Effect of stimulation of anterior hypothalamic area on urinary bladder function of the anesthetized rat

Abstract. The hypothalamus is a key area for the integration of the autonomic features of affective behavior. Hypothalamic defence area (HDA) stimulation evokes major cardiorespiratory changes as well as modifications of general autonomic activity both in the anesthetized and conscious animal. Micturition is due to an increase in pelvic parasympathetic activity and, in the cat, the anterior hypothalamus has been implicated in urinary bladder control with the demonstration of a dorsolateral vesicoconstrictor pathway and a ventromedial inhibitory pathway. In this study we have investigated the effect of electrical and chemical stimulation of the HDA on bladder pressure and contractions in rat. Female rats (n = 15) were anesthetized, paralyzed and ventilated artificially. Arterial blood pressure, heart rate, urinary bladder pressure and pelvic nerve activity were recorded. HDA was electrically (1 ms, 100 Hz, 5–10 s train at intensities up to 150 µA) and chemically (sodium glutamate, 50nl, 2mM) stimulated. For statistical analysis the t–test was used, data were expressed as mean ± SEM. Values of t were taken as significant when p < 0.05.HDA stimulation at 100–150 µA evoked changes of both mean blood pressure (mBP) and bladder pressure (BlP). However, stimulation at < 30µA allowed a distinction within HDA of two different regions, at the same antero–posterior and lateral level, but separated 100–150µm in depth, which evoked differential effects on blood pressure and urinary bladder pressure. Results show that low intensity stimulation at ventral sites evoked a significant increase of mBP (from 102 ± 5.9 to 127 ± 8.6mmHg, n = 10, p < 0.0001) with little changes of BlP (from 12 ± 2.2 to 16 ± 2.9cmH₂O, n = 10, p < 0.0005), whilst at more dorsal sites significant increases of BlP were elicited (from 12 ± 8.3 to 38 ± 4.6cmH₂O,n = 10, p < 0.0001) with only a small rise of mBP (from 102 ± 6.2 to 111 ± 9.8mmHg, n = 10, p < 0.005). Glutamate injections at dorsal sites evoked a rise of BlP (from 11 ± 2.2 to 30 ± 3.0cmH₂O (n = 5; p < 0.0001) with small changes in BP, whilst at ventral sites (n = 4) glutamate microinjections evoked changes in BP but not of BlP. In conclusion stimulation at different sites within HDA can elicit separate changes in BP and BlP.