Lucia Caffino

Repeated exposure to cocaine differently modulates BDNF mRNA and protein levels in rat striatum and prefrontal cortex

In this report we investigated the modulation of the neurotrophin brain‐derived neurotrophic factor (BDNF) following single or repeated injections with cocaine. Dose–response experiments revealed that a single dose of cocaine (5 mg/kg) is sufficient to upregulate BDNF mRNA levels selectively in rat prefrontal cortex 2 h after the injection, an effect that persists at least for 24 h and is paralleled by enhanced expression of mature (m)BDNF protein. Five consecutive injections of the psychostimulant (5 mg/kg) potentiate the increase of BDNF mRNA levels 2 h after the last treatment, presumably as a result of the enhancement of cAMP response element‐binding protein (CREB) phosphorylation, an effect that vanishes 72 h later. Conversely, precursor (pro‐) and mBDNF protein forms were markedly reduced 2 h and 72 h post‐injection in the prefrontal cortex. Interestingly, in the striatum we found that repeated cocaine injection increased pro‐BDNF levels without altering the mature form of the neurotrophin. Our results suggest that cocaine differently affects BDNF transcription and translation in a region‐selective manner, but might also alter neurotrophin processing. These data further support the notion that the corticostriatal network is highly vulnerable to the effects of cocaine, and suggest that abnormal regulation of BDNF expression could contribute, at least in part, to the functional defects observed in drug abusers.

Sub-chronic exposure to atomoxetine up-regulates BDNF expression and signalling in the brain of adolescent spontaneously hypertensive rats: Comparison with methylphenidate

The stimulant methylphenidate and the non-stimulant atomoxetine are widely used for the treatment of Attention-Deficit/Hyperactivity Disorder (ADHD), but the molecular mechanisms of their therapeutic action are not fully understood. The aim of our study was to investigate, in adolescent rats, the sub-chronic effect of these two drugs on neuronal plasticity, through a detailed analysis of BDNF expression and signalling in order to establish the contribution of these mechanisms in the pharmacotherapy of ADHD. Atomoxetine (ATX) up-regulated BDNF mRNA levels in the hippocampus whereas methylphenidate (MPH) increased BDNF gene expression in the nucleus accumbens and caudate-putamen. Opposite effects were seen in the prefrontal cortex, a critical region in attention disorders, where ATX increased while MPH reduced total and exon IV BDNF mRNA levels. Analysis of BDNF-mediated signalling in the prefrontal cortex revealed that ATX enhanced AKT and GSK3β phosphorylation whereas MPH reduced the synaptic levels of trkB, the high-affinity BDNF receptor, and ERK1/2 activation. Our findings show that ATX and MPH exert an opposite modulation of the BDNF system, primarily in prefrontal cortex that, independently from the behavioral control exerted by the two drugs, may be important for long-term consequences on cognitive function.

TAAR1 Modulates Cortical Glutamate NMDA Receptor Function

Trace Amine-Associated Receptor 1 (TAAR1) is a G protein-coupled receptor expressed in the mammalian brain and known to influence subcortical monoaminergic transmission. Monoamines, such as dopamine, also play an important role within the prefrontal cortex (PFC) circuitry, which is critically involved in high-o5rder cognitive processes. TAAR1-selective ligands have shown potential antipsychotic, antidepressant, and pro-cognitive effects in experimental animal models; however, it remains unclear whether TAAR1 can affect PFC-related processes and functions. In this study, we document a distinct pattern of expression of TAAR1 in the PFC, as well as altered subunit composition and deficient functionality of the glutamate N-methyl-D-aspartate (NMDA) receptors in the pyramidal neurons of layer V of PFC in mice lacking TAAR1. The dysregulated cortical glutamate transmission in TAAR1-KO mice was associated with aberrant behaviors in several tests, indicating a perseverative and impulsive phenotype of mutants. Conversely, pharmacological activation of TAAR1 with selective agonists reduced premature impulsive responses observed in the fixed-interval conditioning schedule in normal mice. Our study indicates that TAAR1 plays an important role in the modulation of NMDA receptor-mediated glutamate transmission in the PFC and related functions. Furthermore, these data suggest that the development of TAAR1-based drugs could provide a novel therapeutic approach for the treatment of disorders related to aberrant cortical functions.

Repeated stress prevents cocaine-induced activation of BDNF signaling in rat prefrontal cortex.

In this report we provide evidence that repeated stress prevents cocaine-induced activation of BDNF expression and signaling in rat prefrontal cortex. A single injection of cocaine up-regulates BDNF expression in sham (i.e. unstressed) rats but not in repeatedly stressed rats. Similarly, the expression as well as trafficking of the high affinity BDNF receptor trkB promoted by the psychostimulant is impaired in chronically-stressed rats challenged with cocaine. Moreover, among the different intracellular signaling pathways that can be activated by the neurotrophin, i.e. ERK1/2-, Akt- and PLCgamma-pathway, we found that cocaine is able to selectively activate the ERK1/2 pathway in sham animals, but not in rats exposed to repeated stress. Notably, such changes take place in chronically-stressed animals although they still retain the ability to increase neuronal activity as measured by the enhancement of Arc gene expression. In summary, we have demonstrated that stress globally interferes with BDNF-mediated signaling responses to cocaine challenge, providing key insights into the molecular basis of stress-cocaine interaction and indicating the critical role of the prefrontal cortex in mediating such interaction.

Single session of cocaine intravenous self-administration shapes goal-oriented behaviours and up-regulates Arc mRNA levels in rat medial prefrontal cortex

To separate the direct pharmacological effects of cocaine from those associated with active drug self-administration we employed a yoked control-operant paradigm and investigated the expression of well established markers of the rapid action of cocaine, i.e. the inducible early genes Arc and Zif268 and trophic factors, i.e. brain-derived neurotrophic factor (BDNF) and basic fibroblast growth factor (FGF-2), in rats after a single intravenous (i.v.) cocaine self-administration session. Animals self-administering cocaine (SA, 0.25 mg/0.1 ml saline per infusion, 2-h session) did more active lever-presses than yoked-cocaine (YC) and yoked-vehicle (YV) animals. This goal-oriented behaviour was accompanied by a selective increase in Arc mRNA levels in the medial prefrontal cortex (mPFC). There were no changes in the expression of the other genes in this brain region. mRNA levels of Arc and Zif268 in striatum and Zif268 in the nucleus accumbens markedly increased both in SA and YC animals; but there was no change in the expression of FGF-2 and BDNF. No changes were observed in hippocampus, hypothalamus, frontal cortex, and midbrain in SA and YC animals compared to YV animals in any of the genes. These findings demonstrate that a single session of cocaine i.v. self-administration is sufficient to shape rat behaviour towards goal-directed behaviours and selectively up-regulate Arc expression in mPFC (of SA animals), providing the first evidence that the mPFCs function is already profoundly influenced by the first voluntary cocaine exposure.

Stress and cocaine interact to modulate basic fibroblast growth factor (FGF-2) expression in rat brain

RationaleOur laboratory has previously demonstrated that the expression of basic fibroblast growth factor (FGF-2), a protein involved in survival and maintenance of several cell phenotypes as well as in synaptic plasticity, is modulated by stress (Molteni et al., Brain Res Rev 37:249–258, 2001; Fumagalli et al., Neurobiol Dis 20:731–737, 2005) and cocaine (Fumagalli et al., J Neurochem 96:996–1004, 2006).ObjectivesSince it is widely recognized that stress influences drug seeking, we decided to investigate whether stress, acute or repeated, could influence the changes in FGF-2 gene expression brought about by cocaine.ResultsOur data demonstrate that stress and cocaine interact to produce significant changes on FGF-2 expression in rat prefrontal cortex and striatum. In prefrontal cortex, our experiments demonstrated that a single exposure to stress potentiated cocaine-induced FGF-2 elevation, whereas prolonged stress prevented the modulation of the trophic factor in response to cocaine. In striatum, the magnitude of cocaine-induced FGF-2 response is enhanced by repeated stress, whereas no interaction was observed when acute stress and single exposure to cocaine were combined.ConclusionsOur findings demonstrate that stress interacts with cocaine to alter the pattern of FGF-2 expression in a way that depends on whether stress is acute or chronic and in a regionally selective fashion. These results identify a potential molecular target through which stress alters cellular sensitivity to cocaine and might prove useful in understanding the mechanisms underlying brain vulnerability to stress.

Stress rapidly dysregulates the glutamatergic synapse in the prefrontal cortex of cocaine‐withdrawn adolescent rats

Although several lines of evidence have shown that chronic cocaine use is associated with stress system dysregulation, the underlying neurochemical mechanisms are still elusive. To investigate whether the rapid stress‐induced response of the glutamatergic synapse was influenced by a previous history of cocaine, rats were exposed to repeated cocaine injections during adolescence [from postnatal day (PND) 28–42], subjected to a single swim stress (5 minutes) three days later (PND 45) and sacrificed 15 minutes after the end of this stressor. Critical determinants of glutamatergic homeostasis were measured in the medial prefrontal cortex (mPFC) whereas circulating corticosterone levels were measured in the plasma.

AMPA GluR-A receptor subunit mediates hippocampal responsiveness in mice exposed to stress

Because stress represents a major precipitating event for psychiatric disorders, it is important to identify molecular mechanisms that may be altered in vulnerable individuals when exposed to stress. Here, we studied GluR‐A−/− mice, animals with compromised AMPA receptor signaling, and characterized by a schizophrenic as well as depressive phenotype to investigate changes occurring in response to an acute stress. Wild‐type and GluR‐A−/− mice were exposed to a single immobilization stress and sacrificed immediately after the end of the stress for the analysis of activity regulated genes and of glutamatergic synapse responsiveness. The acute stress produced a marked increase in the hippocampal expression of Arc (activity‐regulated cytoskeletal‐associated protein) in GluR‐A−/−, but not in wild‐type mice, which was associated with a similar increase of phospho‐CaMKII, a partner in the action of Arc. When looking at the glutamatergic response to stress in wild‐type animals, we found that stress increased GluR‐A phosphorylation on serine831, an effect that was paralleled by a significant increase of the phosphorylation of the main NMDA receptor subunits, that is, NR‐1 and NR‐2B. Conversely, the stress‐induced modulation of NMDA receptor subunits was not observed in GluR‐A−/− mice. We suggest that enhanced stress responsiveness in GluR‐A−/− mice may be due, at least in part, to their inability to activate NMDA‐mediated glutamatergic neurotransmission, suggesting that the integrity of AMPA/NMDA receptor function may be important for successful coping under stressful conditions.

Deletion of GABA-B Receptor in Schwann Cells Regulates Remak Bundles and Small Nociceptive C-fibers

The mechanisms regulating the differentiation into non‐myelinating Schwann cells is not completely understood. Recent evidence indicates that GABA‐B receptors may regulate myelination and nociception in the peripheral nervous system. GABA‐B receptor total knock‐out mice exhibit morphological and molecular changes in peripheral myelin. The number of small myelinated fibers is higher and associated with altered pain sensitivity. Herein, we analyzed whether these changes may be produced by a specific deletion of GABA‐B receptors in Schwann cells. The conditional mice (P0‐GABA‐B1fl/fl) show a morphological phenotype characterized by a peculiar increase in the number of small unmyelinated fibers and Remak bundles, including nociceptive C‐fibers. The P0‐GABA‐B1fl/fl mice are hyperalgesic and allodynic. In these mice, the morphological and behavioral changes are associated with a downregulation of neuregulin 1 expression in nerves. Our findings suggest that the altered pain sensitivity derives from a Schwann cell‐specific loss of GABA‐B receptor functions, pointing to a role for GABA‐B receptors in the regulation of Schwann cell maturation towards the non‐myelinating phenotype. GLIA 2014;62:548–565

Acute spinal cord injury reduces brain derived neurotrohic factor expression in rat hippocampus

Spinal cord injury (SCI) is a devastating event which causes dramatic changes in the everyday life of the patient. We have found that acute SCI reduced BDNF expression selectively in the hippocampus of lesioned rats, a decrease which persists at least 1 week, thus identifying the modulation of the neurotrophin biosynthesis as an important mechanism underlying brain vulnerability to SCI. These data are the first to show that SCI alters hippocampal BDNF expression and identify the neurotrophin as a potential target through which SCI changes brain functions, a notion that might prove useful in understanding the mechanisms underlying brain vulnerability to SCI.