LY 171555-induced hyperdefensiveness in the mouse does not implicate benzodiazepine receptors

In naive mice the selective D2 agonist LY171555 dose-dependently (0.5–5 mg/kg) induces defensive responses toward non-aggressive conspecifics. In order to investigate possible anxiogenic properties of the D2 agonist, its behavioural effects were compared with those produced by the benzodiazepine receptor inverse agonist methyl--carboline-3-carboxylate(-CCM) in the elevated plus maze and in social interactions with non-aggressive opponents. When tested in the elevated plus maze, mice injected with LY 171555 (0.005–1 mg/kg) showed no decrease either of the number of entries or of the time spent in the open arms. At 5 mg/kg an actual increase of these two measures was observed. By contrast,-CCM (1–3 mg/kg) dose-dependently decreased both the number of entries and the time spent in the open arms without altering locomotion. The effects of-CCM were antagonized by the benzodiazepine receptor antagonist RO 15-1788 (3 mg/kg) showing a selective involvement of benzodiazepine receptors in their modulation. On the other hand,-CCM, (1–3 mg/kg) did not produce significant effects on defensive behaviour of mice interacting with non-aggressive opponents and the defensive responses of mice treated with 1 mg/kg LY 171555 were not prevented by 5 mg/kg chlordiazepoxide. These results show that DA D2-mediated hyperdefensiveness and anxiety modulated by benzodiazepine receptors are unrelated phenomena and suggest that this behavioural response may represent a model of those forms of fear-related reaction that do not respond to benzodiazepine treatment.     

SKF 38393 potentiates yawning induced by LY 171555: further evidence against the autoreceptor hypothesis of yawning

The effect of concurrent D-1 receptor stimulation by SKF 38393 on the expression o yawning elicited by D-2 receptor stimulation with LY 171555 was studied in the rat. A low dose of SKF 38393 (2.5 mg/kg SC), while failed to elicit yawning, potentiated the effectiveness of LY 171555 in eliciting yawning at all the doses tested (12.5, 25 and 50 g/kg SC) and this effect was abolished by SCH 23390 (0.012 mg/kg SC). The results indicate that in analogy with typical post-synaptic dopaminergic effects (hypermotility-stereotypy), yawning elicited by a D-2 agonist is facilitated by concurrent stimulation of D-1 receptors and therefore is consistent with previous evidence that yawning in response to a D-2 agonist is not mediated by autoreceptors.     

Chronic cocaine enhances defensive behaviour in the laboratory mouse: involvement of D2 dopamine receptors

C57BL/6 male mice injected with a challenge dose (20 mg/kg) of cocaine 72 h after the end of chronic intermittent treatment with the psychostimulant (two daily injections of 20 mg/kg for 10 days) exhibited a clear-cut increase in defensive upright and sideways postures and escape when confronted with a non-drugged conspecific. Treated mice spent 40% of time showing defensive acts over the 5-min testing session. Administration of the selective D2 receptor antagonist (–)-sulpiride (25 mg/kg) before the challenge dose of cocaine completely antagonized the increase in defensive behaviour, while the selective D1 receptor antagonist SCH 23390 (0.25–0.50 mg/kg) did not significantly affect defensive behavioural patterns. These results suggest the involvement of D2 receptors in cocaine-induced hyperdefensiveness. The hypothesis that alteration in D2 receptor functioning produced by chronic cocaine administration may produce hyperdefensiveness possibly due to altered perceptive processes is discussed.     

LY 171555-induced catalepsy and defensive behavior in four strains of mice suggest the involvement of different D2 dopamine receptor systems

The D2 dopamine receptor agonist LY 171555 (0.5 to 5 mg/kg) induces dose-dependent catalepsy in C57BL/6, DBA/2 and BALB/c inbred strains of mice. This effect shows marked strain-dependent differences, since the response of C57BL/6 is significantly lower than those presented by the other two inbred strains at all doses tested. In previous studies we have shown that the D2 agonist at doses ranging from 0.5 to 5 mg/kg induces hyperdefensive responses toward nonaggressive opponents in mice of the C57BL/6 and BALB/c but not of the DBA/2 strain. Here we report that the outbred CD1 mice present both cataleptic and hyperdefensive responses when challenged with LY 171555. Forty-five percent of individuals presenting high defensive response and 11% high cataleptic scores. No correlation was found between catalepsy and hyperdefensiveness in CD1 mice following administration of 1 mg/kg of the D2 agonist. These results suggest that D2 receptor stimulation results in different behavioral responses, possibly mediated by different dopaminergic systems, depending on the genetic make up.     

Role of genotype and dopamine receptors in behaviour of inbred mice in a forced swimming test

The role of genotype in the effects of selective D1 and D2 dopamine agonists and antagonists on behavioural despair (Porsolt's test) was studied. Mice of nine inbred strains showed significant interstrain differences in duration of immobility. The influence of dopaminergic drugs was assessed in six strains characterized by different levels of swimming activity. SKF 38393 (10 mg/kg), an agonist at D1 dopamine receptors, increased swimming activity, while the D1 antagonist SCH 23390 (0.2 and 0.5 mg/kg) reduced it, the effects being genotype dependent. The involvement of D2 dopamine receptors in the regulation of mouse behaviour in the forced swimming test was not so evident; the D2 agonist bromocriptine (10 mg/kg) produced no significant effect. The D2 agonist quinpirole (2.5 mg/kg) increased immobility in the majority of the mouse strains studied, while in CBA mice it resulted in a marked reduction of immobility. The D2 antagonist sulpiride (20 mg/kg) decreased immobility and increased active swimming only in two strains. The present results suggest a different role for D1 and D2 dopamine receptors in the regulation of swimming in the mouse.     

Potentiation of responses to AMPA on central neurones by LY392098 and LY404187 in vivo

Enhancement of AMPA receptor mediated synaptic excitation has the potential to aid in the treatment of several psychiatric conditions. To test such claims there is a need to develop more potent compounds than those presently available and to demonstrate that they cross the blood–brain barrier to affect responses at central AMPA receptors. We have now completed in vivo tests with two such compounds, the newly discovered biarylpropylsulfonamides, LY392098 and LY404187, on spinal and hippocampal neurones in anaesthetised rats. In the initial study on spinal neurones, LY392098 (30–1000 μg/kg i.v.) dose-dependently increased responses to iontophoretically administered AMPA but not those to NMDA. Subsequently in a more detailed follow-up study on hippocampal neurones, LY392098 (1–100 μg/kg i.v.) and LY404187 (1–100 μg/kg i.v.) enhanced in a dose-dependent manner responses to AMPA. Responses to NMDA were also enhanced but to a less extent. Such enhanced responses to NMDA, but not those to AMPA, were reduced by the NMDA antagonist, ketamine (0.5–1 mg/kg i.v.) whereas the selective AMPA antagonist, LY300168 (GYKI53655; 1 mg/kg i.v.), reduced responses to both NMDA and AMPA. LY392098 also potentiated the synaptic excitation of dentate granule cells following perforant path stimulation. These combined data show that, at doses not dissimilar to those affecting behavioural responses (1–1000 μg/kg; see accompanying papers), the two new drugs cross the blood–brain barrier to affect directly the sensitivity of central AMPA receptors and enhance synaptic excitation in vivo.     

In vivo assessment of release and metabolism of dopamine in the ventrolateral striatum of awake rats following administration of dopamine D1 and D2 receptor agonists and antagonists

The ability of specific dopamine (DA) receptor agonists and antagonists to modify the release and metabolism of DA in the ventrolateral striatum of awake rats was assessed using in vivo microdialysis. The specific DA D₂ receptor antagonist, raclopride (0.1, 0.5 and 2.0mg/kg, i.p.), dose-dependently increased release of DA and levels of the metabolites DOPAC and HVA, while the D₂ receptor agonist, quinpirole (0.03, 0.1 and 0.3 mg/kg), decreased levels of DA, DOPAC and HVA. The DA D₁ receptor antagonist, SCH23390 ([R + (+)-8-chloro-2,3,4,5-tetrahydro-3-methyl-5-phenyl-1H-3-benzazepin-7-o]) (0.01, 0.05 and 0.25 mg/kg), produced an increase in DA, DOPAC and HVA but of a lesser magnitude than raclopride. The D₁ agonist SKF38393 (1-phenyl-2,3,4,5-tetrahydro-(1H)-3-benzazepine-7,8-diol) (1.0, 3.0 and 10.0 mg/kg) failed to affect the release of metabolism of DA at any dose. These results support previous findings that activation of D₂ receptors has greater control over in vivo DA function, than drugs specifically affecting D₁ receptors.     

Biphasic firing response of nucleus accumbens neurons elicited by THPB-18 and its correlation with DA receptor subtypes

AIM: To investigate the possibility whether THPB-18 (l-12-shloroscoulerine) possesses the D1 agonist-D2 antagonist action on meso-accumbens-mPFC DA system. METHODS: Single unit spontaneous firing activity was recorded in the nucleus accumbens (NAc) neurons of naive and unilateral-6-hydroxydopamine (6-OHDA)-lesioned Sprague-Dawley rats. The effects of drugs applied intravenously or iontophoretically were determined by thechange of firing rates. RESULTS: Under normal conditions, the systemic administration of THPB-18 produced a decrease-increase biphasic firing pattern in the NAc neurons during cumulative doses. High dose of THPB- 18 was capable of reversing the inhibition induced by both D2 agonist LY171555 and D1/D2 agonist APO on NAc firing activity. Spiperone pretreatment could not block the high dose of THPB-18-induced firing rate increase, which wasreversed by the D1 selective antagonist SCH23390. The tested NAc neurons were effectively inhibited byiontophoretically applied THPB- 18 in 90 % of 6-OHDA-lesioned rats, while THPB- 18 caused variable effects on thefiring of NAc neurons in the neurons of unlesioned rats. The inhibitory effect of THPB-18 was blocked byiontophoretic application of SCH23390, but not D2 antagonist spiperone. CONCLUSION: Similar to l-stepholidine,THPB-18 also possesses the “D1 agonistic-D2 antagonistic“ dual action on the VTA-NAc DA system.AIM: To investigate the possibility whether THPB-18 (l-12-shloroscoulerine) possesses the D1 agonist-D2 antago-nist action on meso-accumbens-mPFC DA system. METHODS: Single unit spontaneous firing activity was re-corded in the nucleus accumbens (NAc) neurons of naive and unilateral-6-hydroxydopamine (6-OHDA)-lesionedSprague-Dawley rats. The effects of drugs applied intravenously or iontophoretically were determined by thechange of firing rates. RESULTS: Under normal conditions, the systemic administration of THPB-18 produced adecrease-increase biphasic firing pattern in the NAc neurons during cumulative doses. High dose of THPB- 18 wascapable of reversing the inhibition induced by both D2 agonist LY171555 and D1/D2 agonist APO on NAc firingactivity. Spiperone pretreatment could not block the high dose of THPB-18-induced firing rate increase, which wasreversed by the D1 selective antagonist SCH23390. The tested NAc neurons were effectively inhibited byiontophoreticaUy applied THPB- 18 in 90 % of 6-OHDA-lesioned rats, while THPB- 18 caused variable effects on thefiring of NAc neurons in the neurons of unlesioned rats. The inhibitory effect of THPB-18 was blocked byiontophoretic application of SCH23390, but not D2 antagonist spiperone. CONCLUSION: Similar to l-stepholidine,THPB-18 also possesses the “D1 agonistic-D2 antagonistic“ dual action on the VTA-NAc DA system.     

Chronic neuroleptics alter the effects of the D1 agonist SK&F 38393 and the D2 agonist LY171555 on oral movements in rats

Vacuous oral movements (OMs) in rats chronically administered haloperidol (HAL), fluphenazine (FLU), or no drug were studied following injections of one of three doses of either a D1 agonist (SK&F 38393) or a D2 agonist (LY171555). Oral movements were observed via closed-circuit television and simultaneously recorded using a computerized video analysis system which measured the distance between two fluorescent dots painted above and below the rat's mouth. SK&F 38393 induced a dose-dependent increase in tremorous oral movements and repetitive chewing movements in the controls; this effect was more pronounced in rats treated with chronic HAL or FLU, both during chronic neuroleptic treatment and even more so when they were tested after drug withdrawal following 5 or 14 months of chronic neuroleptic administration. Conversely, LY171555 produced an inhibition of oral activity at all dose levels in controls. This inhibition was attenuated during chronic administration of HAL or FLU, but returned to control levels (without any signs of supersensitivity) when the animals were retested shortly after discontinuation of neuroleptics. These results indicate that heightened oral movements in rodents following chronic neuroleptic administration can be more clearly induced by D1 than by D2 receptor activation.     

A pharmacological study of dopaminergic receptors in planaria

The dopaminergic receptors of planaria have been studied with pharmacological and biochemical criteria. Dopamine D₁ selective agonists (CY 208243 (10 μg/ml) and SKF 38393 (10 μg/ml)) induced in planaria typical screw-like hyperkinesias, that were inhibited by a D₁ antagonist (SCH 23390 (10 μg/ml)), but not by a D₂ antagonist (sulpiride (1000 μg/ml)). Dopamine D₂ selective agonists (PHNO (5 μg/ml), lisuride (5 μg/ml)) on the contrary induced a typical “C” like curling, that was inhibited by pretreatment with D₂ selective blocking agents, but not by D₁ selective blocking agents. With agonists with a D₁ /D₂ mixed action (apomorphine 60 μg/ml) or with amphetamine (100 μg/ml), the D₁ type movements appeared to be more evident.

Dopamine D₁-selective agonists, mixed action agonists or D₂-selective agonists, all induced a significant increase in levels of cAMP, that was prevented by pretreatment with the specific DA blocking agent.     

Receptor specificity of the 5HT2 receptor antagonist,LY53857

LY53857 is a potent antagonist at vascular 5HT₂ receptors that lacks prominent α₁ or dopamine antagonist activity. The present report investigates the interaction of LY53857 with other receptor mechanisms. LY53857 showed no agonist activity in the guinea pig trachea, guinea pig atria, guinea pig ileum, or rat vas deferens. Furthermore, LY53857 did not antagonize histamine (H₁) or β₂ receptors in the guinea pig trachea, β₁ in the guinea pig atria, muscarinic, or angiotensin I receptors in the guinea pig ileum. However, LY53857 did block α₂ receptors (?log K_B = 6.51) as determined by antagonism of the inhibitory effects of the selective β₂ agonist, UK-14,304, on the twitch response in the guinea pig ileum. LY53857 antagonized β₂ receptors at concentrations approximately 6000-fold higher than necessary to block 5HT₂ receptors (?log K_B = 10.3). Taken in concert, these data support the contention that LY53857 is a highly selective antagonist of 5HT₂ receptors, and that LY53857 is a useful tool with which to probe 5HT₂ receptors and serotonergic mechanisms.     

Potent, stereoselective, and brain region selective modulation of second messengers in the rat brain by (+)LY354740, a novel group II metabotropic glutamate receptor agonist

LY354740 is a highly potent and selective agonist for recombinant Group II mGlu receptors (mGlu2 and mGlu3), which has anxiolytic and drug withdrawal alleviating properties when administered systemically in rats and mice. The modulation of second messengers by LY354740 in rat brain tissues was investigated to understand the cellular basis for the pharmacological and potential therapeutic actions of LY354740. LY354740 potently decreased forskolin-stimulated cAMP formation in slices of the adult rat hippocampus (EC₅₀=22±3 nM) in a stereoselective manner. LY354740 (at 1 μM) greatly (>90%) suppressed forskolin-stimulated cAMP in the cerebral cortex, hippocampus, and striatum, while producing only partial suppression (about 50%) in midbrain regions and olfactory bulb, and no significant cAMP alterations in the cerebellum and brainstem regions. Inhibition of forskolin-stimulated cAMP formation was antagonized by (+)-α-methyl-4-carboxyphenylglycine [(+)MCPG], a competitive mGlu receptor antagonist. LY354740 did not alter phosphoinositide hydrolysis in the rat hippocampus per se, but potentiated stimulation of phophoinositide hydrolysis by the Group I mGlu receptor selective agonist 3,5-dihydroxyphenylglycine (DHPG) or stimulation of cAMP formation by the adenosine receptor agonist 5’-N-ethylcarboxamideoadenosine (NECA). These data indicate that LY354740 is a highly potent, efficacious, and selective Group II mGlu receptor (mGlu 2/3) agonist in the rat brain. The potent, stereoselective, and brain region selective actions of LY354740 on mGlu receptor linked second messenger systems likely underlie the in vivo potency and stereoselectivity of this compound in animal models. Received: 25 February 1998 / Accepted: 18 April 1998     

Amphetamine: Differential effects on defensive flight and motor behavior in the rat

As in previous research, hooded rats treated with an acute high dose of d-amphetamine sulfate (5 mg/kg free base) showed a dramatic defensive flight reaction to a novel stimulus (mechanical robot) that did not elicit flight from saline controls. Both the defense response and stereotypy behavior (repetitive movements and oral, licking chewing) were assessed at eight time periods after injection: 1, 15, 30, 45, 75, 105, 135, and 165 min. The defense response peaked early (15–30 min) after injection and showed a significant decline by 75 min, with no reemergence as stereotypy subsided. Stereotypy peaked later (45 min) and did not decline until 105 min. Tests in the absence of the robot provided a control for motor effects of the drug. Whereas stereotypy occurred in both Robot and No Robot conditions, the defense response occurred only in the Robot condition. These results were thought to provide further evidence that the effects of amphetamine on defensive flight could not be attributed to purely motor reactions. Thus, amphetamine-induced defensive flight may be an appropriate nharmacological model of affective psychosis. As such, it may be helpful in establishing differential pharmacological profiles for effective versus motor potencies of potential antipsychotic compounds.     

Regulation of BDNF expression in primary neuron culture by LY392098, a novel AMPA receptor potentiator

The effects of a novel AMPA receptor potentiator (LY392098) on the expression of brain-derived neurotrophic factor (BDNF) were examined in primary neuron culture. The addition of either AMPA or LY392098 to cortical neurons elicited a time and concentration dependent increase in mRNA encoding BDNF. Moreover, co-addition of subeffective concentrations of AMPA (1 μM) and LY392098 (1 μM) resulted in dramatic increases in both BDNF mRNA (>25-fold) and protein (7-fold) levels, whilst no changes in either NT-3 or NT-4 mRNA were detected. More modest (1.5–2.5-fold) elevations in BDNF mRNA and protein expression were also produced by combinations of AMPA and LY392098 in cerebellar granule cell neurons. In contrast, AMPA and LY392098, either alone or in combination, did not elevate BDNF mRNA levels in primary astroglial cultures. Maximum elevations in BDNF mRNA and protein were produced by 6–12 h of AMPA receptor activation 1–3 h of AMPA receptor activation were required to elevate BDNF mRNA levels. AMPA receptor-mediated increases in BDNF mRNA and protein were abolished by the AMPA antagonist, NBQX, but were unaffected by the NMDA antagonist, MK-801. In cortical neuron cultures, activation of both L-type Ca⁺² channels and mitogen-activated protein (MAP) kinases contribute to AMPA receptor-mediated increases in BDNF mRNA. The ability of LY392098 to increase the expression of BDNF in primary neuron culture indicates this and related biarylpropylsulfonamides may be useful in the treatment of neuropsychiatric disorders.     

Phencyclidine-induced impairment in attention and response control depends on the background genotype of mice: reversal by the mGLU<Subscript>2/3</Subscript> receptor agonist LY379268

Rationale Converging evidence implicates glutamate neurotransmission in attention and inhibitory response control.Objective To investigate how the background genotype contributes to glutamates effects on attention and response control, we examined how phencyclidine (PCP) affected the performance of a five-choice serial reaction time (5-CSRT) task in two inbred mouse strains, C57BL/6N and DBA/2N. We also tested a potent mGlu_2/3 receptor agonist, LY379268, against PCPs effects.Methods Mice were trained on a 5-CSRT task, which measures visual attention and response control until they reached asymptotic performance. Both strains of mice were then injected intraperitoneally with 0.5, 1.5 or 3.0 mg/kg PCP. Doses of 1.0 and 3.0 mg/kg of LY379268 were injected subcutaneously to vehicle or PCP-treated mice.Results At asymptotic performance DBA/2N mice were less accurate and made more anticipatory responses than C57BL/6N. PCP impaired accuracy (% correct) and increased perseverative responses of DBA/2N mice at 1.5 mg/kg. However, at doses up to 3.0 mg/kg it had no effect on these measures in C57BL/6N. In DBA/2N mice 1.5 mg/kg PCP increased anticipatory responses far more than 3.0 mg/kg in C57BL/6N mice. No dose of LY379268 prevented the PCP-induced accuracy deficit of DBA/2N mice. The PCP-induced anticipatory and perseverative responding of DBA/2N mice was reduced by 3.0 mg/kg LY379268, while 1.0 and 3.0 mg/kg reduced anticipatory responding in C57BL/6N.Conclusions The background genotype may determine the effects of PCP on attentional performance and the results confirm the importance of glutamate transmission in some aspects of this performance.     

Effects of mGlu2 or mGlu3 receptor deletions on mGlu2/3 receptor agonist (LY354740)-induced brain c-Fos expression: specific roles for mGlu2 in the amygdala and subcortical nuclei, and mGlu3 in the hippocampus

LY354740 is a potent and selective mGlu2/3 receptor agonist with activity in models of psychiatric disorders (anxiety, psychosis), and early clinical studies in anxiety patients. However, the specific receptor subtypes and brain regions which mediate mGlu2/3 receptor agonist pharmacology/efficacy are not well understood. Here we investigate the effects of deleting mGlu2 or mGlu3 receptors on basal and LY354740-regulated c-Fos expression in mouse brain using mGlu2 or mGlu3 knockout mice. Consistent with our earlier findings, LY354740 administration (20 mg/kg, i.p.) to wild-type mice increased c-Fos expression in specific limbic (central amygdala, bed nucleus of the stria terminalis, midline thalamic nuclei) and non-limbic (thalamic dorsolateral geniculate nucleus, superior colliculus, Edinger-Westphal) structures, while modestly suppressing hippocampal c-Fos expression. The LY354740-induced increases in c-Fos expression in all the above regions were abolished by mGlu2, but not mGlu3, receptor deletion. Interestingly, basal c-Fos expression was significantly increased in the hippocampus of mGlu3, but not mGlu2, receptor knockouts compared to wild-type mice. Moreover, this increase was not suppressed by LY354740, such that in the CA3 region LY354740 now increased c-Fos expression in the mGlu3 knockouts. These results demonstrate that the LY354740-induced increases of c-Fos expression in specific brain regions, including the central and extended amygdala are specifically linked to mGlu2 receptors, and LY354740 suppressions of neuronal activity in the hippocampus are linked to mGlu3 receptors.     

Differential involvement of dopamine D-1 and D-2 receptors in the circling behaviour induced by apomorphine,SK & F 38393, pergolide and LY 171555 in 6-hydroxydopamine-lesioned rats

The antagonistic effect of dopamine (DA) D-1 and D-2 antagonists against circling behaviour induced by various DA agonists in 6-OHDA-lesioned rats has been investigated. DA D-1/D-2 selectivity of agonists in vitro was measured by the stimulatory effect on DA-sensitive adenylate cyclase in rat striatal homogenates (D-1), the inhibitory effect on electrically-induced release of ³H-DA in rabbit striatal slices (D-2) and the affinity to ³H-piflutixol (D-1) and ³H-spiroperidol (D-2) binding sites in rat striatal membranes. The contralateral circling behaviour induced by the DA D-1 agonist SK & F 38393 was blocked by the DA D-1 antagonist, SCH 23390, and by the mixed DA D-1/D-2 antagonist cis(Z)-flupentixol, but was not influenced by the DA D-2 antagonists spiroperidol and clebopride. In contrast, circling behaviour induced by the preferential DA D-2 agonists pergolide and LY 171555 was blocked by clebopride, spiroperidol, and cis(Z)-flupentixol, but weakly or not influenced by SCH 23390. Apomorphine-induced circling behaviour was blocked by cis(Z)-flupentixol, partially antagonized by SCH 23390 and clebopride but not inhibited by spiroperidol, although the time-course of circling was changed. Combinations of SCH 23390 with spiroperidol or clebopride in low doses completely blocked the effect of apomorphine. These results indicate that DA D-1 and D-2 receptors mediate circling behaviour through separate mechanisms which can be independently manipulated with respective agonists and antagonists. Furthermore, the results indicate that both DA D-1 and D-2 receptors are involved in the effect of apomorphine, since selective antagonists induced maximally 50% inhibition. Complete blockade was only found in combination experiments and by the mixed D-1/D-2 antagonists cis(Z)-flupentixol, cis(Z)-clopenthixol, and clozapine.     

Contributions of cysteine 114 of the human D3 dopamine receptor to ligand binding and sensitivity to external oxidizing agents

1. Cysteine 114 (C114) of the human dopamine D3 receptor is located at the helical face of transmembrane segment III (TMIII) near aspartate 110, a counterion for the amine group of catecholamines. The contributions of C114 to receptor function were investigated here using site-directed mutagenetis of C114 to serine.
2. The C114S mutant, as expressed in Sf-9 cells, bound aminotetralin antagonists (UH-232 and AJ-76) and several agonists ((−)3-PPP, apomorphine, pramipexole and quinpirole) with markedly lower affinities as compared to the wild type D3 receptor, but bound other structurally diverse dopaminergic ligands with only minor changes in affinity. Because an N-propyl substituent is the only common structural feature among most affected ligands, we propose that the mutation alters `a propyl cleft'' on the receptor. The mutation hardly affected quinpirole-dependent [³⁵S]-GTPγS binding, suggesting C114 plays a minimal role in receptor-G-protein coupling.
3. N-Ethylmaleimide(NEM), a sulfhydryl modifying agent, blocked ligand binding to the D3 receptor, but not to the C114S mutant. We infer that C114 is the primary residue on the D3 receptor vulnerable to external oxidizing agents. Dopamine D2long and D4₂ receptors contain highly homologous TMIII sequences including an equivalent cysteine residue. However, only the D2long receptor, not the D4₂ receptor, displayed NEM sensitivity similar to that of the D3 receptor.
4. We conclude that C114 is critical for high affinity interactions between the D3 receptor and ligands containing an N-propyl substituent, and unlike its counterpart in the D4₂ receptor, is highly susceptible to external oxidizing agents.

     

特麦角脲对海洛因自身给药大鼠部分脑区多巴胺D2受体及强啡肽蛋白与基因表达的影响

目的探讨特麦角脲治疗海洛因依赖的作用机制。方法成年雄性SD大鼠,随机分为正常对照组、海洛因依赖形成期生理盐水干预组、海洛因依赖形成期特麦角脲干预组、复发期生理盐水干预组和复发期特麦角脲干预组;除正常对照组外,其余4组分别建立海洛因静脉自身给药和线索诱发复发模型,干预后灌注固定,留取各脑区切片,采用免疫组化和原位杂交技术,分别检测各脑区多巴胺D2受体蛋白和mRNA、强啡肽原蛋白、前强啡肽原mRNA表达水平。结果伏核多巴胺D2受体蛋白在海洛因依赖形成期表达下调,在复发期表达上升,多巴胺D2受体基因表达与蛋白表达基本一致,特麦角脲可使复发期受体蛋白表达回降。杏仁核中央核多巴胺D2受体蛋白和基因表达在复发期上调,特麦角脲可使基因表达回降。前额叶多巴胺D2受体蛋白和基因表达在形成期上调,蛋白表达在复发期下调,特麦角脲使复发期基因表达下调。伏核强啡肽蛋白和基因在复发期表达上调,特麦角脲使之回降。杏仁核中央核强啡肽蛋白在复发期表达上调,特麦角脲使之回降。结论海洛因依赖形成期中脑边缘系统多巴胺活动升高,复发期活动降低,特麦角脲对此有双向调节作用。复发期强啡肽活动上升,特麦角脲可使之降低,有治疗海洛因滥用的潜力。     

多巴胺受体系统在诱发产生的大麻酚类戒断症状中不起主要作用(英文)

AIM: To determine the dopaminergic systeminvolvement in precipitated cannabinoid withdrawalsyndrome. METHODS: The dopamine D_1 receptorantagonist SCH23390 or the dopamine D_2 receptorantagonost sulpiride was administered to rats chronicallytreated with either △~9-tetrahydrocannabinol (THC) orvehicle. Subjects were then injected with eitherSR141716A or vehicle and behavior was observed for1 h. RESULTS: Administration of the cannabinoidreceptor antagonist SR141716A to animals chronicallytreated with THC as described by Tsou et al (1995)