Differential effects of intrastriatally infused fully and endcap phosphorothioate antisense oligonucleotides on morphology, histochemistry and prodynorphin expression in rat brain

In the present study, we investigated the selectivity and specificity assoc iated with continuous intrastriatal treatment with antisense oligonucleotid es. Rats were given intrastriatal infusions for 72 h with phosphodiester, a nd fully and endcap phosphorothioated oligonucleotide probes complementary to prodynorphin mRNA. Dynorphin (Dyn) peptide levels were measured by radio immunoassay. The integrity of three other striatal transmitter systems, the neuropeptide Y (NPY)-ergic interneurons, the cholinergic interneurons and the dopaminergic afferent innervation, was assessed histochemically. The gr oss morphology of the striatum and the distribution of fluorescently labell ed antisense probes were also investigated. Brains infused with phosphodies ter probes had tissue Dyn levels not different from control. They also show ed little or no change in staining for NPY, acetylcholineste,rase (AChE) an d tyrosine hydroxylase (TH) and essentially normal striatal gross morpholog y. In contrast, brains treated with fully phosphorothioated oligonucleotide s showed significant decreases in striatal Dyn levels but also severe tissu e damage accompanied by massive cell infiltration and decreases in immunore activities for the striatal neurochemical markers. Fluorescently labelled p hosphorothioate probes were observed widely in the striatum and adjacent st ructures and, presumably retrogradely transported, in the dopamine cell bod ies in the substantia nigra, also revealing the presence of abnormal cellul ar structures within the striatum. By comparison, endcap probes significant ly reduced striatal Dyn levels and showed good tissue penetration without i nducing major changes in tissue morphology or histochemistry of non-dynorph inergic systems, except for cell infiltration. The deleterious tissue effec ts of fully phosphorothioated oligonucleotides and the ineffectiveness of p hosphodiester oligonucleotides in inhibiting protein synthesis suggest that , of the probes examined in this study, endcap oligonucleotides are the mos t useful for in vivo studies in the central nervous system. (C) 2000 Elsevi er Science B.V. All rights reserved.