RECEPTOR REGULATION OF AXON GUIDANCE MOLECULE GENE EXPRESSION

Molecular and Cellular Neuroscience, 2005

Administration of drugs of abuse induces strong molecular adaptations and plasticity within the mesolimbic dopamine (DA) system, a pathway essential for reward-seeking behavior. Little is known about the specific targets involved in this neuroadaptation process, but there are indications that cocaine and other drugs of abuse share the ability to alter the morphology of neuronal dendrites and spines, the primary site of excitatory synapses in the brain. Axon guidance molecules, the very molecular cues that regulate the formation of axon-target connections during development, may mediate these alterations. To test this hypothesis, we investigated mRNA expression changes of 39 axon guidance molecules, including 17 Semaphorins, 12 Ephs, 8 Ephrins and 2 neuropilins in the mesolimbic dopamine system of cocaine-treated animals under different paradigms by mean of DNA-Microarray and quantitative real-time PCR.

Molecular and Cellular Neuroscience, 2004

We have investigated functional roles of EphA/ephrin-A signaling in the development and function of the nigrostriatal system by overexpressing a soluble, broad-range EphA receptor antagonist in the central nervous system of transgenic mice. Adult transgenic mice showed a 30 -40% reduction in the total volume of the substantia nigra (SN) without detectable differences in the number of dopaminergic neurons. Using fluorogold retrograde tracing from the striatum, we detected a 40 -50% reduction in the number of dopaminergic neurons that could be traced from this structure in transgenic mice, suggesting that, a lower proportion of these cells were able to reach the striatum after disruption of EphA/ephrin-A signaling. In spite of this, total dopamine content in the striatum of transgenic mice was comparable to wild type. Analysis of locomotor activity and its regulation by pharmacological treatments that stimulate dopaminergic transmission revealed an unexpected dissociation of the behavioral responses to amphetamine and cocaine. In particular, transgenic mice were relatively insensitive to amphetamine while retaining normal responsiveness to cocaine, which, to the best of our knowledge, represents the first report of a dissociation of the behavioral responses to these two psychostimulants. Together, these results reveal an unexpected role for EphA/ephrin-A signaling in the normal connectivity and function of midbrain dopaminergic neurons.

Journal of Neuroscience, 2009

Dopaminergic neurons in the mesodiencephalon (mdDA neurons) make precise synaptic connections with targets in the forebrain via the mesostriatal, mesolimbic, and mesoprefrontal pathways. Because of the functional importance of these remarkably complex ascending axon pathways and their implication in human disease, the mechanisms underlying the development of these connections are of considerable interest. Despite extensive in vitro studies, the molecular determinants that ensure the perfect formation of these pathways in vivo remain mostly unknown. Here, we determine the embryonic origin and ontogeny of the mouse mesoprefrontal pathway and use these data to reveal an unexpected requirement for semaphorin 3F (Sema3F) and its receptor neuropilin-2 (Npn-2) during mdDA pathway development using tissue culture approaches and analysis of sema3F −/− , npn-2 −/− , and npn-2 −/− ;TH-Cre mice. We show that Sema3F is a bifunctional guidance cue for mdDA axons, some of which have the remarkable ability to regulate their responsiveness to Sema3F as they develop. During early developmental stages, Sema3F chemorepulsion controls previously uncharacterized aspects of mdDA pathway development through both Npn-2-dependent (axon fasciculation and channeling) and Npn-2-independent (rostral growth) mechanisms. Later on, chemoattraction mediated by Sema3F and Npn-2 is required to orient mdDA axon projections in the cortical plate of the medial prefrontal cortex. This latter finding demonstrates that regulation of axon orientation in the target field occurs by chemoattractive mechanisms, and this is likely to also apply to other neural systems. In all, this study provides a framework for additional dissection of the molecular basis of mdDA pathway development and disease.

1999

Dopaminergic neurons in the substantia nigra and ventral tegmental area project to the caudate putamen and nucleus accumbens/olfactory tubercle, respectively, constituting mesostriatal and mesolimbic pathways. The molecular signals that confer target specificity of different dopaminergic neurons are not known. We now report that EphB1 and ephrin-B2, a receptor and ligand of the Eph family, are candidate guidance molecules for the development of these distinct pathways. EphB1 and ephrin-B2 are expressed in complementary patterns in the midbrain dopaminergic neurons and their targets, and the ligand specifically inhibits the growth of neurites and induces the cell loss of substantia nigra, but not ventral tegmental, dopaminergic neurons. These studies suggest that the ligand-receptor pair may contribute to the establishment of distinct neural pathways by selectively inhibiting the neurite outgrowth and cell survival of mistargeted neurons. In addition, we show that ephrin-B2 expression is upregulated by cocaine and amphetamine in adult mice, suggesting that ephrin-B2/EphB1 interaction may play a role in drug-induced plasticity in adults as well.

Brain Research, 2006

In developing brain, Eph receptors and their ephrin ligands (Ephs/ephrins) are implicated in facilitating topographic guidance of a number of pathways, including the nigrostriatal and mesolimbic dopamine (DA) pathways. In adult rodent brain, these molecules are implicated in neuronal plasticity associated with learning and memory. Cocaine significantly alters the expression of select members of this family of axonal guidance molecules, implicating Ephs, ephrins in drug-induced neuroadaptation. The potential contribution of Ephs, ephrins to cocaine-induced reorganization of striatal circuitry brain in primates [Saka, E., Goodrich, C., Harlan, P., Madras, B.K., Graybiel, A.M., 2004. Repetitive behaviors in monkeys are linked to specific striatal activation patterns. J. Neurosci. 24, 7557-7565] is unknown because there are no documented reports of Eph/ephrin expression or function in adult primate brain. We now report that brains of adult old and new world monkeys express mRNA encoding EphA4 receptor and ephrin-B2 ligand, implicated in topographic guidance of dopamine and striatal neurons during development. Their encoded proteins distributed highly selectively in regions of adult monkey brain. EphA4 mRNA levels were prominent in the DA-rich caudate/ putamen, nucleus accumbens and globus pallidus, as well as the medial and orbitofrontal cortices, hippocampus, amygdala, thalamus and cerebellum. Immunocytochemical localization of EphA4 protein revealed discrete expression in caudate/putamen, globus pallidus, substantia nigra, cerebellar Purkinje cells, pyramidal cells of frontal cortices (layers II, III and V) and the subgranular zone of the hippocampus. Evidence for EphA4 expression in dopamine neurons emerged from colocalization with tyrosine-hydroxylase-positive terminals in striatum and substantia nigra and ventral tegmental area cell bodies. The association of axonal guidance molecules with drug-induced reorganization of adult primate brain circuitry warrants investigation.

Molecular Brain Research, 2000

The Eph family tyrosine kinase receptors and their ligands have been implicated in axon guidance and neuronal migration during development of the nervous system. In the current study, we aim to characterize the nature of changes in EphB1 receptor expression following increases or decreases in dopamine activity. Neonatal mice (P3) were injected with 6-hydroxydopamine and allowed 13 days to recover. These animals show a profound depletion of dopamine in all areas assayed, with a corresponding dose-dependent decrease in EphB1 expression. Day 3 pups were also injected either chronically (P3-P16) or acutely (P3 only) with cocaine to determine how enhancing dopamine signaling would affect EphB1 signal density. It was found that both treatments significantly increased expression of EphB1 in the cortex, striatum and substantia nigra. Finally, animals were treated prenatally (E15-E17) with cocaine and sacrificed on P7. These animals also showed an increase in EphB1 signal density, but only in the dopaminergic terminal areas in the cortex and striatum. These studies indicate that dopamine activity regulates developmental expression of the tyrosine kinase receptor EphB1.

Neuroscience, 2011

Cocaine-and amphetamine-regulated transcript (CART) is widespread in the rodent brain. CART has been implicated in many different functions including reward, feeding, stress responses, sensory processing, learning and memory formation. Recent studies have suggested that CART may also play a role in neural development. Therefore, in the present study we compared the distribution pattern and levels of CART mRNA expression in the forebrain of male and female rats at different stages of postnatal development: P06, P26 and P66. At 6 days of age (P06), male and female rats showed increased CART expression in the somatosensory and piriform cortices, indusium griseum, dentate gyrus, nucleus accumbens, and ventral premammillary nucleus. Interestingly, we found a striking expression of CART mRNA in the ventral posteromedial and ventral posterolateral thalamic nuclei. This thalamic expression was absent at P26 and P66. Contrastingly, at P06 CART mRNA expression was decreased in the arcuate nucleus. Comparing sexes, we found increased CART mRNA expression in the anteroventral periventricular nucleus of adult females. In other regions including the CA1, the lateral hypothalamic area and the dorsomedial nucleus of the hypothalamus, CART expression was not different comparing postnatal ages and sexes. Our findings indicate that CART gene expression is induced in a distinct temporal and spatial manner in forebrain sites of male and female rats. They also suggest that CART peptide participate in the development of neural pathways related to selective functions including sensory processing, reward and memory formation.

2012

Opioid receptors located in the ventral tegmental area are known to regulate dopamine (DA) release from mesocortical afferents to medial prefrontal cortex (mPFC) but little is known on whether in this cortical region activation of opioid receptors affect DA receptor signaling. In the present study we show that in mouse mPFC concomitant activation of either d-or l-opioid receptors, but not j-opioid receptors, potentiated DA D1-like receptor-induced stimulation of adenylyl cyclase activity through a G protein bc subunit-dependent mechanism. In tissue slices of mPFC, the combined addition of the opioid agonist leu-enkephalin and the DA D1-like receptor agonist SKF 81297 produced more than additive increase in the phosphorylation state of AMPA and NMDA receptor subunits GluR1 and NR1, respectively. Moreover, in primary cultures of mouse frontal cortex neurons, DA D1-like receptor-induced Ser133 phosphorylation of the transcription factor cyclic AMP responsive element binding protein was potentiated by concurrent stimulation of opioid receptors. Double immunofluorescence analysis of cultured cortical cells indicated that a large percentage of DA D1 receptor positive cells expressed either d-or l-opioid receptor immunoreactivity. These data indicate that in mouse mPFC activation of land d-opioid receptors enhances DA D1-like receptor signaling likely through converging regulatory inputs on bc-stimulated adenylyl cyclase isoforms. This previously unrecognized synergistic interaction may selectively affect DA D1 transmission at specific postsynaptic sites where the receptors are co-localized and may play a role in prefrontal DA D1 regulation of opioid addiction.

Neurochemistry International, 2008

Proceedings of the National Academy of Sciences, 2008

The persistent nature of addiction has been associated with activity-induced plasticity of neurons within the striatum and nucleus accumbens (NAc). To identify the molecular processes leading to these adaptations, we performed Cre/loxP-mediated genetic ablations of two key regulators of gene expression in response to activity, the Ca 2+ /calmodulin-dependent protein kinase IV (CaMKIV) and its postulated main target, the cAMP-responsive element binding protein (CREB). We found that acute cocaine-induced gene expression in the striatum was largely unaffected by the loss of CaMKIV. On the behavioral level, mice lacking CaMKIV in dopaminoceptive neurons displayed increased sensitivity to cocaine as evidenced by augmented expression of locomotor sensitization and enhanced conditioned place preference and reinstatement after extinction. However, the loss of CREB in the forebrain had no effect on either of these behaviors, even though it robustly blunted acute cocaine-induced transcription...