Cloning, phylogenetic analysis and expression of somatolactin and its receptor in Cichlasoma dimerus: their role in long-term background color acclimation.

Somatolactin (SL) and SL receptor (SLR) belong to the growth hormone and cytokine type I receptor superfamilies, respectively. However, further research is required to define the duplications and functions of SL and its receptors in basal vertebrates including environmental background color adaptation in fish. In the present study, we cloned and sequenced SL and its putative receptor (SLR), classified and compared the sequences phylogenetically, and determined SL and SLR mRNA expression levels during long-term background color exposure in Cichlasoma dimerus, a freshwater South American cichlid. Our results show that C. dimerus SL and SLR share high sequence similarity with homologous from other perciform fish. Phylogenetic analysis indicates that C. dimerus SL belongs to the SLα clade sub-group. C. dimerus SLR is clearly a member of the GHR1 receptor subgroup, which includes the experimentally validated SLR from salmonids. Higher transcript levels of SLα in the pituitary and SLR in the epidermis and dermis cells of fish scales were observed in fish following long-term black background color exposure compared to those exposed to a white background. A higher number of melanophores was also observed in fish exposed for 10days to a black background compared to those exposed to a white background. These changes were concomitant to differences in SL or SLR transcript levels found in fish exposed to these two different background colors. Our results suggest, for the first time, that SLR is expressed in fish scales, and that there is an increase in SL in the pituitary and the putative SLR in likely target cells, i.e., melanophores, in long-term black background exposure in C. dimerus.

Effect of S-adenosylmethionine on age-induced hepatocyte damage in old Wistar rats.

Aging is accompanied by changes in the morphology and physiology of organs and tissues, such as the liver. This process might be due to the accumulation of oxidative damage induced by reactive oxygen (ROS) and reactive nitrogen species (RNS). Hepatocytes are very rich in mitochondria and have a high respiratory rate, so they are exposed to large amounts of ROS and permanent oxidative stress. S-Adenosylmethionine (SAMe) is an endogenous metabolite that has shown to exert protective effects on different experimental pathological models in which free radicals are involved. The aim of this study was to investigate the effect of SAMe on age-induced damage in hepatocytes. For this purpose, male and female Wistar rats of 18 and 2 months of age were used. Cells were isolated and, after incubation in the presence or in the absence of SAMe, different parameters were measured. Aging induced a significant increase in nitric oxide, carbon monoxide and cGMP, and a reduction in reduced glutathione, ATP and phosphatidylcholine synthesis, as well as in methionine- adenosyl-transferase and methyl-transferase activities. Incubation of old cells with SAMe prevented all these age-related changes, reaching values in some of the parameters similar to those found in young animals. In conclusion, SAMe seems to have beneficial effects against age-induced damage in hepatocytes.

Postnatal haloperidol eliminates the deficit in circling behavior produced by prenatal exposure to the same drug.

Up to 35% of pregnant women take psychotropic drugs at least once during gestation [Austin and Mitchell, 1998]. From concurrent animal and human evidence, it has been proposed that exposure to several psychoactive medications in utero or during lactation increases the risk for permanent brain disorders. Present preventive or therapy practices applied on humans for this type of long-lasting behavioral alterations are mainly based on empirical results. Here, we test an experimental approach designed to counteract a circling performance deficit that appears in Sprague-Dawley rats at puberty on exposure to the dopaminergic blocker haloperidol (HAL) during gestation [J.L. Brusés, J.M. Azcurra, The circling training: A behavioral paradigm for functional teratology testing, in: P.M. Conn (Ed.), Paradigms for the study of behavior, Acad. Press, New York, 1993, pp. 166-179. Method Neurosci. 14]. Gestational exposure to HAL (GD 5-18, 2.5 mg/kg/day ip) induced the expected circling activity decrease in the offspring at the fifth week of life. When prenatal exposure to HAL was continued through lactation (PD5-21, 1.5 mg/kg/day ip), rats otherwise showed a control-like circling performance. No difference was yet found between lactation-only, HAL-exposed pups and saline (SAL)-treated controls (n=8 each group). We further performed saturating (3H)-spiroperidol (SPI) binding assays on striatal P2 membrane fractions 2 months later. The dopamine-type D2-specific binding results suggested that above circling behavior findings could be partially explained by enduring HAL-induced neurochemical changes. The role of critical periods of sensitivity as transient windows for opportunistic therapies for behavioral teratology is discussed.

Different dopamine D1 and D2 receptors expression after motor activity in the striatal critical period.

Circling training during rat striatum postnatal critical period (PN30 to 37 days) induces a life-lasting co-reduction of muscarinic acetylcholine receptors (mAChR) and dopamine D2 receptors (D2R) binding. Here, we evaluated the expression of D1R and D2R under similar experimental conditions. Trained rats showed a decrease of 40% in D2R binding sites (p<0.01) and of 45% in the D2R mRNA expression which involve short (p<0.05) and long (p<0.01) isoforms. In contrast, D1R binding sites nor its mRNA expression levels were affected by training, indicating a differential synaptic refinement during this ontogenetically fixed period.

Delayed and bilateral changes of GAP-43/B-50 phosphorylation after circling training during a critical period in rat striatum.

During the critical period of activity-dependent plasticity in rat striatum (30-37 days after birth) physiological circling behavior induces delayed modifications in GAP-43/B-50 phosphorylation by PKC. Postexercise, ipsi- and contralateral striatum to the circling direction show a similar temporal pattern of GAP-43/B-50 phosphorylation, with an initial decrease followed by a subsequent increase. However, there is a lag between initiation of the phosphorylation response in this asymmetrical task which does not occur when animals are subjected to exercise under conditions of symmetrical motor activity.

The effects of some porphyrinogenic drugs on the brain cholinergic system.

In central nervous system, acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) hydrolyse acetylcholine. Diminished cholinesterase activity is known to alter several mental and psychomotor functions. The symptoms of cholinergic crisis and those observed during acute attacks of acute intermittent porphyria are very similar. The aim of this study was to investigate if there could be a link between the action of some porphyrinogenic drugs on brain and the alteration of the cholinergic system. To this end, AChE and BuChE activities were assayed in whole and different brain areas. Muscarinic acetylcholine receptor (mAChR) levels were also measured. Results obtained indicate that the porphyrinogenic drugs tested affect central cholinergic transmission. Quantification of mAChR gave quite different levels depending on the xenobiotic. Veronal administration inhibited 50% BuChE activity in whole brain, cortex and hippocampus; concomitantly cortex mAChR was 30% reduced. Acute and chronic isoflurane anaesthesia diminished BuChE activity by 70-90% in whole brain instead cerebellum and hippocampus mAChR levels were only altered by chronic enflurane anaesthesia. Differential inhibition of cholinesterases in the brain regions and their consequent effects may be of importance to the knowledge of the mechanisms of neurotoxicity of porphyrinogenic drugs.