Entactogen Effects of Ketamine: A Reverse-Translational Study.

OBJECTIVE: The authors sought to assess the prosocial, entactogen effects of ketamine. METHODS: Pleasure from social situations was assessed in a sample of participants with treatment-resistant depression from randomized, double-blind, placebo-controlled studies, using four items of the Snaith-Hamilton Pleasure Scale (SHAPS) at five time points over 1 week following treatment with ketamine (0.5 mg/kg intravenously) or placebo. The primary endpoint was postinfusion self-reported pleasure on the four SHAPS items pertaining to social situations, including the item on helping others, between the ketamine and placebo groups. In a rodent experiment, the impact of ketamine on helping behavior in rats was assessed using the harm aversion task. The primary endpoint was a reduction in lever response rate relative to baseline, which indicated the willingness of rats to forgo obtaining sucrose to help protect their cage mate from electric shock. RESULTS: Relative to placebo, ketamine increased ratings of feeling pleasure from being with family or close friends, seeing other people's smiling faces, helping others, and receiving praise, for 1 week following treatment. In the rodent experiment, during the harm aversion task, ketamine-treated rats maintained lower response rates relative to baseline to a greater extent than what was observed in vehicle-treated rats for 6 days posttreatment and delivered fewer shocks overall. CONCLUSIONS: In patients with treatment-resistant depression, ketamine treatment was associated with increased pleasure from social situations, such as feeling pleasure from helping others. Ketamine-treated rats were more likely to protect their cage mate from harm, at the cost of obtaining sucrose. These findings suggest that ketamine has entactogen effects.

Relative to females, male rats are more willing to forego obtaining sucrose reward in order to prevent harm to their cage mate.

RATIONALE: Empathy, or the ability to perceive, share, and act upon the emotions of another, is a crucial social skill and is dysfunctional in autism and schizophrenia. While the complexities of human empathy are difficult to model in rodents, behavioral paradigms utilizing rats which study decision-making in social contexts may provide a translational framework for assessing biological, pharmacotherapeutic, and environmental interventions. OBJECTIVES: Modify and expand upon the three-session rat harm aversion task, which measures the willingness of rats to cease pressing a lever that earns them sucrose reward but delivers a shock to their cage mate. We sought to test the sustainability of harm aversion across seven sessions in male and female rats. METHODS: Same-sex pair-housed rats were assigned as either the observer, which had access to the lever, or the demonstrator, which would receive shocks. After training the observer to press the lever to receive sucrose pellets, the demonstrator was placed into an adjacent chamber at which point lever responses would also deliver a shock. If the observer did not press the lever, no shock and no sucrose was delivered. RESULTS: A sex difference in harm aversion was observed with female rats having significantly higher response rates and decreased response latencies across the seven test sessions, thus delivering more shocks and obtaining more sucrose, relative to males. CONCLUSIONS: These data demonstrate that male rats sustain harm aversion to a greater extent relative to females.

Genetic Disruption of System xc-Mediated Glutamate Release from Astrocytes Increases Negative-Outcome Behaviors While Preserving Basic Brain Function in Rat.

The importance of neuronal glutamate to synaptic transmission throughout the brain illustrates the immense therapeutic potential and safety risks of targeting this system. Astrocytes also release glutamate, the clinical relevance of which is unknown as the range of brain functions reliant on signaling from these cells hasn't been fully established. Here, we investigated system xc- (Sxc), which is a glutamate release mechanism with an in vivo rodent expression pattern that is restricted to astrocytes. As most animals do not express Sxc, we first compared the expression and sequence of the obligatory Sxc subunit xCT among major classes of vertebrate species. We found xCT to be ubiquitously expressed and under significant negative selective pressure. Hence, Sxc likely confers important advantages to vertebrate brain function that may promote biological fitness. Next, we assessed brain function in male genetically modified rats (MSxc) created to eliminate Sxc activity. Unlike other glutamatergic mechanisms, eliminating Sxc activity was not lethal and didn't alter growth patterns, telemetry measures of basic health, locomotor activity, or behaviors reliant on simple learning. However, MSxc rats exhibited deficits in tasks used to assess cognitive behavioral control. In a pavlovian conditioned approach, MSxc rats approached a food-predicted cue more frequently than WT rats, even when this response was punished. In attentional set shifting, MSxc rats displayed cognitive inflexibility because of an increased frequency of perseverative errors. MSxc rats also displayed heightened cocaine-primed drug seeking. Hence, a loss of Sxc-activity appears to weaken control over nonreinforced or negative-outcome behaviors without altering basic brain function.SIGNIFICANCE STATEMENT Glutamate is essential to synaptic activity throughout the brain, which illustrates immense therapeutic potential and risk. Notably, glutamatergic mechanisms are expressed by most types of brain cells. Hence, glutamate likely encodes multiple forms of intercellular signaling. Here, we hypothesized that the selective manipulation of astrocyte to neuron signaling would alter cognition without producing widespread brain impairments. First, we eliminated activity of the astrocytic glutamate release mechanism, Sxc, in rat. This impaired cognitive flexibility and increased expression of perseverative, maladaptive behaviors. Notably, eliminating Sxc activity did not alter metrics of health or noncognitive brain function. These data add to recent evidence that the brain expresses cognition-specific molecular mechanisms that could lead to highly precise, safe medications for impaired cognition.

Possible psychedelic therapeutic mechanism.

Psychedelics act on intracellular serotonin receptors that are not accessible by serotonin alone.

Mechanisms of ketamine and its metabolites as antidepressants.

Treating major depression is a medical need that remains unmet by monoaminergic therapeutic strategies that commonly fail to achieve symptom remission. A breakthrough in the treatment of depression was the discovery that the anesthetic (R,S)-ketamine (ketamine), when administered at sub-anesthetic doses, elicits rapid (sometimes within hours) antidepressant effects in humans that are otherwise resistant to monoaminergic-acting therapies. While this finding was revolutionary and led to the FDA approval of (S)-ketamine (esketamine) for use in adults with treatment-resistant depression and suicidal ideation, the mechanisms underlying how ketamine or esketamine elicit their effects are still under active investigation. An emerging view is that metabolism of ketamine may be a crucial step in its mechanism of action, as several metabolites of ketamine have neuroactive effects of their own and may be leveraged as therapeutics. For example, (2R,6R)-hydroxynorketamine (HNK), is readily observed in humans following ketamine treatment and has shown therapeutic potential in preclinical tests of antidepressant efficacy and synaptic potentiation while being devoid of the negative adverse effects of ketamine, including its dissociative properties and abuse potential. We discuss preclinical and clinical studies pertaining to how ketamine and its metabolites produce antidepressant effects. Specifically, we explore effects on glutamate neurotransmission through N-methyl D-aspartate receptors (NMDARs) and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs), synaptic structural changes via brain derived neurotrophic factor (BDNF) signaling, interactions with opioid receptors, and the enhancement of serotonin, norepinephrine, and dopamine signaling. Strategic targeting of these mechanisms may result in novel rapid-acting antidepressants with fewer undesirable side effects compared to ketamine.

Suppression of pyramidal neuron G protein-gated inwardly rectifying K+ channel signaling impairs prelimbic cortical function and underlies stress-induced deficits in cognitive flexibility in male, but not female, mice.

Imbalance in prefrontal cortical (PFC) pyramidal neuron excitation:inhibition is thought to underlie symptomologies shared across stress-related disorders and neuropsychiatric disease, including dysregulation of emotion and cognitive function. G protein-gated inwardly rectifying K+ (GIRK/Kir3) channels mediate excitability of medial PFC pyramidal neurons, however, the functional role of these channels in mPFC-dependent regulation of affect, cognition, and cortical dynamics is unknown. We used a viral-cre approach in male and female mice harboring a "floxed" version of the kcnj3 (Girk1) gene, to disrupt GIRK1-containing channel expression in pyramidal neurons within the prelimbic cortex (PrL). In males, loss of pyramidal GIRK1-dependent signaling differentially impacted measures of affect and impaired working memory and cognitive flexibility. Unexpectedly, ablation of PrL GIRK1-dependent signaling did not impact affect or cognition in female mice. Additional studies used a model of chronic unpredictable stress (CUS) to determine the impact on PrL GIRK-dependent signaling and cognitive function. CUS exposure in male mice produced deficits in cognition that paralleled a reduction in PrL pyramidal GIRK-dependent signaling akin to viral approaches whereas CUS exposure in female mice did not alter cognitive flexibility performance. Stress-induced behavioral deficits in male mice were rescued by systemic injection of a novel, GIRK1-selective agonist, ML297. In conclusion, GIRK1-dependent signaling in male mice, but not females, is critical for maintaining optimal PrL function and behavioral control. Disruption of this inhibition may underlie stress-related dysfunction of the PrL and represent a therapeutic target for treating stress-induced deficits in affect regulation and impaired cognition that reduce quality of life.

Cannabidiol in treatment of refractory epileptic spasms: An open-label study.

OBJECTIVE: This study aimed to evaluate clinical efficacy and safety of purified pharmaceutical cannabidiol (CBD) as an adjunctive therapy in refractory childhood-onset epileptic spasms (ES). METHODS: Nine patients with ES were enrolled in an Institutional Review Board (IRB)- and Food and Drug Administration (FDA)-approved expanded access investigational new drug trial. Patients received plant-derived highly purified CBD in oral solution in addition to their baseline medications at an initial dosage of 5 mg/kg/day, which was increased by 5 mg/kg/day every week to an initial target dosage of 25 mg/kg/day. Seizure frequency, adverse event, and parents' subjective reports of cognitive and behavioral changes were recorded after 2 weeks and 1, 2, 3, 6, 9, and 12 months of CBD treatment. Responder rates (percent of patients with >50% reduction in ES frequency from baseline) were calculated. Electrographic changes were studied in relation to CBD initiation and clinical response. RESULTS: Overall, the responder rates in 9 patients were 67%, 78%, 67%, 56%, 78%, 78%, and 78% after 2 weeks and 1, 2, 3, 6, 9, and 12 months of CBD treatment, respectively. Three out of nine patients (33%) were ES free after two months of treatment. Parents reported subjective improvements in cognitive and behavioral domains. Side effects, primarily drowsiness, were seen in 89% of patients (n = 8). Eight of the nine (89%) patients had electroencephalographic (EEG) studies prior to and after initiation of CBD. Three out of five patients (60%) had resolution in their hypsarrhythmia pattern. SIGNIFICANCE: Purified pharmaceutical CBD may be an effective and safe adjunctive therapy in refractory ES and may also be associated with improvements in electrographic findings.

Acute Blockade of PACAP-Dependent Activity in the Ventromedial Nucleus of the Hypothalamus Disrupts Leptin-Induced Behavioral and Molecular Changes in Rats.

Leptin signaling pathways, stemming primarily from the hypothalamus, are necessary for maintaining normal energy homeostasis and body weight. In both rodents and humans, dysregulation of leptin signaling leads to morbid obesity and diabetes. Since leptin resistance is considered a primary factor underlying obesity, understanding the regulation of leptin signaling could lead to therapeutic tools and provide insights into the causality of obesity. While leptin actions in some hypothalamic regions such as the arcuate nuclei have been characterized, less is known about leptin activity in the hypothalamic ventromedial nuclei (VMN). Recently, pituitary adenylate cyclase-activating polypeptide (PACAP) has been shown to reduce feeding behavior and alter metabolism when administered into the VMN in a pattern similar to that of leptin. In the current study, we examined whether leptin and PACAP actions in the VMN share overlapping pathways in the regulation of energy balance. Interestingly, PACAP administration into the VMN increased STAT3 phosphorylation and SOCS3 mRNA expression, both of which are hallmarks of leptin receptor activation. In addition, BDNF mRNA expression in the VMN was increased by both leptin and PACAP administration. Moreover, antagonizing PACAP receptors fully reversed the behavioral and cellular effects of leptin injections into the VMN. Electrophysiological studies further illustrated that leptin-induced effects on VMN neurons were blocked by antagonizing PACAP receptors. We conclude that leptin dependency on PACAP signaling in the VMN suggests a potential common signaling cascade, allowing a tonically and systemically secreted neuropeptide to be more precisely regulated by central neuropeptides.

Genetic disruption of ankyrin-G in adult mouse forebrain causes cortical synapse alteration and behavior reminiscent of bipolar disorder.

Genome-wide association studies have implicated the ANK3 locus in bipolar disorder, a major human psychotic illness. ANK3 encodes ankyrin-G, which organizes the neuronal axon initial segment (AIS). We generated a mouse model with conditional disruption of ANK3 in pyramidal neurons of the adult forebrain (Ank-G cKO). This resulted in the expected loss of pyramidal neuron AIS voltage-gated sodium and potassium channels. There was also dramatic loss of markers of afferent GABAergic cartridge synapses, resembling the cortical microcircuitry changes in brains from psychotic patients, and suggesting disinhibition. Expression of c-fos was increased in cortical pyramidal neurons, consistent with increased neuronal activity due to disinhibition. The mice showed robust behavioral phenotypes reminiscent of aspects of human mania, ameliorated by antimania drugs lithium and valproate. Repeated social defeat stress resulted in repeated episodes of dramatic behavioral changes from hyperactivity to "depression-like" behavior, suggestive of some aspects of human bipolar disorder. Overall, we suggest that this Ank-G cKO mouse model recapitulates some of the core features of human bipolar disorder and indicates that cortical microcircuitry alterations during adulthood may be involved in pathogenesis. The model may be useful for studying disease pathophysiology and for developing experimental therapeutics.

Combined chondroitinase and KLF7 expression reduce net retraction of sensory and CST axons from sites of spinal injury.

Axon regeneration in the central nervous system is limited both by inhibitory extracellular cues and by an intrinsically low capacity for axon growth in some CNS populations. Chondroitin sulfate proteoglycans (CSPGs) are well-studied inhibitors of axon growth in the CNS, and degradation of CSPGs by chondroitinase has been shown to improve the extension of injured axons. Alternatively, axon growth can be improved by targeting the neuron-intrinsic growth capacity through forced expression of regeneration-associated transcription factors. For example, a transcriptionally active chimera of Krüppel-like Factor 7 (KLF7) and a VP16 domain improves axon growth when expressed in corticospinal tract neurons. Here we tested the hypothesis that combined expression of chondroitinase and VP16-KLF7 would lead to further improvements in axon growth after spinal injury. Chondroitinase was expressed by viral transduction of cells in the spinal cord, while VP16-KLF7 was virally expressed in sensory neurons of the dorsal root ganglia or corticospinal tract (CST) neurons. After transection of the dorsal columns, both chondroitinase and VP16-KLF7 increased the proximity of severed sensory axons to the injury site. Similarly, after complete crush injuries, VP16-KLF7 expression increased the approach of CST axons to the injury site. In neither paradigm however, did single or combined treatment with chondroitinase or VP16-KLF7 enable regenerative growth distal to the injury. These results substantiate a role for CSPG inhibition and low KLF7 activity in determining the net retraction of axons from sites of spinal injury, while suggesting that additional factors act to limit a full regenerative response.

Cannabidiol as a new treatment for drug-resistant epilepsy in tuberous sclerosis complex.

OBJECTIVE: Tuberous sclerosis complex (TSC) is an autosomal-dominant genetic disorder with highly variable expression. The most common neurologic manifestation of TSC is epilepsy, which affects approximately 85% of patients, 63% of whom develop treatment-resistant epilepsy. Herein, we evaluate the efficacy, safety, and tolerability of cannabidiol (CBD), a nonpsychoactive compound derived from the marijuana plant, as an adjunct to current antiepileptic drugs in patients with refractory seizures in the setting of TSC. METHODS: Eighteen of the 56 patients who have enrolled in our current expanded-access study of cannabidiol for patients with treatment-resistant epilepsy carry a diagnosis of TSC. After an initial baseline period of 1 month, patients began treatment with CBD. The initial dose of 5 mg/kg/day was increased by 5 mg/kg/day every week up to a maximum dose of 50 mg/kg/day, if tolerated. Weekly seizure frequencies, percent change in seizure frequencies, and responder rates were calculated during the 2nd, 3rd, 6th, 9th, and 12th month of treatment with CBD. RESULTS: The median weekly seizure frequency during the baseline period was 22.0 (interquartile range [IQR] 14.8-57.4), which decreased to 13.3 (IQR 5.1-22.1) after 3 months of treatment with cannabidiol. The median percent change in total weekly seizure frequency was -48.8% (IQR -69.1% to -11.1%) after 3 months of treatment. The 50% responder rates over the course of the study were 50%, 50%, 38.9%, 50%, and 50% after 2, 3, 6, 9, and 12 months of treatment with CBD, respectively. In patients taking clobazam concurrently with CBD (n = 12), the responder rate after 3 months of treatment was 58.3%, compared to 33.3% in patients not taking clobazam (n = 6). Twelve (66.7%) of 18 patients in this study experienced at least one adverse event thought possibly related to CBD; the most common adverse events were drowsiness (n = 8, 44.4%), ataxia (n = 5, 27.8%), and diarrhea (n = 4, 22.2%). SIGNIFICANCE: Although double-blind, placebo-controlled trials are still necessary, these findings suggest that cannabidiol may be an effective and well-tolerated treatment option for patients with refractory seizures in TSC.