Plasma concentrations of corticosterone and buprenorphine in rats subjected to jugular vein catheterization.

The present study investigated the postoperative plasma concentrations of corticosterone and buprenorphine in male Wistar and Sprague-Dawley rats, treated with buprenorphine administered either through subcutaneous (SC) injection or through voluntary ingestion (VI). The animals were treated with buprenorphine for pre-emptive analgesia prior to surgical placement of a jugular catheter, followed by automated blood sampling during 96 h. Buprenorphine was administered on a regular basis throughout the experiment, and blood was collected on selected time points. Body weight was measured before and 96 h after surgery. It was found that the two rat stocks responded in a similar manner to both buprenorphine treatments, with the exception of body weight change in Wistar rats, in which body weight was reduced after SC treatment. The plasma concentration of corticosterone was significantly higher in the SC-treated animals than in the VI-treated animals during the first 18 h of the study, while plasma buprenorphine concentration was at least as high and more even over time after VI treatment. The present study shows that buprenorphine administration through VI is suitable for both Wistar and Sprague-Dawley rats, with lower stress response and higher plasma concentrations of buprenorphine than after the traditional SC route of administration.

Effects of voluntarily-ingested buprenorphine on plasma corticosterone levels, body weight, water intake, and behaviour in permanently catheterised rats.

This study investigated the peri- and postoperative effect of pre-emptive analgesia through voluntary ingestion of buprenorphine in Nutella, in male Sprague-Dawley rats. An arterial catheter was inserted and the rats were connected to an automated blood sampling device (AccuSampler). Blood samples were drawn up to 18 h after surgery and the plasma concentrations of corticosterone were quantified. Postoperative changes in water intake and body weight were recorded, and the behaviour of the rats was analysed during two 30-min periods. Pre-emptive oral buprenorphine treatment reduced the plasma corticosterone levels in the postoperative period, compared to controls treated with local anaesthetics. Buprenorphine-treated rats consumed more water and maintained body weight better. Behavioural observations indicated that buprenorphine changed the behaviour in non-operated rats but there was no difference in the operated rats. The present study strengthens the hypothesis that pre-emptive oral buprenorphine in Nutella is suitable for treatment of postoperative pain in rats.

Distribution of [3H]-corticosterone in urine, feces and blood of male Sprague-Dawley rats after tail vein and jugular vein injections.

The present study aimed to investigate the time-course and distribution of [(3)H]-corticosterone in urine, feces and blood of male Sprague-Dawley rats after intravenous administration of a low dose (1 microCi), and to investigate whether different intravenous routes of administration may affect the dynamics of excreted [(3)H]-corticosterone in the feces. One microCi [(3)H]-corticosterone was injected intravenously either through the tail vein in manually restrained rats or through a jugular vein catheter three days after surgical implantation. Urine and feces were collected at different time points over 78 h from the rats injected in the tail vein, and blood and feces were collected over 48 h from rats injected in the jugular vein. In the blood, radioactivity peaked immediately and decreased rapidly within 90 minutes. The radioactivity was excreted in urine within six h and in feces after at least 12 h. Sixty percent of the radioactivity was detected in the urine and 40% in feces during the study period of 78 h. The detected amount of radioactivity in feces was higher and displayed a more pronounced peak 12 h after injection when the substance was administered through a jugular vein catheter compared to tail vein injection. The data obtained in the present study may serve as an important benchmark when choosing time points for fecal collection for quantification of corticosterone or corticosterone metabolites as a non-invasive measure of preceding HPA-axis activation.

Corticosterone concentrations in blood and excretion in faeces after ACTH administration in male Sprague-Dawley rats.

The aim of the present study was to analyse the corticosterone response to exogenous ACTH in the circulation of catheterised male rats and to investigate the sensitivity of faecal corticosterone output as a measure of preceding elevated levels in the circulation. A total of 21 adult male Sprague-Dawley rats permanently catheterised (v. jugularis externa for intravenous administration of ACTH and a. carotis communis for blood sampling), were used. Administration of both 10 and 100 microg/kg ACTH resulted in a rapid and pronounced corticosterone increase three minutes after injection (226 and 220 ng/ml, respectively), but the duration of the response was different. In the 10 microg/kg group, corticosterone levels were significantly elevated for 3-90 min after injection, while in the 100 microg/kg group, the levels remained elevated for 240 min after injection. In faeces, a significant increase during eight hours after ACTH injection was found in the group treated with 100 microg/kg, but not in the group treated with 10 microg/kg. In conclusion, quantification of faecal excretion of corticosteroids is a useful non-invasive measure of prior substantial stress (e.g. surgery), but not sufficiently sensitive to reveal minor stress or acute stress of short duration.

High-resolution genotyping of Chlamydia trachomatis strains by multilocus sequence analysis.

Genotyping of Chlamydia trachomatis is limited by the low sequence variation in the genome, and no adequate method is available for analysis of the spread of chlamydial infections in the community. We have developed a multilocus sequence typing (MLST) system based on five target regions and compared it with analysis of ompA, the single gene most extensively used for genotyping. Sequence determination of 16 reference strains, comprising all major serotypes, serotypes A to L3, showed that the number of genetic variants in the five separate target regions ranged from 8 to 16. The genetic variation in 47 clinical C. trachomatis isolates of representative serotypes (14 serotype D, 12 serotype E, 11 serotype G, and 10 serotype K strains) was analyzed; and the MLST system detected 32 variants, whereas 12 variants were detected by using ompA analysis. Specimens of the predominant serotype, serotype E, were differentiated into seven genotypes by MLST but into only two by ompA analysis. The MLST system was applied to C. trachomatis specimens from a population of men who have sex with men and was able to differentiate 10 specimens of one predominant ompA genotype G variant into four distinct MLST variants. To conclude, our MLST system can be used to discriminate C. trachomatis strains and can be applied to high-resolution molecular epidemiology.

The effect of ketamine on intraspinal acetylcholine release: involvement of spinal nicotinic receptors.

The general anaesthetic ketamine affects the central cholinergic system in several manners, but its effect on spinal acetylcholine release, which may be an important transmitter in spinal antinociception, is unknown. This study aimed to investigate the effect of ketamine on spinal acetylcholine release. Microdialysis probes were placed intraspinally in male rats, and acetylcholine was quantified with HPLC. Anaesthesia was switched from isoflurane (1.3%) to ketamine (150 mg/kg h), which resulted in a 500% increased acetylcholine release. The increase was attenuated during nicotinic receptor blockade (50 microM mecamylamine). The nicotinic receptor agonist epibatidine (175 microM) produced a ten-fold higher relative increase of acetylcholine release during isoflurane anaesthesia compared to ketamine anaesthesia (270% to 27%). Intraspinal administration of ketamine and norketamine both increased the acetylcholine release in high concentrations (100 microM to 10 mM). The results indicate that spinal nicotinic receptors are important for the ketamine-induced acetylcholine release, and that the effect is partly mediated at the spinal level.