Andrzej Plech

Low-dose quinpirole ontogenically sensitizes to quinpirole-induced yawning in rats

It is known that dopamine (DA) receptors can be sensitized by repeated treatments with quinpirole during postnatal development. This study was undertaken to determine whether low-dose quinpirole treatments might sensitize receptors to quinpirole-induced yawning behavior. Rats were treated with quinpirole HCl (50 micrograms/kg per day) or saline at four different periods of ontogeny: a) the 10th day of gestation to day of birth; b) 1st-11th days after birth; c) 12th-22nd days from birth; or d) 23rd-33rd days from birth. The numbers of yawns occurring in 1 h after a challenge dose of quinpirole HCl (50 micrograms/kg, IP) was determined at 6 weeks. Rats exposed prenatally to quinpirole demonstrated increased numbers of yawns following the third dose of quinpirole (2-day interval between doses). In rats exposed postnatally to quinpirole, there was a 70-300% increase in the yawning response, with the greatest response occurring in the group treated with quinpirole from birth to 11 days from birth. The findings demonstrate that quinpirole receptors are sensitized by a low dose of quinpirole, 60-fold lower than previously shown. It is suggested that sensitized receptors are of the DA D3 subclass.

Ethanol inhibits cadmium accumulation in brains of offspring of pregnant rats that consume cadmium

The present study was designed to test the effect of ethanol on cadmium accumulation in tissues of pregnant rats and their offspring. Starting 10 days before mating and continuing until parturition, ethanol (10% v/v) was present in the drinking water of half the rats. Cadmium chloride (CdCl2; 50 ppm) was present in the water of half the rats (+/- ethanol) from the fist day after mating until parturition. On the day of parturition cadmium accumulated to a moderate level in bone (7.3 micrograms/g tissue, wet weight; this and other values, P < 0.05 vs. control), liver (12.9 micrograms/g) and kidney (13.0 micrograms/g) of dams, while the brain had only a low level of cadmium (0.45 microgram/g). In offspring at 6 weeks cadmium accumulated in high amounts in the brain (34.0 micrograms/g), bone (15.9 micrograms), kidney (78.2 micrograms/g) and particularly the liver (227.3 micrograms/g). Ethanol, given simultaneously with cadmium, inhibited cadmium accumulation in brain (1.8 micrograms/g), bone (3.28 micrograms/g) and kidney (61.3 micrograms/g), but enhanced cadmium accumulation in liver (408.7 micrograms/g). At 12 weeks there were only residual levels of cadmium in all tissues of offspring. These findings demonstrate an interaction between 2 known teratogenic agents, with ethanol conferring protection of the brain from cadmium accumulation. The nature of this interaction is not known, but is likely to be related to ethanol induction of metallothionein in the liver and placenta.

Analgesic effect of low-power infrared laser radiation in rats

The aim of the study was to confirm the analgesic effect of low-power laser radiation with a tail-immersion test and check if nitric oxide is involved in laser radiation-induced analgesia in rats. The experiment was performed on male Wistar rats. On the day of experiment the scull of rats was exposed to IR laser radiation for 10 min and antinociceptive effect was determined by means of tail immersion test. The experiments were also performed on 1-NAME and methylene blue pretreated rates, in which both chemicals were administered into right lateral brain ventricle. The results were compared to the ones obtained in the control group in which sham irradiation was made. It was observed that 10 min. exposure to low-power IR laser radiation induced only transient distinct antinociceptive effect in rats. This effect was prevented by ICV. injection of 1-NAME, an inhibitor of nitric oxide synthase and methylene blue, an inhibitor of soluble guanylate cyclase. It seems that nitric oxide is involved in mechanism of low-power laser radiation- induced analgesia.

Enkephalin analogs modified in the aromatic ring of the N-terminal tyrosine residue

Abstract Two analogs of Leu 5 -enkephalin, (1- O -methyltyrosine,5-leucine)-enkephalin and [1-(3′-amino)-tyrosine,5-leucine]-enkephalin, were synthesized by classical methods. Both analogs show high biological potency after injection into the lateral brain ventricle of the rat. In both cases substitution of the Tyr residue of enkephalin leads to a pronounced prolongation of analgesic action, as compared with the unsubstituted peptide.

Leu-enkephalin content in rat brain during prolonged treatment with imipramine or amitriptyline.

The influence of imipramine (IMI) or amitriptyline (AMI) on the level of immunoreactive leu-enkephalin (ir-LENK) in the striatum and hypothalamus was studied in rats. Each drug was given by drinking water once or over periods of 1, 3, 4 and 6 months. The ir-LENK in brain perfusates was measured after 3 or 9 month treatment with IMI. The results obtained indicate that during prolonged administration of IMI the central enkephalinergic system is dynamically changed. We have observed that chronic (but not acute) administration of IMI induced different effects on LENK level in the examined structures than changes caused by treatment with AMI.

Reactivity to thermal pain stimulus in rats exposed to low-energy laser radiation

The influence on pain perception of acute and chronic exposure to infrared laser radiation applied to the skulls of rats is examined. The experiment was carried out on 60 Wistar white male rats. A semiconductive infrared laser (wavelength -- 904 nm, frequency -- 100 Hz, pulse duration -- 10 ns, mean power 10 mW, energy density 1.5 J/cm2) was used. A skull fornix of rats was irradiated with use of a multidiode probe 10 minutes daily for 14 consecutive days. The pain perception was determined by the latency of foot-licking or jumping from the surface of a 56 degree(s)C hot plate. The measurements were made immediately before irradiation, at 1, 5, 10, 15, 20, 25 and 30 minutes after irradiation, and then every 15 minutes until 120 minutes after irradiation. The pain perception is estimated immediately after irradiation, 24 hours after exposure at the 7th and 14th day of irradiation as well as at the 7th and 14th day after the last irradiation. A pretreatment with Naloxone (1 ml/kg of body weight i.p.) was made in a part of the animals in order to evaluate the involvement of the opioid system in the observed effect. Obtained data show that low-energy laser irradiation affects the pain reactivity of rats. The inhibition of the analgesic effect of laser irradiation by the antagonist of opioids -- Naloxone -- and also the prolonged character of this action as a result of direct irradiation of the skull indicate the involvement of the opioid system in the occurrence of laser-induced analgesia.

Behavioural effects of two dipeptides L-phenyl analyl-L-arginine (Phe-L-Arg) and L-phenyl alanyl-D-arginine (Phe-D-Arg) after intracerebroventricular or intrathecal injections in mice

L-phenylalanyl-L-arginine (Phe-L-Arg) and L-phenylalanyl-D-arginine (Phe-D-Arg), dissolved in a physiological saline were injected intrathecally into the lateral brain ventricle, and their behavioural as well as analgesic effects in mice were determined. It was found that a 100 nM dose of either peptide intracerebroventricularly (i.c.v.) injected induced an increase in the locomotor activity and a convulsive effect, whereas the same dose if injected produced a significant analgesic effect. It has been concluded that Phe-L-Arg and Phe-D-Arg have significant but different central effects in mice.