Hypocretin (orexin) facilitates reward by attenuating the antireward effects of its cotransmitter dynorphin in ventral tegmental area.

Hypocretin (orexin) and dynorphin are neuropeptides with opposing actions on motivated behavior. Orexin is implicated in states of arousal and reward, whereas dynorphin is implicated in depressive-like states. We show that, despite their opposing actions, these peptides are packaged in the same synaptic vesicles within the hypothalamus. Disruption of orexin function blunts the rewarding effects of lateral hypothalamic (LH) stimulation, eliminates cocaine-induced impulsivity, and reduces cocaine self-administration. Concomitant disruption of dynorphin function reverses these behavioral changes. We also show that orexin and dynorphin have opposing actions on excitability of ventral tegmental area (VTA) dopamine neurons, a prominent target of orexin-containing neurons, and that intra-VTA orexin antagonism causes decreases in cocaine self-administration and LH self-stimulation that are reversed by dynorphin antagonism. Our findings identify a unique cellular process by which orexin can occlude the reward threshold-elevating effects of coreleased dynorphin and thereby act in a permissive fashion to facilitate reward.

Abnormalities in mitochondrial structure in cells from patients with bipolar disorder.

Postmortem, genetic, brain imaging, and peripheral cell studies all support decreased mitochondrial activity as a factor in the manifestation of Bipolar Disorder (BD). Because abnormal mitochondrial morphology is often linked to altered energy metabolism, we investigated whether changes in mitochondrial structure were present in brain and peripheral cells of patients with BD. Mitochondria from patients with BD exhibited size and distributional abnormalities compared with psychiatrically-healthy age-matched controls. Specifically, in brain, individual mitochondria profiles had significantly smaller areas, on average, in BD samples (P = 0.03). In peripheral cells, mitochondria in BD samples were concentrated proportionately more within the perinuclear region than in distal processes (P = 0.0008). These mitochondrial changes did not appear to be correlated with exposure to lithium. Also, these abnormalities in brain and peripheral cells were independent of substantial changes in the actin or tubulin cytoskeleton with which mitochondria interact. The observed changes in mitochondrial size and distribution may be linked to energy deficits and, therefore, may have consequences for cell plasticity, resilience, and survival in patients with BD, especially in brain, which has a high-energy requirement. The findings may have implications for diagnosis, if they are specific to BD, and for treatment, if they provide clues as to the underlying pathophysiology of BD.

Down syndrome fibroblast model of Alzheimer-related endosome pathology: accelerated endocytosis promotes late endocytic defects.

Endocytic dysfunction is an early pathological change in Alzheimer's disease (AD) and Down's syndrome (DS). Using primary fibroblasts from DS individuals, we explored the interactions among endocytic compartments that are altered in AD and assessed their functional consequences in AD pathogenesis. We found that, like neurons in both AD and DS brains, DS fibroblasts exhibit increased endocytic uptake, fusion, and recycling, and trafficking of lysosomal hydrolases to rab5-positive early endosomes. Moreover, late endosomes identified using antibodies to rab7 and lysobisphosphatidic acid increased in number and appeared as enlarged, perinuclear vacuoles, resembling those in neurons of both AD and DS brains. In control fibroblasts, similar enlargement of rab5-, rab7-, and lysobisphosphatidic acid-positive endosomes was induced when endocytosis and endosomal fusion were increased by expression of either a rab5 or an active rab5 mutant, suggesting that persistent endocytic activation results in late endocytic dysfunction. Conversely, expression of a rab5 mutant that inhibits endocytic uptake reversed early and late endosomal abnormalities in DS fibroblasts. Our results indicate that DS fibroblasts recapitulate the neuronal endocytic dysfunction of AD and DS, suggesting that increased trafficking from early endosomes can account, in part, for downstream endocytic perturbations that occur in neurons in both AD and DS brains.

L-type calcium channels reduce ROS generation in cerebellar granule cells following kainate exposure.

Cerebellar granule cells (CGC) deprived of serum or trophic factors develop sensitivity to kainate neurotoxicity that is mediated by the alpha-amino-3-hydroxy-5-methyl-isoxazole proprionic acid (AMPA) subtypes of glutamate receptors (GluR). The L-type voltage-gated calcium channel (L-type VGCC) blocker nifedipine increases the potency of kainate 50-fold. Thus, one goal of this laboratory is to determine the underlying protective mechanism triggered by calcium influx through this channel. The cell-permeable heavy metal chelator N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine effected complete protection against kainate treatment in the presence of nifedipine, as did the iron chelator deferoxamine. The chelatable heavy metal pool decreased approximately 70% immediately following treatment with kainate, but did not change following kainate/nifedipine treatment. Tetramethylrhhodamine ethyl ester (TMRE) fluorescence, an indicator of mitochondrial membrane potential, decreased approximately 70% following kainate treatment but displayed a more modest decrease ( approximately 15%) when CGC were treated with kainate/nifedipine. Reactive oxygen species (ROS) formation decreased in CGC immediately following kainate treatment but was slightly elevated following kainate/nifedipine treatment. Electron microscopic examinations of the CGC indicated severe swelling and distortion of mitochondria immediately following kainate/nifedipine treatment and the appearance of mitochondrial herniations, whorls, and bridges 2 h later, features that were rarely observed following kainate treatment. These results support the hypothesis that calcium entry through L-type VGCCs protects CGC during kainate treatment by lowering the chelatable heavy metal pool and the mitochondrial membrane potential, thereby mitigating the formation of ROS.