Cranial irradiation with Gaalas laser leads to naloxone reversible analgesia in rats.

Laser irradiation of the rat cranium can produce analgesia. The present experiment investigated the mechanism of such action. 27 rats received all possible combinations of laser (0, 6.4, and 12J/cm2) and naloxone (0, 5, and 10 mg/kg) prior to a hot plate test. Laser (820 nm, KHz pulsing, Omega Laser Systems, London) was applied to the rats' skulls and hind paw lick latencies (in seconds) were recorded immediately, 30 min., and 24 hr. after the administration of treatment. When animals were tested immediately following laser irradiation at 12J/cm2 significant analgesia resulted. Treatment with naloxone at either dose antagonised this effect, but naloxone produced no significant hyperalgesia when given alone. This suggests that opioid peptide mechanisms mediate the analgesic action of low-intensity laser irradiation of the cranium.

Analgesic effects of cranial laser treatment in two rat nociception models.

The present experiments sought to establish dose dependency and time course for effects of cranial laser irradiation in two rodent models of pain. These were the hot plate and tail flick tests, which are both widely used to quantify analgesic drug effects. The laser used was an Omega Biotherapy 3ML (wavelength 820 nM, average power output 100 mW, pulse frequency 5 kHz) and irradiation was applied to rats' shaved heads above the midbrain. In the first experiment, four groups of 10 rats received doses of 0, 6, 12, 18, and 24 J/cm2 in random orders prior to hot plate testing either immediately, 30 min, 1 h or 24 h postlaser. The second study employed three groups of 10 rats receiving 0, 12, and 18 J/cm2 in random orders prior to tail flick testing at the three shorter times above. Latency to lick hind paws on the hot plate was highly significantly prolonged by laser treatment across all doses and time periods, F(4, 126) = 4.51, p < 0.01. There was good dose dependency for immediate observations, but at 24 h 18 J/cm2 was the most effective dose. Laser treatment also delayed tail flick responses at both doses and all time periods, F(2, 54) = 10.60, p < 0.001, but 12 and 18 J/cm2 doses were similar in efficacy.

Direct evidence for mediation of an anticonflict effect of baclofen by GABAb receptors.

The present article reports an experiment on the effects of baclofen (0, 0.5, 1.0, and 2.0 mg/kg) on punished drinking in rats and the modification of these by delta-amino-n-valeric acid (DANVA) (0 and 10.0 mg/kg). Baclofen significantly enhanced punished drinking and this increase was abolished by DANVA, which had no intrinsic anxiogenic activity. It is concluded that GABAb receptors probably mediate this effect of baclofen and that such receptors may be a potential site of anxiolytic drug action.