Andrea Mele

Focal application of alcohols elevates extracellular dopamine in rat brain: a microdialysis study

Dopaminergic systems are thought to play a major role in the stimulant and reinforcing properties of drugs of abuse, including ethanol. The present study describes the effects of local perfusion with ethanol (and other alcohols) on extracellular dopamine in the striatum and nucleus accumbens. Following the establishment of basal dopamine levels (2-3 h), various concentrations of ethanol in artificial CSF (0.01-10% v/v) were slowly perfused through a microdialysis probe. Each dose of ethanol was found to increase dopamine concentrations in both the striatum and nucleus accumbens. This increase was dose-related in the striatum. The exclusion of calcium and inclusion of 12.5 mM magnesium in the perfusion medium prevented, or greatly attenuated the ethanol-induced dopamine (DA) release. Thus, the release of DA by ethanol is exocytotic in nature and involves calcium-dependent processes. The other alcohols tested, namely methanol and butanol, demonstrated a structure-activity relationship together with ethanol, in their ability to increase extracellular DA. The relative potency was butanol greater than ethanol greater than methanol. The diffusion of ethanol into the brain tissue was investigated following perfusion through the probe. Relatively low concentrations of ethanol were found in striatal tissue during perfusion and they declined rapidly with time, following the removal of ethanol from the perfusate. The concentrations of ethanol achieved in brain tissue following focal application through the microdialysis probe were relevant to human intoxication.

GBR12909 antagonizes the ability of cocaine to elevate extracellular levels of dopamine

Rats were administered various IP doses of the high-affinity dopamine (DA) reuptake inhibitor 1-[2-[bis(4-fluorophenyl)methoxy]ethyl]-4-[3-phenylpropyl]piperazine (GBR12909). The caudate nuclei were removed 60 min after drug administration and stored at -70 degrees C. Striatal membranes were prepared later. The results demonstrated that GBR12909 produced a dose-dependent decrease in the binding of [3H]cocaine or [3H]GBR12935 to the DA transporter (ED50 about 10 mg/kg). Saturation binding studies with [3H]GBR12935 showed that this was due to both an increase in the Kd, due to residual drug, and to a decrease in the Bmax. At a dose of 25 mg/kg IP, GBR12909 produced a 50% decrease in the Bmax, and a 3.4-fold increase in the Kd. In the in vivo microdialysis studies, GBR12909 (25 mg/kg IP) produced a modest, long-lasting and stable elevation of extracellular DA. Administration of cocaine through the microdialysis probe to rats pretreated with either saline or GBR12909 (25 mg/kg IP) produced a dose-dependent increase in extracellular DA in both groups. GBR12909 inhibited cocaine-induced increases in extracellular DA by about 50% at all doses. These data collectively indicate that at a dose sufficient to decrease by 50% the Bmax of [3H]GBR12935 binding sites, GBR12909 antagonizes the ability of cocaine to elevate extracellular DA by 50%. Further studies will be needed to evaluate a possible role for GBR12909 in the medical treatment of cocaine addiction.

Stress induces region specific alterations in microRNAs expression in mice.

Several studies have demonstrated that exposure to both acute and chronic aversive stimuli can affect neural activity in different brain areas. In particular it has been shown that stressful events can induce not only short-term changes in neural transmission and gene regulation, but also long-term changes that can lead to structural modification. In this study we investigated, in CD1 mice, the effects of single or repeated exposures to restraint stress (2h for 1 or 5 consecutive days) in the frontal cortex on a crucial class of gene expression regulators, the microRNAs (miRs).First we performed a microarray profiling on RNA extracted from the frontal cortex of mice exposed to acute or repeated restraint stress. The results indicated a prominent increase in the expression levels of different miRs after acute stress while only minor changes were observed after repeated restraint. The Northern blot analysis on selected miRs confirmed an increase after acute restraint for let-7a, miR-9 and miR 26-a/b. Finally, Northern blot analysis of the selected miRs on RNA extracted from the hippocampus of stressed mice demonstrated that such changes were region specific, as no differences were observed in the hippocampus. These data suggest that control of mRNA translation through miRs is an additional mechanism by which stressful events regulates protein expression in the frontal cortex.

Profilin2 contributes to synaptic vesicle exocytosis, neuronal excitability, and novelty‐seeking behavior

Profilins are actin binding proteins essential for regulating cytoskeletal dynamics, however, their function in the mammalian nervous system is unknown. Here, we provide evidence that in mouse brain profilin1 and profilin2 have distinct roles in regulating synaptic actin polymerization with profilin2 preferring a WAVE‐complex‐mediated pathway. Mice lacking profilin2 show a block in synaptic actin polymerization in response to depolarization, which is accompanied by increased synaptic excitability of glutamatergic neurons due to higher vesicle exocytosis. These alterations in neurotransmitter release correlate with a hyperactivation of the striatum and enhanced novelty‐seeking behavior in profilin2 mutant mice. Our results highlight a novel, profilin2‐dependent pathway, regulating synaptic physiology, neuronal excitability, and complex behavior.

Chronic cocaine alters limbic extracellular dopamine. Neurochemical basis for addiction

The extracellular concentration of dopamine in the ventral striatum was measured daily by means of brain microdialysis. Chronic cocaine (10 mg/kg twice daily) altered the dopamine output compared to that in vehicle-injected rats, inducing a pronounced increase in the first 3 days followed by a clear-cut decrease. This reduction in the output of dopamine during chronic cocaine as well as during withdrawal may be neurochemical substrate for the addictive properties of cocaine.

Targeting Group III Metabotropic Glutamate Receptors Produces Complex Behavioral Effects in Rodent Models of Parkinson's Disease

Drugs activating group III metabotropic glutamate receptors (mGluRs) represent therapeutic alternatives to l-DOPA (l-3,4-dihydroxyphenylalanine) for the treatment of Parkinsons disease (PD). Their presynaptic location at GABAergic and glutamatergic synapses within basal ganglia nuclei provide a critical target to reduce abnormal activities associated with PD. The effects of selective group III mGluR agonists (1S,3R,4S)-1-aminocyclopentane-1,3,4-tricarboxylic acid (ACPT-I) and l-(+)-2-amino-4-phosphonobutyric acid (l-AP4) infused into the globus pallidus (GP) or the substantia nigra pars reticulata (SNr) were thus studied in rat models of PD. Bilateral infusions of ACPT-I (1, 2.5, and 5 nmol/μl) into the GP fully reverse the severe akinetic deficits produced by 6-hydroxydopamine nigrostriatal dopamine lesions in a reaction-time task without affecting the performance of controls. Similar results were observed after l-AP4 (1 nmol) or picrotoxin, a GABAA receptor antagonist, infused into the GP. In addition, intrapallidal ACPT-I counteracts haloperidol-induced catalepsy. This effect is reversed by concomitant administration of a selective group III receptor antagonist (RS)-α-cyclopropyl-4-phosphonophenylglycine. In contrast, ACPT-I (0.05, 0.1, and 0.25 nmol) infusions into the SNr enhance the lesion-induced akinetic deficits in control and lesioned rats and do not reverse haloperidol-induced catalepsy. l-AP4 (0.05 nmol) and picrotoxin in the SNr produce the same effects. Together, these results show that activation of group III mGluRs in the GP provides benefits in parkinsonian rats, presumably by modulating GABAergic neurotransmission. The opposite effects produced by group III mGluR activation in the SNr, also observed with a selective mGluR8 agonist, support the use of subtype-selective group III mGluR agonists as a potential antiparkinsonian strategy.

N-methyl-D-aspartate and dopamine receptor involvement in the modulation of locomotor activity and memory processes

Abstract In this study we report on the effects of N-methyl-d-aspartate (NMDA)- and dopamine (DA)-receptor manipulation on the modulation of one-trial inhibitory avoidance response and the encoding of spatial information, as assessed with a non-associative task. Further, a comparison with the well-known effects of the manipulation of these two receptor systems on locomotor activity is outlined. It is well assessed that NMDA-receptor blockage induces a stimulatory action on locomotor activity similar to that exerted by DA agonists. There is evidence showing that the nucleus accumbens is involved in the response induced by both NMDA antagonists and DA agonists. We show results indicating a functional interaction between these two neural systems in modulating locomotor activity, with D2 DA-receptor antagonists (sulpiride and haloperidol) being more effective than the D1 antagonist (SCH 23390) in blocking MK-801-induced locomotion. A different profile is shown in the effects of NMDA antagonists and DA agonists in the modulation of memory processes. In one-trial inhibitory avoidance response, NMDA antagonists (MK-801 and CPP) impair the response on test day, while DA agonists exert a facilitatory effect; furthermore, sub-effective doses of both D1 (SKF 23390) and D2 (quinpirole) are able to attenuate the impairing effect in a way similar to that induced by NMDA antagonists. The effects of NMDA- and DA-acting drugs on the response to spatial novelty, as assessed with a task designed to study the ability of animals to react to discrete spatial changes, are in good accord with the effects observed on passive avoidance. The results show that NMDA as well as DA antagonists, at low doses, selectively impair the reactivity of mice to spatial changes. In a last series of experiments, the possible role of NMDA receptors located in the nucleus accumbens was investigated regarding reactivity to spatial novelty. The experiments gave apparently contrasting results: while showing an impairing effect of focal administrations of NMDA antagonists in the nucleus accumbens on reactivity to spatial novelty, no effect of ibotenic acid lesions of the same structure was observed.

Repeated administration of phencyclidine, amphetamine and MK-801 selectively impairs spatial learning in mice: a possible model of psychotomimetic drug-induced cognitive deficits

Cognitive deficits are a key feature of schizophrenia. N-Methyl-D-aspartate (NMDA) receptor antagonists and amphetamine are known to induce psychotic behaviors and cognitive deficits in animals and humans, often affecting visuo-spatial abilities. Phencyclidine (PCP), MK-801 and amphetamine (AMPH) have been used in pharmacological animal models of schizophrenia, but none of these models has focused so far on spatial learning after repeated administration of the drugs. The objective of this study was to test whether repeated administration of PCP, AMPH or MK-801 influenced the performance of mice in a non-associative spatial learning test. CD-1 male mice were given i.p. daily injections of either saline, PCP (5.0, 10.0 mg/kg), AMPH (2.5, 5 mg/kg) or MK-801 (0.3, 0.6 mg/kg), for 5 days. On day 6 all mice were tested in an open field containing five different objects. After three sessions of habituation, each animals reactivity to object displacement and object substitution was assessed. No significant differences among treatment groups were observed in object exploration or locomotion during the habituation phase. Five days of repeated PCP, AMPH or MK-801 administration selectively and differentially impaired the ability of mice to discriminate a spatial change, while leaving intact the ability to react to a non-spatial change. These data suggest that neurobiological adaptations to drug regimens known to induce psychotic behaviors and alterations in locomotor activity or stereotypies can also alter spatial learning, as assessed in this test, thus indicating that these regimens could also mimic some of the cognitive deficits observed in schizophrenia.

Stress promotes major changes in dopamine receptor densities within the mesoaccumbens and nigrostriatal systems

This study investigated the effects of stress on brain dopamine receptor densities in two inbred strains of mice. Analysis of [3H]SCH23390 binding by quantitative autoradiography revealed that repeated restraint stress significantly increases D1-like receptor density in the nucleus accumbens of mice of the DBA/2 strain whist reducing it in the caudate-putamen of C57BL/6 mice. No significant changes in D2-like receptor quantified by [3H](-)-sulpiride binding were observed in caudate, substantia nigra and accumbens of stressed C57BL/6 mice. Instead, in DBA/2 mice, stress significantly increased D2-like receptor density in the nucleus accumbens whilst reducing it in the substantia nigra. Finally, stress significantly increased D2-like receptor density within the ventral tegmental area of C57BL/6 mice whilst significantly reducing it in mice of the DBA/2 strain. These results indicate that stress promotes major changes in mesoaccumbens and nigrostriatal dopamine receptor densities. The direction of these changes depends on receptor subtype, brain area and strain. Moreover, the opposite changes of D2-like receptor densities promoted by stress in the ventral tegmental area of the two inbred strains of mice suggest that mesoaccumbens dopamine autoreceptors density might be controlled by a major genotype x stress interaction.

Area-specific temporal control of corticospinal motor neuron differentiation by COUP-TFI

Transcription factors with gradients of expression in neocortical progenitors give rise to distinct motor and sensory cortical areas by controlling the area-specific differentiation of distinct neuronal subtypes. However, the molecular mechanisms underlying this area-restricted control are still unclear. Here, we show that COUP-TFI controls the timing of birth and specification of corticospinal motor neurons (CSMN) in somatosensory cortex via repression of a CSMN differentiation program. Loss of COUP-TFI function causes an area-specific premature generation of neurons with cardinal features of CSMN, which project to subcerebral structures, including the spinal cord. Concurrently, genuine CSMN differentiate imprecisely and do not project beyond the pons, together resulting in impaired skilled motor function in adult mice with cortical COUP-TFI loss-of-function. Our findings indicate that COUP-TFI exerts critical areal and temporal control over the precise differentiation of CSMN during corticogenesis, thereby enabling the area-specific functional features of motor and sensory areas to arise.