Scielo RSS <![CDATA[Biological Research]]> https://scielo.conicyt.cl/rss.php?pid=0716-976020050002&lang=en vol. 38 num. 2-3 lang. en <![CDATA[SciELO Logo]]> https://scielo.conicyt.cl/img/en/fbpelogp.gif https://scielo.conicyt.cl <![CDATA[UNA BREVE RELEXIÓN SOBRE FINANCIAMIENTO DE LA <b> <strong>INVESTIGACIÓN CIENTÍFICA, FORMACIÓN DE RECURSOS </strong> <strong>HUMANOS Y PLAN DE INNOVACIÓN Y DESARROLLO</strong></b>]]> https://scielo.conicyt.cl/scielo.php?script=sci_arttext&pid=S0716-97602005000200001&lng=en&nrm=iso&tlng=en <![CDATA[Reply to Nespolo's paper entitled "New invariants and dimensionless numbers: Futile renaissance of old fallacies?"]]> https://scielo.conicyt.cl/scielo.php?script=sci_arttext&pid=S0716-97602005000200002&lng=en&nrm=iso&tlng=en <![CDATA[<strong>Protein synthesis in eukaryotes</strong>: <strong>The growing biological </strong><b> <strong>relevance of cap-independent translation initiation</strong></b>]]> https://scielo.conicyt.cl/scielo.php?script=sci_arttext&pid=S0716-97602005000200003&lng=en&nrm=iso&tlng=en Ribosome recruitment to eukaryotic mRNAs is generally thought to occur by a scanning mechanism, whereby the 40S ribosomal subunit binds in the vicinity of the 5'cap structure of the mRNA and scans until an AUG codon is encountered in an appropriate sequence context. Study of the picornaviruses allowed the characterization of an alternative mechanism of translation initiation. Picornaviruses can initiate translation via an internal ribosome entry segment (IRES), an RNA structure that directly recruits the 40S ribosomal subunits in a cap and 5' end independent fashion. Since its discovery, the notion of IRESs has extended to a number of different virus families and cellular RNAs. This review summarizes features of both cap-dependent and IRES-dependent mechanisms of translation initiation and discusses the role of cis-acting elements, which include the 5'cap, the 5'-untranslated region (UTR) and the poly(A) tail as well as the possible roles of IRESs as part of a cellular stress response mechanism and in the virus replication cycle <![CDATA[<strong><i>Biological Research</i></strong><strong> Impact Factors</strong>: <strong>1998-2004</strong>]]> https://scielo.conicyt.cl/scielo.php?script=sci_arttext&pid=S0716-97602005000200004&lng=en&nrm=iso&tlng=en Ribosome recruitment to eukaryotic mRNAs is generally thought to occur by a scanning mechanism, whereby the 40S ribosomal subunit binds in the vicinity of the 5'cap structure of the mRNA and scans until an AUG codon is encountered in an appropriate sequence context. Study of the picornaviruses allowed the characterization of an alternative mechanism of translation initiation. Picornaviruses can initiate translation via an internal ribosome entry segment (IRES), an RNA structure that directly recruits the 40S ribosomal subunits in a cap and 5' end independent fashion. Since its discovery, the notion of IRESs has extended to a number of different virus families and cellular RNAs. This review summarizes features of both cap-dependent and IRES-dependent mechanisms of translation initiation and discusses the role of cis-acting elements, which include the 5'cap, the 5'-untranslated region (UTR) and the poly(A) tail as well as the possible roles of IRESs as part of a cellular stress response mechanism and in the virus replication cycle <![CDATA[The effect of temperature and irradiance on the growth and carotenogenic capacity of seven strains of <i>Dunaliella salina</i> (Chlorophyta) cultivated under laboratory conditions]]> https://scielo.conicyt.cl/scielo.php?script=sci_arttext&pid=S0716-97602005000200005&lng=en&nrm=iso&tlng=en The carotenogenic microalga Dunaliella salina is cultivated as a natural source of ß-carotene. The 9-cis isomer of ß-carotene is found only in natural sources having commercial advantages over the all-trans isomer due to its high liposolubility and antioxidant power. High irradiance appears to stimulate specifically all-trans ß-carotene accumulationin D. salina, whereas low temperature apparently elicits ß-carotene and 9-cis ß-carotene production. We studied the effect of temperature and irradiance on the growth and the carotenogenesis of three Chilean (CONC-001, CONC-006 and CONC-007) and four non-Chilean (from Mexico, China, Australia and Israel) strains of D. salina cultivated under two photon flux densities (40 and 110 μmol photons.m-2.s-1) and two temperatures (15 and 26ºC). The Chilean strain CONC-001 and all of the non-Chilean strains exhibited the highest growth rates and the maximum cell densities, whereas the Chilean strains CONC-006 and CONC-007 showed the lowest values in both parameters. The Australian strain showed the highest accumulation of total carotenoids per unit volume (40.7 mg.L-1), whereas the Chilean strains CONC-006 and CONC-007, the only ones isolated from Andean environments, yielded the highest amounts of carotenoids per cell (61.1 and 92.4 pg.cell_1, respectively). Temperature was found to be more effective than irradiance in changing the qualitative and quantitative carotenoids composition. The Chilean strains accumulated 3.5-fold more &#ß;-carotene than the non-Chilean strains when exposed to 15ºC and, unlike the non-Chilean strains, also accumulated this pigment at 26ºC. The 9-cis/all-trans ß-carotene ratio was > 1.0 in all treatments for all strains, and the values were not greatly influenced by either temperature or photon flux density. Physiological and biotechnological implications of these results are discussed <![CDATA[<strong>Role of the phosphatase PP4 in the activation of JNK-1 in prostate carcinoma cell lines PC-3 and LNCaP resulting in increased AP-1 and EGR-1 activity </strong>]]> https://scielo.conicyt.cl/scielo.php?script=sci_arttext&pid=S0716-97602005000200006&lng=en&nrm=iso&tlng=en The specific signaling connections between the mitogen-activated protein kinases (MAPK) such as c-Jun N-terminal kinase (JNK-1) and phosphatases PP4 and M3/6, affecting the family of early nuclear factors, is complex and remains poorly understood. JNK-1 regulates cellular differentiation, apoptosis and stress responsiveness by up-regulating early nuclear factors such as c-Jun, a member of the activating protein (AP-1) family, and the Early Growth Factor (EGR-1). C-Jun, when phosphorylated by c-Jun N-terminal kinase (JNK-1) associates with c-Fos to form the AP-1 transcription factor that activates gene expression. We have investigated the regulation of the JNK-1 kinase by co-transfecting phosphatases PP4 and M3/6 in prostate cancer cell lines PC-3 and LNCaP, which have been previously stimulated with human EGF or cisplatin. Co-transfections of plasmids expressing the JNK-1 and the serine/threonine phosphatases PP4 resulted in a significant increase in JNK-1 activity in both PC3 and LNCaP cells. In contrast, co-transfection of JNK-1 with the dual specific phosphatase serine/threonine M3/6 showed only a marginal effect in JNK-1 activity. The phosphatase M3/6 also failed in blocking the induction of JNK-1 activity observed in presence of PP4. The higher activity of JNK-1 was associated with increased activities of the factors c-Jun/AP-1 and EGR-1. This suggests that JNK-1 activity in PC-3 and LNCaP cells requires not only active PP4 for stable maintenance but also suggests that the relative degree of phosphorylation of multiple cellular components is the determinant of JNK-1 stability. <![CDATA[<strong>Roles of nibrin and ATM/ATR kinases on the G2 checkpoint under endogenous or radio-induced DNA damage </strong>]]> https://scielo.conicyt.cl/scielo.php?script=sci_arttext&pid=S0716-97602005000200007&lng=en&nrm=iso&tlng=en Checkpoint response to DNA damage involves the activation of DNA repair and G2 lengthening subpathways. The roles of nibrin (NBS1) and the ATM/ATR kinases in the G2 DNA damage checkpoint, evoked by endogenous and radio-induced DNA damage, were analyzed in control, A-T and NBS lymphoblast cell lines. Short-term responses to G2 treatments were evaluated by recording changes in the yield of chromosomal aberrations in the ensuing mitosis, due to G2 checkpoint adaptation, and also in the duration of G2 itself. The role of ATM/ATR in the G2 checkpoint pathway repairing chromosomal aberrations was unveiled by caffeine inhibition of both kinases in G2. In the control cell lines, nibrin and ATM cooperated to provide optimum G2 repair for endogenous DNA damage. In the A-T cells, ATR kinase substituted successfully for ATM, even though no G2 lengthening occurred. X-ray irradiation (0.4 Gy) in G2 increased chromosomal aberrations and lengthened G2, in both mutant and control cells. However, the repair of radio-induced DNA damage took place only in the controls. It was associated with nibrin-ATM interaction, and ATR did not substitute for ATM. The absence of nibrin prevented the repair of both endogenous and radio-induced DNA damage in the NBS cells and partially affected the induction of G2 lengthening. <![CDATA[F(ab')<sub>2 </sub>antibody fragments against <i>Trypanosoma cruzi</i> calreticulin inhibit its interaction with the first component of human complement]]> https://scielo.conicyt.cl/scielo.php?script=sci_arttext&pid=S0716-97602005000200008&lng=en&nrm=iso&tlng=en Trypanosoma cruzi calreticulin (TcCRT), described in our laboratory, retains several important functional features from its vertebrate homologues. We have shown that recombinant TcCRT inhibits the human complement system when it binds to the collagenous portion of C1q. The generation of classical pathway convertases and membrane attack complexes is thus strongly inhibited. In most T. cruzi-infected individuals, TcCRT is immunogenic and mediates the generation of specific antibodies. By reverting the C1q / TcCRT interaction, a parasite immune evasion strategy, these antibodies contribute to the host / parasite equilibrium. In an in vitro correlate of this situation, we show that the C1q / TcCRT interaction is inhibited by F(ab')2 polyclonal anti-TcCRT IgG fragments. It is therefore feasible that in infected humans anti-TcCRT antibodies participate in reverting an important parasite strategy aimed at inhibiting the classical complement pathway. Thus, membrane-bound TcCRT interacts with the collagenous portion C1q, and this C1q is recognized by the CD91-bound host cell CRT, thus facilitating parasite internalization. Based on our in vitro results, it could be proposed that the in vivo interaction between TcCRT and vertebrate C1q could be inhibited by F(ab')2 fragments anti-rTcCRT or against its S functional domain, thus interfering with the internalization process <![CDATA[Human intoxication with paralytic shellfish toxins: Clinical parameters and toxin analysis in plasma and urine]]> https://scielo.conicyt.cl/scielo.php?script=sci_arttext&pid=S0716-97602005000200009&lng=en&nrm=iso&tlng=en This study reports the data recorded from four patients intoxicated with shellfish during the summer 2002, after consuming ribbed mussels (Aulacomya ater) with paralytic shellfish toxin contents of 8,066 ± 61.37 mg/100 gr of tissue. Data associated with clinical variables and paralytic shellfish toxins analysis in plasma and urine of the intoxicated patients are shown. For this purpose, the evolution of respiratory frequency, arterial blood pressure and heart rate of the poisoned patients were followed and recorded. The clinical treatment to reach a clinically stable condition and return to normal physiological parameters was a combination of hydration with saline solution supplemented with Dobutamine (vasoactive drug), Furosemide (diuretic) and Ranitidine (inhibitor of acid secretion). The physiological condition of patients began to improve after four hours of clinical treatment, and a stable condition was reached between 12 to 24 hours. The HPLC-FLD analysis showed only the GTX3/GTX2 epimers in the blood and urine samples. Also, these epimers were the only paralytic shellfish toxins found in the shellfish extract sample <![CDATA[Allometric scaling of biological rhythms in mammals]]> https://scielo.conicyt.cl/scielo.php?script=sci_arttext&pid=S0716-97602005000200010&lng=en&nrm=iso&tlng=en A wide spectrum of cyclic functions in terrestrial mammals of different size, from the 3-gram shrew to the 3-ton elephant, yields an allometric exponent around 0.25, which is correlated _ as a kind of common denominator _ with the specific metabolic rate. Furthermore, the applicability of these empirical findings could be extrapolated to chronological events in the sub-cellular realm. On the other hand, the succession of growth periods (T98%) until sexual maturity is reached also follows the 1/4 power rule. By means of Verhulst's logistic equation, it has been possible to simulate three different biological conditions, which means that by modifying the numerical value of only one parameter, revertible physiological and pathological states can be obtained, as for instance isostasis, homeostasis and heterostasis <![CDATA[Estrogen supplementation failed to attenuate biochemical indices of neutrophil infiltration or damage in rat skeletal muscles following ischemia]]> https://scielo.conicyt.cl/scielo.php?script=sci_arttext&pid=S0716-97602005000200011&lng=en&nrm=iso&tlng=en This study examined the effects of estrogen supplementation on markers of neutrophil infiltration and damage in skeletal muscle of rats following ischemia. Male and female gonad-intact rats, with or without 14 days of estrogen supplementation were subjected to two hours of hind-limb ischemia and sacrificed at 24, 48 or 72 hours post-ischemia. Control animals were sacrificed without ischemia. Plantaris and red and white gastrocneimus muscles were removed and assayed for myeloperoxidase (MPO), a marker of neutrophil infiltration, and glucose-6-phosphate dehydrogenase (G6PD) and ß-glucuronidase (<img border=0 width=8 height=15 id="_x0000_i1026" src="http://fbpe/img/bres/v38n2-3/existe.gif" align=absbottom>GLU), as markers of muscle damage. Significant elevations of MPO, G6PD and <img border=0 width=8 height=15 id="_x0000_i1027" src="http://fbpe/img/bres/v38n2-3/existe.gif" align=absbottom>GLU activities were observed at various time points post-ischemia. No systematic differences between genders were noted in any of the measures. Estrogen supplementation in both male and female animals failed to significantly attenuate post-ischemia increases in MPO, G6PD and <img border=0 width=8 height=15 id="_x0000_i1028" src="http://fbpe/img/bres/v38n2-3/existe.gif" align=absbottom>GLU activities in any of the muscles studied and in some cases accentuated activities of some of these measures. Unlike previous findings following exercise in skeletal muscle, this study failed to demonstrate estrogen-induced attenuation of indices of neutrophil infiltration or damage in skeletal muscles of rats up to 72 hours following ischemia. This demonstrates that estrogen may not consistently attenuate neutrophil infiltration and that a number of variables including damage modality, tissue or estrogen level may influence this. <![CDATA[Effects of neuromuscular blocking agents on central respiratory chemosensitivity in newborn rats]]> https://scielo.conicyt.cl/scielo.php?script=sci_arttext&pid=S0716-97602005000200012&lng=en&nrm=iso&tlng=en Neuromuscular blocking agents suppress central respiratory activity through their inhibitory effects on preinspiratory neurons and the synaptic drive from preinspiratory neurons to inspiratory neurons. Central CO2-chemosensitive areas, which partly consist of CO2-excited neurons, in the rostral ventrolateral medulla are thought to provide tonic drive to the central respiratory network and involve cholinergic mechanisms, which led us to hypothesize that neuromuscular blocking agents can inhibit CO2-excited neurons and attenuate respiratory CO2 responsiveness. To test this hypothesis, we used isolated brainstem-spinal cord preparations from newborn rats. The increase of C4 burst frequency induced by a hypercapnic superfusate, i.e. respiratory CO2 responsiveness, was suppressed by the application of neuromuscular blocking agents, either d-tubocurarine (10, 100μM) or vecuronium (100μM). These agents (40μM) also induced hyperpolarization and decreases in firing frequency of CO2-excited neurons in the rostral ventrolateral medulla. Our results demonstrate that neuromuscular blocking agents inhibit CO2-excited tonic firing neurons and attenuate respiratory CO2 responsiveness. <![CDATA[Response to the gonadotropin releasing hormone agonist leuprolide in immature female sheep androgenized <i>in utero</i>]]> https://scielo.conicyt.cl/scielo.php?script=sci_arttext&pid=S0716-97602005000200013&lng=en&nrm=iso&tlng=en Similar to women with Polycystic Ovary Syndrome (PCOS), female sheep treated prenatally with testosterone (T-females) are hypergonadotropic, exhibit neuroendocrine defects, multifollicular ovarian morphology, hyperinsulinemia and cycle defects. Hypergonadotropism and multifollicular morphology may in part be due to developmentally regulated increase in pituitary responsiveness to GnRH and may culminate in increased ovarian estradiol production. In this study, we utilized a GnRH agonist, leuprolide, to determine the developmental impact of prenatal testosterone exposure on pituitary-gonadal function and to establish if prenatal exposure produces changes in the reproductive axis similar to those described for women with PCOS. Eight control and eight T-females were injected intravenously with 0.1 mg of leuprolide acetate per kilogram of body weight at 5, 10 and 20 weeks of age. Blood samples were collected by means of an indwelling jugular vein catheter at 0, 3, 6, 9, 12, 18, 24, 30, 36, 42 and 48 hours after leuprolide. Area under the curve (AUC) of LH response to leuprolide increased progressively between the three ages studied (P<0.05). AUC of LH in T-females was higher than in control females of the same age at 5 and 10 weeks of age (P<0.05), but similar at 20 weeks of age. AUC of estradiol response was lower at 10 but higher at 20 weeks of age in T-females compared to controls of the same age (P<0.05). Our findings suggest that prenatal T treatment alters the pituitary and ovarian responsiveness in a manner comparable to that observed in women with PCOS. <![CDATA[<strong><i>In vivo</i></strong><strong> and <i>in vitro</i> estrogenic and progestagenic actions of Tibolone </strong>]]> https://scielo.conicyt.cl/scielo.php?script=sci_arttext&pid=S0716-97602005000200014&lng=en&nrm=iso&tlng=en Estrogen and progestin combination in hormone replacement therapy (HRT) increases the incidence of breast cancer, but decreases the endometrial cancer risk of unopposed estrogen. Therefore, a SERM such as Tibolone, that delivers the beneficial, but not the adverse side effects, of steroid hormones would be clinically advantageous. However, data from the Million Women Study suggests that Tibolone increases the risk of both breast and endometrial cancer. Herein, we assessed the estrogenic and progestagenic actions of Tibolone using transvaginal sonography studies and an in vitro model of breast (ZR-75, MCF7) and endometrial cancer (Ishikawa). The known cancer associated proteins (ER, EGFR, STAT5, tissue factor and Bcl-xL) were selected for study. Transvaginal sonography demonstrated that postmenopausal women treated with Tibolone displayed a thinner endometrium than in the late proliferative phase, but had a phenotype characteristic of the secretory phase, thus demonstrating the estrogenic and progestagenic actions of this SERM. In vitro, Tibolone acted as an estrogen in downregulating ER and upregulating Bcl-xL, yet as progesterone, increasing STAT5 and tissue factor in breast cancer cells. The increase in tissue factor by Tibolone correlated with its coagulative potential. Interestingly, EGFR was up-regulated by progesterone in the breast and by estrogen in endometrial cells, while Tibolone increased protein levels in both cell types. In conclusion, this study further demonstrates the estrogenic and progestagenic nature of Tibolone. The pattern of regulation of known oncogenes in cells of breast and endometrial origin dictates caution and vigilance in the prescription of Tibolone and subsequent patient monitoring <![CDATA[Altered dopamine levels induced by the parasite <i>Profilicollis antarcticus</i> on its intermediate host, the crab <i>Hemigrapsus crenulatus</i>]]> https://scielo.conicyt.cl/scielo.php?script=sci_arttext&pid=S0716-97602005000200015&lng=en&nrm=iso&tlng=en A serotonergic pathway is apparently involved in parasite-host interactions. Previous studies conducted in our laboratory showed increased rates in oxygen consumption and alterations in body posture in the crab Hemigrapsus crenulatus parasitized by the acanthocephalan, Profilicollis antarcticus. Such changes may be related to the functions described for biogenic amines in crustaceans. During the infective stage the acanthocephalans live freely in the hemocelomic cavity, suggesting that the possible alteration induced by biogenic amines may be related to their neurohormonal function in crustaceans. To test whether the presence of P. antarcticus produced neurohormonal changes in its intermediate host, H. crenulatus, we analyzed serotonin and dopamine levels in the host using HPLC with electrochemical detection. Two groups of 11 female crabs were studied; one group was artificially inoculated with two cystacanths while the other was used as the control. Our results show a dramatic increase in hemolymph dopamine, but not serotonin in H. crenulatus parasitized by the acanthocephalan P. antarcticus. Our results, along with those reported by Maynard (1996), suggest a parasite-specific strategy involved in the behavior alteration caused by the acanthocephalans on their intermediate host. The use of a biogenic amine as a mechanism of interaction by the parasites gives them an endless number of alternative potential actions on their intermediate hosts <![CDATA[Tissue mRNA expression in rat of newly described matrix metalloproteinases]]> https://scielo.conicyt.cl/scielo.php?script=sci_arttext&pid=S0716-97602005000200016&lng=en&nrm=iso&tlng=en Matrix metalloproteinases (MMPs) comprise a large group of endoproteinases that degrade all protein components of the extracellular matrix. Functionally, MMPs contribute to several different physiological as well as pathological conditions. The number of newly described MMPs has increased in recent years, although current knowledge about their expression pattern in various tissues remains incomplete. Here we analyzed the relative mRNA expression of the most recently described MMPs _ MT5-MMP (MMP-24), MT6-MMP (MMP-25), MMP-27 and epilysin (MMP-28) _ in a broad selection of rat tissues using real time-PCR. MMP-24 mRNA was found to be widely expressed with predominance in the central nervous system. MMP-25 mRNA, in contrast, exhibited peak expression levels in testis, kidney and skeletal muscle, differing from previously described distribution patterns in humans. mRNAs for MMP-27 and MMP-28 were generally expressed at a lower level. All four MMPs studied were detected at higher mRNA levels in bone and kidney, suggesting a possible role of these MMPs in physiological processes within these two organs. The present study highlights the differential distribution pattern of newly described MMPs among different tissues and underlines differences in the mRNA expression between different species. <![CDATA[Genetic polymorphism of GSTM1 in women with breast cancer and interact with reproductive history and several clinical pathologies]]> https://scielo.conicyt.cl/scielo.php?script=sci_arttext&pid=S0716-97602005000200017&lng=en&nrm=iso&tlng=en Due to the conflicting results regarding the association between breast cancerand the GSTM1 null mutation, our aim was to research this associationin a Brazilian population and correlations withsmoking, reproductive history and several clinical pathologies. A case-control study was performed on 105 women with breast cancer and 278 controls. Extraction of DNA was accomplished according to the protocol of the GFX® kit and polymorphism analysis by the PCR technique. The control and experimental groups were compared and statistical analysis assessed by X² or Fisher's exact test. The deletion in the GSTM1 gene in the breast cancer group had a prevalence of 32 (30.4%) individuals with the presence of null mutation. In the control group, the null mutation was present in 104 (37.4%) women. Upon comparison of the two groups, no statistically significant difference of the GSTM1 gene was observed, with an odds ratio (OR) of 0.74, 95%, confidence interval (CI) 0.45 - 1.20, p = 0.277. The results conclusively show that singlegene GSTM1 polymorphisms do not confer a substantial risk of breastcancer to its carriers. Furthermore, in this study no correlation was found between GSTs andsmoking, reproductive history and several clinical pathologies with respect to cancer risk. <![CDATA[A Lux-like Quorum Sensing System in the Extreme Acidophile <i>Acidithiobacillus ferrooxidans</i>]]> https://scielo.conicyt.cl/scielo.php?script=sci_arttext&pid=S0716-97602005000200018&lng=en&nrm=iso&tlng=en The genome of the acidophilic, proteobacterium Acidithiobacillus ferrooxidans, contains linked but divergently oriented genes, termed afeI and afeR, whose predicted protein products are significantly similar to the LuxI and LuxR families of proteins. A possible promoter and Lux box are predicted upstream of afeI. A cloned copy of afeI, expressed in E. coli, encodes an enzyme that catalyzes the production of a diffusible compound identified by gas chromatography and mass spectrometry as an unsubstituted N-acyl homoserine lactone (AHL) of chain length C14. This AHL can be detected by a reporter strain of Sinorhizobium meliloti Rm41 suggesting that it is biologically active. The reporter strain also responds to extracts of the supernatant of A. ferrooxidans grown to early stationary phase in sulfur medium indicating that a diffusible AHL is produced by this microorganism. Semi-quantitative RT-PCR experiments indicate that afeI and afeR are expressed maximally in early stationary phase and are more expressed when A. ferrooxidans is grown in sulfur- rather than iron-containing medium. Given the predicted amino acid sequence and functional properties of AfeI and AfeR it is proposed that A. ferrooxidans has a quorum sensing system similar to the LuxI-LuxR paradigm. <![CDATA[Wheel-running and rest activity pattern interaction in two octodontids (<i>Octodon degus</i>, <i>Octodon bridgesi</i>)]]> https://scielo.conicyt.cl/scielo.php?script=sci_arttext&pid=S0716-97602005000200019&lng=en&nrm=iso&tlng=en Wheel-running and other non-photic stimuli influence the rest-activity pattern of diurnal and nocturnal mammals. A day to night inversion of phase preference of activity was described among Octodon degus, when exposed to ad-libitum wheel running. We have studied the rest-activity pattern response in presence of ad libitum wheel-running in wild-captured male individuals from two species of genus Octodon: O. degus (n=9, crepuscular-diurnal) and O. bridgesi (n=3, nocturnal). After two months of habituation to laboratory conditions, recordings were performed in isolation chambers under a 12:12 light-dark schedule with or without access to a running wheel. Actograms were constructed from data obtained by an automated acquisition system. O. bridgesi were also recorded under constant darkness, with or without access to wheel-running. Entrained to the light-dark schedule, a crepuscular pattern of activity was evident for O. degus, whereas O. bridgesi displayed a robust nocturnal chronotype. The activity of O. degus observed during the dark phase was enhanced when wheel-running was allowed. No significant change in phase preference was observed for O. bridgesi when wheel-running was allowed. A lengthening of endogenous period was observed in O. bridgesi after wheel-running exposure under constant darkness. Nocturnal and diurnal octodontids exhibit different masking responses to wheel-running. <![CDATA[XLVIII <strong>REUNIÓN ANUAL DE LA</strong><b> <strong>SOCIEDAD DE BIOLOGÍA DE CHILE</strong></b> <b>XII REUNION ANUAL DE LA SOCIEDAD DE ECOLOGÍA DE CHILE</b> <b>XXVII CONGRESO CHILENO DE MICROBIOLOGÍA</b>]]> https://scielo.conicyt.cl/scielo.php?script=sci_arttext&pid=S0716-97602005000200020&lng=en&nrm=iso&tlng=en Wheel-running and other non-photic stimuli influence the rest-activity pattern of diurnal and nocturnal mammals. A day to night inversion of phase preference of activity was described among Octodon degus, when exposed to ad-libitum wheel running. We have studied the rest-activity pattern response in presence of ad libitum wheel-running in wild-captured male individuals from two species of genus Octodon: O. degus (n=9, crepuscular-diurnal) and O. bridgesi (n=3, nocturnal). After two months of habituation to laboratory conditions, recordings were performed in isolation chambers under a 12:12 light-dark schedule with or without access to a running wheel. Actograms were constructed from data obtained by an automated acquisition system. O. bridgesi were also recorded under constant darkness, with or without access to wheel-running. Entrained to the light-dark schedule, a crepuscular pattern of activity was evident for O. degus, whereas O. bridgesi displayed a robust nocturnal chronotype. The activity of O. degus observed during the dark phase was enhanced when wheel-running was allowed. No significant change in phase preference was observed for O. bridgesi when wheel-running was allowed. A lengthening of endogenous period was observed in O. bridgesi after wheel-running exposure under constant darkness. Nocturnal and diurnal octodontids exhibit different masking responses to wheel-running.