[Effects of temperature on the viability and infectivity of preparasitic larvae of Romanomermis yuanenesis]

Romanomermis yuanenesis (Mermithidae: Nematoda) was found in Henan, China (Song and Peng, 1987), which has a broad host range in Culicinae mosquito and has been used successfully in field test for control of culex tritaeniorhynchus, culex fatigans and Aedes albopictus in Sichuan, Yunnan, Guangxi and Henan Provinces. This study was attempted to determine the viability and infectivity of preparasitic larvae in various temperatures. The cultures containing R. yuanenesis eggs were flooded 2h with distilled water, filtered and blocked with 1% agarose. Put the filter paper into water, then the motile preparasites separated from the unhatched eggs and got through the agarose membrane into water. About 200ml water containing preparasites free from eggs were held at 26 degrees C-28 degrees C, 16 degrees C-18 degrees C and -2 degrees C to 2 degrees C for test. The motility or lack of motility was used as the criterion to distinguish the living and dead nematodes. The rate of infection of mosquitoes and the rate of parasitism of nematodes were used to show the infectivity of the preserved preparasites. The results showed that at -2 degrees C to 2 degrees C, more than 90% of preparasitic larvae of R. yuanenesis survived for 8 days and the rate of mosquito infection was 87.5% to 100%, but at 26 degrees C-28 degrees C and 16 degrees C-18 degrees C the survival times of 90% preparasites were only 24 hours and 48 hours respectively. It indicates the low temperature preservation may prolong the survival time and keep the infectivity of these preparasitic larvae.

Hepatic biotransformation in rodents and physicochemical properties of 23(R)-hydroxychenodeoxycholic acid, a natural alpha-hydroxy bile acid

The hepatic biotransformation in the rat and hamster of 23(R)-hydroxychenodeoxycholic acid (23(R)OH-CDCA), the alpha-hydroxy derivative of CDCA, was defined; some physiological and physicochemical properties were also assessed. 23(R)OH-CDCA was isolated from duck bile; [24-14C]23(R)OH-CDCA was synthesized. The compound was administered intravenously to anesthetized biliary fistula rats at doses of 1, 3, or 5 mu mol/kg-min and to hamsters at 3 mu mol/min-kg. Biliary bile acids and radioactivity were analyzed by thin-layer chromatography (TLC), high pressure liquid chromatography (HPLC), and gas chromatography-mass spectrometry (GC-MS). Recovery of radioactivity in bile was incomplete (50-70% of infused dose); some was also recovered as breath 14CO2. Radioactivity in bile was present as unchanged compound (25-50%, dose-dependent) and its conjugates (with taurine, with glycine, or with glucuronate). Nor-CDCA (C23) was present in bile (in both unconjugated and conjugated form), indicating that 23(R)OH-CDCA had undergone oxidative decarboxylation (alpha-oxidation) with loss of the C-24 carboxyl group. The alpha-oxidation was 20 +/- 5% (mean +/- SD) of administered dose in the rat and was not dose-dependent; in hamsters, alpha-oxidation was 35 +/- 8%. In rats, the S isomer of 23OH-CDCA also underwent alpha-oxidation (10 +/- 2%). Nor-CDCA also underwent 6beta-hydroxylation to form nor-alpha-muricholic acid, as well as reduction of its C-23 carboxyl group to form the C23 alcohol. The taurine conjugate of 23(R)OH-CDCA [23(R)OH-CDC-tau] was prepared synthetically and characterized by 1H-NMR. By surface tension measurements, it had a critical micellization concentration (CMC) of 3.5 mM (in 0.15 M Na+), as compared to 1.8 mM for CDC-taurine. Aqueous solubility of 23(R)OH-CDCA increased markedly above pH 5, compared to pH 7 for CDCA. When incubated with cholylglycine hydrolase, 23(R)OH-CDC-tau was deconjugated at a rate one-fourth that of CDC-tau. It is concluded that the presence of a 23(R)-hydroxyl group in a 3alpha, 7alpha-dihydroxy bile acid alters its metabolism in the rodent hepatocyte, as evidenced by inefficient conjugation with taurine or glycine, alpha-oxidation to nor (C23) bile acid, and reduction of the nor bile acid to the primary alcohol. The taurine conjugate of 23(R)OH-CDCA, a major biliary bile acid of marine mammals and wading birds, is a biological detergent with properties superior to those of the taurine conjugate of CDCA. Natural C23 nor-bile acids may be formed by alpha-oxidation of alpha-hydroxy C24 bile acids.

Immunoregulatory role of neurotransmitters

The nervous and endocrine systems modulate the immune system functions through releasing neurotransmitters, neuropeptides and endocrine hormones as they regulate the other physiological functions. The immune system in turn communicates with the nervous and endocrine systems through secreting immunocompetent substances. In this report we review our concepts and evidence concerning the immunoregulatory role of acetylcholine (ACh) and monoamine neurotransmitters which include noradrenaline (NA), 5-hydroxytryptamine (5-HT) and dopamine (DA). The immunoregulatory role comprises two aspects, the modulation of immune functions by neurotransmitters and the effect of the immune system on nervous system functions. The inhibition of ACh biosynthesis in the central nervous system (CNS) caused the enhancement of the humoral immune response of rats to sheep red blood cells (SRBC); by contrast, the inhibition of acetyl-cholinesterase (AChE) activity in the CNS resulted in the suppression of the immune response. It seems that ACh in the brain plays an immunoinhibitory role. The role can be blocked by atropine, a muscarinic antagonist, but not by hexamethonium, a nicotinic antagonist. During the humoral immune response (days 3-6 after SRBC injection), activity of AChE in the hypothalamus and hippocampus was strikingly lower. It is suggested that a functional connection is present in the ACh of the brain and the immune system. In vitro, ACh at 10(-9) to 10(-4) mol/l dose range significantly strengthened the spleen cell proliferation induced by concanavalin (Con A). The action of ACh only occurred either before or just after T lymphocytes were activated through muscarinic cholinergic receptors. In vivo, the depletion of monoamine neurotransmitters or only NA in the CNS caused the impairment of the anti-SRBC response of rats. During the phases of days 2-7 post-immunization, the metabolic alterations of NA, 5-HT and DA emerged in the CNS and the lymphoid organs of rats, which mainly exhibited that in the peak periods of the antibody response, the metabolism of the monoamine neurotransmitters in the hypothalamus and hippocampus was markedly increased, but NA content in the spleen and thymus was significantly decreased. These results provide evidence for the bidirectional information exchange network between the monoamine neurotransmitters and the immune system. Exposure to NA (at 10(-8)-10(-5) mol/l concentration range) in vitro was shown to inhibit the Con A-induced proliferation of the rat spleen cells. This effect of NA was related to the early events involved in the initiation of T cell proliferation and was mediated by either alpha- or beta-adrenergic receptors. The evidence that altering 5-HT level in the central or peripheral nervous systems through various ways of administering the drugs to regulate 5-HT biosynthesis led to the variations of the antibody response, and that cyproheptadine, an antagonist of serotoninergic receptors, can block the action of 5-HT show that 5-HT may exert an immunoinhibitory effect, which appears to be mediated via the peripheral mechanism to relate to the 5-HT receptors. However, the antibody response can cause changes in 5-HT metabolism in the CNS. The possible reasons for these results are discussed. Collectively, the antibody response arouses the metabolic variations of ACh, NA, 5-HT and DA in the central and peripheral nervous systems and then, these alterations can in turn influence immune function through neurotransmitter relevant receptors present on the immunocytes. The purpose of this interaction is most likely to maintain the homeostasis of the immune and other physiological functions.

Reversal of the antinatriuretic effect of prostaglandin E2 by verapamil in the rat

Previous studies have demonstrated that prostaglandin E2 (PGE2) infusion increases intrarenal angiotensin-II (ANG-II) formation and decreases sodium excretion in the rat. PGE2 infusion may have direct tubular effects or indirect effects through increased intrarenal ANG-II. In the present study, the calcium channel blocker verapamil was used to determine whether it would reverse the PGE2-induced decrease in sodium excretion. To minimize any systemic and hemodynamic influences, verapamil and PGE2 were infused directly into the renal interstitium via a chronically implanted matrix. Fractional sodium excretion (FENa), glomerular filtration rate (GFR), mean arterial pressure (MAP), and plasma renin activity (PRA) were measured before and during renal interstitial infusion of PGE2 (10(-5) M) and/or verapamil (10(-3) M) in rats pretreated with indomethacin. The renal interstitial infusion of PGE2 alone significantly decreased FENa (delta-1.0 +/- 0.2%), whereas the addition of verapamil reversed the effect of PGE2 and significantly increased FENa (delta 2.6 +/- 0.3%, n = 9). The renal interstitial infusion of verapamil alone markedly increased FENa (delta 1.7 +/- 0.3%, n = 7), and this natriuresis was accompanied by a significant decrease in PRA (delta-0.6 +/- 0.1 ng/ml/h, p < 0.05). The addition of PGE2 to the interstitial infusion did not further affect FENa or PRA. There was a significant difference between the effect of interstitial PGE2 infusion and interstitial PGE2 infusion and interstitial verapamil infusion on PRa (delta 1.9 +/- 0.8 vs. delta -0.6 +/- 0.1 ng/ml/h, p < 0.05). GFR and MAP remained unchanged in response to the renal interstitial infusion of PGE2 and/or verapamil. In conclusion, verapamil reversed the PGE2-induced antinatriuresis in the rat.

Factors accounting for different responses of pulmonary and cerebral vessels to hypoxia

The roles of sympathicus, sensory neuropeptides (SNP), cyclooxygenase metabolites (COX-M), lipoxygenase metabolites (LOX-M), endothelium derived relaxing factor (EDRF), reactive oxygen (ROS) and potassium channels (PC) in the hypoxic pulmonary vasoconstriction (HPV) and hypoxic cerebral vasodilation (HCVD) were investigated in intact rats, rabbits and dogs. The results showed that during hypoxia, the excitation of sympathicus caused a constriction of both pulmonary and cerebral vessels, while SNP, EDRF and the opening of voltage sensitive PC caused the dilation of both of them; LOX-M mediated HPV and HCVD, COX-M might serve as their modulators; the blockade of ATP sensitive PC induced by hypoxia mediated HPV, but had no effect on HCVD; the reduction of O2-. in the lung might potentiate HPV, however, O2-. remained unchanged in brain during hypoxia. It is suggested that the alterations of LOX-M, ROS and the ATP sensitive PC are the factors accounting for the difference in the response of pulmonary and cerebral vessels to hypoxia.

[The effect of intra-aortic balloon pumping in case of left main coronary artery stenosis]

In order to improve perfusion of coronary artery in case of coronary artery stenosis, effect of intra-aortic balloon pumping (IABP) on coronary blood flow (CBF) was investigated. To this end hemodynamic parameters of heart functions with and without stenosis were analysed under IABP. Hemodynamic effect of IABP was obviously influenced by the coronary artery stenosis.

Comparison of systemic and direct intrarenal angiotensin II blockade on sodium excretion in rats

To dissociate the renal effects from the systemic effects of angiotensin II blockade, the present study was designed to determine the effects of systemic and renal interstitial infusion of the specific angiotensin II (ANG II) receptor antagonist, losartan, on blood pressure and sodium excretion in rats fed a low-, normal, or high-sodium diet. Fractional sodium excretion (FENa) and mean arterial pressure (MAP) were measured in rats before and during systemic infusion of losartan (10 mg/kg) or renal interstitial infusion of losartan (3 mg/kg) by means of a chronically implanted matrix. In rats fed a low- or normal sodium diet, systemic infusion of losartan markedly decreased MAP (delta -21 +/- 2, delta -10 +/- 2 mmHg, respectively; P < 0.05) with an accompanying fall in FENa (delta -0.10 +/- 0.05, delta -0.91 +/- 0.40%, respectively; P < 0.05). In contrast, preferential blockade of renal ANG II with renal interstitial losartan infusion resulted in an increase in FENa (delta 0.13 +/- 0.04, delta 0.95 +/- 0.45%, respectively; P < 0.05) and no significant change in MAP. In rats fed a high-sodium diet, both systemic and renal interstitial infusion of losartan increased FENa (delta 1.90 +/- 0.26, delta 1.40 +/- 0.56%, respectively; P < 0.05). Although systemic infusion of losartan decreased MAP (delta -4.4 +/- 0.6 mmHg, P < 0.05) in rats fed a high-sodium diet, the reduction in MAP was much less than that in rats fed a low- and normal sodium diet.(ABSTRACT TRUNCATED AT 250 WORDS)

Development of a polymer-enzyme immunoassay method and its application

Both poly(N-isopropylacrylamide) and poly(N-isopropylacrylamide)-antibody (PINP-Ab)-labelled enzyme adhered quickly and tightly to cellulose acetate/nitrate membrane either below (less efficiently) or above (more efficiently) the lower critical solution temperature, and the retention of PINP-Ab on the membrane increased over 30-fold when compared with the unconjugated Ab. These characteristics were used to develop a novel polymer-enzyme-linked immunoassay method: homogeneous antigen-antibody immune-complexation reaction and a heterogeneous separation process. By using a simple horseradish-peroxidase-labelled antibody as a probe, we applied this method to the detection of human serum hepatitis B surface antigen (HBsAg). This immunoassay system can detect as little as 1 ng/ml of HBsAg. The advantages of this method are: (a) fast homogeneous immune complexation; (b) a rapid heterogeneous separation process; (c) high sensitivity; and (d) low non-specific background.

Changes of cellular morphology and nuclear DNA content in different nasopharyngeal epithelium from different patients

Cellular morphology and nuclear DNA content were measured with point-counting technique and flow cytometry (FCM) respectively in normal nasopharyngeal epithelium (NE), tissue adjacent to carcinoma (ATC) and nasopharyngeal carcinoma (NPC). The results showed that all 20 patients with NE showed diploid, whereas 38 (38%) of 101 patients with NPC, 7 (58%) of 12 patients with recurrent NPC, 6 (30%) of 20 patients with ATC and 2 (33%) of 6 patients with NE positive to EBVCA-IgA test showed nondiploid. A total of 19 morphometric parameters of the cell were measured and calculated. The results showed that with malignant transformation of NE, most of the cellular morphometric parameters gradually increased in numerical values while no marked difference was shown between normal NE and simple hyperplasia or metaplasia in terms of cytomorphometric characteristics. Most of the parameters in dysplasia changed significantly as compared with those normal NE, simple hyperplasia or metaplasia and NPC groups. Cytomorphometric analysis seems to give strong support to the concept that dysplasia is among the transitional stages of disease process between normal NE and NPC. Our results show that morphometric analysis and FCM may offer valuable and objective criteria in the early diagnosis of NPC and premalignant disease.

Predictors for failure of Pneumocystis carinii pneumonia prophylaxis. Multicenter AIDS Cohort Study

OBJECTIVE

To identify clinical and epidemiological factors associated with failure of Pneumocystis carinii pneumonia (PCP) prophylaxis in those receiving primary and secondary prophylaxis.

DESIGN

Longitudinal cohort study of participants infected with human immunodeficiency virus type 1 in the Multicenter AIDS Cohort Study who used PCP prophylaxis regimens after their T-helper lymphocyte counts had decreased to less than 0.200 x 10(9)/L (200/microL).

MAIN OUTCOME MEASURE

Occurrence or recurrence of PCP.

RESULTS

A total of 476 participants reported taking one or more of the following regimens: trimethoprim-sulfamethoxazole (TMP-SMX), dapsone, and/or aerosolized pentamidine--367 as primary prophylaxis and 109 as secondary prophylaxis after a previous episode of PCP. A total of 92 (20%) developed PCP despite prophylaxis. The mean failure rates per person-year of follow-up were 16.0% for those receiving primary prophylaxis and 12.1% for those receiving secondary prophylaxis (P = .19). Median times to death after initiation of primary or secondary prophylaxis were 2.0 and 1.2 years, respectively. The main predictor for failure of PCP prophylaxis was profound T-helper lymphocytopenia; 86% of failures occurred after T-helper cell counts decreased to less than 0.075 x 10(9)/L and 76% occurred after counts decreased to less than 0.050 x 10(9)/L. In multivariate time-dependent analysis, when compared with counts between 0.100 x 10(9)/L and 0.200 x 10(9)/L, the risk ratio for failure with counts less than 0.050 x 10(9)/L was 2.90 (P < .001). Once T-helper cell counts were considered, fever was the only other health status indicator that predicted subsequent PCP (ie, a time-dependent risk ratio of 2.22; P = .01). Use of TMP-SMX as the prophylaxis regimen was protective but did not eliminate failure (ie, a time-dependent risk ratio of 0.55; P = .03).

CONCLUSIONS

These findings strongly support identifying improved methods of PCP prophylaxis once T-helper cell counts decrease to less than 0.075 x 10(9)/L or 0.100 x 10(9)/L. Given this severe degree of immunosuppression, an inherently more effective regimen against P carinii is required.

High-specificity neurological localization using a connectionist model

Most previous connectionist models for diagnosis have been developed using error backpropagation. While these systems function reasonably well, they have been limited by their need for a large database of test cases, to situations where a single disorder is present, and by the large number of connections required between fully-connected sets of processing units. Here we describe a recently developed connectionist model that overcomes these limitations. This approach can reuse existing causal knowledge bases, works well in situations where multiple disorders can occur simultaneously, and does not require fully-connected sets of processing units. We demonstrate that the accuracy of this model is comparable to that of more conventional AI programs using the same knowledge base in determining precisely the site of brain damage in a group of 50 stroke patients. These results support the conclusion that connectionist models can effectively use pre-existing causal knowledge bases from AI systems, and that they can function accurately when handling actual clinical problems.

Glycine and GABAA antagonists reduce the inhibition of primate spinothalamic tract neurons produced by stimulation in periaqueductal gray

Amino acids are demonstrated to be important neurotransmitters mediating the inhibitory transmission from nucleus raphe magnus to spinal nociceptive dorsal horn neurons. In this study, the role of glycine and GABA in the inhibitory processes evoked by stimulation in periaqueductal gray (PAG) of responses of primate spinothalamic tract (STT) neurons to cutaneous mechanical and thermal stimuli was investigated by examining the effects of strychnine and bicuculline, antagonists of glycine and GABAA receptors, respectively, introduced into the dorsal horn through a microdialysis fiber. The inhibitory effects of iontophoretic application of glycine and GABAA agonists on STT cell activity evoked by noxious mechanical stimulation of the skin were selectively blocked by their specific antagonist, strychnine or bicuculline, infused into the dorsal horn. Similarly, intra-spinal application of strychnine or bicuculline resulted in a significant reduction in the PAG stimulation-induced inhibition of responses of STT cells to cutaneous stimuli. This reduction was mainly on the PAG-induced inhibition of the responses to noxious mechanical stimuli. Our results suggest that glycinergic and GABAergic inhibitory interneurons in the spinal cord dorsal horn synapsing on STT cells are activated during stimulation in PAG and contribute to descending antinociceptive actions.

Markers of thromboembolization in a bovine ex vivo left ventricular assist device model

The production of blood microemboli (BME) was studied using an ex vivo exteriorized left ventricular assist device (LVAD) model in calves. Each of eight calves received a series of three LVADs, each operating for 24 hr. Blood microemboli were measured directly by a laser (624 nm and 828 nm) light scattering microemboli detection (LSMD) system through the LVAD outflow cannula and by constant pressure filtration (CPF) of blood samples from the LVAD outflow cannula. Hematologic parameters were also measured. After LVAD removal, perivalvular thrombi were evaluated using polar coordinate mapping. The average LSMD and CPF results correlated. For example, in one series of three calves, one ventricle exhibited significantly greater thrombogenesis than did the other ventricles, as indicated by both the LSMD and CPF results. In a series of five calves, one calf developed an abnormally high activated thromboplastin time (APTT), even in the absence of heparin. For two of the three ventricles tested in that calf, microemboli concentration (CPF), Factor XII activity, level of fibrin degradation products (FDP), and accumulated thrombus were significantly lower than for the other calves. The whole blood viscosity (WBV, at 230 s-1) in this calf also decreased to lower values than were seen with the other calves.

Hyperglycemia delays rostral initiation sites during neural tube closure

Neural tube defects contribute greatly to perinatal loss, physical handicap, mental retardation and other developmental defects, yet the mechanisms through which they occur are poorly understood. One hindrance to the study of these defects at the cellular and molecular levels is the low frequency with which they arise in susceptible animals. The present study utilizes a culture system for the study of rodent exencephaly, an animal model of human anencephaly, in which a high frequency of affected animals are obtained by culture in hyperglycemic rat serum. Rat embryos were dissected at day 9.5 from timed-pregnant Sprague-Dawley dams and cultured under standard conditions developed by New [Biol. Rev. (1978) 53,81-122]. Embryos cultured under elevated glucose conditions are able to close the caudal neural tube with the failure of neural tube closure limited to the rostral neuralepithelium. In this report we present the novel finding that, although at the end of culture frequently only the hindbrain region remains open, the normal sequence of events expected during rostral closure anterior to the hindbrain is markedly delayed. In embryos cultured in hyperglycemic serum, both rostral initiation sites II and III are significantly delayed. The degree of delay increases with increasing glucose concentration in the culture medium. These studies support the use of this defined in vitro model of anencephaly for studies of the molecular and cellular bases underlying the failure of hindbrain closure and demonstrate that sufficient numbers of affected animals can be produced to obtain significant results.(ABSTRACT TRUNCATED AT 250 WORDS)

[Hypertension inducing cerebrovascular damage and effecting on cerebral infarction]

Cerebrovascular damage of renovascular hypertensive rats (RHR) was observed under light microscope and electron microscope, and the cerebral collateral vessels of RHR were observed with vascular casts. In focal cerebral ischemia of RHR, the infarct volume was measured by TTC staining in combination with computer image processing and analysis. When hypertension persisting longer, there were hyalinosis in small arterial walls, luminal narrowing and basement membrane thickening in capillaries, decreased collateral vessels, and occluded microvessels. In cerebral ischemia, the infarct volume was large and could not be improved. The results demonstrated that the key to prevent stroke is to prevent and treat hypertension as early as possible.

[Study on endocytosis and nuclear accumulation of epidermal growth factor (EGF) in normal C3H mouse fibroblast cells C3H10 T1/2C18 and 3H-TdR transformed counterpart cells]

In this study, we investigated endocytosis and nuclear accumulation of epidermal growth factor (EGF) in normal C3H mouse embryo fibroblast cells C3H10 T1/2 C18 (designated NC3H10) and 3H-TdR transformed counterpart cells (designated TC3H10). The results revealed that 125I-labelled EGF bound to the receptor on the cell surface of the two cell lines was subsequently endocytosed and translocated from the cell membrane to the nucleus, where it progressively accumulated. NC3H10 showed more EGF accumulation in nucleus than TC3H10 (p < 0.05). SDS-polyacrylamide gel electrophoresis revealed that the endocytosed 125I-EGF associated with the nucleus was intact, with negligible breakdown products present. The nuclear accumulation of intact EGF in the mentioned cell lines exposed to ammonium chloride (a lysosomal inhibitor) was higher than the control (p < 0.05). These results suggested that receptor-mediated endocytosis and nuclear accumulation of EGF may play an important role in mediation some of the action of EGF.

[Preliminary mechanism studies of siwenmycin on the inhibition of nucleic acid syntheses]

Siwenmycin, isolated from a streptomyces culture, is a new member of aclacinomycin analogues. It exhibited a remarkable inhibitory effect on the biosynthesis of DNA and RNA in vivo. In order to recognize the mechanism of the inhibitions, the reactions of siwenmycin to DNA template, DNA polymerase I and RNA polymerase were studied. Experimental results showed that siwenmycin could intercalate DNA, but it did not inhibit DNA polymerase I-mediated DNA repair replication and T7RNA polymerase-mediated DNA transcription. This indicates that siwenmycin is not a damage to the DNA template function, nor will it inhibit DNA polymerase I and T7RNA polymerase, though it can intercalate DNA.

[Electrophoretic analysis of isoenzyme and protein patterns of Romanomermis yunanensis and R. culicivorax (Nematoda:Mermithidae)]

Isoenzyme electrophoretic patterns of lactate dehydrogenase (LDH), malate dehydrogenase (MDH), esterase (EST) and peroxidase (PO) of post-parasitic juveniles and adults of Romanomermis yunanensis and R. culicivorax were analysed by disc electrophoresis, respectively. The protein patterns of the two species of Romanomermis were compared by vertical slab SDS polyacrylamide gel electrophoresis. The results showed marked differences in isoenzyme patterns (number of bands and/or Rf) of LDH and MDH between the two species of Romanomermis, but the similar positions of isoenzyme bands denoted a certain genetic relationship between them. No band was found in the isoenzyme patterns of PO and EST. Distinct differences in protein pattern were observed between the two species of Romanomermis, but some common bands in pattern reflected the phylogenetic relationships of these species. The differences of isoenzyme and protein patterns observed in this study have provided the reason for identifying and differentiating the two species of Romanomermis at the molecular level.

Simple Systems That Exhibit Self-Directed Replication

Biological experience and intuition suggest that self-replication is an inherently complex phenomenon, and early cellular automata models support that conception. More recently, simpler computational models of self-directed replication called sheathed loops have been developed. It is shown here that "unsheathing" these structures and altering certain assumptions about the symmetry of their components leads to a family of nontrivial self-replicating structures, some substantially smaller and simpler than those previously reported. The dependence of replication time and transition function complexity on initial structure size, cell state symmetry, and neighborhood are examined. These results support the view that self-replication is not an inherently complex phenomenon but rather an emergent property arising from local interactions in systems that can be much simpler than is generally believed.

Minimizing complexity in cellular automata models of self-replication

Understanding self-replication from an information processing perspective is important because, among other things, it can shed light on molecular mechanisms of biological reproduction and on prebiotic chemical evolution. Intuition, biological knowledge, and early computational models of self-replication all suggested that self-replication is an inherently complex process. In this paper we describe recent computational studies that challenge this viewpoint. We summarize our recent work with cellular automata models of simple yet non-trivial self-replicating structures called unsheathed loops. For example, one unsheathed loop consists of only six components and requires only 20 rules to specify the local intercomponent interactions needed to bring about replication. The implication of this work is that, when viewed as an emergent property of numerous local, concurrent interactions between components, self-replicating systems can be substantially simpler than is generally recognized.