A single-vector intersectional AAV strategy for interrogating cellular diversity and brain function.

As discovery of cellular diversity in the brain accelerates, so does the need for tools that target cells based on multiple features. Here we developed Conditional Viral Expression by Ribozyme Guided Degradation (ConVERGD), an adeno-associated virus-based, single-construct, intersectional targeting strategy that combines a self-cleaving ribozyme with traditional FLEx switches to deliver molecular cargo to specific neuronal subtypes. ConVERGD offers benefits over existing intersectional expression platforms, such as expanded intersectional targeting with up to five recombinase-based features, accommodation of larger and more complex payloads and a vector that is easy to modify for rapid toolkit expansion. In the present report we employed ConVERGD to characterize an unexplored subpopulation of norepinephrine (NE)-producing neurons within the rodent locus coeruleus that co-express the endogenous opioid gene prodynorphin (Pdyn). These studies showcase ConVERGD as a versatile tool for targeting diverse cell types and reveal Pdyn-expressing NE+ locus coeruleus neurons as a small neuronal subpopulation capable of driving anxiogenic behavioral responses in rodents.

Indirect and direct cannabinoid agonists differentially affect mesolimbic dopamine release and related behaviors.

The cannabinoid system is being researched as a potential pharmaceutical target for a multitude of disorders. The present study examined the effect of indirect and direct cannabinoid agonists on mesolimbic dopamine release and related behaviors in C57BL/6J (B6) mice. The indirect cannabinoid agonist N-arachidonoyl serotonin (AA-5-HT) indirectly agonizes the cannabinoid system by preventing the metabolism of endocannabinoids through fatty acid amide hydrolase inhibition while also inhibiting transient receptor potential vanilloid Type 1 channels. Effects of AA-5-HT were compared with the direct cannabinoid receptor Type 1 agonist arachidonoyl-2'-chloroethylamide (ACEA). In Experiment 1, mice were pretreated with seven daily injections of AA-5-HT, ACEA, or vehicle prior to assessments of locomotor activity using open field (OF) testing and phasic dopamine release using in vivo fixed potential amperometry. Chronic exposure to AA-5-HT did not alter locomotor activity or mesolimbic dopamine functioning. Chronic exposure to ACEA decreased rearing and decreased phasic dopamine release while increasing the dopaminergic response to cocaine. In Experiment 2, mice underwent AA-5-HT, ACEA, or vehicle conditioned place preference, then saccharin preference testing, a measure commonly associated with anhedonia. Mice did not develop a conditioned place preference or aversion for AA-5-HT or ACEA, and repeated exposure to AA-5-HT or ACEA did not alter saccharin preference. Altogether, the findings suggest that neither of these drugs induce behaviors that are classically associated with abuse liability in mice; however, direct cannabinoid receptor Type 1 agonism may play more of a role in mediating mesolimbic dopamine functioning than indirect cannabinoid agonism. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

Impulsive choice in two different rat models of ADHD-Spontaneously hypertensive and Lphn3 knockout rats.

Introduction: Impulsivity is a symptom of attention-deficit/hyperactivity disorder (ADHD) and variants in the Lphn3 (Adgrl3) gene (OMIM 616417) have been linked to ADHD. This project utilized a delay-discounting (DD) task to examine the impact of Lphn3 deletion in rats on impulsive choice. "Positive control" measures were also collected in spontaneously hypertensive rats (SHRs), another animal model of ADHD. Methods: For Experiment I, rats were given the option to press one lever for a delayed reward of 3 food pellets or the other lever for an immediate reward of 1 pellet. Impulsive choice was measured as the tendency to discount the larger, delayed reward. We hypothesized that impulsive choice would be greater in the SHR and Lphn3 knockout (KO) rats relative to their control strains - Wistar-Kyoto (WKY) and Lphn3 wildtype (WT) rats, respectively. Results: The results did not completely support the hypothesis, as only the SHRs (but not the Lphn3 KO rats) demonstrated a decrease in the percent choice for the larger reward. Because subsequent trials did not begin until the end of the delay period regardless of which lever was selected, rats were required to wait for the next trial to start even if they picked the immediate lever. Experiment II examined whether the rate of reinforcement influenced impulsive choice by using a DD task that incorporated a 1 s inter-trial interval (ITI) immediately after delivery of either the immediate (1 pellet) or delayed (3 pellet) reinforcer. The results of Experiment II found no difference in the percent choice for the larger reward between Lphn3 KO and WT rats, demonstrating reinforcement rate did not influence impulsive choice in Lphn3 KO rats. Discussion: Overall, there were impulsivity differences among the ADHD models, as SHRs exhibited deficits in impulsive choice, while the Lphn3 KO rats did not.

An assessment of executive function in two different rat models of attention-deficit hyperactivity disorder: Spontaneously hypertensive versus Lphn3 knockout rats.

Attention-deficit/hyperactivity disorder (ADHD) a common neurodevelopmental disorder of childhood and often comorbid with other externalizing disorders (EDs). There is evidence that externalizing behaviors share a common genetic etiology. Recently, a genome-wide, multigenerational sample linked variants in the Lphn3 gene to ADHD and other externalizing behaviors. Likewise, limited research in animal models has provided converging evidence that Lphn3 plays a role in EDs. This study examined the impact of Lphn3 deletion (i.e., Lphn3-/- ) in rats on measures of behavioral control associated with externalizing behavior. Impulsivity was assessed for 30 days via a differential reinforcement of low rates (DRL) task and working memory evaluated for 25 days using a delayed spatial alternation (DSA) task. Data from both tasks were averaged into 5-day testing blocks. We analyzed overall performance, as well as response patterns in just the first and last blocks to assess acquisition and steady-state performance, respectively. "Positive control" measures on the same tasks were measured in an accepted animal model of ADHD-the spontaneously hypertensive rat (SHR). Compared with wildtype controls, Lphn3-/- rats exhibited deficits on both the DRL and DSA tasks, indicative of deficits in impulsive action and working memory, respectively. These deficits were less severe than those in the SHRs, who were profoundly impaired on both tasks compared with their control strain, Wistar-Kyoto rats. The results provide evidence supporting a role for Lphn3 in modulating inhibitory control and working memory, and suggest additional research evaluating the role of Lphn3 in the manifestation of EDs more broadly is warranted.

Cerebellar Modulation of Mesolimbic Dopamine Transmission Is Functionally Asymmetrical.

Cerebral and cerebellar hemispheres are known to be asymmetrical in structure and function, and previous literature supports that asymmetry extends to the neural dopamine systems. Using in vivo fixed potential amperometry with carbon fiber microelectrodes in anesthetized mice, the current study assessed hemispheric lateralization of stimulation-evoked dopamine in the nucleus accumbens (NAc) and the influence of the cerebellum in regulating this reward-associated pathway. Our results suggest that cerebellar output can modulate mesolimbic dopamine transmission, and this modulation contributes to asymmetrically lateralized dopamine release. Dopamine release did not differ between hemispheres when evoked by medial forebrain bundle (MFB) stimulation; however, dopamine release was significantly greater in the right NAc relative to the left when evoked by electrical stimulation of the cerebellar dentate nucleus (DN). Furthermore, cross-hemispheric talk between the left and right cerebellar DN does not seem to influence mesolimbic release given that lidocaine infused into the DN opposite to the stimulated DN did not alter release. These studies may provide a neurochemical mechanism for studies identifying the cerebellum as a relevant node for reward, motivational behavior, saliency, and inhibitory control. An increased understanding of the lateralization of dopaminergic systems may reveal novel targets for pharmacological interventions in neuropathology of the cerebellum and extending projections.

Comparing phasic dopamine dynamics in the striatum, nucleus accumbens, amygdala, and medial prefrontal cortex.

Midbrain dopaminergic neurons project to and modulate multiple highly interconnected modules of the basal ganglia, limbic system, and frontal cortex. Dopamine regulates behaviors associated with action selection in the striatum, reward in the nucleus accumbens (NAc), emotional processing in the amygdala, and executive functioning in the medial prefrontal cortex (mPFC). The multifunctionality of dopamine likely occurs at the individual synapses, with varied levels of phasic dopamine release acting on different receptor populations. This study aimed to characterize specific aspects of stimulation-evoked phasic dopamine transmission, beyond simple dopamine release, using in vivo fixed potential amperometry with carbon fiber recording microelectrodes positioned in either the dorsal striatum, NAc, amygdala, or mPFC of anesthetized mice. To summarize results, the present study found that the striatum and NAc had increased stimulation-evoked phasic dopamine release, faster dopamine uptake (leading to restricted dopamine diffusion), weaker autoreceptor functioning, greater supply levels of available dopamine, and increased dopaminergic responses to DAT blockade compared to the amygdala and mPFC. Overall, these findings indicate that phasic dopamine may have different modes of communication between striatal and corticolimbic regions, with the first being profuse in concentration, rapid, and synaptically confined and the second being more limited in concentration but longer lasting and spatially dispersed. An improved understanding of regional differences in dopamine transmission can lead to more efficient treatments for disorders related to dopamine dysfunction.