Alteration in antinociception, locomotion and brain monoamine synthesis in rats with portacaval shunts.

Rats with portacaval shunt, although showing no changes in their spontaneous pain threshold, did display an increased sensitivity of analgesic responses to morphine injection. In addition, these portacaval-shunted animals had a lower level of spontaneous motor activity and a reduced sensitivity of locomotor stimulant responses to amphetamine administration. However, these portacaval-shunted animals displayed same thermoregulatory responses to various ambient temperatures as those of normal unoperated or sham-operated animals. Biochemical examination revealed that these portacaval-shunted animals had a higher indoleamine synthesis in both the hypothalamus and the brain stem, but had a lower catecholamine synthesis in both the hypothalamus and the corpus striatum. The data suggest that alterations in antinociceptive and locomotor stimulant responses of the portacaval-shunted animals correlate with patterns of monoamine synthesis in different brain regions (patterns that differed from those observed in normal unoperated animals or in sham-operated animals).