Alberto Cozzolino

Involvement of adenosine A2A receptors in the induction of c-fos expression by clozapine and haloperidol.

Acute administration of the atypical antipsychotic clozapine induced a regional pattern of c-fos expression characterized by an increase in Fos–like-immunoreactivity (FLI) in the prefrontal and prelimbic/infralimbic cortices, nucleus accumbens, and lateral septum and a weak activation of FLI in the striatum. Haloperidol, similarly to clozapine, increased FLI in the nucleus accumbens and lateral septum, but it did not induce FLI in prefrontal and prelimbic/infralimbic cortices. Moreover, haloperidol increased FLI in the striatum. To gain insight into the mechanism by which clozapine and haloperidol induced FLI in these brain structures, we evaluated whether blockade of adenosine A2A receptors could influence these effects. The selective and high-affinity A2A receptor antagonist SCH 58261 (5 mg/kg) completely abolished FLI induced by clozapine (20 mg/kg) in all subdivisions of the nucleus accumbens (rostral pole, shell and core) and striatum, but did not affect the number of Fos-like positive neurons in the prefrontal, prelimbic/infralimbic cortices, and lateral septum. SCH 58261 (5 mg/kg) reduced FLI induced by haloperidol (0.1 mg/kg) in the striatum, lateral septum, and all nucleus accumbens subdivisions. In contrast, FLI induced by 0.5 mg/kg of haloperidol in the shell and core of the nucleus accumbens was not affected by SCH 58261. The results show that adenosine A2A receptors participate in the induction of FLI by clozapine and haloperidol and support the concept that A2A receptors are involved in the mediation of antipsychotic effects.

Blockade of muscarinic receptors potentiates D1 dependent turning behavior and c-fos expression in 6-hydroxydopamine-lesioned rats but does not influence D2 mediated responses

In rats with a unilateral 6-hydroxydopamine lesion of the dopaminergic nigrostriatal pathway, blockade of muscarinic receptors by scopolamine potentiates the contralateral turning induced by selective dopaminergic D1 agonists (SKF 38393, A 68930), but does not influence the contralateral turning induced by the D2 agonist LY 171555. Studies on the expression of the early gene c-fos as reflected by the immunohistochemical demonstration of the Fos protein, show that administration of scopolamine (5 mg/kg, i.p.) potentiates c-fos expression elicited by SKF 38393 (1.5 mg/kg, s.c.) in the caudate-putamen of the lesioned side. The results indicate that cholinergic transmission is differentially involved in the behavioral expression of D1 versus D2 receptor stimulation in a denervated condition and suggest that blockade of central cholinergic transmission might be useful in improving the antiparkinsonian efficacy of D1 receptor agonists.

l-Dopa stimulates c-fos expression in dopamine denervated striatum by combined activation of D-1 and D-2 receptors

Administration of L-dopa to unilaterally 6-hydroxydopamine-lesioned rats, activates the early gene c-fos in the lesioned caudate-putamen. D-1 receptor blockade by SCH 23390, prevented L-dopa-induced Fos-like immunoreactivity in the whole caudate-putamen, while D-2 receptor blockade by raclopride reduced Fos-like immunoreactivity only in the dorso-lateral portion. The results suggest that L-dopa induces c-fos primarily through an activation of D-1 receptors, while D-2 receptor stimulation plays a facilitatory influence on D-1-mediated c-fos expression.

Stimulation of dopamine transmission in the dorsal caudate nucleus by pargyline as demonstrated by dopamine and acetylcholine microdialysis and Fos immunohistochemistry

The effect of pargyline on dopamine neurotransmission was investigated by trans-striatal microdialysis combined with Fos immunohistochemistry. Pargyline, 75 mg/kg i.p., increased dopamine and acetylcholine output while drastically decreased dopamine deaminated metabolites. Administration of pargyline resulted in the appearance of Fos-positive nuclei distributed along a gradient around the dialysis probe. Pretreatment with the D1 antagonist SCH 23390 potentiated the effect of pargyline on dopamine output while preventing that on acetylcholine output and on Fos formation. Similarly, lack of calcium in the perfusion medium abolished the effect of pargyline on dopamine and acetylcholine output and on Fos formation. In rats not implanted with dialysis probes pargyline administration resulted in only rare Fos-positive nuclei in the dorsal caudate. The present study indicates that pargyline stimulates dopamine transmission in the dorsal caudate in the area around the dialysis probe but not distant from the fibre or in unimplanted rats. This effect appears to reflect an interaction between the drug-induced changes and those locally elicited by the probe.

Combined Microdialysis and Fos Immunohistochemistry for the Estimation of Dopamine Neurotransmission in the Rat Caudate‐Putamen

Abstract: Extracellular dopamine (DA) concentrations estimated by transcerebral dialysis and D1‐dependent c‐fos expression, as demonstrated by Fos immunohistochemistry, were studied after blockade of DA reuptake by GBR‐12909. Rats implanted with dialysis probes in the dorsal caudate‐putamen did not show any Fos‐positive neuronal labeling in the implanted area or in the rest of the caudate‐putamen. Administration of GBR‐12909 dose‐dependently increased DA output in dialysates and resulted in the appearance in the caudate‐putamen of Fos‐positive neurons whose density was related to the dose of GBR‐12909 and to the increase in extracellular concentrations of DA. The D1 antagonist SCH‐23390 blocked GBR‐12909‐induced activation of Fos while potentiating the stimulation of DA output. The results show that following blockade of DA reuptake by GBR‐12909, the induction of Fos is related to stimulation of D1 receptors by extracellular DA. Combination of brain dialysis with Fos immunohistochemistry might provide a method for estimating the functional significance of extracellular DA as measured by brain microdialysis.

Hippocampal θ activity after systemic administration of a non-peptide δ-opioid agonist in freely-moving rats: relationship to D1 dopamine receptors

Abstract Hippocampal θ activity was acquired and processed off-line from digitized EEG recordings after subcutaneous (s.c.) administration of the non-opioid δ agonist BW 373U86 (0.5–2.5 mg/kg) in freely-moving rats. Relative θ power spectral analysis, implemented by a signal processing software, showed that BW 373U86 induced a dose-dependent increase in the slow component of θ band (Type 2 θ), while movement-related fast θ band (Type 1 θ) failed to show significant changes. Moreover, the increase in relative Type 2 θ power showed a maximal change at 1 mg/kg of BW 373U86, while higher doses, although effective in increasing relative Type 2 θ, induced locomotion and irregularly increased Type 1 hippocampal θ activity. The administration of 10.0 mg/kg of the δ antagonist Naltrindole (NLI) 30 min before BW 373U86, abolished hippocampal Type 2 θ increase. The rise of relative Type 2 θ power induced by BW 373U86 (1–2.5 mg/kg) was greatly attenuated by 0.1 mg/kg of the selective dopamine (DA) D1 antagonist SCH 23390. Administration of 0.1 mg/kg of SCH 23390 alone did not modify hippocampal Type 2 θ. These results indicate that δ receptors modulate the expression of hippocampal Type 2 θ and dopamine, through D1 receptors, exerts a permissive role on this influence.

Positive and negative interactions in the behavioural expression of D1 and D2 receptor stimulation in a model of Parkinsonism: role of priming.

Previous exposure to a dopaminergic agonist (priming) strongly potentiates contralateral turning behaviour in response to D1 and D2 agonists in unilaterally 6-hydroxydopamine-lesioned rats. In order to study the influence of priming on the behavioural interaction of D1 and D2 receptors, we examined the effect of selective D1 and D2 receptor blockade on the contralateral turning induced by the mixed D2/D2 agonist apomorphine in drug-naive and primed 6-hydroxydopamine-lesioned rats. In drug-naive rats, apomorphine induced a dose-related, apparently monophasic rotation curve. Administration of selective D1 (SCH 23390) or D2 (raclopride) antagonists abolished the contralateral turning induced by 0.1 mg/kg of apomorphine and partially inhibited that induced by 0.5 mg/kg. In primed rats low doses of apomorphine (0.05 mg/kg) induced an apparently monophasic contralateral turning which was reduced by D1 receptor blockade and completely abolished by D2 receptor blockade; a higher dose of apomorphine (0.1 mg/kg) instead elicited a biphasic (two-peak) pattern of rotation. After this dose of the agonist, blockade of D1 or D2 receptors abolished the second peak of rotation but, while D1 blockade reduced the total number of turns, D2 blockade failed to do so. Quantitative analysis of the interaction between D1 and D2 receptors in the overall turning effect, as well as in the time-course of turning behaviour, indicates that D1 and D2 receptors interact not only positively but also negatively. After higher doses of apomorphine, both negative and positive interactions take place sequentially during the time-course of apomorphine action and provide a clue for explaining the two-peak pattern of rotation observed after apomorphine in rats previously exposed to the drug.

Blockade ofNMDA receptors differentially affectsD-1 andD-2 mediated turning behavior in the 6-hydroxydopamine model of Parkinson.

SummaryIn rats with unilateral lesion of the nigrostriatal dopaminergic pathway, L-DOPA induces contralateral turning through activation of denervated D-1 and D-2 receptors. Blockade of N-methyl-D-aspartate (NMDA) receptors by the non-competitive antagonist (+)MK-801, potentiated the contralateral turning induced by L-DOPA as well as that induced by the D-1 agonist SKF 38393, while D-2 mediated turning was almost completely inhibited. Administration of the D-1 antagonist SCH 23390 blocked (+)MK-801-induced potentiation of L-DOPA contralateral turning, confirming the D-1 nature of the effects observed. Immunohistochemical studies on the early gene c-fos, which is known to be activated by stimulation of supersensitive D-1 receptors, revealed sparse c-fos positive nuclei in the lesioned CPu after SKF 38393, while after combined administration of (+)MK-801 and SKF 38393 dense labelling was obtained. Blockade of NMDA receptors, differentially affects D-1 and D-2 mediated turning behavior, suggesting that different neuronal pathways are involved in the mediation of D-1 and D-2 responses.

Priming of the Behavioral Expression of Dopamine-Receptor Supersensitivity in the Basal Ganglia: Pharmacological and Biochemical Studies

In drug-naive rats unilaterally lesioned with 6-hydroxydopamine (6-OHDA) from 17 days, stimulation of D-1 receptors by SKF 38393 (2 mg/kg s.c.) failed to induce contralateral turning. Administration, three days before, of a single dose of a dopaminergic agonist which elicited contralateral turning, made SKF 38393 very active in producing contralateral turning (priming). The effectiveness of the D-1/D-2 agonist apomorphine as a primer of SKF 38393-induced turning was critically dependent on the interval between the administration of the two agonists. Effectiveness was minimal after 3 h, increased after 6–12 h, peaked at 72 h and was reduced after 10 days. In drug-naive 6-OHDA lesioned rats, administration of the selective antagonists SCH 23390 (D-1) or raclopride (D-2) abolished apomorphine induced contralateral turning, while in primed rats both antagonists only modified the pattern of apomorphine turning but failed to abolish it. Analysis of D1 receptor binding in striata of drug-naive and primed rats, showed no change in the Bmax and Kd, while dopamine stimulated adenylate cyclase showed a decreased Km, for dopamine in the lesioned side after priming. Finally, administration of the N-Methyl-D-Aspartate (NMDA) receptor antagonist (+) MK 801 in conjunction with apomorphine, prevented the ability of apomorphine to act as a primer, indicating that the NMDA receptor exerts a permissive role on priming.

The Influence of Priming on the Behavioral Expression of Dopamine Receptor Supersensitivity in Basal Ganglia

The D-1 agonist SKF 38393 (2 mg/kg s.c.) failed to induce contralateral turning in drug-naive rats, lesioned unilaterally with 6-hydroxydopamine (6-OHDA) from 17 days, while elicited intense contralateral turning 90 days post lesion. Priming with a single administration of a dopaminergic (DA) agonist which elicited contralateral turning by itself, made SKF 38393 very active in producing contralateral turning in rats, lesioned with 6-OHDA from 17 days. The effectiveness of the D-1/D-2 agonist apomorphine as a primer of SKF 39393 induced turning was critically dependent on the interval between the administration of the two agonists. Effectiveness was minimal with an interval of 3 h, increased after 6–12 h, peaking at 72 h and was reduced after 10 days. Priming took place also when the primer and SKF 38393 were administered in different environment, indicating that priming in not dependent from behavioral conditioning. Finally, administration of the N-Methyl-D-Aspartate (NMDA) receptor antagonist (+) MK 801 in conjunction with apomorphine prevented its ability to act as a primer, indicating that the NMDA receptors exert a permissive role on priming.