Hypo- and hyperthyroidism affect neuropeptide glutamic-acid-isoleucine (NEI) concentration in discrete brain areas of adult male rats

AYALA CAROLINA; VALDEZ SUSANA R; NAVARRA MORERO MARÍA LUJÁN; SOAJE MARTA; CARREÑO NORMA B; SANCHEZ MÓNICA SILVINA; BITTENCOURT JAKSON CIONI; JAHN GRACIELA A; CELIS MARÍA ESTER

Florencia

Congreso; 8TH IBRO WORLD CONGRESS OF NEUROSCIENCE. International Brain Research Organization (IBRO); 2011

International Brain Research

Neuropeptide glutamic-acid-isoleucine amide (NEI) derived from pp-MCH, inhibits thyrotropin releasing hormone (TRH) release in mediobasal hypothalamus. To investigate the relationship between NEI and the hypothalamic-pituitary-thyroid (HPT) axis, we studied the effect of hypothyroidism (hypoT) and hyperthyroidism (hyperT) on NEI content in brain areas related to metabolism and reproduction, and whether such alterations are related to the time of day. Adult male Wistar rats were divided into control and treated: hypoT received PTU 0.1 g/l in drinking water during 7 and 24 days, hyperT received L-T4 250 µg/kg sc daily for 4 days. Animals were sacrificed in the morning (10.00-12.00 h) and afternoon (17.00-19.00 h). Trunk blood was collected; pineal gland, brain and posterior pituitary (PP) were obtained. Coronal brain slices of 1 mm were serially sectioned from 0.12 mm anterior to bregma to approximately −3.48 mm posterior to bregma according to Paxinos and Watson Atlas, Ed. 2007. The hypothalamic areas of interest were microdissected. NEI content was determined by radioimmunoassay (RIA). HypoT and hyperT were confirmed by determination of triiodothyronine, total thyroxine, and thyrotropin levels by RIA. Statistical analysis was performed using two-way ANOVA with Bonferroni post-test. In all areas, except in OVLT+AVPV, NEI concentration was similar in the controls, hypoT-7 had a very small effect in NEI levels but hypoT-24 induced NEI reductions in the morning and afternoon in PeFLH and PVH, only in the morning in OVLT+AVPV and ME+Arc, and in POA only in the afternoon. HyperT induced higher NEI concentrations in the POA in the morning and in the ME+Arc and Pi in the afternoon. There is a direct relationship between NEI concentrations and thyroid hormone levels, being lower in hypothyroidism and higher in hyperthyroidism. Thyroid hormones have a differential regulation of NEI levels in several brain areas probably through regulation of its synthesis, release or degradation.