Thesis (Ph. D.)--Ohio State University, 2007. / Title from first page of PDF file. Includes bibliographical references (p. 144-147).

Proefschrift Universiteit Maastricht. / Met bibliogr., lit. opg. - Met samenvatting in het Nederlands.

<p>Animals must continuously move through the environment in pursuit of the goals required to maintain homeostasis. In vertebrates, this is accomplished through an ever-changing pattern of muscle contraction in a multipurpose body, and coordinated by a hierarchy of neural circuits acting in parallel. At the lower levels of this hierarchy, spinal circuits control muscle force and length. One level above that, brainstem, midbrain and cortical circuits control various aspects of body configuration as well as a number of self-contained motor functions including locomotion and orientation. A still-higher level of organization is controlled by the basal ganglia, a set of subcortical nuclei that appear to be responsible for continuously orchestrating the extent and direction of various motor programs and body configurations for the sake of controlling a still higher level of perceptual variable, such as proximity to food. In this way, the basal ganglia orchestrate the performance of motor functions to achieve a single goal in the same way that a conductor orchestrates the performance of musicians in a symphony to achieve a single song. </p><p>Despite the continuous and graded nature of animal behavior, researchers have traditionally studied the basal ganglia in the context of highly controlled experimental tasks or neglected to record continuous measures of behavioral outputs. To address this gap, the following experiments were designed investigate role of the basal ganglia in continuously modulating unconstrained goal directed movements. In the first set of experiments (chapter 2), mice stood on a small covered perch which was continuously tipped left and right along the roll plane while neural activity was recorded wirelessly. During each recording session, mice were exposed to slow and fast speeds of postural disturbance. Pressure pads were mounted in the left and right floor of the perch to monitor mouse movement. In both putative dopamine and GABA neurons, we found two basic patterns of neural activity; one class of cell increased firing with tip to the left and decreased with tip to the right while the other class decreased firing with tip to the left and increased with tip to right. This correlation between neural firing rate and instantaneous postural disturbance is continuous and very high. The correlation is seen for both slow and fast disturbances. The majority of cells recorded fell into one of these two categories. Pressure pad readout, as expected, revealed paw forces on the left pad to increase with tilt to the left and decrease with tilt to the right while the opposite pattern was observed on the right pad. These results show continuous and graded modulation of activity in the substantia nigra during performance of an ongoing motor task and suggest that BG outputs, rather than monolithically disinhibiting brainstem motor structures, instead coordinate behavior by continuously specifying desired states of lower systems. </p><p>In the second set of experiments (chapter 3), we employed continuous motion tracking of the head in parallel with neural recording from the substantia nigra pars reticulata during a simple goal-directed task. In this study, mice were water deprived and then positioned on a perch equipped with a movable drinking spout. During each session, mice performed a simple reward-guided task in which sucrose solution was delivered in small quantities after the presentation a cue. The purpose of this task was to elicit voluntary head movements and to investigate the relationship between these continuous movements and the activity of GABA output neurons. A typical reward-directed behavior involved the movement of the whole head and body to collect the sucrose solution following its delivery. However, movements during each individual trial were unique. For all movements, the majority of GABA cells were found to either positively or negatively correlate with either X or Y axis head position vector components. These correlations were very high, and not due to averaging artifacts as trial-by-trial correlation between movement and neural activity can be clearly observed. These correlations were also independent of the presence of a reward. These data show for the first time a continuous and quantitative relationship between basal ganglia output and body posture. It is hypothesized that these signals represent reference signals sent to downstream postural and orientation controllers. In this case a baseline level of GABA activity would represent neutral reference position, and changes in activity above and below this level represent increased or decreased reference positions. </p><p>In the third set of experiments (chapter 4), we recorded from dopamine neurons in the substantia nigra pars compacta during the same task as in chapter 3. The purpose of this task was to investigate the correlation between dopamine activity and movement kinematics during goal-directed behavior. Animals were found to produce movements at the onset of the cue and also at reward delivery. Dopamine-classified cells show phasic firing or pausing at the onset of each of these movements. When compared to head movement kinematics, these patterns of neural activity correlate highly with different vector components of head acceleration and velocity; up, down, left and right. Importantly, these correlations are continuous and exist throughout the entire recording session. These correlations are also independent of the presence of reward. To test the ‘causality’ of these observed patterns, we also employed optogenetics to stimulate substantia nigra dopamine neurons expressing channel rhodopsin 2 (Chr2) while head movements were recorded and quantified. We found that stimulation of ChR2-expressing animals could elicit head movement while stimulation of control animals had no effect. Combined, these data suggest that dopamine is responsible for controlling the velocity of transitions between different body postures.</p> / Dissertation

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Schizophrenia is among the most debilitating mental disorders, yet the pathophysiology remains unclear. The basal ganglia, a region of the brain involved in motor, cognitive, and sensory processes, may be involved in the pathophysiology of schizophrenia. Some, but not all, neuroimaging studies suggest abnormalities of the basal ganglia in schizophrenia. However, previous studies have examined whole basal ganglia nuclei as opposed to using a unified basal ganglia complex that incorporates anterior-posterior divisions, dorsal-ventral divisions, and gray-white matter segmentation. The hypothesis for the present study was that basal ganglia sub-regions forming functionally relevant subdivisions might be different in schizophrenia. Magnetic resonance imaging scans were acquired from 25 first-episode schizophrenia subjects and 24 healthy subjects. Using manual and automated neuroimaging techniques, total and segmented (gray-white matter) volumes were obtained for the caudate, putamen, and globus pallidus. For the striatum (caudate and putamen), total and segmented volumes were obtained for their respective sub-regions. These sub-regions were restructured into associative, limbic, and sensorimotor subdivisions. Schizophrenia subjects had 6% smaller gray matter volumes for the caudate and 8% smaller gray matter volumes for the associative striatum relative to healthy subjects. Basal ganglia function was studied by examining performance on a neuropsychological test that assesses frontostriatal functioning. For male subjects there was a significant negative correlation between volume of the associative striatum and performance on the neuropsychological test (r=-0.57, p=0.03). Smaller volumes of the associative striatum were associated with more errors on the neuropsychological test. This test was specific to the associative striatum, as another neuropsychological test did not reveal any correlation. In schizophrenia subjects, the relationship between basal ganglia volumes and motor symptoms severity was examined. For antipsychotic-naive subjects there was a significant negative correlation between volume of the motor striatum and severity of Parkinsonism (r=-0.65, p=0.03). The present study suggests that total basal ganglia nuclei volumes are not different in schizophrenia, but gray matter volumes of total basal ganglia nuclei and subdivisions forming functional units may be different in schizophrenia. Structural abnormalities involving the basal ganglia may lead to disrupted functional circuits in schizophrenia. / Medicine, Faculty of / Graduate

G proteins are alpha-beta-gamma heterotrimers in the resting state, bound to GDP and complexed with the unbound receptor. Once the receptor becomes occupied, the alpha subunit exchanges GDP for GTP, becomes activated, and dissociates from the receptor and can stimulate or inhibit many intracellular activities such as phosphorylation and channel conductance. For example, Gs and Golf alpha subunits stimulate and Gi alpha subunits inhibit adenylyl cyclase. Go alpha subunits are abundant in brain, but are of unknown function. cDNAs for the alpha subunit have been cloned. In order to examine the relative distributions of G proteins in the brain, we used in situ hybridization with radiolabelled synthetic oligonucleotide probes. By using a tyrosine hydroxylase antibody, we found that the dopaminergic neurons of the substantia nigra and the noradrenergic neurons of the locus ceruleus express mRNA for the alpha subunits for each of Gi, Go, and Gs. We noted a paucity of Gs mRNA in the striatum. This was surprising because the basal ganglia contain a dopamine-stimulated adenylyl cyclase activity which has been assumed to be transduced by Gs. Also, immunohistochemistry, immunoblotting, and cholera ADP-ribosylation indicated a very high level of Gs alpha-like protein in the striatum. In order to ascertain which specific G protein we were detecting, we made probes to a new G protein previously identified in the olfactory system. Golf is a stimulatory G protein with size and sequence characteristics similar to those of Gs. The cholera toxin ADP-ribosylation site and C-terminal region to which the antibody was made are identical. We made oligonucloetide probes to the translated and untranslated portions of Golf alpha. High levels Golf mRNA and protein were detected in the striatum and nucleus accumbens, in addition to the expected high levels in the olfactory tubercle. Northern blot studies indicated that Golf transcripts are approximately ten-fold more abundant than Gs alpha transcripts in the striatum. These data indicate that Golf in not an olfactory-specific G protein. It is also the major stimulatory G protein in the basal ganglia. The selective expression of high levels of Golf in dopamine-rich forebrain areas suggest that it may couple DI dopamine receptors to adenylyl cyclase. The role of Golf in dopaminergic neurotransmission and neuropsychiatric disease should be considered. / Medicine, Faculty of / Graduate

Animals must respond to external cues and changes in internal state by modifying their behavior. The basal ganglia are a collection of subcortical nuclei that contribute to action selection by integrating sensorimotor, limbic and reward information to control motor output. In early life, however, animals display distinct behavioral responses to risk and reward and enhanced vulnerability to neuropsychiatric disease. This arises from the postnatal maturation of brain structures such as the striatum, the main input nucleus of the basal ganglia. Here, using biochemical, electrophysiological and behavioral approaches in transgenic mice, I have explored the molecular and circuit mechanisms that control striatal maturation. In Chapter 1, I begin by reviewing the structure, physiology and function of the basal ganglia, with an emphasis on the striatum. I then describe the existing literature on the development and maturation of striatal neurons and their afferents. In Chapter 2, I review the molecular mechanisms of macroautophagy, a lysosomal degradation pathway that has recently been implicated in the regulation of neurotransmission, including its contribution to neuronal development, neurotransmitter release, and postsynaptic function. The subsequent chapters can be split into two themes. In the first, encompassing chapters 3 and 4, I characterize the postnatal maturation of striatal physiology and define circuit mechanisms that control this process. In Chapter 3, I demonstrate that dopamine (DA) neurotransmission in the striatum initiates the maturation of striatal projection neuron (SPN) intrinsic excitability. I show that DA signaling leads to the maturation of SPN excitability via increased activity of the potassium channel, Kir2. Interestingly, introduction of DA beginning in adulthood could not rescue SPN hyperexcitability while it could during the juvenile period. In Chapter 4, I characterize the maturation of cholinergic interneurons (ChIs) in the striatum and describe the biophysical mechanisms that drive increases in spontaneous activity that occur in ChIs during postnatal development. Finally, I show that the functional maturation of ChIs leads to changes in DA release during the postnatal period. The second theme includes Chapters 5 and 6, in which I explore the role of macroautophagy in striatal function and development. In chapter 5, I used biochemical approaches to show that autophagic flux is suppressed postnatally in the striatum due to increased signaling through the kinase activity of the mammalian target of rapamycin. In Chapter 6, I generated conditional knockouts of Atg7, a required macroautophagy gene, in different populations of SPNs and find that macroautophagy plays cell-type specific roles in SPN physiology. In one subtype of SPNs, macroautophagy regulates intrinsic excitability via degradation of Kir2 channels, which is the first demonstration of macroautophagic control of neuronal excitability. Finally, in Chapter 7, I conclude with a general discussion, where I highlight themes in the molecular and circuit mechanisms of striatal maturation and their implication for neurodevelopmental disease.

The striatopallidal (indirect) pathway is considered as the main modulatory locus for the basal ganglia control of motor functions. According to the classic basal ganglia model, the striatopallidal pathway inhibits motor activity mainly via its projection to globus pallidus (GPe). However, striatopallidal medium spiny neurons (MSNs) form extensive feedback and lateral inhibitory networks via their collaterals. Thus, the striatopallidal pathway may control motor activity either through its projections onto GPe or through the striatal collaterals. To further define the circuit mechanism whereby the striatopallidal pathway controls motor activity, we have developed two new optogenetic transgenic mouse lines expressing channelrhodospin-2 (ChR2) or archaerhodopsin-3 (Arch) selectively in the striatopallidal neurons under the Adora2a gene promoter. Consistent with previous optogenetic studies, we found that ChR2 activation and Arch silencing of the striatopallidal neurons in dorsolateral striatum (DLS) suppressed and increased motor activity, respectively. However, contrary to the prediction from the classical model, we found that selective activation of the striatopallidal axon projections in GPe increased locomotor activity. Thus, light stimulation of MSN cell bodies and collaterals in DLS, versus stimulation in GPe axon projections, produced opposite motor responses. This led us to reassess the function of the striatopallidal collaterals and to test the hypothesis that the profuse projections and collaterization within the striatum may contribute to striatopallidal pathway control of motor activity. We found that ChR2-mediated activation of the striatopallidal neurons in DLS induced c-Fos expression in ChR2/GFP-positive MSNs. Conversely, Arch-mediated silencing of the striatopallidal neurons induced c-Fos expression and MAPK phosphorylation in Arch/GFP-negative MSNs surrounding the Arch/GFP-positive MSNs. This c-Fos/pMAPK expression pattern in MSNs is consistent with the suppression of GABA release in GFP-positive cells, resulting in the induction of c-Fos in GFP-negative cells having collateral connections with the GFP-positive cells. Together, our findings revealed a previously unrecognized complexity and novel motor control mechanism of the striatopallidal pathway: activation of striatopallidal projections to GPe increases motor activity while activation of striatopallidal neurons and collaterals in the DLS may contribute to motor suppression. These findings call for a revisit of GPe as a potential locus for deep brain stimulation in Parkinson’s disease.

The objective of this study was to determine how neurons within the right atrial ganglionated plexus (RAGP) and posterior atrial ganglionated plexus (PAGP) interact to modulate right atrial chronotropic, dromotropic, and inotropic function, particularly with respect to their extracardiac vagal and sympathetic efferent neuronal inputs. Surgical ablation of the PAGP (PAGPx) attenuated vagally mediated bradycardia by 26%; it reduced heart rate slowing evoked by vagal stimulation superimposed on sympathetically mediated tachycardia by 36%. RAGP ablation (RAGPx) eliminated vagally mediated bradycardia, while retaining the vagally induced suppression of sympathetic-mediated tachycardia (-83%). After combined RAGPx and PAGPx, vagal stimulation still reduced sympathetic-mediated tachycardia (-47%). After RAGPx alone and after PAGPx alone, stimulation of the vagi still produced negative dromotropic effects, although these changes were attenuated compared with the intact state. Negative dromotropic responses to vagal stimulation were further attenuated after combined ablation, but parasympathetic inhibition of atrioventricular nodal conduction was still demonstrable in most animals. Finally, neither RAGPx nor PAGPx altered autonomic regulation of right atrial inotropic function. These data indicate that multiple aggregates of neurons within the intrinsic cardiac nervous system are involved in sinoatrial nodal regulation. Whereas parasympathetic efferent neurons regulating the right atrium, including the sinoatrial node, are primarily located within the RAGP, prejunctional parasympathetic-sympathetic interactions regulating right atrial function also involve neurons within the PAGP.