Age-dependent effects on the inter-relationships between dopamine and GABA, noradrenaline, serotonin or taurine

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Puerto de la Cruz, Tenerife (2003) J Physiol 548P, O27

Oral Communications: Age-dependent effects on the inter-relationships between dopamine and GABA, noradrenaline, serotonin or taurine

P. Cano, F. Chacón, V. Jiménez, M.P. Alvarez, D.P. Cardinali† and A.I. Esquifino

Departamentos de Bioquímica y Biología Molecular III and *Biología Celular, Facultad de Medicina, UCM, Madrid, Spain and †Departamento de Fisiología, Facultad de Medicina, UBA, Buenos Aires, Argentina

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The existence of interrelating mechanisms between the neurotransmitters involved in prolactin secretion regulation has been suspected from the data previously published in reference to dopamine (DA) and λ-amino butiric acid (GABA) or to DA and serotonin (5-HT) at the hypothalamic level in basal conditions (Esquifino et al. 1999). However, the concentration of each neurotransmitter studied follows a 24 h variation. The aim of this work was to analyse the interactive mechanisms among these neurotransmitters from the chronobiological point of view.

The 24 h variations of DA, noradrenaline (NA), 5-HT, GABA and taurine (Tau) were studied in 2- and 18-month-old male rats. Groups of eight young (2 months) and eight middle-aged (18 months) male rats of the Wistar strain were killed, by decapitation, at six time intervals around the clock, beginning at 09.00 h. Both biogenic amines and amino acid neurotransmitter determinations were performed by specific HPLC techniques. Statistical significance was determined by one-way ANOVA, Cosinor and Scheffe test.

The 24 h variations of DA, NA, 5-HT, GABA and Tau in the median eminence were specific for each neurotransmitter analysed in young rats, although some of these patterns disappeared or changed in middle aged rats. Both DA and NA patterns exhibited a positive polynomial correlation (P < 0.03) in the younger group and disappeared in middle-aged rats. Also DA and 5-HT showed a positive lineal correlation (P < 0.04) that remained in middle-age rats (P < 0.02). As for NA, DA and GABA exhibited a positive polynomial correlation (P < 0.04) in young rats and disappeared in middle-aged rats. As for NA and GABA, DA and Tau exhibited a positive polynomial correlation (P < 0.03) in young rats and disappeared in middle-aged rats.

The interactions of DA with any other neurotransmitter analysed in this study explain the circadian changes in plasma prolactin level. This correlation disappeared in middle aged rats and partially explains the modification in the circadian secretion of prolactin. All these data suggest that there are age-related changes in the interactive mechanisms among neurotransmitters at the median eminence level that explain, at least in part, the changes in plasma prolactin levels that occurred with age.

Where applicable, experiments conform with Society ethical requirements.

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