Neurotensin inhibition of GABAergic transmission via mGluR-induced endocannabinoid signalling in rat periaqueductal grey.

Neurotensin modulates pain via its actions within descending analgesic pathways which include brain regions such as the midbrain periaqueductal grey (PAG). The aim of this study was to examine the cellular actions of neurotensin on PAG neurons. Whole cell patch clamp recordings were made from rat midbrain PAG slices in vitro to examine the postsynaptic effects of neurotensin and its effects on GABA(A) mediated inhibitory postsynaptic currents (IPSCs). Neurotensin (100-300 nM) produced an inward current in subpopulations of opioid sensitive and insensitive PAG neurons which did not reverse over membrane potentials between -50 and -130 mV. The neurotensin induced current was abolished by the NTS1 and NTS1/2 antagonists SR48692 (300 nM) and SR142948A (300 nM). Neurotensin also produced a reduction in the amplitude of evoked IPSCs, but had no effect on the rate and amplitude of TTX-resistant miniature IPSCs. The neurotensin induced inhibition of evoked IPSCs was reduced by the mGluR5 antagonist MPEP (5microM) and abolished by the cannabinoid CB(1) receptor antagonist AM251 (3 microM). These results suggest that neurotensin produces direct neuronal depolarisation via NTS1 receptors and inhibits GABAergic synaptic transmission within the PAG. The inhibition of synaptic transmission is mediated by neuronal excitation and action potential dependent release of glutamate, leading to mGluR5 mediated production of endocannabinoids which activate presynaptic CB(1) receptors. Thus, neurotensin has cellular actions within the PAG which are consistent with both algesic and analgesic activity, some of which are mediated via the endocannabinoid system.

Antidepressant-like effects of the nociceptin/orphanin FQ receptor antagonist UFP-101: new evidence from rats and mice.

Receptor antagonist and knockout studies have demonstrated that blockade of signalling via nociceptin/orphanin FQ (N/OFQ) and its receptor (NOP) has antidepressant-like effects in mice submitted to the forced swimming test (FST). The aim of the present study was to explore further the antidepressant-like properties of the NOP antagonist UFP-101 in different species (mouse and rat) and using different assays [FST and tail suspension test (TST)], and to investigate the mechanism(s) involved in its actions.UFP-101 (10 nmol i.c.v.) reduced immobility time of Swiss mice in the TST (mean+/-SEM) from 179+/-11 to 111+/-10 s. N/OFQ (1 nmol i.c.v.) was without effect per se, but fully prevented the effect of UFP-101. The spontaneous immobility time of NOP(-/-) CD1-C57BL/6J-129 mice in the TST was much lower than that of wild-type (NOP(+/+)) littermates (75+/-11 vs. 144+/-17 s) or of Swiss mice. UFP-101 (10 nmol i.c.v.) decreased immobility time (-65%) and increased climbing time (71%) in rats submitted to the FST. In rat brain slices, N/OFQ (100 nM) triggered robust K(+)-dependent hyperpolarizing currents in locus coeruleus and dorsal raphe neurons. UFP-101 (3 microM) fully prevented N/OFQ-induced currents, but was inactive per se. Fluoxetine, desipramine (both 30 mg/kg i.p.) and UFP-101 (10 nmol i.c.v.) reduced immobility time of mice in the FST. The serotonin synthesis inhibitor p-chlorophenylalanine methylester (PCPA, 4 x 100 mg/kg per day i.p.) prevented the antidepressant-like effects of fluoxetine and UFP-101 (but not desipramine), whereas N-(2-chloroethyl)- N-ethyl-2-bromobenzylamine (DSP-4, neurotoxic for noradrenergic neurons; 50 mg/kg i.p., 7 days beforehand), suppressed only the effect of desipramine. Neither pretreatment affected spontaneous immobility time per se.Thus, UFP-101 exhibits pronounced antidepressant-like effects in different species and animal models, possibly by preventing the inhibitory effects of endogenous N/OFQ on brain monoaminergic (in particular serotonergic) neurotransmission. Participation of the N/OFQ-NOP receptor system in mood modulation sets new potential targets for antidepressant drug development.

Release of immunoreactive brain-derived neurotrophic factor in the spinal cord of the rat following sciatic nerve transection.

Using the antibody microprobe method, the sites of spinal release of immunoreactive brain-derived neurotrophic factor (BDNF) was studied in normal rats, and rats with prior sciatic nerve transection. In normal rats, a significant basal release of immunoreactive BDNF was found in the superficial dorsal horn. Following sciatic nerve transection (performed 14 days previously), release of BDNF was found throughout the whole of the dorsal horn, extending into deeper laminae. Electrical stimulation of the ipsilateral sciatic nerve at a strength adequate to excite either A fibres (20 Hz at 2x threshold voltage) or A and C fibres (2 Hz at 20x threshold voltage) did not alter the basal release of immunoreactive BDNF in normal or in nerve-injured rats. The results suggest that BDNF is released from the central terminals of primary afferent fibres, but such release is not solely dependent upon action potential invasion of these terminals. The increased extent of release following nerve transection is consistent with the hypothesis that BDNF plays a role in the central response to peripheral nerve injury.

The long-term effect of epidural administration of butamben suspension on nerve injury-induced allodynia in rats.

UNLABELLED: Although local anesthetics can, in some situations, alleviate neuropathic pain, currently available preparations are short-acting and nonselective, producing, for example, motor dysfunction. Clinical studies report that a novel suspension preparation of butamben has the advantage of a prolonged duration of action, and it can be used epidurally, without impairment of motor function. In this behavioral study, we investigated the effect of the epidural administration of a 5% butamben suspension on nerve injury-induced allodynia. Behavioral studies were performed using an established animal model of neuropathic pain, which involves a partial ligation of the sciatic nerve. Nociceptive thresholds to mechanical stimulation were determined by the paw withdrawal method. The allodynia to mechanical stimulation induced by partial nerve ligation was significantly attenuated by daily injections, for 5 days, of 10 microL of butamben suspension. The analgesia lasted at least 7 days after the final injection. Daily injections of 10 microL of vehicle, for 5 days, had no significant effect on allodynia. During the period of daily injections, both the butamben and vehicle treated rats had temporary impairment of motor coordination compared with untreated controls. Motor function recovered after the final injection. Neither daily injections of butamben for 2 or 3 days, nor smaller volumes for 5 days (2.5-5 microL), had a long-lasting effect. We conclude that repeated epidural administration of butamben suspension for several days provides long-lasting analgesia in rats with nerve injury-induced allodynia to mechanical stimulation. IMPLICATIONS: In this animal behavioral study, using rats with nerve injury-induced pain, we examined the possible long-term analgesic effects of epidural administration of a suspension of the local anesthetic, butamben. We found that multiple doses for several days were required to provide a prolonged analgesia.

The association between flexibility and running economy in sub-elite male distance runners.

The purpose of this study was to examine the association between nine measures of limb and trunk flexibility and running economy. Within a week prior to running economy assessment, and after 10 min of jogging at 3.13 m.s-1, 19 well-trained male sub-elite distance runners underwent two complete sets of lower limb and trunk flexibility assessments. Runners then completed two 10-min running economy assessment sessions on consecutive days at 4.13 m.s-1 following two 30-min sessions of treadmill accommodation at 4.13 m.s-1. Intraclass correlation coefficients indicated that the repeated flexibility measurements were highly reliable (X R = 0.92 +/- 0.09), as were the two running economy appraisals (R = 0.99). Correlational analyses revealed that dorsiflexion (r = 0.65) and standing hip rotation (r = 0.53) were significantly (P < or = 0.05) associated with the mean aerobic demand of running, such that runners who were less flexible on these measures were more economical. Although speculative, these results suggest that inflexibility in certain areas of the musculoskeletal system may enhance running economy in sub-elite male runners by increasing storage and return of elastic energy and minimizing the need for muscle-stabilizing activity.

Sixty argon laser-assisted anastomoses in rats: macroscopic and histological studies.

The present in vivo study was undertaken to evaluate the patency rate and histological appearance of 30 venous anastomoses and 30 carotid anastomoses in Wistar rats using a laser. An argon laser was used with the following parameters: power, 100 mW; time, 3 seconds; continuous mode; spot, 200 microns (fluence, 950 J/cm2; irradiance. 320 W/cm2). The macroscopic appearance and patency rate were evaluated at different postoperative intervals (30 days and 60 days). In the venous group, the patency rate was 100% with no saccular pseudo-aneurysm. In the arterial group, the patency rate was 93% with three saccular pseudo-aneurysms and two thromboses. Histological studies noted slight and transitory modifications of the media in the arterial group. In the venous group, the modifications appeared under the endothelium. Since the procedure was similar in both groups, the lack of pseudo-aneurysm formation in the venous group can be explained by a lower intravascular pressure.

Determination of efficient parameters for argon laser-assisted anastomoses in rats: macroscopic, thermal, and histological evaluation.

The aim of this study was to determine efficient parameters for an argon laser (spot diameter = 200 microns) to obtain and reproduce vessel anastomoses. It was performed in two groups of Wistar rats. In the first group (89 Laser impacts on 10 carotids), the fluence was continuously adjusted from 30 to 3,000 J/cm2 in order to determine efficient sets of parameters (power from 90-200 mW, pulse duration from 0.1 to 5 seconds, pulsed or continuous mode). In the second group, 30 end-to-end carotid anastomoses were performed. The results were evaluated by macroscopic thermal, and histological studies. The second group proved the efficiency of the selected parameters. Vessel welding was obtained with 100 mW, 3 seconds, continuous mode (fluence = 950 J/cm2, irradiance = 320 W/cm2) for a mean temperature of 77 degrees C corresponding to collagen denaturation. In the second group the patency rate was 93% (28/30) with three pseudo-aneurisms and two thromboses. Histological studies noted slight modifications of the media.