Autonomic efferents affect intake of imbalanced amino acid diets by rats.
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An anorectic response occurs following ingestion of imbalanced amino acid (IMB) diets. There are three phases to this response: 1, recognition of the IMB diet; 2, conditioned development of an aversion to the IMB diet; and 3, adaptation. Blockade of peripheral serotonin-3 (5-HT3) receptors or vagotomy attenuates Phase 2 of the anorectic response. We investigated whether sympathetic efferents interact with the ventral gastric branch (VGB), by cutting it (X), or with the 5-HT3 receptor in these responses. First, VGBX and sham-operated (SHAM) groups were injected with vehicle or phenoxybenzamine (alpha-blocker), or nadolol (beta-blocker) before introducing the IMB diet. At 3 h suppression of the IMB diet ingestion was unchanged, showing no sympathetic efferent effect on Phase 1. Intake of the IMB diet increased 12-24 h later only in the SHAM+phenoxybenzamine group, so the VGB was necessary for alpha-blockade to enhance IMB diet intake during Phase 2 or possibly Phase 3. On days 2-5, intakes by the SHAM+phenoxybenzamine, VGBX+phenoxybenzamine and VGBX+nadolol groups were elevated. Therefore, alpha-blockade enhanced adaptation alone, but VGBX was necessary for beta-receptor blockade to augment Phase 3 adaptation. Both sympathetic efferents and the VGB are involved in Phases 2-3. Second, rats received vehicle or nadolol or scopolamine (nonselective muscarinic blocker) or pirenzepine (muscarinic M-1 receptor blocker),w+/-tropisetron (5-HT3 blocker). Pirenzepine attenuated the tropisetron effect between 6-9 h, but then pirenzepine and nadolol enhanced the tropisetron effect between 9-12 h. Scopolamine attenuated the tropisetron effect between 9-12 h. While neither experiment showed effects during the recognition phase, the autonomic and serotonergic systems interact in the learned and adaptive responses to IMB diets.
author list (cited authors)
Bellinger, L. L., Williams, F. E., Lucente, J., Pavelka, J., Dixon, K. D., & Gietzen, D. W.
complete list of authors
Bellinger, Larry L||Williams, Fred E||Lucente, James||Pavelka, Jason||Dixon, Kimberly D||Gietzen, Dorothy W