DORSOMEDIAL HYPOTHALAMIC-LESIONS ALTER INTAKE OF AN IMBALANCED AMINO-ACID DIET IN RATS

Within 3 h of ingesting an imbalanced amino acid diet (IAAD), rats sho w attenuated intake. The associated conditioned taste aversion can be ameliorated by giving the serotonin, receptor blocker, tropisetron (TR OP). A recent c-fos study indicated that the dorsomedial hypothalamic nucleus (DMN) may be activated 2-3 h after ingestion of IAAD. In Exper iment 1, DMN-lesioned rats (DMNL) or sham-operated (SHAM) rats were in jected with saline (SAL) or TROP just before introduction of IAAD. By 3 h, SAL-DMNL rats consumed more (P < 0.01) of the IAAD than did the S AL-SHAM rats. Thereafter, over the next 21 h, the intake of the SAL-DM NL group returned to control levels. TROP treatment enhanced the intak e of the treated groups; the TROP and the lesion effect were additive (P < 0.01). By d 4 of receiving the IAAD, the DMNL groups were eating less than SHAM rats (P < 0.05). The data suggest that the DMN may be i nvolved in the early detection of the amino acid deficiency induced by IAAD, is not involved in the TROP effect and is necessary for proper long-term adaptation to an IAAD.