Continuous measurement of cerebral blood volume in rats with the photoelectric technique: effect of morphine and naloxone

The validity of a photoelectric method for continuous cerebral blood volume (CBV) measurement was tested and modified for the rat's brain. A new way of introducing a miniature light source between the two hemispheres and fixing a light sensitive silicone blue cell to the outer surface of the parietal bone was developed. Light extinction factor of the rat's blood was determined experimentally (Eb rat = 1.38 +/- 0.15) in order to calculate absolute CBV value in this species, resulting in a 4.77 +/- 0.13 vol % absolute CBV value. Data obtained in anesthetized, artificially ventilated rats by simultaneous recording of CBV and local cerebral blood flow (H2-gas clearance technique) show that local hypothalamic blood flow decreased significantly after morphine (1.0 mg/kg s.c.), while total CBV remained unchanged. Opiate receptor blockade with naloxone (1.0 mg/kg s.c.) on the contrary, as well as naloxone and morphine administration, caused no change in local hypothalamic blood flow, but resulted in a significant increase of total cerebral blood volume.