Modulação dos sistemas GABAérgico e glutamatérgico na secreção hipotalâmica de ocitocina sob condições hiperosmóticas

Abstract

In mammals, the osmolality of extracellular fluid is a main factor for maintenance hydro electrolyte balance. Thus, changes in osmolality are detected by specialized hypothalamic cell, thereby starting a neurochemical signaling with glutamatergic and GABAergic system involvement, which may trigger the oxytocin release. However, the way of GABA glutamate aminoacids relationship could modulate the oxytocin release under hyperosmolality is till poorly understood. In this context, the aim in present study was characterize the hypertonic medium effect in GABA glutamate extracellular levels and its relationship with oxytocin release in the hypothalamus in vitro. For this, male wistar rats (270-300g) were kept under standard laboratory conditions. After decapitation, the brain was quickly removed and the hypothalamic fragments were immediately dissected in cold Krebs Ringer Bicarbonate Glucose Buffer (KRBG), and were transferred to perifusion chambers containing KRBG isotonic (280 mOsm/Kg H₂O), at flow rate of 0.5-1.0 ml/min, medium effluent was collected every during 15 min. The hypertonic stimulation (340 mOsm/kg H2O) was performed during 3 minutes. Glutamate, GABA and oxytocin levels were determined by reverse phase high-performance liquid chromatograph (HPLC) system. The measurements of glutamate showed an increased release only after decrease in GABA concentration. This release temporal profile motivated us to add GABA (3 mM) during osmotic stimulation, resulting in blockage of glutamate release previously observed. Moreover the results showed oxtocin release by hypertonic solution may also depend on a GABA decrease. The present study suggests that oxytocin release stimulated by hypertonicity depends on altering the relationship GABA / glutamate.