An adaptable microcomputer program for recording behavior durations

The uroprotection of mesna on cyclophosphamide cystitis in rats. Its consequences on behaviour and brain activities

We studied the uroprotective effect of mesna, at doses of 40-300 mg/kg/i.p., in single or fractioned injections, on the development of cyclophosphamide (CP, 100 mg/kg/i.p.) cystitis in rats. The study concerns the histological, behavioural and nervous aspects of the disease. The specific effects of mesna, when injected alone, have also been considered. The mesna itself does not have specific deleterious effects, except at a dose of 300 mg/kg which provokes a moderate vesical inflammation although without consequence on the animal's behaviour. Mesna offers good protection against CP cystitis for only certain posologies. The uroprotective effects of mesna reach maxima at doses of 40-100 mg/kg and for fractioned injections given over the entire time frame of the urinary toxic release. The uroprotective effects of other posologies are only partial. The nervous activities were studied through the expression of Fos protein. The repetitive intraperitoneal injection of mesna induced a spinal activity and a preferential contralateral activity of the trigemino/reticular areas of the brainstem spinal cord junction--an effect which was reduced in the presence of CP. The prevention of cystitis by mesna was accompanied only by a reduction in spinal Fos activity, the supraspinal activities remaining high and in strict relationship with the vagal afferent activity. In conclusion, the uroprotective effect of mesna, which requires appropriate posologies, has led to the confirmation of the spinal actions of the CP cystitis, probably via the pelvic nerve, but did not allow a clear distinction between the consequences of the systemic (vagal) and local (spinal, pelvic) actions of CP at supraspinal level.

Opioid stimulation in the ventral tegmental area facilitates the onset of maternal behavior in rats

This research investigated the effect of an increase or decrease in opioid activity in the ventral tegmental area (VTA) on the onset of maternal behavior in rats. In Experiment 1, the latency to show maternal behavior toward foster rat pups (sensitization latency) was determined in maternally naive female rats given either nothing or a unilateral intra-VTA injection of morphine sulfate (MS) (0.0, 0.01, 0.03, 0.1 or 0.3 microgram), on the first three days of a 10-day period of constant exposure to pups. Rats treated with 0.03 microgram MS had significantly shorter sensitization latencies than did rats treated with 0.0 microgram MS, 0.01 microgram MS, or receiving no treatment (higher doses of morphine produced intermediate results). The facilitating effect of intra-VTA MS on the onset of maternal behavior was blocked by pretreatment with naltrexone hydrochloride and was found to have a specific site of action in the VTA (MS injections dorsal to the VTA were ineffective). In Experiment 2, sensitization latencies were determined in periparturitional rats given a bilateral intra-VTA injection of either the opioid antagonist naltrexone methobromide (quaternary naltrexone), its vehicle, a sham injection, or left untreated 40 min after delivery of the last pup. The mothers' own pups were removed at delivery; mothers were nonmaternal at the time of testing. Quaternary naltrexone treatment produced significantly slower sensitization to foster pups than did control conditions. Total activity and pup-directed activity did not differ significantly with treatment. The results demonstrate that increased opioid activity in the VTA facilitates the onset of maternal behavior in inexperienced nonpregnant female rats, and decreased opioid activity in the VTA disrupts the rapid onset of maternal behavior at parturition.

The peripheral antinociceptive effect of morphine in a rat model of facial pain

The present study compared the peripheral and systemic antinociceptive effect of morphine on formalin-induced facial pain behavior in the rat. Formalin (5%, 50 microliters) was injected subcutaneously into the vibrissal pad of adult rats (250-300 g). Morphine sulfate at doses of 100-1000 micrograms was subcutaneously injected locally (same area) or systemically (in the neck), 30 min before, or simultaneously with, formalin. The typical biphasic face grooming response, consisting of an early phasic phase (0-6 min) and a delayed tonic phase (12-42 min), displayed by control animals, was suppressed by both local and systemic administration of morphine; this effect was dose dependent. However, the suppression of the early phase with local morphine administration 30 min before formalin could be significantly greater (49-52%) than with systemic administration, depending on the dose used. Administration of local morphine simultaneously with formalin produced up to 34% reduction in the early and an additional 32% reduction of the late phases of face grooming, compared to systemic injections. Local injection of naloxone (10 micrograms) almost completely reversed the antinociceptive effect of 1000 micrograms of morphine (early phase 85 +/- 7%, late phase 100 +/- 26% reduction), whereas the same dose of naloxone applied systemically (i.p.) produced only partial reversal (early phase 29 +/- 16%, late phase 36 +/- 1% reduction). This study further indicates that locally administered morphine can exert an analgesic effect superior to systemic administration in the case of inflammatory and non-inflammatory pain through a peripheral site of action. These results support the clinical use of peripheral opioid administration in the treatment of human painful conditions.

Fos expression in the medullary dorsal horn of the rat after chronic constriction injury to the infraorbital nerve

Chronic constriction injury to the rat's infraorbital nerve (IoN-CCI) induces asymmetric face grooming directed to the injured nerve territory and, beginning at 7-12 days postoperative, hyperresponsiveness to mechanical stimulation in this territory (B.P. Vos, A.M. Strassman, and R.J. Maciewicz, 1994, J. Neurosci. 14:2708-2723). To examine central mechanisms involved in these behavioral alterations, changes in nonevoked and mechanical stimulation-evoked fos-like immunoreactivity (fos-LI) following IoN-CCI were quantified in the medullary dorsal horn. Following the appearance of hyperresponsiveness in IoN-CCI rats, experimental and matched sham-operated rats were anesthetized with urethane and received either no stimulation or repeated stimulation with either a 2- or 15-g von Frey hair applied to the hairy skin between vibrissae B3-4/C3-4 on the operated side. Unstimulated IoN-CCI rats had increased fos-LI in laminae I-IV of the ipsilateral medullary dorsal horn. In both groups, mechanical stimulation produced a distinct pattern of fos-LI in the ipsilateral medullary dorsal horn, the quantity of which was related to stimulus intensity. For both stimulus intensities, the total amount and the rostrocaudal spread of evoked fos-LI were significantly larger in IoN-CCI rats. In IoN-CCI rats, stimulation-evoked increases in fos-LI were proportionally larger in laminae I-II than in III-IV. This laminar effect was also present in sham-operated rats but only for 15-g stimulation. Neither condition nor stimulus intensity affected fos-LI in the contralateral medullary dorsal horn. Positive correlations were found between the behavioral parameters of increased trigeminal nociceptive activity and the total amount of fos-LI in the ipsilateral medullary dorsal horn. The results demonstrate that IoN-CCI induces significant alterations in the central processing of afferent signals, which may underlie behavioral manifestations of increased nociceptive activity.

The NMDA antagonist Memantine blocks pain behavior in a rat model of formalin-induced facial pain

Recent studies have provided evidence that excitatory amino acid antagonists can exert analgesic effects in animals. These studies, however, have focused primarily on phasic pain or hyperalgesia rather than tonic pain. The present study evaluates the effects of systemic administration of Memantine (1-amino-3,5-dimethyl-adamantane), a clinically used N-methyl-D-aspartate (NMDA) receptor antagonist, on formalin-induced phasic and tonic pain behavior in the rat. Memantine (2.5, 5.0, 10.0 and 20.0 mg/kg) or normal saline was injected i.p. 1 h prior to a s.c. injection of formalin (5%, 50 microliters) into the vibrissal pad of adult rats (n = 5/group). Pain behavior was measured by the number of seconds of formalin-induced face grooming during a 42-min post-injection observation period. Saline-injected animals displayed a biphasic face-grooming response, consisting of an early, phasic phase (0-6 min) and a delayed, prolonged tonic phase (12-42 min). Memantine at doses of 2.5-10 mg/kg produced a significant dose-related inhibition of the second phase (65-93%) and a much smaller inhibition of the first phase (up to 52%). A higher dose (20 mg/kg) further inhibited both phases but also produced other motor effects (increased exploratory and decreased freezing behavior, hind-paw weakness and gait ataxia) which were not observed at the lower doses. These results suggest that the NMDA receptor antagonist Memantine can block formalin-induced tonic and, to a lesser extent, phasic pain, at doses that do not alter observed motor behaviors.

An adaptable microcomputer program for monitoring behavior

We describe an improvement of a flexible and easy to use program for monitoring and recording behavior durations with IBM-compatible microcomputers and a companion program that provides additional versatility for handling data. Up to 35 behaviors or events can be monitored, and processing speed is fast enough to measure even very rapidly performed behaviors. No specialized hardware is required, and the data files that are created are compatible with commercially available software packages for statistical analysis.

Amniotic fluid ingestion enhances opioid-mediated but not nonopioid-mediated analgesia

Ingestion of amniotic fluid or placenta by rats has been shown to enhance several types of opioid-mediated analgesia: that induced by morphine, footshock, vaginal/cervical stimulation, and late pregnancy. This enhancement has also been blocked by administration of opioid antagonists. The present study was designed to examine further the specificity of the enhancement effect for opioid-mediated analgesia by testing for enhancement following administration of aspirin, a nonopioid analgesic. The formalin test was used as the pain threshold assay. Amniotic fluid or beef bouillon was administered by orogastric tube to rats that were treated either with morphine sulfate or saline, or pretreated with naltrexone, then treated with aspirin or vehicle. Both morphine and aspirin treatments produced analgesia. Amniotic fluid significantly enhanced the analgesia produced by morphine, but did not enhance the analgesia produced by aspirin, further suggesting that the enhancing effect of amniotic fluid ingestion is specific for opioid-mediated analgesia, such as that existing at the start of parturition.