Perinatal protein deprivation facilitates accumbal ERK phosphorylation in cocaine-sensitized adult rats.

In previous studies we described that perinatal protein deprivation facilitates the development and expression of behavioral sensitization to cocaine. In this research, we explored whether the increased reactivity observed in deprived (D) versus control (C) rats is also evident during drug-free withdrawal periods. Considering that activation of the extracellular signal-regulated protein kinase (ERK) is suggested to be involved in cocaine-induced behavioral sensitization, we study the effects of perinatal protein deprivation on phosphorylated ERK2 (pERK2) protein levels in the NAc (core and shell) during different drug-free withdrawal periods. To induce behavioral sensitization, C- and D-rats received a daily injection of cocaine (5-10 mg/kg, i.p.) for 7 days and locomotor activity was performed on days 1 and 7. Cocaine-sensitized animals were left drug-free and pERK2 was assessed on withdrawal days (WD) 1, 4, 7 and 21. In the NAc core, cocaine induced ERK signaling pathway activation in a dose-dependent manner, and only D-rats showed a significant increase in pERK2 protein levels with the lowest dose of cocaine (5 mg/kg). Moreover, sensitized C-rats with 10 mg/kg showed an increase in pERK2 levels from WD7 while D-rats showed this activation on WD4, which remained increased on WD7 and 21. In contrast, in the NAc shell, only sensitized D-rats with cocaine 10 mg/kg showed ERK2 activation on WD21. These results suggest that perinatal protein deprivation facilitates the molecular processes involved in neuronal plasticity occurring during withdrawal.

Perinatal undernutrition facilitates morphine sensitization and cross-sensitization to cocaine in adult rats: a behavioral and neurochemical study.

The development of sensitization to the locomotor effects of morphine and cross-sensitization between morphine and cocaine were evaluated in adult rats submitted to a protein malnutrition schedule from the 14th day of gestation up to 30 days of age (D-rats), and compared with well-nourished animals (C-rats). Dose-response curves to morphine-induced locomotor activity (5, 7.5, 10 or 15 mg/kg, i.p., every other day for 5 days) revealed a shift to the left in D-rats compared to C-rats. This implies that D-rats showed behavioral sensitization to the lower dose of morphine used (5 mg/kg), which was ineffective in C-rats. Furthermore, when a cocaine challenge (10 mg/kg, i.p) was given 48 h after the last morphine administration, only D-rats exhibited cross-sensitization in morphine-pretreated animals (7.5 and 10 mg/kg). In order to correlate the differential response observed with the functioning of the mesocorticolimbic dopaminergic system, extracellular dopamine (DA) levels were measured in the nucleus accumbens (core and shell) and the dorsal caudate-putamen. A challenge with cocaine in morphine pre-exposed animals produced an increase in DA release, but only in the nucleus accumbens "core" of D-rats. Similar DA levels were found in the nucleus accumbens "shell" and in the dorsal caudate-putamen of both groups. Finally, these results demonstrate that D-rats had a lower threshold for developing both a progressive behavioral sensitization to morphine and a cross-sensitization to cocaine. In accordance with these behavioral findings, a higher responsiveness of the nucleus accumbens core, expressed by increased DA levels, both basal and after cocaine challenge, was observed in D-rats.

Increased rewarding properties of morphine in perinatally protein-malnourished rats.

In the current research, we assessed the influence of a protein malnutrition schedule from the 14th day of gestation up to 40 days of age (D-rats) on the rewarding properties of morphine in adult rats by means of the conditioned place preference paradigm. Well-nourished animals (C-rats) administered with different doses of morphine (0.75, 1.5, 3, 6, 12 or 24 mg/kg i.p.) exhibited a conditioning place preference with doses of 3 and 6 mg/kg, whereas in D-rats such a conditioning effect was observed with doses of 1.5 and 3 mg/kg. No adverse effects were observed in either C- or D-rats for the higher doses of morphine. In addition, when animals of both groups were pretreated twice a day for 3 days with increasing doses of morphine (5, 10 and 20 mg/kg s.c.), only D-rats elicited sensitization to the conditioning effect with the lowest dose of morphine (0.75 mg/kg i.p.). Furthermore, sensitized D-rats showed a selective and significant increase in FosB expression in the nucleus accumbens (core and shell), basolateral amygdala and medial prefrontal cortex, brain areas that are functionally related to the rewarding neural circuit. These results demonstrate that a deficient nutritional status during the perinatal period results in adult subjects having neural alterations, leading to an increased responsiveness to morphine and/or enhanced reinforcement effects, which correlates with an overexpression of FosB in selective brain areas related to the rewarding network.

Perinatal protein malnutrition enhances rewarding cocaine properties in adult rats.

The rewarding properties of cocaine were assessed in adult rats submitted to a protein malnutrition schedule from the 14th day of gestation up to 40 days of age (deprived rats), as compared with well-nourished animals (control rats) using the conditioned place preference paradigm. Dose-response curves to cocaine (3, 5, 10, 15, 30, 45 or 60 mg/kg i.p.) revealed in deprived rats a conditioning effect with doses of 5 and 10mg/kg; doses of 15 and 30 mg/kg did not show any conditioning place preference and doses of 45 and 60 mg/kg revealed a significant aversive effect. In control rats, cocaine elicited place preference with doses of 10, 15 and 30 mg/kg, whereas 45 and 60 mg/kg did not show either conditioning or aversive effects. Furthermore, sensitization to the conditioning effect of cocaine was obtained in deprived animals with a low dosage of cocaine, that was ineffective in controls (5 mg/kg/day for 10 days). Related to the higher rewarding effects, sensitized deprived rats showed a selective and significant increase in FosB expression in nucleus accumbens (core and shell) and basolateral amygdala, brain areas related to the rewarding neuronal circuits. These results suggest that a deficient nutritional status during early life may induce in adult subjects an increased responsiveness to behavioral effects of cocaine and/or enhanced its reinforcement properties.

Increased neuronal activity in locus coeruleus from adult rats undernourished at perinatal age: its reversal by desipramine.

The spontaneous activity of locus coeruleus (LC) noradrenergic neurons was assessed by single unit recording in adult recovered rats undernourished at perinatal age as compared with wellnourished animals. Locus coeruleus activity, measured by the firing rate of noradrenergic neurons and the number of spontaneously active cells/track was significantly higher in deprived rats than in controls. In addition, dose-response curves for the inhibitory LC activity of clonidine showed a shift to the right in deprived animals indicating a subsensitivity of alpha2-adrenergic autoreceptors. This fact suggests an alteration in the negative feedback mechanism mediated by somatodentritic alpha2 autoreceptors that modulate the activity of LC neurons, and may account for the behavioral alterations attributed to early undernutrition. Repeated desipramine (DMI) administration to deprived rats reduced LC activity to values comparable to controls, which were not affected after a similar treatment. These data extend to previous reports on long-lasting or permanent plastic changes in the CNS induced by early undernutrition, which may be reverted by pharmacological manipulations. In addition, these results support the hypothesis that alterations induced by early undernutrition are in the same direction as and resemble those described for patients with panic disorders. Furthermore, together with behavioral alterations and selective anxiolytic effect of DMI and other drugs with antipanic effects described in early malnourished rats, the present data support the proposal that perinatally deprived rats may be a useful model for screening drugs with potential antipanic activity.

Effects of chronic risperidone on central noradrenergic transmission.

In the present work, we investigated the effects of chronic risperidone administration on the activity of locus coeruleus noradrenergic neurons. In addition, the effect of chronic risperidone administration on the basal level of norepinephrine in the prefrontal cortex was evaluated. Results of this research showed that chronic risperidone administration increased the activity of locus coeruleus noradrenergic neurons. The sensitivity of alpha(2)-adrenoceptors in the somatodendritic region of the locus coeruleus was assessed by using the ID(50) of clonidine. Results indicated that the firing rate of locus coeruleus noradrenergic neurons was the same in risperidone-treated rats and controls. Similarly, the ID(50) for (+/-)-2,5-dimetoxy-4-iodoamphetamine (DOI), an agonist of 5-HT(2) receptors which inhibits the activity of locus coeruleus neurons by acting on these receptors, did not show any differences between the firing rate of these neurons in risperidone treated rats and controls. Unlike controls, chronically treated rats showed a significant decrease in norepinephrine levels in the prefrontal cortex. The decreased release of norepinephrine following continuous risperidone administration could be explained by the sustained increase in locus coeruleus neuronal activity after chronic risperidone administration. This low norepinephrine level in the prefrontal cortex may contribute to the relief of certain negative schizophrenic symptoms and to the improvement of cognitive function.

Permanent alteration of central noradrenergic system by prenatally administered amphetamine.

Amphetamine-induced psychosis is frequently associated with a chronic, high-dose, daily pattern of amphetamine exposure. In the present study we investigate the effects of prenatal exposure to amphetamine during the development of the central noradrenergic (NA) system in adult rats. Pregnant Wistar rats were given 4 mg/kg/day of d-amphetamine (AMPH), subcutaneously, from gestational day 8 to 21. No additional drug treatment was given to the animals until the beginning of the experiments, in adult, control and prenatally amphetamine treated rats. Since we study the electrophysiology and neurochemistry of the central NA system, we investigated the electric activity of locus coeruleus (LC) norepinephrine (NE) neurons and the levels of NE on prefrontal cortex. What we found, was a decreased number of spontaneously active cells in the LC nucleus with a lower pattern of discharge whereas, the basal levels of NE in the prefrontal cortex, was greatly increased. The increased cortical NE levels, observed in the present study may account for the proposed hyperactive NA system being responsible for some psychotic symptoms observed in paranoid schizophrenia. Besides, our results concerning the permanent alteration observed in the central NA system, in rats prenatally exposed to amphetamine, raise the possibility that this animal model may be useful to further study the neurobiologic alterations underlying certain clinical features involved in some psychosis such as schizophrenia.

Fighting during shock exposure attenuates the reduction in the number of low-affinity GABAA sites in the cerebral cortex.

Rats were submitted either singly or in pairs to a series of foot-shocks. Immediately following the stress event, animals were sacrificed and the binding of low-affinity GABAA sites assayed in the cerebral cortex. A reduced number of sites was observed in rats singly shocked. However, rats shocked in pairs and thus afforded the opportunity to fight during the shock did not present changes in the density of GABAA receptors as compared to unstressed animals. Our data may suggest that fighting during an aversive event could decrease the deleterious consequence of a highly stressful experience.

Perinatal protein deprivation enhances the anticonflict effect measured after chronic ethanol administration in adult rats.

The anticonflict effects of ethanol, diazepam and pentobarbital were evaluated in adult rats fed a low protein diet during the perinatal period in the plus-maze test, after single injections and following chronic ethanol administration (1 g.kg-1.d-1 for 30 d). Reactivity to the anticonflict effect of these drugs was similar in control and protein-deprived rats after acute treatment. After chronic ethanol administration, control rats showed tolerance to ethanol and cross-tolerance (i.e., lower reactivity) to the anxiolytic effect of diazepam and pentobarbital. Conversely, protein-deprived rats showed greater reactivity to ethanol and lack of cross-tolerance to diazepam and pentobarbital following chronic ethanol treatment. A significantly greater density of cortical gamma-aminobutyric acid receptors subtype A (GABA-A) was detected in protein-deprived rats after chronic ethanol administration compared with the density after chronic saline treatment, whereas no differences were observed in nourished controls. This suggests that the greater anxiolytic activity detected in protein-deprived rats may correlate with higher GABA-A receptor density.

Antidepressants reverse the inhibition of shock-induced aggression elicited by a prior inescapable shock.

Animals were exposed to long-duration inescapable shock (IS) and six days later submitted in pairs to a foot-shock session in order to induce shock-elicited aggression (SIF). Shocked rats subsequently displayed a lower aggressive response as compared to unshocked animals. This reduction was prevented by repeated treatment with different antidepressant drugs administered either prior or following IS exposure. In addition, rats chronically administered with antidepressant drugs before the IS showed less inactivity during the application of the uncontrollable aversive event. These data indicate that persistent administration with these pharmacological compounds prevent the induction and impede the further expression of the reduced aggressive response induced by a previous IS.

Behavioral reactivity following 5-MeODMT administration in 5,7-DHT-pretreated killer rats.

Grouped, nonkiller and killer animals were centrally injected either with vehicle or with 5,7-dihydroxytryptamine. After a period of 7-10 days, forepaw treading and hindlimb abduction were induced by 5-MeODMT administration in all sham and lesioned rats. As expected, behavioral supersensitivity was observed in grouped and nonkiller lesioned rats. A reduced increase in 5-MeODMT-induced behaviors was obtained in killer lesioned animals. 5-HT uptake studies showed a comparable reduction of 5-HT uptake within all the lesioned rats. This evidence suggests an altered capacity to promote adaptive changes on 5-HT sites in killer rats following the destruction of central serotonergic fibers.

Perinatal undernutrition affects brain modulatory capacity of beta-adrenergic receptors in adult rats.

Rats submitted to a protein deprivation schedule from the perinatal period until 50 d of age (dams and/or rats fed an 8% casein diet) and then fed a commercial nonpurified diet for at least 90 d were assayed to evaluate the up- and down-regulation of beta-adrenergic receptors in brain structures following prolonged (7 d) treatment with propranolol or desipramine, drugs that induce changes in receptor density. Propranolol produced up-regulation (increased Bmax) in the frontal cortex of both control and deprived animals, whereas desipramine treatment did not induce down-regulation in the frontal cortex or hippocampus of experimental rats, as it did in control rats. The lack of the down-regulation effect in response to desipramine treatment in deprived rats may be an alteration of adaptive mechanisms, which may contribute to the behavioral abnormalities attributed to early undernutrition.

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

A behavioral reactivity study on 5-HT1 and 5-HT2 sites of isolated killer and non-killer rats and on raphe lesioned killer and non-killer animals was undertaken, 5-HT1 reactivity was measured by a rank intensity scale on the forepaw treading and hind-limb abduction induced by 5-MeODMT. 5-HT2 reactivity was determined by the "shaking" behavior following 5-HTP. No behavioral differences on 5-HT1 and 5-HT2 sites were observed between isolated killer or non-killer animals. Similarly, comparable values of "shakes" were obtained on killer and non-killer lesioned rats. On the contrary, 5-MeODMT, induced a lower behavioral response on lesioned killer as compared to lesioned non-killer. This different behavioral response can not be explained by a probable difference of 5-HT terminals denervation since a similar reduction of 5-HT brain uptake was observed between both groups of rats. Finally, the decreased reactivity of 5-HT1 sites may be an index of a lower 5-HT neurotransmission and could therefore provide an explanation of the appearance of muricidal activity in some but not in all the lesioned rats.

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

A behavioral reactivity study on 5-HT1 and 5-HT2 sites of isolated killer and non-killer rats and on raphe lesioned killer and non-killer animals was undertaken, 5-HT1 reactivity was measured by a rank intensity scale on the forepaw treading and hind-limb abduction induced by 5-MeODMT. 5-HT2 reactivity was determined by the [quot ]shaking[quot ] behavior following 5-HTP. No behavioral differences on 5-HT1 and 5-HT2 sites were observed between isolated killer or non-killer animals. Similarly, comparable values of [quot ]shakes[quot ] were obtained on killer and non-killer lesioned rats. On the contrary, 5-MeODMT, induced a lower behavioral response on lesioned killer as compared to lesioned non-killer. This different behavioral response can not be explained by a probable difference of 5-HT terminals denervation since a similar reduction of 5-HT brain uptake was observed between both groups of rats. Finally, the decreased reactivity of 5-HT1 sites may be an index of a lower 5-HT neurotransmission and could therefore provide an explanation of the appearance of muricidal activity in some but not in all the lesioned rats.