Luigi Cervo

Effects of dopaminergic and glutamatergic receptor antagonists on the acquisition and expression of cocaine conditioning place preference

A balanced conditioning place preference (CPP) paradigm was used to study the role of dopamine D1 and D2 and glutamatergic NMDA and AMPA/kainate receptors on the acquisition and expression of cocaine place conditioning. The D1 receptor antagonist SCH 23390 (0.1-0.2 mg/kg i.p.), administered before cocaine during the training phase, significantly blocked the establishment of place conditioning (acquisition) but had no effect when administered before testing for place preference in the absence of cocaine (expression). Similar results were obtained with the non-competitive NMDA receptor antagonist MK-801 (0.1-0.5 mg/kg i.p.). The D2 receptor antagonist (-)-sulpiride (50-100 mg/kg i.p.) had no effect on either acquisition or expression of cocaine CPP. The AMPA/kainate receptor antagonist DNQX, administered intracerebroventricularly (0.2-3 micrograms/10 microliters), blocked cocaine CPP when given before testing but not when given before cocaine during the training trials. The results suggest that dopaminergic D1 (but not D2) and glutamatergic NMDA receptors are involved in the primary rewarding properties of cocaine (as assessed by the establishment of CPP) whereas the AMPA/kainate receptors are important only for the behaviour elicited by the stimuli previously associated with the drug action (CPP expression). The implications for the treatment of cocaine craving and relapse are discussed.

Genotype-Dependent Activity of Tryptophan Hydroxylase-2 Determines the Response to Citalopram in a Mouse Model of Depression

Polymorphism of tryptophan hydroxylase, the rate-limiting enzyme in the synthesis of brain serotonin (5-HT), is associated with less synthesis of brain 5-HT in DBA/2J and BALB/c than in C57BL/6J and 129/Sv mice. We selected the forced swimming test, a mouse model used to assess the antidepressant potential of drugs, and neurochemical techniques to study strain differences in the response to citalopram, a selective 5-HT reuptake inhibitor. Citalopram reduced immobility time in C57BL/6J and 129/Sv mice but had no such effect in DBA/2J and BALB/c mice. The drug reduced accumulation of 5-hydroxytryptophan (5-HTP), an indicator of 5-HT synthesis, in C57BL/6J and 129/Sv mice but much less in DBA/2J and BALB/c mice. Pretreatment with tryptophan raised 5-HTP accumulation and reinstated the antidepressant-like effect of citalopram in DBA/2J and BALB/c mice, whereas pharmacological inhibition of 5-HT synthesis prevented the effect of citalopram in C57BL/6J and 129/Sv mice. Because there were no strain differences in catecholamine synthesis, locomotor activity, and brain levels of citalopram at the end of the behavioral test, the results suggest that the failure of citalopram to reduce immobility time in DBA/2J and BALB/c mice is attributable to genotype-dependent impairment of 5-HT synthesis. Interstrain comparisons could probably be a useful strategy for understanding the mechanisms underlying the response to selective serotonin reuptake inhibitors.

8-hydroxy-2-(di-N-propylamino) tetralin, a selective serotonin1A receptor agonist, blocks haloperidol-induced catalepsy by an action on raphe nuclei medianus and dorsalis

The selective serotonin1A receptor agonist 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT) was studied for its ability to reverse haloperidol-induced catalepsy in rats. Given subcutaneously 8-OH-DPAT (0.06-0.5 mg/kg), dose-dependently antagonized the catalepsy induced by 1 mg/kg of haloperidol. Intraventricular injection of the serotonin (5-HT) neurotoxin 5,7-dihydroxytryptamine (5,7-DHT), which caused marked depletion of 5-HT in brain, did not change haloperidol-induced catalepsy per se, but completely antagonized the anticataleptic effect of subcutaneously administered 8-OH-DPAT. When injected directly into the median or dorsal raphe nucleus, 8-OH-DPAT, in doses ranging from 0.2 to 5 micrograms/0.5 microliter, reduced the catalepsy induced by haloperidol. The results suggest that the activation of 5-HT1A receptors, probably those located presynaptically on 5-HT-containing cell bodies, reduces the catalepsy induced by haloperidol.

Selective antagonism at dopamine D3 receptors attenuates cocaine-seeking behaviour in the rat

Dopamine (DA) D3 receptors have been suggested to play a role in mechanisms underlying the ability of drug-associated cues to induce drug-seeking behaviour. The present study investigated whether SB-277011-A, a selective DA D3 receptor antagonist, modulates reinstatement of cocaine-seeking behaviour induced by cocaine-associated stimuli. The study also explored whether or not this modulation is generable to seeking behaviours associated with a nutritive reinforcer such as sucrose. Separate groups of rats were trained to associate discriminative stimuli (SD) with the availability of cocaine or sucrose pellets vs. non-reward under a FR1 schedule of reinforcement. Each reinforced response was followed by a response-cue signalling a 20-s time-out (TO). After the self-administration training criterion was met, rats underwent extinction during which cocaine, sucrose pellets and SDs were withheld. Reinstatement tests, separated by 3 d during which rates of responding under extinction conditions remained at the criterion, were performed by presenting SDs non-contingently together with the contingent presentation of response-cues signalling a 20-s TO. Within- and between-subjects experimental designs revealed that 10 and 30 mg/kg SB-277011-A attenuated reinstatement of cocaine-seeking. SB-277011-A (10 mg/kg) did not modify conditioned reinstatement triggered by sucrose pellet-associated cues. These results, provided they can be extrapolated to abstinent human addicts, suggest the potential therapeutic use of selective DA D3 receptor antagonists for the prevention of cue-controlled cocaine-seeking and relapse.

Role of central serotonergic neurons in the effect of sertraline in rats in the forced swimming test

Sertraline, administered i.p. in single doses or as three injections in 24 h, significantly reduced the immobility of rats in the forced swimming test at 64 and 100 mumol/kg. The effect of three doses of 64 mumol/kg in 24 h was not modified in animals treated i.p. with metergoline (5 mg/kg) 3 h before testing. I.c.v. administration of 150 micrograms 5,7-dihydroxytryptamine, which depleted brain serotonin, or infusion of 6 micrograms 6-hydroxydopamine in the locus coeruleus, which markedly depleted noradrenaline in terminal regions, was also ineffective. The effect of 64 mumol/kg sertraline, once daily for 7 days, was not modified by i.c.v. 5,7-dihydroxytryptamine. The effect of three doses of 64 mumol/kg sertraline in 24 h was instead completely antagonized by 100 mg/kg sulpiride given 90 min before testing. The exact mechanism of this effect and its relevance for the favourable effects of sertraline in human depression remain to be clarified.

Multiple drug delivery hydrogel system for spinal cord injury repair strategies

The multifactorial pathological progress of spinal cord injury (SCI) is probably the main reason behind the absence of efficient therapeutic approaches. Hence, very recent highlights suggest the use of new multidrug delivery systems capable of local controlled release of therapeutic agents. In this work, a biocompatible hydrogel-based system was developed as multiple drug delivery tool, specifically designed for SCI repair strategies. Multiple release profiles were achieved by loading gel with a combination of low and high steric hindrance molecules. In vitro, in vivo and ex vivo release studies showed an independent combination of fast diffusion-controlled kinetics for smaller molecules together with slow diffusion-controlled kinetics for bigger ones. A preserved functionality of loaded substances was always achieved, confirming the absence of any chemical stable interactions between gel matrix and loaded molecules. Moreover, the relevant effect of the cerebrospinal fluid flux dynamics on the drug diffusion in the spinal cord tissue was here revealed for the first time: an oriented delivery of the released molecules in the spinal cord tract caudally to the gel site is demonstrated, thus suggesting a more efficient gel positioning rostrally to the lesion.

The role of the mesolimbic dopaminergic system in the despramine effect in the forced swimming test

The effects of sulpiride isomers injected into the nucleus accumbens on the anti-immobility activity of desipramine in rats were studied to clarify the role of dopamine receptors. (-)-Sulpiride 100 ng/0.5 microliters injected bilaterally into the nucleus accumbens 5 min before testing reduced the effect of a 7-day treatment with 10 mg/kg per day desipramine in the swimming test but 5 micrograms/0.5 microliter (+)-sulpiride injected in the same area had no effect. Fluphenazine, 5 micrograms/0.5 microliter, or 6-hydroxydopamine-induced depletion of dopamine in the nucleus accumbens also reduced the anti-immobility effect of desipramine. The data further support the hypothesis that dopamine transmission in the nucleus accumbens has a permissive role in the effect of desipramine in the forced swimming test.

Roles of 5-HT1A receptors in the dorsal raphe and dorsal hippocampus in anxiety assessed by the behavioral effects of 8-OH-DPAT and S 15535 in a modified Geller–Seifter conflict model

8-OH-DPAT [8-hydroxy-2-(di-N-propylamino)tetralin], a 5-HT(1A) receptor agonist, and S 15535 (4-benzodioxan-5-yl)1-(indan-2-yl)piperazine, a partial agonist at 5-HT(1A) receptors, were administered into the dorsal raphe nucleus and dorsal hippocampus and their behavioral effects were assessed in a modified Geller-Seifter conflict model. Injected into the dorsal raphe nucleus 8-OH-DPAT, 1 microg but not 0.04 or 0.2 microg 0.5 microl(-1), and S 15535, 2.5 microg but not 0.1 or 0.5 microg 0.5 microl(-1), significantly increased punished responding with no effect on rates of unpunished or time-out responding. WAY 100635, a selective 5-HT(1A) receptor antagonist, injected subcutaneously at 0. 3 mg kg(-1) 30 min before 1 microg 8-OH-DPAT or 2.5 microg S 15535 in the dorsal raphe, completely antagonized their effects on punished responding. At doses ranging from 1 to 10 microg microl(-1) injected into the CA1 region of the dorsal hippocampus neither 8-OH-DPAT nor S 15535 modified punished responding or the rates of time-out. At the highest doses, 8-OH-DPAT significantly reduced unpunished responding whereas S 15535 had the opposite effect. The results suggest that stimulation of 5-HT(1A) receptors in the dorsal raphe nucleus has anxiolytic-like effects whereas stimulation of postsynaptic receptors in the dorsal hippocampus has no anxiolytic or anxiogenic effects, at least judging from changes in rates of punished responding. These results are compatible with the hypothesis that 5-HT(1A) receptor agonists and partial agonists attenuate anxiety by reducing serotonergic transmission in brain areas innervated by the dorsal raphe nucleus.

c-Jun N-terminal kinase regulates soluble Aβ oligomers and cognitive impairment in AD mouse model.

Background: Neuropathological mechanisms in Alzheimer disease (AD) are partially unknown. Results: Chronic JNK inhibition with a cell-permeable peptide (CPP) rescues memory deficits, LTP impairment, and reduces Aβ oligomers in a mouse model that mimics AD. Conclusion: JNK is crucial in AD neurodegenerative mechanisms. Significance: CPPs offer an important tool to interfere with neurodegeneration. JNK is a promising target against AD. Alzheimer disease (AD) is characterized by cognitive impairment that starts with memory loss to end in dementia. Loss of synapses and synaptic dysfunction are closely associated with cognitive impairment in AD patients. Biochemical and pathological evidence suggests that soluble Aβ oligomers correlate with cognitive impairment. Here, we used the TgCRND8 AD mouse model to investigate the role of JNK in long term memory deficits. TgCRND8 mice were chronically treated with the cell-penetrating c-Jun N-terminal kinase inhibitor peptide (D-JNKI1). D-JNKI1, preventing JNK action, completely rescued memory impairments (behavioral studies) as well as the long term potentiation deficits of TgCRND8 mice. Moreover, D-JNKI1 inhibited APP phosphorylation in Thr-668 and reduced the amyloidogenic cleavage of APP and Aβ oligomers in brain parenchyma of treated mice. In conclusion, by regulating key pathogenic mechanisms of AD, JNK might hold promise as innovative therapeutic target.

Evidence of a preferential role of brain serotonin in the mechanisms leading to naloxone-precipitated compulsive jumping in morphine-dependent rats

Various drugs acting on brain serotonin or catecholamines were administered concurrently with morphine during the development of dependence or before naloxoneprecipitated withdrawal syndrome. Of the various drugs only cyproheptadine, a serotonin antagonist, and piribedil, a dopamine agonist, reduced the frequency of jumping (but not of diarrhea or ptosis) when administered with morphine during development of dependence. When administered before naloxone, d-fenfluramine, a serotonin releaser, markedly reduced jumping, but not diarrhea and ptosis, and clonidine blocked these latter signs without affecting the frequency of jumping. Of the other drugs examined only phenoxybenzamine reduced diarrhea in morphine-abstinent rats. It is suggested that serotonin is involved in the mechanisms which lead to compulsive jumping during naloxoneprecipitated withdrawal, whereas adrenergic sites on which clonidine acts are mainly involved in the expression of signs, such as ptosis and diarrhea. No clear evidence was obtained of a role for dopamine in the withdrawal signs studied.