Didier Desor

Sialorphin, a natural inhibitor of rat membrane-bound neutral endopeptidase that displays analgesic activity

Sialorphin is an exocrine and endocrine signaling mediator, which has been identified by a genomic approach. It is synthesized predominantly in the submandibular gland and prostate of adult rats in response to androgen steroids and is released locally and systemically in response to stress. We now demonstrate that the cell surface molecule to which sialorphin binds in vivo in the rat kidney is the membrane-anchored neutral endopeptidase (neprilysin; NEP, EC 3.4.24.11). NEP plays an important role in nervous and peripheral tissues, as it turns off several peptide-signaling events at the cell surface. We show that sialorphin prevents spinal and renal NEP from breaking down its two physiologically relevant substrates, substance P and Met-enkephalin in vitro. Sialorphin inhibited the breakdown of substance P with an IC50 of 0.4–1 μM and behaved as a competitive inhibitor. In vivo, i.v. sialorphin elicited potent antinociceptive responses in two behavioral rat models of injury-induced acute and tonic pain, the pin-pain test and formalin test. The analgesia induced by 100–200 μg/kg doses of sialorphin required the activation of μ- and δ-opioid receptors, consistent with the involvement of endogenous opioid receptors in enkephalinergic transmission. We conclude that sialorphin protects endogenous enkephalins released after nociceptive stimuli by inhibiting NEP in vivo. Sialorphin is a natural systemically active regulator of NEP activity. Furthermore, our study provides evidence that it is a physiological modulator of pain perception after injury and might be the progenitor of a new class of therapeutic molecules.

Ethological comparison of the effects of a bovine αs1-casein tryptic hydrolysate and diazepam on the behaviour of rats in two models of anxiety

A bovine alpha s1-casein tryptic hydrolysate was previously demonstrated to display an anxiolytic-like activity in the conditioned defensive burying and in the elevated plus-maze models when i.p. injected. The present study assessed the anxiolytic-like effects of this tryptic hydrolysate after an oral administration in rats faced to the same behavioural situations using diazepam as a reference. In a first experiment, the behavioural effects of the hydrolysate in the conditioned defensive burying test were investigated at doses ranging 5-50 mg/kg. The results showed that the minimal dose required to elicit an anxiolytic-like activity is 15 mg/kg. In a second experiment, the alpha s1-casein tryptic hydrolysate (15 mg/kg, p.o.) was demonstrated to display an anxiolytic-like activity similar to diazepam (3 mg/kg, p.o.) in the conditioned defensive burying test and the elevated plus-maze. However, the ethological analysis of behaviour indicated that this hydrolysate has a different activity compared to diazepam. While diazepam induced a disinhibition state in rats, possibly related to the risk-taking behaviour observed after a benzodiazepine ingestion in humans, the tryptic hydrolysate did not display such a side effect. These results suggest that the mechanism of action of the bovine alpha s1-casein tryptic hydrolysate may differ from that of diazepam.

Behavioral evaluation of visceral pain in a rat model of colonic inflammation.

A new rat model was established up to evaluate the antinociceptive effect of compounds in visceral pain. The test consisted in measuring the performance of rats in an aversive light stimulus avoidance experimental device. Rats with TNBS-induced colitis had a lower number of total active lever pressings and did not discriminate the active lever from the inactive one. Morphine (1 mg/kg, s.c.) and CI-977 (0.001 mg/kg, s.c.) treatment restored the level of pressing activity of animals and their ability to discriminate the active lever from the inactive one. Naloxone treatment antagonized the improvement of performance produced by morphine. The results obtained indicate that this behavioral paradigm may be used to evaluate the antinociceptive potential of compounds.

Effects of lifelong intervention with an oligofructose-enriched inulin in rats on general health and lifespan.

Ageing is associated with changes in physiology and morphology; nutritional strategies to decrease morbidity and to prolong life are of high interest. The aim of the study was to investigate the effects of lifelong supplementation with an oligofructose-enriched inulin on morphological and biological markers and lifespan in male and female rats. Male and female rats, age 3 months, were randomised into two groups to receive either a diet with 10 % of an oligofructose-enriched inulin (Synergy 1) or a standard diet (control) for 27 months. The rats were weighed every 2 weeks and their food intake was evaluated on four successive days every 4-6 weeks. Samples were taken at 12, 18 and 24 months of age. During the whole intervention period, male rats receiving Synergy 1 (SYN1-M) displayed lower body weight, cholesterol and plasma triacylglycerolaemia compared with the controls (Cont-M). The survival rate at 24 months of age of SYN1-M rats was 35.3 % greater than that of Cont-M rats. In female rats, the Synergy 1 supplementation (SYN1-F) group also reduced body weight, cholesterol and triacylglycerolaemia levels, but results were less consistent over the experiment. The survival rate at 24 months of age in SYN1-F rats was 33.3 % greater compared with that of the control (Cont-F) group. To conclude, lifelong intervention with Synergy 1 improved biological markers during ageing and survival rate (lifespan) of rats.

Anxiolytic‐like effects and safety profile of a tryptic hydrolysate from bovine alpha s1‐casein in rats

The anxiolytic activity and adverse benzodiazepine‐like effects of a bovine alpha s1‐casein tryptic hydrolysate (CH) were evaluated. The effects of CH orally administered at doses of 5 and 15 mg/kg were compared with those of diazepam (DZ) at 3 mg/kg in the conditioned defensive burying test. Rats treated either with CH at 15 mg/kg or with DZ showed a decrease in anxiety. A drug‐related difference was observed in terms of duration, as the anxiolytic‐like action of CH was maintained after 7 days with twice‐daily administration, whereas that of DZ was not. CH and DZ were then evaluated for their potential effects on memory in a passive avoidance paradigm. CH‐treated rats had significantly longer latencies before entering the dark compartment where they were previously delivered a shock, indicating better retention relative to DZ‐treated rats. In the final test, CH and DZ were evaluated for place preference, an index of the possible addictive potential of these substances. DZ‐treated rats spent more time in the compartment associated with drug exposure than control rats. This effect was not found in CH‐treated rats. Thus, CH did not display side effects associated with DZ, despite its affinity for gamma‐aminobutyric acid(A) (GABAA) receptors. Specific linking of CH on GABAA receptor function involved in anxiolysis, but not on that implied in memory‐impairing effects, may be hypothesized to explain its specific activity. This profile might render it advantageous for nutritional purposes.

Neurobehavioral maturation of offspring from epileptic dams: study in the rat lithium-pilocarpine model.

In the present study, we explored the consequences of epilepsy on the neurobehavioral development of the offspring in a rat model of spontaneous epilepsy, the lithium-pilocarpine model of temporal lobe epilepsy not dependent on genetic factors and in animals not receiving any antiepileptic treatment. Status epilepticus was induced by lithium-pilocarpine in female rats. After the occurrence of spontaneous seizures the rats were mated and the neurobehavioral development of the offspring was explored. Rat pups were cross-fostered early after birth. We hence obtained pups born from or raised by epileptic or non-epileptic dams. On the dams, we performed a follow-up of maternal care during pregnancy. On the pups, we performed a follow-up of classical parameters of development such as body weight and eyelid opening, and subjected the pups to various tests representative of neurobehavioral maturation extending from postnatal day 4 (PD4) to PD30 (righting reflex, suspension time, negative geotaxis, open field, locomotor coordination and eight arm maze). Altogether our data show that rat pups born from or raised by epileptic dams develop as well as control pups raised by control dams. Intriguingly, pups born from lithium-pilocarpine exposed dams and raised by control mothers tend to have better scores than the two other groups in all tests. This indicates that the exposure to seizures during pregnancy is not harmful for the development of the fetus.

Behavioural and cognitive effects of oligofructose-enriched inulin in rats.

The behavioural and cognitive effects of oligofructose-enriched inulin at the doses of 5 and 10 % in the diet, orally ingested daily during 2 weeks, were investigated using a functional observational battery (FOB) and the light extinction test in male Wistar rats. Control rats received a standard diet and were tested in the same test situations. The behavioural effects were assessed 2 d before and 14 d after the beginning of the treatment period and the cognitive effects were investigated after the administration period by lever-pressing activity and learning discrimination using the light extinction test paradigm. In general, the study demonstrated that oligofructose-enriched inulin at 5 % in the diet, and particularly at 10 % in the diet, caused relaxing-like effects, stimulated and increased the general activity and interest of the rats to the test environment. In addition, both doses of oligofructose-enriched inulin showed significant effects on learning discrimination in male rats, in comparison with the control diet. These results suggest that oligofructose-enriched inulin, particularly at the dose of 10 %, improves cognitive performances in the light extinction test and the well-being of male rats using the FOB.