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Biomedical subjects

J García Ramos

Publications and source records attributed to J García Ramos.

At least 19 recordsLinked to original sources
PubMed1994

On the phasic reflex bronchodilation in the cat.

In records of tracheal pressure or flow taken from anesthetized cats appear large pressure-negative, or air inflow excursions, in response to single pulses applied to the central end of the vagus nerve. These responses have been attributed to phasic bronchodilation and not only due to the brief contractions of inspiratory muscles that occur as part of the total responses. Phasic bronchodilation responses appear mainly during inspiration but they may also occur in the expiratory phase through facilitation, during post-hyperventilatory apnea or that induced by constant current (d.c.) vagal stimulation. They are significantly reduced after lung sympathectomy. These bronchomotor responses showed long term depression (LTD) after spontaneous or reflexly evoked hiccups, and long term potentiation (LTP) after repetitive, or d.c. vagal stimulation. They are also potentiated on the experimental conditions that include exaggerated sympathetic activity. These and some other characteristics described indicate that bronchomotor responses are legitimate and can be used to follow the changes in excitability of the central generator of breathing.

Animals↗
PubMed1991

Phasic activity in the airways smooth muscle.

In anesthetized cats and rats additional observations were made on the oscillations that are usually seen in breathing pressure or flow records. It was confirmed that these oscillations have the same properties as those phasic responses to vagal stimulation since they interfere with each other. It was also confirmed that this type of activity represents a different phenomenon from the known tone changes, and that it depends from sympathetic control of the airways smooth muscle. The possible determinant role of the mechanical factors as stimuli was examined by applying positive or negative pressure pulses at the free end of the tracheal cannula and by the study of some other conditions in which there is a sudden lung distension. At this respect, pressure, volume and rate of air flow in the airways seemed to be all important as stimuli. The initial state of tension of the bronchial walls is also important. The obtained results suggest that mechanical stimulation is normally effective against a background of facilitatory influence from the sympathetic system.

Animals↗
PubMed1986

Aminoacids and oscillatory electrocortical activity.

The effects of the local application of glutamate, aspartate, glycine, GABA and dl-alanine were studied upon the intact and isolated cortices of barbiturate anesthetized cats and upon the intact cortex of similarly anesthetized terrapin turtles. Repetitive responses following the DCR's, and the strychnine spikes, were observed, and sometimes a long duration oscillatory regular activity appeared after the treatment with those aminoacids. The oscillations had a frequency similar to that of the waves in a sleep spindle. They also occurred in the isolated cortex. The negativity of the DCR's may show different susceptibility from that of the negative component of the strychnine spikes, to the depressant action of the aminoacids. The conclusion is that the oscillatory electrocortical activity occurs in the cortex out from some subcortical influence. As a possible mechanism, it is suggested the establishment of a circus-movement type of activity involving the neurons and their dendritic apical and basilar branches. The aminoacids could act by favoring the opening of the low-resistance junctions present between dendrites, thus facilitating its synchronized activity.

Action Potentials↗
PubMed1977

On the mechanism of the cortical depression induced by afferent stimulation.

The cortical depression induced by the stimulation of some afferent fibers affects strychnine spikes elicited in two different ways: by direct electrical stimulation, and through the evoked potentials induced at the somatosensory area by single shocks to the radial nerve. The effects on these two types of responses were found to be very similar, which was taken to indicate that the site of action of the mechanism involved is the same, that is, the non-synaptic membranes of the dendrites of pyramidal neurons. It is suggested that the depressant action is mediated through the serotonergic neurons, since the previous administration of 5,6-Dihydroxytryptamine (5,6-DHT) blocked the changes. The 5-Hydroxytryptamine (5-HT) liberated would act as a neurohumoral agent, since the synaptic mechanisms do not seem to be involved and the effects are manifested in a diffuse manner.

Animals↗
PubMed1977

Cortical effects of the electrical stimulation of the locus coeruleus.

The results of the electrical stimulation of the locus coeruleus in curarized cats, and the effects upon the observed cortical responses of 5,6-dihydroxytryptamine or 6-hydroxydopamine injected intracisternally or applied in the subarachnoideal space were studied. The changes were followed on the strychnine spikes produced after the topical application of this drug. Stimulation of the locus coeruleus elicited a response in every area of the cortex explored. The response was complex, showed a phase of depression and a phase of enhancement both mixed in different proportions. The depressant reaction was more marked with lower strengths of stimulation and the enhancement reactions appeared more evident with the stronger stimuli. Both these reactions were blocked by the previous administration of 6-hydroxydopamine and only the depressant one was practically abolished by 5,6-dihydroxytryptamine. It is concluded that a complex interaction exists between the noradrenergic neurons of the locus coeruleus and the serotonergic neurons, probably those of the raphe nuclei. It is suggested that the axons of the noradrenergic neurons in their way to the cortex, give off collaterals that innervate some serotonergic neurons. The monoamines liberated by these axon terminals at the cerebral cortex would act as neurohumoral agents.

Animals↗
PubMed1975

On the role of catecholamines in the humoral modulation of the electrocortical activity in the cat.

By using the mescaline or the strychnine spikes as indicators of electrocortical activity it was found that they are increased in size by some catecholamines topically applied. These spikes showed late and long-lasting changes after somatic, as well as after autonomic afferent stimulation. The latter induced by cyanide, light asphyxia, intravenous injections of adrenaline or noradrenaline, and after a small dose of 6-hydroxydopamine. After a dose of this last substance, high enough to deplete the catecholamines of the brain, the late increase in amplitude of the cortical potentials observed following afferent stimulation disappeared leaving a long lasting reduction in that amplitude. The hypothesis is presented that the noradrenaline liberated by the adrenergic nerve fibers reaching the upper layers of the cortex acts on the nonsynaptic dendritic membranes modulating their activity in a humoral-like way. The pattern of this facilitating effect has a different temporal course and is longer lasting than that which is to be expectec only by the arrival of impulses at the cortex during the persistence of the neuronal activation induced by the information input to the CNS.

Animals↗