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Parkinson's disease (PD) is a neurodegenerative disease characterized by a loss of dopaminergic neurons in the substantia nigra. There is a need for genetic animal models of PD for screening and in vivo testing of novel restorative therapeutic agents. Although current genetic models of PD produce behavioral impairment and nigrostriatal dysfunction, they do not reproduce the loss of midbrain dopaminergic neurons and 3,4-dihydroxyphenylalanine (L-DOPA) reversible behavioral deficits. Here, we demonstrate that Pitx3-deficient aphakia (ak) mice, which have been shown previously to exhibit a major loss of substantia nigra dopaminergic neurons, display motor deficits that are reversed by L-DOPA and evidence of "dopaminergic supersensitivity" in the striatum. Thus, ak mice represent a novel genetic model exhibiting useful characteristics to test the efficacy of symptomatic therapies for PD and to study the functional changes in the striatum after dopamine depletion and L-DOPA treatment.

Chronic hypercortisolemia is a hallmark of neuroendocrine and psychiatric disorders, such as Cushing's disease and depression. Whether cortisol directly contributes to the altered mood and anxiety symptoms seen in these diseases remains unclear. To address this, the authors have modeled hypercortisolemia by administering corticosterone in the drinking water of female Swiss Webster mice for 17 or 18 days (13 mg/kg). Light-dark emergence, startle habituation, and startle reactivity were measured. Chronic but not acute treatment with corticosterone increased the latency to emerge into the light compartment, an anxiogenic-like effect. Chronic corticosterone treatment did not affect startle habituation, but did reduce startle reactivity. This study suggests that chronic hypercortisolemia may contribute to anxiety-related behavior in patients with Cushing's disease and depression.