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Biomedical subjects

C M Brooks

Publications and source records attributed to C M Brooks.

At least 109 records · Page 6Linked to original sources
PubMed1966

Activity of neurones in the paraventricular nucleus of the hypothalamus and its control.

1. Activity of the paraventricular nucleus neurones was recorded by micro-electrodes during resting conditions and while various osmotic, chemical, direct and indirect neural stimuli were applied. This activity was correlated with evidence of oxytocin release by recording milk ejection responses.2. Seventy-four per cent of all paraventricular nucleus neurones were osmosensitive in that firing was augmented following close arterial injection of hypertonic solutions (1 ml. 1 M-NaCl in 10-15 sec). A very few neurones showed decreased activity and in twenty-two per cent no change at all occurred following injection. Evidence indicated that the observed depressions of cellular firing rate were due to other than osmotic stimulation.3. In post-partum cats an osmotically-induced neurone discharge increase was accompanied by a milk ejection response equivalent to that produced by 2-3 m-u. of oxytocin.4. Paraventricular neurones were also sensitive to acetylcholine. Intracarotid injections of 40-80 mug of acetylcholine greatly increased discharge rates and caused a very definite milk ejection response.5. Stimulation of the nipples by gentle suction, but not by electrical shock, and distension of the uterus in post-partum cats increased unit discharge in the paraventricular nucleus and evoked a milk ejection response.6. Neurones of the paraventricular nucleus, unlike those of the supraoptic nucleus, did not appear to be specifically responsive to electrical stimulation of skin and muscle afferent or of central nervous structures. Such stimuli did cause slight augmentations or depressions in firing rates of cells within and adjacent to the paraventricular nuclei, but many neurones were unaffected. Stimuli such as those applied appeared to have a general central effect involving paraventricular as well as many other neurones.7. Direct electrical excitation of the pituitary stalk produced a milk ejection response in post-partum cats. Electrical pulses applied to the paraventricular nuclei were less effective for reasons discussed.

Acetylcholine↗
PubMedDate not supplied

Norepinephrine, potassium and overdrive suppression.

The influence of norepinephrine on ventricular overdrive suppression and attendant potassium shifts has been studied in isolated perfused canine hearts with complete atrioventricular block. It was found that: 1) there is a potassium loss during the drive and a potassium uptake after the drive); 2) reducing the driving rate from 240 to 120/min decreases potassium loss; 3) norepinephrine increases potassium uptake and spontaneously beating ventricles and during the recovery from 120/min drive; 4) norepinephrine enhances K loss during and after a 240/min drive; 5) norepinephrine shortens the overdrive pause under all the conditions tested; 6) in ventricles driven at a constant rate, norepinephrine causes a small loss of ptoassium; 7) reserpinized hearts show a small potassium loss during drive and a larger potassium uptake after drive; yet, the suppression is longer; 8) norepinephrine increases K loss with drive and decreases overdrive suppression in reserpinized hearts; 9) norepinephrine enhances the increase in oxygen consumption caused by overdrive; and 10) norepinephrine antagonizes the depressant effect of high [K]0 on automaticity. It is concluded that norepinephrine shortens the pause independently of potassium levels and antagonizes the inhibittory influence of high K. The effect or norepinephrine on K movements depends on the ventricular rate and such rate-dependence is related to oxygen availability with respect to the increased metabolic demand.

Animals↗