title: Caspase inhibitor infusion protects an avian song control circuit from seasonal-like neurodegeneration.
abstract: Sex steroids such as androgens and estrogens have trophic effects on the brain and can ameliorate neurodegeneration, and the withdrawal of circulating steroids induces neurodegeneration in several hormone-sensitive brain areas. Very little is known about the underlying molecular mechanisms that mediate neuronal regression caused by hormone-withdrawal, however. Here we show that reduction of programmed cell death by local infusion of caspase inhibitors rescues a telencephalic nucleus in the adult avian song control system from neurodegeneration that is induced by hormone withdrawal. This treatment also has trans-synaptic effects that provide some protection of an efferent target region. We found that unilateral infusion of caspase inhibitors in vivo in adult white-crowned sparrows rescued neurons within the hormone-sensitive song nucleus HVC (used as a proper name) from programmed cell death for as long as seven days after withdrawal of testosterone and a shift to short-day photoperiod and that the activation of caspase-3 was reduced by 59% on average in the ipsilateral HVC compared with the unmanipulated contralateral HVC. Caspase inhibitor infusion near HVC was sufficient to preserve neuron size ipsilaterally in a downstream nucleus, the robust nucleus of the arcopallium. This is the first report that sustained local application of caspase inhibitors can protect a telencephalic brain area from neurodegeneration in vivo and that a degenerating neural circuit rescued with caspase inhibitors produces sufficient trophic support to protect attributes of a downstream target that would otherwise degenerate. These results strengthen the case for the possible therapeutic use of caspase inhibitors under certain neurodegenerative conditions.
authors.affiliation: Graduate Program in Neurobiology and Behavior, University of Washington, Seattle, Washington 98195-1525, USA. ckthomps@u.washington.edu
authors.forename: Christopher K
authors.initials: CK
authors.lastname: Thompson
authors.forename: Eliot A
authors.initials: EA
authors.lastname: Brenowitz
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D053148:Caspase 3 / Q000378:metabolism*; D015853:Cysteine Proteinase Inhibitors / Q000008:administration & dosage*; D013196:Dihydrotestosterone / Q000008:administration & dosage; D016503:Drug Delivery Systems; D004958:Estradiol / Q000008:administration & dosage; D007839:Functional Laterality; D008297:Male; D009410:Nerve Degeneration / Q000139:chemically induced / Q000517:prevention & control*; D009434:Neural Pathways / Q000187:drug effects; D017440:Photoperiod; D046370:Sparrows; D013687:Telencephalon / Q000473:pathology*; D013739:Testosterone / Q000008:administration & dosage; D013997:Time Factors
chemical_list: D015853:Cysteine Proteinase Inhibitors; D013196:Dihydrotestosterone; D013739:Testosterone; D004958:Estradiol; D053148:Caspase 3