A crucial question in drug addiction research concerns whether the varying reports of dopamine-independent and dopamine-dependent motivation can be integrated. According to one theory, the prior drug history of a subject — that is to say, whether they have received minimal or chronic drug exposure — determines whether opiate motivation is dependent upon the brainstem tegmental pedunculopontine nucleus (TPP) or dopamine neurotransmission. The biological analogue of this change is thought to be a switch in the signalling properties (from hyperpolarizing to depolarizing) of ventral tegmental area (VTA) gamma-aminobutyric acid subtype-A (GABAA) receptors. In this thesis, I demonstrate that the mechanisms underlying opiate motivation can be selected artificially by manipulating the signalling properties of VTA GABAA receptors, irrespective of the past drug history of the subject. Furthermore, I suggest that these same VTA GABAA receptors also play a similar role in controlling ethanol motivation. Indeed, the mechanisms underlying ethanol motivation can be doubly dissociated in a manner similar to that observed with opiates. However, whereas opiate motivation is TPP-dependent in the drug-naive state, I found that ethanol motivation was dependent on dopamine neurotransmission (via the D2 receptor) in drug-naive animals. Conversely, ethanol motivation was TPP-dependent in ethanol-deprived mice (as opposed to opiate motivation being dopamine-dependent in opiate-deprived animals). These effects are consistent with a VTA GABAA receptor switching mechanism identical to the one seen in the case of opiate motivation.

A crucial question in drug addiction research concerns whether the varying reports of dopamine-independent and dopamine-dependent motivation can be integrated. According to one theory, the prior drug history of a subject — that is to say, whether they have received minimal or chronic drug exposure — determines whether opiate motivation is dependent upon the brainstem tegmental pedunculopontine nucleus (TPP) or dopamine neurotransmission. The biological analogue of this change is thought to be a switch in the signalling properties (from hyperpolarizing to depolarizing) of ventral tegmental area (VTA) gamma-aminobutyric acid subtype-A (GABAA) receptors. In this thesis, I demonstrate that the mechanisms underlying opiate motivation can be selected artificially by manipulating the signalling properties of VTA GABAA receptors, irrespective of the past drug history of the subject. Furthermore, I suggest that these same VTA GABAA receptors also play a similar role in controlling ethanol motivation. Indeed, the mechanisms underlying ethanol motivation can be doubly dissociated in a manner similar to that observed with opiates. However, whereas opiate motivation is TPP-dependent in the drug-naive state, I found that ethanol motivation was dependent on dopamine neurotransmission (via the D2 receptor) in drug-naive animals. Conversely, ethanol motivation was TPP-dependent in ethanol-deprived mice (as opposed to opiate motivation being dopamine-dependent in opiate-deprived animals). These effects are consistent with a VTA GABAA receptor switching mechanism identical to the one seen in the case of opiate motivation.

Mu opioid receptors (MOPs) in the pain pathway contribute to morphine analgesia. Morphine also stimulates reward/reinforcement through disinhibition of dopaminergic (DA) neurones in the ventral tegmental area (VTA), an effect implicated in its abuse and dependence. We hope to develop approaches to achieve sustained analgesia without affecting reward by exploiting differential MOP signalling mechanisms in the pain and reward pathways. MOPs, delta opioid receptors (DOPs) and β-arrestin2 (BAR2) are all necessary components of the signalling complex in nociceptive neurones for morphine analgesic tolerance; c-Src (a tyrosine kinase), thought to couple to MOP receptors through BAR2 has also been implicated. To investigate opioid receptor signalling in response to morphine we used a variety of different techniques that included behavioural measures of nociception, reinforcement and locomotion and electrophysiological methods to study DRG neurones from the pain pathway and brain slices containing VTA neurones. This study in mice confirms that morphine administered subcutaneously (SC) causes analgesia, analgesic tolerance, and has psychomotor effects leading to enhanced locomotion and reinforcement. In VTA neurones morphine and the selective MOP receptor agonist DAMGO caused concentration-dependent inhibition of the frequency of IPSCs. All these actions of morphine were absent from MOP-/- mice. Morphine exhibited reduced potency as 1) an analgesic, 2) stimulator of locomotion, 3) a reinforcer in CPP and 4) an inhibitor of sIPSC frequency, when applied to MOP+/- mice or their VTA neurones. Morphine analgesic tolerance developed faster and to a greater extent in MOP+/- mice than in WT mice. DOP-/- mice exhibited morphine analgesia with less tolerance, as did BAR2-/- mice. BAR2-/- mice also exhibited reduced morphine locomotion and an increased sensitivity to morphine reinforcement. Morphine tolerance was absent from BAR2-/-//DOP-/- mice. The inhibition of sIPSC frequency by morphine was reduced in BAR2+/- and BAR2-/- VTA neurones. Dasatinib and PP2 (c-Src tyrosine kinase inhibitors) prevented the development of morphine tolerance in WT and MOP+/- mice and dasatinib caused its reversal in the latter. The drugs had no significant analgesic effect alone. Dasatinib did not affect morphine preference or locomotor activation. PP2 reduced morphine’s inhibition of sIPSC frequency. As c-Src inhibition does not appear to alter the psychomotor effects produced by morphine and it acts to reduce morphine analgesic tolerance. We believe that cSrc is an attractive target to prevent the development of morphine analgesic tolerance without affecting hedonic homeostasis.

Indiana University-Purdue University Indianapolis (IUPUI) / Alcohol use disorder (AUD) and nicotine dependence often result in serious health problems and are top contributors to preventable deaths worldwide. Co-addiction to alcohol and nicotine is the most common form of polysubstance abuse. Epidemiological studies indicate that more than 80% of individuals diagnosed with AUD concurrently use nicotine. The prevalence of alcohol and nicotine comorbidity may stem from interconnected mechanisms underlying these disorders. A better understanding of how these drugs interact and the biological basis behind the high comorbidity rates could generate key targets for the development of more effective treatments for AUD and nicotine dependence. The following experiments utilized four similar overall groups consisting of vehicle, ethanol (EtOH), nicotine (NIC), and EtOH+NIC. Chapter Two investigated the efficacy of naltrexone and varenicline, the pharmacological ‘gold standards’ for treating AUD and nicotine dependence, on voluntary drug intake by rats selectively bred for high EtOH drinking. The results indicated that the standard treatments for AUD and nicotine dependence were effective at reducing consumption of the targeted reinforcer but neither reduced EtOH+NIC co-use/abuse. Chapter Three examined the effects of peri-adolescent EtOH drinking on the ability of NIC infused into the posterior ventral tegmental area (pVTA) to stimulate dopamine release within the nucleus accumbens (NAc) shell during adulthood. The results suggest a cross-sensitization to NIC produced by peri-adolescent EtOH consumption demonstrated by a leftward and upward shift in the dose response curve. Chapter Four investigated the effects of intra-pVTA infusions on NAc shell neurochemistry, EtOH reward within the NAc shell, and the role of brain-derived neurotrophic factor (BDNF) on EtOH reward within that region. The data indicated that only EtOH+NIC significantly increased glutamate, dopamine, and BDNF in the NAc shell. Repeated pretreatment with EtOH+NIC also enhanced EtOH reward in the NAc shell and BDNF infusions were sufficient to recapitulate these findings. Collectively, the data indicate that concurrent exposure to EtOH and NIC results in unique neuroadaptations that promote future drug use. The failure to develop effective pharmacotherapeutics for AUD or nicotine dependence could be associated with examining potential targets in models that fail to reflect the impact of polydrug exposure. / 2020-04-03

Projection neurons of nucleus accumbens (NAC) of the rat were identified by either antidromic activation from stimulation of midbrain ventral tegmental area-substantia nigra (VTA-SN) regions, or by tracing axons of intracellularly labeled NAC neurons into the ventral pallidum. The morphology of these NAC projection neurons were determined to be medium spiny neurons similar to those identified in the caudate-putamen.

Thesis advisor: Michael A. McDannald / The ability to appropriately respond to threats is critical for survival. Disruptions in the neural circuits underlying threat responding are studied in animal models and have clinical implications for anxiety disorders in humans. Pavlovian fear conditioning has been extensively used to study the behavioral and neural basis of defensive systems for threat in animals. In a typical procedure, a cue is paired with foot shock, and subsequent cue presentation elicits freezing, a behavior linked to predator detection. Studies have since shown a fear conditioned cue can elicit locomotion, a behavior that - in addition to jumping, and rearing - is linked to imminent or occurring predation. Yet, the full neural circuit for conditioned, activity-promoting behaviors (e.g. locomotion, jumping, and rearing) remains unclear. The overarching goal of this dissertation is to demonstrate that a fear conditioned cue elicits a variety of defensive behaviors and to probe the neural circuit responsible for the expression of such activity-promoting defensive behaviors. To address the lack of research on activity-promoting defensive behaviors, I conducted experiments to observe multiple behaviors during fear discrimination over a baseline of reward seeking and constructed temporal ethograms of behavior. To improve efficiency in behavior scoring for future projects, I devised and trained a machine learning pipeline using convolutional neural networks. To aid in the understanding of the full neural circuit for activity-promoting defensive behaviors, I investigated the role of dopaminergic neurons of the ventral tegmental area in the expression of the defensive behaviors we observed during fear discrimination. Ultimately, the findings in this dissertation contribute to our general understanding of fear behavior in animals and may inform therapeutic strategies for anxiety disorders. / Thesis (PhD) — Boston College, 2024. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Psychology and Neuroscience.

Thesis advisor: Michael A. McDannald / The ability to appropriately respond to threats is critical for survival. Disruptions in the neural circuits underlying threat responding are studied in animal models and have clinical implications for anxiety disorders in humans. Pavlovian fear conditioning has been extensively used to study the behavioral and neural basis of defensive systems for threat in animals. In a typical procedure, a cue is paired with foot shock, and subsequent cue presentation elicits freezing, a behavior linked to predator detection. Studies have since shown a fear conditioned cue can elicit locomotion, a behavior that - in addition to jumping, and rearing - is linked to imminent or occurring predation. Yet, the full neural circuit for conditioned, activity-promoting behaviors (e.g. locomotion, jumping, and rearing) remains unclear. The overarching goal of this dissertation is to demonstrate that a fear conditioned cue elicits a variety of defensive behaviors and to probe the neural circuit responsible for the expression of such activity-promoting defensive behaviors. To address the lack of research on activity-promoting defensive behaviors, I conducted experiments to observe multiple behaviors during fear discrimination over a baseline of reward seeking and constructed temporal ethograms of behavior. To improve efficiency in behavior scoring for future projects, I devised and trained a machine learning pipeline using convolutional neural networks. To aid in the understanding of the full neural circuit for activity-promoting defensive behaviors, I investigated the role of dopaminergic neurons of the ventral tegmental area in the expression of the defensive behaviors we observed during fear discrimination. Ultimately, the findings in this dissertation contribute to our general understanding of fear behavior in animals and may inform therapeutic strategies for anxiety disorders. / Thesis (PhD) — Boston College, 2024. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Psychology and Neuroscience.

Maternal behaviours are those that increase offspring survival. Estrogens affect maternal behaviour by activating Estrogen Receptors (ER) in the brain. Maternal brain plasticity was explored by characterizing the effects of exposure to a mixture of environmental pollutants on number of ERs. Following exposure to the toxicants during pregnancy and lactation, brains of female rats were collected, sectioned at 30 μm and immunohistochemistry for ERα performed. Immuno-positive cells in the mPOA, VTA and NAc were counted. A two way ANOVA revealed no main effect of Treatment on the number of immunopositive cells for all three brain regions. However, a significant difference between the High and Low Doses with the high dose reducing the number of ERα+ cells in the mPOA and VTA. Our work showcases the importance of studying the effects of multiple chemical co-exposures on the mother's brain, as maternal brain changes impact maternal behaviour consequently affecting offspring neurodevelopment.

The involvement of dopamine (DA) in the emotional and psychiatric disturbances associated with schizophrenia and psychomotor stimulant abuse is well known; however, the mechanism by which DA mediates fear expression and anxiety is not well defined. Accordingly, the objective of the present thesis was to determine the fear-motivational functions of DA neurons in the ventral tegmental area (VTA) and to examine the role of DA in fear extinction using the potentiated startle paradigm. In Experiment 1, it was observed that electrical stimulation of the VTA produced a pronounced increase in the amplitude of the acoustic startle reflex. In subsequent experiments fear-potentiated startle was assessed following axon-sparing N-methyl-D-aspartic acid (NMDA) lesions of the VTA and after bilateral intra-VTA infusion of the DA D_2/3 receptor agonist quinpirole (Experiments 2-4). The NMDA lesions resulted in substantial cell loss in the medial ventral tegmentum and blocked fear-potentiated startle. Similarly, inhibition of DA neuronal activity associated with locally-administered quinpirole suppressed the expression of the conditioned fear-induced increase in startle amplitudes. The quinpirole results implicate DA neuronal functioning in fear motivation. To explore further the involvement of DA in aversive emotional behavior, pharmacological experiments were conducted in which the effects of peripherally-administered DA agonist drugs on fear extinction were assessed. Subjects in Experiment 5 received an acute injection of either cocaine hydrochloride (40.0 mg/kg), d-amphetamine sulphate (5.0 mg/kg), the D_2/3 agonist quinpirole hydrochloride (5.0 mg/kg), or the D₁-type agonist SKF 38393 (5.0 mg/kg) during a single extinction session following fear acquisition. Animals treated with cocaine, d-amphetamine, and SKF 38393 exhibited fear-potentiated startle, whereas quinpirole treatment failed to alter fear extinction to the nonreinforced conditioned stimulus (CS). Also, it was revealed using a within-subjects design in Experiment 6 that cocaine administration reinstated fear-potentiated startle following extinction. Taken together, the results of the present experiments suggests fundamental role for DA and DA D₁ receptors in fear expression. It was proposed that VTA DA neurons gate levels of aversive emotional arousal within the amygdala-based fear system.

The mesolimbic dopamine system, including dopaminergic projections from the ventral tegmental area (VTA) to nucleus accumbens (NAc), is critically involved in the development of addiction to many drugs of abuse, including cocaine (CA). Although there is an attractive hypothesis that the modifications of mesolimbic reward circuit following repeated drug exposure are responsible for cocaine-addicted causes behaviors change, however, our understanding in the underlying molecular mechanisms at the neural circuit level is still in its infancy. It has been suggested PKMzeta, a constitutively active atypical isoform of PKC, plays a critical role in spatial memory formation and long-term synaptic potentiation in hippocampus. To define the relationship among PKMzeta, CA-induced synaptic long-term potentiation and CA addiction, we examined the regulation of PKMzeta after CA administration in Sprague-Dawley rat. We found single CA injection elicits an increase in PKMzeta protein expression in the VTA region. The increase was first observed 10 min after CA administration and lasted for 7 days, the longest sampling time point of our experimental design. The PKMzeta protein expression can also be induced in 10 minutes while incubating the acute isolated brain slice with CA, the expression within 1 hr can be eliminated at the present of Chelerythrine (PKC inhibitor) and ZIP (PKMzeta inhibitor) suggests a positive feedback loop. The PKMzeta mRNA expression can be induced within 1 hr, and Actinomycin d (transcription inhibitor) had no effect on the PKMzeta protein expression indicating CA increases PKM£a translation from preexisting PKM£a mRNA. Furthermore,real time PCR-based analysis showed resembling increase profile ofPKM£a mRNA after single CA injection, suggesting a co-upregulation of transcription and translation of PKM£a after CA administration in VTA. Eticlopride (dopamine receptor D2-subtype antagonist) ¡BSCH-23390(dopamine receptor D1-subtype antagonist)¡BH-89 (PKA inhibitor)¡B Wortmannin (PI3K inhibitor)¡BPD98059 (MEK1 inhibitor) decreasedcocaine-induced PKM£a expression within 1 hr in VTA. On the contrary, KN-62 (CaMK II inhibitor) has no obvious effect on PKM£a expression. CA challenge not only induces the PKM£a expression in the VTA region but also in the NAc and hippocampus region. The CA-induced PKM£a expression is more obvious in elder group (>45 days in age) than younger group (18~30 days in age), similar results also showed in the locomotor activity assay. Prenatal CA exposure decreased the postnatal CA-induced PKM£a expression and the locomotor sensitivity in younger group. Overall, results from our current experiments have raised the possibility of PKM£a involvement in CA addiction. How CA regulates PKM£a expression and the context dependence between PKM£a and CA-induced behavior change and synaptic long-term potentiation remains further elucidation.