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At least 487 records · Page 27Linked to original sources
PubMed1978

Comparison of firing patterns and sensory responsiveness between supraoptic and other hypothalamic neurons in the unanesthetized sheep.

Adult Southdown ewes were surgically prepared with pituitary stimulating electrodes, carotid and jugular cannulae, and a cranial platform-cylinder arrangement for chronic single unit recording. Isolated neurons (n = 112) in the region of the supraoptic nucleus (SON) were identified by pituitary stalk stimulastion as AD + (antidromically invaded) SON neuroendocrine cells (n = 75) or AD--(not antidromically invaded) SON neurons (n = 37). Spontaneous firing pattern distribution and sensory evoked behavior of these SON region neurons were compared with activity recorded from 112 randomly located non-identified neurons of extra-SON areas of the hypothalamus. Spontaneous discharge activity was categorized into six distinct firing pattern types: continuously active slow (CAS), continuously active fast (CAF), continuously active bursting (CAB), continuously active regular (CAR), low frequency bursting (LFB), and high frequency bursting (HFB). These 6 firing pattern types were characterized by computer analysis and their mean order independent statistical parameters compared. Bursting discharge patterns (LFB, HFB, and CAB) were compared with respect to mean burst duration, burst mean firing rate, and interburst interavls. Ninety-three per cent of all neurons maintained a stable discharge pattern in the absence of apparent stimuli. Occasionally CAS and CAF neurons spontaneously generated spike clusters sufficient to give the transient appearance of a bursting discharge pattern and LFB neurons lapsed spontaneously into CAS acitivity. All 6 firing pattern types recorded from non-identified extra-SON neurons were also recorded in the SON region. However, spontaneously discharging AD+ SON neurons exhibited only continuously active slow (CAS), continuously active fast (CAF), and low frequency bursting (LFB) activity. The total absence of high frequency bursting (HFB), continuously active regular (CAR), and continuously active bursting (CAB) patterns of discharge from AD+ SON neurons suggests that AD- SON neurons exhibiting these firing patterns may function as interneurons, pacemaker neurons, or receptor neurons. A significant number of LFB discharging neurons were recorded in widespread extra-SON regions of the hypothalamus, indicating this discharge pattern may not be unique to magnocellular neuroendocrine cells. AD+ SON LFB neurons sampled in this study demonstrated a significantly longer mean interburst interval (20.86 sec) compared to extra-SON LFB neurons (12.43 sec). No AD+ SON neuron tested was significantly sensitive to non-specific sensory arousal or sleep-waking state changes. In extra-SON areas of the hypothalamus, 11 of 75 neurons tested to sensory arousal and 6 of 19 neurons tested to sleep-waking changes responded with significant changes in mean firing rate (MFR); no significant difference between firing pattern types was demonstrated in arousal or sleep-waking sensitivity...

Animals↗
PubMed1993

Firing patterns of nucleus accumbens neurons during cocaine self-administration in rats.

The firing patterns of neurons in the nucleus accumbens (NA) were recorded in rats trained to self-administer cocaine via response contingent intravenous drug infusions. Recordings were obtained from permanently implanted multiple electrode arrays (8 microwires) inserted bilaterally into the NA and/or ventral striatum (NA-VS) in animals exhibiting stable responding (inter-infusion intervals, INT) during test sessions consisting of 16-30 drug delivery episodes. Electronically isolated and identified NA-VS neurons showed distinct patterns of phasic increases in firing relative to the occurrence of the reinforced lever press. Two particular firing patterns, however, were repeatedly encountered in different animals. In one type, a marked increase was observed in discharge following response contingent drug delivery. A second firing pattern showed two distinct temporally separated brief firing peaks (bursts), one immediately prior to the initiation of responding, and the other a brief discharge commencing within 200 ms after the initiation of drug delivery. The time between firing peaks was found to be modifiable by changing the response/reward (FR) ratio for drug delivery. A third finding was that the correlates of the self-administration response were not solely the result of drug infusion since, (1) phasic firing increases were not observed when the drug was delivered non-contingently during the same session and, (2) the emergence of patterns was frequently delayed within the session until after drug self-administration behavior stabilized at regular INTs. The findings are discussed in terms of the significance of NA-VS neuron firing correlates for the initiation and maintenance of cocaine self-administration.

Action Potentials↗
PubMed1987

Firing patterns of human limbic neurons during stereoencephalography (SEEG) and clinical temporal lobe seizures.

Comparisons of the patterns of neuronal firing and stereoencephalography (SEEG) recorded from the same microelectrodes chronically implanted in the human limbic system were made in order to study neuronal electrogenesis at onset and during propagation of focal partial complex seizures. Alert or sleeping patients were monitored during spontaneous subclinical seizures (no alterations in consciousness detectable), during auras reported by the patients as typical, and during clinical seizures with loss of consciousness, movements and post-ictal confusion. During subclinical SEEG seizures (ipsilateral, normal consciousness), few neurons increased firing (estimated at only 7%) either at the focus or at propagated sites. During auras, with altered consciousness, there were relatively few neurons that increased firing, with the estimate about 14% or twice as many as during a subclinical seizure. During the onset of a clinical seizure that involved loss of consciousness, movements and post-ictal confusion, many neurons were recruited into increased firing, with an estimate of approximately 36%. During this increased electrogenesis, neurons fired briefly in association with high-frequency local SEEG; however, the bursts were shorter than the SEEG seizure pattern. Apparently, other local neurons were recruited to fire in bursts to sustain sufficient axonal driving for widespread propagation of the seizure. When the focal SEEG slowed, the units stopped firing, which suggested that the 'focal' seizure need not be sustained for more than several seconds because propagated seizure activity was self-sustaining at distant structures. The data lead to the conclusion that SEEG seizures can be generated focally by synchronous firing of fewer than 10% of neurons in the 'epileptic pool.' However, when greater percentages of neurons are recruited in the 'epileptic focus' there is greater propagation to widespread sites, especially contralaterally, which will produce clinical partial complex seizures.

Action Potentials↗
PubMed1988

Recurrent inhibition of firing motoneurones in man.

The effects of antidromic stimulation of large motoneurones on firing small motoneurones of soleus muscle have been studied. Against the background of rhythmic firing of small motor units (MUs) activated during weak voluntary muscle contraction, thick efferents of the tibialis posterior nerve were selectively stimulated and an M response was evoked in which small MUs were not involved. This provided a means of avoiding antidromic stimulation of the motoneurone under study and, thus, analysing the effect of stimulation without its summation with after-hyperpolarization. The background firing rate of MUs was 4.5-9.2/sec. PSTHs revealed a distinct inhibitory effect with a latency of 35-40 msec (slightly exceeding the latency of monosynaptic reflex) and duration 5-30 msec. It was concluded that the short-latency inhibition could be identified as recurrent inhibition. The effectiveness of recurrent inhibition evaluated by the lengthening of the interspike interval was shown to depend on the arrival time of the volley in the interval and on the background firing rate of the motoneurone. When the inhibitory volley arrived at the beginning of the interspike interval it was ineffective. This indicates that in the investigated range of firing rates the motoneurone is unable to exert an inhibitory effect on its own firing via recurrent collaterals. The inhibitory volley became highly effective at the end of an interspike interval, when the membrane potential approached threshold. The lengthening of interspike interval was more marked at a lower firing rate of the motoneurone. An increase in the background firing rate reduced the extent of recurrent inhibition (at a rate above 10/sec up to its complete ineffectiveness).(ABSTRACT TRUNCATED AT 250 WORDS)

Electroencephalography↗
PubMed1993

Prazosin modulates the firing pattern of dopamine neurons in rat ventral tegmental area.

Previous studies have indicated a noradrenergic modulation of midbrain dopamine cell activity. The effects of systemic administration of the alpha 1-adrenoceptor antagonist prazosin and the alpha 2-antagonist idazoxan on midbrain dopamine cell firing were now studied with extracellular recording from single dopamine neurons in the ventral tegmental area of chloral hydrate-anaesthetized male rats. Prazosin (0.15-0.6 mg/kg i.v.) dose dependently decreased burst firing and regularized the firing pattern of dopamine neurons, while the firing rate was unaffected. The prazosin-induced effects were abolished by pretreatment with reserpine. Idazoxan (0.5-2.0 mg/kg i.v.) increased firing rate and burst firing and made the firing pattern less regular, probably by increasing adrenergic transmission via blockade of presynaptic alpha 2-adrenoceptors. The effects of idazoxan were blocked by prazosin. The present results indicate that noradrenergic neurons modulate the dopamine cell firing pattern via excitatory postsynaptic alpha 1-adrenoceptors. This mechanism might be involved in the pathogenesis and pharmacological treatment of schizophrenia.

Adrenergic alpha-Antagonists↗
PubMed1988

Changes in the firing properties of neurons in the dentate gyrus with denervation and reinnervation: implications for behavioral recovery.

The present study evaluates how the activity of neurons in the dentate gyrus of adult rats is affected by removal of the projection from the ipsilateral entorhinal cortex (EC) and by the reinnervation which follows this injury. We evaluated the average firing rate and characterized interstimulus interval (ISI) parameters for single units in the granule cell layer of the dentate gyrus in two ways: (I) by recording the activity of single neurons prior to and at 15 min and 2, 4, 6, and 8 h. following a unilateral EC lesion; and (II) by calculating average rates for samples of neurons at 2, 4, 6, 8, and 14 days postlesion. Of a sample of 31 neurons whose activity was recorded before and after an EC lesion, 27 (87%) showed decreased activity, and 4 (13%) showed increased activity. The average prelesion firing rate for all cells was 6.5 spikes/s, and the average rate decreased to 2.5 spikes/s at 15 min postlesion. The average firing rate remained depressed for the 8-h recording session, although it was not possible to maintain the recordings for all cells. Evaluations of ISI histograms revealed three general types: (a) a skewed distribution with a single peak; (b) a bimodal distribution with an early peak at intervals of a few ms and a later peak at approximately the same interval as the distributions with single peaks; (c) cells with low firing rates and more or less rectangular distributions. Cells producing each type of ISI histogram exhibited decreases in firing after EC lesions. However, the 4 neurons that exhibited increases in firing had relatively low firing rates prior to the lesion. There were no significant changes in the coefficient of variation or skewness of the ISI histograms following the lesions. The statistical dependency of successive ISIs as revealed by serial correlograms was relatively low in the prelesion sample, and showed no consistent change following the lesion. Comparison of the average firing rates of different samples of neurons at 2-14 days postlesion revealed that the average activity of neurons in the granule cell layer remained depressed at 2 and 4 days postlesion. However, the activity recovered to a level comparable to the prelesion control by 8 days postlesion. The time course of recovery of unit activity was comparable to the time course of sprouting as revealed by previous electrophysiological studies.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1995

Ethanol withdrawal induces increased firing in inferior colliculus neurons associated with audiogenic seizure susceptibility.

Ethanol withdrawal (ETX) in ethanol-dependent rats results in susceptibility to seizures, including generalized tonic-clonic audiogenic seizures (AGS). The inferior colliculus (IC) is strongly implicated in AGS initiation during ETX, but IC neuronal mechanisms subserving AGS are unclear. The present study examined IC (central nucleus) single neuronal firing during repeated (4 day) intragastric ethanol administration and during ETX. This involved microwire electrodes implanted chronically into freely moving rats and acoustic stimulation in intensities up to 105 dB SPL. During initial ethanol administration the animals were stuporous, and IC spontaneous neuronal firing and acoustically evoked firing at high stimulus intensities were significantly reduced. This firing reduction is consistent with the action of ethanol to enhance gamma-aminobutyric acid (GABA)-mediated inhibition, which is prominent in IC neurons at high stimulus intensities. During ETX the animals were agitated, and spontaneous IC neuronal firing and acoustically evoked firing at all stimulus intensities were significantly increased during the period of AGS susceptibility. Previous studies indicate that IC neuronal responses are tightly regulated by GABA and glutamate. The IC firing increases during ETX in the present study may involve the down-regulation of GABAA receptors and supersensitivity of glutamate receptors reported to occur during ETX. Previous studies also indicate that focal blockade of GABAA receptors or activation of glutamate receptors produces AGS susceptibility in normal rats. Therefore, the IC neuronal firing increases observed in the present study may play a critical role in initiation of AGS during ethanol withdrawal.

Acoustic Stimulation↗
PubMed1977

Porcelain shade stability after repeated firing.

There were no color changes detected in the first five firings for both air- and vacuum-fired porcelain. Slight changes were noticed in subsequent firings. These color changes were more noticeable in the air-fired samples than in the vacuum-fired samples. However, changes in the porcelain color after repeated firing were not sufficiently significant to cause rejection of the samples. The porcelain shade remains stable with repeated firing if the firing procedure is carefully carried out.

Color↗
PubMed1987

Motor unit firing intervals and other parameters of electrical activity in normal and pathological muscle.

The analysis of the firing intervals of motor units has been suggested as a diagnostic tool in patients with neuromuscular disorders. Part of the increase in number of turns seen in patients with myopathy could be secondary to the decrease in motor unit firing intervals at threshold force of the motor units, as noted in previous studies. In the brachial biceps muscle we have studied the firing intervals of 164 motor units in 14 controls, 140 motor units in 13 patients with myopathy and 86 motor units in 8 patients with neurogenic disorders, and related the findings to those of the turns analysis and the analysis of properties of individual motor unit potentials. To ensure comparable conditions we have examined motor unit firing intervals and turns at a force of 10% of maximum. The average of motor unit firing intervals and of interval variability was the same in controls and in patients, and the diagnostic yield of the motor unit firing intervals analysis was none. Although the number of turns increased with decreasing motor unit firing intervals, this relation was physiological rather than pathophysiological. In patients with neurogenic disorders, interval variability indicated unstable firing in severely affected muscles.

Action Potentials↗
PubMed1985

Firing properties of substantia nigra dopaminergic neurons in freely moving rats.

Single unit recordings were obtained from putative dopaminergic neurons in the substantia nigra of awake, freely moving rats. The cells exhibited waveforms, range of firing rates and types of firing patterns identical to those of identified DA neurons of anesthetized or paralyzed rats. Two firing patterns were observed: single spike activity and a bursting mode with spikes of progressively diminished amplitude and increased duration within each burst. The degree of burst firing varied considerably among the cells and individual cells sometimes switched from one pattern of firing (e.g. predominantly single spike) to another (e.g. bursting), although the determinants of these transitions are, at this time, unclear. Putative DA neurons were inhibited by i.v. apomorphine and excited by i.v. haloperidol. Haloperidol also reversed the apomorphine-induced inhibition of firing. Inhibitions and excitations were associated with a reduction and elevation, respectively, in burst firing. The effects of the two drugs were identical to their effects in immobilized rats. In several cases, a putative DA neuron was observed to fire all of its spikes in near coincidence with at least one other cell with identical electrophysiological characteristics. This form of interaction (i.e. presumed electrical coupling) between DA cells is only rarely observed in anesthetized or paralyzed rats and may play a significant role in the normal functioning of the nigrostriatal DA system.

Action Potentials↗
PubMed1988

Effects of intraperitoneal administration of apomorphine and the isomers of 3-(1-propyl-3-piperidinyl)phenol on the firing activity of substantia nigra dopamine neurons: comparison of agonist efficacies and development of acute tolerance.

The effects of intraperitoneal administration of apomorphine, (+)-3-PPP, and (-)-3-PPP on slow-(less than 4 spikes/sec) and fast-(greater than 4 spikes/sec) firing dopaminergic neurons in the substantia nigra zona compacta of rats anesthetized with chloral hydrate were assessed. All compounds completely inhibited slow-firing dopaminergic neurons. When a dose-response was determined by administering each dose in a single bolus injection, apomorphine and (+)-3-PPP produced dose-related inhibitions of fast-firing dopaminergic neurons, with the largest dose of each compound completely inhibiting nearly all cells tested. In contrast, (-)-3-PPP only partially inhibited (50%) fast-firing dopaminergic neurons. Thus, on fast-firing neurons, (-)-3-PPP had the profile of a partial agonist, while apomorphine and (+)-3-PPP demonstrated greater efficacy than (-)-3-PPP. Pretreatment while doses of apomorphine, (+)-3-PPP, or (-)-3-PPP that partially inhibited the activity of dopaminergic neurons antagonized the complete inhibitory effects of a dose of apomorphine that normally produced complete inhibition of neuronal firing. In addition, pretreatment with doses of (+)-3-PPP that partially inhibited the activity of cells antagonized the complete inhibitory effects of a dose of (+)-3-PPP that, normally produced complete inhibition of neuronal firing. From the antagonism studies alone, it was not clear if tachyphylaxis or partial agonist activity accounted for the observed antagonisms. However, since apomorphine and (+)-3-PPP completely inhibited the activity of fast-firing DA neurons, it is proposed that they antagonize by inducing a dose- and time-dependent tachyphylaxis. In contrast, (-)-3-PPP is proposed to antagonize by virtue of its partial agonist activity.

Action Potentials↗
PubMed1989

The effects of adrenalectomy, corticotropin releasing factor and vasopressin on the sympathetic firing rate of nerves to interscapular brown adipose tissue in the Zucker rat.

The firing rate of the sympathetic efferent nerves to interscapular brown adipose tissue (IBAT) is lower in the obese rat compared with the lean rat. The present experiments show that adrenalectomy has no effect on nerve firing rate in the lean rat and a small but statistically nonsignificant effect in the obese rat. Injection of corticotropin releasing factor (CRF) into the IIIrd ventricle produced a dose dependent increase in the firing rate of the sympathetic nerves to interscapular brown adipose tissue (IBAT) in both lean and obese rats. The basal (unstimulated) level of firing was lower in the obese rat compared with the lean rat and remained significantly below lean values at each dose. The minimum dose of CRF to see an effect (125 ng) and the dose at which maximum effect on nerve firing rate was observed (500 ng) was similar in both genotypes. Injection of adrenocorticotropic hormone (ACTH) had no effect on nerve firing rate to IBAT. Central administration of vasopressin produced a significant increase in sympathetic firing rate to IBAT in both lean and obese rats. The temperature of IBAT was also significantly increased with vasopressin and the duration of the response was longer compared with CRF, but the minimum dose to see an effect was higher (2.5 micrograms). The response to vasopressin was greater in the obese rat compared with the lean rat but the maximum firing rate did not achieve levels observed in lean rats. Chronic infusion of CRF into the IIIrd ventricle of obese rats resulted in a reduction of food intake and body weight gain but IBAT mitochondrial GDP binding was unaltered by the treatment. These data are consistent with the hypothesis that the defect in the obese Zucker rat may be due to a glucocorticoid inhibition of CRF and/or vasopressin action in the CNS.

Adipose Tissue, Brown↗
PubMed1988

The effects of a worksite health promotion program on the wives of fire fighters.

One method of increasing the cost-effectiveness of worksite health promotion programs is to develop programs that also have an impact on risk factors of family members and friends of the employees. In this study, 41 wives of fire fighters were interviewed concerning changes the fire fighters and they had made in their health habits--exercise, weight, and consumption of fats, fruits/vegetables, and cereal/whole grain breads--in the previous year. Thirty-two were wives of fire fighters who had received a worksite health promotion program and nine were wives of fire fighters who had not yet received the program. Findings of our exploratory study strongly suggest that wives of fire fighters who received information were more aware of the program (93% vs 56%), had greater exposure to the written diet plan (72% vs 11%) and guide to high fat foods (72% vs 0%) than controls. Furthermore, the intervention led to changes in the fire fighters' health habits that were reported by the wives. No significant changes in the wives' health habits occurred as a result of the intervention, although the changes were in the predicted direction in every category; changes by the wives were, however, related to changes by fire fighters. Involvement of the fire fighters in the preparation of meals and sharing of information from the intervention program by the participant with the wife, were related to change in health habits of the wives.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

Movement-dependent after-effects in the firing of the spindle endings from the de-efferented muscles of the cat hindlimb.

The muscle spindle reactions evoked by the servo-controlled changes in the muscle length or external load were studied on the de-efferented muscles in experiments on cats under Nembutal anaesthesia. The activity of 39 primary and 10 secondary endings of the muscle spindles from four hindlimb extensor muscles: soleus, plantaris, lateral and medial heads of gastrocnemius has been recorded during servo-controlled changes in muscle length (L-control) or external load (P-control). Slow linear reciprocating (triangular) signals and their modification with fixation of the controlled parameter at the same level at forward and reverse phases were used as commands for the muscle stretcher. The steady firing rates in primary and secondary endings during fixation of muscle length or external load were shown to be strongly dependent on the direction of previous changes in these parameters. The firing rates were always higher after preceding lengthening (loading) and lower after shortening (unloading). These rate uncertainties in the steady firing of spindle endings at the same level of controlled parameter could be as much as 15-20 p.p.s. The revealed dependence of the spindle ending firing on the past history of the muscle movement was denoted as movement-dependent after-effects. Two kinds of movement-dependent after-effects in the firing of the spindle endings can be observed: (1) the movement-dependent ones being studied in the present work, and (2) those connected with the conditioning fusimotor stimulation and described elsewhere. Their common origin is supposed to be connected with the hysterical (thixotropic) properties of the intrafusal muscle fibres. Similarity of the movement-dependent after-effects in L- and P-control conditions was shown to be connected with a resemblance of the length-firing rate [F(L)] and load-firing rate [F(P)] hysterical loops registered during reciprocating movements. Both kinds of loops were in a clock-wise direction, their comparison in normalized form showed that F(L) loops were always broader than F(P) ones. Isotonic and isometric uncertainty vectors were introduced to analyse quantitatively the hysterical effects in the spindle firing and their relation to the muscle hysteresis proper. Uncertainty vectors connect the points of equal load (isotonic uncertainty vectors) and equal length (isometric uncertainty vectors) on F(L) and F(P) loops correspondingly. The projections of both uncertainty vectors onto the Y-axis give the rate uncertainty coinciding in sign for both cases, whereas their projections onto the X-axis differ in sign, being positive for isometric uncertainty vectors (the tension uncertainty) and negative for isotonic uncertainty vectors (the length uncertainty).(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1993

Fluctuations in pyramid-pyramid excitatory postsynaptic potentials modified by presynaptic firing pattern and postsynaptic membrane potential using paired intracellular recordings in rat neocortex.

Single axon excitatory connections between pairs of neocortical pyramidal neurons were studied using paired intracellular recordings in layers II/III and IV of coronal slices of adult rat somatosensory/motor cortex. Excitatory postsynaptic potentials evoked with different presynaptic firing patterns and at different postsynaptic membrane potentials were compared. Two methods of statistical analysis were used in attempts to determine whether changes in mean excitatory postsynaptic potential amplitude were due to presynaptic or postsynaptic modifications. Analysis of the decrease in mean excitatory postsynaptic potential amplitude associated with increases in presynaptic firing rate were consistent with a change in probability of transmitter release. Paired pulse depression appeared to exhibit both presynaptic and postsynaptic components when the interspike interval was < 10 ms, but could be explained simply by a decrease in probability of release with interspike intervals between 10 and 80 ms. Previous studies had demonstrated that these excitatory postsynaptic potentials are partially mediated by N-methyl-D-aspartate receptors. In contrast to the apparently presynaptic effects of firing pattern, postsynaptic membrane depolarization appeared to produce an increase in quantal amplitude. In addition to this increase at low frequencies, a form of frequency-dependent, self-potentiation involving the recruitment of an additional, longer-latency postsynaptic component occurred at higher presynaptic firing rates. The possibility is discussed that two different mechanisms are involved in the replacement of vesicles at release sites. Over a few tens of milliseconds (paired-pulse depression) availability of releasable transmitter may be determined by the rate of replacement of discharged vesicles from a readily releasable pool of vesicles. Over longer periods of firing at 0.33-2 Hz, the readily releasable pool may become exhausted and require replenishment. Postsynaptic depolarization increases the duration of these excitatory postsynaptic potentials, facilitating summation and enables two components of excitatory postsynaptic potential enhancement at N-methyl-D-aspartate receptor-mediated synapses; one that is present at all firing rates and relates simply to voltage dependent events and one that occurs at higher firing rates and involves a gradual, time dependent event. These data also indicate that the optimal pyramidal firing pattern if another pyramid is to be activated is a tonic, or brief burst pattern at relatively low repetition rates. Long bursts of many presynaptic spikes recruit little that is not activated by pairs of spikes. This situation is in stark contrast to the results obtained in the following paper in which excitatory inputs from pyramids to non-pyramids are described.

Animals↗
PubMed1993

N-methyl-D-aspartate induces regular firing patterns in the cat lateral habenula in vivo.

The present study was undertaken to elucidate the action of excitatory amino acids in the dorsal diencephalic pathway. Single neurons in the lateral habenula of halothane-anesthetized cats were recorded extracellularly, and excitatory amino acid receptor agonists and antagonists were applied by iontophoresis. Most neurons in the lateral habenula were spontaneously active. This spontaneous firing could be inhibited by kynurenic acid, a broad spectrum antagonist of excitatory amino acid receptors, but not by the selective N-methyl-D-aspartate receptor antagonist 2-amino-7-phosphono-heptanoic acid. Iontophoretic application of alpha-amino-3-hydroxy-5-methyl-5-isoxazolepropionate, quisqualate and kainate mostly elicited a non-burst, regular firing pattern which was sensitive to kynurenic acid. Surprisingly, 116 (96%) out of 121 neurons in the lateral habenula responded to iontophoretic application of N-methyl-D-aspartate with a regular non-burst firing pattern, in contrast to previously published observations from other brain regions where N-methyl-D-aspartate predominantly elicited phasic firing patterns. When cells were recorded with electrode assemblies where one iontophoretic barrel contained MgCl2 or MgSO4, only 10 (43%) out of 23 cells responded with regular firing upon application of N-methyl-D-aspartate, while 13 (57%) now displayed a phasic firing pattern. In these cells iontophoretically applied alpha-amino-3-hydroxy-5-methyl-5-isoxazolepropionate or quisqualate still evoked only regular firing. In a few cases, an initially regular N-methyl-D-aspartate-induced firing pattern could be changed to a phasic pattern following active ejection of Mg2+ ions.(ABSTRACT TRUNCATED AT 250 WORDS)

2-Amino-5-phosphonovalerate↗
PubMed2004

Does sympathetic nerve discharge affect the firing of myelinated cutaneous afferents in humans?

In clinical practise, the notion that some complex regional pain syndromes (CRPS) are associated with sympathetic facilitation of nociceptive transmission is widespread. However, physiological increases in cutaneous sympathetic nerve activity have not been found to influence the firing properties of cutaneous polymodal nociceptive (high-threshold mechano-heat sensitive) fibers in human subjects. Whether the same applies to low-threshold cutaneous mechanoreceptors is not known. Such an effect could be relevant for sympathetic facilitation of nociception, given that tactile afferents are implicated in the allodynia associated with CRPS. This issue was addressed by recording the responses of single cutaneous mechanoreceptors in the glabrous skin of the finger pads to constant mechanical stimuli, at rest and during physiological increases in cutaneous sympathetic activity produced by arousal stimuli. Unitary recordings were made from 17 rapidly adapting (15 FAI and 2 FAII) and 20 slowly adapting (9 SAI and 11 SAII) afferents located in the finger pads via tungsten microelectrodes inserted percutaneously into the median nerve at the wrist in nine subjects. A servomotor applied 1 s constant-displacement ramp-and-hold indentations to the receptor-bearing digit every 3 s. Displacement and compression force were recorded. Blood flow in the finger pad and sweating in the palm were measured contralaterally. Increases in cutaneous sympathetic outflow caused only modest changes in the spontaneous and compression-evoked firing of tactile afferents. These changes were usually (for 26/37 afferents) related to the associated decreases in skin blood flow. The latency from the start of the ramp stimulus to the onset of firing was inversely correlated to flow (i.e. unit response was delayed during vasoconstriction) for 11/31 units (7/15 FAI, 1/2 FAII, 2/9 SAI, 1/5 SAII), whereas no units showed a positive correlation. Compression-evoked firing rates were positively correlated to flow (i.e. vasoconstriction reduced firing rates) for 14/31 units (2/15 FAI, 1/2 FAII, 7/9 SAI, 4/5 SAII), whereas no units showed a negative correlation. 10/11 SAII afferents exhibited spontaneous background firing, which increased for 4 and decreased for 4 in response to arousal stimuli, presumably reflecting their sensitivity to changes in skin stretch associated with sympathetically mediated reductions in blood volume in the finger pad. Two afferents showed no change, but nor was there significant vasoconstriction in these recordings. Thus, arousal stimuli reduced rather than augmented tactile afferent firing. The close relation to blood flow for all types of afferents, and the different responses among SAII afferents, suggest that sympathetically mediated changes in afferent firing properties are indirect, i.e. secondary to changes in the mechanoreceptors' tissue environment rather than to a direct sympathetic effect on the endings.

Adult↗
PubMed2005

Properties of Barrington's neurones in cats: units that fire inversely with micturition contraction.

Barrington's nucleus contains neurones that decrease their firing during micturition contraction, as well as neurones that increase their firing during this phase. These neurones are commonly termed inverse neurones and direct neurones, respectively. The aims of the present study were to determine whether inverse neurones send descending axons to the spinal cord and to clarify how these neurones regulate bladder contractility. Forty-five single neurones were recorded from the dorsolateral pontine tegmentum. Spinal-projecting neurones were identified by antidromic stimulation of the spinal cord. More than half of inverse neurones were located outside Barrington's nucleus. Only three were spinal-projecting neurones. The results were in marked contrast with direct neurones that we studied previously: the majority of them were located within Barrington's nucleus, and 56% were spinal-projecting neurones. The firing frequency of inverse neurones ranged between 6 and 37 Hz during the relaxation phase of the micturition contraction-relaxation rhythm. The firing of all neurones began to decrease within 8 s after the onset of micturition contraction. During micturition contraction, neurones displayed little firing, being virtually silent (n = 29) or displayed weak tonic firing (3-11 Hz; n = 16). All neurones began to increase their firing within 8 seconds after the onset of bladder relaxation. These results suggest that inverse neurones do not trigger bladder contraction or relaxation, despite the finding that a few of them send descending axons to the spinal cord. One possible role of the inverse neurone is to regulate firing activities of direct neurones in Barrington's nucleus.

Action Potentials↗