Neuroscience
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Anhedonia is a core symptom of clinical depression. Two brain neuropeptides that have been implicated in anhedonia symptomology in preclinical depression models are dynorphin and orexin; which are concentrated along lateral hypothalamic dopamine reward pathways. These affect regulating neuropeptides modulate each other's function, implicating an interactive dysfunction between them in anhedonia symptomology. ⋯ But orexin was reduced in the VTA and mPFC. Also, dynorphin and orexin were both diminished in the hypothalamus which is noteworthy since nearly all hypothalamic orexin cells co-express dynorphin. These findings suggest that orexin and dynorphin function may be imbalanced between the hypothalamus and mesocortical dopaminergic brain regions in depression.
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For midbrain dopamine (DA) neurons to respond to sensory events, the presence of a stimulus must first be detected. Where is the signal that activates DA neurons coming from? Here we show that DA responses to a vibrotactile stimulus lag significantly behind those of the primary somatosensory cortex, but they arise with a latency that closely matches the onset of premotor neurons known to encode perceptual decisions. In agreement with previous findings, these data suggest that sensory evoked DA activity does not signal a stimulus physical presence but arises from the output of a perceptual decision.
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Brain edema is an important complication of acute hepatic encephalopathy (AHE), and astrocyte swelling is largely responsible for its development. Elevated blood and brain ammonia levels have been considered as major etiological factors in this edema. In addition to ammonia, recent studies have suggested that systemic infection, inflammation (and associated cytokines (CKs)), as well as endotoxin (lipopolysaccharide (LPS)) are also involved in AHE-associated brain edema. ⋯ CM derived from ECs treated with ammonia, along with antioxidants (AOs) or the NF-κB inhibitor BAY 11-7082, when added to astrocytes resulted in a significant reduction in cell swelling, as compared to the effect of CM from ECs-treated only with ammonia. We also identified increased nuclear NF-κB expression in rat brain cortical ECs in the thioacetamide (TAA) model of AHE. These studies suggest that ECs significantly contribute to the astrocyte swelling/brain edema in AHE, likely as a consequence of oxidative/nitrative stress and activation of NF-κB.
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The hippocampus is required for short-term memory and contains both excitatory pyramidal cells and inhibitory interneurons. These cells exhibit various forms of synaptic plasticity, the mechanism underlying learning and memory. More recently, endocannabinoids were identified to be involved in synaptic plasticity. ⋯ We observed that the expression of endocannabinoid biosynthetic enzyme mRNA does occur within interneurons and that it is coexpressed with type I metabotropic glutamate receptors, suggesting interneurons have the potential to produce endocannabinoids. We also identified that CA3 and CA1 pyramidal cells express endocannabinoid biosynthetic enzyme mRNA. Our data provide the first molecular biological evidence for putative endocannabinoid production in interneurons, suggesting their potential ability to regulate endocannabinoid-mediated processes, such as synaptic plasticity.
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Cholecystokinin (CCK) is a neuropeptide widely distributed in the mammalian brain. This peptide regulates many physiological functions and behaviors, such as cardio-respiratory control, thermoregulation, nociception, feeding, memory processes and motivational responses, and plays a prominent role in emotional responses including anxiety and depression. CCK-expressing brain regions involved in these functions remain unclear and their identification represents an important step towards understanding CCK function in the brain. ⋯ This procedure efficiently reduced CCK levels locally. shCCK-treated animals showed reduced levels of anxiety in the elevated plus-maze, and lower despair-like behavior in the forced swim test. Our data demonstrate that CCK expressed in the BLA represents a key brain substrate for anxiogenic and depressant effects of the peptide. The study also suggests that elevated amygdalar CCK could contribute to panic and major depressive disorders that have been associated with CCK dysfunction in humans.