Increased extracellular calcium in the posterior hypothalamus lowers blood pressure

With the discovery of calcium-sensing receptors in the brain, extracellular calcium levels have taken on new meaning relative to neural function. The current study investigated the effect of increased levels of extracellular calcium in the posterior hypothalamus on blood pressure. To modify extracellular calcium, guide shafts were inserted into the posterior hypothalamus of male Sprague-Dawley rats (280-350g) one week prior to placement of a concentric microdialysis probe (200 um O.D. x 1 mm fiber tip). The probe was attached to a swivel and an infusion of low bicarbonate artificial CSF containing 1 mMol Ca⁺⁺ was started at a flow rate of 2 ul/min. After 24 hrs, the effect of high calcium was tested. The testing session consisted of three 30 min timed recordings of BP followed by a 30 min period during which the calcium content of the dialysate was increased to 10 mMol. A 90 min recovery period followed. BP was analyzed in 10 min blocks. Within 10 min of the start of the calcium infusion MAP fell by 10 mmHg (p<.001) and remained depressed for 40 min. MAP gradually recovered to baseline over the ensuing 50 min. The results show that increased extracellular calcium in the posterior hypothalamus lowers blood pressure.