Theta oscillations in anterior cingulate cortex and orbitofrontal cortex differentially modulate accuracy and speed in flexible reward learning.

Flexible reward learning relies on frontal cortex, with substantial evidence indicating that anterior cingulate cortex (ACC) and orbitofrontal cortex (OFC) subregions play important roles. Recent studies in both rat and macaque suggest theta oscillations (5-10 Hz) may be a spectral signature that coordinates this learning. However, network-level interactions between ACC and OFC in flexible learning remain unclear. We investigated the learning of stimulus-reward associations using a combination of simultaneous in vivo electrophysiology in dorsal ACC and ventral OFC, partnered with bilateral inhibitory DREADDs in ACC. In freely behaving male and female rats and using a within-subject design, we examined accuracy and speed of response across distinct and precisely defined trial epochs during initial visual discrimination learning and subsequent reversal of stimulus-reward contingencies. Following ACC inhibition, there was a propensity for random responding in early reversal learning, with correct vs. incorrect trials distinguished only from OFC, not ACC, theta power differences in the reversal phase. ACC inhibition also hastened incorrect choices during reversal. This same pattern of change in accuracy and speed was not observed in viral control animals. Thus, characteristics of impaired reversal learning following ACC inhibition are poor deliberation and weak theta signaling of accuracy in this region. The present results also point to OFC theta oscillations as a prominent feature of reversal learning, unperturbed by ACC inhibition.

Dissociable contributions of basolateral amygdala and ventrolateral orbitofrontal cortex to flexible learning under uncertainty.

Reversal learning measures the ability to form flexible associations between choice outcomes with stimuli and actions that precede them. This type of learning is thought to rely on several cortical and subcortical areas, including highly interconnected orbitofrontal cortex (OFC) and basolateral amygdala (BLA), and is often impaired in various neuropsychiatric and substance use disorders. However, unique contributions of these regions to stimulus- and action-based reversal learning have not been systematically compared using a chemogenetic approach and particularly before and after the first reversal that introduces new uncertainty. Here, we examined the roles of ventrolateral OFC (vlOFC) and BLA during reversal learning. Male and female rats were prepared with inhibitory DREADDs targeting projection neurons in these regions and tested on a series of deterministic and probabilistic reversals during which they learned about stimulus identity or side (left or right) associated with different reward probabilities. Using a counterbalanced within-subject design, we inhibited these regions prior to reversal sessions. We assessed initial and pre-post reversal changes in performance to measure learning and adjustments to reversals, respectively. We found that inhibition of vlOFC, but not BLA, eliminated adjustments to stimulus-based reversals. Inhibition of BLA, but not vlOFC, selectively impaired action-based probabilistic reversal learning, leaving deterministic reversal learning intact. vlOFC exhibited a sex-dependent role in early adjustment to action-based reversals, but not in overall learning. These results reveal dissociable roles for BLA and vlOFC in flexible learning and highlight a more crucial role for BLA in learning meaningful changes in the reward environment.

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 Parkinson's 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 h. 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 ketamine's 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.

Preclinical evidence in support of repurposing sub-anesthetic ketamine as a treatment for L-DOPA-induced dyskinesia.

Parkinson's disease (PD) is the second most common neurodegenerative disease. Pharmacotherapy with L-DOPA remains the gold-standard therapy for PD, but is often limited by the development of the common side effect of L-DOPA-induced dyskinesia (LID), which can become debilitating. The only effective treatment for disabling dyskinesia is surgical therapy (neuromodulation or lesioning), therefore effective pharmacological treatment of LID is a critical unmet need. Here, we show that sub-anesthetic doses of ketamine attenuate the development of LID in a rodent model, while also having acute anti-parkinsonian activity. The long-term anti-dyskinetic effect is mediated by brain-derived neurotrophic factor-release in the striatum, followed by activation of ERK1/2 and mTOR pathway signaling. This ultimately leads to morphological changes in dendritic spines on striatal medium spiny neurons that correlate with the behavioral effects, specifically a reduction in the density of mushroom spines, a dendritic spine phenotype that shows a high correlation with LID. These molecular and cellular changes match those occurring in hippocampus and cortex after effective sub-anesthetic ketamine treatment in preclinical models of depression, and point to common mechanisms underlying the therapeutic efficacy of ketamine for these two disorders. These preclinical mechanistic studies complement current ongoing clinical testing of sub-anesthetic ketamine for the treatment of LID by our group, and provide further evidence in support of repurposing ketamine to treat individuals with PD. Given its clinically proven therapeutic benefit for both treatment-resistant depression and several pain states, very common co-morbidities in PD, sub-anesthetic ketamine could provide multiple therapeutic benefits for PD in the future.

Ten-Hour Exposure to Low-Dose Ketamine Enhances Corticostriatal Cross-Frequency Coupling and Hippocampal Broad-Band Gamma Oscillations.

Introduction: Treatment-resistant depression, post-traumatic stress disorder, chronic pain, and L-DOPA-induced dyskinesia in Parkinson's disease are characterized by hypersynchronous neural oscillations. Sub-anesthetic ketamine is effective at treating these conditions, and this may relate to ketamine's capacity to reorganize oscillatory activity throughout the brain. For example, a single ketamine injection increases gamma (∼40 Hz) and high-frequency oscillations (HFOs, 120-160 Hz) in the cortex, hippocampus, and striatum. While the effects of single injections have been investigated, clinical ketamine treatments can involve 5-h up to 3-day sub-anesthetic infusions. Little is known about the effects of such prolonged exposure on neural synchrony. We hypothesized that hours-long exposure entrains circuits that generate HFOs so that HFOs become sustained after ketamine's direct effects on receptors subside. Methods: Local-field recordings were acquired from motor cortex (M1), striatum, and hippocampus of behaving rats (n = 8), and neural responses were measured while rats received 5 ketamine injections (20 mg/kg, i.p., every 2 h, 10-h exposure). In a second experiment, the same animals received injections of D1-receptor antagonist (SCH-23390, 1 mg/kg, i.p.) prior to ketamine injection to determine if D1 receptors were involved in producing HFOs. Results: Although HFOs remained stable throughout extended ketamine exposure, broad-band high-frequency activity (40-140 Hz) in the hippocampus and delta-HFO cross-frequency coupling (CFC) in dorsal striatum increased with the duration of exposure. Furthermore, while ketamine-triggered HFOs were not affected by D1 receptor blockade, ketamine-associated gamma in motor cortex was suppressed, suggesting involvement of D1 receptors in ketamine-mediated gamma activity in motor cortex. Conclusion: Prolonged ketamine exposure does not enhance HFOs in corticostriatal circuits, but, instead, enhances coordination between low and high frequencies in the striatum and reduces synchrony in the hippocampus. Increased striatal CFC may facilitate spike-timing dependent plasticity, resulting in lasting changes in motor activity. In contrast, the observed wide-band high-frequency "noise" in the hippocampus suggests that ketamine disrupts action-potential timing and reorganizes connectivity in this region. Differential restructuring of corticostriatal and limbic circuits may contribute to ketamine's clinical benefits.

Sequential co-delivery of miR-21 inhibitor followed by burst release doxorubicin using NIR-responsive hollow gold nanoparticle to enhance anticancer efficacy.

Previous literature and our study showed the delivery sequence of microRNA inhibitor and chemotherapeutic compounds achieve distinct therapeutic anticancer efficacy. Yet, it is challenging to use nanoparticle to achieve sequential drug delivery. In the current study, we designed sequential co-delivery system using a near-infrared-radiation (NIR) responsive hollow gold nanoparticle (HGNPs) to achieve sequential release of microRNA inhibitor (miR-21i)/doxirubicin(Dox) in order to achieve synergistic efficacy. PAMAM modified HGNPs was used to encapsulate miR-21i and Dox. Upon entering tumor cells, miRNA-21i was released first to sensitize the cancer cells, the subsequent burst release of Dox was achieved by NIR triggered collapse of HGNPs. This sequential delivery of miRNA-21i and Dox produced a synergistic apoptotic response, thereby enhancing anticancer efficacy by 8-fold and increasing anti-cancer stem cell activity by 50-fold. The sequential delivery of miR-21i and Dox using HGNPs under NIR after intravenous administration showed high tumor accumulation and significantly improved efficacy, which was 4-fold compared to free Dox group. These data suggested that the sequential co-delivery of miR-21i followed by burst release Dox using NIR-responsive HGNPs sensitized cancer cells to chemotherapeutic compound, which provided a novel concept for co-delivery miRNA inhibitors and chemotherapeutic compounds to enhance their efficacy.

Long-term effects of exposure to methamphetamine in adolescent rats.

BACKGROUND: Flexible cognition is a set of processes mediated by the prefrontal cortex (PFC), an area of the brain that continues to develop during adolescence and into adulthood. Adult rodents exhibit impairments specific to reversal learning across various dosing regimens of methamphetamine (mAMPH). For adolescent rodents, ongoing PFC development can be assessed by discrimination reversal learning, a task dependent on frontostriatal integrity. The task may also index an increased vulnerability for mAMPH sampling in adulthood. METHODS: The purpose of the present study was to investigate the long-term effects of escalating, adolescent mAMPH exposure on reversal learning, a PFC-dependent task (Experiment 1) and the likelihood of later sampling of mAMPH in adulthood (Experiment 2). RESULTS: Unlike previous research in adult-treated rats, our results show more generalized learning impairments after adolescent mAMPH exposure to include both attenuated visual discrimination as well as reversal learning. Additionally, we found that rats pre-exposed to mAMPH during adolescence consumed significantly more drug in adulthood. Intake of mAMPH was positively correlated with this learning. Taken together, these findings show that even modest exposure to mAMPH during adolescence may induce general learning impairments in adulthood, and an enduring sensitivity to the effects of mAMPH.