Cowen, S. L. | bioRxiv Science

bioRxiv2022

Heterogeneous patterns of ventral tegmental area neuronal activity coordinate nucleus accumbens dopamine release

Dopamine release in the ventral striatum is fundamental to adaptive appetitive behavior. Frustratingly, technological, and methodological hurdles have limited the investigation of the mechanisms that drive phasic dopamine release. Although dopamine neuron activation in the ventral tegmental area (VTA) surely results in dopamine release, how populations of these neurons coordinate their activities in time to modulate the temporal pattern of release remains unclear. Additionally, burgeoning evidence suggests that control over striatal dopamine release is not solely regulated by the burst firing of VTA neurons or even cell-body activation of these neurons. Here, we recorded VTA neurons while simultaneously monitoring pharmacologically induced phasic dopamine release events in the ventral striatum (nucleus accumbens core) of anesthetized rats. On average, dopaminergic and non-dopaminergic neurons increased activity at the time of the onset of release and decreased at the time of peak release; however, the tuning of individual VTA neurons to dopamine release was notably heterogenous, with subsets of neurons responding prior to release, at release onset, or during release. Other neurons were notably silent during release but active otherwise. Interestingly, both putative dopaminergic and non-dopaminergic neurons expressed this temporally heterogeneous response pattern. Furthermore, the firing activity of dopaminergic, but not non-dopaminergic neurons, correlated with the magnitude of dopamine release. These data suggest that populations of VTA neurons become active at distinct times of a dopamine release event to sculpt the temporal pattern of release.

neuroscience↗

bioRxiv2020

Spectral Signatures of L-DOPA-Induced Dyskinesia Depend on L-DOPA Dose and are Suppressed by Ketamine

L-DOPA-induced dyskinesias (LID) are debilitating motor symptoms of dopamine-replacement therapy for Parkinsons disease (PD) that emerge after years of L-DOPA treatment. While there is an abundance of research into the cellular and synaptic origins of LID, less is known about how LID impacts systems-level circuits and neural synchrony, how synchrony is affected by the dose and duration of L-DOPA exposure, or how potential novel treatments for LID, such as sub-anesthetic ketamine, alter this activity. Sub-anesthetic ketamine treatments have recently been shown to reduce LID, and ketamine is known to affect neural synchrony. To investigate these questions, we measured movement and local-field potential (LFP) activity from the motor cortex (M1) and the striatum of preclinical rodent models of PD and LID. In the first experiment, we investigated the effect of the LID priming procedures and L-DOPA dose on neural signatures of LID. Two common priming procedures were compared: a high-dose procedure that exposed unilateral 6-hydroxydopamine-lesioned rats to 12 mg/kg L-DOPA for 7 days, and a low-dose procedure that exposed rats to 7 mg/kg L-DOPA for 21 days. Consistent with reports from other groups, 12 mg/kg L-DOPA triggered LID and 80-Hz oscillations; however, these 80-Hz oscillations were not observed after 7 mg/kg administration despite clear evidence of LID, indicating that 80-Hz oscillations are not an exclusive signature of LID. We also found that weeks-long low-dose priming resulted in the emergence of non-oscillatory broadband gamma activity (> 30 Hz) in the striatum and theta-to-high-gamma cross-frequency coupling (CFC) in M1. In a second set of experiments, we investigated how ketamine exposure affects spectral signatures of low-dose L-DOPA priming. During each neural recording session, ketamine was delivered through 5 injections (20 mg/kg, i.p.) administered every 2 hours. We found that ketamine exposure suppressed striatal broadband gamma associated with LID but enhanced M1 broadband activity. We also found that M1 theta-to-high-gamma CFC associated with the LID on-state was suppressed by ketamine. These results suggest that ketamines therapeutic effects are region specific. Our findings also have clinical implications, as we are the first to report novel oscillatory signatures of the common low-dose LID priming procedure that more closely models dopamine replacement therapy in individuals with PD. We also identify neural correlates of the anti-dyskinetic activity of sub-anesthetic ketamine treatment.

pathology↗