ABSTRACr Electrical stimulation with radiofrequency fields amplitude-modulated at brain wave frequencies increased 45Ca2+ efflux from isolated chicken cerebral tissue. The response was not sensitive to variations of the calcium concentration (0-4.16 mM) in the bathing solution but was enhanced by addition of H+ (0.108 mM HCl) and inhibited in the absence of normal bicarbonate levels (2.4 mM) Addition of lanthanum to the bicarbonate-free solution restored electrical responsiveness, but the stimulus decreased instead of increasing 4FCa2+ efflux. It is suggested that low-frequency, weak, extracellular electric gradients may be transdueed in a specific class of extracellular negative binding sites normally occupied by Ca2+ and susceptible to competitive H+ binding.

The in vivo uptake of 45Ca by certain areas of the rat brain and by the pituitary gland was investigated under normal conditions and in states of cold stress. The uptake of 45Ca was highest in the pituitary gland followed in decreasing order by the superior colliculus, medulla, cerebellum, thalamus, hippocampus and the cortex. Cold stress conditions induced an increase in uptake of 45Ca in the cortex, hippocampus, cerebellum, medulla and the pituitary gland. Our findings suggest that cold stress induces a change in the permeability for calcium in blood‐brain and blood‐pituitary barriers.

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