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Open Access Publications from the University of California

Scholarly Works (13 results)

  • Thesis
  • Peer Reviewed
UC Davis Electronic Theses and Dissertations (2023)

The cerebellum (CB) has long been considered a purely motor structure. However, studies over the last few decades have revealed vital contributions of the cerebellum to a wide array of non-motor functions including a key role in limbic processing. The CB is involved in both the experience of emotion and in controlling the appropriate autonomic, cognitive, and behavioral responses, and plays an important part in all phases of emotional memory, including acquisition, consolidation, storage and retrieval, and extinction. Cerebellar dysfunction has been associated with various neurological and neuropsychiatric disorders such as cognitive affective syndrome, schizophrenia, anxiety, and depression. To accomplish so much in both the motor and cognitive domains, the CB is thought to integrate diverse inputs and send predictions about optimal behavioral outputs to the rest of the brain. However, the pathways and mechanisms involved in this type of processing remain poorly understood. The goal of my dissertation was to investigate how the CB may coordinate limbic processing through newly discovered long-range circuits. Chapter 2 details anatomical and electrophysiological evidence for new pathways connecting the CB to the amygdala through the limbic thalamus, in particular the centromedial (CM) and parafascicular (PF) nuclei. This includes rigorous anatomical tracing as well as mechanistic analysis using ex vivo slice electrophysiology combined with fine-tuned pharmacological and optogenetic manipulations to establish evidence for synaptic connectivity. In Chapter 3, we investigated connections from the cerebellum to the nucleus accumbens (NAc) through nodes in the CM and PF thalamus and the ventral tegmental area (VTA) using anatomical tracing, in vivo electrophysiology, and circuit specific optogenetic manipulations. Finally, Chapter 4 summarizes an investigation into the functional role of the CB-PF circuit in fear memory, extinction learning, and anxiety using targeted optogenetic manipulations of projections during behavioral tasks as well as in vivo electrophysiological recordings to test connectivity with the BLA. Overall, this dissertation details work which has provided novel insights into the cerebellum’s role in the context of emotional learning, the necessity of specific pathways in non-motor behavior, and the signaling properties within the relevant circuits.

    • Thesis
    • Peer Reviewed
    UC Davis Electronic Theses and Dissertations (2023)

    Although the cerebellum is now recognized as part of a long-range brain network that serves limbic functions and motivated behavior, knowledge of cerebello-limbic connectivity is limited, and nearly nothing is known about how the cerebellum connects functionally to the nucleus accumbens (NAc), a region well-known for its role in social, reward, and motivated behaviors. In my first chapter, I report the first electrophysiological evidence that stimulation of cerebellar nuclei in mice of both sexes modulates spiking activity in both NAc core and medial shell. NAc neurons respond with fast excitation and slower, less synchronized inhibition. Fast responses would be well poised to support rapid communication of information critical to the control of motivated behavior, whereas slower responses may be suggestive of a regulatory function, such as gain control. In my second chapter I describe anatomical connections via tracing experiments to chart cerebellar nuclei-NAc pathways identified disynaptic pathways that recruit the ventral tegmental area (VTA) and intralaminar thalamus (Centromedial and Parafascicular nuclei) as intermediary, monosynaptically-connected nodes. Optogenetic activation of cerebellar axons in each of these nodes was sufficient to evoke responses, primarily excitatory, in both NAc core and medial shell. These pathways and the functional connectivity they support could underlie the role of the cerebellum in motivated behavior and further elucidate our growing understanding of the non-motor cerebellum.

      Cover page: Examination of Novel Circuits Linking the Cerebellum and Nucleus Accumbens
      • Article
      • Peer Reviewed
      UC Davis Previously Published Works (2014)
      The complex manner in which patterns of presynaptic neural activity are translated into short-term plasticity (STP) suggests the existence of multiple presynaptic calcium (Ca(2+)) sensors, which regulate the amplitude and time-course of STP and are the focus of this review. We describe two canonical Ca(2+)-binding protein domains (C2 domains and EF-hands) and define criteria that need to be met for a protein to qualify as a Ca(2+) sensor mediating STP. With these criteria in mind, we discuss various forms of STP and identify established and putative Ca(2+) sensors. We find that despite the multitude of proposed sensors, only three are well established in STP: Munc13, protein kinase C (PKC) and synaptotagmin-7. For putative sensors, we pinpoint open questions and potential pitfalls. Finally, we discuss how the molecular properties and modes of action of Ca(2+) sensors can explain their differential involvement in STP and shape net synaptic output.
        Cover page: Translating neuronal activity at the synapse: presynaptic calcium sensors in short-term plasticity
        • Article
        • Peer Reviewed
        UC Davis Previously Published Works (2014)
        Posttetanic potentiation (PTP) is a widely observed form of short-term plasticity lasting for tens of seconds after high-frequency stimulation. Here we show that although protein kinase C (PKC) mediates PTP at the calyx of Held synapse in the auditory brainstem before and after hearing onset, PTP is produced primarily by an increased probability of release (p) before hearing onset, and by an increased readily releasable pool of vesicles (RRP) thereafter. We find that these mechanistic differences, which have distinct functional consequences, reflect unexpected differential actions of closely related calcium-dependent PKC isoforms. Prior to hearing onset, when PKCγ and PKCβ are both present, PKCγ mediates PTP by increasing p and partially suppressing PKCβ actions. After hearing onset, PKCγ is absent and PKCβ produces PTP by increasing RRP. In hearing animals, virally expressed PKCγ overrides PKCβ to produce PTP by increasing p. Thus, two similar PKC isoforms mediate PTP in distinctly different ways.
          Cover page: Calcium-Dependent PKC Isoforms Have Specialized Roles in Short-Term Synaptic Plasticity
          • Article
          • Peer Reviewed
          UC Davis Previously Published Works (2016)

          Unlabelled

          Post-tetanic potentiation (PTP) is a widespread form of short-term synaptic plasticity in which a period of elevated presynaptic activation leads to synaptic enhancement that lasts tens of seconds to minutes. A leading hypothesis for the mechanism of PTP is that tetanic stimulation elevates presynaptic calcium that in turn activates calcium-dependent protein kinase C (PKC) isoforms to phosphorylate targets and enhance neurotransmitter release. Previous pharmacological studies have implicated this mechanism in PTP at hippocampal synapses, but the results are controversial. Here we combine genetic and pharmacological approaches to determine the role of classic PKC isoforms in PTP. We find that PTP is unchanged in PKC triple knock-out (TKO) mice in which all calcium-dependent PKC isoforms have been eliminated (PKCα, PKCβ, and PKCγ). We confirm previous studies and find that in wild-type mice 10 μm of the PKC inhibitor GF109203 eliminates PTP and the PKC activator PDBu enhances neurotransmitter release and occludes PTP. However, we find that the same concentrations of GF109203 and PDBu have similar effects in TKO animals. We also show that 2 μm GF109203 does not abolish PTP even though it inhibits the PDBu-dependent phosphorylation of PKC substrates. We conclude that at the CA3 to CA1 synapse Ca(2+)-dependent PKC isoforms do not serve as calcium sensors to mediate PTP.

          Significance statement

          Neurons dynamically regulate neurotransmitter release through many processes known collectively as synaptic plasticity. Post-tetanic potentiation (PTP) is a widespread form of synaptic plasticity that lasts for tens of seconds that may have important computational roles and contribute to short-term memory. According to a leading mechanism, presynaptic calcium activates protein kinase C (PKC) to increase neurotransmitter release. Pharmacological studies have also implicated this mechanism at hippocampal CA3 to CA1 synapses, but there are concerns about the specificity of PKC activators and inhibitors. We therefore used a molecular genetic approach and found that PTP was unaffected when all calcium-dependent PKC isozymes were eliminated. We conclude that PKC isozymes are not the calcium sensors that mediate PTP at the CA3 to CA1 synapse.
            Cover page: Calcium-Dependent Protein Kinase C Is Not Required for Post-Tetanic Potentiation at the Hippocampal CA3 to CA1 Synapse
            • Article
            • Peer Reviewed
            UC Davis Previously Published Works (2021)
            Post-tetanic potentiation (PTP) is a form of short-term plasticity that lasts for tens of seconds following a burst of presynaptic activity. It has been proposed that PTP arises from protein kinase C (PKC) phosphorylation of Munc18-1, an SM (Sec1/Munc-18 like) family protein that is essential for release. To test this model, we made a knock-in mouse in which all Munc18-1 PKC phosphorylation sites were eliminated through serine-to-alanine point mutations (Munc18-1SA mice), and we studied mice of either sex. The expression of Munc18-1 was not altered in Munc18-1SA mice, and there were no obvious behavioral phenotypes. At the hippocampal CA3-to-CA1 synapse and the granule cell parallel fiber (PF)-to-Purkinje cell (PC) synapse, basal transmission was largely normal except for small decreases in paired-pulse facilitation that are consistent with a slight elevation in release probability. Phorbol esters that mimic the activation of PKC by diacylglycerol still increased synaptic transmission in Munc18-1SA mice. In Munc18-1SA mice, 70% of PTP remained at CA3-to-CA1 synapses, and the amplitude of PTP was not reduced at PF-to-PC synapses. These findings indicate that at both CA3-to-CA1 and PF-to-PC synapses, phorbol esters and PTP enhance synaptic transmission primarily by mechanisms that are independent of PKC phosphorylation of Munc18-1.SIGNIFICANCE STATEMENT A leading mechanism for a prevalent form of short-term plasticity, post-tetanic potentiation (PTP), involves protein kinase C (PKC) phosphorylation of Munc18-1. This study tests this mechanism by creating a knock-in mouse in which Munc18-1 is replaced by a mutated form of Munc18-1 that cannot be phosphorylated. The main finding is that most PTP at hippocampal CA3-to-CA1 synapses or at cerebellar granule cell-to-Purkinje cell synapses does not rely on PKC phosphorylation of Munc18-1. Thus, mechanisms independent of PKC phosphorylation of Munc18-1 are important mediators of PTP.
              Cover page: Presynaptic Short-Term Plasticity Persists in the Absence of PKC Phosphorylation of Munc18-1.
              • Article
              • Peer Reviewed
              UC Davis Previously Published Works (2014)
              In presynaptic boutons, calcium (Ca(2+)) triggers both neurotransmitter release and short-term synaptic plasticity. Whereas synaptotagmins are known to mediate vesicle fusion through binding of high local Ca(2+) to their C2 domains, the proteins that sense smaller global Ca(2+) increases to produce short-term plasticity have remained elusive. Here, we identify a Ca(2+) sensor for post-tetanic potentiation (PTP), a form of plasticity thought to underlie short-term memory. We find that at the functionally mature calyx of Held synapse the Ca(2+)-dependent protein kinase C isoforms α and β are necessary for PTP, and the expression of PKCβ in PKCαβ double knockout mice rescues PTP. Disruption of Ca(2+) binding to the PKCβ C2 domain specifically prevents PTP without impairing other PKCβ-dependent forms of synaptic enhancement. We conclude that different C2-domain-containing presynaptic proteins are engaged by different Ca(2+) signals, and that Ca(2+) increases evoked by tetanic stimulation are sensed by PKCβ to produce PTP.DOI: http://dx.doi.org/10.7554/eLife.03011.001.
                Cover page: Protein kinase C is a calcium sensor for presynaptic short-term plasticity
                • Article
                • Peer Reviewed
                UC Davis Previously Published Works (2014)
                Precise control of gene expression plays fundamental roles in brain development, but the roles of chromatin regulators in neuronal connectivity have remained poorly understood. We report that depletion of the NuRD complex by in vivo RNAi and conditional knockout of the core NuRD subunit Chd4 profoundly impairs the establishment of granule neuron parallel fiber/Purkinje cell synapses in the rodent cerebellar cortex in vivo. By interfacing genome-wide sequencing of transcripts and ChIP-seq analyses, we uncover a network of repressed genes and distinct histone modifications at target gene promoters that are developmentally regulated by the NuRD complex in the cerebellum in vivo. Finally, in a targeted in vivo RNAi screen of NuRD target genes, we identify a program of NuRD-repressed genes that operate as critical regulators of presynaptic differentiation in the cerebellar cortex. Our findings define NuRD-dependent promoter decommissioning as a developmentally regulated programming mechanism that drives synaptic connectivity in the mammalian brain.
                  Cover page: Promoter Decommissioning by the NuRD Chromatin Remodeling Complex Triggers Synaptic Connectivity in the Mammalian Brain
                  • Article
                  • Peer Reviewed
                  UC Davis Previously Published Works (2023)
                  The cerebellum, traditionally associated with motor coordination and balance, also plays a crucial role in various aspects of higher-order function and dysfunction. Emerging research has shed light on the cerebellum's broader contributions to cognitive, emotional, and reward processes. The cerebellum's influence on autonomic function further highlights its significance in regulating motivational and emotional states. Perturbations in cerebellar development and function have been implicated in various neurodevelopmental disorders, including autism spectrum disorder and attention deficit hyperactivity disorder. An increasing appreciation for neuropsychiatric symptoms that arise from cerebellar dysfunction underscores the importance of elucidating the circuit mechanisms that underlie complex interactions between the cerebellum and other brain regions for a comprehensive understanding of complex behavior. By briefly discussing new advances in mapping cerebellar function in affective, cognitive, autonomic, and social processing and reviewing the role of the cerebellum in neuropathology beyond the motor domain, this Mini-Symposium review aims to provide a broad perspective of cerebellar intersections with the limbic brain in health and disease.
                    Cover page: Cognitive-Affective Functions of the Cerebellum
                    • Article
                    • Peer Reviewed
                    UC Davis Previously Published Works (2021)
                    The hippocampus can be divided into distinct segments that make unique contributions to learning and memory. The dorsal segment supports cognitive processes like spatial learning and navigation while the ventral hippocampus regulates emotional behaviors related to fear, anxiety and reward. In the current study, we determined how pyramidal cells in ventral CA1 respond to spatial cues and aversive stimulation during a context fear conditioning task. We also examined the effects of high and low frequency stimulation of these neurons on defensive behavior. Similar to previous work in the dorsal hippocampus, we found that cells in ventral CA1 expressed high-levels of c-Fos in response to a novel spatial environment. Surprisingly, however, the number of activated neurons did not increase when the environment was paired with footshock. This was true even in the subpopulation of ventral CA1 pyramidal cells that send direct projections to the amygdala. When these cells were stimulated at high-frequencies (20 Hz) we observed feedforward inhibition of basal amygdala neurons and impaired expression of context fear. In contrast, low-frequency stimulation (4 Hz) did not inhibit principal cells in the basal amygdala and produced an increase in fear generalization. Similar results have been reported in dorsal CA1. Therefore, despite clear differences between the dorsal and ventral hippocampus, CA1 neurons in each segment appear to make similar contributions to context fear conditioning.
                      Cover page: High-Frequency Stimulation of Ventral CA1 Neurons Reduces Amygdala Activity and Inhibits Fear
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