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Biomedical subjects

P Lomax

Publications and source records attributed to P Lomax.

At least 73 records · Page 4Linked to original sources
PubMed1976

Dopaminergic involvement in withdrawal hypothermia and thermoregulatory behavior in morphine dependent rats.

Thermoregulatory behavior was assessed in the rat by measuring the time taken to escape from a radiant heat source. The time to excape and the rise in core temperature accompanying exposure to heat were greater in morphine dependent (1 X 75 mg SC pellet implant for 72 hr) than in control rats. Injection of naloxone (1 mg/kg) into dependent rats produced a withdrawal hypothermia and decreased the time taken to escape from the heat source. Since rats undergoing withdrawal avoided heat at the same time that their core temperature was falling, the hypothermia is most likely due to a downward setting of the central thermostats rather than a direct activation of heat loss pathways. Both the withdrawal hypothermia and the behavioral changes were blocked by pimozide pretreatment (0.5 mg/kg) implicating a dopaminergic mechanism in the downward setting of the thermostats. Administration of naloxone 144 hr after pellet implantation produced similar effects to those in the 72 hr implanted group. Injection of morphine sulfate (4 mg/kg) 144 hr after implantation increased both the core temperature and the time taken to escape from heat suggesting that the effect of morphine in the dependent rat is to produce an upward setting of the thermostats.

Animals↗
PubMed1976

Brain amines and spontaneous epileptic seizures in the Mongolian gerbil.

The seizure sensitive (WJL)UC) strain of Mongolian gerbils has been used to investigate the effects of drugs that modify central monoamine activity on spontaneous epileptiform seizures. Increasing central norepinephrine and dopamine levels significantly reduced the severity of the seizures and the importance of dopamine was further demonstrated by the protection from seizures after administration of the dopaminergic agonist apomorphine. These data indicate that a search for differences in regional levels, or turnover rates, of these amines between seizure sensitive and seizure resistant strains of gerbils might be profitable in determining the genetic deficit underlying the seizure phenomenon in these animals.

Animals↗
PubMed1976

Changes in sensitivity to apomorphine during morphine dependence and withdrawal in rats.

Stereotyped behavior induced by injection of apomorphine hydrochloride (10 mg/kg i.p) was measured in control rats, rats made dependent on morphine and dependent rats undergoing naloxone-precipitated withdrawal. The dose of apomorphine chosen was approximately the ED50 dose, so that changes in sensitivity to apomorphine in either direction could be determined. Rats which had received a subcutaneous morphine (75 mg) pellet implant 72 hours previously demonstrated an increased sensitivity to apomorphine when compared with placebo-implanted controls. During withdrawal precipitated by injection of naloxone hydrochloride (0.2 mg/kg i.p.) this increased sensitivity disappeared. Naloxone alone, in a dose of 1.0 mg/kg but not 0.2 mg/kg, significantly antagonized apomorphine-induced stereotyped behavior and these effects of apomorphine were also reduced by an acute injection of morphine sulfate (10 mg/kg). The significance of these findings with regard to changes in central dopaminergic systems during dependence and withdrawal is discussed.

Animals↗
PubMed1975

Histamine H1- and H2-receptors in the central thermoregulatory pathways of the rat.

The effects of pyrilamine and burimamide (histamine H1- and H2-receptor blockers, respectively) on the hypothermic response to histidine loading have been studied in rats. The antagonists were injected into one of three sites in the brain: the preoptic/anterior hypothalamic nuclei, the lateral ventricle, or the third ventricle. Only injections of burimamide into the third ventricle blocked the hypothermic response to systemic injection of histidine. Behavioral studies revealed that, after histidine, the animals increased their time of exposure to a heat lamp, which suggests that efferent heat loss pathways had been activated. Previous studies have shown that H1-receptor antagonists will block the hypothermic effect of histamine injected into the rostral hypothalamus. These data suggest that there are, at least, two sets of histaminergic receptors on the neuronal pathway through the hypothalamus: H1-receptors in the rostral hypothalamus and H2-receptors on neurons lying close to the wall of the third ventricle. Activation of this thermoregulatory pathway leads to increased heat loss and a fall in body temperature.

Animals↗
PubMed1975

The Mongolian gerbil (Meriones unguiculatus) as a model for the study of the epilepsies: EEG records of seizures.

EEG recordings have been made from freely moving, seizure sensitive gerbils during seizures of varying severity. The localization of seizure activity in various brain areas and the generalization of this activity could be correlated with the observed motor manifestations. Paroxysmal observed motor manifestations. Paroxysmal bursting has also been recorded in the parietal cortex of a xeizure sensitive animal in which no concomitant peripheral motor activity was evident. These observations strengthen the suggestion that selectively bred epileptic strains of Meriones unguiculatus may be a suitable animal model for the study of the epilepsies.

Animals↗
PubMed1975

Acute and chronic effects of beta9-tetrahydrocannabinol on seizures in the gerbil.

Beta9-THC was injected daily for 6 days into gerbils from our breeding colony that exhibit spontaneous epileptiform seizures. At a dose of 20 mg/kg no effect was seen on the latency, duration or severity of the seizures induced after 1 and 6 days of treatment. Delta9-THC (50 mg/kg) completely abolished the seizures after a single injection but tolerance developed to this effect so that no protection was afforded after 6 daily doses. Severe toxic signs were evident at the higher dose level with marked depression of spontaneous motor activity. The toxic effect increased progressively with chronic treatment and half the animals failed to survive.

Animals↗