Recent studies have indicated that some patients with Alzheimer’s disease (AD) experience undetected focal seizures, which could contribute to and/or worsen overall disease burden (e.g. cognitive function and neuropsychiatric comorbidities). Genetic variants in presenilin 2 (PSEN2) are associated with early-onset AD and result in a loss of normal PSEN2 function. Patients with PSEN2 mutations also experience seizures more frequently than age-matched individuals without AD. There are over 30 clinically approved antiseizure drugs (ASDs), which have been proposed to be effective in controlling these seizures, and thus reducing disease burden. ASD efficacy and tolerability is not, however, frequently determined in aged rodent seizure models nor in rodent models with AD-associated genotypes. This project thus aimed to establish the dose-dependent efficacy of mechanistically-distinct approved ASDs in the well-established mouse 6 Hz model of focal seizures, using both female and male PSEN2 knockout (KO) mice. Seizure susceptibility in PSEN2 variant mouse models of AD is generally understudied; most work previously has been conducted in amyloid precursor protein-overexpressing models. We thus first quantified the median convulsant current (CC50) in the 6 Hz model of focal seizures with male and female PSEN2 KO mice aged 3-4 months. The CC50 of female PSEN2 KO mice was 34.4 mA [95% confidence intervals 30.4-38.5]; in males it was 41.9 mA [39.3-46.9]. Candidate ASDs (valproic acid, lamotrigine, carbamazepine, levetiracetam, and perampanel) were then administered via intraperitoneal (IP) injection in a dose-related manner to assess dose-related seizure control in the 6 Hz test. Preliminary results indicate that PSEN2 KO mice may be more sensitive to administration of valproic acid than wild-type mice. This study is definitively addressing whether loss of normal PSEN2 function promotes any overt changes in the anticonvulsant efficacy of clinically-approved ASDs to better inform management of focal seizures in patients with AD.

Neuropeptide S (NPS) is a neuropeptide produced primarily in two regions of the hindbrain, the locus coeruleus (LC) and the Kolliker-Fuse nucleus. The LC-NPS population is particularly interesting because of the LC’s role in norepinephrine production and subsequent transmission throughout the brain. Previous work has found that when NPS is injected into the amygdala, it results in an anxiolytic phenotype, implicating NPS and its G-protein coupled receptor (NPSr1) in anxiety-related behaviors. Using fluorescent in situ hybridization, a method which allows visualization of single RNA molecules within cells via fluorescent probes, we found preliminarily, that the orbitofrontal cortex (OFC) has dense expression of NPSr1 RNA. This is significant as the OFC is involved in higher-order cognition including social, reward-learning, and anxiety-like behaviors. For example, OFC neurons respond to social interaction as well as food cues, and inactivation of the OFC results in increased anxiety-like behavior. The LC is also known to send projections to the OFC that have been largely unexplored. Therefore, to better understand and characterize the connection between the LC and OFC we utilized in vivo fiber photometry to assess endogenous OFC-NPSr1 activity during reward-learning, social interaction, and innate behaviors. Our studies aim to uncover the functional role of LC-NPS release in the OFC.

Opioids like morphine or fentanyl have high therapeutic value as analgesics for acute and chronic pain. Unfortunately, they also have a high propensity for abuse. Previous research has indicated that the rewarding and analgesic properties of opioids may be dissociated in the brain, though how they do so remains unresolved. Endogenous and exogenous opioids act on four specialized 7 transmembrane g-protein coupled receptors (GPCRs). One of these opioid receptors is the mu-opioid peptide receptor (MOPR), which is thought to be the primary target of morphine and fentanyl. The nucleus accumbens (NAc) has long been recognized as a significant reward center of the brain that has a high density of MOPR’s. Current work in the lab by Dr. Castro and myself has shown that a circuit from the dorsal raphe nucleus (DRN) to the NAc underlies MOPR control of reward and motivation. Specifically, we have shown that MORs are activated by the endogenous ligand enkephalin on DRN terminals in the medial shell of NAc to enhance motivation. While these studies clarify the NAc MOPR motivational circuit, they leave unresolved what intracellular mechanisms are recruited by MOPRs to modulate neural activity. This is of great interest considering that various properties of opioids (analgesia vs. reward vs. respiration) may be driven by one of two different signaling pathways, the G-Protein pathway or the beta-arrestin pathway. Therefore, the primary goal of my project is to determine which pathway is specifically recruited in this circuit to drive enhanced motivation. We will use optogenetic and targeted viral modulation approaches to manipulate the DRN to NAc circuit and determine whether distinct signaling cascades mediate MOPR control of motivation. These results will be the first investigation into how specific signaling cascades contribute to motivated behaviors in a cell-type, temporally restricted, in vivo manner.

Learning and forgetting are two key processes that keep our memories in balance. In the past few decades, we have learned a great deal about mechanisms associated with memory formation and consolidation. However, little is known about the molecular mechanisms of forgetting, despite its importance in human health. Here, we take advantage of the nematode C. elegans – a living animal with a simple nervous system of 302 neurons – to explore the mechanisms behind forgetting. In particular, we focus on the decay of associative olfactory learning and the regulation of this decay after experience of pathogenic bacteria. Previous studies have shown that worms acquire an associative memory linking starvation experience and the olfactory response. After prolonged exposure to a preferred odor during starvation, worms exhibit a diminished response towards the preferred odor. However, upon returning to a food source, the attractive response toward the preferred odor recovers within 3-4 hours, indicating the loss of the associative olfactory memory. We found that the rate of memory loss, quantified by measuring the time course of recovery of the olfactory response, depends on the type of food source (bacterial strain) that worms experience. Specifically, exposing worms to pathogenic bacteria PA14, compared to the regular food source OP50, leads to a quicker loss of the associative olfactory memory. Our results further show that the acceleration of memory loss is mediated by a conserved transcription factor DAF-16/FOXO, as daf-16 mutants exhibited similar rates of memory loss regardless of OP50 or PA14 experience. Together, these findings demonstrate an unexpected role of DAF-16/FOXO in memory decay induced by exposure to pathogens. 

Reward is a driving force for animal and human behavior. Reinforcing behaviors with rewards leads to enhanced learning ability, which can either promote behaviors that increase survival, or lead to maladaptive behaviors. The nucleus accumbens (NAc) and ventral tegmental area (VTA) are brain regions established to be involved in reward processing and have significant neural connectivity. Recent studies have identified a long-range GABAergic neural circuit connecting these two regions, however previous studies focus primarily on dopaminergic neurons. These inhibitory GABAergic neurons synapse with cholinergic interneurons within the NAc shell (NAcSh). Further, the dorsal and ventral subdivisions within the NAcSh have been shown to have different neural connectivity. To investigate the role of this circuit, I performed fiber photometry recordings of neural activity in GABAergic terminals in the dorsal and ventral NAcSh during reward reinforced behavior in mice. The recordings show an increase in GABAergic neural during reward consumption in the ventral, but not the dorsal, NAcSh. I also recorded the activity of NAcSh cholinergic interneurons as well as acetylcholine activity in the dorsal and ventral NAc shell. These recordings show that cholinergic neural activity as well as acetylcholine activity are reduced during reward consumption in the ventral, but not dorsal, NAcSh, reflecting the inhibition by the GABA neurons during this time. I also used the inhibitory photo-activatable chloride pump JAWS to inhibit GABAergic projections during reward consumption, finding that animals made reduced reward seeking events and consumed fewer rewards when JAWS is activated. Collectively, these results indicate GABAergic projections from the VTA to specifically the ventral NAcSh function in reward reinforcement by inhibiting cholinergic activity during reward consumption. These results characterize a previously unknown neural circuit and help us better understand psychiatric disorders like depression and addiction that impact these circuits. 

Previous studies indicate that CNS administration of oxytocin (OT) reduces body weight in male high fat diet-induced obese (DIO) rodents by reducing food intake and increasing energy expenditure (EE). We recently demonstrated that hindbrain [fourth ventricular (4V)] administration of OT elicits weight loss and elevates interscapular brown adipose tissue temperature (TIBAT; surrogate marker of increased EE) in male DIO rats. What remains unclear is whether chronic CNS OT can impact body weight in female high fat diet-fed (HFD) rats and whether this involves activation of hindbrain OT receptors. We hypothesized that OT-induced stimulation of hindbrain OT receptors reduces weight gain and adiposity, in part, by reducing energy intake and increasing BAT thermogenesis in female HFD-fed rats. To test this hypothesis, we measured the effects of chronic 4V OT (≈16.1 ug/day) or vehicle infusions over 28 days on body weight, adiposity and energy intake in female HFD-fed (60% kcal from fat) rats (N=7-8/group). We found that chronic 4V OT reduced weight gain (P<0.05) and relative fat mass (P<0.05) in randomly cycling female HFD-fed rats. These effects were attributed, in part, to reduced energy intake evident during weeks 2 (P<0.05), 3 (P<0.05) and 4 (P<0.05). To assess if hindbrain OT administration also elevates BAT thermogenesis, we examined the effects of acute 4V OT (1, 5 ug) or vehicle on TIBAT in a separate group of female HFD-fed rats (N=8/group). We found that the low dose (1 ug) elevated TIBAT at 0.75, 1, 1.25, 1.5 and 2-h post-injection (P<0.05); the higher dose (5 ug) elevated TIBAT at 0.75, 1, 1.25, 1.5, 1.75 and 2-h post-injection (P<0.05). Together, these findings support the hypothesis that oxytocin action in the hindbrain reduces body weight gain and adiposity by reducing energy intake and increasing BAT thermogenesis in female HFD-fed rats.