帕金森病模型大鼠行为学改变与黒质致密部多巴胺能神经元存活率之间的相关性

目的探讨线刀损毁内侧前脑束建立的帕金森病模型大鼠行为学改变与黒质致密部多巴胺能神经元存活率之间的相关性。方法采用可伸缩线刀切断大鼠内侧前脑束建立单侧损伤的帕金森病大鼠模型;皮下注射阿朴吗啡后测试大鼠的旋转行为;取中脑黑质切片进行酪氨酸羟化酶免疫组织化学染色,通过计数黑质致密部酪氨酸羟化酶阳性神经元的数目得到多巴胺能神经元存活率。结果模型组大鼠损伤侧酪氨酸羟化酶阳性神经元的数目明显下降,而由阿朴吗啡诱导的旋转行为明显增加。结论线刀损毁术后4周,帕金森病模型大鼠由阿朴吗啡诱导的旋转行为和黒质致密部多巴胺能神经元存活率之间存在着明显的负相关。     

The effect of chronic levodopa on haloperidol induced behavioral supersensitivity in the guinea pig

The effect of chronic levodopa-carbidopa administration (200 mg/kg for 21 days) on guinea pigs rendered behaviorally supersensitive by the prior administration of haloperidol (.5 mg/kg for 21 days) was examined. Animals who showed an increased behavioral response to apomorphine after chronic haloperidol administration were treated with levodopa-carbidopa and then apomorphine - induced stereotypy was reexamined. Although the chronic levodopa control groups and the chronic haloperidol control remained supersensitive to the behavioral effect of apomorphine, the haloperidol-levodopa group's behavioral response to apomorphine returned to normal. Both chronic dopaminergic antagonist and agonist administration have been demonstrated to induce heightened apomorphine-induced stereotypy and this has been interpreted as a reflection of altered striatal dopamine receptor site sensitivity. The finding that the serial administration of a chronic dopaminergic antagonist followed by a chronic dopaminergic agonist results in a return to normal of a striatal dopamine receptor-dependent behavior suggests that these chronic treatments affect dopamine receptor sites by different mechanisms of action. Since neuroleptic induced dopaminergic supersensitivity in animals is an accepted model of tardive dyskinesia, levodopa may also reverse dopaminergic supersensitivity in patients and might be a potential therapeutic agent in tardive dyskinesia.     

Proerectile effects of apomorphine in mice

Dopaminergic pathways play a key role in the central control of sexual behavior. Stimulation of central dopaminergic receptors elicits penile erection in a variety of species and has been proposed as a treatment option for erectile dysfunction in humans. The present study investigated the proerectile effects of apomorphine in mice. In this species, subcutaneous injection of apomorphine (range: 0.11-110 microg/kg sc) elicited three different behavioral responses: erection, erection-like responses and genital grooming. Proerectile effects of apomorphine were dose-dependent. More than 50% of mice displayed erections after administration of 1.1-11 microg/kg of apomorphine sc. Proerectile effects of apomorphine were blocked by haloperidol, a central D2 antagonist, but not by domperidone, a peripherally active dopaminergic antagonist. We conclude that apomorphine elicits erection in mice. This effect is dose-dependent and due to activation of central D2 dopaminergic receptors. The mouse model may be useful for pharmacological approaches designed to provide a better understanding of the central mechanisms of penile erection and sexual behavior.     

DNA-DEPENDENT RNA POLYMERASES FROM RAT BRAIN, AND RNA SYNTHESIS IN GLIAL AND NEURONAL CELL-ENRICHED FRACTIONS, AFTER PROTEIN RESTRICTION

Abstract— An assay for the dopaminergic agonist, apomorphine, is described. The assay is capable of detecting as little as 3 pmol of apomorphine. The basis of the assay is the O-methylation of apomorphine utilizing S-[methyl-³H]adenosyl-L-methionine and a partially purified catechol-O-methyl transferase to form [methyl-³H]apocodeine. The radiolabeled apocodeine is purified by solvent partition. Following systemic administration of apomorphine, the compound is uniformly distributed throughout the brain of the rat: there is no selective accumulation of apomorphine in dopaminergic regions of the brain. The level of apomorphine found in the substantia nigra is as great as the level found in the caudate-putamen. This latter observation, in addition to a variety of other evidence, raises the possibility that some of the in vivo effects of apomorphine may occur via an action of the drug within the substantia nigra, rather than by an action within the caudate-putamen.     

The influence of beta-LPH fragments on alpha-MSH release: the involvement of a dopaminergic system

β-Endorphin was able to enhance plasma α-MSH levels in rats after intracerebroventricular injection. This effect could be inhibited by naloxone or by removing tyrosine from position 61 of the peptide. Neither α- and γ-endorphin nor their des-tyrosine analogs appeared to be able to modify plasma α-MSH levels. The stimulating effect of β-endorphin on plasma α-MSH levels could be completely blocked by a simultaneous injection of apomorphine, in an amount in which apomorphine itself had no effect on α-MSH levels in plasma. A single injection of haloperidol increased plasma α-MSH levels in a dose related manner. A dose of haloperidol, which caused an apomorphine antagonizable increase in plasma α-MSH, did not modify β-endorphin elevated α-MSH levels. A high concentration of haloperidol was able to stimulate the basal release of α-MSH from isolated pituitaries $\text{in bitro}$, whereas β-endorphin appeared to be inactive in this respect.These observations indicate a central opiate receptor-mediated influence of β-endorphin on α-MSH release and the possible involvement of a dopaminergic system, mediating the β-endorphin effect.     

Pharmacological profile of the abeorphine 201-678, a potent orally active and long lasting dopamine agonist

The central dopaminergic effects of an abeorphine derivative 201-678 were compared to those of apomorphine and bromocriptine in different model systems. After oral administration, this compound induced contralateral turning in rats with 6-hydroxydopamine induced nigral lesions and exhibited strong anti-akinetic properties in rats with 6-hydroxydopamine induced hypothalamic lesions. It decreased dopamine metabolism in striatum and cortex, but did not modify noradrenaline and serotonin metabolism in the rat brain. 201-678 counteracted the in vivo increase of tyrosine hydroxylase activity induced by gamma-butyrolactone. In vitro it stimulated DA-sensitive adenylate cyclase and inhibited acetylcholine release from rat striatal slices. This compound had high affinity for 3H-dopamine and 3H-clonidine binding sites. These results indicate that 201-678 is a potent, orally active dopamine agonist with a long duration of action. Furthermore it appears more selective than other dopaminergic drugs.     

Effect of monoamine receptor agonists and antagonists on cyclic AMP accumulation in human cerebral cortex slices.

In human cerebral cortex slices noradrenaline, isoproterenol (a beta-adrenergic agonist), dopamine, apomorphine (a dopaminergic agonist), and serotonin stimulated cyclic AMP formation: noradrenaline greater than or equal to isoproterenol greater than dopamine = apomorphine = serotonin. Clonidine (and alpha-adrenergic agonist) was ineffective in stimulating cyclic AMP formation in temporal cortex slices. The stimulatory effect of noradrenaline and isoproterenol was blocked by propranolol (a beta-adrenergic blocker) but not by phentolamine (an alpha-adrenergic blocker). Pimozide (a selective dopaminergic antagonist) inhibited the increase of cyclic AMP formation induced by dopamine or apomorphine but not that induced by noradrenaline, isoproterenol, or serotonin. Neither propranolol or phentolamine had any effect on dopamine- or serotonin-stimulated cyclic AMP formation. Chlorpromazine blocked the increase of cyclic AMP formation induced by noradrenaline, dopamine or serotonin, while cyproheptadine, a putative central serotonergic antagonist, was ineffective. These observations suggest that there may be at least two monoamine-sensitive adenylate cyclases in human cerebral cortex which have the characteristics of a beta-adrenergic and a dopaminergic receptor, respectively, and also possibly a serotonergic receptor.     

Effects of short- and long-acting dopamine agonists on sensitized dopaminergic neurotransmission in rats with unilateral 6-OHDA lesions

The effects of short and long-acting dopamine agonists on sensitized dopaminergic transmission in an animal model of Parkinson's disease were investigated. Rats with 6-hydroxydopamine (6-OHDA) lesions of the left nigrostriatal dopaminergic pathway were pre-exposed i.p. to 50 mg/kg methyl levodopa for 10 days. After a 7-day withdrawal period, these animals were treated with saline i.p., 0.05 mg/kg apomorphine s.c., or 0.5 mg/kg cabergoline i.p., once daily for 7 days. On the 8th day, rats in each treatment group received a challenge dose of 0.05 mg/kg apomorphine or saline s.c. The temporal changes in the number of rotations away from the 6-OHDA lesion side were evaluated after the challenge. The apomorphine challenge increased the number of rotations more markedly in the apomorphine pretreated rats than in the other pretreatment groups. In cabergoline pretreated rats, the number of rotations was significantly lower than that of saline-pretreated animals. Pretreatment with saline did not alter the apomorphine sensitivity of rotational behavior. These findings suggest that the repeated administration of long-acting dopamine agonists may reduce sensitized dopaminergic transmission in dopamine-depleted rats, whereas short-acting ones may further enhance sensitization of the transmission process.     

Catecholaminergic mechanisms of reinforcement: Direct assessment by drug self-administration

Reinforcing qualities in rats were shown by i.v. doses of two dopaminergic agonists, apomorphine and piribedil, and one noradrenergic agonist, clonidine, both in tests for primary reinforcement as seen in self-administration behavior and for conditioned reinforcement. Pretreatment with a dopaminergic blocker (haloperidol) interfered with the reinforcing effectiveness of apomorphine whereas an inhibitor of norepinephrine biosynthesis (U-14, 624) did not. Haloperidol also inhibited piribedil-based reinforcement. Pretreatment with an α-adrenergic blocking agent (phenoxybenzamine) inhibited the reinforcing effect of clonidine. These studies indicate that activation of either central dopaminergic or noradrenergic receptors can result in positive reinforcing effects.     

Apomorphine Does Not Alter Amphetamine-Induced Dopamine Release Measured in Striatal Dialysates

Amphetamine facilitates the release of dopamine from nerve terminals, but the mechanisms underlying this effect have not been fully delineated. The present experiments were designed to test the extent to which amphetamine-induced dopamine release is dependent on impulse flow and autoreceptor function in dopaminergic neurons. Rats were pretreated with a low dose of apomorphine (0.05 mg/kg) to inhibit dopamine neuronal activity, and the striatal dopaminergic response to amphetamine (0.5 mg/kg) was assessed by in vivo dialysis in freely moving animals. Consistent with previous results, apomorphine alone substantially decreased, whereas amphetamine increased, striatal dialysate dopamine concentrations. However, whereas apomorphine pretreatment decreased the locomotor response to amphetamine, the amphetamine-induced increase in dialysate dopamine was unaffected. These results indicate that amphetamine-facilitated dopamine release is independent of neuronal firing and autoreceptor regulation, consistent with the putative accelerative exchange-diffusion mechanism of amphetamine-induced dopamine release. Other possible mechanisms underlying the inhibitory effects of apomorphine on amphetamine locomotor activation are discussed.     

Low-dose apomorphine reduces serum homovanillic acid concentrations in schizophrenic patients

This study was carried out to evaluate the postulated dopaminergic autoreceptor regulatory effect in man of low-dose apomorphine. Behavior and serum homovanillic acid concentrations following low-dose apomorphine were investigated. Five medicated chronic schizophrenic patients had serum homovanillic acid concentrations measured by mass fragmentography before and after 0.005 mg/kg of apomorphine or saline placebo. Results demonstrate significant reductions in serum homovanillic acid concentrations in all five subjects following apomorphine as compared with placebo. These findings present direct evidence of a specific dopamine autoreceptor effect of low-dose apomorphine in schizophrenic patients.     

Microwave facilitation of domperidone antagonism of apomorphine-induced stereotypic climbing in mice

The dopaminergic agonist apomorphine produced dose-dependent stereotypic climbing behavior in mice housed in cages with vertical bars. This drug effect was competitively inhibited by systemic pretreatment with the centrally acting dopaminergic antagonist haloperidol but not by microwave irradiation (2.45 GHz, 20 mW/cm2, CW, 10 min) nor by systemic pretreatment with domperidone, a dopaminergic antagonist that only poorly penetrates the blood-brain barrier (BBB). Yet when mice were systemically pretreated with domperidone and then subjected to microwave irradiation (as above), the apomorphine effect was significantly reduced. Microwave irradiation also facilitated antagonism of the apomorphine effect by low and otherwise ineffective systemic pretreatment doses of haloperidol. Apomorphine-induced stereotypic climbing behavior was also reduced by domperidone administered intracerebrally, which bypassed the BBB. Exposure of intracerebral domperidone-pretreated animals to microwave irradiation failed to increase the degree of antagonism. These findings indicate that microwave irradiation can facilitate central effects of domperidone, a drug which acts mainly in the periphery. One possible explanation for these findings is that microwave irradiation alters the permeability of the BBB and increases the entry of domperidone to central sites of action.     

Neurochemical evidence for denervation supersensitivity: the effect of unilateral substantia nigra lesions on apomorphine-induced increases in neostriatal acetylcholine levels

Unilateral lesions of the nigro-neostriatal dopaminergic projection were induced by injections of 6-hydroxydopamine into the zona compacta of the substantia nigra. This resulted in a reduction of neostriatal dopamine to less than 6 percent of the control side. Two months later intraperitoneal injections of apomorphine (1 mg/kg) produced contralateral turning and a significant increase in neostriatal acetylcholine levels. The increase was significantly greater in the neostriatum ipsilateral to the lesion than in the intact side. Haloperidol (1 mg/kg) produced a significant decrease in neostriatal acetylcholine but this decrease did not differ between the “denervated” and intact neostriata. The nigral 6-hydroxydopamine lesions did not by themselves affect neostriatal acetylcholine levels. The fact that apomorphine produces a greater increase in neostriatal acetylcholine after lesions of the dopaminergic nigro-neostriatal projection supports earlier behavioral data suggestive of denervation supersensitivity of neostriatal dopaminergic receptors after these lesions.     

Naloxone potentiation of apomorphine-induced stereotypic climbing in mice and interaction with mu-, sigma- and kappa-opiate drugs

Pretreatment with the narcotic antagonist naloxone produced a dose-related potentiation of mouse stereotypic climbing behavior induced by the dopaminergic agonist apomorphine. In further experiments, mice were also pretreated with various drugs specific for mu-opiate receptors (morphine), sigma-opiate receptors (N-allylnormetazocine) and kappa-opiate receptors (ketocyclazocine). Doses of morphine that alone did not affect apomorphine-induced climbing antagonized naloxone potentiation of apomorphine. Doses of N-allylnormetazocine that did not influence apomorphine stereotypy also reversed naloxone potentiation of apomorphine. On the other hand, ketocyclazocine alone exerted a behavioral suppressant effect upon apomorphine- induced stereotypic climbing, however, these same doses failed to prevent naloxone potentiation of apomorphine.     

Central dopaminergic and serotoninergic systems in the regulation of adrenal tyrosine hydroxylase.

Administration of the dopamine receptor agonists apomorphine, piribedil and bromocryptine caused an increase in adrenal tyrosine hydroxylase (TH; tyrosine-3-monooxygenase, EC 1.14.16.2) which could be partially abolished by prior injection of the dopamine blocker haloperidol. Injection of L-dihydroxyphenylalanine, along with the decarboxylase inhibitor carbidopa, also led to a highly significant increase in adrenal TH activity. Intraventricular injection of 5,7-dihydroxytryptamine (DHT), which destroys serotonin neurons, doubled adrenal TH activity in both normal and hypophysectomized rats. Splanchnicotomy abolished this effect of DHT. The increase in enzyme activity mediated by DHT could be partially prevented by peripheral administration of L-5-hydroxytryptophan together with carbidopa. Blockade of serotoninergic functions with the antagonist methiothepin also increased adrenal TH activity. The interrelationship between the dopamine and the presumed serotonin system was investigated. Intraventricular injection of 6-hydroxydopamine partially prevented the DHT-induced increase in adrenal TH activity. Administration of haloperidol to DHT-treated rats had the same effect. This suggests that an intact dopaminergic system is required. When DHT and either apomorphine or piribedil were adminstered simultancously the dopamine agonist-induced increase was potentiated. An intact serotoninergic system is therefore not required for dopamine function. Thus, the increase in adrenal TH activity is associated with either stimulation of central dopamine receptors or destruction of serotonin neurons. It is suggested that dopaminergic and serotoninergic systems are involved in the regulation of adrenal TH and that these systems have net excitatory and inhibitory roles, respectively. Furthermore, the present evidence favors the view that the interaction between the two systems is sequential, with the serotonin system preceding the dopamine one.     

Dopaminergic modulation of the septo-hippocampal cholinergic system activity under stress

The effects of the dopaminergic agonist apomorphine or the antagonist sulpiride on high affinity choline uptake and newly synthesized acetylcholine release by hippocampal synaptosomal preparations, were examined in rats subjected to immobilization stress. Increased dopamine uptake by septal synaptosomal preparations was taken as evidence for increased mesoseptal dopaminergic activity in response to stress. While apomorphine treatment failed to alter choline uptake or acetylcholine release in unhandled rats, it did however prevent the stress-induced increase in these cholinergic parameters. In contrast, after treatment with sulpiride both choline uptake and acetylcholine release were increased in unhandled rats, as they were after acute stress. Acute stress of sulpiride treated rats however resulted in changes similar to those produced by administration of either sulpiride or stress separately. We conclude that the mesoseptal dopaminergic system plays an important role in modulating the activity of the septo-hippocampal cholinergic system under stress.     

The potentiating effect of naloxone upon apomorphine-induced hyperthermia

Intravenous or intracerebroventricular pretreatment with the narcotic antagonist naloxone in rabbits significantly enhanced the magnitude of the hyperthermic response to the dopaminergic agonist apomorphine. Naloxone did not potentiate the hyperthermic action of either amphetamine or lysergic acid diethylamide. Apomorphine-in induced hyperthermia was sensitive to antagonism by haloperidol, cyproheptadine and p-chlorophenylalanine. However in rabbits pretreated with any of the above antagonists, administration of naloxone five minutes prior to apomorphine challenge restored the hyperthermic effect of apomorphine. Increasing the dose of the apomorphine challenge likewise surmounted the antagonism. It was concluded from these data that naloxone exerts a potentiating influence upon apomorphine drug effect in naive rabbits as well as rabbits pretreated with antagonists of apomorphine-induced hyperthermia.     

Extracellular Striatal Concentrations of Endogenous 3,4-Dihydroxyphenylalanine in the Absence of a Decarboxylase Inhibitor: A Dynamic Index of Dopamine Synthesis In Vivo

Abstract: Basal levels of endogenous 3,4-dihydroxyphenylalanine (DOPA) were detected by HPLC coupled with coulometric detection in dialysates from freely moving rats implanted 48–72 h earlier with transversal dialysis fibers in the dorsal caudate. Because decarboxylase inhibitor is absent in the Ringer's solution, this method allows monitoring of basal output of dopamine (DA) and 3,4-dihydroxyphenylacetic acid, as well as DOPA. Extracellular DOPA concentrations were reduced by the tyrosine hydroxylase inhibitor α-methylparatyrosine (200 mg/kg, i.p.) and by the dopaminergic agonist apomorphine (0.25 mg/kg, s.c.). The dopaminergic antagonist haloperidol (0.2 mg/kg, s.c.) stimulated DOPA output by about 60% over basal values. γ-Butyrolactone, at doses of 700 mg/kg, i.p., which are known to block dopaminergic neuronal firing and which reduce DA release, stimulated DOPA output maximally by 130% over basal values. Tetrodotoxin, which blocks DA release by blocking voltage-dependent Na⁺ channels, increased DOPA output maximally by 100% over basal values. The results indicate that basal DOPA can be detected and monitored in the extracellular fluid of the caudate of freely moving rats by transcerebral dialysis and can be taken as a dynamic index of DA synthesis in pharmacological conditions.     

溶酶体抑制剂对小鼠行为学与黑质多巴胺神经元的影响

目的初步探讨溶酶体抑制剂对小鼠行为学及多巴胺神经元功能的影响。方法于小鼠右侧中脑黑质（SN）区,立体定向微量注入溶酶体抑制剂和蛋白酶体抑制剂。观察阿朴吗啡诱导的小鼠旋转行为改变以及行为学变化;检测黑质区酪氨酸羟化酶（TH）阳性细胞数。结果阿朴吗啡未能诱导出小鼠旋转行为。蛋白酶体抑制剂组为10～15圈。多巴胺损害程度与溶酶体的剂量相关。磷酸氯喹25μmol/L时多巴胺神经元几乎没有损害作用;50μmol/L时局部区域多巴胺神经元有轻微损害;100μmol/L时损害明显;200μmol/L时黑质区注射局部神经元损害最严重,黑质注射区未见有神经元存在。1～4周呈现出较为明显逐渐恢复的特点。结论溶酶体功能抑制与多巴胺神经元凋亡相关,不同剂量溶酶体抑制剂在不同时间对多巴胺神经功能的损害不同。     

Neuroleptic-induced dopamine hyposensitivity

In contrast to dopaminergic hypersensitivity induced by most neuroleptic drugs including fluphenazine, thioridazine induced hyposensitivity to subsequent apomorphine stereotypy in rats. The difference between thioridazine and fluphenazine may relate in part to anticholinergic properties of thioridazine, but appears to involve additional mechanisms. Differences in dopaminergic sensitization may be important to the management and prevention of tardive dyskinesia an iatrogenic disorder associated with chronic exposure to neuroleptics.