Serotonin 1B receptors (5-HT1BRs) are involved in cocaine reward via regulating activity of dopamine neurons. The 5-HT1BR agonist CP-94,253 or 5-HT1BR overexpression in the nucleus accumbens shell (NAcSh) enhances cocaine intake during maintenance of daily self-administration (SA) but inhibits intake after 21 days of abstinence in male rats. My central hypothesis is that CP-94,253 acts at 5-HT1BRs located on the terminals of NAcSh GABA neurons that undergo regulatory changes in response to cocaine SA and subsequent abstinence resulting in an abstinence-induced switch in the functional effects of CP-94,253 in both male and female rats. In the first series of experiments, I compared the functional effects of CP-94,253 in female rats to male rats: 1) during maintenance of daily cocaine SA, 2) after 21-60 days abstinence, and 3) during the resumption of cocaine SA after abstinence (i.e. model of relapse). I found that CP-94,253 enhanced cocaine intake and breakpoints on a high-effort progressive ratio schedule of cocaine reinforcement during maintenance regardless of sex. By contrast, CP-94,253 attenuated cocaine intake after 21 days of abstinence and during the relapse test, regardless of sex. These findings suggest: 1) an abstinence-induced inhibitory effect of the 5-HT1BR agonist occurs in both sexes, 2) these inhibitory effects are long-lasting, and 3) the agonist may provide a novel therapeutic for cocaine use disorders. I next used RNAscope in situ hybridization to measure regulatory changes in 5-HT1BR mRNA expression and its co-expression with GABAergic and glutamatergic cell markers in the lateral and medial NAcSh subregions after abstinence from cocaine. I found no significant changes in these measures in either subregion of NAcSh after prolonged abstinence in either sex; however, I did observe that 95% of 5-HT1BR mRNA is co-localized in GABAergic neurons, whereas <2% is co-localized in glutamatergic cells. Future research investigating abstinence-induced, functional changes in 5-HT1BRs in subregions of the NAcSh is an alternate approach to further test my hypothesis. This research is important for the development of 5-HT1BR agonists as putative treatments of cocaine use disorders.

This dissertation examines dog training in the United States to see how it is implemented and practiced and the potential ramifications for our pet dogs. In Chapter 2, word-based analysis compared the words practicing dog trainers use to describe their work and examined how gender and experience differ between methodologies. Given both the vast history of dog training and the variety of training information available to dog owners, in Chapter 3, I surveyed undergraduate students to determine where dog guardians obtain their information and how they might tackle dog problem behavior. Of 100 practicing dog trainers, only 20%, mostly female trainers using non-aversive methods, were certified. When asked who they asked for dog training advice, most dog guardians reached out to friends, family, or online sources and only about 20% ever attended a formal dog training class. In Chapter 4, dogs were walked on four different types of leash walking equipment which were attached to a strain gauge to assess if these equipment were any better or worse at reducing a dog’s pulling force; dogs pulled most on a martingale collar and there were no statistically significant differences among the other equipment types to each other. Through behavior analysis, none of the dogs in our study showed impaired welfare. In Chapter 5, I compared e-collar training to non-aversive methods in the ability to stop chasing of a lure. Dogs experiencing e-collar stimulation were successful in stopping chase of the lure both during training sessions and in testing. None of the dogs in either non-aversive group was successful in the tests. The findings did not indicate that dogs in the e-collar group, or the non-aversive groups, differed in welfare. As in Chapter 4, despite the lack of immediate negative welfare effects for the dogs experiencing aversive methods like the e-collar, given the demonstrated evidence for Chapters 2 and 3 that individuals who use these aversive tools, either practicing trainers or the general public, may lack the foundation to properly implement them, I recommend caution in their public sale and do not advocate for their use.

The rate at which an operant is produced has often functioned as a fundamental measure of the efficacy of a reinforcer. Previous research has shown that operant behavior is typically organized into bouts implying that rate of responding is a composite of bout-initiation rate, within-bout response rate, and mean bout length. However, it is still unclear whether this organization of behavioral responses into bouts is a product of the motivational processes or a property that arises from the location of an organism in space. To test this proximity hypothesis, two-response sequences were intermittently reinforced: either pressing one lever twice (manipulandum proximal to response termination) or pressing each of two levers, located on either side of an operant chamber, once (manipulandum distal to response termination). In Experiment 1, rats were first trained to lever press for food on a VI schedule before being exposed to the alternation paradigm. Experiment 1 consisted of three phases. In Phase 1, food-deprived rats learned the alternation paradigm under a tandem variable time (VT) 150-s fixed-ratio (FR) 1 schedule of reinforcement. Phase 2 and 3 increased the FR requirement from 1 to 3 or 5 and removed food deprivation, respectively, to examine their effect on response-rate components. In Experiment 2, rats switched between trials consisting of pressing a single lever repeatedly or alternating between two levers for reward. Following stable behavior, lever pressing was extinguished in both trial types to the effect of extinction on response-rate components. Overall, behavioral bouts persisted under the alternation paradigm suggesting that they reflect motivational states and not just location. Additionally, bout-initiation rate decreased with increased response effort and decreased deprivation. Taken together, these results provide support for the use of response-bout analysis to evaluate the value of a reinforcer and its sensitivity to pharmacological manipulations.

Autism spectrum disorder (ASD) is characterized by deficits in flexible cognition and social behavior. The most common atypical brain structure in ASD, the cerebellum, has multisynaptic connections through the cerebellar nuclei (CN) and thalamus to cognitive- and social-associated brain regions, yet formation and modulation of these pathways are not fully understood. Additionally, a CN output mechanism, perineuronal nets (PNNs), structure and function are undefined. PNNs are specialized extracellular matrix structures whose appearance is associated with the end of the critical period of plasticity and have been implicated in learning and neurodevelopmental disorders, but their role in the CN during development is unknown.To examine the role of CN on cognition, CN activity was increased or decreased in both male and female mice using Designer Receptors Exclusively Activated by Designer Drugs (DREADDs) from postnatal day 21-35. Learning and reversal was analyzed using a pairwise visual discrimination task. Social behavior was assessed using a classic three-chamber assay and analyzed using SLEAP (Social Leap Estimates Animal Poses). A marker of critical periods, perineuronal nets (PNNs), was examined to understand relationships between neural development and behavior. Interestingly, adolescent CN disruption did not alter task acquisition, yet correct choice reversal performance was dependent on DREADD manipulation and sex. CN inhibition improved reversal learning in males (5 days faster to criteria) and CN excitation improved female reversal learning (10 days faster to criteria) compared to controls. Analysis of social behavior revealed male social preference was abolished in CN manipulated groups, whereas females failed to demonstrate a social preference. Interestingly, CN manipulation in females regardless of direction, reduced PNN intensity, whereas in males only CN inhibition reduced PNN intensity. PNN intensity negatively correlated with reversal performance. CN PNN intensity showed no relation to social behavior. These data suggest chronic adolescent CN manipulation may have compensatory changes in PNN structure and CN output to improve reversal learning and PNN function was unrelated to social behavior. This study provides new evidence for CN in non-motor functions and sex-dependent differences in behavior and CN plasticity.

Variations in menopause etiologies, from surgical manipulation to a natural transition, can impact cognition in both healthy and neurodegenerative aging. Although abundant research has demonstrated impacts from surgical versus transitional menopause, such as variations in timing of menopause, both variations in initiation of menopause and length of time since menopause, but not all avenues have been systematically evaluated. Further, assessments of variations in hormone therapies have demonstrated marked outcomes on the brain and cognition in different menopause etiologies, and results can differ depending on type of hormone, combination of hormones, dose, route of administration, among other factors, in regard to healthy aging. Further, the impact of the endocrine system on neurodegenerative disease is multifaceted. Research has highlighted that the endocrine system not only impacts neurodegeneration, such as in Alzheimer’s disease (AD), but that fluctuations in the endocrine system might be strong mediators in disease prevalence and progression. This dissertation seeks to understand how factors such as menopause etiology, biological sex, and hormone therapy impact normative and neurodegenerative aging. Assessments in a rat model of normal aging of progestogen-based hormone therapy given during the transition to menopause demonstrated attenuation of impairment seen with transitional menopause that was working memory specific. In evaluating a rat model of AD, there were distinct trends in neuropathology and associated cognitive changes in males and females with and without gonadal hormone deprivation. Further, assessment of transitional menopause in this AD model yielded an interaction between follicular depletion and genotype for neuropathology that was not present in cognitive assessments. Together, these dissertation chapters highlight that there are a multitude of factors to consider when evaluating effects of menopause and that these variations in experience underscore a need for personalized medicine when selecting therapeutic targets for healthy and neurodegenerative aging that includes consideration of overall hormone milieu and menopause history. Further, these data suggest that the inclusion of males and females in the study of AD-related factors is crucial for understanding disease progression.

Social stress during adolescence has been linked to increased ethanol intake in adulthood. It is unknown if social stress during adolescence also causes changes in the patterns of drinking, such as drinking in bouts instead of spreading out each drink. Animal models of social stress utilize mice and social isolation. Half of the mice used in this experiment were isolated for their adolescent period, whereas the other half were housed in groups. In Phase 1, mice completed a two-bottle choice Drinking in the Dark (DID) procedure in order to model binge drinking and measure ethanol intake. In Phase 2, mice completed a free choice behavioral task, choosing between milk alone and milk mixed with ethanol. Phase 1 showed increased ethanol intake in females and in mice that were isolated. Within this phase, there was also a sex x treatment interaction, with isolated males drinking significantly more alcohol than social males. Phase 2 also showed that females drink more ethanol than males but showed no difference in their pattern of drinking. In addition, there was a sex x treatment x reinforcer interaction, demonstrating that isolated females drank significantly more vehicle than any other group. These results reaffirm that adolescent social stress is linked to increased ethanol intake, yet may not change the pattern of drinking. This suggests that the effects of social isolation during adolescence on patterns of drinking should be investigated further.

The capacity to track time in the seconds-to-minutes range, or interval timing, appears to be at least partially dependent on intact hippocampal (HPC) function. The current dissertation sought to dissociate timed responses, non-timed responses, and motivational aspects of behavior in order to propose a role of the HPC in specific timing sub-processes. In Chapter 2, effects of dorsal HPC (dHPC) lesions on temporal responding in a switch-timing task revealed a critical role of dHPC in the acquisition of interval timing criteria. Following dHPC lesions, the start time of responding was systemically shortened, in a manner that was enhanced and sustained when encoding a novel long interval, consistent with a memory-based account of dHPC function in timed responding. Chapter 3 investigated effects of chronic stress, which has been shown to reliably induce HPC dendritic retraction, on interval timing, utilizing response-initiated schedules of reinforcement, which facilitate deconvolution of timing and motivation. This revealed task-dependent effects on interval timing and motivation, where stress induced transient effects on motivation in a prospective timing task, but transient effects on the variability of timed responding in a retrospective timing task, consistent with an effect on memory function in interval timing. Chapter 4 sought to bring timed responding, motivation, and non-timed behaviors under stronger procedural control, through the implementation of a response-initiated timing-with-opportunity-cost task, in which a cost is imposed on temporal food-seeking by the presence of a concurrent source of probabilistic reinforcement. This arrangement garnered strong schedule control of behavior, and revealed individual-subject differences in the effects of reward devaluation, such that it affected motivation in some rats, but temporal responding in others. Using this methodology, Chapter 5 investigated initial temporal entrainment of behavior under pharmacological deactivation of dHPC and revealed its critical involvement in updating memory to new temporal contingencies. Together, data from this dissertation contrast with prior conclusions that the HPC is not involved in learning temporal criteria, and instead suggest that its function is indeed critical to encoding temporal intervals in memory.

Cocaine use disorders (CUDs) and human immunodeficiency virus (HIV) are a common comorbidity, although it is largely unknown whether HIV interacts with cocaine abstinence to uniquely alter neuroimmune function and whether HIV may modulate the efficacy of medications intended to treat CUDs. My dissertation research demonstrates using preclinical rodent models of drug self-administration and craving that systemic exposure to the HIV protein gp120 produces a unique profile of neuroimmune changes within the nucleus accumbens core (NAc core) that is distinct from early cocaine abstinence alone. After a protracted period of abstinence, gp120 exposure abolished the effect of the dopamine D3 receptor (D3R) partial agonist MC-25-41, which successfully attenuated cue-induced cocaine seeking in non-exposed rats. Further probing the role of downstream, intracellular neuroimmune function on cue-induced cocaine seeking, I examined the role of the nuclear factor kappa B (NF-κB) signaling pathway within the NAc core on cue-induced cocaine seeking after a period of protracted abstinence across sex and reinforcer type. I demonstrated that knockdown of the p65 subunit of NF-κB results in a decrease in cue-induced cocaine seeking in males, but not in females. This effect was specific to cocaine, as p65 knockdown did not affect cue-induced sucrose seeking in either males or females. Moreover, I examined expression levels of the extracellular matrix enzyme MMP-9 within the NAc core, as it is regulated by NF-κB and is an important mediator of cue-induced cocaine seeking and associated synaptic plasticity. I demonstrated that males express higher levels of MMP-9 within the NAc compared to females, and that p65 knockdown decreases NAc core MMP-9 in males but not females among cocaine cue-exposed animals. Altogether, these results suggest that immunotherapeutic medications may be useful tools in the treatment of CUDs, particularly among males that are disproportionately impacted by HIV.

Capacity limits of the human nervous system require important or rewarding information to be prioritized and encoded over less important or rewarding information. The present dissertation aims to identify structural and functional neural correlates of reward-motivated memory encoding. Chapter 1 reviews studies of reward-motivated memory encoding and their neural correlates, as well as the structure and function of dopaminergic midbrain circuits. Chapter 2 presents a study that utilizes electroencephalography (EEG) to determine which of two hypothesized processes underly the influence of reward value on episodic memory. One hypothesis is that value engages prefrontal executive control processes, so that valuable stimuli engage an elaborative rehearsal strategy that benefits memory. A second hypothesis is that value acts through the reward-related midbrain dopamine system to modulate synaptic plasticity in hippocampal and cortical efferents, thereby benefiting memory encoding. The results revealed that EEG signals thought to index dopamine-driven attention allocation were modulated by reward value and were positively correlated with individual differences in behavioral measures of memory prioritization. Chapter 3 employs diffusion-weighted magnetic resonance imaging (MRI) to dissociate heterogenous functional circuits of the midbrain reward system. The results comport with primate histology and show that midbrain circuits are differentially predictive of impulsivity and of attention-deficit hyperactivity disorder (ADHD). Chapter 4 presents a study that also employs diffusion-weighted MRI. The findings replicate Chapter 3 in dissociating heterogenous functional circuits of the midbrain reward system. Additionally, the structural integrity of midbrain-hippocampus circuits was quantified. Structural integrity of these circuits was positively correlated to behavioral measures of memory prioritization. These findings suggest that structural and functional measures of the dopaminergic reward system may underlie reward-motivated memory encoding in humans.