Magnocellular hypothalamic neurons in Brattleboro rats can accumulate, transport, and translate exogenous [ArgeJvasopressin (AVP) mRNA after injection in the hypothalamo-hypophysial tract in amounts sufficient to reverse transiently the animals' characteristic diabetes insipidus. In the present study, different preparations of hypothalamic RNA extracted from normal rats or synthetic AVP RNA were injected into the lateral hypothalamus ofBrattleboro rats. Poly(A)-RNA and poly(A)+ RNA from which tails were removed by RNase H digestion were much more effective than poly(A)+ RNA in expressing AVP in the magnocellular hypothalamic neurons and in raising urine osmolarity. Synthetic AVP RNA lacking a poly(A) tail also produced a very potent dose-dependent diabetes insipidus reversal. Our results suggest that a short or absent poly(A) tail may facilitate the accumulation, transport, or expression of exogenous AVP mRNA by magnoceilular neurons.We previously reported that oxytocin mRNA can be found associated with the secretory vesicles within the axonal compartment of rat hypothalamo-neurohypophysial system neurons (1).[Arg8]Vasopressin (AVP) mRNA has also been found in the axonal compartment by several investigators (2-7). Previous studies indicate that the length of total hypothalamic AVP mRNA poly(A) tail is increased from 250 to 400 nucleotides following a hyperosmotic stimulus (8). Structural changes in the AVP mRNA have also been found to be associated with its translocation; using osmotically challenged rats, Mohr et al. (9) have shown that the poly(A) tail length of AVP mRNA is progressively shortened during axonal transport in the hypothalamo-neurohypophysial tract and is virtually nonexistent by the time it reaches the posterior lobe.More recently, we have studied the functional significance of the intraaxonal mRNA by experiments with the Brattleboro rat. This naturally occurring mutant rat, with a single base deletion in exon B of the propressophysin gene (10), is unable to translate functional AVP and has chronic diabetes insipidus, a condition characterized by the inability to concentrate urine. When total RNA extracted from the hypothalami of osmotically challenged normal rats was microinjected into the hypothalamo-neurohypophysial tract of homozygous Brattleboro rats, AVP mRNA was accumulated by magnocellular neurons, transported, and translated into immunoreactive vasopressin (11). Exogenous mRNA from normal rats and synthetic AVP RNA were both capable of causing a temporary correction of diabetes insipidus as well as production of significant plasma levels of immunoreactive AVP. Control injections with total RNA extracted from the cortex or hypothalamic RNA digested with RNase, as well as injections with the sense RNA probe into the lateral ventricle or into the cerebral cortex, were all ineffective in changing urine osmolarity or vasopressin levels.In an effort to increase the concentration of specific AVP mRNA in the RNA extract, we initially sought to enrich the polyadenylylated fraction by pas...

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