DC potential changes recorded between brain and skull in the rabbit after eating and drinking

Abstract

DC potential changes have been recorded between electrodes in the brain and the occipital bone in unanesthetized, unrestrained rabbits with chronically implanted electrodes and effects of eating and drinking on the DC potentials have been observed. When the animal was deprived of food and water for more than 15 h: 1. (1) Drinking water (15–130 ml) induced a marked positive shift, which reached its maximum (up to 2.0 mV) in 10–20 min and returned to the control level in 45–70 min. The extent of the positive DC potential shift was directly proportional to the amount of water consumed. Drinking isotonic saline induced more prolonged changes of lesser amplitude. 2. (2) Eating dry alfalfa pellets induced a marked negative DC shift which reached a maximum (up to 700 μV) in 10–20 min after the cessation of eating and recovered its former level in 50–90 min after eating. There was a tendency toward a linear relationship between the amount of food eaten and the degree of the DC shift. 3. (3) The effects of eating (negative shift) and drinking (positive shift) interfered with each other when the rabbit took food and water in rapid succession. Eating vegetables (carrots) which contain water as well as solid material induced a slight gradual negative shift while eating but no further negative shift subsequently; the effect was very similar to that which followed combined eating and drinking. 4. (4) The i.v. injection of hypertonic solution induced an immediate negative shift. These changes were extensive only when the DC potential was measured between brain and skull and no definite localized changes were observed in the hypothalamus. These DC shifts were considered to be blood-brain barrier potential alterations due to changes in the osmotic pressure of the blood plasma rather than of intracerebral origin.