Exogenous GM1 ganglioside increases accumbal BDNF levels in rats.

Gangliosides are compounds that are abundant throughout the CNS, participating actively in neuroplasticity. We previously described that exogenous GM1 ganglioside pretreatment enhances the rewarding properties of cocaine, evidenced by a lower number of sessions and/or dosage necessary to induce conditioned place preference (CPP). Since GM1 pretreatment did not modify cocaine's pharmacokinetic parameters, we suspected that the increased rewarding effect found might be mediated by BDNF, a neurotrophic factor closely related to cocaine addiction. This study was performed to investigate the possibility that GM1 may induce changes in BDNF levels in the nucleus accumbens (NAc), a core structure in the brain's reward circuitry, of rats submitted to three conditioning sessions with cocaine (10 mg/kg, i.p.). The results demonstrate that GM1 administration, which showed no rewarding effect by itself in the CPP, induced a significant increase of BDNF protein levels in the NAc, which may account for the increased rewarding effect of cocaine shown in the CPP paradigm.

GM1 ganglioside enhances the rewarding properties of cocaine in rats.

GM1 pretreatment enhanced the rewarding properties of cocaine as assessed in the conditioned place preference paradigm. This effect was shown by the lower dosage of cocaine necessary to induce conditioning compared with rats receiving cocaine alone, as well as by the fewer number of sessions necessary to induce place preference. GM1 pretreatment did not modify the plasma level of cocaine, but it induced a significant increase in the brain cocaine level compared with animals receiving cocaine alone. In order to evaluate the possibility that GM1 pretreatment may alter the pharmacokinetic parameters of cocaine, the brain and plasma esterase activities, the plasma bound/free cocaine ratio and the brain blood barrier permeability to i.v. Evans Blue administration were assessed. None of these parameters was modified by the GM1 administration. In addition, GM1 (100microM) did not alter the dopamine transporter inhibition induced by cocaine (10(-7)-10(-5)M), as determined by the uptake of [(3-)H]-dopamine in the microsacs of nucleus accumbens. In conclusion, GM1 pretreatment, which did not have any effect per se, increased the rewarding effect of cocaine, a phenomenon correlated with a significant increase in the brain cocaine levels. The different pharmacokinetic parameters evaluated, as well as the inhibitory effect of cocaine on the dopamine transporter, were not modified by GM1, but it modifies the brain cocaine disposition. Thus, the mechanisms by which GM1 enhanced the rewarding effects of cocaine merit further study.

Pharmacological reactivity to cocaine in adult rats undernourished at perinatal age: behavioral and neurochemical correlates.

The influence of neuronal alterations induced by early undernutrition on the stimulant effect of cocaine was assessed in adult rats submitted to a protein deprivation schedule at perinatal age. To evaluate the sensitization phenomenon induced by repeated cocaine administration, different groups of control (C) and deprived (D) rats received a daily injection of cocaine (5, 10 or 15 mg/kg, i.p.) for 16 days. Behavioral parameters were assessed every two days in an open-field. Dose-response curves obtained with different doses of cocaine used revealed a shift to the left in the locomotor activity curves of D rats compared to controls. Thus, D animals showed a clear behavioral sensitization to the lower dose of cocaine, whereas this phenomenon was only observed in C rats for the higher dose used. To correlate this differential development of sensitization with neurochemical parameters, we assessed extracellular dopamine (DA) levels in nucleus accumbens (core and shell) and in the dorsal caudate-putamen, using a microdialysis technique. A challenge with cocaine in cocaine pre-exposed animals produced a different increase in DA output only in nucleus accumbens "core" of D animals. Comparable DA levels were observed in nucleus accumbens shell and in dorsal caudate-putamen of both groups. These results demonstrate that D rats had a lower threshold developing a progressive behavioral sensitization following repeated cocaine administration, as well as higher responsiveness of the nucleus accumbens (core) expressed by increased DA release.

Locus coeruleus activity in perinatally protein-deprived rats: effects of fluoxetine administration.

We have previously described an increased locus coeruleus activity in perinatally protein-deprived rats. Since locus coeruleus dysfunction has been involved in different types of anxiety disorders and considering the modulating action of serotonergic transmission on locus coeruleus activity, we assessed the effect of fluoxetine, a selective serotonin reuptake inhibitor (SSRI), on locus coeruleus activity as measured by the firing rate and the number of spontaneously active cells/track. Repeated fluoxetine administration reduced locus coeruleus activity in both control and protein-deprived rats, although the reduction was greater in protein-deprived rats. Dose-response curves for the inhibitory effect of clonidine showed subsensitivity of alpha2-adrenergic autoreceptors in protein-deprived rats, a phenomenon reversed by fluoxetine treatment. Dose-response curves for the inhibitory effect of 2,5-dimethoxy-4-iodoamphetamine (DOI) were similar in both groups of rats. Following fluoxetine administration, subsensitivity to this effect developed in control but not in protein-deprived rats. Extracellular noradrenaline level in the prefrontal cortex, as measured by microdialysis procedure, was higher in protein-deprived rats compared to controls, and this difference was reduced after fluoxetine administration. A challenge with yohimbine increased the extracellular noradrenaline level in control but not in protein-deprived rats, suggesting subsensitivity of alpha2-adrenergic autoreceptors in early protein malnourished animals. These results stress the complexity of plastic changes induced by early protein malnutrition and sustain the hypothesis that perinatally protein-deprived rats may represent a useful animal model for screening antipanic agents.

Different behavioral reactivicty of 5-HT1 sites between killer and non-Killer rats after midbrain raphe lesion

Se realizaron estudios de la reactividad conductual de receptores serotoninérgicos de tipo 5-HTl y 5-HT2, en ratas "Killer" (K) y "non-Killer" (NK), obtenidos por aislamiento social o por lesión de los núcleos dorsal y medial del rafe. La reactividad de los receptores tipo 5-HTl fue medida en una escala de intensidad arbitraria para los síntomas de "forepaw treading" y "hindlimb abduction" luego de la administración de 5-MeODMT, mientras que la reactividad de los sitios 5-HT2 fue determinada a través del comportamiento de "wet dog shake", inducido por la administración de 5-hidroxitriptófano. No se observaron diferencias en las conductas mediadas por los sitios 5-HTl y 5-HT2 entre los animales aislados. De igual manera, se obtuvieron valores similares en el "wet dog shake" de ratas lesioandas K y NK. Por el contrario, 5- MeODMT indujo una menor respuesta conductual en las ratas lesionadas K en comparación con las lesionadas NK. Esta alteración en la respuesta conductual no es consecuencia de una desnervación neuronal diferente en el sistema serotoninérgico central, ya que no hubo modificaciones en el "uptake" de 5-Ht en las estructuras cerebrales analizadas entre estos dos grupos experimentales de ratas. Esta menor reactividad de los sitios 5-HTl podría reflejar una neurotransmisión serotoninérgica disminuida y aportaría una probable explicación a la aparición de la actvidad muricida en algunos pero no en todos los animales lesionados

Different behavioral reactivicty of 5-HT1 sites between killer and non-Killer rats after midbrain raphe lesion

Se realizaron estudios de la reactividad conductual de receptores serotoninérgicos de tipo 5-HTl y 5-HT2, en ratas "Killer" (K) y "non-Killer" (NK), obtenidos por aislamiento social o por lesión de los núcleos dorsal y medial del rafe. La reactividad de los receptores tipo 5-HTl fue medida en una escala de intensidad arbitraria para los síntomas de "forepaw treading" y "hindlimb abduction" luego de la administración de 5-MeODMT, mientras que la reactividad de los sitios 5-HT2 fue determinada a través del comportamiento de "wet dog shake", inducido por la administración de 5-hidroxitriptófano. No se observaron diferencias en las conductas mediadas por los sitios 5-HTl y 5-HT2 entre los animales aislados. De igual manera, se obtuvieron valores similares en el "wet dog shake" de ratas lesioandas K y NK. Por el contrario, 5- MeODMT indujo una menor respuesta conductual en las ratas lesionadas K en comparación con las lesionadas NK. Esta alteración en la respuesta conductual no es consecuencia de una desnervación neuronal diferente en el sistema serotoninérgico central, ya que no hubo modificaciones en el "uptake" de 5-Ht en las estructuras cerebrales analizadas entre estos dos grupos experimentales de ratas. Esta menor reactividad de los sitios 5-HTl podría reflejar una neurotransmisión serotoninérgica disminuida y aportaría una probable explicación a la aparición de la actvidad muricida en algunos pero no en todos los animales lesionados (AU)