<p>Finding and consuming food and water are among the most critical functions for an animal's survival. Food seeking (e.g., exploration and approach) and consummatory (e.g., licking, chewing, swallowing) behaviors are usually highly controlled, resulting in stable food intake, body mass, and fat stores in humans and laboratory animals. These variables are thought to be governed by homeostatic control systems that closely regulate many aspects of feeding behavior. However, the homeostatic mechanisms underlying these processes are often disrupted in humans, resulting in either hyperphagia or hypophagia. Despite many decades of investigations into the regulatory circuits of animals and humans, the neural circuits that underlie voluntary feeding are unclear. There have been considerable advances into understanding how the brain is able to broadly regulate food consumption (e.g., the role of circulating hormones on food intake and body weight). As much work has focused on hypothalamic mechanisms, relatively little is known about how other neural systems contribute to specific aspects of food seeking and consumption. </p><p> The basal ganglia have been implicated in many aspects of motivated behavior including appetitive and consummatory processes. However, the precise role that basal ganglia pathways play in these motivated behaviors remain largely unknown. One reason for this is that the basal ganglia are functionally and anatomically heterogeneous, with distinct functional circuit elements being embedded within overlapping tissue. Until recently, tools permitting identification and manipulation of molecularly defined neuron populations were unavailable. </p><p> The following experiments were designed to assess the role of the basal ganglia in regulating appetitive and consummatory behavior in mice. The first experiment (Chapter 2) examines the relationship between neural activity in the substantia nigra¬, a¬ major output nucleus of the basal ganglia, and an animal's motivational state. Both dopaminergic and GABAergic neurons show bursts of action potentials in response to a cue that predicts a food reward in hungry mice. The magnitude of this burst response is bidirectionally modulated by the animal's motivational state. When mice are sated prior to testing, or when no pellets can be consumed, both motivational state and bidirectional modulation of the cue response are unchanging. </p><p> The second set of experiments (Chapter 3 and 4) utilizes a mouse model of hyperdopaminergia: Dopamine transporter knockout mice. These mice have persistently elevated synaptic dopamine. Consistent with a role of dopamine in motivation, hyperdopaminergic mice exhibit enhanced food seeking behavior that is dissociable from general hyperactivity. Lentiviral restoration of the dopamine transporter into either the dorsolateral striatum or the nucleus accumbens, but not the dorsomedial striatum, is sufficient to selectively reduce excessive food seeking. The dopamine transporter knockout model of hyperdopaminergia was then used to test the role of dopamine in consummatory processes, specifically, licking for sucrose solution. Hyperdopaminergic mice have higher rates of licking, which was due to increased perseveration of licking in a bout. By contrast, they have increased individual lick durations, and reduced inter-lick-intervals. During extinction, both knockout and control mice transiently increase variability in lick pattern generation while reducing licking rate. Yet they show very different behavioral patterns. Control mice gradually increase lick duration as well as variability in extinction. By contrast, dopamine transporter knockout mice exhibited more immediate (within 10 licks) adjustments--an immediate increase in lick duration variability, as well as more rapid extinction. These results suggest that the level of dopamine can modulate the persistence and pattern generation of a highly stereotyped consummatory behavior like licking, as well as new learning in response to changes in environmental feedback. </p><p> The final set of experiments was designed to test the relationship between consummatory behavior and the activity of GABAergic basal ganglia output neurons projecting from the substantia nigra pars reticulata to the superior colliculus, an area that has been implicated in regulating orofacial behavior. Electrophysiological recording from mice during voluntary drinking showed that activity of GABAergic output neurons of the substantia nigra pars reticulata reflect the microstructure of consummatory licking. These neurons exhibit oscillatory bursts of activity, which are usually in phase with the lick cycle, peaking near the time of tongue protrusion. Dopaminergic neurons, in contrast, did not reflect lick microstructure, but instead signaled the boundaries of a bout of licking. Neurons located in the lateral part of the superior colliculus, a region that receives direct input from GABAergic projection neurons in the substantia nigra pars reticulata, also reflected the microstructure of licking with rhythmic oscillations. These neurons, however, showed a generally opposing pattern of activity relative to the substantia nigra neurons, pausing their firing when the tongue is extended. To test whether perturbation of the nigrotectal pathway could influence licking behavior, channelrhodopsin-2 was selectively expressed in GABAergic neurons of the substantia nigra and the axon terminals within the superior colliculus were targeted with optic fibers. Activation of nigrotectal neurons disrupted licking in a frequency-dependent manner. Using optrode recordings, I demonstrate that nigrotectal activation inhibits neurons in the superior colliculus to disrupt the pattern of licking. </p><p> Taken together, these results demonstrate that the basal ganglia are involved in both appetitive and consummatory behaviors. The present data argue for a role of striatonigral dopamine in regulating general appetitive responding: persistence of food-seeking. Nigraltectal GABA neurons appear to be critical for consummatory orofacial motor output.</p> / Dissertation

There have been few studies investigating the eye movement behavior of Parkinson’s disease patients during fixation. This study objectively measured the eye movements of 36 patients with Parkinson’s disease, and 20 age matched controls. Stimuli consisted of ten standardized text passages first organized by Miller and Coleman. In addition, subjects followed a randomly displaced step jump target motion. Pendular nystagmus was found in all Parkinson’s subjects, with an average frequency of 7.44 Hz. Saccadic peak velocity and duration along the main sequence were not statistically different from controls. A slower rate of reading was also noted in the Parkinson’s group in terms of characters per minute, but with no more regressions than normal. Rate of square wave jerks was also found to be normal. This suggests that the hallmark feature of eye movements in Parkinson’s disease is a pendular nystagmus during fixation, and all saccadic activity to be normal.

The basal ganglia are a collection of sub-cortical nuclei involved in the execution of a range of motor and cognitive behaviours. The striatum is the input nucleus of the basal ganglia, receiving major excitatory innervation from the cerebral cortex and intralaminar thalamic nuclei. The main target of these two pathways are the principal striatal neurons, the medium-sized spiny neurons (MSNs), which are subdivided based on their axonal targets and the expression of molecular markers. Direct pathway neurons project to the output nuclei of the basal ganglia and express the D, dopamine receptor subtype, whereas indirect pathway MSNs project to the output nuclei via the globus pallidus, and express the D2 receptor. The striatum also contains interneurons that are essential in processing information within striatum; the cholinergic interneuron is of particular interest due to its role in reward-related behaviour. The aim of this study was to examine the cortical and thalamic innervation of subtypes of striatal neurons. To examine whether the cortical or thalamic afferents selectively innervate direct or indirect pathway neurons, transgenic mice expressing GFP under either the D, or D2 receptor promoter were used. Striatal sections from these mice were immunostained to reveal the GFP and selective markers of the cortical and thalamic afferents, VGluTI and VGluT2, respectively. A quantitative electron microscopic examination ofsynaptic connectivity was carried out. The results indicate that there is no selectivity of either the cortical or thalamic pathway for D, or D2 expressing MSNs. Thus both direct and indirect pathway MSNs are involved in the processing of both cortical and thalamic information The cortical and thalamic innervation to cholinergic interneurons was also examined. Stimulation of cortex and thalamus in vivo in anaesthetised rats resulted in short-latency excitatory responses in identified cholinergic interneurons, indicative of monosynaptic connections. After recording, cholinergic interneurons were filled with neurobiotin. The synaptic innervation from cortex and thalamus was then examined in two individual, electrophysiologically characterised, and neurochemically identified cholinergic interneurons. One neuron received input from both cortex and thalamus, whereas the other neuron received input from the thalamus only. These results provide anatomical and physiological data illustrating how the excitatory inputs to striatum innervate cholinergic interneurons.

Glutamic Acid Decarboxylase (GAD) is a rate-limiting enzyme responsible for synthesis of the inhibitory neurotransmitter GABA. Dopaminergic denervation in rodents by unilateral injections of 6-OHDA or MPTP causes an increase in Gad67 mRNA in the striatum, which is further exacerbated by administration of L-Dopa (Horvath et al., 2011; Katz et al., 2005 Bacci et al., 2002). Denervation of nigrostriatal neurons is the key pathological hallmark of Parkinson's disease, which results in hypokinetic movement and rigidity. Medium spiny projection neurons of the striatum comprise 95% of the neuronal population and utilize Gad67 (encoded by the Gad1 gene) for the synthesis of basal levels of GABA. The contribution of Gad67 to GABA signaling in medium spiny projection neurons in the striatum has not been thoroughly understood in normal or Parkinsonian states. Mice with a deletion in Gad67 in Gpr88 expressing neurons were generated by crossing mice with a floxed exon 2 of Gad1 with mice expressing Cre recombinase under the control of the Gpr88 promoter. The aim of this study was first, to characterize mice with a deletion in striatal Gad67 by immunohistochmical, electriophysiological and behavioral examination to determine whether Gad67 expression contributes to sensorimotor and learning tasks. And next, to investigate whether a downregulation in striatal Gad67 would decrease dyskinesia and affect the impaired motor symptoms following dopaminergic denervation with a unilateral 6-OHDA lesion and subsequent treatment with L-Dopa. In this study, neuronal Gpr88 expression was indicated by GFP reporter expression, which resulted from Cre-mediated excision of exon 2 of the Gad1 gene. Gpr88 expression was confirmed in the striatum, olfactory tubercle, cortex and brain stem. Furthermore, Gpr88 was confined to striatonigral and striatopallidal MSNs in the striatum. Additionally, Cre-mediated GFP reporter expression indicated that Gpr88 expression occurs throughout various brain regions, including the motor and visual areas of the cortex, amygdala, hippocampus and cerebellum during development. The developmental expression of Gpr88 seems to be a highly regulated process that occurs throughout the brain. In the conditional knockout mouse, deleting striatal Gad67 resulted in an upregualtion of Gad67 in the globus pallidus and downregulation in the substantia nigra. The changes in Gad67 expression indicate the effects of inactivating GABAergic signaling in striatonigral and striatopallidal MSNs in the direct and indirect pathways. Mice with a deletion in striatal Gad67 demonstrated compromised performance in spatial learning in the Morris water maze, suggesting that GABAergic striatal signaling in the direct and indirect pathways accounts for cue-based learning and spatial memory. However, inactivation of GABAergic signaling in striatonigral and striatopallidal MSNs does not account for motor deficits such as bradykinesia, akinesia or hypokinesia in intact mice; instead it perpetuates hyperkinetic motor activity. In the second experiment of this study, dopaminergic denervation by a unilateral 6-OHDA lesion induced bradykinesia and hypokinetic motor behavior, as demonstrated by impaired performance in the rota-rod and pole test. Additionally, L-Dopa administration to 6-OHDA lesioned mice evoked abnormal involuntary movements (AIMs) to the same degree in all dyskinetic mice. A deletion in striatal Gad67 did not decrease symptoms of dyskinesia, nor cause a lessening of motor impairment caused by dopaminergic denervation. Complete inactivation of the indirect pathway is believed to limit the inhibition of unwanted actions and may perpetuate dyskinesia, even when striatonigral MSNs of the direct pathway are inactive.

Doctor of Philosophy (PhD) / The investigation into the relationship between neural plasticity in the rat forebrain associated with opiate-induced behaviours yielded two major results. The major finding of the functional neuroanatomy of acute morphine dependence was that doses of naloxone that induced hyperalgesia following a brief exposure to morphine, in previously drug-naïve rats, caused a specific induction of the inducible transcription factor (itf) proteins c-Fos and zif268 in the extended amygdala. Moreover, doses of naloxone that caused a simple reversal in morphine analgesia failed to induce itf proteins in these same brain regions. This increase in itf proteins was specific to regions of the extended amygdala that receive and process nociceptive information relayed via the spino-parabrachio-amygdaloid pathway and was not observed in other regions that are involved in supraspinal pain modulation such as the rostral ventromedial medulla and the periaqueductal gray. We also found that acute morphine increased c-Fos protein in the basolateral amygdala and the major output nucleus of the central amygdala the medial subdivision. Acute morphine also up-regulated c-Fos protein in striatal, midbrain, and hypothalamic nuclei. A unique finding of the current study was that prolonged exposure to morphine was required to induce c-Fos in these brain regions, as the subsequent administration of naloxone 30-minutes after morphine either reversed or blocked this induction. These results indicate the potential role of the amygdala in analgesia following systemic morphine and in pain facilitation during acute morphine abstinence. Investigation into the neurons and circuitry that undergo long-term neuroplasticity in response to repeated morphine exposure revealed that network-level changes in the distribution of Fos protein in the nucleus accumbens and striatum predicted both tolerance to catalepsy and psychomotor sensitisation. Drug-naïve rats became profoundly cataleptic following morphine, an effect that rats with a drug-history became tolerant. Rats with a history of morphine exposure showed an increase in stereotyped behaviours compared to drug-naïve rats. The major finding of this study was that a shift in the induction of c-Fos protein from a matrix predominance in drug-naïve rats toward a patch predominance in drug-sensitised rats in the accumbens core predicted both tolerance to catalepsy and sensitisation of oral stereotyped behaviours. Acute injection of morphine in a drug-naïve rat induced catalepsy and increased the number of c-Fos-positive neurons in matrix striatopallidal projection neurons of the rostral accumbens core. An increase in activity of striatopallidal projection neurons, which give rise to the indirect pathway, could potentially increase inhibitory drive to the pedunculopontine nucleus (PPN). The PPN, long known as a site of termination for basal ganglia output, is thought to direct the outflow of incentive-motivational and sensorimotor information from the nucleus accumbens to pons, medullary, and spinal cord nuclei translating the incentive impact of the stimuli into appropriate motor, autonomic and emotive responses (Winn et al., 1997). Inhibition of this nucleus would cause the animal to be unable to initiate a movement and in effect lock up, which is precisely what cataleptic postures look like. In contrast c-Fos-positive neurons were decreased in the rostral matrix and increased in patch striatonigral projection neurons along the rostro-caudal extent of the accumbens core when morphine was administered to drug-sensitised rats. Striatonigral neurons located in the patch give rise to the direct pathway innervating the dopaminergic neurons in both substantia pars compacta and the dopamine rich islands in the substantia nigra pars reticulata (Berendse et al., 1992; Gerfen, 1992; Furuta et al., 2002). Activity of this pathway is thought to be involved in the initiation of movement (Gerfen, 1992; Gerfen and Wilson, 1996), however, when this pathway is overstimulated as is the case when morphine is injected in drug-sensitised rats this could potentially cause increased activity of PPN neurons leading to repetitive psychomotor behaviours or stereotypy. This data adds to the growing body of evidence that suggests that long-term neuroadaptations induced by drugs of abuse including morphine that lead to behavioural sensitisation involves the circuitry that includes the nucleus accumbens.

Parkinson’s disease (PD) and dystonia are movement disorders related to dysfunctions of basal ganglia (BG). Deep brain stimulation (DBS) of the subthalamic nucleus (STN) and internal globus pallidus (GPi) are treatments for PD and dystonia. Previous research indicated that abnormally elevated oscillatory activities at the theta (3-10 Hz) beta frequency bands (11-30 Hz) may be related to parkinsonian and dystonic motor symptoms but their precise roles are not well understood. Recently, DBS of the pedunculopontine nucleus region (PPNR) has been used to treat PD patients with postural and gait dysfunctions, but movement-related PPNR activities had not been explored. We aimed to investigate movement-related local field potentials (LFP) recorded from the BG and PPNR in PD and dystonia patients. We recorded STN LFP from PD patients and subsequently applied the intrinsic STN theta, beta, and gamma (31-100 Hz) frequencies through DBS to study their effects on PD motor signs. We also recorded movement-related PPNR LFP in PD patients and movement-related GPi activities in patients with primary dystonia. Finally, we simultaneously recorded movement-related activities from the GPi and the motor thalamus in a patient with secondary dystonia. We found that DBS at the dopamine-dependent and movement-related intrinsic STN gamma frequencies, were as effective as traditionally used high frequencies (130-185 Hz) in reducing PD motor signs, but theta and beta frequencies did not worsen motor symptoms. Voluntary movements modulated two discrete movement-related frequencies in the theta and beta bands in the PPNR and these two frequencies interacted with the sensorimotor and frontal cortices during movements. We showed that voluntary movements modulated beta and gamma frequencies in the GPi. A resting ~5-18 Hz coherence between the GPi bilaterally was attenuated during movements in patients, which may be related to dystonia because this 5-18Hz coherence was also present between the GPi and motor thalamus in the patient with secondary dystonia. Our findings indicated that intrinsic STN gamma frequency oscillations were likely prokinetic rhythms but theta and beta frequencies may not contribute to PD motor symptoms. Voluntary movements modulated theta and beta frequencies in the PPNR, which may explain why PPNR DBS uses lower frequencies than those of the BG. The 5-18 Hz oscillatory activities in the BG-thalamic circuit may be a feature of dystonia.

Parkinson’s disease (PD) and dystonia are movement disorders related to dysfunctions of basal ganglia (BG). Deep brain stimulation (DBS) of the subthalamic nucleus (STN) and internal globus pallidus (GPi) are treatments for PD and dystonia. Previous research indicated that abnormally elevated oscillatory activities at the theta (3-10 Hz) beta frequency bands (11-30 Hz) may be related to parkinsonian and dystonic motor symptoms but their precise roles are not well understood. Recently, DBS of the pedunculopontine nucleus region (PPNR) has been used to treat PD patients with postural and gait dysfunctions, but movement-related PPNR activities had not been explored. We aimed to investigate movement-related local field potentials (LFP) recorded from the BG and PPNR in PD and dystonia patients. We recorded STN LFP from PD patients and subsequently applied the intrinsic STN theta, beta, and gamma (31-100 Hz) frequencies through DBS to study their effects on PD motor signs. We also recorded movement-related PPNR LFP in PD patients and movement-related GPi activities in patients with primary dystonia. Finally, we simultaneously recorded movement-related activities from the GPi and the motor thalamus in a patient with secondary dystonia. We found that DBS at the dopamine-dependent and movement-related intrinsic STN gamma frequencies, were as effective as traditionally used high frequencies (130-185 Hz) in reducing PD motor signs, but theta and beta frequencies did not worsen motor symptoms. Voluntary movements modulated two discrete movement-related frequencies in the theta and beta bands in the PPNR and these two frequencies interacted with the sensorimotor and frontal cortices during movements. We showed that voluntary movements modulated beta and gamma frequencies in the GPi. A resting ~5-18 Hz coherence between the GPi bilaterally was attenuated during movements in patients, which may be related to dystonia because this 5-18Hz coherence was also present between the GPi and motor thalamus in the patient with secondary dystonia. Our findings indicated that intrinsic STN gamma frequency oscillations were likely prokinetic rhythms but theta and beta frequencies may not contribute to PD motor symptoms. Voluntary movements modulated theta and beta frequencies in the PPNR, which may explain why PPNR DBS uses lower frequencies than those of the BG. The 5-18 Hz oscillatory activities in the BG-thalamic circuit may be a feature of dystonia.

The neuropathology of Tourette Syndrome (TS) is poorly characterized. This thesis provides the first quantitative stereologic immunohistochemical study of the basal ganglia in TS. TS is a childhood neuropsychiatric disorder characterized by motor and vocal tics. Previous imaging studies found alterations in caudate (Cd) and putamen (Pt) volumes. To investigate possible alterations in cell populations, postmortem basal ganglia tissue from individuals with TS and normal controls (NC) was analyzed using unbiased stereological techniques. A markedly higher (>160% of control) total neuron number and density was found in the internal segment of the globus pallidus (GPi) of TS (p<0.025). An increased number (>220% of control) and proportion of these GPi neurons were positive for the calcium-binding protein parvalbumin (PV) in the tissue from TS subjects (p<0.025). In contrast, a lower number (<60% of control) of neurons was observed in the external segment (GPe) (p<0.025). In addition, there was a lower density of PV-positive interneurons in both Cd (<50% of control) and Pt (<65% of control) (p>0.025). The imbalance in striatal and GPi inhibitory neuron distribution suggests that the functional dynamics of cortico-striato-thalamic circuitry are fundamentally altered in severe, persistent TS.

Previous studies have indicated that persons with autism spectrum disorder have distinct cerebella, striatum, and an impaired ability to anticipate implicit learning sequences; also, previous research indicates anatomic connections among these regions. Investigating distinctions in connectivity and impairments in the ability to anticipate implicit sequences linked to ASD would help clarify some of the core deficits associated with the disorder. This dissertation sought to explore differences in functional connectivity among the cerebellum, thalamus, and striatum. This dissertation also sought to determine if an impaired ability to anticipate implicit sequences is associated with ASD. Twelve ASD participants and 11 control participants were scanned using an MRI while engaged in a modified serial reaction task. The findings indicate that the cerebellum and the striatum are functionally connected and the thalamus mediates this connection. The results indicate that ASD participants have stronger connections than the control, and ASD participants demonstrated some impairments in learning. However, there was not enough evidence to link ASD to an impaired ability to anticipate implicit sequences. This dissertation recommends that future studies consider the roles that these distinct connections play in symptoms of ASD. / text

Speech, writing, and tool-use are all prime examples of everyday learned motor skills that together with dance, music, and sports performance represent the full glory of human cultural expression afforded by dexterous digits, limbs, and bodies. Learning to subconsciously move parts of our body is an underappreciated function of the brain. This dissertation aims to illuminate this process through a series of studies using the zebra finch as a model system. It addresses two major questions. First, what level of modularity is involved in motor learning? Specifically, can we decompose complex learned skills, such as the zebra finch song, into their distinct components such as spectral and temporal aspects? And if so, how independent are these various aspects of motor skill learning and execution from one another? Second, to what degree are the basal ganglia, essential and phylogenetically conserved parts of the motor system, involved in different aspects of motor skill learning? In Chapter 1 of this dissertation, I describe the complex learned vocalization of the zebra finch as a model for understanding these questions, highlighting the use of a rapid and well-controlled learning paradigm termed conditional auditory feedback (CAF). In Chapter 2, using CAF, focal lesions and recordings, I test the role of a songbird basal ganglia pathway in distinct aspects of motor learning. I find that the basal ganglia pathway is necessary for learning spectral but not temporal aspects of the song whereas a pre-motor cortical area encodes changes in the temporal but not spectral structure, suggesting a modularity in birdsong motor learning. In Chapter 3, I infer the mechanisms underlying the basal ganglia-independent temporal learning. Further CAF experiments demonstrate that the nervous system is capable of flexibly modifying temporal structure in one part of the song without affecting the timing in the rest of the song, uncovering yet another level of modularity in encoding song structure. Chapters 2 and 3 provide evidence for the modularity in learning the mean spectral and temporal structure. However, motor performance is also characterized by its trial-to-trial variability around the mean. In Chapter 4, I describe CAF experiments to interrogate the neural basis underlying changes in variability around a mean. I show that spectral variability can be modulated in a very specific manner and independently in different parts of the song. I show that this temporally-specific modulation of variability is mediated by the basal ganglia. Overall, the dissertation suggests that complex motor skills emerge from basic functional modules that independently learn, modulate, and control distinct aspects of learned motor output.