Brief early handling increases morphine dependence in adult rats.

Short early manipulations of rodent postnatal environment may trigger long-term effects on neurobiological and behavioural phenotypes in adulthood. However, little is known about such effects of handling on the vulnerability to develop drug dependence. The present study aimed to analyze the long-term effects of a brief handling (1 min) on morphine and ethanol dependence and on the preproenkephalin (PPE) mRNA and mu opioid receptor levels. Handled rats showed a significant increase in morphine (25mg/l) but not ethanol (10%) consumption and preference after 7 weeks and no difference in morphine (2 and 5mg/kg) conditioned place preference. No difference of preproenkephalin mRNA and mu opioid receptor levels was detected in the mesolimbic system between both groups. These data emphasize that human brief handling, which can lead to morphine dependence development, constitutes in itself an experimental treatment and not a control condition.

Maternal deprivation increases vulnerability to morphine dependence and disturbs the enkephalinergic system in adulthood.

Maternal deprivation can trigger long-lasting molecular and cellular modifications in brain functions and might facilitate the appearance of pathogenic behaviors. This study focuses on the vulnerability to develop morphine dependence in adult rats that were separated from their mother and littermates for 3 h per day for 14 d after birth and examines the adaptive changes in the enkephalinergic pathways. Place-preference conditioning was observed with 2 mg/kg morphine in deprived rats, whereas 5 mg/kg morphine was necessary to induce conditioning in nondeprived animals. A prolonged morphine conditioning was shown in deprived rats. A strong increase in oral morphine self-administration behavior and preference was observed in deprived rats. Only a very slight increase in preference for sucrose solution, a more ethological reinforcer known to interact with the opioid system, was shown in deprived rats. These results indicate that this postnatal environment change leads to a hypersensitivity to the reinforcing properties of morphine and to the development of morphine dependence. A significant decrease in preproenkephalin mRNA expression was observed in the nucleus accumbens and the caudate-putamen nucleus of deprived rats. The basal extracellular levels of the Met-enkephalin-like immunoreactivity in the nucleus accumbens were significantly lower in deprived rats when compared with nondeprived animals, whereas no change in mu-opioid receptor binding occurred. These results strongly support that maternal deprivation leads to a basal hypoactivity of the enkephalinergic system and hypersensitivity to morphine effects. Together, our results suggest that maternal deprivation in pups likely represents a risk factor for morphine dependence in adult rats.

Abnormal postnatal ontogeny of the locus coeruleus in the epileptic mutant mouse quaking.

The tonic-clonic convulsions of the quaking mutant mice have been shown to be associated with the hyperplasia of the nucleus locus coeruleus, the origin of most brain noradrenergic neurons. In the present study, the postnatal ontogeny of the locus coeruleus has been studied by tyrosine hydroxylase immunolabeling in the mutant mice quaking and their controls at postnatal days 1, 30 and 90. In the control mice, the number of immunoreactive neuronal cell bodies increased significantly in the rostral half of the locus coeruleus between birth and postnatal day 30, while it decreased significantly in the caudal half between birth and adulthood. Thus, during postnatal maturation, the distribution of locus coeruleus neurons was shifted in the rostral direction. In the quaking mutant mice, while the increase of immunolabeling between birth and postnatal day 30 was observed in the rostral half of the locus coeruleus, no diminution could be found in the caudal half between birth and adulthood. As a result, the rostral shift of tyrosine hydroxylase immunoreactivity was not observed. Consequently, in adult mice, the caudal part of the mutants locus coeruleus appeared to contain significantly more neurons than the corresponding region in the controls. These results indicate that the hyperplasia of the locus coeruleus of the quaking mice that we had previously reported results from an alteration of the postnatal maturation of this nucleus. This developmental abnormality might be a primary determinant of the inherited epilepsy of the quaking mutant mice.

The mitochondrial toxin 3-nitropropionic acid induces striatal neurodegeneration via a c-Jun N-terminal kinase/c-Jun module.

Impairments in mitochondrial energy metabolism are thought to be involved in most neurodegenerative diseases, including Huntington's disease (HD). Chronic administration of 3-nitropropionic acid (3-NP), a suicide inhibitor of succinate dehydrogenase, causes prolonged energy impairments and replicates most of the pathophysiological features of HD, including preferential striatal degeneration. In this study, we analyzed one of the mechanisms that could account for this selective 3-NP-induced striatal degeneration. In chronically 3-NP-infused rats, the time course of motor behavioral impairments and histological abnormalities was determined. Progressive alterations of motor performance occurred after 3 d. By histological analysis and terminal deoxynucleotidyl transferase-mediated biotinylated UTP nick end-labeling staining, we found a selective neurodegenerescence in the striatum, occurring first in its dorsolateral (DL) part. Activation of c-Jun N-terminal kinase (JNK) was analyzed from brain sections of these rats, using immunocytochemical detection of its phosphorylated form. Activation of JNK occurred progressively and selectively in the DL of the striatum and was followed by c-Jun activation and expression in the same striatal region. To elucidate the role of the JNK/c-Jun module in 3-NP-induced striatal degeneration, we then used primary striatal neurons in culture, in which we replicated neuronal death by application of 3-NP. We found strong nuclear translocation of activated JNK that was rapidly followed by phosphorylation of the transcription factor c-Jun. Overexpression of a dominant negative version of c-Jun, lacking its transactivation domain and phosphorylation sites for activated JNK, completely abolished 3-NP-induced striatal neurodegeneration. We thus conclude that a genetic program controlled by the JNK/c-Jun module is an important molecular event in 3-NP-induced striatal degeneration.

Behavioural and biochemical evidence for interactions between Delta 9-tetrahydrocannabinol and nicotine.

Behavioural and pharmacological effects of Delta9-tetrahydrocannabinol (THC) and nicotine are well known. However, the possible interactions between these two drugs of abuse remain unclear in spite of the current association of cannabis and tobacco in humans. The present study was designed to analyse the consequences of nicotine administration on THC-induced acute behavioural and biochemical responses, tolerance and physical dependence. Nicotine strongly facilitated hypothermia, antinociception and hypolocomotion induced by the acute administration of THC. Furthermore, the co-administration of sub-threshold doses of THC and nicotine produced an anxiolytic-like response in the light - dark box and in the open-field test as well as a significant conditioned place preference. Animals co-treated with nicotine and THC displayed an attenuation in THC tolerance and an enhancement in the somatic expression of cannabinoid antagonist-precipitated THC withdrawal. THC and nicotine administration induced c-Fos expression in several brain structures. Co-administration of both compounds enhanced c-Fos expression in the shell of the nucleus accumbens, central and basolateral nucleus of the amygdala, dorso-lateral bed nucleus of the stria terminalis, cingular and piriform cortex, and paraventricular nucleus of the hypothalamus. These results clearly demonstrate the existence of a functional interaction between THC and nicotine. The facilitation of THC-induced acute pharmacological and biochemical responses, tolerance and physical dependence by nicotine could play an important role in the development of addictive processes.

Role of Dopaminergic D2 Receptors in the Regulation of Glutamic Acid Decarboxylase Messenger RNA in the Striatum of the Rat.

Levels of messenger RNA (mRNA) encoding glutamic acid decarboxylase (GAD) and preproenkephalin (PPE) were measured by Northern blot and in situ hybridization analyses in the striatum of the rat, after chronic injections of two neuroleptics, sulpiride and haloperidol. The Northern blot analysis showed that the chronic injection of sulpiride at high doses (80 mg/kg, twice a day, 14 days) increased striatal GAD and PPE mRNA levels by 120% and 78% respectively, when compared to vehicle-injected rats. Haloperidol injections at relatively low doses (1 mg/kg, once a day, 14 days) produced parallel increases in GAD (40%) and PPE (52%) mRNA levels. After in situ hybridization densitometric measurements were performed on autoradiograms from rats treated with sulpiride, haloperidol or vehicle. The distribution of GAD and PPE mRNA signals in control rats was homogeneous along the rostrocaudal extension of the striatum. A similar increase was found along this axis after sulpiride (20%) and haloperidol (30%) treatments. The cellular observation of hybridization signals showed that grain density for GAD mRNA was increased in a majority of striatal cells after both treatments. By contrast, the PPE mRNA hybridization signal only increased in a subpopulation of neurons. The effects of such treatments were also analysed by measuring GAD activity in the striatum and in its output structures, the globus pallidus and the substantia nigra. After the administration of sulpiride, GAD activity was not modified in the striatum but increased in the globus pallidus (by 17%). After haloperidol treatment, GAD activity was increased in the globus pallidus (20%) and the substantia nigra (17%). It is concluded that the interruption of dopaminergic transmission, more precisely the D2 receptor blockade, promotes in striatopallidal neurons an increase in GAD mRNA accompanied by an increase in GAD activity and PPE mRNA. A possible regulation of GAD mRNA and GAD activity in striatonigral neurons is also discussed.