties of GT1 neurons was also used. Both experimental and modeling results indicated that inactivation of the tetrodotoxin-sensitive Na(+) channels by sustained depolarization accounted for a reduction in the amplitude of the spike upstroke. The ensuing decrease in tetraethylammonium-sensitive K(+) current activation slowed membrane repolarization, leading to AP broadening. This change in firing pattern increased the total L-type Ca(2+) current and facilitated AP-driven Ca(2+) entry. The leftward shift in the current-voltage relation of the L-type Ca(2+) channels expressed in GT1 cells allowed the depolarization-induced AP broadening to facilitate Ca(2+) entry despite a decrease in spike amplitude. Thus the gating properties of the L-type Ca(2+) channels expressed in GT1 neurons are suitable for promoting AP-driven Ca(2+) influx in receptor- and non-receptor-depolarized cells.     

Profound alterations in the intrinsic excitability of cerebellar Purkinje neurons following neurotoxin 3-acetylpyridine (3-AP)-induced ataxia in rat: new insights into the role of small conductance K+ channels

Alterations in the intrinsic properties of Purkinje cells (PCs) may contribute to the abnormal motor performance observed in ataxic rats. To investigate whether such changes in the intrinsic neuronal excitability could be attributed to the role of Ca(2+)-activated K(+) channels (K(Ca)), whole cell current clamp recordings were made from PCs in cerebellar slices of control and ataxic rats. 3-AP induced profound alterations in the intrinsic properties of PCs, as evidenced by a significant increase in both the membrane input resistance and the initial discharge frequency, along with the disruption of the firing regularity. In control PCs, the blockade of small conductance K(Ca) channels by UCL1684 resulted in a significant increase in the membrane input resistance, action potential (AP) half-width, time to peak of the AP and initial discharge frequency. SK channel blockade also significantly decreased the neuronal discharge regularity, the peak amplitude of the AP, the amplitude of the afterhyperpolarization and the spike frequency adaptation ratio. In contrast, in ataxic rats, both the firing regularity and the initial firing frequency were significantly increased by the blockade of SK channels. In conclusion, ataxia may arise from alterations in the functional contribution of SK channels, to the intrinsic properties of PCs.     

Immunohistochemical Study of Immunophilin 1–15 Fragment in Intact Frog Brain,and in the Brain and Spinal Cord of Intact and Spinal Cord Hemisectioned Rats

Previously by immunohistochemical technique the distribution of immunophilin 1–15 fragment (IphF) isolated from bovine hypothalamus was examined in various tissues (heart, lung), including immune system organs (spleen and thymus) of intact rats. IphF-like immunoreactivity (IphF-LI) was revealed in several cell types: lymphocytes, monocytes, macrophages and mast cells. In the present study the immunohistochemical localization of IphF was examined in intact rat and frog brains. In rat brain several cell groups concentrated particularly in the supraoptic nucleus (SON) of hypothalamus, medulla oblongata (reticular formation, olives, hypoglossal and facial motor nuclei) and cerebellum (lateral cerebellar nucleus) demonstrated IphF-LI. In frog hypothalamus (SON) the same working dilution (1:5000) of IphF-antiserum revealed very strong immunoreactivity. In the paraventricular nucleus (PVN) IphF-LI varicosities were scattered around the immunonegative cells. The second cell groups showing IphF-LI in the frog brain were gliocytes (mainly the astrocytes). Besides, IphF distribution was investigated in rats subjected to hemisection of spinal cord (SC) with and without administration of proline-rich polypeptide (PRP). PRP was isolated from bovine neurohypophysis neurosecretory granules, produced by magnocellular nuclei of hypothalamus. Hemisection of SC led to changes of IphF distribution in the hypothalamus. In PRP treated animals IphF showed no immunoreactivity. PRP is suggested to act as a neurotransmitter and neuroregulator.     

Testing excitability in human firing motoneurons during the interspike interval

Monosynaptic testing of excitability in firing triceps surae muscle motoneurons activated during volitional contraction was performed using a technique for recording potentials from single motor units and by producing H-reflex. Motoneuronal excitability was assessed according to level of firing index. Motoneuronal firing index decreased during transition from a low background rhythmic firing rate of less than 6 spikes/sec to one of 6–8 spikes/sec. It hardly changed with a further rise in rate to 12 spikes/sec. The dependence between firing index and spike rate are put down to changes occurring in motoneuronal excitability during the interspike interval. Findings indicate that in the low frequency range of motoneuronal firing characteristic of natural muscle contraction, discharge rate may be considered one of the factors determining excitability in the motoneuron and hence its transmission qualities.Institute of Problems in Information Transmission, Academy of Sciences of the USSR. Translated from Neirofiziologiya, Vol. 19, No. 2, pp. 210–216, March–April, 1987.     

Predicting the Responses of Repetitively Firing Neurons to Current Noise

We used phase resetting methods to predict firing patterns of rat subthalamic nucleus (STN) neurons when their rhythmic firing was densely perturbed by noise. We applied sequences of contiguous brief (0.5–2 ms) current pulses with amplitudes drawn from a Gaussian distribution (10–100 pA standard deviation) to autonomously firing STN neurons in slices. Current noise sequences increased the variability of spike times with little or no effect on the average firing rate. We measured the infinitesimal phase resetting curve (PRC) for each neuron using a noise-based method. A phase model consisting of only a firing rate and PRC was very accurate at predicting spike timing, accounting for more than 80% of spike time variance and reliably reproducing the spike-to-spike pattern of irregular firing. An approximation for the evolution of phase was used to predict the effect of firing rate and noise parameters on spike timing variability. It quantitatively predicted changes in variability of interspike intervals with variation in noise amplitude, pulse duration and firing rate over the normal range of STN spontaneous rates. When constant current was used to drive the cells to higher rates, the PRC was altered in size and shape and accurate predictions of the effects of noise relied on incorporating these changes into the prediction. Application of rate-neutral changes in conductance showed that changes in PRC shape arise from conductance changes known to accompany rate increases in STN neurons, rather than the rate increases themselves. Our results show that firing patterns of densely perturbed oscillators cannot readily be distinguished from those of neurons randomly excited to fire from the rest state. The spike timing of repetitively firing neurons may be quantitatively predicted from the input and their PRCs, even when they are so densely perturbed that they no longer fire rhythmically.     

Effects of acetylcholine and cholinergic transmission blockers on neuronal spike activity in the cat motor cortex associated with conditioned reflex

The effects of direct application of acetylcholine (ACh) and m- and n-cholinoreceptor blockers on test cells were investigated in waking cats having developed instrumental lever-pressing conditioned reflex. Changes were recorded in both spontaneous and invoked firing activity in a functionally homogeneous group of motor cortex cells, in which increased discharge rate usually preceded the start of conditioned reflex movements. It was found, however, that ACh increased spontaneous activity considerably in some of the neurons tested and reduced it moderately in others. Atropine sharply reduced background activity in cortical neurons while preserving spike response to presentation of a conditioned stimulus and n-cholino-blockers such as hexonium and (occasionally) tubocurarine inhibited spike response produced by conditioned stimuli; background activity was slightly inhibited by hexonium and reinforced by tubocurarine. It was concluded that ACh put out by cholinergic fibers helps to maintain background firing activity level in cortical neurons under naturally occurring conditions, acting via m-cholinoreceptors, whereas factors influencing generation of spike discharges associated with performance of conditioned reflex movements are mediated by n-cholinoreceptors.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 21, No. 5, pp. 579–589, September–October, 1989.     

Enhancement of spike-timing precision by autaptic transmission in neocortical inhibitory interneurons

In vivo studies suggest that precise firing of neurons is important for correct sensory representation. Principal neocortical neurons fire imprecisely when repeatedly activated by fixed sensory stimuli or current depolarizations. Here we show that in contrast to pyramidal neurons, firing in neocortical GABAergic fast-spiking (FS) interneurons is quite precise. FS interneurons are self-innervated by powerful GABAergic autaptic connections reliably activated after each spike, suggesting that autapses strongly regulate FS-cell spike timing. Indeed, blockade of autaptic transmission degraded temporal precision in multiple ways. Under these conditions, realistic dynamic-clamp hyperpolarizing autapses restored precision of spike timing, even in the presence of synaptic noise. Furthermore, firing precision was increased in pyramidal neurons by artificial GABAergic autaptic conductances, suggesting that tightly coupled synaptic feedback inhibition regulates spike timing in principal cells. Thus, well-timed inhibition, whether autaptic or synaptic, facilitates precise spike timing and promotes synchronized cortical network oscillations relevant to several behaviors.     

Firing rhythmicity in the neocortex in vivo and in vitro under sustained iontophoretic excitation

Extracellular recordings were made from the cat intact neocortex and guinea-pig neocortical slices during microiontophoretic application of amino acid neurotransmitters. Spike train autocorrelation analysis showed a high stability of firing patterns in the intact neocortex. When excitation of a cell was increased in a step-wise manner with glutamate iontophoresis only an enhancement of the rate of firing was observed. The rhythmic component, which was mainly due to periodic multiple discharges, remained up to the highest firing frequencies. In contrast to the in vivo observation, glutamate, aspartate or K⁺ iontophoresis in cortical slices resulted in firing pattern alternations (always from bursts or irregular activity to regular spike firing) as well as an increase in firing rate. In slices the periodic component was typically due to single-spike regularity and its frequency rose with an increase of firing rate. The comparison of autocorrelogram alternations in vivo and in vitro suggests that the temporal organization of spike trains in the intact cortex is under tight external control and is defined mainly by neuronal interactions, whereas virtually all the neurons in vitro are very sensitive to the same iontophoretic influences and their individual outputs easily change according to the excitation (depolarization) level. The coincidence of the lowest frequencies of single-spike regularity in the in vitro preparation (5–7 Hz and 8–10 Hz) with theta- and alpha-rhythms in the electroencephalogram (EEG), and with single unit firing rhythmicity in the whole brain, may represent the basis of a unit-circuit resonance and provide a high stability of these EEG-rhythms.Abbreviations ACF autocorrelation function - BFA background firing activity - EEG electroencephalogram     

Ionic basis of methacholine-induced shrinkage of dissociated eccrine clear cells

Summary Apical membrane currents were recorded from the taste pore of single taste buds maintained in the tongue of the rat, using a novel approach. Under a dissection microscope, the 150-m opening of a saline-filled glass pipette was positioned onto single fungiform papillae, while the mucosal surface outside the pipette was kept dry. Electrical responses of receptor cells to chemical stimuli, delivered from the pipette, were recorded through the pipette while the cells remained undamaged in their natural environment. We observed monophasic transient currents of 10-msec duration and 10–100 pA amplitude, apparently driven by action potentials arising spontaneously in the receptor cells. When perfusing the pipette with a solution of increased Na but unchanged Cl concentration, a stationary inward current (from pipette to taste cell) of 50–900 pA developed and the collective spike rate of the receptor cells increased. At a mucosal Na concentration of 250mm, the maximal collective spike rate of a bud was in the range of 6–10 sec^–1. In a phasic/tonic response, the high initial rate was followed by an adaptive decrease to 0.5–2 sec^–1. Buds of pure phasic response were also observed. Amiloride (30 m) present in the pipette solution reversibly and completely blocked the increase in spike rate induced by mucosal Na. Amiloride also decreased reversibly the stationary current which depended on the presence of mucosal Na (inhibition constant near 1 m). During washout of amiloride, spike amplitudes were first small, then increased, but always remained smaller than the amiloride-blockable stationary current of the bud. This is understandable since the stationary current of a bud arises from a multitude of taste cells, while each current spike is presumably generated by just one taste cell. We suggest that, in a Na-sensitive receptor cell, (i) the apical amiloride-blockable Na inward current serves as a generator current causing cell depolarization and firing of action potentials, and (ii) each current spike recorded from the taste pore arises mainly from a modulation of the apical Na inward current of this cell, because the action potential generated by the taste cell will transiently decrease or abolish the driving force for the apical Na inward current. The transients are indicators of receptor cell action potentials, which appear to be physiological responses of taste cellsin situ.     

Antidromic indentification of hypothalamic neurosecretory cells in rats

Characteristics of antidromic action potentials of neurons of the paraventricular and supraoptic nuclei of the rat hypothalamus were studied during stimulation of the hypothalamo-hypophyseal tract by stimuli of varied amplitude and frequency. Step-like changes were found in spike latency in response to an increase in strength (up to 1.5–2.5 thresholds) or frequency (over 100 Hz) of stimulation, as well as cases with variation of the degree of division of the peak into A and B components. Injection of leu-enkephalin analog into the third ventricle or intravenous injection of NaCl solution (1 M) caused reversible changes in the level of excitability of antidromically activated neurons: leu-enkephalin mainly increased the latent period and threshold of action potential generation and reduced the reproducible frequency of stimulation to 10 Hz, whereas NaCl had the opposite effect. The results indicate that when the adopted criteria of antidromic identification of neurosecretory cells are used the level of their excitability must be taken into account.A. A. Ukhtomskii Physiological Research Institute, A. A. Zhdanov Leningrad State University. Translated from Neirofiziologiya, Vol. 14, No. 6, pp. 585–591, November–December, 1982.     

Background firing in cortical neurons with blockade of synaptic inhibition in guinea pig neocortical slices maintained in vitro

The effects of 100 µM picrotoxin on neuronal background firing were investigated in guinea pig neocortical slices maintained in vitro. Picrotoxin or bicuculline application is known to bring about an abrupt increase in background firing or the onset of spontaneous epileptiform volleys at a higher excitatory and inhibitory level in the in vivo than in the in vitro cortex. Blocking GABA-ergic inhibition hardly affected the pattern of background spike trains, although stimuli-induced response did become epileptiform. Findings from this research would thus indicate that any inhibitory processes taking place during in vitro background activity are only very slight and exert no significant effect on this activity.Institute of Biological Physics, Academy of Sciences of the USSR, Pushchino. Translated from Neirofiziologiya, Vol. 21, No. 1, pp. 16–24, January–February, 1989.     

Potassium currents in presynaptic hair cells of Hermissenda.

Apart from their primary function as balance sensors, Hermissenda hair cells are presynaptic neurons involved in the Ca(2+)-dependent neuronal plasticity in postsynaptic B photoreceptors that accompanies classical conditioning. With a view to beginning to understand presynaptic mechanisms of plasticity in the vestibulo-visual system, a locus for conditioning-induced neuronal plasticity, outward currents that may govern the excitability of hair cells were recorded by means of a whole-cell patch-clamp technique. Three K+ currents were characterized: a 4-aminopyridine-sensitive transient outward K+ current (IA), a tetraethyl ammonium-sensitive delayed rectifier K+ current (IK,V), and a Ca(2+)-activated K+ current (IK,Ca). IA activates and decays rapidly; the steady-state activation and inactivation curves of the current reveal a window current close to the apparent resting voltage of the hair cells, suggesting that the current is partially activated at rest. By modulating firing frequency and perhaps damping membrane oscillations, IA may regulate synaptic release at baseline. In contrast, IK,V and IK,Ca have slow onset and exhibit little or no inactivation. These two K+ currents may determine the duration of the repolarization phase of hair-cell action potentials and hence synaptic release via Ca2+ influx through voltage-gated Ca2+ channels. In addition, IK,Ca may be responsible for the afterhyperpolarization of hair cell membrane voltage following prolonged stimulation.     

The hypothalamic magnocellular system in the domestic fowl

Summary In the rostral hypothalamus of the domestic fowl, the magnocellular neurosecretory nuclei show a peculiar differentiation. Golgi studies of the supraoptic and paraventricular nuclei of the fowl reveal at least two major cell types: 1) large multipolar neurons, and 2) small interneurons. Golgi impregnations provide a detailed cytoarchitectural picture of the large-sized cells; the latter may well correspond to the neurosecretory cells demonstrated in the same regions by selective staining, and immunocytochemical and electron microscopical techniques.Electron microscopically, neuronal perikarya are observed to contain variable amounts of neurosecretory granules (100–200 nm in diameter; mean diameter of 160 nm) scattered throughout the cytoplasm. The diameters of these granules do not differ statistically in the two principal nuclear areas examined. The perikarya of these neurons display only a few axosomatic synapses containing electron-lucent and dense-cored vesicles (70–90 nm in diameter). Numerous nerve terminals of this type also end on the dendritic ramifications in the surrounding neuropil.     

Firing activity of "diapause hormone" producing cells in the male silkmoth,Bombyx mori

Diapause hormone (DH) originally identified to be a factor originating from neurosecretory cells in the suboesophageal ganglion acts on developing ovaries to produce diapause eggs in a female silkmoth, Bombyx mori. A male silkmoth has homologous neurosecretory cells, but little is known of the physiological nature of the cells and actions of their products. We examined the long-term firing activity of putative DH-producing neurosecretory cells and hormonal activity of their products in male pupae that had been experienced different environmental regimens for diapause induction. Firing activity patterns of male labial cells strongly depended on diapause types of pupae: cells in a diapause-type male were active throughout the pupal period, whereas the same cells in a non-diapause-type male were usually inactive during the early two-thirds of the pupal period. A male pupa with electrically active labial cells could induce diapause eggs in a female pupa connected parabiotically to that male. The firing activity of male neurosecretory cells and hormonal action of their products are qualitatively the same as in the female previously examined. We suggest that there is no evident sexual dimorphism in the physiological and biochemical nature of neurosecretory cells producing DH and the amidated peptide DH has different functions in a male.