Subcellular localization of the antidepressant-sensitive norepinephrine transporter

<p>Abstract</p> <p>Background</p> <p>Reuptake of synaptic norepinephrine (NE) via the antidepressant-sensitive NE transporter (NET) supports efficient noradrenergic signaling and presynaptic NE homeostasis. Limited, and somewhat contradictory, information currently describes the axonal transport and localization of NET in neurons.</p> <p>Results</p> <p>We elucidate NET localization in brain and superior cervical ganglion (SCG) neurons, aided by a new NET monoclonal antibody, subcellular immunoisolation techniques and quantitative immunofluorescence approaches. We present evidence that axonal NET extensively colocalizes with syntaxin 1A, and to a limited degree with SCAMP2 and synaptophysin. Intracellular NET in SCG axons and boutons also quantitatively segregates from the vesicular monoamine transporter 2 (VMAT2), findings corroborated by organelle isolation studies. At the surface of SCG boutons, NET resides in both lipid raft and non-lipid raft subdomains and colocalizes with syntaxin 1A.</p> <p>Conclusion</p> <p>Our findings support the hypothesis that SCG NET is segregated prior to transport from the cell body from proteins comprising large dense core vesicles. Once localized to presynaptic boutons, NET does not recycle via VMAT2-positive, small dense core vesicles. Finally, once NET reaches presynaptic plasma membranes, the transporter localizes to syntaxin 1A-rich plasma membrane domains, with a portion found in cholera toxin-demarcated lipid rafts. Our findings indicate that activity-dependent insertion of NET into the SCG plasma membrane derives from vesicles distinct from those that deliver NE. Moreover, NET is localized in presynaptic membranes in a manner that can take advantage of regulatory processes targeting lipid raft subdomains.</p

Excitatory drive onto dopaminergic neurons in the rostral linear nucleus is enhanced by norepinephrine in an α1 adrenergic receptor-dependent manner

Dopaminergic innervation of the extended amygdala regulates anxiety-like behavior and stress responsivity. A portion of this dopamine input arises from dopamine neurons located in the ventral lateral periaqueductal gray (vlPAG) and rostral (RLi) and caudal linear nuclei of the raphe (CLi). These neurons receive substantial norepinephrine input, which may prime them for involvement in stress responses. Using a mouse line that expresses eGFP under control of the tyrosine hydroxylase promoter, we explored the physiology and responsiveness to norepinephrine of these neurons. We find that RLi dopamine neurons differ from VTA dopamine neurons with respect to membrane resistance, capacitance and the hyperpolarization-activated current, Ih. Further, we found that norepinephrine increased the frequency of spontaneous excitatory postsynaptic currents (sEPSCs) on RLi dopamine neurons. This effect was mediated through the α1 adrenergic receptor (AR), as the actions of norepinephrine were mimicked by the α1-AR agonist methoxamine and blocked by the α1-AR antagonist prazosin. This action of norepinephrine on sEPSCs was transient, as it did not persist in the presence of prazosin. Methoxamine also increased the frequency of miniature EPSCs, indicating that the α1-AR action on glutamatergic transmission likely has a presynaptic mechanism. There was also a modest decrease in sEPSC frequency with the application of the α2-AR agonist UK-14,304. These studies illustrate a potential mechanism through which norepinephrine could recruit the activity of this population of dopaminergic neurons

Operant Sensation Seeking Requires Metabotropic Glutamate Receptor 5 (mGluR5)

Pharmacological and genetic studies have suggested that the metabotropic glutamate receptor 5 (mGluR5) is critically involved in mediating the reinforcing effects of drugs of abuse, but not food. The purpose of this study was to use mGluR5 knockout (KO), heterozygous (Het), and wildtype (WT) mice to determine if mGluR5 modulates operant sensation seeking (OSS), an operant task that uses varied sensory stimuli as a reinforcer. We found that mGluR5 KO mice had significantly reduced OSS responding relative to WT mice, while Het mice displayed a paradoxical increase in OSS responding. Neither KO nor Het mice exhibited altered operant responding for food as a reinforcer. Further, we assessed mGluR5 KO, Het and WT mice across a battery of cocaine locomotor, place preference and anxiety related tests. Although KO mice showed expected differences in some locomotor and anxiety measures, Het mice either exhibited no phenotype or an intermediate one. In total, these data demonstrate a key role for mGluR5 in OSS, indicating an important role for this receptor in reinforcement-based behavior

Strain Differences in Stress Responsivity Are Associated with Divergent Amygdala Gene Expression and Glutamate-Mediated Neuronal Excitability

Stress is a major risk factor for numerous neuropsychiatric diseases. However, susceptibility to stress and the qualitative nature of stress effects on behavior differ markedly among individuals. This is partly because of the moderating influence of genetic factors. Inbred mouse strains provide a relatively stable and restricted range of genetic and environmental variability that is valuable for disentangling gene–stress interactions. Here, we screened a panel of inbred strains for anxiety- and depression-related phenotypes at baseline (trait) and after exposure to repeated restraint. Two strains, DBA/2J and C57BL/6J, differed in trait and restraint-induced anxiety-related behavior (dark/light exploration, elevated plus maze). Gene expression analysis of amygdala, medial prefrontal cortex, and hippocampus revealed divergent expression in DBA/2J and C57BL/6J both at baseline and after repeated restraint. Restraint produced strain-dependent expression alterations in various genes including glutamate receptors (e.g., Grin1, Grik1). To elucidate neuronal correlates of these strain differences, we performed ex vivo analysis of glutamate excitatory neurotransmission in amygdala principal neurons. Repeated restraint augmented amygdala excitatory postsynaptic signaling and altered metaplasticity (temporal summation of NMDA receptor currents) in DBA/2J but not C57BL/6J. Furthermore, we found that the C57BL/6J-like changes in anxiety-related behavior after restraint were absent in null mutants lacking the modulatory NMDA receptor subunit Grin2a, but not the AMPA receptor subunit Gria1. Grin2a null mutants exhibited significant (~30%) loss of dendritic spines on amygdala principal neurons under nonrestraint conditions. Collectively, our data support a model in which genetic variation in glutamatergic neuroplasticity in corticolimbic circuitry underlies phenotypic variation in responsivity to stress

Strain Differences in Stress Responsivity Are Associated with Divergent Amygdala Gene Expression and Glutamate-Mediated Neuronal Excitability

Stress is a major risk factor for numerous neuropsychiatric diseases. However, susceptibility to stress and the qualitative nature of stress effects on behavior differ markedly among individuals. This is partly because of the moderating influence of genetic factors. Inbred mouse strains provide a relatively stable and restricted range of genetic and environmental variability that is valuable for disentangling gene–stress interactions. Here, we screened a panel of inbred strains for anxiety- and depression-related phenotypes at baseline (trait) and after exposure to repeated restraint. Two strains, DBA/2J and C57BL/6J, differed in trait and restraint-induced anxiety-related behavior (dark/light exploration, elevated plus maze). Gene expression analysis of amygdala, medial prefrontal cortex, and hippocampus revealed divergent expression in DBA/2J and C57BL/6J both at baseline and after repeated restraint. Restraint produced strain-dependent expression alterations in various genes including glutamate receptors (e.g., Grin1, Grik1). To elucidate neuronal correlates of these strain differences, we performed ex vivo analysis of glutamate excitatory neurotransmission in amygdala principal neurons. Repeated restraint augmented amygdala excitatory postsynaptic signaling and altered metaplasticity (temporal summation of NMDA receptor currents) in DBA/2J but not C57BL/6J. Furthermore, we found that the C57BL/6J-like changes in anxiety-related behavior after restraint were absent in null mutants lacking the modulatory NMDA receptor subunit Grin2a, but not the AMPA receptor subunit Gria1. Grin2a null mutants exhibited significant (~30%) loss of dendritic spines on amygdala principal neurons under nonrestraint conditions. Collectively, our data support a model in which genetic variation in glutamatergic neuroplasticity in corticolimbic circuitry underlies phenotypic variation in responsivity to stress

Neuropeptide Y and corticotropin-releasing factor bidirectionally modulate inhibitory synaptic transmission in the bed nucleus of the stria terminalis

Abstract Neuropeptide Y (NPY) and corticotropin-releasing factor (CRF) have opposing effects on stress and anxiety. Both can modify synaptic activity through their binding to NPY receptors (YRs) and CRF receptors (CRFRs) respectively. The bed nucleus of the stria terminalis (BNST) is a brain region with enriched expression of both NPY and YRs and CRF and CRFRs. A component of the &apos;&apos;extended amygdala&apos;&apos;, the BNST is anatomically wellsituated to integrate stress and reward-related processing in the CNS, regulating activation of the hypothalamic-pituitary-adrenal (HPA) axis and reward circuits. Using whole-cell recordings in a BNST slice preparation, we found that NPY and CRF inhibit and enhance GABAergic transmission, respectively. Pharmacological experiments suggest that NPY depresses GABAergic transmission through activation of the Y2 receptor (Y2R), while both pharmacological and genetic experiments suggest that CRF and urocortin enhance GABAergic transmission through activation of the CRF receptor 1 (CRFR1). Further, the data suggest that NPY acts to regulate GABA release, while CRF enhances postsynaptic responses to GABA. These results suggest potential anatomical and cellular substrates for the robust behavioral interactions between NPY and CRF