Joseph J. Jacob

Facilitation de réactions nociceptives par la naloxone chez la souris et chez le rat

The effects of graded doses of naloxone on nociceptive reactions of mice and rats of different strains were studied using a hot plate technique.Enhancements were observed provided the control reaction times were long enough, a condition which was fulfilled for the jumping reaction at different temperatures of the hot plate (50‡ C, 55‡ C, 65‡ C, 80‡ C in mice-55‡ C in rats) but for the licking reaction only at the lowest temperature (50‡ C in mice). Enhancement was dose-related up to a ceiling effect. Nalorphine had no such overt action. As low doses of naloxone (0.1–1 mg/kg s.c.) were effective, the enhancement is most simply accounted for by interactions at the level of the specific opioid receptors, some of which are suggested. The phenomenon might be relevant to the interpretation of the mechanisms of precipitated abstinence.

Local inhibition of inflammatory pain by naloxone and its N-methyl quarternary analogue

Inflammation was induced in rats by intraplantar administration of carrageenan (500 micrograms in 0.1 ml). Nociceptive thresholds were measured on both inflamed and contralateral hindpaws with the pressure test of Randal and Sellito. Low doses (0.03-10 micrograms/kg) of naloxone hydrochloride (Nx) or of methylnaloxone methylsulfonate (MeNx) were injected 4 h after carrageenan in the inflamed paw: Nx (3 micrograms) and MeNx (1-10 micrograms) diminished inflammatory pain; a slight, nonspecific hyperalgesia was observed in the contralateral paw after Nx, MeNx or NaCl. Neither drug was effective when injected s.c. at the same doses and time; however activities were shown to be influenced by the experimental schedule. Low s.c. doses of Nx antagonized the analgesia produced by s.c. morphine whereas MeNx did not. This work demonstrates the local site of the analgesic action of the doses of Nx and MeNx used here, bringing new evidence in favour of the existence of cutaneous opioid receptors. Opiate antagonists might inhibit inflammatory pain by interacting with a particular population of cutaneous receptors and (or) by being dealkylated locally into agonists.

5-hydroxytryptamine binding to synaptic membranes from rat brain

Abstract The 3 H-5HT binding capacity of rat brain synaptic membranes prepared by density gradient centrifugation has been investigated using a rapid ultrafiltration technique. A saturable, high affinity (K D = 1.10 −9 M), 5HT displaceable binding has been found. It is thermosensitive, temperature dependent and pH dependent. 5HT and related tryptamines are the most effective displacers of bound 3 H-5HT, whereas compounds which are not structurally related to 5HT (chlorpromazine, imipramine, cyproheptadine and cinanserine) and other neuro-transmitters (noradrenalin, dopamine) are ineffective. The distribution of 5HT-specific binding sites in the brain is related to serotonergic input. We conclude that these 5HT binding sites might possibly represent 5HT receptor sites.

Stress hyperalgesia in rats: An experimental animal model of anxiogenic hyper-algesia in human

Emotional, non-noxious stress consisting of inescapable holding or exposure to novelty were found to produce clearcut and reproducible hyperalgesia in the rat. The mechanisms of the two stress hyperalgesia appeared to be different: 1) hypophysectomy enhanced holding hyperalgesia but reduced novelty hyperalgesia, indicating that pituitary factors respectively compensate (through opioids ?) and participate (through ACTH ?) in stress hyperalgesia; 2) diazepam did not alter holding hyperalgesia but abolished novelty hyperalgesia. The two types of stress hyperalgesia might represent animal models of anxiogenic hyperalgesia observed in human: as for clinical anxieties, they are alleviated or not by diazepam.

The effect of medial hypothalamus lesions on pain control

In the rat, discrete electrolytic lesions located in 6 different parts of the medial hypothalamus (MH) are shown to induce clearcut hyperalgesia. During a time limit of 14 days following the lesions, no other obvious deficits were noticed (in sensory and/or motor functions, affectivity towards conspecifics, food and water intake). Three nociceptive reactions (tail withdrawal, vocalization, vocalization after-discharge) were tested and their thresholds measured following electrical stimulation of the tail. The lesions aimed at the rostral part of the arcuate nucleus, as well as at ventromedial and dorsomedial nuclei, produced the most profound hyperalgesia. The possible involvement of the endorphinergic and enkephalinergic systems known to be located in the MH is discussed. The relation between the hyperalgesic effects of MH lesions and various structures (limbic areas, descending pain control system, pituitary) is also considered.

Decrease of [3H]5-HT high affinity binding and 5-HT adenylate cyclase activation after kainic acid lesion in rat brain striatum

PREVIOUSLY, we observed that the binding of 5-HT to synaptosomal membrane enriched fractions occurred with a high affinity constant (K, = 1-3 nM) and was saturable, reversible and 5-HT specific (FILLION et al., 1976, 1977, 1978). In the same preparation, we established the existence of a serotoninergic sensitive adenylate cyclase (EC 4.6.1.1) activated with a high apparent affinity constant ( K , in the nanomolar range) and specific for 5-HT (FILLION et a[., 1977). Kainic acid is now extensively used to induce the degeneration of nerve cell bodies in a given area (SCHWARCZ et al., 1977; COYLE et al., 1978; STEPHEN et al., 1978). In this report, it is shown that the degeneration of striatal neurones leads to a total loss of the high affinity binding of C3H]5-HT and, in parallel, to a total loss of the serotoninergic adenylate cyclase activation. This supports the hypothesis that the observed serotoninergic sites represent the post-synaptic 5-HT receptor system.

[3H]5-HT binding sites and 5-HT-sensitive adenylate cyclase in glial cell membrane fraction.

Glial cell membrane fractions were prepared using glial cells preparations isolated from horse brain striatum. [3H]5-HT binding was measured by the filtration technique and the adenylate cyclase activity determined by measuring the cAMP production using a radioimmunoassay. Serotonin binds to glial membrane fractions with an affinity corresponding to a dissociation constant Kd = nM. The corresponding site is serotoninergic specific: [3H]5-HT binding is inhibited by 5-HT agonists (5 OH NM-DMT, 5-MeOHT, 5-MeOH-DMT, NN-DMT) or antagonists (cinanserine, cyproheptadine, methysergide, LSD) and not (or poorly) inhibited by non-serotoninergic related drugs. The population of sites binding 5-HT, present in neuronal membrane preparations and determined in parallel assays is distinct from that observed in glial preparations. The glial membrane fractions contains an adenylate cyclase activated by 5-HT with an apparent affinity constant close to 1 microM. It is serotonin-specific and clearly distinct from the DA-stimulated adenylate cyclase present in the same preparation. The sites binding 5-HT and activating the adenylate cyclase with low affinities might be directly related. This system, clearly distinct from the postsynaptosomal serotoninergic receptor, represents presumably a glial serotoninergic receptor; however, it cannot be totally excluded that these sites may refer to presynaptic membranes.

Serotonin sensitive adenylate cyclase in horse brain synaptosomal membranes

Abstract In different membranal preparations isolated from horse brain stritum we have shown the existence of an adenylate cyclase system sensitive to serotonin (5-HT). Activation of the adenylate cyclase was determined by measuring cAMP using a radioimmunoassay. This serotoninergic sensitive enzyme is characterized by a high apparent affinity constant (in the nanomolar range), located on synaptosomal membranes. It is inhibited by antiserotoninergic drugs (cyproheptadine, cinanserin, methysergide, LSD), and synergistically activated by GTP. This serotoninergic activation is clearly additive to the activation induced by dopamine. It appears different from the adenylate cyclase system previously described in the literature which is also activated by 5-HT, but which has a low apparent affinity constant (in the micromolar range); the latter is apparently located in non-synaptosomal membranes, and its activation by 5-HT is non-additive to the activation induced by dopamine. The serotoninergic sensitive adenylate cyclase reported in this study, might be related to the serotoninergic binding system which we have previously described which has similar affinity constant, a similar subcellular distribution and which is inhibited in the same concentration ranges by antiserotoninergic drugs. These two systems might represent a synaptosomal serotoninergic receptor complex.

Actions of 5-hydroxytryptamine and 5-hydroxytryptophan injected by various routes on the rectal temperature of the rabbit

Abstract By systemic, intracisternal or intracerebroventricular routes, graded doses of 5-hydroxytryptamine (creatinine sulphate or hydrogen maleinate) and of d , l -5-hydroxytryptophan elicited the same general pattern of effects on the temperature of wake rabbits: falls in temperature which were gradually superceded by rises in temperature. The effective dosages were much lower when the drugs were injected into the CSF than when administered systematically. Effects obtained by the intracisternal and by the intracerebroventricular routes were similar. Rises in temperature were reproducible, and were not artefacts resulting from osmotic or ionic imbalance or pyrogen contamination. Temperature falls varied with certain experimental features. They were more easily obtained with the amino acid than with the amine and were more frequently observed with the latter when conditions allowed for some pyrogen contamination. Inhibition of monoamine oxidases by phenylisopropylhydrazine resulted in marked potentiation of falls and rises observed after amine or amino acid injection into the CSF: the falls, however, occurred rarely. After systemic injection, temperature rises were potentiated, but the falls were not. The effectiveness of amine and amino acid administration by different routes, and before and after monoamine oxidase inhibition, are discussed. The present results stress the dual direction of the central thermic effects of exogenous and endogenous 5-hydroxytryptamine, and give some support to its possible participation in pharmacological and physiological variations in the temperature of the rabbit.

Acute physical dependence in the waking dog after a single low dose of morphine

In the waking dog, a small dose of morphine (0·1 mg/kg intravenously) was sufficient (1) to induce a quite appreciable state of sedation which might be more closely related to clinical analgesia than experimental nociception, and (2) to allow for precipitation of clear-cut signs of abstinence (agitation, tachycardia, tachypnoea, mydriasis, hyperthermia, tremors, salivation, urination) when naloxone (3 mg/kg subcutaneously) was injected 1·5 hours later.