Striatal dopamine neurotransmission is altered in age- and region-specific manner in a Parkinson's disease transgenic mouse.

Dopamine (DA) plays a critical role in striatal motor control. The drop in DA level within the dorsal striatum is directly associated with the appearance of motor symptoms in Parkinson's disease (PD). The progression of the disease and inherent disruption of the DA neurotransmission has been closely related to accumulation of the synaptic protein α-synuclein. However, it is still unclear how α-synuclein affects dopaminergic terminals in different areas of dorsal striatum. Here we demonstrate that the overexpression of human α-synuclein (h-α-syn) interferes with the striatal DA neurotransmission in an age-dependent manner, preferentially in the dorsolateral striatum (DLS) of PDGF-h-α-syn mice. While 3-month-old mice showed an increase at the onset of h-α-syn accumulation in the DLS, 12-month-old mice revealed a decrease in electrically-evoked DA release. The enhanced DA release in 3-month-old mice coincided with better performance in a behavioural task. Notably, DA amplitude alterations were also accompanied by a delay in the DA clearance independently from the animal age. Structurally, dopamine transporter (DAT) was found to be redistributed in larger DAT-positive clumps only in the DLS of 3- and 12-month-old mice. Together, our data provide new insight into the vulnerability of DLS and suggest DAT-related dysfunctionalities from the very early stages of h-α-syn accumulation.

Anesthetics fragment hippocampal network activity, alter spine dynamics, and affect memory consolidation.

General anesthesia is characterized by reversible loss of consciousness accompanied by transient amnesia. Yet, long-term memory impairment is an undesirable side effect. How different types of general anesthetics (GAs) affect the hippocampus, a brain region central to memory formation and consolidation, is poorly understood. Using extracellular recordings, chronic 2-photon imaging, and behavioral analysis, we monitor the effects of isoflurane (Iso), medetomidine/midazolam/fentanyl (MMF), and ketamine/xylazine (Keta/Xyl) on network activity and structural spine dynamics in the hippocampal CA1 area of adult mice. GAs robustly reduced spiking activity, decorrelated cellular ensembles, albeit with distinct activity signatures, and altered spine dynamics. CA1 network activity under all 3 anesthetics was different to natural sleep. Iso anesthesia most closely resembled unperturbed activity during wakefulness and sleep, and network alterations recovered more readily than with Keta/Xyl and MMF. Correspondingly, memory consolidation was impaired after exposure to Keta/Xyl and MMF, but not Iso. Thus, different anesthetics distinctly alter hippocampal network dynamics, synaptic connectivity, and memory consolidation, with implications for GA strategy appraisal in animal research and clinical settings.