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Biomedical subjects

R Velluti

Publications and source records attributed to R Velluti.

At least 19 recordsLinked to original sources
PubMed2001

The brain decade in debate: VII. Neurobiology of sleep and dreams.

This article is a transcription of an electronic symposium held on February 5, 2001 by the Brazilian Society of Neuroscience and Behavior (SBNeC) during which eight specialists involved in clinical and experimental research on sleep and dreaming exposed their personal experience and theoretical points of view concerning these highly polemic subjects. Unlike most other bodily functions, sleep and dreaming cannot, so far, be defined in terms of definitive functions that play an ascribable role in maintaining the organism as a whole. Such difficulties appear quite clearly all along the discussions. In this symposium, concepts on sleep function range from a protective behavior to an essential function for maturation of the nervous system. Kleitman's hypothesis [Journal of Nervous and Mental Disease (1974), 159: 293-294] was discussed, according to which the basal state is not the wakeful state but sleep, from which we awake to eat, to protect ourselves, to procreate, etc. Dreams, on the other hand, were widely discussed, being considered either as an important step in consolidation of learning or simply the conscious identification of functional patterns derived from the configuration of released or revoked memorized information.

Animals↗
PubMed1999

Changes in the cerebral blood flow in postlingual cochlear implant users.

Five postlingually deaf patients (age range 28-58 years) with multichannel cochlear implants were examined with single photon emission tomography (SPECT) (triple-head rotating gamma camera). Changes in the regional cerebral blood flow (rCBF) after intravenous administration of technetium-99m ethyl cysteinate dimer (Tc-99m ECD) were assessed through a stimulation paradigm, consisting of: i) click stimuli (75 dB SPL) in the ear that was to be implanted, 2 weeks before surgery; ii) stimulation with the same click, one month after initial fitting; iii) stimulation with hearing sequential Spanish sentences one month after initial fitting. The results showed a significant increase in the rCBF in the primary left auditory area and in the right auditory cortex, in conditions ii) and iii). The rCBF also showed a significant asymmetrical increase in the frontal lobes when the patient was hearing sequential sentences (condition iii)) with asymmetrical distribution among patients. These results are discussed, principally the correlation between speech discrimination scores and the rCBF distribution in the frontal and temporal lobes.

Adult↗
PubMed1994

Temperature dependence of two-tone rate suppression in the northern leopard frog, Rana pipiens pipiens.

The existence region of two-tone rate suppression in frog low-frequency auditory-nerve fibers was found to include a suppressive region below a fiber's characteristic frequency, contrary to previous reports. In response to 3 degrees C rise in core temperature, the area and the best suppressive frequency (BSF) of the low-side suppressive region significantly increased. Increasing core temperature of the frog by 6 degrees C resulted in significant changes in the high-side suppressive region: Its area decreased, and its BSF and best suppressive threshold (BST) increased. Constant-temperature control trials were designed to partially simulate the relative movement of the probe tone within the excitatory tuning curve which occurred during temperature shifts. Lowering the probe tone by 0.5 oct had no effect on the low-side suppressive region, but significantly increased the area and lowered the BSF and BST of the high-side suppressive region. Temperature shifts in the frog appear to have a differential effect on the low-side and high-side suppressive areas of low-frequency auditory-nerve fibers. Moreover, excitation and suppression also respond differentially to temperature shifts.

Acoustic Stimulation↗
PubMed1992

Single unit activity in the guinea-pig cochlear nucleus during sleep and wakefulness.

The effects of waking and sleep on the response properties of auditory units in the ventral cochlear nucleus (CN) were explored by using extracellular recordings in chronic guinea-pigs. Significant increases and decreases in firing rate were detected in two neuronal groups, a) the "sound-responding" and b) the "spontaneous" (units that do not show responses to any acoustic stimuli controlled by the experimenter). The "spontaneous" may be considered as belonging to the auditory system because the corresponding units showed a suppression of their discharge when the receptor was destroyed. The auditory CN units were characterized by their PSTH in response to tones at their characteristic frequency and also by the changes in firing rate and probability of discharge evaluated during periods of waking, slow wave and paradoxical sleep. The CNS performs functions dependent on sensory inputs during wakefulness and sleep phases. By studying the auditory input at the level of the ventral CN with constant sound stimuli, it was shown that, in addition to the firing rate shifts, some units presented changes in the temporal probability of discharge, implying central actions on the corresponding neurons. The mean latency of the responses, however, did not show significant changes throughout the sleep-waking cycle. The auditory efferent pathways are postulated to modulate the auditory input at CN level during different animal states. The probability of firing and the changes in the temporal pattern, as shown by the PSTH, are thus dependent on both the auditory input and the functional brain state related to the sleep-waking cycle.

Acoustic Stimulation↗
PubMed1991

A search for a mesencephalic periaqueductal gray-cochlear nucleus connection.

Horseradish peroxidase placed into the ventral mesencephalic periaqueductal gray (PAG) and in the lateral superior olivary complex region demonstrated indirect paths towards the cochlear nucleus (CN). Because no direct connections could be observed, a pathway throughout the auditory efferent system was proposed. The results suggest three possibilities: 1) The PAG is connected to the lateral superior peri-olivary complex synapsing with known efferent fibers that reach the CN; 2) Neurons located at the dorsal PAG were demonstrated to be connected to the inferior colliculus (IC). The possibility of synapses with known neurons that run from IC to the CN is postulated; 3) Neurons in the trapezoid body, which are partially associated with a system that communicates with the CN, are also connected to and from the PAG. The present results anatomically support an extracellular study (1) describing PAG actions on CN units.

Animals↗
PubMed1990

Periaqueductal gray influence on anteroventral cochlear nucleus unitary activity and naloxone effects.

The effect of periaqueductal gray (PAG) electrical stimulation on the response properties of auditory and 'spontaneously' firing units (abolished when the cochlea is destroyed) in the anteroventral cochlear nucleus (AVCN) was explored using extracellular recordings in acute guinea-pigs. Significant increases and decreases in firing rate were detected in both neuronal groups: only 4% of the sound-responding units were insensitive to PAG stimulation while the 'spontaneous' units showed significantly smaller changes in firing rate in response to PAG stimulation. The auditory AVCN neurons were categorized both by their sound post stimulus time (PST) histograms at their characteristic frequency (CF) and the changes in the probability of discharge after PAG stimulation while the tone burst was maintained constant. PAG was implicated in pain input modulation through enkephalin actions. Because enkephalins have been also observed at the CN level, a pharmacological approach administering naloxone was carried out. We observed that 1) naloxone abolished the unit discharge shifts observed after PAG stimulation and 2) when the drug was injected without PAG stimulation, it produced changes in the firing, increasing or decreasing, and shifts in the probability of discharge versus time, even in cases in which the firing rate was not altered. An involvement of the auditory efferent pathways to CN is postulated and a possible enkephalinergic factor is suggested as a modulator of the auditory input at this level. The probability of discharge observed in the PSTH at the AVCN is dependent on the auditory input plus the central efferent action to its neurons.

Acoustic Stimulation↗
PubMed1989

Correlative changes of auditory nerve and microphonic potentials throughout sleep.

Gross cochlear potentials in response to alternating clicks and pure tone bursts were recorded in guinea-pigs with chronically implanted electrodes in the round window during sleep and the awake state. A significant increase in both averaged potentials, the compound auditory nerve action potential (cAP) and cochlear microphonics (CM) occurred in slow wave sleep (SWS) with a subsequent diminution in paradoxical sleep (PS) periods. The cAP, CM, amplitude and area averages were similar during quiet wakefulness and in PS. Moreover, as an episode of PS progressed, the recorded potentials continued to decrease. On the other hand, increased averaged values were again observed during a subsequent episode of SWS. An involvement of the efferent olivo-cochlear bundle is postulated, first, because it is the only known pathway connecting the CNS and the auditory periphery and, second, because several key pre-receptor variables (middle ear muscles and ossicles and sound-source ear relation) were either abolished or altered dramatically.

Acoustic Stimulation↗
PubMed1988

A functional viewpoint on paradoxical sleep-related brain regions.

Slow wave sleep is a condition for paradoxical sleep (PS) expression. The lower brain stem is able to produce the known PS phenomena but, in order to do so in all its functional magnitude, it depends on the rest of the brain. There are physiological conditions that appear as necessary to develop the PS. A group of basic functions, i.e., respiration, cardiovascular, brain oxygen availability, temperature, etc., have to go on in a non-homeostatic fashion during this state. Other conditions to be met are: the cut-off of the motor output and a different central control of the sensory input. During PS, phasic pO2 changes were observed in some nuclear structures characterized by a dramatic increase in the amplitude of oscillations. These changes were found in a number of subcortical, cerebellar and brain stem regions and were never observed neither in the neocortex, the specific thalamic nuclei nor in the white matter. It is postulated that these variations are due to a local increase in neuronal activity in PS during a decrease of the local homeostatic oxygen control. All the physiological changes above mentioned have a common anatomical denominator: the pons and medulla. Upon this region, proposed as the PS FINAL COMMON REGION, conveges rostral and caudal information making it the executor of all PS phenomena. The pons, on the other hand, has a bioelectrical activity of its own during PS, i.e., the ponto-geniculo-occipital spikes (PGO). This activity spreads through the brain and cerebellum. The cerebellum also participates in sleep physiology: the pO2 oscillations pattern and PGO are present in all of its parts, cortex and nuclei, being, the spike activity, dependent of a cholinergic pontine region. The pons shows a particular duality during PS. It is part of the FINAL COMMON REGION for PS phenomena and, at the same time, it is the origin of the PGO activity.

Animals↗
PubMed1986

Differential effects of benzodiazepines on cochlear and auditory nerve responses.

The influence exerted by chlordiazepoxide or midazolam upon auditory nerve compound action potential (cAP) and cochlear microphonic (CM) has been analyzed in chronic as well as in acutely prepared guinea pigs. Pre-receptorial variables were carefully controlled. The benzodiazepines dissociated the cochlear recorded potentials, increasing the cAP amplitude, in response to clicks, and decreasing the CM area, produced by a coherent pure tone pip. Both responses were dose related. A direct effect upon the cochlea was eliminated by local infusion of the drugs. It was also demonstrated to be a specific benzodiazepinic action because the use of an antagonist, Ro 15-1788, abolished the effect. Benzodiazepines could have increased the GABAergic activity at the pontine origins of the olivo-cochlear bundle or in the reticulo-cochlear fibers. These are the only central pathways that could be responsible for the effects obtained at the cochlea or auditory nerve levels. We suggest that this is the cause of the withdrawal of inhibitory tonus from the primary afferent fibers mediated by the efferent system (lateral superior olive), as may occur during dishabituation. It may also be the cause of the CM decrement, but the effect in this case would be exerted mainly through another set of efferent fibers (trapezoid body nucleus).

Action Potentials↗
PubMed1985

Spontaneous cerebellar nuclei PGO-like waves in natural paradoxical sleep and under reserpine.

PGO-like spikes were described in chronically implanted cats at the cerebellar nuclei, dentatus, fastigii and interpositus, bipolarly and monopolarly recorded during natural paradoxical sleep. They showed close similarities with known PGO at occipital cortex and lateral geniculate nucleus: wave form, duration and amplitude were coincident. Moreover fast activity frequency increment in the last part of slow wave sleep also was observed at cerebellar loci. The peak-to-peak latency measurements demonstrated that the occipital cortex PGO lagged the nucleus dentatus PGO-like waves in 20-22 msec. The phasic cerebellar waves were not always related to eye movements. Acute experiments with a previous low dose of reserpine showed the PGO-like spikes when an exploring electrode penetrated a cerebellar nucleus. Chronically implanted cats, treated with reserpine, showed the phasic cerebellar waves during wakefulness and, after a few days, during the recovered paradoxical sleep. Based on electrophysiology and the reserpine experiments a common pontine generating mechanism for PGO and cerebellar PGO-like activity is proposed. It is also hypothesized that the cerebellum could participate in sleep physiology mainly related to phasic events without excluding a tonic function.

Animals↗
PubMed1985

An electrochemical approach to sleep metabolism: a pO2 paradoxical sleep system.

Oxygen cathodes chronically implanted in the cat brain recorded changes of local oxygen concentration during paradoxical sleep. Phasic high amplitude pO2 changes were consistently observed in some regions and were characterized by a dramatic increase in the amplitude of the oscillations. The regions displaying these responses included part of the reticular formation, hypothalamus, amygdala and cerebellum which we refer to as the "pO2 paradoxical sleep system." This pO2 pattern was not observed in white matter, in the neocortex or in specific thalamic nuclei. It is postulated that the phasic response is due to a local increase of neuronal activity requiring increased oxygen availability and augmented protein synthesis during paradoxical sleep and may form part of a system related to "plastic" phenomena.

Amygdala↗
PubMed1983

Effect of xipamide and furosemide on guinea pig cochlear recorded potentials.

The effects of furosemide and xipamide on guinea pig cochlear potentials were studied under acute conditions. Auditory nerve action potentials (AP) and cochlear microphonics (CM) were depressed by both diuretics in a dose-related manner. Furosemide was more effective on AP than on CM. In contrast, the xipamide-induced reductions of AP and CM were similar. Our results suggest that the depressive effects of furosemide or xipamide may be related to a direct action on cochlear mechanisms.

Action Potentials↗
PubMed1977

Human cortical pO2.

A human cortical pO2 rhythm similar to that described in cats was demonstrated. It bears close correlation to behavioral states such as weaking and slow wave sleep. Induced changes in cerebral blood flow, through carotid compression, has been detected as qualitative variations in local oxygen availability, at the oxygen cathode tip.

Blood Flow Velocity↗