Julián González

Reptilian waking EEG: slow waves, spindles and evoked potentials

Signal spectral analysis procedures were used to compute the power spectrum of Gallotia galloti lizards EEG at different (5-35 degrees C) body temperatures. EEG power spectra were mainly characterized by a low frequency peak between 0.5 and 4 Hz which was present at the different body temperatures. A second spectral peak, corresponding to spindles of similar pattern to the sleep spindles of mammals, also appears in the spectra. The peak frequency of the spindles increased with the body temperature. Flash evoked potentials were characterized by a slow triphasic component upon which a spindle was superimposed, adopting a morphology similar to the K complexes of mammalian sleep. The characteristics of this EEG and evoked potentials support the hypothesis of homology between the waking state of the reptiles and the slow wave sleep of mammals.

Evolution of wakefulness, sleep and hibernation: From reptiles to mammals

Thus far, most hypotheses on the evolutionary origin of sleep only addressed the probable origin of its main states, REM and NREM. Our article presents the origin of the whole continuum of mammalian vigilance states including waking, sleep and hibernation and the causes of the alternation NREM-REM in a sleeping episode. We propose: (1) the active state of reptiles is a form of subcortical waking, without homology with the cortical waking of mammals; (2) reptilian waking gave origin to mammalian sleep; (3) reptilian basking behaviour evolved into NREM; (4) post-basking risk assessment behaviour, with motor suspension, head dipping movements, eye scanning and stretch attending postures, evolved into phasic REM; (5) post-basking, goal directed behaviour evolved into tonic REM and (6) nocturnal rest evolved to shallow torpor. A small number of changes from previous reptilian stages explain these transformations.

Nonlinear, fractal, and spectral analysis of the EEG of lizard, Gallotia galloti

Electroencephalogram (EEG) from dorsal cortex of lizard Gallotia galloti was analyzed at different temperatures to test the presence of fractal or nonlinear structure during open (OE) and closed eyes (CE), with the aim of comparing these results with those reported for human slow-wave sleep (SWS). Two nonlinear parameters characterizing EEG complexity [correlation dimension (D2)] and predictability [largest Lyapunov exponent (λ1)] were calculated, and EEG spectrum and fractal exponent β were determined via coarse graining spectral analysis. At 25°C, evidence of nonlinear structure was obtained by the surrogate data test, with EEG phase space structure suggesting the presence of deterministic chaos (D2 ∼6, λ1 ∼1.5). Both nonlinear parameters were greater in OE than in CE and for the right hemisphere in both situations. At 35°C the evidence of nonlinearity was not conclusive and differences between states disappeared, whereas interhemispheric differences remained for λ1. Harmonic power always increased with temperature within the band 8-30 Hz, but only with OE within the band 0.3-7.5 Hz. Qualitative similarities found between lizard and human SWS EEG support the hypothesis that reptilian waking could evolve into mammalian SWS.

Autonomic mediation of short-term cardiovascular oscillations after acute hemorrhage in conscious rats

Abstract The role of the autonomic in the renin-angiotensin (R-A) activities in short-term cardiovascular control during the bradycardic phase following severe hemorrhage was investigated in conscious rats. Spectral analysis of beat-to-beat fluctuations of the R-R interval (RRI), systolic (SBP) and diastolic (DPP) blood pressure in the 0.01–5.Hz range was carried out under control conditions and following a bleeding of 30% of total blood volume, with and without i.v. injection of atropine (2 mg/kg), prazosin (2 mg/kg), propranolol (5 mg/kg) or captopril (7 mg/kg). The bradycardac stage was characterized by: ( i ) an increase of the three oscillatory components exhibited by RRI variability which appears driven by vagal activity and buffered by β-adrenergic activity, while the increase of the slower LF (0.01–0.2 Hz) oscillations seems driven by the slow α-adrenergic control; ( ii ) a decrease of SBP and DBP oscillations and absence of SBP-RRI correlation in the MF band (0.2–0.5 Hz) possibly related to a decrease in the sympathetic drive of SBP-MF and DBP-MF oscillations and in RRI baroreflex control; ( iii ) an increase in LF oscillations of SBP and even more of DBP that seems driven by the slow α-and β-adrenergic control and buffered by the R-A control, responses possibly related to an increase of LF oscillations of peripheral resistance; ( iv ) the persistence of high SBP-RRI correlation in the LF band and in the respiratory band (1–3 Hz); the former seem to reflect the existence of a slow baroreflex control mediated by β-adrenergic activity, the latter appears to be caused by feedforward mechanical effects of RRI changes on SBP.

Firing regulation in dopaminergic cells: effect of the partial degeneration of nigrostriatal system in surviving neurons

Two mechanisms for firing rate regulation were identified in dopaminergic nigrostriatal cells (DA cells), one of a renewal nature which prevents short and long interspike intervals (ISIs) and the other of a no‐renewal nature which compensates long ISIs with short ISIs and vice versa. Renewal regulation was found in 96% of DA cells and less frequently in nigrocollicular (63%), nigrothalamic (61%) and nigropeduncular (50%) nigral GABA cells. No‐renewal regulation was found in 77% of DA cells, and was only observed in 8% of GABA cells. Thus, most DA cells showed both regulatory mechanisms, which justifies the low variability in their firing rate and the low oscillation of extracellular striatal dopamine previously reported. DA cells surviving a partial degeneration of the nigrostriatal system did not show alterations in their firing rate and burst firing but presented a marked disturbance for no‐renewal regulation. Under these conditions, small fluctuations in firing rate are not compensated for in time, which could be one of the factors responsible for the motor fluctuations often observed in advanced Parkinsons disease.

Neuronal activity in the substantia nigra in the anaesthetized rat has fractal characteristics. Evidence for firing-code patterns in the basal ganglia

Current models of the basal ganglia assume a firing-rate code for information processing. We have applied five complementary computing methods to assess firing patterns in 188 cells of the substantia nigra in the anaesthetized rat. Fractal firing activity was found in 100% of nigral cells projecting to the superior colliculus, in 51% of cells projecting to the thalamus and in 33% of cells projecting to the pedunculopontine nucleus, but was practically absent in dopaminergic nigrostriatal neurons (3%). The finding of fractal firing patterns may lead to a better understanding of the normal operational mode and pathological manifestations of the basal ganglia.

Power spectral analysis of short-term RR interval and arterial blood pressure oscillations in lizard (Gallotia galloti): Effects of parasympathetic blockade☆

Spontaneous short-term oscillations in consecutive beat-to-beat RR interval (RRI) and systolic blood pressure (SBP) values of lizards (Gallotia galloti) in basal conditions and under parasympathetic blockade with atropine at 23°C body temperature were investigated using spectral analysis. In control conditions, both RRI and SBP spectra exhibited two major oscillations in very low (VLF 0.008–0.030 Hz) and low (LF 0.030–0.100 Hz) frequencies. Most lizards presented a high frequency (HF) respiratory peak in the SBP spectra whenever the lizards ventilatory pattern was rhythmic. Parasympathetic blockade decreased all RRI oscillations and LF and HF oscillationsof SBP. VLF and LF oscillations of RRI and SBP were still clearly present after blockade, which shows that other neural or humoral systems different from parasympathetic could mediate also low frequency RRI and SBP variability. SBP-RRI cross-spectral analysis showed in control conditions a linear relationship between SBP and RRI variations in the VLF, LF and HF bands, with SBP variations leading RRI; the parasympathetic limb of the baroreflex seems to be involved in maintaining the SBP-RRI coherence in the LF and perhaps in the HF band.

Applications of Fractal and Non-linear Time Series Analysis to the Study of Short-term Cardiovascular Control

The short-term cardiovascular control system is reviewed from the analysis of the heart rate, respiration and blood pressure beat-to-beat variability signals. The present state of the art concerning fractal and non-linear techniques as applied to the cardiovascular system and the differences between both approaches are highlighted. We present results obtained in mammals from statistics, such as the fractal exponent, the correlation dimension or the maximal Lyapunov exponent and discuss the convenience of these indexes for characterizing the irregularity present in the signals. Finally, the interdependence between the systems involved in the cardiovascular control is addressed. Recent results obtained from interdependence indexes between the cardio, respiratory and vascular signals are discussed and their convenience in physiological studies and clinical applications are stressed.

Asymmetric sleep in rats

Five Wistar rats were surgically implanted with cortical and parietal electrodes for conventional polysomnography to test for sleep-related EEG asymmetries during 48 hours of continuous recording. When the animals were grouped not according to right–left dominance (which would represent a population bias) but instead according to preferred vs non-preferred hemisphere, significant light/dark circadian changes in side dominance were found in delta power during NREM; in theta and beta power during REM; and in alpha 1, alpha 2, and theta power during wakefulness. The changes have been interpreted as a response to temporal variations in the capability to respond to environmental challenges.

Cardiac responses to temperature in the lizard Gallotia galloti

1. 1. Electrocardiograms of Gallotia galloti have been processed by a computerized system, to investigate the quantitative relationship between cardiac physiological processes assessed by the ECG intervals and body temperature changes. 2. 2. Electrocardiographic event (RR, PR, RT, QRS and TP) durations decrease exponentially with body temperature. Thus, the influence of body temperature changes on the cardiac cycle (RR interval), atrioventricular conduction time (PR interval), ventricular depolarization (QRS complex) and cardiac rest time (TP period) have been studied in terms of regression coefficients. 3. 3. The cardiac events most affected by body temperature changes were the cardiac rest period and the atrioventricular conduction time and the least affected were the RT interval and ventricular depolarization. 4. 4. The decrease of relative cardiac rest time together with the increase of relative RT interval appear to be the main factors that contribute to the increase of heart rate as body temperature increases.