Evidence for biorhythmicity from the preoptic nucleus of the rainbow trout Salmo gairdnerii under freely swimming conditions--an electrophysiological study

This study describes a technique which allows continuous recording of MUA (Multiple Unit Activity), from the NPO (Preoptic Nucleus), DAP (Dorsal Aortic blood Pressure) and ECG (Electrocardiogram) in freely swimming rainbow trout. From the 21 trout tested, six trout (29%) clearly showed rhythmic patterns of MUA during the five post-operative days (D2-D6). The mean length of rhythmic MUA was about 18 hr (range 6-33 hr) among the six trout during the recording days. Periodic MUA occurred approximately eight times/hr and lasted about 2 min. The maximal frequency of discharges was 20-30 spikes per sec. No change occurred in the mean level of blood pressure from the first operative day to the following post-operative days, where rhythmic MUA appeared or reappeared. These results demonstrate the existence of biorhythmicity within the NPO of freely swimming trout and suggest parallel oscillations in neurohormones secretion.     

Effects of nimodipine on multiunit activity of several brain structures following acute global cerebral ischemia-anoxia in cats.

The effects of nimodipine, a 1,4-dihydropyridine calcium channel blocker, on multiunit activity (MUA) of several brain structures were investigated in cats during 6 h immediately following acute global cerebral ischemia-anoxia induced by a 10 min cardiorespiratory arrest (CRA), as well as in cats exposed to sham procedures corresponding to CRA. Four groups of cats were studied: 1) CRA and continuous administration of nimodipine, 1 microgram/kg/min iv during 6 h; 2) CRA and continuous administration of vehicle; 3) sham and continuous administration of nimodipine as in group 1; 4) sham and vehicle as in group 2. MUA and electroencephalogram disappeared during ischemia-anoxia; their progressive recovery occurred throughout the hours following CRA, although 6 h after CRA MUA was still lower than its control prearrest values in all the recorded subcortical structures. Delta-like waves, isolated spikes, and bursts of fast EEG waves occurred during the recovery of EEG activity. Nimodipine inhibited the otherwise increasing MUA in mesencephalic reticular formation, hippocampus and putamen, but not in ventromedial hypothalamus, during the hours following acute global cerebral ischemia-anoxia. Absence of isolated spikes and bursts of fast EEG activity was noted in the EEG of CRA-, nimodipine-treated cats. Nimodipine significantly reduced MUA in hippocampus but not in other cerebral structures in cats of the sham treated group. The results suggest the involvement of 1,4 dihydropyridine sensitive calcium channels in the cellular mechanisms related to neuronal activity after cerebral ischemia-anoxia, and the possible relationship between the effects of nimodipine on MUA and better functional conditions of the central nervous system after acute global cerebral ischemia-anoxia.     

Brain injury following cardiorespiratory arrest in cats. Effects of alphaxalone-alphadolone

The effects of alphaxalone-alphadolone acetate (27.07 microM/kg-7.68 microM/kg) on neurologic injury following acute cerebral ischemia induced by an 8 min cardiorespiratory arrest (CRA) were investigated in cats through the analysis of neurological deficit scores and brain electrical activity; i.e., electroencephalogram (EEG) from parieto-occipital cortices and EEG and multiunit activity (MUA) from mesencephalic reticular formation (MRF). The CRA resulted from electrically induced cardiac arrest and stopping of mechanical ventilation in paralyzed cats which were successfully resuscitated within the immediate 4 min after the end of CRA. Two groups of cats were studied: I. Untreated, which received saline iv; II. Treated, which received alphaxalone-alphadolone acetate iv, 7-9 min after the end of CRA. Neuromuscular blockade and mechanical ventilation were maintained until 8 h following the CRA; then the cats were allowed to recover spontaneous respiratory activity. EEG phenomena were different in untreated and treated cats during this immediate post-arrest period. The former showed rhythmic bursts of fast (12-20 Hz) EEG activity at 1-2 sec intervals from 15-20 min until 3-4 h after the CRA, abundant spikes and delta-like waves. By contrast, administration of alphaxalone-alphadolone acetate resulted in burst suppression EEG pattern during 1 h. Progressive recovery of background EEG activity occurred afterwards. MUA from MRF disappeared during the CRA, however 6 h later the mean MUA frequency in untreated cats ranged between 32-46% and in treated cats 18-27% of their control mean frequencies during paradoxical sleep (100%). Daily electrographic records were performed in all the cats during quiet attentive behavior at each of the five days following the CRA. Significant differences were found in the frequency distributions of MUA from MRF (1st day, p less than 0.01; 5th day, p less than 0.01) as well as in the cortical EEG waves (1st day, p less than 0.01; 5th day, p less than 0.05) before and after the CRA in the untreated group. A wide dispersion of MUA values, and increased proportions of delta and theta-like waves and spindle bursts, besides a significantly high (p less than 0.001) number of spikes occurred in these EEG records the days following the CRA. The frequency distributions of MUA and EEG did not significantly differ before and after the CRA in the treated group; however, a significantly high (p less than 0.05) number of spikes was found in treated cats following the CRA.(ABSTRACT TRUNCATED AT 400 WORDS)     

Role of purinergic cotransmission in the sympathetic control of arterial pressure variability in conscious rats

Previous studies have shown that the sympathetically mediated oscillations of arterial pressure (AP), the so-called Mayer waves, are shifted from 0.4 to 0.6 Hz after acute alpha-adrenoceptor blockade in conscious rats. This raises the possibility that, under physiological conditions, Mayer waves are mediated by the conjoint action of norepinephrine and other sympathetic cotransmitters. To evaluate the possible role of the cotransmitter ATP in determining the frequency of Mayer waves, AP and renal sympathetic nerve activity (RSNA) were simultaneously recorded in 10 conscious rats with cardiac autonomic blockade before and after acute blockade of P2 receptors with pyridoxal phosphate-6-azophenyl-2',4'-disulfonic acid. P2 receptor blockade did not alter the mean level and overall variability of AP and RSNA but shifted peak coherence between AP and RSNA from 0.43 +/- 0.02 to 0.22 +/- 0.01 Hz. A model of the sympathetic limb of the arterial baroreceptor reflex was designed to simulate Mayer waves at 0.2 and 0.6 Hz, with norepinephrine and ATP, respectively, acting as the sole sympathetic cotransmitter. When both cotransmitters acted in concert, a single oscillation was observed at 0.4 Hz when the gain ratio of the adrenergic to the purinergic components was set at 15. The model thus accounted for an important role for ATP in determining Mayer wave frequency, but not in sustaining the mean level of AP or controlling its overall variability.     

Evaluation of respiratory modulation on the pulse wave amplitude in low-birth-weight neonate.

A slow oscillation of sympathetic vasoconstriction (Mayer waves) which is affected by the respiratory movements seems to appear as the fluctuation of pulse wave amplitude (PPG.P-P) in the frequency domain (0.1 Hz). Whether the vasomotor in low frequency has appeared in the pulse wave of the neonate and whether Mayer waves appear as the pulse wave oscillation of the immature low-birth-weight neonate are not fully understood from the point of autonomic nerve regulation mechanism. We therefore analyzed the frequency characteristics of PPG.P-P, respiration wave and its amplitude (RW.P-P) together with the heart rate variability (HRV) to examine the relationships between the frequency spectra.     

Estradiol increases multiunit electrical activity in the A15 area of ewes exposed to inhibitory photoperiods

Seasonal anestrus in ewes results from an increase in response to the negative feedback action of estradiol (E(2)). This increase in the inhibitory effects of E(2) is controlled by photoperiod and appears to be mediated, in part, by dopaminergic neurons in the retrochiasmatic area of the hypothalamus (A15 group). This study was designed to test the hypothesis that E(2) increases multiunit electrical activity (MUA) in the A15 during inhibitory long days. MUA was monitored in the retrochiasmatic area of 14 ovariectomized ewes from 4 h before to 24 h after insertion of an E(2)-containing implant subcutaneously. In six of these ewes, MUA activity was also monitored before and after insertion of blank implants. Three of the 14 ewes were excluded from analysis because E(2) failed to inhibit LH. When MUA was recorded within the A15, E(2) produced a gradual increase in MUA that was sustained for 24 h. Blank implants failed to increase MUA in the A15 area, and E(2) did not alter MUA if recording electrodes were outside the A15. These data demonstrate that E(2) increases MUA in the A15 region of ewes and are consistent with the hypothesis that these neurons mediate E(2) negative feedback during long photoperiods.     

Circadian oscillation of the multiple unit activity in the guinea pig suprachiasmatic nucleus

Summary In the guinea pig with chronically implanted electrodes, neuronal multiple unit activity (MUA) was recorded inside and outside the suprachiasmatic nucleus (SCN). Long-term recording of the SCN indicated distinct daily rhythms with a daytime peak in MUA during a 24-h light-dark (LD 1212) cycle. On the other hand, MUA recorded from adjacent hypothalamic regions outside the SCN showed a phase reversal with a nighttime peak, similarly to the rat. The amplitude of the rhythms recorded outside the SCN was much smaller (one-half to one-quarter) than that inside the SCN. These rhythms persisted during constant darkness indicating characteristics of endogenous circadian rhythmicity. When the external lightdark cycle was delayed abruptly for 12 h, MUA rhythms showed a gradual phase shift taking 7–10 days for complete reentrainment. Overt behavior including sleep-wakefulness did not show significant and consistent daily or circadian rhythms in spite of the distinct oscillation in neuronal activity inside the SCN.Abbreviations SCN suprachiasmatic nucleus - MUA multiple unit activity     

Gain-induced oscillations in blood pressure

 “Mayer waves” are long-period (6 to 12 seconds) oscillations in arterial blood pressure, which have been observed and studied for more than 100 years in the cardiovascular system of humans and other mammals. A mathematical model of the human cardiovascular system is presented, incorporating parameters relevant to the onset of Mayer waves. The model is analyzed using methods of Liapunov stability and Hopf bifurcation theory. The analysis shows that increase in the gain of the baroreflex feedback loop controlling venous volume may lead to the onset of oscillations, while changes in the other parameters considered do not affect stability of the equilibrium state. The results agree with clinical observations of Mayer waves in human subjects, both in the period of the oscillations and in the observed age-dependence of Mayer waves. This leads to a proposed explanation of their occurrence, namely that Mayer waves are a gain-induced oscillation. Received: 15 September 1997/Revised version: 15 March 1998     

Spectrum analysis of blood pressure and cardiac rate in the conscious rat

Intrafemoral pulsatile blood pressure of conscious rats was computed to generate evenly spaced signals (systolic, diastolic, mean blood pressure, heart rate) at 200 ms intervals. This equidistant sampling allowed a direct spectral analysis using a Fast Fourier Transform algorithm. Systolic blood pressure and heart rate exhibited low frequency oscillations (Mayer waves, 20-605 mHz) and a high frequency peak related to respiration (1,765 mHz). The diastolic blood pressure and the mean blood pressure only exhibited low frequency oscillations. This procedure could be useful to analyze the various components of blood pressure variability.     

Modulation of cardiovascular response to dynamic exercise by fastigial nucleus

Mongrel dogs (n = 34) were used to record the cardiovascular responses during submaximal exercise-tolerance tests (ETT) before and after the placement of lesions in rostral portions of the cerebellar fastigial nucleus (FN). Sterile surgical procedures were used to implant solid-state pressure transducers into the left ventricle or descending aorta (anesthesia 1% halothane in O2) and multipolar stainless steel electrodes into FN (anesthesia alpha-chloralose 115 mg/kg iv). Heart rate (HR), maximal left ventricular systolic pressure ( LVPmax ) and its first derivative ( dLVP /dt), and mean arterial blood pressure (MAP) were recorded during a motorized treadmill ETT. Electrolytic direct-current or radio-frequency lesions were made through the indwelling FN electrodes, and the ETT was repeated following 10-14 days recovery. Two-way analysis of variance (ANOVA), with repeated measures on one, and one-way ANOVA for simple effects indicated a significant reduction in HR and MAP (P less than 0.01) but not LVPmax and dLVP /dt occurred during exercise as a result of rostral FN lesions. Although the trend for reduced LVPmax and dLVP /dt was also evident, a relatively greater decrease in blood pressure occurred in the peripheral vasculature during exercise. It was concluded that FN acts as a modulator of HR and MAP during dynamic exercise because of the observed deficits, and because FN is known to both send efferent projections to medullary vasomotor areas and receive projections from motor cortex and muscle and joint afferents.     

Blood pressure changes during running in humans: the "beat" phenomenon

In 20 runners the intra-arterial blood pressure changes determined by a long-distance run and by a maximal bicycle ergometric test were recorded by means of the portable Oxford system. A peculiar pattern of the phasic waves was observed throughout the run: continuous rhythmic pulse pressure oscillations ranging in frequency between 4 and 28/min and unrelated to respiration were detected. The shape of these oscillations prompted us to investigate whether they were due to a "beat" phenomenon, that is, to the combined effect of two waves with a nearly equal frequency. To test this hypothesis, during the run 10 athletes carried a fluid-filled container around the chest. The pressure waves recorded in the container were added by computer to those recorded intra-arterially during bicycle ergometry. The resultant harmonic showed a pattern similar to that recorded in the athlete's radial artery during running. Conversely, by subtracting the pressure waves recorded in the container from those simultaneously recorded at the radial artery during running, nearly flat tracings were obtained. The source of the beat phenomenon has therefore been identified in the wave, which generates inside the aorta and the great vessels at each foot-strike shock.     

Damped oscillation of the lateral hypothalamic multineuronal activity synchronized to daily feeding schedules in rats with suprachiasmatic nucleus lesions.

In male Wistar rats with chronically implanted electrodes, multiple-unit activity (MUA) was recorded from the lateral hypothalamus (LH) and ventromedial hypothalamus (VMH). Blinded rats with bilateral suprachiasmatic nucleus (SCN) lesions showed no circadian rhythm in MUA or motor activity when food was available ad libitum. However, under a restricted-feeding schedule (food was available from 1400 to 1600 hr; water was always available) lasting for 10 days, a gradual increase of MUA of the LH developed, starting 3-4 hr prior to the feeding time. The elevated MUA lasted up to 6-7 hr after feeding and subsequently returned to the baseline level. This circadian rhythm of MUA of the LH persisted up to 4 days under total food deprivation, with quickly decreasing amplitude after termination of the schedule. MUA rhythm in VMH was less obvious than that in LH. Also, general motor activity showed a rhythm comparable to that of MUA, but it was less prominent. The elevated MUA in the LH prior to the feeding time may have been neural substrate of anticipatory activity appearing under the restricted-feeding schedule. These findings may suggest the existence of a quickly damping oscillator mechanism in the brain, presumably in the LH, which can be induced by daily feeding cues in the absence of the SCN.     

Renal SNA as the primary mediator of slow oscillations in blood pressure during hemorrhage

Blood pressure contains a distinct low-frequency oscillation often termed the Mayer wave. This oscillation is caused by the action of the sympathetic nervous system on the vasculature and results from time delays in the baroreflex feedback loop for the control of sympathetic nerve activity (SNA) in response to changes in blood pressure. In this study, we used bilateral renal denervation to test the hypothesis that it is SNA to the kidney that contributes a large portion of the vascular resistance associated with changes in the strength of the slow oscillation in blood pressure. In conscious rabbits, SNA and blood pressure were measured during hemorrhage (blood withdrawal at 1.35 ml. min(-1). kg(-1) for 20 min). Spectral analysis identified a strong increase in power at 0.3 Hz in SNA and blood pressure in the initial compensatory phase of hemorrhage before blood pressure started to fall. However, in a separate group of renal denervated rabbits, although the power of the 0.3-Hz oscillation under control conditions in blood pressure was similar, it was not altered during hemorrhage. Wavelet analysis revealed the development of low-frequency oscillations at 0.1 Hz in both intact and denervated animals. In conclusion, we propose that changes in the strength of the oscillation at 0.3 Hz in arterial pressure during hemorrhage are primarily mediated by sympathetic activity directed to the kidney.     

Influence of castration and testosterone on pineal multi-unit activity in quail.

Pineal multiple unit electrical activity was recorded in unanaesthetized quail maintained under a short or long daily photoperiod. Both spontaneous and flash-induced multiple unit firing were recorded in intact, castrated or superior cervical ganglionectomized birds. The effects of testosterone administration were tested in each experimental group. 10 Whereas orchidectomy led to a substantial rise in pineal multi-unit activity (MUA), testosterone propionate injection resulted in a markedly decreased MUA in castrates. A smaller decrease in MUA was caused by androgen treatment in intact or ganglionectomized birds. Androgen treatment of controls and ganglionectomized quail was not so effective in reducing pineal activity as was lengthening the photoperiod from 6L-18D to 18L-6D. 20 Repetitive photic stimulations resulted in a significant suppression of pineal MUA in all intact, castrated and ganglionectomized quail, whether or not testosterone was administered.     

Functional organization of local neuronal networks in the cat neocortex. Dependence on the food motivation

The multiple unit activity (MUA) from clusters of adjacent neurones in deep layers of the frontal and motor cortex was recorded in alert cats with different levels of alimentary motivation. Up to 7 spike trains were selected from the MUA. Neurones in the local circuits could be divided into 2 groups: large neurones with prevailing divergent characteristics, and small neurones with prevailing convergent characteristics. A 24-hour food deprivation altered the cross-correlation interneuronal connections with a time delay within the range of 2 to 100 ms.     

Norepinephrine reuptake, baroreflex dynamics, and arterial pressure variability in rats

This study examined the effect of norepinephrine reuptake blockade with desipramine (DMI) on the spontaneous variability of the simultaneously recorded arterial pressure (AP) and renal sympathetic nerve activity (SNA) in conscious rats. Acute DMI administration (2 mg/kg iv) depressed AP Mayer waves ( approximately 0.4 Hz) and increased low-frequency (<0.2 Hz) components of AP variability. DMI decreased renal SNA variability, especially due to the abolition of oscillations related to Mayer waves. To examine whether DMI-induced changes in AP and renal SNA variabilities could be explained by alterations in the dynamic characteristics of the baroreceptor reflex loop, the frequency responses of mean AP to aortic depressor nerve stimulation were studied in urethan-anesthetized rats. DMI accentuated the low-pass filter properties of the transfer function without significantly altering the fixed time delay. The frequency responses of iliac vascular conductance to stimulation of the lumbar sympathetic chain were studied in an additional group of anesthetized rats. DMI did not markedly alter the low-pass filter properties of the transfer function and slightly increased the fixed time delay. These results suggest that the DMI-induced decrease in the dynamic gain of the baroreceptor reflex is responsible for the decreased spontaneous renal SNA variability and the accompanying increased AP variability. The "slowing down" of baroreflex responses cannot be attributed to an effect of DMI at the vascular neuroeffector junction.     

Experimental studies on the effects of vibration and noise on sympathetic nerve activity in skin

Multi-unit sympathetic activity was recorded at elbow level from median nerve fascicles supplying glabrous skin of the left hand in five healthy subjects. The resultant vasomotor responses accompanying the neural activity were monitored by simultaneous recordings of skin blood flow using the laser doppler method and skin temperature in the innervation zones. No significant change in sympathetic activity was observed during handgrip exercise of the right hand under a constant gripping force of 2 kg. Subjects maintained the same gripping force of the right hand during exposure in random order to local vibration and/or noise, each type of exposure lasting 5 min with intervals of 20 min. A two-peaked significant increase in outflow from sympathetic nerves was observed during local exposure of the right hand to vibration with a frequency of 60 Hz and an acceleration of 50 m.s-2, followed by a postexposure period which revealed a relative suppression of sympathetic nerve activity and a significant increase in blood flow. Noise at 100 dB(A) showed only an initial effect on skin sympathetic nerve activity (SSA), whereas when combined with local vibration at 60 Hz, a pronounced increase in neural activity was noticed, indicating a combined effect of vibration and noise. These results from direct recordings of SSA suggest a sympathetic vasomotor reflex mechanism triggered by local vibration stimuli to the hand.     

Heterogeneity of psychophysiological stress responses in fibromyalgia syndrome patients

Dysregulated psychophysiological responses have been observed in patients with fibromyalgia syndrome (FMS), although the results are inconsistent. Surface electromyographic (EMG), systolic and diastolic blood pressure, heart rate (HR), and skin conductance levels (SCLs) were continuously recorded at baseline, and during a series of stress and relaxation tasks in 90 FMS patients and 30 age and sex matched healthy controls (HCs). The patient sample demonstrated lower baseline EMG levels compared to the HCs on all tasks. In contrast, the patients displayed elevated HR and SCL (sympathetic vasomotor and sudomotor indices, respectively) during both stress tasks. A cluster analysis identified four psychophysiological response patterns: 63.3% of HCs showed increased muscle tension and stable cardiovascular responses; 34.8% of FMS patients showed a pattern of increased sympathetic vasomotor reactivity with stable sudomotor and reduced muscular response; 12.2% of FMS patients showed a pattern of increased sympathetic sudomotor reactivity connected with increased sympathetic vasomotor response and reduced muscular response; and, in contrast, 46.7% of FMS patients showed a pattern of parasympathetic vasomotor reactivity and reduced sudomotor as well as muscular response. The identification of low baseline muscle tension in FMS is discrepant with other chronic pain syndromes and suggests that unique psychophysiological features may be associated with FMS. The different psychophysiological response patterns within the patient sample support the heterogeneity of FMS.     

On the reliability of the Penaz cuff during systemic and local fingertip vasodilatation at rest and in exercise

To compare the readings of blood pressure by the Riva-Rocci (RR) method with those of peripheral arterial pressure (PAP) as recorded by the Finapres (FP) device, exercise was performed by six male subjects on a cycle ergometer at a constant exercise intensity of 140 W. In addition, forearm volume was determined by impedance plethysmography. At rest, systolic FP values exceeded RR values by greater than or equal to 10 mmHg. During 60-min exercise both values at first increased almost in parallel with each other. While RR reached a plateau after 3 min, FP then started to decrease continuously up to the 10th min and finally stabilized at 20-30 mmHg below RR. The impedance values showed a similar declining slope, indicating vasodilatation. To separate the effects of sympathetic drive from heat elicited vasodilatation, a second experimental series was performed with ischaemic static calf exercise (5 min, 90 N), since this increases the sympathetic tone but prevents systemic heat distribution. In contrast to findings reported from intra-arterial measurements, no exercise effect on the pulse pressure amplification was obtained. However, the heating of one fingertip distal to the FP-cuff led to a significant decrease in PAP compared to the control recording made simultaneously from the other hand. It was concluded that heat induced vasodilatation may make FP unrepresentative of systemic blood pressure, in particular during exercise. Moreover, the FP-cuff seemed to induce substantial vasoconstriction due to venous occlusion. The FP method would therefore be useful for monitoring continuously systemic blood pressure if no (dilative) vasomotor changes occurred or their ranges and time courses were known sufficiently well.     

Heterogeneity of psychophysiological stress responses in fibromyalgia syndrome patients

Dysregulated psychophysiological responses have been observed in patients with fibromyalgia syndrome (FMS), although the results are inconsistent. Surface electromyographic (EMG), systolic and diastolic blood pressure, heart rate (HR), and skin conductance levels (SCLs) were continuously recorded at baseline, and during a series of stress and relaxation tasks in 90 FMS patients and 30 age and sex matched healthy controls (HCs). The patient sample demonstrated lower baseline EMG levels compared to the HCs on all tasks. In contrast, the patients displayed elevated HR and SCL (sympathetic vasomotor and sudomotor indices, respectively) during both stress tasks. A cluster analysis identified four psychophysiological response patterns: 63.3% of HCs showed increased muscle tension and stable cardiovascular responses; 34.8% of FMS patients showed a pattern of increased sympathetic vasomotor reactivity with stable sudomotor and reduced muscular response; 12.2% of FMS patients showed a pattern of increased sympathetic sudomotor reactivity connected with increased sympathetic vasomotor response and reduced muscular response; and, in contrast, 46.7% of FMS patients showed a pattern of parasympathetic vasomotor reactivity and reduced sudomotor as well as muscular response. The identification of low baseline muscle tension in FMS is discrepant with other chronic pain syndromes and suggests that unique psychophysiological features may be associated with FMS. The different psychophysiological response patterns within the patient sample support the heterogeneity of FMS.