The uptake, turnover, distribution, toxicity and behavioral effects of antisense vasopressin oligonucleotides were investigated to define how these compounds interact with neural tissue to inhibit translation of a target mRNA. Both phosphorothioate modified and unmodified oligonucleotides are rapidly taken up by mammalian neural tissue. Turnover of the unmodified oligonucleotide was found to be fast (t1/2 < 1 h) relative to the phosphorothioate modified oligonucleotide (t1/2 = 12 h). The phosphorothioate vasopressin antisense oligonucleotide suppressed vasopressin synthesis in vivo at concentrations below the toxic threshold of approximately 5 microM. Intracranial injections of phosphorothioate antisense oligonucleotide into the region of the SON in vivo, resulted in a small decrease in vasopressin mRNA and a compensatory drinking response within the first 24 h, consistent with a deficit in vasopressin translation with kinetics similar to those observed in vitro. Water intake returned to normal by the second day indicating relatively rapid clearance of the oligonucleotide and minimal side effects. Although the mechanisms of accumulation and details of the molecular interactions are still unknown, our observation of preferential uptake and/or retention of oligonucleotide within a subset of neurons in vitro suggests some process of selective targeting. Thus, low concentrations of oligonucleotides targeted to the untranslated 5' end of vasopressin mRNA can be effective for the acute and reversible control of vasopressin synthesis in mammalian CNS with relatively rapid onset of behavioral effects and minimal side effects.