ABSTRACT
This study examined the effects of selective, central noradrenergic dennervation with 6-hydroxydopamine (6-OHDA) on the expression of type 4 phosphodiesterases (PDE4). Twenty-one days following i.c.v. injection of 6-OHDA (200 microg) hypothalamus, neostriatum, and cerebellum were dissected. Infusion of 6-OHDA reduced norepinephrine (NE) content in all the brain areas examined (to 17%, 76% and 16% of sham-operated controls in hypothalamus, striatum, and cerebellum, respectively). 6-OHDA injections also reduced dopamine levels in hypothalamus (53%) and neostriatum (68%). Administration of desipramine (20 mg/kg, i.p.) 30 min prior to 6-OHDA injection protected neostriatal and cerebellar noradrenergic neurons NE levels (110-122% of the control levels). Desipramine partially attenuated the 6-OHDA-mediated decrease in NE content of hypothalamus, but had little or no effect on either striatal or hypothalamic dopamine (DA) levels. Western blot analysis using a PDE4A-selective antibody revealed three major bands (109 kDa PDE4A5, 102 kDa PDE4AX and 76 kDa PDE4A1) in hypothalamus and striatum. Infusion of 6-OHDA decreased the expression of PDE4A5 and PDE4AX but not of PDE4A1 in hypothalamus, as determined by quantitative Western blotting. Pretreatment of rats with desipramine attenuated the 6-OHDA-induced down-regulation of PDE4A5 and PDE4AX bands in hypothalamus. The PDE4B selective antibody K118 labels 5 major bands in all the brain regions studied. One hundred kDa PDE4B3, 86 kDa PDE4B2 and a 78 kDa PDE4B band was identified using recombinant proteins. Treatment of rats with 6-OHDA resulted in a 52% decrease in the PDE4B3 and 58% decrease in 78 kDa PDE4B variant in hypothalamus; administration of desipramine attenuated the 6-OHDA-induced down-regulation of both PDE4B variants. Neither 6-OHDA nor desipramine altered striatal PDE4A or PDE4B isozymes. In contrast, cerebellar PDE4B3 variant is up-regulated by 6-OHDA treatment and were partially normalized to control values by desipramine pretreatment. These data demonstrate that PDE4 subtypes are differentially regulated by presynaptic noradrenergic activity and may play an important role in the maintaining homeostasis of noradrenergic signal transduction in rat brain.
