Loss-of-function mutations in parkin are the major cause of early-onset familial Parkinson's disease. To investigate the pathogenic mechanism by which loss of parkin function causes Parkinson's disease, we generated a mouse model bearing a germline disruption in parkin. Parkin؊/؊ mice are viable and exhibit grossly normal brain morphology. Quantitative in vivo microdialysis revealed an increase in extracellular dopamine concentration in the striatum of parkin؊/؊ mice. Intracellular recordings of medium-sized striatal spiny neurons showed that greater currents are required to induce synaptic responses, suggesting a reduction in synaptic excitability in the absence of parkin. Furthermore, parkin؊/؊ mice exhibit deficits in behavioral paradigms sensitive to dysfunction of the nigrostriatal pathway. The number of dopaminergic neurons in the substantia nigra of parkin؊/؊ mice, however, is normal up to the age of 24 months, in contrast to the substantial loss of nigral neurons characteristic of Parkinson's disease. Steady-state levels of CDCrel-1, synphilin-1, and ␣-synuclein, which were identified previously as substrates of the E3 ubiquitin ligase activity of parkin, are unaltered in parkin؊/؊ brains. Together these findings provide the first evidence for a novel role of parkin in dopamine regulation and nigrostriatal function, and a non-essential role of parkin in the survival of nigral neurons in mice. Parkinson's disease (PD)1 is an age-related movement disorder characterized by bradykinesia, rigidity, resting tremor, and postural instability. The neuropathologic hallmarks of PD are the loss of dopaminergic neurons in the substantia nigra (SN) and the presence of intraneuronal cytoplasmic inclusions known as Lewy bodies. The clinical manifestations of PD are due to progressive degeneration of dopaminergic neurons in the pars compacta of the SN that give rise to the nigrostriatal pathway, causing dopamine (DA) depletion in the striatum, where it is required for normal motor function. Little is known about the mechanisms of PD pathogenesis and nigral degeneration, although DA neurons have been shown to be susceptible to oxidative stress (1), mitochondrial defects (2), and environmental toxins (3).The recent identification of genes linked to familial forms of PD (FPD) makes it possible to investigate the pathogenic mechanism by employing genetic approaches (4 -6). Over fifty recessively inherited mutations, including deletion, frameshift, nonsense, and missense mutations, have been identified in parkin in large numbers of families, making parkin the major gene responsible for early-onset FPD (7-10). Although the first report linked parkin mutations to autosomal recessive juvenile parkinsonism (AR-JP) with atypical clinical features (5), many more cases identified subsequently were considered typical early-onset FPD with symptoms often indistinguishable from sporadic PD (9, 11). Autopsies of limited numbers of patients showed selective loss of dopaminergic neurons in the SN either in the absence (12-15) or in the ...

Mouse models of neuropsychiatric diseases provide a platform for mechanistic understanding and development of new therapies. We previously demonstrated that knockout of the mouse homologue of CNTNAP2, in which mutant forms cause Cortical Dysplasia and Focal Epilepsy syndrome (CDFE), displays many features parallel to the human disorder. Since CDFE has high penetrance for autism spectrum disorder (ASD) we performed an in vivo screen for drugs that treat abnormal social behavior in Cntnap2 mutant mice and found that acute administration of the neuropeptide oxytocin improved social deficits. We found a decrease in the number of oxytocin immunoreactive neurons in the paraventricular nucleus (PVN) of the hypothalamus in mutant mice and an overall decrease in brain oxytocin levels. Administration of a selective melanocortin receptor 4 agonist, which causes endogenous oxytocin release, also acutely rescued the social deficits, an effect blocked by an oxytocin antagonist. We confirmed that oxytocin neurons mediated the behavioral improvement by activating endogenous oxytocin neurons in the paraventricular hypothalamus with Designer Receptors Exclusively Activated by Designer Drugs (DREADD). Last, we showed that chronic early postnatal treatment with oxytocin led to more lasting behavioral recovery and restored oxytocin immunoreactivity in the PVN. These data demonstrate dysregulation of the oxytocin system in Cntnap2 knockout mice and suggest that there may be critical developmental windows for optimal treatment.

Overexpression or mutation of α-synuclein (α-Syn), a protein associated with presynaptic vesicles, causes familial forms of Parkinson’s disease in humans and is also associated with sporadic forms of the disease. We used in vivo microdialysis, tissue content analysis, behavioral assessment, and whole-cell patch clamp recordings from striatal medium-sized spiny neurons (MSSNs) in slices to examine dopamine transmission and dopaminergic modulation of corticostriatal synaptic function in mice overexpressing human wild-type α-Syn under the Thy1 promoter (α-Syn mice). Tonic striatal extracellular dopamine and 3-methoxytyramine levels were elevated in α-Syn mice at 6 months of age, prior to any reduction in total striatal tissue content, and were accompanied by an increase in open-field activity. Dopamine clearance and amphetamine-induced dopamine efflux were unchanged. The frequency of MSSN spontaneous excitatory postsynaptic currents (sEPSCs) was lower in α-Syn mice. Amphetamine reduced sEPSC frequency in wild types (WTs) but produced no effect in α-Syn mice. Furthermore, whereas quinpirole reduced and sulpiride increased sEPSC frequency in WT mice, they produced the opposite effects in α-Syn mice. These observations indicate that overexpression of α-Syn alters dopamine efflux and D2 receptor modulation of corticostriatal glutamate release at a young age. At 14 months of age, the α-Syn mice presented with significantly lower striatal tissue dopamine and tyrosine hydroxylase content relative to WT littermates, accompanied by an L-DOPA-reversible sensory motor deficit. Together, these data further validate this transgenic mouse line as a slowly progressing model of Parkinson’s disease and provide evidence for early dopamine synaptic dysfunction prior to loss of striatal dopamine.

Hypocretin (Hcrt or orexin) somas are located in the hypothalamus and project widely to forebrain and brainstem regions, densely innervating monoaminergic and cholinergic cells. Loss of Hcrt function results in the sleep disorder narcolepsy. However, the normal pattern of Hcrt release across the sleep-wake cycle is unknown. We monitored Hcrt-1 release in the basal forebrain, perifornical hypothalamus, and locus ceruleus (LC) across the sleep-wake cycle using microdialysis in freely moving cats and a sensitive solid phase radioimmunoassay. We found that the peptide concentration in dialysates from the hypothalamus was significantly higher during active waking (AW) than during slow-wave sleep (SWS). Moreover, Hcrt-1 release was significantly higher during rapid eye movement (REM) sleep than during SWS in the hypothalamus and basal forebrain. We did not detect a significant difference in release across sleep-waking states in the LC, perhaps because recovered levels of the peptide were lower at this site. Because there was a trend toward higher levels of Hcrt-1 release during AW compared with quiet waking (QW) in our 10 min dialysis samples, we compared Hcrt-1 levels in CSF in 2 hr AW and QW periods. Hcrt-1 release into CSF was 67% higher during AW than during QW. Elevated levels of Hcrt during REM sleep and AW are consistent with a role for Hcrt in the central programming of motor activity.