Daily Changes of GABA and Taurine Concentrations in Various Hypothalamic Areas Are Affected by Chronic Hyperprolactinemia

Abstract

This study was designed to characterize, in anterior, mediobasal, and posterior hypothalamic and median eminence, the 24h changes of gamma aminobutyric acid (GABA) and taurine (TAU) contents in adult male rats and to analyze whether chronic hyperprolactinemia may affect these patterns. Rats were turned hyperprolactinemic by a pituitary graft. Plasma prolactin (PRL) levels increased after pituitary grafting at all time points examined. A disruption of the circadian rhythm was observed in pituitary-grafted rats, whereas GABA and TAU content followed daily rhythms in all areas studied in controls. In the mediobasal hypothalamus, two peaks for each amino acid were found at midnight and midday. In the anterior hypothalamus, GABA and TAU showed only one peak of concentration at midnight. In the posterior hypothalamus, the values of both GABA and TAU were higher during the light as compared to the dark phase of the photoperiod. In the median eminence GABA content peaked at 20:00h, the time when TAU exhibited the lowest values. Hyperprolactinemia abolished the 24h changes of GABA in the mediobasal hypothalamus and reduced its content as compared to controls. Hyperprolactinemia advanced the diurnal peak of TAU to 12:00h in the mediobasal hypothalamus and did not modify the 24:00h peak. In the anterior hypothalamus, hyperprolactinemia increased GABA and TAU contents during the light phase while it decreased them during the dark phase of the photoperiod. In the posterior hypothalamus hyperprolactinemia did not modify GABA or TAU patterns as compared to controls. In the median eminence hyperprolactinemia increased the 20:00h peak of GABA and shift advanced the decrease in TAU content at 20:00h and its maximum at 24:00h as compared to controls. These data show that GABA and TAU content exhibit specific daily patterns in each hypothalamic region studied. PRL differentially affects the daily pattern of these amino acids in each hypothalamic region analyzed.

Superior Cervical Ganglionectomy Effects on Median Eminence and Anterior and Mediobasal Hypothalamic Taurine Content in Male Rats: Effects of Hyperprolactinemia

“…More recently a correlation between plasma prolactin levels and TAU content has been demonstrated in the hypophysiotropic area of the hypothalamus and the median eminence as a function of age [20]. Moreover, hyperprolactinemia modifies TAU content in the hypophysiotropic area of the hypothalamus [21]. All these data confirm the existence of interactions between TAU and prolactin [14,15,18] that may be involved in the modulation not only of hypothalamic pituitary axis activity but also in other physiological functions, like the immune response [22].…”

“…Also, high prolactin levels differentially modify TAU content in the median eminence and the hypothalamic areas studied, as was reported earlier [21]. As prolactin was shown to inhibit the noradrenergic activity of the peripheral nervous system [29], hyperprolactinemia may modify the interrelationship mechanisms between prolactin and the peripheral innervation to regulate TAU distribution within the hypothalamus.…”

“…Considering that TAU has recently been involved in the modulation of pituitary hormone secretion [14,18,20,21], the changes in the content of this amino acid induced by superior cervical ganglionectomy may be related to altered prolactin, GH or ACTH secretion from the pituitary. During wallerian degeneration of the norad-renergic terminals after superior cervical ganglionectomy, the reduction in TAU content at the median eminence and the mediobasal hypothalamus may explain the reduction in plasma prolactin and GH levels associated with this phenomenon, considering that this amino acid stimulates prolactin and GH secretions from the pituitary [16,[17][18][19]29].…”

Preliminary evidence of reduced occipital GABA concentrations in puerperal women: a 1H-MRS study

“…While secretion of prolactin from anterior pituitary cells is under inhibitory control of both dopamine and GABA (Melis et al 1984;Apud et al 1989), hyperprolactinemia disrupts the diurnal rhythm of GABA synthesis and, thus, concentration in various hypothalamic regions (Duvilanski et al 2003). In addition, prolactin inhibits 5 alpha-reductase activity, thus leading to decreased conversion of progesterone to steroids (such as ALLO) in the rat ovary (Takada et al 1984).…”

Dysregulation of Circadian Rhythms Following Prolactin‐Secreting Pituitary Microadenoma

“…Thus, hyperprolactinemia might alter the metabolic activity of the central component of the circadian rhythm system. Furthermore, hyperprolactinemia in pituitary-grafted rats was found to alter the daily changes of hypothalamic amino acids (Esquifino et al, 2000) and inhibitory neurotransmitters (Duvilanski et al, 2003). These findings indicate that the hypersecretion of prolactin can also interfere with the transmission of circadian information at the intermediate levels of "slave" oscillators postulated by hierarchical models (Abe et al, 2002;Kriegsfeld et al, 2003).…”