Hypothalamic and thalamic blood flow during somatic afferent stimulation in dogs

The effect of somatic afferent C fiber stimulation on regional cerebral blood flow (rCBF) and cerebral tissue available oxygen (aO2) was studied in 20 dogs under chloralose anesthesia. Mean arterial blood pressure, arterial Pco2, and pH were stabilized before and during the 3-min stimulation of the sciatic nerves (20 V, 300 ms, 15 Hz). Combined gold+platinum electrodes were chronically implanted into the ventral posterolateral nucleus of the thalamus, ventromedial nucleus of the hypothalamus, and into the white matter. Tissue aO2 and rCBF of these regions were measured polarographically, the latter by the H2-gas clearance technique. Blood flow changed from 42 +/- 2.1 to 28 +/- 1.7 ml/100 g per min (cerebrovascular resistance (CVR), from 2.91 +/- 0.29 to 4.31 +/- 0.52 resistance units (RU) in the thalamus, from 59 +/- 5.0 to 47 +/- 5.0 ml/100 g per min (CVR: from 2.46 +/- 0.28 to 2.92 +/- 0.35 RU) in the hypothalamus, and from 21 +/- 1.0 to 17 +/- 0.8 ml/100 g per min (CVR: from 6.367 +/- 0.35 to 7.672 +/- 0.40 RU) in the white matter during ipsilateral stimulation. Contralateral stimulation of the sciatic nerves caused a more moderate but likewise significant drop in rCBF and an increase in CVR except in the white matter. Parallel to these changes, tissue aO2 decreased by 25 +/- 2% in the thalamic and by 19 +/- 2% in the hypothalamic area, relative to the prestimulation level.