Reactivity of the cholinoceptive cortical neurons to the repeated action of acetylcholine

Three groups of sensorimotor cortical cholinoceptive neurons have been established in albino rats according to the dynamics of reactivity to repeated action of acetylcholine. There are neurons with decreased, increased or unchanged response to transmitter microintophoretic application. Dependence of the dynamics of background and evoked activity on the duration of excitatory reaction component induced by transmitter has been discovered. It was concluded that the duration of the given component is a significant and informative functional parameter of cortical neurons.     

Reactivity of the cortical neurons to acetylcholine in rats

Activity of 55 neurons of the sensorimotor cerebral cortex of rats was recorded at iontophoretic application of acetylcholine. 36% of neurons exhibited an excitatory reaction, 30%--inhibitory-excitatory, 18%--inhibitory-excitatory-inhibitory and 16%--excitatory-inhibitory reactions; the type of reaction, in contrast to its expressiveness, did not depend on the the type of reaction, in contrast to its expressiveness, did not depend on the strength of phoresis current. Duration of the excitatory components entering reactions of all neurons formed a continuous series of values in the range of 1.4 to 16 s and had 2 maxima--at the 4-th and 8-th seconds. It is suggested that duration of this component of reaction reflects important functional properties of the nerve cell.     

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.     

Characteristics of the increased response to electrical stimulation of ileum preparations from morphine pretreated guinea pigs.

The relationship between electrical stimulus voltage or pulse duration and the tension generated in the resulting contractions has been studied in control and morphine tolerant guinea pig ileum preparations. A greater maximal tension was observed in the morphine tolerant preparations. Since the response of the preparations to exogenous applied acetylcholine was unchanged, the increase in tension probably reflected an increase in the amount of acetylcholine released by each stimulus. No change in threshold voltage for stimulation was observed. A neuronally mediated, opiate insensitive, component of the response to electrical stimulation has been demonstrated. This component was unchanged in morphine tolerant preparations. Naloxone did not affect the relationship between stimulus pulse duration and response tension in control or morphine tolerant preparations. These results provide further evidence that morphine tolerance is associated with general changes in the properties of opiate sensitive neurons which can be demonstrated in the absence of opiate drugs.     

GABA-mediated echo duration selectivity of inferior collicular neurons of Eptesicus fuscus, determined with single pulses and pulse–echo pairs

When insectivorous bats such as Eptesicus fuscus emit ultrasonic signals and analyze the returning echoes to hunt insects, duration selectivity of auditory neurons plays an important role in echo recognition. The success of prey capture indicates that they can effectively encode progressively shortened echo duration throughout the hunting process. The present study examines the echo duration selectivity of neurons in the central nucleus of the bat inferior colliculus (IC) under stimulation conditions of single pulses and pulse–echo (P–E) pairs. This study also examines the role of gamma-aminobutyric acid (GABA)ergic inhibition in shaping echo duration selectivity of IC neurons. The data obtained show that the echo duration selectivity of IC neurons is sharper when determined with P–E pairs than with single pulses. Echo duration selectivity also sharpens with shortening of pulse duration and P–E gap. Bicuculline application decreases and GABA application increases echo duration selectivity of IC neurons. The degree of change in echo duration selectivity progressively increases with shortening of pulse duration and P–E gap during bicuculline application while the opposite is observed during the GABA application. These data indicate that the GABAergic inhibition contributes to sharpening of echo duration selectivity of IC neurons and facilitates echo recognition by bats throughout different phases of hunting.     

Bicuculline application affects discharge pattern and pulse-duration tuning characteristics of bat inferior collicular neurons

This study examines the contribution of GABAergic inhibition to the discharge pattern and pulse duration tuning characteristics of 101 bat inferior collicular neurons by means of bicuculline application to their recording sites. When stimulated with single pulses, 56 (55%) neurons discharged 1 or 2 impulses (phasic responders), 42 (42%) discharged 3–10 impulses (phasic bursters) and 3 (3%) discharged impulses throughout the stimulus duration (tonic responders). Bicuculline application increased the number of impulses and changed the discharge patterns of 66 neurons. Using 50% difference between maximal and minimal responses as a criterion, the duration tuning characteristics of these neurons can be described as band-pass (20, 20%), long-pass (17, 17%), short-pass (33, 32%), and all-pass (31, 31%). Each band-pass neuron discharged maximally to a specific duration (the best duration) which was at least 50% larger than the neuron's responses to a long-duration pulse and a short-duration pulse. In contrast, each long- or short-pass neuron discharged maximally to a range of long or short duration pulses. Bicuculline application changed the duration tuning characteristics of 65 neurons. Possible mechanisms underlying duration tuning characteristics and the behavioral relevance to bat echolocation are discussed. Accepted: 4 November 1998     

Postnatal changes in the overall postsynaptic currents evoked in CA1 pyramidal neurons of the rat hippocampus

Evoked fast postsynaptic currents (fPSCs) during the postnatal development of rats (postnatal day 6-70, P6-P70) were systematically examined in hippocampal CA1 pyramidal neurons using whole-cell recordings with biocytin-filled electrodes. Focal stimulation of the stratum radiatum in the CA1 region elicited fPSCs in 80% of the neurons P6-7, 90% of P9-10, and 100% of > or =P11. In neurons P6-7, the fPSCs were exclusively inward and had multiple (on average 5.6) peaks. The fPSCs increased in amplitude with the growth of dendritic arborization, but decreased in the number of peaks. A distinct outward fPSC following the inward fPSC emerged in neurons > or =P11 and was abolished by bicuculline (50 microM). Bicuculline increased the amplitude and duration of the initial inward fPSC (fEPSC) in all age groups and characteristically recruited the polysynaptic second component of fEPSCs in neurons P11-P21. No spontaneous periodic inward current was detected in any age group after blocking GABAA receptors. The coapplication of DL-2-amino-5-phosphonopentanoic acid (AP5, 100 microM) with bicuculline did not eliminate the polysynaptic second component, but the second component was only elicited in slices in which the CA3 region was kept intact. Moreover, the bicuculline- and AP5-resistant second component was due to the burst activity of CA3 pyramidal neurons, which were excited through excitatory recurrents of the Schaffer collaterals. Plausible physiological functions of the generation of the second component in vivo were discussed.     

Processing of sensory signals by a non-spiking neuron in the leech

The non-spiking neurons 151 are present as bilateral pairs in each midbody ganglion of the leech nervous system and they are electrically coupled to several motorneurons. Intracellular recordings were used to investigate how these neurons process input from the mechanosensory P neurons in isolated ganglia. Induction of spike trains (15 Hz) in single P cells evoked responses that combined depolarizing and hyperpolarizing phases in cells 151. The phasic depolarizations, transmitted through spiking interneurons, reversed at around -20 mV. The hyperpolarization had two components, both reversing at around -65 mV, and which were inhibited by strychnine (10 micromol l(-1)). The faster component was transmitted through spiking interneurons and the slower component through a direct P-151 interaction. Short trains (<400 ms) of P cell spikes (15 Hz) evoked the phasic depolarizations superimposed on the hyperpolarization, while long spike trains (>500 ms) produced a succession of depolarizations that masked the hyperpolarizing phase. The amplitude and duration of the hyperpolarization reached their maximum at the initial spikes in a train, while the depolarizations persisted throughout the duration of the stimulus train. Both phases of the response were relatively unaffected by the spike frequency (5-25 Hz). The non-spiking neurons 151 processed the sensory signals in the temporal rather than in the amplitude domain.     

Temporally patterned pulse trains affect directional sensitivity of inferior collicular neurons of the big brown bat, Eptesicus fuscus

The directional sensitivity of inferior collicular neurons of the big brown bat, Eptesicus fuscus, was studied under free field stimulation conditions with 3 temporally patterned trains of sound pulses which differed in pulse repetition rate and duration. The directional sensitivity curves of 92 neurons studied can be described as hemifield, directionally-selective, or non-directional according to the variation in the number of impulses with pulse train direction. When these neurons were stimulated with all 3 pulse trains, the directional sensitivity curves of 50 neurons was unchanged but that of the other 42 neurons changed from one type into another. When these pulse trains were delivered at high pulse repetition rate and short pulse duration, they significantly sharpened the directional sensitivity of two thirds of the neurons examined by reducing the angular range and increasing the slope of their impulse directional sensitivity curves. These pulse trains also sharpened the slope of the threshold directional sensitivity curves of 25 neurons studied. However, when directional sensitivity of collicular neurons was determined with pulse trains that differed only in pulse repetition rate or in pulse duration, significant sharpening of directional sensitivity was rarely observed in all experimental conditions tested. Possible mechanisms underlying these findings are discussed.     

Inhibitory and activatory effects of dopamine on neurons in slices of the compact zone of theSubstantia nigra of rats

Effects of dopamine on the background spike activity of functionally (according to their electrophysiological characteristics) identified dopaminergic (DA) or non-dopaminergic (non-DA) neurons of the compact zone of thesubstantia nigra were studied on slices of the midbrain of adult rats. In the majority of DA neurons, dopamine suppressed the background activity in a dose-dependent manner. Sensitivity of these cells to dopamine varied within a wide range: IC₅₀, the concentration providing the 50% maximum effect, equalled from 3 to 3,000 µM in different units. A part of DA neurons responded to dopamine with an increase in their activity. Mixed responses, in which an initial suppression of impulsation was replaced by a slow-developing activation, was observed in some neurons. Non-DA neurons usually responded to dopamine by an enhancement of impulsation; yet, the cells with inhibitory or mixed responses similar to those of DA neurons could be found in this population as well. Sensitivity of non-DA neurons to dopamine was about the same as that of DA-cells, without the dependence on the direction of responses. S(–)-suipiride, a blocker of D₂ receptors, decreased the inhibitory component of all tested responses to dopamine both in DA and non-DA neurons and evoked no changes in the excitatory component. At the same time, R(+)-SCH 23390 HC1, a blocker of D₁ receptors, suppressed the activatory component of responses with no effect on the inhibitory component. We conclude that both types of DA receptors, D₂ and D₁ receptors, can be present on the DA and non-DA neurons. Dopamine, influencing these receptors, suppresses or facilitates, respectively, the spike activity of these cells. The relative amount of such receptors is the main factor determining the pattern and dynamics of the integral response to dopamine application. The possible functional role of the presence of both D₁ and D₂ receptors on the membrane of a single neuron is discussed.Neirofiziologiya/Neurophysiology, Vol. 27, No. 4, pp. 268–277, July–August, 1995.     

GABAergic inhibition shapes frequency tuning and modifies response properties in the superior olivary nucleus of the leopard frog

The role of gamma-aminobutyric acid (GABA)ergic inhibition in shaping the excitatory frequency tuning of 74 neurons in the superior olivary nucleus of the leopard frog, Rana pipiens, was studied using iontophoretic application of the GABA(A) receptor antagonist, bicuculline methiodide. For 37 neurons, bicuculline application broadened and/or changed the configuration of the excitatory frequency-tuning curve. Results indicate that GABA-mediated inhibition not only sharpens the tuning curves of neurons but also plays a critical role in creating new frequency tuning properties in the superior olivary nucleus. Bicuculline application affected other neuronal response properties as well. Spontaneous firing rate increased 11-338% for 18 of 59 neurons. For 32 of 58 neurons there was an increase in stimulus-evoked discharge rate and a change in rate-level function. There was no qualitative effect on the discharge pattern of 60 neurons, though 2 tonically responding neurons did show an increase (> 30%) in response duration. Additional roles for GABAergic inhibition in monaural signal analysis are discussed.     

Neuronal activity of the external oculomotor nucleus during saccadic eye movement in the waking cat

The activity of antidromically identified abducens nucleus motoneurons and inter-nuclear neurons has been recorded during saccadic eye movements in the alert cat. The activity of these neurons has been demonstrated to be the sum of a velocity component proportional to eye velocity plus a position component proportional to instantaneous eye position during the movement. Results are discussed in relation to proposed models about the generation of saccadic eye movements.     

Analysis of function of the glutamatergic and GABAergic mediator systems in the olfactory cortex of spontaneously hipertensive rats in vitro

The effect of persistent hypertension on neuronal activity and synaptic transmission has been studied on olfactory cortex slices of SHR rats. The profilies of focal potentials in hypertensive rats demonstrated a short duration of the 2-amino-3-(5-methyl-3-hydroxyisoxazol-4-yl)-propanoic acid (AMPA) component of excitatory postsynaptic potential (EPSP), a small amplitude and long duration of the N-methyl D-aspartate (NMDA) component of EPSP, and a large amplitude of the GABA_B-dependent slow inhibitory postsynaptic potentials. The sensitivity of glutamate receptors responsible for the generation of AMPA- and NMDA-mediated EPSPs was low after the exposure to 1 mM L-glutamate. The amplitudes of the AMPA- and NMDA-mediated EPSPs decreased. Tetanization of slices from hypertensive rats induced a short-term potentiation followed by a depression. The data obtained indicate that persistent hypertension has depressive effects on the basic glutamatergic and GABAergic parameters of synaptic activity of neurons as well as on learning and memory. Apparently, these processes were evoked by glutamate excitotoxicity in the brain of hypertensive rats.     

Automated Food-Procuring Movement-Related Neuronal Activity in the Basolateral Amygdala of the Rat

We studied the impulse activity of neurons of the basal and lateral amygdalar nuclei generated when experimental animals (rats) performed fast stereotyped food-procuring movements by the forelimb. Within the basolateral amygdala, there are neurons whose activity is related to different stages of getting off the food, and according to the characteristics of their spiking these neurons should be divided into a number of subpopulations. Activation forestalling the movement initiation by 0.5-1.0 sec was observed in most neurons of the basolateral amygdala; this is considered a manifestation of excitation related to a motivation component of the food-procuring behavior. Activation of amygdalar neurons following movement initiation can result from generation in this structure of additional excitation necessary for successful performance of a complete food-procuring motor cycle.     

A Stochastic Model of the Repetitive Activity of Neurons

A recurrent model of the repetitive firing of neurons responding to stimuli of long duration is given. The model assumes a deterministic threshold potential and a membrane potential which is composed of both deterministic and random components. The model accurately reproduces interval statistics obtained from different neurons discharging repetitively over a wide range of discharge rates. It is shown that the model has three important parameters; the time course of threshold recovery following a discharge, the variance of the random component, and the level of excitatory drive. The model is extended, by the use of hyperpolarizing afterpotentials, to include negative correlation between successive interspike intervals.     

Recovery cycle of neurons in the inferior colliculus of the FM bat determined with varied pulse-echo duration and amplitude

The recovery cycle of auditory neurons is an important neuronal property which underlies a bat's ability in analyzing returning echoes and to determine target distance (i.e., echo ranging). In the same token, duration selectivity of auditory neurons plays an important role in pulse recognition in bat echolocation. Because insectivorous bats progressively vary the pulse parameters (repetition rate, duration, and amplitude) during hunting, the recovery cycle of auditory neurons is inevitably affected by their selectivity to other co-varying echo parameters. This study examines the effect of pulse duration and amplitude on recovery cycle of neurons in the central nucleus of the inferior colliculus (IC) of the FM bat, Pipistrellus abramus, using biologically relevant pulse-echo (P-E) pairs with varied duration and amplitude difference. We specifically examine how duration selectivity may affect a neuron's recovery cycle. IC neurons have wide range of recovery cycle and best duration (BD) covering P-E intervals and duration occurring different phases of hunting. The recovery cycle of most IC neurons increases with P-E duration and amplitude difference. Most duration-selective IC neurons recover rapidly when stimulated with biologically relevant P-E pairs. As such, neurons with short BD recover rapidly when stimulated with P-E pairs of short duration and small P-E amplitude difference. Conversely, neurons with long BD recover rapidly when stimulated with P-E pairs of long duration and large P-E amplitude difference. These data suggest that bats may potentially utilize the response of IC neurons with different BD and recovery cycle to effectively perform echo detection, recognition of echo duration and echo ranging throughout a target approaching sequence.     

Some effects of proctolin on the cardiac ganglion of the Maine Lobster, Homarus americanus (Milne Edwards)

The neuropeptide proctolin has excitatory effects on the isolated lobster cardiac ganglion. Selective application to the anterior cell body region produces a dose-dependent (10(-8)--10(-5) M) prolonged depolarization of large anterior cells as well as marked increases in burst frequency and/or duration. In ganglia which have been silenced with tetrodotoxin, proctolin application to anterior cells elicits long-lasting depolarizing responses which are accompanied by a 10-30% increase of the apparent membrane input resistance. Higher proctolin concentrations produce high-frequency trains of driver potentials. It is proposed that a proctolin like peptide may serve a neurohumoral role in the lobster cardiac ganglion and that the anterior motor neurons exhibit endogenous rhythmicity in its presence.     

The effect of oxytocin on potential-dependent calcium current in snail neurons, Helix pomatia.

1. The effect of external application of oxytocin on inward calcium current in dialyzed snail neurons has been investigated under clamp conditions. 2. External application of oxytocin in a dose-dependent manner (Kd 0.9 microM) inhibits inward calcium current in dialyzed neurons of the snail, Helix pomatia. 3. Inhibition of calcium current developed with the time constant of about 2 min. The degree of restoration of calcium current after oxytocin washout depends on duration of oxytocin action. 4. It has been suggested that inhibition of calcium current by oxytocin occurs in two stages, the initial one is more fast and reversible and the second one--more slow and irreversible. The participation of soluble second messengers in the inhibitory effect of oxytocin on calcium current is discussed.     

Evidence for vasoactive intestinal polypeptide (VIP) altering the firing rate of preoptic,septal and midbrain central gray neurons

The effect of the iontophoretic application of vasoactive intestinal polypeptide (VIP) on the extracellular electrical activity (neuronal firing rate) of 91 neurons localized in the preoptic (PO), septal (S) region and midbrain central gray (MCG) was studied in urethane-anesthetized female rats. When applied in minute quantities, VIP induced both excitatory ($\text{N = 14}$) and inhibitory ($\text{N = 8}$) changes in the membrane excitability of PO and S neurons (total $\text{N = 58}$), while only inhibitory ($\text{N = 9}$) changes were observed in the MCG neurons (total $\text{N = 33}$; thus 24 MCG neurons were found to be unresponsive to VIP). The latency and duration of the VIP-induced response was, for the most part, characterized by a rapid onset and persisted for the duration of the ejecting pulse. However, five out of the 58 PO and S neurons and one out of the 33 MCG neurons did show responses that were longer and more variable in latency and duration. Of 26 PO neurons recorded and tested with VIP, only five neurons were determined to be antidromically identified (AI) as having their axons in the median eminence. The application of VIP increased the neuronal firing rate in two AI PO neurons, decreased the activity in one, and was ineffective in altering the activity in two other AI PO neurons. The VIP-induced changes in the neuronal firing rate appear to be specific and reproducible, and not related to the ejecting current nor pH of the solution. The results suggest that VIP, a gastrointestinal hormone that is also localized in the brain, can alter the neuronal firing rate of hypothalamic and midbrain neurons, thus providing additional evidence for its possible influence on brain and neuroendocrine function.     

Neurofilament protein triplet immunoreactivity in the dorsal root ganglia of the guinea-pig

Summary Immunoreactivity for the neurofilament protein triplet was investigated in neurons of the dorsal root ganglia of the guinea-pig by using a battery of antibodies. In unfixed tissue, nearly all neurons in these ganglia demonstrated some degree of neurofilament protein triplet immunoreactivity. Large neurons generally displayed intense immunoreactivity, whereas most small to medium-sized neurons showed faint to moderate immunoreactivity. Double-labelling immunofluorescence demonstrated that most antibodies to the individual subunits of the neurofilament protein triplet had the same distribution and intensity of labelling in sensory neurons. Increasing durations of tissue fixation in aldehyde solutions selectively diminished neurofilament protein triplet immunoreactivity in small to medium-sized neurons. Double-labelling with neurofilament protein triplet antibodies in combination with antibodies to other neuronal markers, such as neuron-specific enolase, substance P and tyrosine hydroxylase, showed that tissue processing conditions affect the degree of co-localization of immunoreactivity to the neurofilament protein triplet and to these other neuronal markers. These results indicate that, with a judicious manipulation of the duration of tissue fixation, neurofilament protein triplet immunoreactivity can be used in combination with other neuronal markers to distinguish groups of neurons according to their size and chemical coding.