Differential effects of quinelorane and pergolide on behaviour, blood pressure, and body temperature of spontaneously hypertensive rats and Wistar-Kyoto rats

CHL1 depletion affects dopamine receptor D2-dependent modulation of mouse behavior

Introduction

The dopaminergic system plays a key role in the appropriate functioning of the central nervous system, where it is essential for emotional balance, arousal, reward, and motor control. The cell adhesion molecule close homolog of L1 (CHL1) contributes to dopaminergic system development, and CHL1 and the dopamine receptor D2 (D2R) are associated with mental disorders like schizophrenia, addiction, autism spectrum disorder and depression.

Methods

Here, we investigated how the interplay between CHL1 and D2R affects the behavior of young adult male and female wild-type (CHL+/+) and CHL1-deficient (CHL1-/-) mice, when D2R agonist quinpirole and antagonist sulpiride are applied.

Results

Low doses of quinpirole (0.02 mg/kg body weight) induced hypolocomotion of CHL1+/+ and CHL1-/- males and females, but led to a delayed response in CHL1-/- mice. Sulpiride (1 mg/kg body weight) affected locomotion of CHL1-/- females and social interaction of CHL1+/+ females as well as social interactions of CHL1-/- and CHL1+/+ males. Quinpirole increased novelty-seeking behavior of CHL1-/- males compared to CHL1+/+ males. Vehicle-treated CHL1-/- males and females showed enhanced working memory and reduced stress-related behavior.

Discussion

We propose that CHL1 regulates D2R-dependent functions in vivo. Deficiency of CHL1 leads to abnormal locomotor activity and emotionality, and to sex-dependent behavioral differences.

Haloperidol and methylphenidate alter motor behavior and responses to conditioned fear of Carioca Low-conditioned Freezing rats

Animal models are important tools for studying neuropsychological disorders. Considering their limitations, a more extensive translational research must encompass data that are generated from several models. Therefore, a comprehensive characterization of these models is needed in terms of behavior and neurophysiology. The present study evaluated the behavioral responses of Carioca Low-conditioned Freezing (CLF) rats to haloperidol and methylphenidate. The CLF breeding line is characterized by low freezing defensive responses to contextual cues that are associated with aversive stimuli. CLF rats exhibited a delayed response to haloperidol at lower doses, needing higher doses to reach similar levels of catatonia as control randomly bred animals. Methylphenidate increased freezing responses to conditioned fear and induced motor effects in the open field. Thus, CLF rats differ from controls in their responses to both haloperidol and methylphenidate. Because of the dopamine-related molecular targets of these drugs, we hypothesize that dopaminergic alterations related to those of animal models of hyperactivity and attention disorders might underlie the observed phenotypes of the CLF line of rats.

Prepulse inhibition of acoustic startle in spontaneously hypertensive rats

Prepulse inhibition is modulated by dopaminergic drugs and is disrupted in attention-deficit hyperactivity disorder, as well as mental illnesses such as schizophrenia. Spontaneously hypertensive rats (SHR) have been proposed as an animal model of attention-deficit hyperactivity disorder and show marked alterations of dopaminergic regulation of behaviour. SHR showed significantly lower startle amplitude than Wistar-Kyoto (WKY) rats and Sprague-Dawley (SD) rats, but no difference in startle habituation. Baseline percentage prepulse inhibition was higher in SHR and WKY rats than in SD rats. Treatment with amphetamine caused significant disruption of prepulse inhibition in SHR and WKY rats, but not SD rats. In contrast, treatment with apomorphine caused prepulse-dependent disruption of prepulse inhibition in SD rats only. Both MK-801 and 8-OH-DPAT treatment caused disruption of prepulse inhibition in all three rat strains. This study shows differential changes in startle level and prepulse inhibition in SHR, however these rats are not uniformly different from either WKY rats or SD rats and WKY rats differ in a number of respects from SD rats. In conclusion, these data further reveal altered dopaminergic regulation of behaviour in SHR, but also shows that caution is needed about the control strain used to compare these animals with.

Interaction of the dopamine D2 receptor agonist quinpirole with sympathetic vasomotor tone and the central action of rilmenidine in conscious rabbits

Previous studies in conscious rats have shown that systemic administration of the dopamine D2 receptor agonist quinpirole causes a centrally-mediated increase in blood pressure which is associated with increased plasma levels of noradrenaline and adrenaline. In addition, treatment with quinpirole caused a marked inhibition of the antihypertensive effect of centrally-acting sympatho-inhibitory drugs such as clonidine, rilmenidine and alpha-methyldopa, suggesting an interaction at the level of sympathetic vasomotor tone. The main aim of the present study was investigate in conscious rabbits the effect of quinpirole on renal sympathetic nerve activity. In addition, we studied the effect of pretreatment with quinpirole on responses to additional quinpirole injections or rilmenidine treatment. Quinpirole treatment caused a prolonged dose-dependent increase in blood pressure and heart rate. Additional injection of quinpirole, 30 min after the first treatment, caused a significantly smaller pressor response (7+/-2 vs. 17+/-2 mm Hg). Injection of rilmenidine caused a larger decrease in blood pressure in rabbits which had been pretreated with quinpirole than in controls (-28+/-3 vs. -14+/-3 mm Hg). Total renal sympathetic nerve activity was markedly increased by quinpirole treatment (3.5-fold), an effect which could be attributed to both increased amplitude and increased frequency of the renal nerve signal. After a second injection of quinpirole, 30 min after the first treatment, only total renal sympathetic nerve activity and amplitude were increased and the effects were reduced. These results show marked actions of quinpirole on renal sympathetic nerve activity in conscious rabbits. However, the previously described apparent desensitisation to the antihypertensive effect of rilmenidine could not be observed in rabbits, suggesting marked species differences in the mechanism and site of action of rilmenidine.

Pretreatment with the dopamine agonist quinpirole inhibits central antihypertensive mechanisms in rats

1. Intravenous or central treatment of spontaneously hypertensive rats (SHR) with the dopamine D2 receptor agonist quinpirole caused a short-lasting pressor response with little effect on heart rate. 2. At 30 min after intravenous administration of quinpirole, the antihypertensive effect of rilmenidine was significantly inhibited. This interaction of quinpirole and rilmenidine was similarly observed when quinpirole was administered either intravenously (0.3 or 0.1 mg/kg), in the lateral cerebral ventricles (0.1 mg/kg) or intracisternally (0.1 mg/kg) or when rilmenidine was administered intravenously (1 mg/kg) or intracisternally (0.1 mg/kg). 3. The apparent desensitization to the antihypertensive effect of rilmenidine 30 min after pretreatment with quinpirole was not observed after a 4 or 24 h interval. 4. These data suggest that quinpirole has prolonged effects on central sympathetic vasomotor mechanisms that are the target of centrally acting antihypertensive drugs. These and previous results show a functional interaction between central dopamine D2 receptor activation and sympathetic responses mediated by a wide range of different receptors, including imidazoline and 5-hydroxytryptamine 5-HT1A-receptors and alpha 2-adrenoceptors.

Pretreatment with quinpirole inhibits the central antihypertensive effects of rilmenidine and alpha-methyldopa in conscious rats

Treatment of conscious spontaneously hypertensive rats (SHR) with the dopamine D2 receptor agonist quinpirole causes a short-lasting pressor response and apparent desensitisation to the effects of subsequent injections of quinpirole or central antihypertensives such as clonidine. In the present study, a number of aspects of this apparent desensitisation were investigated. Thirty minutes after intravenous injection of quinpirole into spontaneously hypertensive rats, treatment with the dopamine D2 receptors antagonist raclopride caused a significant fall in blood pressure. At this time point, circulating levels of vasopressin were not significantly different compared to controls. In Brattleboro rats, the pressor response to quinpirole was reduced in the first 15 min after injection, but not difference in blood pressure was observed at later time points. In SHR which had been treated with quinpirole, the central antihypertensive effects of rilmenidine or alpha-methyldopa were significantly inhibited. By contrast, the bradycardia induced by these drugs was similar in quinpirole-treated rats and controls. Quinpirole pretreatment caused an enhancement of the hypotension but a reduction of the reflex tachycardia after intravenous treatment with hydralazine. In SHR treated with methylatropine and quinpirole, the upper plateau of the sympathetic baroreceptor-heart rate reflex curve was reduced. These results show that treatment with quinpirole has marked effects on central sympathetic vasomotor mechanisms which are the target of antihypertensive drugs such as rilmenidine and alpha-methyldopa. At least some of these effects may occur at the level of the sympathetic baroreflex. Moreover, while the effects of quinpirole on sympathetic regulation are prolonged, the initial pressor response is counteracted by an as yet unidentified compensatory mechanism which can be unmasked when quinpirole is displaced from its receptor by dopamine D2 receptor antagonist treatment.