Ricardo Santos

Serotonin receptor activation in rats previously deprived of REM sleep.

The effects of serotonin precursors (L-5-hydroxytryptophan and L-tryptophan, with or without MAO inhibitors) and of agonists (quipazine and 5-methoxy-N,N-dimethyltryptamine-MeO-DMT) were studied in 3 day REM-deprived or control rats, by recording the presence of the serotonin syndrome and the number of head shakes. The REM sleep-deprived rats showed a larger incidence of the serotonin syndrome and a greater number of head shakes in comparison to the control animals, when challenged with the serotonin precursors. Conversely, REM sleep deprivation did not modify the responsiveness of rats to 0.75-6.0 mg/kg of MeO-DMT and to 2.4-6.0 mg/kg of quipazine. However, REM-deprived rats reacted less than controls to 0.3-1.25 mg/kg of quipazine. Increased turnover due to REM sleep deprivation could explain the augmented responsiveness of the rats to the serotonin precursors. Conversely, the decreased responsiveness to quipazine could result from receptor hyposensitivity due to intense receptor activation, caused by the increased turnover, during the 3 day period of REM sleep deprivation.

How REM sleep deprivation and amantadine affects male rat sexual behavior.

There are conflicting findings about the sexual effects of REM sleep deprivation (REMd). Otherwise, several studies show a dopaminergic hypersensitivity after REMd. The effect of REMd and amantadine (AMA) was studied for standard measures and temporal patterning in the first experiment, in four groups: normal with vehicle, normal with AMA (5.0 and 10 mg/kg), REMd with vehicle and REMd with AMA (5.0 and 10.0 mg/kg). REMd reduced mount latency (ML), intromission latency (IL) and mount number (MN) and increased copulatory efficiency (CE) and hit rate factor. REMd also reduced the mount bout number (MBN) and increased the sexual interaction (mount bout time, MBT) among male and female during copula. AMA stimulates initiation and hit rate factors and accelerates the temporal patterning of sexual behavior, evoking fewer and quicker mount bouts. In the experiments with combination of REMd and AMA administration, AMA did not increase behavior effects evoked by REM deprivation, probably due to a top or a bottom effect, depending on the measures considered. A second experiment studied the effects of AMA (1.25 to 5.0 mg/kg) and REMd on the sexual reflexes of nonimmobilized male rats. REMd enhanced the AMA effects upon the seminal emission reflex, but inhibited the penile erection reflex elicited by 1.25 mg/kg of AMA. Curiously, our results showed that REMd, like AMA, a dopaminergic agonist, causes similar effects of sexual behavior in the male rat, particularly those related to arousal mechanism and hit rate factor. The results are discussed and the effects of REMd probably involve dopaminergic hypersensitivity and increased sexual motivational response.

Lung morphometry and MMP-12 expression in rats treated with intraperitoneal nicotine.

Nicotine, a toxic tobacco component, plays an important role in the development of cardiovascular and lung diseases in smokers. Our objective was to investigate the effects of the intraperitoneal (i.p.) nicotine treatment in lung morphology. Wistar male rats (3-4 months old) were divided in five groups, a control one, and other groups treated with nicotine (1 mg/kg/day) for 8 days and sacrificed after 24, 48, 96, and 192 h. Morphometry was used to estimate the lung alveolar parenchyme and septal elastic fibers changes, and immunohistochemistry was performed to detect macrophage metalloelastase (MMP-12) and quantify vessels by immunolabelling with alpha-smooth muscle cells. Thickening of the alveolar septa was present in all nicotine groups, and associated with mononuclear cell infiltration, angiogenesis, and irregular areas of collapse. After 96 h, rat lungs showed macrophage, expressing MMP-12, that was also present after 192 h of recovery. Pleural and parenchyma inflammation, fibrosis and macrophage were also seen after 192 h. Intraperitoneal nicotine treated rats exhibited an increase of the volume fraction of alveolar parenchyme, a reduction of volume and surface fraction septal elastic fibers, and an increase of the numerical fraction of microvasculature vessels compared to control ones. MMP-12 was detected in groups of macrophages Wistar rats lung exhibited a progressive morphological damage after 192 hours of recovery, after 8 daily doses of 1 mg/kg body weight on i.p. nicotine.

Amantadine stimulates sexual behavior in male rats

The effects of amantadine on sexual behavior, penile erection, and seminal emission of male rats was studied. Amantadine significantly decreased latency of mounts in all doses (1.25 to 50 mg/kg), and decreased the number of mounts and intromission latency at the highest doses used. The lowest dose of amantadine significantly increased ejaculation latency and intromission frequency, while higher doses significantly reduced it, which indicates a biphasic response of the drug. Additionally, seminal emission, erections, and genital grooming were significantly induced by amantadine. Amantadine-induced seminal emissions were impaired by spinal cord transection, which suggests the involvement of supraspinal structures in the drug action. Haloperidol and atropine sulphate significantly reduced seminal emissions and penile erections induced by amantadine. These results demonstrate that amantadine stimulates sexual behavior and genital reflexes in male rats and suggest a facilitatory effect of the drug that probably involves different mechanisms of action.

Central responses to cholinergic drugs of REM sleep deprived rats

The present work studied the effects of REM sleep deprivation on the responses to cholinomimetic drugs in rats. Cataleptic behavior induced by pilocarpine, oxotremorine and eserine was not modified by previous REM sleep deprivation. On the other hand, the intensity of oxotremorine- and eserine-induced tremors, but not that of pilocarpine, was clearly augmented in the REMd rats and latency to the first tremor was shorter. REM sleep deprivation also potentiated the convulsions induced by nicotine. Two hypothetical mechanisms through which REM sleep deprivation could lead to the described hyperresponsiveness to cholinomimetic drugs are discussed.

Validation of a new computerized system for recording and analysing drug-induced tremor in rats.

INTRODUCTION Certain drugs can induce tremor in small animals and can be used as Parkinsons disease or essential experimental tremor models. However, the use of arbitrary scales for evaluating tremor in experimental models is limited by observer subjectivity. Progress in electronics and computer science has allowed a more precise quantification of tremor. The objective of the present study was to validate a newly developed low-cost method of spectral registration and analysis of tremor in free-moving rats. METHODS Male Wistar rats, 3-4 months of age, previously placed for 5 min inside a sensor cage, were administered with different doses of eserine (0.25-1.5 mg/kg), oxotremorine (0.25-1.5 mg/kg) or harmaline (7.5-60 mg/kg). Drug-induced tremor was recorded during 10 min using a computerized system composed of force transducers, a signal conditioning circuit, a digitizing interface and a microcomputer. The signal transmitted to the computer was quantified, stored and analyzed for its amplitude and frequency by means of specific programs. RESULTS Tremor was induced with an amplitude that was dose-dependent for all drugs used. Tremor frequency was dose-dependent for oxotremorine and eserine, but not for harmaline. The performance of the system was compared with that of other systems described in behavioral instrumentation literature. DISCUSSION The present data indicate that the new system is capable of detecting the tremor induced by drugs, and that the programs used for spectral analysis allow the quantification of the amplitude and the frequency of the tremor in free-moving rats.

Preventing L-NAME inhibitory effects on rat sexual behavior with hydralazine, isradipine or captopril co-treatment.

The effects of the chronic oral treatment with N(G)-nitro-L-arginine methyl ester (L-NAME), separately or in combination with isradipine, captopril or hydralazine, on standard and temporal patterning sexual behavior of male rats were evaluated. L-Arginine and filtered water were used as control. L-NAME treatment decreased the copulatory rate and hit rate factors of sexual behavior. However, the initiation factor and temporal patterning were less modified by the drug. After 14 days of L-NAME treatment suspension the male rat sexual response was recovered. The three antihypertensive agents were able to reverse partially or totally the inhibitory effects of L-NAME, suggesting that the chronic oral treatment with L-NAME induces penile erection dysfunction by peripheral mechanisms. The present results suggest that chronic oral treatment with nitric oxide (NO) synthase inhibitor can be a relevant and powerful peripheral erectile dysfunction model to evaluate the effects of drugs on erectile function of male rats.

Red lacrimal secretion (chromodacryorrhea) induced by cholinergic drugs in rats subjected to the watertank technique

Red tears (chromodacryorrhea) in rats are due to porphyrin pigments secreted by Harders glands and are believed to involve muscarinic mechanisms. Chromodacryorrhea was observed in rats treated with pilocarpine, oxotremorine and neostigmine and this response was blocked by anticholinergic drugs. However, in rats deprived of rapid eye movement (REM) sleep (REMd) for 3 days, through the watertank technique, chromodacryorrhea did not develop even when cholinergic agonists were given in doses severalfold higher than those active in non-REMd animals. Decrease of chromodacryorrhea also was obtained in rats previously treated with neostigmine; conversely, previous treatment with atropine induced an increased chromodacryorrhea when the rats were further challenged with pilocarpine and oxotremorine. It is proposed that the absence of red tears in REMd rats might be due to a down regulation of peripheral cholinergic receptors.

Triiodothyronine (T3) modifies cholinergic-induced hypothermia and tremor in rats

Hypothermia and tremor responses of oxotremorine and eserine were studied in rats after several T3 treatment regimens. The T3 antagonized oxotremorine-induced hypothermia and failed to antagonize eserine hypothermic effect, but potentiated oxotremorine- and eserine-induced tremors. Acetylcholinesterase activity was not altered in T3 rats. The hypothetical mechanisms to explain changes of central cholinergic responses caused by T3 are discussed.

Nicotine pretreatment diminished physostigmine-induced tremor in rats.

The aim of this work was evaluate the effects of acute and chronic nicotine pretreatment in the physostigmine-induced tremor in rats. Wistar male rats (3-4 months) were pretreated acutely with different nicotine doses (0, 0.1, 0.5 or 1.0 mg/kg) 10 min before physostigmine (0 and 0.5 mg/kg) treatment and then the tremor was registered by computerized system for 10 min. In another group, rats were pretreated acutely with 0.1 mg/kg of nicotine, recovered at different times (30 or 70 min), and were registered for physostigmine-induced tremor. Nicotine was also used chronically with equal doses for 8 days and recovered at 2, 7 or 21 days before registration of physostigmine-induced tremor. Tremor spectral analysis was performed for amplitude and frequency quantification. Our data show that the acute and chronic nicotine pretreatments alter physostigmine spectrum profile. Nicotine decreased physostigmine-induced tremor amplitude (p<0.05), without changing its tremor frequency. In acutely pretreated rats, recovery experiments showed return of physostigmine-induced tremor for control levels after 70 min, but after 8 days of chronic nicotine pretreatment recovery was delayed 3 weeks. The data analysis shows that acute or chronic nicotine administration can alleviate the physostigmine-induced tremor. Chronic nicotine pretreatment has a long tremor alleviation effect of physostigmine-induced tremor. Possible mechanisms involving the nicotine effects on the physostigmine-induced tremor are discussed.