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PubMed2002

Modulation of membrane traffic by mechanical stimuli.

All cells experience and respond to mechanical stimuli, such as changes in plasma membrane tension, shear stress, hydrostatic pressure, and compression. This review is an examination of the changes in membrane traffic that occur in response to mechanical forces. The plasma membrane has an associated tension that modulates both exocytosis and endocytosis. As membrane tension increases, exocytosis is stimulated, which acts to decrease membrane tension. In contrast, increased membrane tension slows endocytosis, whereas decreased tension stimulates internalization. In most cases, secretion is stimulated by external mechanical stimuli. However, in some cells mechanical forces block secretion. External stimuli also enhance membrane and fluid endocytosis in several cell types. Transduction of mechanical stimuli into changes in exocytosis/endocytosis may involve the cytoskeleton, stretch-activated channels, integrins, phospholipases, tyrosine kinases, and cAMP.

Animals↗
PubMed1982

Visual response properties of zebrafish tectal cells.

The visual properties of zebrafish tectal cells have been studied with a variety of stimulation routines. These include illumination of the whole receptive field and of the surround, use of moving edges, very small spots, bars of varying orientations, moving spots with varying direction and speeds, growing discs, and pairs of spots whose presentation varies in position and sequence. A number of properties correlate with the classification scheme set forth in the preceding paper. Type B cells, unlike other types, are insensitive to moving stimuli. Experiments involving surround stimulation show that type S cells have inhibitory surrounds while those of type I do not. Type I cells, however, exhibit several properties which are consistent with an intratectal delayed inhibitory mechanism operating within the receptive field. These properties include the response to moving edges and growing stimuli, and the dependence of response duration on the size of a flashed stimulus. Various explanations of these properties are considered, and a specific model is proposed which states that cells of type I receive inhibitory input from neighbouring tectal cells of the same physiological type. The properties involved may be of direct importance in the visual behavior of the fish.

Animals↗
PubMed1995

Sensitization of spinal neurons by non-noxious stimuli in the awake but not anesthetized state.

BACKGROUND: The observation that peripheral trauma causes enhanced spinal neuronal excitability has provided the scientific rationale for the concept of "pre-emptive analgesia." The premise has been that only noxious stimuli cause sensitization in sensory pathways, but this premise has not been tested in the conscious state. METHODS: Responses of single spinal neurons were recorded in instrumented sheep that were untrained and free from drugs or recent surgery, in either fully conscious or halothane-anesthetized states. Receptive field (RF) size was measured before and after non-noxious mechanical conditioning stimulation. RESULTS: Noxious conditioning stimuli in anesthetized sheep caused enlargement of RF areas, as expected. Conditioning with nonpainful scratching or other stimuli was without effect in anesthetized animals; in marked contrast, it caused enlargement of RF size in conscious animals, in which 29 of 33 wide dynamic range units but only 1 of 12 low-threshold mechanoreceptive neurons were affected. CONCLUSIONS: Sensitization of spinal sensory neurons evidently is a process that is not restricted to pathologic pain states but rather that occurs under normal physiologic conditions independent of painful stimuli. The significance of such sensitization processes therefore needs reevaluation. The sensitization triggered by non-nociceptive afferents is likely to be opioid-resistant and therefore may contribute to the rather disappointing results seen in several clinical trials of "pre-emptive analgesia."

Anesthesia, Inhalation↗
PubMed1988

Specificity-related suppression of responses to binary mixtures in olfactory receptors of the Colorado potato beetle.

Responses of antennal olfactory receptors of the Colorado potato beetle (Leptinotarsa decemlineata Say) to stimulation with 5 general green odour components, i.e. cis-3-hexen-1-ol, trans-2-hexenal, cis-3-hexenyl acetate, trans-2-hexen-1-ol and 1-hexanol, were recorded extracellularly. Response spectra derived from these recordings cannot be classified into distinct reaction types. The spectra overlap in their sensitivity to individual stimuli, but there are differences in their degree of specialization with a gradual conversion from generalist to specialist receptors. Moreover, specialization is found to different stimuli. Receptor reactions to stimulation with binary mixtures of 3 of these compounds indicated that suppression of the response to one chemical by another is very common in olfactory receptor cells. The more a receptor is specialized, the stronger is this suppression. Suppression in narrowly tuned olfactory receptor neurones, therefore, is expected to play a fundamental role in the recognition of natural odour blends.

Animals↗
PubMed1983

Flocculectomy and unit activity in the vestibular nuclei during visual-vestibular interactions.

Activity of neurons in the vestibular nuclei of alert monkeys was recorded extracellularly after total unilateral and bilateral flocculectomy and partial paraflocculectomy. Type 1 horizontal cells that were encountered after flocculectomy responded to visual and vestibular stimuli and to conflict stimulation, i.e., to rotation in a subject-stationary visual surround, as do vestibular neurons in the normal animal. The major difference between neurons in the normal and lesioned animals was that more time was needed to reach steady state firing levels during optokinetic stimulation at a constant velocity after operation. As shown previously (Waespe et al. 1983) the longer time course is related to increased initial retinal slip velocities that occur after flocculectomy as a result of an inability to change eye velocity rapidly in response to visual stimulation. It does not signify a change in the dynamics of neurons in the vestibular nuclei that mediate the vestibulo-ocular reflex (VOR). The similarity in modulation of horizontal Type 1 vestibular neurons in normal and flocculectomized monkeys makes it unlikely that floccular Purkinje cells suppress the horizontal VOR in the monkey during conflicting visual and vestibular stimuli by inhibiting or disfacilitating secondary or tertiary vestibular neurons. This is consistent with earlier findings that indicate that visual-oculomotor pathways responsible for ocular pursuit or for rapid changes in OKN do not go through the vestibular nuclei. Rather the point of interaction of the flocculus output with the VOR appears to be external to the vestibular nuclei. There was a close correspondence between the slow phase velocity of nystagmus and unit activity in the vestibular nuclei under a wide variety of test conditions after flocculectomy. This is consistent with the postulate that frequencies of vestibular nuclei neurons represent a summation of activity in direct vestibulo-oculomotor pathways and indirect pathways that include the velocity storage mechanism. These are the major remaining sources of activity that generate slow phases of nystagmus after the direct visual-oculomotor pathways have been partially interrupted by flocculectomy (Waespe et al. 1983). Horizontal Type 1 neurons which responded to vestibular and optokinetic stimulation with increases in frequency above 1 spike/s/degree/s were rarely encountered after flocculectomy. These cells were present on the normal side in a monkey after unilateral flocculectomy. We infer that vestibular nuclei neurons that project mossy fibers to the flocculus are inactivated or disappear as a result of surgical ablation of their axons. This could also contribute to the reduced gain of vestibular nystagmus, OKAN and off-vertical nystagmus that was observed in some of the animals after lesion.

Animals↗
PubMed1991

Ectopic excitability of injured nerves in monkey: entrained responses to vibratory stimuli.

1. The responses to mechanical stimulation of myelinated fibers that originate from an acutely cut nerve or a neuroma were studied in the anesthetized monkey. The superficial radial or sural nerve was tightly ligated and cut. Either immediately (acute experiment) or 2-6 wk later (chronic experiment), single-unit recording techniques were used to record the evoked neural activity after vibratory mechanical stimulation (5-100 Hz; 50-800 microns) near the injury site. 2. The 30 myelinated afferents studied in the chronic experiments displayed an entrained response (1 action potential for each stimulus cycle) to vibratory stimuli applied at or near the nerve injury site. For 19 fibers, the minimum amplitude for entrainment was determined as a function of frequency (tuning curve). For 11 others, complete tuning curves were not obtained, although the frequency range over which they were most sensitive could be estimated. The afferents could be classified into three groups on the basis of the frequency range over which they were most sensitive: 1) a low-frequency group that was most sensitive to frequencies less than or equal to 5 Hz (n = 7), 2) a mid-frequency group that was most sensitive to a broad range of frequencies (i.e., 20-75 Hz, n = 13), and 3) a high-frequency group that was most sensitive to frequencies greater than or equal to 100 Hz (n = 10). These three response classes are similar to the three classes of response associated with the different low-threshold mechanoreceptors (i.e., slowly and rapidly adapting and Pacinian-like mechanoreceptors).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1997

Differential effects of nitrous oxide and propofol on myogenic transcranial motor evoked responses during sufentanil anaesthesia.

We have compared the effects of 50% nitrous oxide and propofol, each administered concurrently with sufentanil, on the amplitudes and latencies of the compound muscle action potential (CMAP) response to transcranial electrical stimulation. Using a crossover design, 12 patients undergoing spinal surgery were exposed to both 50% nitrous oxide and propofol, the latter in a bolus-infusion regimen. Six patients received nitrous oxide first and six received propofol first. CMAP were recorded from the tibialis anterior muscle in response to both single and paired transcranial electrical stimuli. With single pulse stimulation, median CMAP amplitude was significantly greater during administration of nitrous oxide than propofol (nitrous oxide 335 (10th-90th percentiles 35-849) microV; propofol 36 (0-251) microV) (P < 0.01). With paired stimulation, there was no significant difference in CMAP amplitude during the two regimens (nitrous oxide 1031 (296-1939) microV; propofol 655 (0-1867) microV). The results indicate that propofol caused more depression of transcranial electrical motor evoked responses than 50% nitrous oxide but that the difference was probably clinically unimportant when a paired stimulation paradigm was used.

Adolescent↗
PubMed1989

[Hemodynamic and medicamentous modification of stimulated atrial natriuretic factor secretion].

The secretion of atrial natriuretic factor (ANF) and its adaptation to pharmacologic and hemodynamic interventions were investigated in 36 patients with sinus rhythm. To provoke standardized secretion of ANF all patients underwent two periods of rapid right ventricular pacing for 4 min with a 15 min interval. Immediately after the first pacing eight patients received 5 mg verapamil, 10 patients 5 mg atenolol and 10 patients 4 mg molsidomine intravenously. Eight patients remained untreated and served as controls. The amounts of atrial pressure increments due to pacing were identical (70% over basal pressure) in all patients. After molsidomine, but not after the other drugs, basal right atrial pressure was lowered. In controls the secretion of ANF due to the second stimulation was significantly (2.5-fold) larger than the secretion induced by the first stimulation. In patients receiving verapamil the secretion response after the second pacing was blunted. Atenolol did not affect the release of ANF. After molsidomine the upward regulation of the ANF secretion rate - seen in controls - was abolished. Thus, the myoendocrine cells are capable for a fast upward regulation of their ANF secretion rate after repeated stimuli. Verapamil directly blocks stimulated ANF secretion, whereas beta-blockade shows no effect. Molsidomine seems to impair enhanced ANF release by lowering basal atrial pressure.

Adult↗
PubMed1987

[Changes in the concentration of extracellular potassium in the cerebral cortex with different parameters of electrical stimulation].

In anesthetized cats, a recording macroelectrode, a K+-sensitive microelectrode and a stimulating electrode were placed on the surface of the suprasylvian gyrus. As the duration or intensity of stimulus increased, the amplitude of K+-potential reflecting the changes in the extracellular concentration of K+ ions (delta [K+]o) was augmented, while the half time of decay decreased. delta [K+]o also increased when the number of stimuli increased. Repetitive tetanic stimulation resulted in impairment of the effect also in the case when [K+]o following the preceding stimulus, reached the initial level. K-potential started to decay in the course of prolonged tetanic stimulation; impairment of the neuronal activity is supposed to underlie this event.

Animals↗
PubMed1988

Effects of thalamic parafascicular stimulation on the periaqueductal gray and adjacent reticular formation neurons. A possible contribution to pain control mechanisms.

To investigate the mechanism of analgesic effect of electrical stimulation of the thalamic parafascicular nucleus (Pf), we studied modulations of neuronal activities in the periaqueductal gray (PAG) and the adjacent reticular formation (RF) in response to Pf electrical and peripheral noxious stimulations in the rat. Extracellular single unit activities were recorded from 129 neurons in the PAG and adjacent RF under light halothane anesthesia. Pf stimulation caused neuronal responses in approximately 80% of the PAG and adjacent RF neurons, and noxious stimulation in 75%, with predominant excitatory responses to either stimulation. When the responses to the two stimuli were tested in the same neurons (n = 69), 91% responding to noxious stimuli also responded to Pf stimuli, again with predominant excitatory responses to either stimulation. The PAG and adjacent RF neurons that were verified antidromically to project to the nucleus raphe magnus (NRM), showed a similar pattern of response (n = 20). These results suggest that a sizeable population of neurons in the PAG and adjacent RF receives excitatory effects from the Pf and noxious afferents, and that part of these neurons projects to the NRM, which inhibits the dorsal horn cells of the spinal cord (the descending pain suppression system). Thus, part of the mechanism of the analgesic effects of Pf stimulation is due to activation of the descending pain suppression system by exciting the PAG and adjacent RF neurons. A possible role of noxious afferents on the negative feedback to pain mediation through this descending system also has to be considered.

Animals↗
PubMed2004

Perinatal changes of brain-derived neurotrophic factor in pre- and fullterm neonates.

BACKGROUND: Brain-derived neurotrophic factor (BDNF) is abundant in brain and peripheral nerves, affects normal development, growth and survival and is implicated in immune response. AIM: To determine in single preterm (P) and fullterm (F) neonates, circulating intra- and extrauterine levels of BDNF, supposingly reflecting their neuronal and immune maturity. STUDY DESIGN: Prospective study. SUBJECTS: Thirty healthy, appropriate for gestational age (AGA) F (mean gestational age 39.2+/-1.4 weeks), 15 healthy AGA P (29.4+/-1.3 weeks), and their mothers. OUTCOME MEASURES: BDNF was measured by enzyme immunoassay methods in the serum of: mothers at the first stage of labor (MS), the umbilical cord (UC) and the neonates on days 1 (N1) and 4 (N4) postpartum. RESULTS: Levels of BDNF in (a). FMS did not differ from PMS, but both were significantly higher than respective (F or P) UC, N1 and N4 (p ranging from <0.01 to <0.001), (b). FUC, FN1 and FN4 were significantly higher than PUC (p<0.001), PN1 (p<0.03) and PN4 (p<0.02), respectively, (c). PN1 increased significantly as compared to PUC (p<0.05). CONCLUSIONS: Higher BDNF MS levels may reflect the mature nervous and immune systems of mothers. Higher BDNF levels in F than P may also be due to advanced maturity in the former. Increased BDNF levels in PN1 as compared to PUC may indicate stimulation of immune response with exposure to antigenic stimuli from the extrauterine environment. Nevertheless, this stimulation is insufficient in P, who by decreasing N4 levels are by far less protected than F.

Adult↗
PubMed1982

[Antidromal identification of hypothalamic neurosecretory cells in the rat].

Characteristics of antidromic action potentials of neurons in hypothalamic paraventricular and supraoptic nuclei were investigated during stimulation of hypothalamo-hypophyseal tract by stimuli of different amplitude and frequency. At tract stimulation with increased strength (1.5-2.5 times threshold) or frequency (above 100/s) discrete changes in antidromic action potential latency as well as variation of the spike fractionation in response to testing stimulus were observed. Leu-enkephaline administration into the third ventricle and intravenous injection of 1M NaCl solution reversibly changed the excitability of the antidromically activated neuron: leu-enkephaline mostly increased the latent period and the threshold of spike generation and decreased their capability to follow the stimulation frequency up to 10 Hz, whereas NaCl produced opposite effects. The data obtained indicate the necessity to take into account the excitability of the neurosecretory cell when using the accepted criteria of their antidromic identification.

Animals↗
PubMedDate not supplied

Activation and suppression of the trapezius muscle induced by transcranial magnetic stimulation.

Motor evoked potentials (MEPs) and silent periods (SPs) in the trapezius muscle induced by transcranial magnetic stimulation (TMS) were investigated in 15 healthy subjects. Stimuli were applied with a Novametrix Magnetic stimulator using a 14 cm circular coil 4 cm lateral to the vertex on the biauricular line. Surface electrodes were used for simultaneous bilateral electromyographic recordings of the trapezius. TMS invariably induced contralateral MEPs (latency 10.5 +/- 1.3 ms, mean +/- SD), with ipsilateral responses in 53% of the subjects (latency 11.1 +/- 2.5 ms). The mean duration of the SPs was approximately 90 ms on both sides. There were no significant side differences between any of the MEP or SP parameters. To study the influence of subcortical inhibition phenomena TMS induced responses were assessed following electrical mental nerve stimulation with interstimulus intervals (ISI) of 0-100 ms. MEP latencies significantly increased at ISI of 10-100 ms, whereas MEP amplitudes and SPs did not change. These findings may reflect a trigeminal induced exteroceptive suppression of trapezius muscle activity.

Accessory Nerve↗
PubMed1993

Triggered propagated contractions in human atrial trabeculae.

OBJECTIVE: Mechanical stretch and rapid release of locally damaged regions of rat cardiac trabeculae due to contraction of undamaged cells during the regular twitch have been shown to trigger local aftercontractions in the damaged region. These aftercontractions appear to propagate along the length of the trabeculae and to precede triggered arrhythmias. The aim of this study was to determine whether triggered propagated contractions can also be elicited in human cardiac tissue. METHODS: Trabeculae were dissected from a biopsy of the right atrial appendage which was obtained during cardiac surgery. They were mounted horizontally, superfused with a modified Krebs-Henseleit solution, and monitored with a video system. Force was measured with a silicon strain gauge; sarcomere length was measured with laser diffraction techniques. Triggered contractions were elicited in 10 trabeculae following trains of 15 stimuli at a rate of 2 Hz, separated by 15 s rest intervals, at 21 degrees C and a [Ca2+]o above 5.0 mM. RESULTS: Both video analysis and sarcomere length recordings showed that the contractions started at one end of the trabeculae and travelled from there as a localised contraction along the muscle. Increasing [Ca2+]o or the number of conditioning stimuli increased force of the stimulated twitches up to a maximum; further increase of [Ca2+]o or the number of stimuli was accompanied by a decrease of force. Force of the triggered propagated contractions increased monotonically with increasing [Ca2+]o and number of stimuli, while the interval between last stimulus and the peak of the force transient (or latency) decreased progressively, and propagation velocity increased monotonically. Propagation velocity was calculated from the interval between peak sarcomere shortening at two sites and the distance between these sites, as well as from the ratio between the length of the muscle and the duration of the force transient in the remainder of the trabeculae. With increasing temperature at constant [Ca2+]o twitch force increased while latency, force, and duration of the force transient decreased. At 37 degrees C, localised contractions travelling along the muscle could still be induced at sufficiently increased [Ca2+]o. For all interventions, propagation velocity varied from 0.8 to 3.9 mm.s-1. CONCLUSIONS: Contractions can be elicited in human atrial cardiac trabeculae. These contractions have the same basic characteristics as the triggered propagated contractions that have been described previously in rat ventricular trabeculae.

Arrhythmias, Cardiac↗
PubMed2006

Limited plasticity of difference neurons in the visual cortex and hippocampus in rabbits during the oddball (random substitutions) test.

The activity of 41 visual cortex neurons and 20 hippocampal field CA1 neurons was studied in rabbits during application of the oddball stimulation paradigm using color stimuli of different intensities. Among these cells, about one third were plastic cells (34% of cortical cells and 37% of hippocampal cells). These neurons showed significant increases in late responses, at times 200-500 and 200-1000 msec for visual cortex neurons and 300-550 msec for hippocampal neurons, to rare deviant stimuli of lesser intensity as compared with responses to the frequent standard stimuli of greater intensity. The initial peak of the response (40-120 msec), the "difference discharge," remained stable in responses to deviant and standard stimuli throughout the experiment. It is suggested that the strengthening of the late components of neuron responses to rare deviant stimuli (limited plasticity) reflects inclusion of the mechanisms of the orientational reflex.

Animals↗
PubMed1983

[The effects of electric stimulation of the visual cortex of the cat in a behavior model of placing reaction].

In 5 alert cats, the dependence of latency and probability of placing reaction on the parameters of electrical stimulation of visual cortex (the pulse duration and frequency in a series, number of pulses in a series) was studied. The values of current parameters were analogous to those that aroused human phosphens. The results revealed the conformity of the dependence of phosphens and cat's motor reaction on the current parameters. An addition of sound or electrocutaneous stimuli to the current stimulation decreases the threshold of the motor reaction and increases its probability. It is particularly obvious in case of weak and middle intensity currents when the probability of correct reactions to the current is insignificant.

Animals↗
PubMed1991

Unmyelinated primary afferent fiber stimulation depletes dynorphin A (1-8) immunoreactivity in rat ventral horn.

The present study demonstrates many dynorphin (DYN)-immunoreactive fibers and presumed presynaptic terminals in rat lumbar ventral horn. The fibers and terminals seem to arise largely from DYN-containing intrinsic neurons in the dorsal horn. The majority of the presumed terminals closely surround a subpopulation of motoneurons that tend to be located in flexor motoneuron columns. Acute C fiber, but not A fiber, primary afferent stimulation depletes the ventral horn DYN immunostaining. We interpret these findings to indicate that the spinal DYN neurons are well positioned to serve both as modulators of nociceptive input and as interneurons in motor reflexes. We further hypothesize that the depletion of DYN-immunoreactivity that follows either acute C fiber stimulation or intense nociceptive stimuli may be the trigger for the upregulation in spinal cord DYN that occurs in models of chronic pain states.

Afferent Pathways↗