Modelling the response of scalp sensory receptors to transcranial electrical stimulation

Transcranial electrical stimulation of the brain causes considerable discomfort to the patient. The purpose of the study was to find out whether this could be affected by the choice of stimulation parameters. A spherical volume conductor model of the head and active compartmental models of a pyramidal motor nerve and scalp nociceptor were used in combination to simulate the scalp nociception to transcranial electrical stimulation. Scalp nociceptors were excited at distances of several centimetres from the electrodes. The size of the excited scalp area correlated with the length of the stimulation pulse. The area was 12.3, 20.4 and 26.0 cm2, for a 10 micros, 100 micros and 1 ms constant current pulse, respectively. With a 100 micros constant current pulse, the threshold for motor excitation was 205mA and, for nociception, it was 51 mA. There was no significant difference between constant current and capacitor discharge pulses or between electrodes of different sizes. The results imply that the use of very short stimulation pulses can reduce the pain. If a topical anaesthesia is used to reduce the pain, it has to be applied on a large area around the electrodes.

Direction-specific motion blindness induced by focal stimulation of human extrastriate cortex

Motion blindness (MB) or akinetopsia is the selective disturbance of visual motion perception while other features of the visual scene such as colour and shape are normally perceived. Chronic and transient forms of MB are characterized by a global deficit of direction discrimination (pandirectional), which is generally assumed to result from damage to, or interference with, the motion complex MT+/V5. However, the most characteristic feature of primate MT-neurons is not their motion specificity, but their preference for one direction of motion (direction specificity). Here, we report that focal electrical stimulation in the human posterior temporal lobe selectively impaired the perception of motion in one direction while the perception of motion in other directions was completely normal (unidirectional MB). In addition, the direction of MB was found to depend on the brain area stimulated. It is argued that direction specificity for visual motion is not only represented at the single neuron level, but also in much larger cortical units.

Mouse strain variation in maximal electroshock seizure threshold

Maximal electroshock seizure threshold (MEST) is a classical measure of seizure sensitivity with a wide range of experimental applications. We determined MEST in nine inbred mouse strains and one congenic strain using a procedure in which mice are given one shock per day with an incremental (1 mA) current increase in each successive trial until a maximal seizure (tonic hindlimb extension) is elicited. C57BL/6J and DBA/2J mice exhibited the highest and lowest MEST, respectively, with the values of other strains falling between these two extremes. The relative rank order of MEST values by inbred strain (highest to lowest) is as follows: C57BL/6J > CBA/J = C3H/HeJ > A/J > Balb/cJ = 129/SvIMJ = 129/SvJ > AKR/J > DBA/2J. Results of experiments involving a single electroconvulsive shock given to separate groups of mice at different current intensities suggest that determination of MEST by the method used is not affected by repeated sub-maximal seizures. Overall, results document a distinctive mouse strain distribution pattern for MEST. Additionally, low within strain variability suggests that environmental factors which affect quantification of MEST are readily controlled under the conditions of this study. We conclude that MEST represents a useful tool for dissecting the multifactorial nature of seizure sensitivity in mice.

A prospective study of motor recovery following multiple subpial transections

A prospective study of motor recovery was undertaken in a patient scheduled to undergo multiple subpial transections (MST) of right sensorimotor cortex. Pre-transection, functional MRI (fMRI) and cortical stimulation mapping confirmed left hand motor control within right primary motor cortex. Immediately post-transection, behavioral testing demonstrated preserved strength bilaterally but decreased dexterity in the left hand. Seven weeks post-transection, dexterity returned to normal and left hand finger tapping corresponded with multiple bilateral foci of fMRI activation. At 16 weeks, fMRI activation returned to pre-transection levels. These data indicate that cortical injury due to MST resulted in the temporary recruitment of distant cortical sites which presumably subserved normal motor function during recovery.

In vivo assessment of skin electroporation using square wave pulses

The application of short-duration high-voltage pulses to the skin has been shown to enhance transdermal drug delivery by several orders of magnitude and to transiently permeabilize cells in tissue. Both exponentially decaying (ED) pulses and square wave (SW) pulses have been applied. The latter have also been used for electrochemotherapy. To date, their effect on skin integrity has not been analyzed. The scope of this work was (i) to investigate the effect induced by SW pulses on the stratum corneum and the skin, (ii) to evaluate the safety issue associated with electroporation, (iii) to contribute to the understanding of drug transport. Biophysical techniques (transepidermal water loss, chromametry, impedance and laser Doppler velocimetry or imaging measurement) and histological methods were combined to provide a global picture of the effects. Ten SW pulses applied to the skin induced a mild impairment of the skin barrier function and a dramatic decrease in skin resistance. These changes were reversible. A transient decrease (<5 min) in blood flow was observed. Neither inflammation, nor necroses were observed. These studies confirm the tolerance of the skin to square wave pulses in vivo.

Corticospinal volleys and compound muscle action potentials produced by repetitive transcranial stimulation during spinal surgery

OBJECTIVES

To report our experience with neurophysiological monitoring of corticospinal function using compound muscle action potentials (CMAPs) produced by repetitive transcranial electrical stimulation in a large series of patients, after defining optimal stimulus parameters in a small group of patients.

METHODS

In 100 patients undergoing spinal surgery, corticospinal volleys were recorded using epidural electrodes, or CMAPs were recorded from innervated muscles, or both techniques were used to monitor spinal cord function. In subsets of patients, stimulus parameters were varied to determine the optimal parameters for CMAP recordings, using the corticospinal volleys to guide the initial choice.

RESULTS

Recordings of corticospinal volleys indicated that less energy was delivered to the cortex if the duration of each stimulus in the stimulus train was brief (e.g. 50 micros) and that there was attenuation of D and I waves in the corticospinal volley when the interstimulus interval in the train was <5 ms. An interstimulus interval of 5 ms proved significantly more effective than an interstimulus interval of 2 ms in evoking CMAPs, but resulted in a more complex, dispersed electromyographic (EMG) potential. The superiority of the 5 ms interval did not depend on stimulus intensity or the existence of pre-existing neurological deficit. Using trains of 5 pulses of duration 50 micros, interstimulus interval 5 ms and intensity 500 V, satisfactory CMAPs could be recorded in 55 of 82 patients, significantly less often in neurologically impaired patients than in neurologically normal subjects. Epidural recordings of the corticospinal volley were obtained in 61 of 69 patients, again more often in neurologically normal subjects.

CONCLUSIONS

When epidural recordings can be made, direct recordings of corticospinal activity are probably more reliable than recordings of CMAPs. However, epidural recordings are not suitable under all circumstances, and the ability to record CMAPs reliably represents an advance in intraoperative monitoring. Under the anaesthetic conditions used in the present study, the optimal stimulus parameters consist of a train of 5 stimuli of 50 micros duration at an interstimulus interval of 5 ms and an intensity of 500 V.

Wavelet-crosscorrelation analysis can help predict whether bursts of pulse stimulation will terminate afterdischarges

OBJECTIVE

Extraoperative cortical localizing stimulation (LS) is a standard clinical tool used to assess brain function before epilepsy surgery. However, LS can produce unwanted afterdischarges (ADs). We previously have shown that brief pulses of electrical stimulation (BPS) can terminate ADs caused by cortical stimulation. Our objective was to assess whether wavelet-crosscorrelation analysis could help predict the conditions under which BPS would be most likely to terminate ADs.

METHODS

We used wavelet-crosscorrelation analysis to get wavelet-correlation coefficients (WCC), and determine time lag (TL) and absolute value of TL (ATL) between two electrodes. For Analysis-1, we compared WCC and ATL in epoch 1 which was before LS, epoch 2 which was after LS but before BPS, and epoch 3 which was after BPS. For Analysis 2, we compared WCC and ATL during epoch 1 under 4 conditions: epochs when ADs subsequently terminated within 2 s after the end of BPS (1A), terminated within 2-5 s (1B), did not terminate within 5 s (1C), and when ADs did not appear (1D).

RESULTS

We found that BPS efficacy in terminating ADs was predicted by (1) low correlation and (2) slow propagation speed between electrode pairs in the 2-10 s period before stimulation.

CONCLUSIONS

Wavelet-crosscorrelation analysis can help predict conditions during which BPS can abort ADs. It is possible that similar analyses could help predict when BPS or other interventions could abort clinical seizures.

[Role of electric stimulation in apnea syndromes]

The sleep apnoea syndrome is the best known apnoeic syndrome. It is observed in 4% of men and 2% of women. Nasal ventilation with continuous positive pressure is the best treatment for most patients. To date, electrical stimulation has a limited role in its treatment as it is used only when the apnoea requires ventilation by tracheotomy. This electrogenic ventilation requires so-called diaphragmatic stimulators. Although severe bradycardia may occur during sleep apnoea, there is usually no indication for cardiac pacing. However, recent publications have reported an anti-apnoeic effect of permanent atrial pacing. The modes of action remain unclear but these results support other recently reported data concerning the value of pacing in cardiac failure, the high incidence of sleep apnoea in cardiac failure patients and the possibility of diagnosing and monitoring apnoea by minute ventilation sensors. Therefore, there appears to be a field of research for cardiac pacing in apnoea syndromes. The authors review the principal reported data on the indications and possibilities of extra-cardiac and cardiac stimulation in apnoeic syndromes.

The effects of prolonged intracortical microstimulation on the excitability of pyramidal tract neurons in the cat

This study was conducted to examine the excitability changes induced in cerebral cortical neurons during prolonged microstimulation with a spatially dense microelectrodes array. The arrays of 16 iridium microelectrodes were implanted chronically into the postcruciate gyrus of cats. Neuronal responses characteristic of single pyramidal tract axons (ULRs) were recorded in the medullary pyramid. 7 h of pulsing of individual electrodes at 50 Hz and at 4 nC/ph induced little or no change in the ULRs' electrical thresholds. The thresholds also were quite stable when 4 of the 16 microelectrodes were pulsed on each of 14 consecutive days. However, when all 16 microelectrodes were pulsed for 7 h at 4 nC/ph, the threshold of approximately half of the ULRs became elevated. Recovery of excitability required 2-18 days. Prolonged sequential (interleaved) pulsing of the 16 microelectrodes induced less depression of excitability than did simultaneous pulsing, but only when the stimulus amplitude was low (12 A, 1.8 nC/ph). Stimulation at a higher amplitude (15 nC/ph) induced much more depression of excitability. These findings imply that multiple processes mediate the stimulation-induced depression of neuronal excitability. The data also demonstrate that the depression can be reduced by employing a stimulus regimen in which the inherent spatial resolution of the array is maximized (sequential pulsing at an amplitude in which there is minimal overlap of the effective current fields).

Adaptation and habituation to an open field and responses to various stressful events in animals with neonatal lesions in the amygdala or ventral hippocampus

A rat model of neurodevelopmental psychopathological disorders, designed to determine neurodevelopmental deficits following damage to the brain early in life, was used to investigate behavioural changes in adaptation and habituation to an open field and responses to different kinds of stressful events. Animals with bilateral ibotenic acid lesions in the amygdala or ventral hippocampus on day 7 or 21 of life were compared to sham-operated animals. According to the model it was assumed that behavioural changes in animals lesioned on day 7, but not in animals lesioned on day 21 of life, were caused by maldevelopment of one or more structures connected to the damaged area. Animals lesioned in the amygdala or ventral hippocampus on day 7, but not animals lesioned in these structures on day 21 of life, displayed decreased (within-session) adaptation and (between-session) habituation to the open field and a decrease in immobility in the forced swim test, whereas only animals lesioned in the amygdala displayed enhanced general activity. These results were indicative of neurodevelopmental deficits. No changes in stress-induced hyperthermia were found, while animals lesioned in the amygdala both on day 7 or 21 of life exhibited decreased conditioned ultrasonic vocalizations. These latter results suggest that the amygdala is implicated in the conditioned stress-induced response. The contribution of the present findings to the animal model of neurodevelopmental disorders like schizophrenia and possible brain structures and neurotransmitter systems involved in the neurodevelopmental deficits are discussed.

Prenatal cocaine exposure increases mesoprefrontal dopamine neuron responsivity to mild stress

Children whose mothers used cocaine during pregnancy appear to have an increased incidence of certain neurobehavioral deficits. Rodent models of prenatal cocaine exposure have mimicked these deficits in the offspring, yet the biochemical basis of the behavioral abnormalities is unknown. We have been able to reproduce short-term memory deficits in our rat intravenous model of prenatal cocaine exposure, and as short-term memory is dependent on the function of dopamine neurons innervating the medial prefrontal cortex, we hypothesized that prenatal cocaine induces a dysfunction in the regulation of this pathway. Here we report that mild footshock stress, which preferentially activates the mesoprefrontal dopamine system, leads to an enhanced increase in dopamine turnover in the ventromedial prefrontal cortex of adolescent (postnatal day 35-37) rats exposed to cocaine in utero, suggesting that the dopamine neurons innervating this region are hyperresponsive in these rats. Thus, this biochemical alteration may be central to some of the cognitive deficits exhibited by offspring that were exposed to cocaine during fetal development.

Electrical stimulation of transforming growth factor-beta 1 secretion by human dermal fibroblasts and the U937 human monocytic cell line

The in vitro effects on human dermal fibroblasts and the U937 human monocytic cell line of three phases of electrical microcurrents generated by the ACE Stimulator were investigated. The growth and viability of growing and confluent dermal fibroblasts were not directly influenced by the separate microcurrent phases. One form of microcurrent (designated phase 1) stimulated both dermal fibroblasts and U937 cells to secrete transforming growth factor-beta 1 (TGF-beta 1), which is an important regulator of cell-mediated inflammation and tissue regeneration, but none of the three phases stimulated secretion of the pro-inflammatory cytokine interleukin-6 by U937 cells. The stimulation of TGF-beta 1 secretion in these experiments was not dramatic (a median increase over control levels of 20-30%), although it could be biologically significant.

Synapse-associated protein 97 selectively associates with a subset of AMPA receptors early in their biosynthetic pathway

The regulation of AMPA receptors at the postsynaptic membrane is a fundamental component of synaptic plasticity. In the hippocampus, the induction of long-term potentiation increases the delivery of GluR1, a major AMPA receptor subunit in hippocampal pyramidal neurons, to the synaptic plasma membrane through a mechanism that requires the PDZ binding domain of GluR1. Synapse-associated protein 97 (SAP97), a member of the membrane-associated guanylate kinase family, is believed to associate with AMPA receptors (AMPARs) containing the GluR1 subunit, but the functional significance of these interactions is unclear. We investigated the interaction of GluR1 with SAP97, the only PDZ protein known to interact with GluR1. We find that interactions involving SAP97 and GluR1 occur early in the secretory pathway, while the receptors are in the endoplasmic reticulum or cis-Golgi. In contrast, few synaptic receptors associate with SAP97, suggesting that SAP97 dissociates from the receptor complex at the plasma membrane. We also show that internalization of GluR1, as triggered by NMDAR activation, does not require SAP97. These results implicate GluR1-SAP97 interactions in mechanisms underlying AMPA receptor targeting.

Conventional anticonvulsant drugs in the guinea-pig kindling model of partial seizures: effects of acute carbamazepine

This study addressed the anticonvulsant effect of carbamazepine (CBZ) in the guinea-pig kindling model to further test this model for the screening of anticonvulsant drugs. We analysed plasma concentrations of CBZ at various time intervals after intraperitoneal injection of either 10, 25 or 40 mg/kg CBZ. Behavioural toxicity was assessed at 0.5 h postinjection using quantitative locomotor tests, as well as scores on a sedation/muscle relaxation rating index. The anticonvulsant efficacy of CBZ was evaluated from measurements of afterdischarge threshold (ADT), afterdischarge duration (ADD), and behavioural seizure severity at three phases of kindling: non-kindled, kindling acquisition (early and late) and kindled (50+ ADs). ADD and seizure severity were also measured in response to both threshold and suprathreshold kindling stimulation. Plasma levels of CBZ were within, or higher, than the human therapeutic range at the time of behavioural testing and kindling. CBZ exerted slight effects in guinea-pigs on the sedation rating index but not the behavioural tests. CBZ increased ADT and reduced ADD and seizure severity throughout all phases of kindling, indicating that the guinea-pig model correctly predicts CBZ's anticonvulsant effect. CBZ in the guinea-pig kindling model produced consistent anticonvulsant activity that did not appear to be dependent on stimulation intensity.

Conventional anticonvulsant drugs in the guinea-pig kindling model of partial seizures: effects of acute phenytoin

This study addressed some of the controversial issues surrounding the anticonvulsant effect of phenytoin, and the predictive validity of the guinea-pig kindling model for the screening of anticonvulsant drugs. Following an intraperitoneal injection of either 50 or 75 mg/kg phenytoin, we analysed plasma concentrations of phenytoin at various time intervals. Behavioural toxicity was assessed at 0.5 h postinjection using quantitative locomotor tests, as well as scores on a sedation/muscle relaxation rating index. The anticonvulsant efficacy of phenytoin was evaluated from measurements of afterdischarge threshold (ADT), afterdischarge duration (ADD) and behavioural seizure severity at three phases of kindling: non-kindled, kindling acquisition (early and late) and kindled (50+ ADs). ADD and seizure severity were also measured in response to both threshold and suprathreshold kindling stimulation. Plasma levels of phenytoin corresponded to the human therapeutic range at the time of behavioural testing and kindling. Phenytoin did not exert significant adverse effects in guinea-pigs on both the behavioural tests and rating index. Phenytoin increased ADT in non-kindled and kindled guinea-pigs and effectively reduced ADD and seizure severity, indicating that the guinea-pig model correctly predicted phenytoin's anticonvulsant effect. Phenytoin produced reliable anticonvulsant activity in the guinea-pig at threshold stimulation but a somewhat reduced efficacy on seizure severity at suprathreshold stimulation intensities. Kindling in the guinea-pig is a valid model of human partial seizures.

Mechanisms by which AC leakage currents cause complete hemodynamic collapse without inducing fibrillation

INTRODUCTION

The first study of weak alternating current (AC) stimulation in closed chest humans showed that complete hemodynamic collapse can occur below the threshold for inducing ventricular fibrillation (VF), a heretofore unknown danger to patients. This article, and the accompanying simulation article, explore the mechanisms responsible for the collapse.

METHODS AND RESULTS

A quadripolar pacing catheter was placed in the right ventricle (RV) of six dogs. The tip of the catheter (17 mm2) carried 5 seconds of AC stimulation ranging from 10 to 160 Hz and 10 to 1,000 microA. The lead II body surface ECG, femoral artery pressure, and a bipole from the proximal pair of electrodes on the RV catheter were recorded 2 seconds before, during, and 2 seconds after stimulation. Based on the blood pressure, every episode was categorized as VF, COLLAPSE without VF, extrasystolic without COLLAPSE (EFFECT), or having caused no effect (NSR). The electrical activation interval (interspike interval [ISI]) from the RV bipole was compared with the mechanical activation interval, determined from M-mode ultrasound. COLLAPSE is associated with a short ISI (NSR = 408+/-110 msec; EFFECT = 305+/-113 msec; COLLAPSE = 179+/-25 msec; P < 0.001) with a high degree of regularity (P < 0.001): coefficient of variation of ISI for COLLAPSE (0.038+/-0.069) versus VF (0.389+/-0.222), EFFECT (0.420+/-0.241), and NSR (0.016+/-0.048). Electrical activation and mechanical activation rates occurred at integer multiples of the AC stimulation period.

CONCLUSION

COLLAPSE (86+/-37 microA; minimum 50 microA in two animals) occurs below the VF threshold (108+/-28 microA) by causing rapid, regular excitation.

Transcranial magnetic stimulation differentially affects speed and direction judgments

This study was conducted to determine whether humans' judgments about the speed and direction of moving stimuli was differentially affected by transcranial magnetic stimulation (TMS). Subjects viewed two successively presented moving stimuli that differed from each other both in speed and direction of motion. Single-pulse TMS was applied either medially (approximately 2 cm above the inion) or laterally (approximately 5 cm lateral to and 4 cm above the inion), while subjects judged the speed and direction differences. The physical stimulation (visual and TMS) was identical on the two tasks, as was discriminability (d') when TMS was not applied. We found significant criterion (beta) shifts on the speed discrimination task at both stimulation sites. Specifically, on TMS trials the proportion of "slower" judgments increased significantly, consistent with subjective reports that stimuli often appeared to slow when TMS was applied. The subjective reports indicated no corresponding change in perceived direction. We also found that speed discriminability was impaired significantly more than direction discriminability, but only when TMS was applied medially. Indeed, after controlling for TMS-related changes in reaction time, speed discriminability was impaired significantly, while direction discriminability remained largely intact. This dissociation suggests that the sensory response constraining speed discrimination is at least partially independent from the sensory response constraining direction discrimination. Combined with previous psychophysical data, the present data suggest a double dissociation between speed and direction discrimination in humans.

Roles of central interleukin-1 on stress-induced-hypertension and footshock-induced-analgesia in rats

Central interleukin-1 (IL-1) plays an important role in mediating the neural, endocrine, and behavioral responses to stressors. Here we tested whether central IL-1 is involved in stress-induced hypertension or footshock (FS)-induced-analgesia. We observed that: (1) intracerebral ventricular injection of (ICV) IL-1beta induced pressor responses; (2) hypertension induced by IL-1beta was blocked by ICV an IL-1 antagonist, IL-1ra; (3) ICV IL-1ra attenuated the pressor response induced by FS but intravenous injection of IL-1ra did not significantly reduce this response; (4) the hypertensive response to conditioned fear stimuli was reversed by ICV IL-1ra; (5) FS-induced-analgesia was attenuated by ICV IL-1ra and this effect disappeared 15 min after ICV IL-1ra. These results suggest that both the pressor response to FS or conditioned fear stimuli and short lasting analgesia induced by FS are mediated by central IL-1.

Seizures induce phase shifts of rat circadian rhythms

RATIONALE

Epileptic seizures may alter neuroendocrinological cycles. Light pulses induce phase shifts in circadian rhythms. Using hippocampal-kindled rats to ensure maximal clinical expression, we determined if seizures likewise induce phase shifts.

METHODS

We monitored the circadian rhythm of temperature (CRT) with intraperitoneal radiotelemetry in rats (n=21) isolated from time cues and light for 3-week trials. Seizures were triggered with hippocampal electrical stimulation at different circadian phases. Optimized, least-error phase shifts were calculated from preictal and postictal CRTs. Induced seizures were referenced to CRT (t(max)=00:00, 24-h circadian cycle).

RESULTS

Phase shifts (individual responses=57) differed across the circadian cycle. Rather than forming a clear phase-response curve, phase shifts were especially variable between 00:00 and 06:00 h.

CONCLUSIONS

This study demonstrates that electrically-induced seizures induce advances and delays in CRT in a phase-dependent fashion but in a pattern different from typical light-induced phase shifts. Disorders of circadian regulation may contribute to some of the altered endogenous cycles associated with epilepsy.

Postvibration depression of the H-reflex as a result of a dual mechanism: an experimental study in humans

Changes in amplitude of the soleus H (S(H))-reflex and its neurographic correlates (P(1) and P(2) waves) after vibration of the soleus muscle have been evaluated as a function of mechanical stimulation frequency, duration of the conditioning train, and test stimulus intensity. Additional experiments aimed at assessing the nervous system mechanisms underlying the postvibration depression (PVD) have been performed. In particular, homonymous (S(HMR) or S(H)) versus heteronymous (S(HTR)) soleus response, evoked respectively by tibial nerve and femoral nerve electrical stimulation, the effectiveness of sub-H threshold tibial nerve conditioning volleys on the S(HTR), and the respective effects of a brief passive stretching of the quadriceps and soleus muscles on the recovery of both the S(HMR) and S(HTR) after vibration of the homologous muscle were investigated under suitable experimental conditions. It was found that PVD occurs in the absence of changes in amplitude of the P(1) wave and the S(HTR), is paralleled by a reduced effectiveness of tibial nerve-conditioning volleys on the S(HTR) and is shortened consistently by brief passive stretching of the homologous muscle. It follows that PVD may be the result of a long-lasting reduction of the transmitter release from Ia presynaptic terminals depending, at least in part, on a protracted postvibration Ia afferent discharge caused by spindles thixotropy. These findings may provide a better understanding of the pathophysiologic mechanisms underlying spasticity in humans.

Long-term change in synaptic transmission in CA3 circuits followed by spontaneous rhythmic activity in rat hippocampal slices

The relevance of long-term potentiation (LTP) at excitatory synapses in CA3 circuits to generation of spontaneous epileptiform bursts in CA3 was investigated using rat hippocampal slices. CA3 pyramidal cells were antidromically stimulated through Schaffer collaterals. Evoked field potentials were extracellularly recorded from the stratum pyramidale and the stratum radiatum in CA3. Therefore, field potentials reflecting recurrent excitatory post-synaptic potentials (EPSPs) and inhibitory post-synaptic potentials (IPSPs) were positive at the stratum pyramidale and negative at the stratum radiatum. First, we tested how the amplitude of the evoked field potentials depends on a gamma-aminobutyric acid (GABA(A)) antagonist. Both of the positive and negative field potential peaks reduced in the medium containing penicillin (2 mM) or bicuculline (20 microM). This suggests that unmasked EPSPs due to suppression of IPSPs do not result in an increase in the evoked potentials. Second, CA3 pyramidal cells were antidromically stimulated by tetanic stimulation of Schaffer collaterals in order to induce LTP at synapses in CA3 circuits. Both of the positive and negative field potentials increased, suggesting that recurrent EPSPs were enhanced by tetanic stimulation. Induction of LTP at recurrent excitatory synapses was followed by spontaneous epileptiform bursts which persisted throughout experiments (approximately 1.5 h), while LTP of afferent synaptic potential evoked by hilar test stimulation was not induced. These results suggest that LTP at the afferent synapses is not necessary to spontaneous epileptiform bursts in CA3, but LTP at excitatory synapses between CA3 pyramidal cells contribute to spontaneous epileptiform bursts.

[Effects of several different irritation factors on leukocytes adhesion in microvessels]

AIM

The interrelation of adhesion between leukocyte and endothelium was studied by several irritation factors.

METHODS

Leukocyte adhesion was observed by impulse electricity irritation, ischemia/reperfusion, endotoxin and IL-8 in venular of rat mesentery.

RESULTS

The results showed these irritation factors resulted in a significant increase in the number of leukocytes adhesion along the venular endothelium of rat mesentery. IL-8 leaded to the most increase of leukocytes adhesion. Especially treated by IL-8 for 30 minutes. The number of leukocytes adhesion of the others was approximately identical.

CONCLUSION

The study suggests that impulse electricity irritation, ischemia/reperfusion, endotoxin and IL-8 are able to induce leukocytes and endothelium adhesion, and IL-8 of them has the most effect.

Stress-induced sensitization of CRH-ir but not P-CREB-ir responsivity in the rat central nervous system

There is some evidence that a traumatic life event can induce long-term alterations in corticotropin-releasing hormone (CRH) producing neurons in humans, which may play a role in the pathophysiology of anxiety disorders, including post-traumatic stress disorder (PTSD). To study the long-term effects of a traumatic event on brain CRH-immunoreactivity (CRH-ir) and phospho-cAMP response element binding protein-immunoreactivity (P-CREB-ir), rats were exposed to a single session of foot shocks (preshocked) or no shocks (control). Two weeks later half of the control rats and half of the preshocked rats received an electrified prod in the home cage for 15 min and behavior was recorded. Fifteen minutes after the removal of the prod rats were perfused and brain sections were stained for CRH-ir and P-CREB-ir. There was no basal difference between preshocked and control rats in brain CRH-ir and P-CREB-ir. Exposure to the electrified prod induced a significant increase in CRH-ir in the paraventricular nucleus of the hypothalamus, the median eminence and the central amygdala in preshocked rats, but not in control rats. The electrified prod increased the number of P-CREB-ir neurons in the paraventricular nucleus of the hypothalamus and the locus coeruleus, but the preshock experience did not affect this response. In an additional experiment with a similar design plasma hormone levels were measured 14 days after the foot shocks. The preshock experience sensitized the shock prod-induced ACTH and corticosterone response. No behavioral differences between preshocked and control rats were found during the shock prod tests. We suggest that long-term stress-induced changes in neuropeptide dynamics of CRH-ir neurons may play a role in long-term stress-induced neuroendocrine sensitization.