Behavioral activity of some novel aporphines in rats with 6-hydroxydopamine lesions of caudate or nucleus accumbens

Fabrication and Characterization of Dissolving Microneedles for Transdermal Drug Delivery of Apomorphine Hydrochloride in Parkinson's Disease

PURPOSE

We fabricated and characterized polyvinyl alcohol (PVA)-based dissolving microneedles (MNs) for transdermal drug delivery of apomorphine hydrochloride (APO), which is used in treating the wearing-off phenomenon observed in Parkinson's disease.

METHODS

We fabricated MN arrays with 11 × 11 needles of four different lengths (300, 600, 900, and 1200 μm) by micromolding. The APO-loaded dissolving MNs were characterized in terms of their physicochemical and functional properties. We also compared the pharmacokinetic parameters after drug administration using MNs with those after subcutaneous injection by analyzing the blood concentration of APO in rats.

RESULTS

PVA-based dissolving MNs longer than 600 μm could effectively puncture the stratum corneum of the rat skin with penetrability of approximately one-third of the needle length. Although APO is known to have chemical stability issues in aqueous solutions, the drug content in APO-loaded MNs was retained at 25°C for 12 weeks. The concentration of APO after the administration of APO-loaded 600-μm MNs that dissolved completely in skin within 60 min was 81%. The absorption of 200-μg APO delivered by MNs showed a Tmax of 20 min, Cmax of 76 ng/mL, and AUC0-120 min of 2,829 ng・min/mL, compared with a Tmax of 5 min, Cmax of 126 ng/mL, and AUC0-120 min of 3,224 ng・min/mL for subcutaneous injection. The bioavailability in terms of AUC0-120 min of APO delivered by MNs was 88%.

CONCLUSION

APO-loaded dissolving MNs can deliver APO via skin into the systemic circulation with rapid absorption and high bioavailability.

Reliability of behavioral test with fish: How neurotransmitters may exert neuromodulatory effects and alter the biological responses to neuroactive agents

Toxic agents such as pharmaceuticals and pesticides are continuously dispersed especially in the aquatic environment, as a result of human use. Their presence in the environment presents serious concerns, since these compounds interfere with the normal function of the central nervous system (CNS), causing behavior alterations, whose consequences are difficult to predict. However, behavioral responses, even those that occur after exposure to neurotoxic agents, might be modulated by the release of neurotransmitters in the brain of exposed organisms, making even more difficult to ascertain the real consequences of pollution by neurotoxic or neuroactive agents. This study aimed to understand the potential of dopamine as neuromodulator in cases of acute exposure to a pesticide (the carbamate carbofuran) and to a therapeutic agent (the benzodiazepinic drug diazepam) in the freshwater fish Gambusia holbrooki. After acute exposure to both carbofuran and to diazepam it was possible to observe deleterious alterations in the motor function, reflected by significant reductions of both average speed and distance in exposed animals. These changes were later diminished and reverted by dopamine exposure. Despite the indications obtained from our experiments, more research is needed to clarify the consequences of these behavior alterations in a more integrative perspective, namely by adding behavioral endpoints of increased ecological relevance to the adopted experimental design.

Glutaminergic signaling in the caudate nucleus is required for behavioral sensitization to methylphenidate

Methylphenidate (MPD) is a widely prescribed psychostimulant for the treatment of attention deficit hyperactivity disorder, and is growing in use as a recreational drug and academic enhancer. MPD acts on the reward/motive and motor circuits of the CNS to produce its effects on behavior. The caudate nucleus (CN) is known to be a part of these circuits, so a lesion study was designed to elucidate the role of the CN in response to acute and chronic MPD exposure. Five groups of n = 8 rats were used: control, sham CN lesions, non-specific electrolytic CN lesions, dopaminergic-specific (6-OHDA toxin) CN lesion, and glutaminergic-specific (ibotenic acid toxin) CN lesions. On experimental day (ED) 1, all groups received saline injections. On ED 2, surgeries took place, followed by a 5-day recovery period (ED 3-7). Groups then received six daily MPD 2.5 mg/kg injections (ED 9-14), then three days of washout with no injection (ED 15-17), followed by a re-challenge with the previous 2.5 mg/kg MPD dose (ED 18). Locomotive activity was recorded for 60 min after each injection by a computerized animal activity monitor. The electrolytic CN lesion group responded to the MPD acute and chronic exposures similarly to the control and sham groups, showing an increase in locomotive activity, i.e. sensitization. The dopaminergic-specific CN lesion group failed to respond to MPD exposure both acute and chronically. The glutaminergic-specific CN lesion group responded to MPD exposure acutely but failed to manifest chronic effects. This confirms the CN's dopaminergic system is necessary for MPD to manifest its acute and chronic effects on behavior, and demonstrates that the CN's glutaminergic system is necessary for the chronic effects of MPD such as sensitization. Thus, the dopaminergic and glutaminergic components of the CN play a significant role in differentially modulating the acute and chronic effects of MPD respectively.

Selective bilateral lesion to caudate nucleus modulates the acute and chronic methylphenidate effects

The psychostimulant methylphenidate (MPD) is currently the most prescribed drug therapy for attention deficit hyperactivity disorder (ADHD) and is used by students as a cognitive enhancer. The caudate nucleus (CN) is a structure within the motive circuit where MPD exerts its effects, it is known to contain high levels of dopaminergic cells and directly influence motor activity. The objective of this study was to understand the role of CN in response to acute and chronic administration of MPD. Specific and non-specific bilateral ablations were created in the CN using electrolytic lesion and 6-Hydoxydopamine (6-OHDA). Four groups of rats were used: control (n=4), sham (n=4), CN electrolytic lesion group (n=8) and CN 6-OHDA injected group (n=8). On experimental day one (ED 1) all rats received a saline injection and baseline locomotive activity was recorded. On ED 2 and ED 3 CN sham, electrolytic lesion and/or 6-OHDA injected groups were made followed by four to five days recovery (ED 3-7), followed by six daily 2.5 mg/kg MPD injections (ED 9-14), three days of washout (ED 15-17) and an MPD re-challenge of drug proceeding the washout days (ED 18). Locomotor activity was obtained at ED 1, 8, 9, and 18 using an open field assay. The results show that the CN electrolytic lesion group responded to the acute and chronic MPD administration similar to the control and sham group, while the CN 6-OHDA injected group prevented the acute and the chronic effects of MPD administration. One possible interpretation why nonspecific electroyltic lesioning of the CN failed to prevent acute and chronic effects of MPD administration is due to destruction of both the direct and the indirect CN pathways which act as an inhibitory/excitatory balance, electroylticelectroyltic. The selective dopaminergic lesioning prevented the effects of MPD administration suggesting that dopaminergic pathways in CN play a significant role in the effects of MPD.

Possible role of neuropeptides in obsessive compulsive disorder

The most consistent finding in clinical research of obsessive compulsive disorder (OCD) is the significant treatment advantage of potent serotonin uptake inhibitors (SUIs) over other classes of antidepressant and antianxiety drugs. Clinical neurobiological studies of OCD, however, have yielded limited and inconsistent evidence for significant fundamental abnormalities in monoamine systems including serotonin, norepinephrine and dopamine. Furthermore, one-third to one-half of OCD patients do not experience a clinically meaningful improvement with SUI treatment. Investigation beyond the monoamine systems may be necessary in order to more fully understand the pathophysiology of obsessive-compulsive symptoms and develop improved treatments. Evidence from preclinical studies suggests that neuropeptides may have important influences on memory acquisition, maintenance and retrieval; grooming, maternal, sexual and aggressive behavior; fixed action patterns; and stereotyped behavior; these phenomena may relate to some features of OCD. In addition, extensive interactions have been identified in the brain between neuropeptidergic and monoaminergic systems, including co-localization among specific populations of neurons. The purpose of this review is to present the current knowledge of the role of neuropeptides in the clinical neurobiology of children, adolescents and adults with OCD focusing primarily on results from pharmacological challenge and cerebrospinal fluid studies. Where evidence exists, developmentally regulated differences in neuropeptide function between children and adolescents versus adults with OCD will be emphasized; these data are intended to underscore the potential importance of establishing the age of symptom onset (childhood versus adult) in individual patients with OCD participating in clinical neurobiological investigations. Likewise, where information is available, differences in measures of neuropeptides between patients with non-tic-related OCD versus tic-related OCD will be highlighted; these data will demonstrate the critical value of diagnostic precision, as these two particular subtypes of OCD may have different neurochemical underpinnings.

A quantitative estimate of the role of striatal D-2 receptor proliferation in dopaminergic behavioral supersensitivity: the contribution of mesolimbic dopamine to the magnitude of 6-OHDA lesion-induced agonist sensitivity in the rat

Rats with unilateral depletions of neostriatal dopamine display increased sensitivity to dopamine agonists estimated to be 30 to 100 x in the 6-hydroxydopamine (6-OHDA) rotational model. Given that mild striatal dopamine D-2 receptor proliferation occurs (20-40%), it is difficult to explain the extent of behavioral supersensitivity by a simple increase in receptor density. This study was designed to investigate the quantitative aspects of the rotational behavior model utilizing constrained non-linear curve fitting routines. A dose-response curve for the rotational response arising from apomorphine stimulation of the normosensitive striatum was obtained in animals bearing unilateral lesions of striatal efferents (predominantly the striato-nigral pathway as previously described). After the control dose-response experiment, rats received a dopamine- (DA) depleting lesion in the contralateral hemisphere. In one group, 6-OHDA was infused into the medial forebrain bundle (MFB), a placement which is common in the literature and is known to deplete DA in both the striatum and nucleus accumbens. In a second group of rats, 6-OHDA was infused into the globus pallidus at a site which depletes caudate DA, but leaves n. accumbens DA relatively intact. The two experimental groups were tested in identical apomorphine-induced rotation dose-response experiments. The ED50's of the MFB- and caudate-lesioned rats were reduced by 36 and 5.8 fold, respectively, as compared to the control dose-response curve. The MFB and caudate lesions depleted striatal DA and produced a 30 and 36% increase in striatal D-2 binding sites, respectively. Modeling the behavioral and biochemical data with the null model for receptor occlusion indicated that increased striatal D-2 receptor density could account for the magnitude of behavioral supersensitivity in neither the MFB-lesioned group, nor even in the caudate-lesioned group. Thus simple up-regulation or D-2 receptors is unlikely to account for supersensitization as measured in the rotational model. Further, we suggest that quantitative modeling of such hypotheses is a valuable experimental technique for assessing relationships between biochemical and behavioral variables.

The neuroethological approach to obsessive-compulsive disorder

Advances in the neurobiology of obsessive-compulsive disorder (OCD) have raised the possibility that animal models in general and neuroethological models in particular may be useful in understanding and investigating this illness. One neuroethologically oriented model is that of canine acral lick dermatitis. In this report, we review the advantages and limitations of animal models of OCD. Preliminary data on the use of fluoxetine in the treatment of canine acral lick dermatitis are discussed.

Glucocorticoid regulation of neuropeptide mRNAs in the rat striatum

Expression of the preprotachykinin (PPT) mRNA and of the preproenkephalin (PPE) mRNA in the rat striatum has been assessed by in situ hybridization. The results demonstrate that the PPT mRNA is regulated by glucocorticoids such that adrenalectomized (ADX) animals replaced with corticosterone for 5 days expressed higher levels of the mRNA than ADX animals. The corticosterone-induced increase in striatal PPT mRNA was evident after 16 h, but not after 2 h, of corticosterone treatment of ADX animals. Elevation of circulating corticosterone levels in intact rats by acute restraint stress, or by corticosterone injection did not change the level of PPT mRNA in the striatum. In intact rats there was a diurnal variation in the level of striatal PPE mRNA expression; adrenalectomy resulted in a decrease in the mRNA level and did not abolish the diurnal variation in expression. The level of PPT mRNA in the striatum was also decreased in response to ADX, but there were no significant diurnal changes in the expression of the PPT mRNA either in the intact or in the ADX animals.

Behavioral effects of a dimethylsulfonium analog of dopamine after injection into the nucleus accumbens and the striatum

We have previously synthesized a chemical analog of dopamine (DA) in which the amine group has been replaced by a permanently charged dimethylsulfonium group. In the present study, we have determined whether this compound can exert DA agonist activity in the nucleus accumbens by comparing its effects with those of DA. When DA was injected into the nucleus accumbens of rats pretreated with nialamide, a monoamine oxidase inhibitor, there was marked stimulation of locomotor activity. Similarly, after intraaccumbens injection, the sulfonium analog also produced a marked stimulation of locomotor activity, and this effect was inhibited by the DA receptor antagonist, haloperidol (0.2 mg/kg, IP). However, the sulfonium analog did not stimulate locomotor activity when rats were pretreated with saline instead of nialamide. In addition, the stimulation of locomotor activity produced by the sulfonium analog in rats pretreated with nialamide was completely inhibited by the DA synthesis inhibitor, alpha-methyl-p-tyrosine. These results suggest that the stimulation of locomotor activity by the sulfonium analog is mediated indirectly through the release of DA. The sulfonium analog was able to produce marked contralateral circling after it was injected into the striatum of rats on the side of the brain in which DA nerve terminals were previously destroyed with 6-hydroxydopamine. Similarly, the sulfonium analog produced a marked stimulation of locomotor activity after it was injected into the nucleus accumbens of rats that were previously injected into this region with 6-hydroxydopamine. These results suggest that the sulfonium analog of dopamine can exert direct as well as indirect DA agonist activity.

Effects of serotonergic activity in nucleus accumbens septi on drug-induced circling

The effects of injections of 5-hydroxytryptamine (5-HT) into the nucleus accumbens and lesions of the nucleus accumbens induced by 5,7-dihydroxytryptamine (5,7-DHT) on drug-induced circling were investigated in rats with unilateral nigrostriatal lesions induced by 6-hydroxydopamine (6-OHDA). Injections of 5-HT (60-120 micrograms in 1 microliter; 1 microliter/min) into the nucleus accumbens caused a significant decrease in the circling response to 5.0 mg/kg of d-amphetamine (s.c.). The distribution of radioactivity after intracerebral injections of [3H]5-HT using these parameters showed that although much of the injected material was retained in the nucleus accumbens there was also considerable spread to the frontal cortex. However, in further behavioural experiments, using an injection procedure (0.5 microliter; 0.11 microliter/min) which caused much greater retention of injected material in the nucleus accumbens, with minimal spread to the frontal cortex, the ability of 5-HT injected into the accumbens to block amphetamine-induced circling was not diminished. Moreover, injections of 5-HT into the frontal cortex did not have any effect on amphetamine-induced circling. Lesions of the nucleus accumbens induced by 5,7-DHT caused a significant enhancement of the contralateral circling response to 1.0 mg/kg of apomorphine and a similar but non-significant tendency to increase the circling responses to several other doses of apomorphine and amphetamine. The results provide evidence that serotonergic mechanisms in the nucleus accumbens inhibit circling behaviour generated by unilateral activation of nigrostriatal dopaminergic mechanisms.

Role of nigral dopamine in amphetamine-induced locomotor activity

Dopamine (100 micrograms) injected into the substantia nigra pars reticulata of rats pretreated with the monoamine oxidase inhibitor, pargyline, resulted in a stimulation of locomotor activity. Bilateral injection of the dopamine antagonist haloperidol (5 micrograms) into the substantia nigra pars reticulata resulted in a reduction of the locomotor activity evoked by a low dose of amphetamine (1.25 mg/kg s.c.). These results suggest that the release of dopamine from nigral dendrites is involved in amphetamine-induced locomotor activity.

Nigral dopaminergic mechanisms in drug-induced circling

Unilateral injections of dopamine into the substantia nigra pars reticulata of pargyline-pretreated rats caused a prolonged, contralateral circling, similar in magnitude to that elicited by the injection of the same amount of dopamine intrastriatally. Contralateral circling was also elicited by the unilateral intranigral injection of amphetamine (after pargyline pretreatment), or by the dopamine agonists ergometrine and SKF 38393. In contrast, bilateral intranigral injection of the dopamine antagonist haloperidol greatly reduced the amphetamine-induced circling of rats with unilateral 6-hydroxydopamine-induced nigrostriatal lesions. These results support the hypothesis that dopaminergic mechanisms in the substantia nigra are involved in motor behavior.

Inhibition of drug-induced circling by GABA-ergic activity in the nucleus accumbens

Injections of GABA (125-500 micrograms in 1 microliter) or muscimol (40-200 ng in 1 microliter) into the nucleus accumbens markedly reduced the amphetamine-induced circling of rats with unilateral 6-hydroxydopamine (6-OHDA)-induced lesions of nigrostriatal dopamine neurons. The potency of muscimol was approximately 10(4) times that of GABA. Muscimol exerted a similar effect when injected in a smaller volume (0.5 microliter) at a slower rate (0.11 microliter/min), a procedure which was shown to reduce the spread of injected [3H]muscimol. Intra-accumbens injections of subconvulsive doses of picrotoxin had no effect on amphetamine-induced circling. Intra-accumbens muscimol (40 ng, 0.5 microliter, 0.11 microliter/min) also reduced the contralateral circling evoked by apomorphine in rats with unilateral 6-OHDA-induced lesions of the nigrostriatal pathway and bilateral 6-OHDA-induced lesions of the mesolimbic dopamine terminals. These results suggest that GABA-ergic activity in the nucleus accumbens exerts an inhibitory influence on drug-induced circling. At least part of this action is at a step beyond the release of dopamine from mesolimbic terminals.

Comparative assessment of dopamine agonist aporphines as anticonvulsants in two models of reflex epilepsy

The anticonvulsant action of various aporphine derivatives that act on dopamine receptors has been investigated in two genetically determined animal models--DBA/2 mice with sound-induced seizures and baboons Papio papio with photically-induced seizures. Protection against the clonic and tonic phases of the seizures response in DBA/2 mice was seen for 15-60 min after (-)2,10,11-trihydroxy-N-n-propylnoraporphine (1.25 mg/kg) and (-)10,11-methyl-enedioxy-N-n-propylnoraporphine (0.625-1.25 mg/kg) and for 30-60 min after (-)2,10,11-trihydroxyaporphine (31.25 mg/kg). Short-lasting protection (up to 30 min) was seen following (-)2,10,11-trihydroxy-N-ethyl-noraporphine (1.25-6.25 mg/kg). Changes in audiogenic seizure susceptibility were accompanied by piloerection, ptosis and loss of spontaneous locomotor and exploratory behaviour. No protection was seen after (-)norapomorphine (0.05-18.75 mg/kg). All the compounds (including norapomorphine) significantly lowered rectal temperature, although the time course of this effect was often longer than that of protection against audiogenic seizures. In baboons, marked reductions in photomyoclonic responses were seen following (-)10,11-methylenedioxy-N-n-propylnoraporphine (0.25 mg/kg, lasting up to 2h); (-)2,10,11-trihydroxy-N-n-propylnoraporphine (0.5-2.5 mg/kg, lasting up to 7 h); (-)2,10,11-trihydroxyaporphine (5 mg/kg, duration of action 1-4 h) and (-)2,10,11-trihydroxy-N-ethylnoraporphine (6.25 mg/kg, lasting 2 h). Little change in responsiveness followed administration of (-)norapomorphine 1.25 or 6.25 mg/kg. Changes in photosensitivity were accompanied by yawning and pupil dilatation. (-)10,11-Methylenedioxy-N-n-propylnoraporphine (0.5-6.25 mg/kg) was also administered orally in baboons.(ABSTRACT TRUNCATED AT 250 WORDS)