Correlation of regional cerebral blood flow and change of plasma sodium concentration during genesis and satiation of thirst

Abstract

Positron emission tomography studies were conducted during genesis of moderate thirst by rapid i.v. infusion of hypertonic saline (0.51 M) and after satiation of thirst by drinking water. The correlation of regional cerebral blood flow with the change in the plasma Na concentration showed a significant group of cerebral activations in the anterior cingulate region and also a site in the middle temporal gyrus and in the periaqueductal gray. Strongest deactivations occurred in the parahippocampal and frontal gyri. The data are consistent with an important role of the anterior cingulate in the genesis of thirst.

Figure 1

Diagram of the effect on plasma [Na], plasma osmolality, and thirst score of 10 normal subjects as a result of the sequence of events in the experimental paradigm. After control estimations and baseline PET scans, a rapid i.v. infusion of 0.51 M NaCl was given. Blood specimens were taken and thirst scores were determined midway through and at the conclusion of infusion. Maximum thirst occurred a mean of 43 min later, when a blood specimen was collected and a PET scan was made. The subjects then irrigated their mouths with water. Five mintues later, a PET scan was made. Then the subjects were permitted to drink water to satiation. Blood was collected, and a PET scan was made 3 min after this. A PET scan was made 14, 45, and 60 min after drinking. A further blood specimen was collected for analysis 60 min after drinking. The data are presented as means ± SEM, and the PET scans are designated by arrows. Statistically significant changes are indicated by the asterisks. Asterisks placed above the observation points indicate a significant change from control observations. Asterisks placed between the observation points indicate a significant change between the two observations. ∗, P < 0.05; ∗∗, P < 0.01; ∗∗∗, P < 0.005.

Figure 2

The correlation of regional cerebral blood flow and the change in plasma [Na] derived from 99 PET scans from 10 subjects after the experimental sequence described in Fig. 1. In these saggital sections, a minus sign designates the left side, a plus sign designates the right side, and numbers indicate distance in millimeters from the midline. The sections are at x = −8, x = −6, and x = +2 and show activations (red-yellow) and deactivations (blue-green). The color coding of Z scores is shown in the figure. The anterior cingulate activations on the left side are evident.