Philippe Protais

Climbing behavior induced by apomorphine in mice: a simple test for the study of dopamine receptors in striatum

Mice treated with low doses of apomorphine tend to adopt a vertical position along the walls of their cage. Optimal conditions have been defined to obtain a reliable dose-response relationship.This peculiar behavior appears to be elicited by stimulation of dopamine receptors in the striatum: it is suppressed after coagulation of this structure while it is facilitated when these receptors are made hypersensitive by previous treatments with 6-hydroxydopamine or haloperidol; on the other hand, it is not modified by coagulation of the nucleus accumbens.The relative efficacy of various agonists and antagonists of dopamine receptors have been determined on this test.It appears that this stereotyped behavior might represent a convenient mean to assess the stimulation of striatal dopamine receptors in mice.

High-affinity [3H]GBR 12783 binding to a specific site associated with the neuronal dopamine uptake complex in the central nervous system

We labelled the neuronal dopamine uptake system by using the potent dopamine uptake inhibitor GBR 12783 in its tritiated form (18.3 Ci/mmol). The binding of [3H]GBR 12783 to rat striatal membranes was saturable and specific with a Kd of 1.6 nM and a Bmax of 10.3 pmol X mg protein-1 as determined by Scatchard analysis. [3H]GBR 12783 binding to rat striatal membranes was inhibited by dopamine uptake inhibitors with IC50 highly correlated with their IC50 for inhibiting [3H]dopamine uptake by a rat striatal synaptosomal preparation. The rank order of potency was the following: GBR 12783 greater than amfonelic acid greater than mazindol greater than pyrovalerone greater than nomifensine greater than benztropine greater than amineptine greater than methylphenidate greater than cocaine. Substrates of dopamine uptake competed with [3H]GBR 12783 binding at concentrations higher than those at which they inhibited [3H]dopamine uptake. In rats with a unilateral section of the medial forebrain bundle, the decrease in [3H]GBR 12783 binding to membranes prepared from the ipsilateral striatum was equal to the decrease in [3H]dopamine uptake by a synaptosomal preparation obtained from the same striatum. [3H]GBR 12783 bound in a sodium-dependent manner to membranes prepared from striatum, nucleus accumbens and tuberculum olfactorium. GBR 12783 displayed an approximately 150-fold lower affinity for the cortical norepinephrine uptake system labelled with [3H]desipramine than for the dopamine transport complex labelled with [3H]GBR 12783. [3H]GBR 12783 appears an attractive tool for the selective characterization of the dopamine uptake system in vitro.

Acute Stress in Pregnant Rats: Effects on Growth Rate, Learning, and Memory Capabilities of the Offspring

Growth rate of the offspring of female rats stressed by the presence of a cat at the 10th or the 19th gestational day was lower than that of controls whereas footshocks administered at the same periods did not significantly influence growth rate of the young. Whatever the nature of the stress and the time when it was administered to the mother, the death rate of the young rats was much greater than that in controls. When adult, the offspring of stressed mothers exhibited learning and memory impairments in a delayed alternation task as well as in passive avoidance conditioning. Alteration of these cognitive functions is interpreted in terms of subtle dysfunctions in the development of the nervous system through modifications of the hormonal components of the mothers, particularly eventual alterations of the nervous system biochemistry of the offspring.

Chronic stress in pregnant rats: effects on growth rate, anxiety and memory capabilities of the offspring.

Female rats were repeatedly stressed for 10 periods of 15 min by the presence of a cat, at the 10th (S10) or the 19th (S19) gestational day. The litter from stressed females often contained a majority of males or a majority of females, especially in the S19 group. The death of pups was dramatically high in the S19 group and, compared with controls, growth of the surviving animals was slower. When adult, their long-term memory was altered and they exhibited an aversive behavior relative to wide areas. Moreover, cognitive alterations were revealed by the low level of exploration and the inability to rapidly process the relevant environmental cues. These deficits resemble those of psychiatric patients who had been submitted to pre-natal stress.

Pharmacological characteristics of dopamine receptors involved in the dual effect of dopamine agonists on yawning behaviour in rats

Increasing doses of apomorphine (APO) induced the dose-dependent appearance of yawns in rats at doses up to 0.1 mg X kg-1 and their disappearance from 0.1 to 0.6 mg X kg-1. A similar biphasic effect on yawning was observed with increasing doses of n-propyl norapomorphine, piribedil, S 584, bromocriptine, lergotrile, lisuride, CQ 32084 and L-DOPA. APO, n-propyl norapomorphine, piribedil and CQ 32084 had similar ED50 on the induction of sniffing and on the disappearance of yawns. All the neuroleptics tested antagonized the yawns induced by 0.1 mg X kg-1 APO. Increasing doses of haloperidol, chlorpromazine, mezilamine, metoclopramide and thioridazine made the yawns reappear in rats injected with 0.6 mg X kg-1 APO. The ID50 were similar to those for the antagonism of sniffing. On the other hand, increasing doses of clozapine, (+/-)- or (-)-sulpiride, veralipride and DAN 2163 did not make the yawns reappear in rats injected with 0.6 mg X kg-1 APO although sniffing was antagonized. These results are discussed in terms of the ability of sulpiride, veralipride and DAN 2163 to distinguish between the dopamine (DA) receptors involved in the appearance of yawns at low doses of DA agonists and in their disappearance at higher doses. The decreased APO-induced yawning observed concomitantly with increased sniffing in rats with 6-hydroxydopamine-lesioned olfactory tubercles suggests that yawning and sniffing could be mutually exclusive.

Rapid development of hypersensitivity of striatal dopamine receptors induced by alpha-methylparatyrosine and its prevention by protein synthesis inhibitors.

Abstract Modifications in the sensitivity of target-cells to DA or agonists in mouse striatum have been assesses both behaviorally, by scoring a stereotyped behaviour elicited by apomorphine and biochemically, by measurement of HVA and DA levels to evaluate the activity of the feedback loop controlling nigro-striatal neurons. Following the acute administration of α-MPT, hypersensitivity develops in a few hours and decays progressively in 3 days. Since the development of hypersensitivity is prevented by the administration of cycloheximide or anisomycin, two inhibitors of protein synthesis, it is hypothesized that it migth be accounted for by synthesis of new receptor sites.

A gradual score to evaluate the climbing behaviour elicited by apomorphine in mice

Mice treated with apomorphine tend to adopt a vertical position in a stereotyped manner. A quantal evaluation of this behaviour, taking into account its frequency and duration, leads to a biphasic dose-response curve that reveals opposite actions of the dopamine agonist.

Increased in vivo binding of 3H-Pimozide in mouse striatum following repeated administration of haloperidol

Abstract The in vivo binding of 3 H-pimozide in brain has been used to reveal modified DA receptors in a state of “disuse hypersensitivity”, i.e. in mice chronically-treated with haloperidol. The i.v. injection of increasing doses of 3 H-pimozide allows to detect a saturable binding of the neuroleptic obtained by substracting the radioactivity found in the cerebellum (non-specific binding) from that recovered in the striatum, indicating a maximal capacity of binding sites of about 40pmol.g −1 tissue. Following increasing duration of haloperidol treatment the binding of 3 H-pimozide in the striatum progressively increases, as well as the behavioral responsiveness to apomorphine. It appears that the changes in 3 H-pimozide binding are due to an increased maximal capacity of the binding sites for the neuroleptic (by about 40%) without significant change in the apparent affinity. The rapid appearance of behavioral hypersensitivity before any significant changes in 3 H-pimozide binding is discussed.

Decreased responsiveness to low doses of apomorphine after dopamine agonists and the possible involvement of hyposensitivity of dopamine ‘autoreceptors’

Apomorphine in low dosage (0.3 mg/kg) inhibits climbing behavior, a stereotyped motor activity, in mice. Pretreatment with apomorphine in low doses (0.125 or 0.25 mg/kg) or with piribedil (25 mg/kg), a weak dopamine agonist, results in a less marked inhibitory effect of the test dose of apomorphine. Apomorphine in low dosage or piribedil are also able to antagonize the increase in striatal homovanillic acid elicited by treatment with gammabutyrolactone. Thus, low stimulation of dopamine receptors can regulate the synthesis and release of dopamine even in the absence of impulse flow in dopaminergic neurons, and the initial stimulation of the receptors mediating such effects may lead to a state of hyposensitivity to further stimulation. The hypothesis that such receptors are autoreceptors is discussed.

Changes in dopamine receptors in mouse striatum following morphine treatments.

Abstract Presynaptic opiate receptors previously evidenced on striatal dopaminergic nerve-endings might mediate an inhibition of dopaminergic transmission by morphine. We have now assessed on behavioral and biochemical tests the development of disuse hypersensitivity to dopamine (DA) following morphine treatments. 1. 1. A long-lasting increase in behavioral responsiveness to apomorphine regarding the climbing behavior, a stereotyped motor behavior mediated by striatal DA receptors, is shown to develop after a single dose of morphine. However after chronic treatments the behavioral data are difficult to interpret. 2. 2. After an initial rise, striatal HVA levels are significantly depressed for several days. 3. 3. Binding of 3 H-domperidone to striatal DA receptors is slightly enhanced. All these changes, although less marked, are reminiscent of those observed during typical hypersensitivity developing following chronic blockade of DA receptors by neuroleptics. The primary action of morphine on DA transmission is discussed.