Roles for the Uptake\u3csub\u3e2\u3c/sub\u3e Transporter OCT3 in Regulation of Dopaminergic Neurotransmission and Behavior

Transporter-mediated uptake determines the peak concentration, duration, and physical spread of released monoamines. Most studies of monoamine clearance focus on the presynaptic uptake1 transporters SERT, NET and DAT. However, recent studies have demonstrated the expression of the uptake2 transporter OCT3 (organic cation transporter 3), throughout the rodent brain. In contrast to NET, DAT and SERT, OCT3 has higher capacity and lower affinity for substrates, is sodium-independent, and is multi-specific, with the capacity to transport norepinephrine, dopamine, serotonin and histamine. OCT3is insensitive to inhibition by cocaine and antidepressant drugs but is inhibited directly by the glucocorticoid hormone corticosterone. Thus, OCT3 represents a novel, stress hormone-sensitive, monoamine transport mechanism. Incorporating this transporter into current models of monoaminergic neurotransmission requires information on: A) the cellular and subcellular localization of the transporter; B) the effects of OCT3 inhibitors on monoamine clearance; and C) the consequences of decreased OCT3-mediated transport on physiology and/or behavior. This review summarizes studies describing the anatomical distribution of OCT3, its cellular and subcellular localization, its contribution to the regulation of dopaminergicsignaling, and its roles in the regulation of behavior. Together, these and other studies suggest that both Uptake1 and Uptake2 transporters play key roles in regulating monoaminergic neurotransmission and the effects of monoamines on behavior

Organic Cation Transporter 3: A Cellular Mechanism Underlying Rapid, Non-Genomic Glucocorticoid Regulation of Monoaminergic Neurotransmission, Physiology, and Behavior

Corticosteroid hormones act at intracellular glucocorticoid receptors (GR) and mineralocorticoid receptors (MR) to alter gene expression, leading to diverse physiological and behavioral responses. In addition to these classical genomic effects, corticosteroid hormones also exert rapid actions on physiology and behavior through a variety of non-genomic mechanisms, some of which involve GR or MR, and others of which are independent of these receptors. One such GR-independent mechanism involves corticosteroid-induced inhibition of monoamine transport mediated by “uptake2” transporters, including organic cation transporter 3 (OCT3), a low-affinity, high-capacity transporter for norepinephrine, epinephrine, dopamine, serotonin and histamine. Corticosterone directly and acutely inhibits OCT3-mediated transport. This review describes the studies that initially characterized uptake2 processes in peripheral tissues, and outlines studies that demonstrated OCT3 expression and corticosterone-sensitive monoamine transport in the brain. Evidence is presented supporting the hypothesis that corticosterone can exert rapid, GR-independent actions on neuronal physiology and behavior by inhibiting OCT3-mediated monoamine clearance. Implications of this mechanism for glucocorticoid-monoamine interactions in the context-dependent regulation of behavior are discussed

Organic Cation Transporter 3 (OCT3) Is Localized to Intracellular and Surface Membranes in Select Glial and Neuronal Cells Within the Basolateral Amygdaloid Complex of Both Rats and Mice

Organic cation transporter 3 (OCT3) is a high-capacity, low-affinity transporter that mediates corticosterone-sensitive uptake of monoamines including norepinephrine, epinephrine, dopamine, histamine and serotonin. OCT3 is expressed widely throughout the amygdaloid complex and other brain regions where monoamines are key regulators of emotional behaviors affected by stress. However, assessing the contribution of OCT3 to the regulation of monoaminergic neurotransmission and monoamine-dependent regulation of behavior requires fundamental information about the subcellular distribution of OCT3 expression. We used immunofluorescence and immuno-electron microscopy to examine the cellular and subcellular distribution of the transporter in the basolateral amygdaloid complex of the rat and mouse brain. OCT3-immunoreactivity was observed in both glial and neuronal perikarya in both rat and mouse amygdala. Electron microscopic immunolabeling revealed plasma membrane-associated OCT3 immunoreactivity on axonal, dendritic, and astrocytic processes adjacent to a variety of synapses, as well as on neuronal somata. In addition to plasma membrane sites, OCT3 immunolabeling was also observed associated with neuronal and glial endomembranes, including Golgi, mitochondrial and nuclear membranes. Particularly prominent labeling of the outer nuclear membrane was observed in neuronal, astrocytic, microglial and endothelial perikarya. The localization of OCT3 to neuronal and glial plasma membranes adjacent to synaptic sites is consistent with an important role for this transporter in regulating the amplitude, duration, and physical spread of released monoamines, while its localization to mitochondrial and outer nuclear membranes suggests previously undescribed roles for the transporter in the intracellular disposition of monoamines

Natural and Synthetic Corticosteroids Inhibit Uptake\u3csub\u3e2\u3c/sub\u3e-Mediated Transport in CNS Neurons

In addition to exerting actions via mineralocorticoid and glucocorticoid receptors, corticosteroids also act by inhibiting uptake2, a high-capacity monoamine transport system originally described in peripheral tissues. Recent studies have demonstrated that uptake2 transporters are expressed in the brain and play roles in monoamine clearance, suggesting that they mediate some corticosteroid effects on physiological and behavioral processes. However, the sensitivity of brain uptake2 to many natural and synthetic corticosteroids has not been characterized. Cultured rat cerebellar granule neurons (CGNs) were previously shown to exhibit corticosterone-sensitive accumulation of the uptake2 substrate1-methyl-4-phenylpyridinium (MPP+). We examined the expression of uptake1 and uptake2 transporters in CGNs, and tested the effects of a variety of natural and synthetic corticosteroids on accumulation of [3H]-MPP+ by these cells. Cultured rat CGNs expressed mRNA for three uptake2-like transporters: organic cation transporters 1 and 3, and the plasma membrane monoamine transporter. They did not express mRNA for the dopamine or norepinephrine transporters, and expressed very little mRNA for the serotonin reuptake transporter. Accumulation of [3H]-MPP+ by CGNs was dose-dependently inhibited by corticosterone and decynium-22, known inhibitors of uptake2. Accumulation of MPP+ was also dose-dependently inhibited, with varying efficacies, by aldosterone, 11-deoxycorticosterone, cortisol, and cortisone, and by the synthetic glucocorticoids betamethasone, dexamethasone and prednisolone, and the glucocorticoid receptor antagonist RU38486. These studies demonstrate that uptake2 in the CNS is inhibited by a variety of natural and synthetic corticosteroids, and suggest that inhibition of uptake2-mediated monoamine clearance may underlie some behavioral and physiological effects of these hormones

Stress-Induced Cocaine Seeking Requires a Beta-2 Adrenergic Receptor-Regulated Pathway from the Ventral Bed Nucleus of the Stria Terminalis That Regulates CRF Actions in the Ventral Tegmental Area

The ventral bed nucleus of the stria terminalis (vBNST) has been implicated in stress-induced cocaine use. Here we demonstrate that, in the vBNST, corticotropin releasing factor (CRF) is expressed in neurons that innervate the ventral tegmental area (VTA), a site where the CRF receptor antagonist antalarmin prevents the reinstatement of cocaine seeking by a stressor, intermittent footshock, following intravenous self-administration in rats. The vBNST receives dense noradrenergic innervation and expresses β adrenergic receptors (ARs). Footshock-induced reinstatement was prevented by bilateral intra-vBNST injection of the β-2 AR antagonist, ICI-118,551, but not the β-1 AR antagonist, betaxolol. Moreover, bilateral intra-vBNST injection of the β-2 AR agonist, clenbuterol, but not the β-1 agonist, dobutamine, reinstated cocaine seeking, suggesting that activation of vBNST β-2 AR is both necessary for stress-induced reinstatement and sufficient to induce cocaine seeking. The contribution of a β-2 AR-regulated vBNST-to-VTA pathway that releases CRF was investigated using a disconnection approach. Injection of ICI-118,551 into the vBNST in one hemisphere and antalarmin into the VTA of the contralateral hemisphere prevented footshock-induced reinstatement, whereas ipsilateral manipulations failed to attenuate stress-induced cocaine seeking, suggesting that β-2 AR regulate vBNST efferents that release CRF into the VTA, activating CRF receptors, and promoting cocaine use. Last, reinstatement by clenbuterol delivered bilaterally into the vBNST was prevented by bilateral vBNST pretreatment with antalarmin, indicating that β-2 AR-mediated actions in the vBNST also require local CRF receptor activation. Understanding the processes through which stress induces cocaine seeking should guide the development of new treatments for addiction

Redundance of Δ\Delta-isobar Parameters in Effective Field Theories

It is shown that the off-shell parameters in the interaction Lagrangian of pions, nucleons, and $\Delta$-isobars are redundant in the framework of effective field theories. Our results also suggest the necessity of including the $\Delta$ as an explicit dynamical degree of freedom.Comment: 11 pages, RevTex, no figures, a minor error corrected, to appear in PL

Sexual Differentiation of Circadian Clock Function in the Adrenal Gland

Sex differences in glucocorticoid production are associated with increased responsiveness of the adrenal gland in females. However, the adrenal-intrinsic mechanisms that establish sexual dimorphic function remain ill defined. Glucocorticoid production is gated at the molecular level by the circadian clock, which may contribute to sexual dimorphic adrenal function. Here we examine sex differences in the adrenal gland using an optical reporter of circadian clock function. Adrenal glands were cultured from male and female Period2::Luciferase (PER2::LUC) mice to assess clock function in vitro in real time. We confirm that there is a pronounced sex difference in the intrinsic capacity to sustain PER2::LUC rhythms in vitro, with higher amplitude rhythms in adrenal glands collected from males than from females. Changes in adrenal PER2::LUC rhythms over the reproductive life span implicate T as an important factor in driving sex differences in adrenal clock function. By directly manipulating hormone levels in adult mice in vivo, we demonstrate that T increases the amplitude of PER2::LUC rhythms in adrenal glands of both male and female mice. In contrast, we find little evidence that ovarian hormones modify adrenal clock function. Lastly, we find that T in vitro can increase the amplitude of PER2::LUC rhythms in male adrenals but not female adrenals, which suggests the existence of sex differences in the mechanisms of T action in vivo. Collectively these results reveal that activational effects of T alter circadian timekeeping in the adrenal gland, which may have implications for sex differences in stress reactivity and stress-related disorders

All the Brain\u27s a Stage for Serotonin: The Forgotten Story of Serotonin Diffusion across Cell Membranes

In the conventional model of serotonin neurotransmission, serotonin released by neurons in the midbrain raphe nuclei exerts its actions on forebrain neurons by interacting with a large family of post-synaptic receptors. The actions of serotonin are terminated by active transport of serotonin back into the releasing neuron, which is mediated by the serotonin reuptake transporter (SERT). Because SERT is expressed pre-synaptically and is widely thought to be the only serotonin transporter in the forebrain, the conventional model does not include serotonin transport into post-synaptic neurons. However, a large body of evidence accumulating since the 1970s has shown that serotonin, despite having a positive charge, can cross cell membranes through a diffusion-like process. Multiple low-affinity, high-capacity, sodium-independent transporters, widely expressed in the brain, allow the carrier-mediated diffusion of serotonin into forebrain neurons. The amount of serotonin crossing cell membranes through this mechanism under physiological conditions is considerable. Most prominent textbooks fail to include this alternative method of serotonin uptake in the brain, and even most neuroscientists are unaware of it. This failure has limited our understanding of a key regulator of serotonergic neurotransmission, impeded research on the potential intracellular actions of serotonin in post-synaptic neurons and glial cells, and may have impeded our understanding of the mechanism by which antidepressant medications reduce depressive symptoms