Autonomic efferents affect intake of imbalanced amino acid diets by rats.
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.
Bellinger
Larry L
LL
Department of Biomedical Sciences, Baylor College of Dentistry, a member of The Texas A and M University System Health Science Center, 3302 Gaston Avenue Dallas, TX 75246, USA. lbellinger@bcd.tamhsc.edu
Williams
Fred E
FE
Lucente
James
J
Pavelka
Jason
J
Dixon
Kimberly D
KD
Gietzen
Dorothy W
DW
D000596:Amino Acids / Q000008:administration & dosage* / Q000633:toxicity; D000818:Animals; D000855:Anorexia / Q000139:chemically induced; D017776:Autonomic Pathways / Q000187:drug effects* / Q000502:physiology; D004044:Dietary Proteins / Q000008:administration & dosage* / Q000633:toxicity; D004525:Efferent Pathways / Q000187:drug effects / Q000502:physiology; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D013997:Time Factors
D000596:Amino Acids; D004044:Dietary Proteins