Abstract

The effects of ether or pentobarbital anesthesia during the intracisternal administration of norepinephrine-H³ were studied in rat brain. More radioactivity was retained in brains of rats anesthetized with pentobarbital than in those of unanesthetized controls or ether-anesthetized animals. Of the various brain regions studied, this effect was most marked in the hypothalamus. Pentobarbital, however, had no apparent effect when administered after norepinephrine-H³. Pentobarbital also increased the levels of brain urea-C¹⁴ after its intracisternal injection but had no effect upon H₂³O or antipyrine-C¹⁴ (substances for which there is no permeability barrier). These data suggest that permeability rather than circulatory factors may be affected by pentoharbital. Norepinephrine-H³ administered intracisternally during pentobarbital anesthesia was less readily depleted from brain by reserpine than was norepinephrine-H³ which had been administered during ether anesthesia. The findings suggest that pentobarbital may influence the relative distribution of the administered amine into different binding sites (possibly extraneuronal) or may decrease the loss of the labeled compound into blood from cerebrospinal fluid. Finally, the results of these experiments indicate that the intracisternal injection technique is a rapid, effective and reproducible means of bypassing the blood-brain barrier and labeling endogenous brain stores of norepinephrine.