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J J Wright

Publications and source records attributed to J J Wright.

125 records · Page 7Linked to original sources
PubMed1976

Effect of brain stimulation on aldosterone secretion in the rhesus monkey (Macaca Mulatta).

The lateral hypothalamus, and various sites within the limbic system and frontal lobe of the rhesus monkey brain were electrically stimulated using chronically implanted electrodes. A considerble increase in plasma aldosterone levels was observed after stimulation of the lateral hypothalamic area, certain localized sites in the cingulate area, and lower medial parts of the frontal lobe. Inactive sites included most of the amygdala, hippocampus, and basal ganglia, together with other areas within the frontal lobe and cingulate gyrus. Stimulation of all active areas was followed by an increase in plasma renin activity. Plasma cortisol also increased considerably after hypothalamic stimulation but in the case of extra-hypothalamic sites the cortisol response was much less.

Aldosterone↗
PubMed1976

Effect of adrenergic blockade and dexamethasone on the aldosterone response to brain stimulation in the rhesus monkey.

The increase in aldosterone and plasma renin activity (PRA) observed after stimulation of extrahypothalamic sites within the brain of the rhesus monkey was prevented by the prior administration of the beta-adrenergic blocking agent propranolol. alpha-Adrenergic blockade by phentolamine had no inhibiting effect. Propranolol only partially reduced the response of aldosterone to lateral hypothalamic stimulation in spite of inhibition of PRA; a partial reduction in aldosterone was also obtained from this site after dexamethasone treatment without any effect on PRA. It was concluded that the increase in aldosterone observed after extra-hypothalamic stimulation was mediated mainly through the renin-angiotensin mechanism whereas in the case of the hypothalamus, release of ACTH was also a contributory factor.

Adrenocorticotropic Hormone↗
PubMed1976

Selective N-actylation of gentamicin antibiotics-synthesis of 1-N-acyl derivatives.

Treatment of acid addition salts of aminoglycoside-aminocyclitol antibiotics of the gentamicin-sisomicin class, with one equivalent of triethylamine and an acylating agent results in selective formation of 1-N-acyl derivatives. This is in contrast to acylation of the antibiotic free bases which results in preferential acylation of other basic centres in the molecule. Origins of the observed selectivity are discussed. In vitro antibacterial activities of several new 1-N-acy1 derivatives of gentamicin, sisomicin and verdamicin are reported.

Acylation↗
PubMedDate not supplied

Toward an integrated continuum model of cerebral dynamics: the cerebral rhythms, synchronous oscillation and cortical stability.

Continuum models of cerebral cortex with parameters derived from physiological data, provide explanations of the cerebral rhythms, synchronous oscillation, and autonomous cortical activity in the gamma frequency range, and suggest possible mechanisms for dynamic self-organization in the brain. Dispersion relations and derivations of power spectral response for the models, show that a low frequency resonant mode and associated travelling wave solutions of the models' equations of state can account for the predominant 1/f spectral content of the electroencephalogram (EEG). Large scale activity in the alpha, beta, and gamma bands, is accounted for by thalamocortical interaction, under regulation by diffuse cortical excitation. System impulse responses can be used to model Event-Related Potentials. Further classes of local resonance may be generated by rapid negative feedbacks at active synapses. Activity in the gamma band around 40 Hz, associated with large amplitude oscillations of pulse density, appears at higher levels of cortical activation, and is unstable unless compensated by synaptic feedbacks. Control of cortical stability by synaptic feedbacks offers a partial account of the regulation of autonomous activity within the cortex. Synchronous oscillation occurs between concurrently excited cortical sites, and can be explained by analysis of wave motion radiating from each of the co-active sites. These models are suitable for the introduction of learning rules-most notably the coherent infomax rule.

Cerebral Cortex↗
PubMedDate not supplied

The maximum range and timing of excitatory contextual modulation in monkey primary visual cortex.

Contextual modulations of receptive field properties by distal stimulus configurations have been shown for a variety of stimulus paradigms. A survey of excitatory contextual modulation data for V1 shows the maximum scale of interactions, measured in terms of distance in V1, to be between 10 mm and 30 mm. Different types of excitatory contextual modulation in V1 occur throughout the interval of 40-250 ms after stimulus delivery. This window provides opportunity for global propagation of visual contextual information to a subset of V1 neurons, via several routes within the visual system. We propose a number of experiments and analyses to confirm the results from this empirical survey.

Animals↗