Abstract Neurotrophic factors are required for the proliferation, maturation, and guidance of neurons during development, but they also play critical roles in the adult brain. The disruption of neurotrophic factor expression and signaling by stress has been hypothesized to contribute to an individual’s vulnerability to depression. Conversely, neurotrophic factors have been shown to be critical for antidepressant effects, including the rapid action of ketamine and scopolamine. This chapter provides an overview of neurotrophic factors, with a focus on brain-derived neurotrophic factor (BDNF), in depression and the complexity of recent findings. It also discusses the essential role of BDNF in antidepressant action, including rapid antidepressant effects of ketamine and scopolamine.
Chapter 6 reviews the phenotypes of the constitutive Mecp2 KO mutant mice, those generated by expressing RTT -causing mutations, and conditional Mecp2 KO mice in comparison to clinical phenotypes presented in patients with RTT. It also covers therapeutic approaches currently reported using these RTT -model mice.
Recent advances in mouse genetics have opened many new avenues of research in which to explore gene function in the brain, and contributions to the pathophysiology and treatment of psychiatric disorders. The use of the mouse to explore gene function has contributed a better understanding of the role of specific genes in the nervous system including their influence on neural circuits and complex behavior. This chapter explores current approaches to manipulate gene function in a mouse. Genetically modified mice allow for the investigation of a particular gene in vivo. The approaches discussed highlight recent advances to specifically overexpress or disrupt a specific gene of interest in the brain. We also highlight viral-mediated gene transfer approaches to allow for spatial and temporal control of gene function.
Ketamine produces rapid antidepressant action in patients with major depression or treatment-resistant depression. Studies have identified brain-derived neurotrophic factor (BDNF) and its receptor, tropomyosin receptor kinase B (TrkB), as necessary for the antidepressant effects and underlying ketamine-induced synaptic potentiation in the hippocampus. Here, we delete BDNF or TrkB in presynaptic CA3 or postsynaptic CA1 regions of the Schaffer collateral pathway to investigate the rapid antidepressant action of ketamine. The deletion of Bdnf in CA3 or CA1 blocks the ketamine-induced synaptic potentiation. In contrast, ablation of TrkB only in postsynaptic CA1 eliminates the ketamine-induced synaptic potentiation. We confirm BDNF-TrkB signaling in CA1 is required for ketamine's rapid behavioral action. Moreover, ketamine application elicits dynamin1-dependent TrkB activation and downstream signaling to trigger rapid synaptic effects. Taken together, these data demonstrate a requirement for BDNF-TrkB signaling in CA1 neurons in ketamine-induced synaptic potentiation and identify a specific synaptic locus in eliciting ketamine's rapid antidepressant effects.
Differential display of hippocampal tissue after entorhinal cortex lesion (ECL) revealed decreases in mRNA encoding the neuronal hyperpolarization-activated, cyclic nucleotide-gated channel HCN1. In situ hybridization confirmed that hippocampal transcripts of HCN1, but not HCN2/3/4, are down-regulated after ECL. Expression recovered at approximately 21 days after lesion (dal). Immunohistochemistry demonstrated a corresponding regulation of HCN1 protein expression in CA1-CA3 dendrites, hilar mossy cells and interneurons, and granule cells. Patch-clamp recordings in the early phase after lesion from mossy cells and hilar interneurons revealed an increase in the fast time constant of current activation and a profound negative shift in voltage activation of Ih. Whereas current activation recovered at 30 dal, the voltage activation remained hyperpolarized in mossy cells and hilar interneurons. Granule cells, however, were devoid of any detectable somatic Ih currents. Hence, denervation of the hippocampus decreases HCN1 and concomitantly the Ih activity in hilar neurons, and the recovery of h-current activation kinetics occurs parallel to postlesion sprouting.
