Posterodorsal amygdala lesions reduce feeding stimulated by 8-OH-DPAT

Injections of the serotonin (5-HT)(1A) agonist, 8-hydroxy-2(di-n-propylamino)tetralin, (8-OH-DPAT), either systemically or into the midbrain raphe nuclei, elicit food intake in otherwise satiated rats. Lesions of the paraventricular nucleus of the hypothalamus are well known for producing long-term overeating, but past research has excluded this site as a potential locus for short-term 8-OH-DPAT feeding effects. More recent work shows that small lesions of the posterodorsal amygdala (PDA) elicit overeating in their own right. Since this and related regions of the amygdala receive 5-HT innervations from the dorsal raphe nucleus (DRN), we determined if PDA lesions might alter feeding after injecting 8-OH-DPAT into this midbrain region. Adult female rats received either bilateral electrolytic lesions of the PDA or sham lesions. After recording weight gains for over 1 month, all rats were implanted with DRN cannulae, then randomly tested every 3-4 days for 1 h intake of standard lab chow after 0, 0.4, 0.8 or 1.6 nmol injections of 8-OH-DPAT. Additional 90 min measures of intake were also made after 0 vs. 250 microg (760 nmol) 8-OH-DPAT s.c. At the two highest DRN doses tested, lesioned rats showed 50% less intake compared to shams. A similar profile emerged after the single s.c. dose. These results suggest that the PDA may be an important locus at which reduced release of endogenous 5-HT stimulates feeding. Alternatively, the PDA may represent part of a larger brain circuit whose integrity is necessary for eliciting intake in response to a variety of feeding stimuli.