Slow Adaptation Process Research Articles

Enhancement of butyrate production in the rat caecocolonic tract by long-term ingestion of resistant potato starch.

Some data suggest that the colonic microflora may adapt to produce more butyrate if given time and the proper substrate. To test this hypothesis, we investigated the effect of prolonged feeding of resistant potato starch on butyrate production. Rats were fed on either a low-fibre diet (basal) or the same diet supplemented with 90 g resistant potato starch/kg (PoS) for 0.5, 2 and 6 months. Short-chain fatty acid (SCFA) concentrations were determined in caecal and colonic contents at the end of each ingestion period. Total SCFA concentration increased over time throughout the caecocolonic tract with PoS, but was not modified with the basal diet. While propionate concentration was unchanged, butyrate concentration was highly increased by PoS at each time period in both the caecum and colon. Moreover, the butyrogenic effect of PoS increased over time, and the amount of butyrate was increased 6-fold in the caecum and proximal colon and 3-fold in the distal colon after 6 months compared with 0.5 months. Accordingly, the ratio butyrate:- total SCFA increased over time throughout the caecocolonic tract (12.6 (SE 2.8) v. 28 (SE 1.8)% in the caecum, 10.5 (SE 1.4) v. 26.8 (SE 0.9)% in the proximal colon, and 7.3 (SE 2.4) v. 23.9 (SE 2.7)% in the distal colon at 0.5 v. 6 months respectively), while the proportion of acetate decreased. Neither the proportion nor the concentration of butyrate was modified over time with the basal diet. Butyrate production was thus promoted by long-term ingestion of PoS, from the caecum towards the distal colon, which suggests that a slow adaptive process occurs within the digestive tract in response to a chronic load of indigestible carbohydrates.

Pacemaker activity in a sensory ending with multiple encoding sites: the cat muscle spindle primary ending.

1. A combined physiological, histological and computer modelling study was carried out on muscle spindles of the cat tenuissimus muscle to examine whether there was any correlation between the functional interaction of putative encoding sites, operated separately by static and dynamic fusimotor neurones, and the topological structure of the preterminal branches of the primary sensory ending. 2. Spindles, whose I a responses to stretch and separate and combined static and dynamic fusimotor stimulation were recorded in physiological experiments, were located in situ. Subsequently the ramifications of the sensory ending were reconstructed histologically, and the topology of the branch tree was used in computer simulations of I a responses to examine the effect of the electronic separation of encoding sites on the static-dynamic interaction pattern. 3. Interactions between separate static and dynamic inputs, manifest in responses to combineed stimulation, were quantified by a coefficient of interaction (Ci) which, by definition, was 1 for strictly linear summation of separate inputs and zero for maximum occlusion between inputs. 4. For the majority of spindles static-dynamic interactions were characterized by pronounced occlusion (C1 < 0.35). In these spindles putative encoding sites (the peripheral heminodes of the branches supplying the intrafusal fibres activated by individual fusimotor efferents) were separated by a minimum conduction path of between three and ten myelinated segments (2-9 nodes of Ranvier). In contrast, significant summation (C1, approximately 0.7) was found in only one spindle. In this case putative encoding sites were separated by a single node. 5. Occlusion was not due to encoder saturation and it could not be accounted for by any other known physiological mechanisms (intrafusal fatigue or unloading). It is therefore attributed to competitive pacemaker interaction between encoding sites which are largely selectively operated by static and dynamic fusimotor efferents. 6. Model simulations of real preterminal-branch tree structures confirmed that short conduction paths between encoding sites were associated with manifest summation, whereas longer minimum conduction paths favoured pronounced occlusion. 7. In the extreme, occlusion could be so pronounced as to give rise to negative values of C1 during critical segments of response cycles. This was associated with lower discharge rates during combined static and dynamic stimulation than the higher of the individual stimulation effects. This phenomenon is referred to as hyperocclusion. Computer simulations demonstrated that hyperocclusion could be accounted for by a slow ionic adaptation process. e.g. by a very slowly activating K+ conductance.

NaCl transport and ultrastructure of opercular epithelium from a freshwater‐adapted euryhaline teleost, Fundulus heteroclitus

We adapted killifish to defined freshwater (FW: 1.0 mM Na+, 1.0 mM Cl−, + 0.1 mM Ca2+) and by fluorescence light microscopy and scanning and transmission electron microscopy found that the opercular epithelium retained mitochondria rich (MR) cells that were significantly larger but less numerous than in SW-acclimated tissues. Opercular epithelia mounted in vitro with FW bathing the mucosal surface take up Cl− against a large negative inside transepithelial potential (Vt, grand mean −64.1 mV) and concentration gradient; the observed flux ratio was significantly different (P < 0.001) from that predicted for passive ion distribution but the net flux was consistently negative. The Na+ flux ratio suggested that Na+ was passively distributed. Vt was largely a Na+ diffusion potential, based on unilateral manipulations of [Na+]. Cl− unidirectional uptake was unaffected by mucosally added SITS (0.1 mM) but was inhibited by SCN− (1.0 mM) and by anaerobiosis. Killifish transferred from SW to FW for 48 h had reduced Cl− secretion by the opercular epithelium compared to SW controls but had not yet developed Cl− uptake, indicating a slow adaptive process for development of Cl− absorptive transport. Opercular epithelia of FW adapted fish, if bathed with isotonic saline on both sides, has a modest net Na+ and Cl− uptake, unlike SW opercular epithelium that strongly secretes Cl− under similar conditions. FW killifish opercular epithelium may provide a model to study ion regulation by euryhaline fish. J. Exp. Zool. 277:23–37, 1997. © 1997 Wiley-Liss, Inc.

Short‐term and long‐term memory in single cells

Many approaches have been used to study short- and long-term memory. Bacteria detect chemical gradients using a memory obtained by the combination of a fast excitation process and a slow adaptation process. This model system, which has the advantages of extensive genetic and biochemical information, shows no features of long-term memory. To study long-term memory, neural cell line systems have been developed that exhibit two phenomena associated with learning and memory, habituation and potentiation. The expression of these phenomena in clonal cell lines, devoid of synaptic connections, makes it possible to study the biochemical and molecular mechanisms that contribute to short-term and long-term memory.

Stability Bounds for Slow Adaptation: An Integral Manifold Approach

This paper presents scheme for reduced order adaptive control in discrete time using slow adaptation and regressor filtering. Because the stability of slow adaptation does not rely on driving the tracking error to exactly zero, the scheme allows additive disturbances and makes no assumption about the order of the plant, controller, or reference model. These assumption are replaced by an assumption that the RMS tracking error has a minimum in the set of stabilizing controllers. Conditions are given for the adaptive system to possess a uniformly asymptotically stable solution and an estimate of the region of attraction is provided. The system is shown to have an integral manifold upon which the slow adaptation takes place. Since the manifold describes exactly the slow adaptation process, the stability analysis, which uses deterministic discrete time averaging results, does not require linearization. Although the results require some a priori knowledge, all of the assumptions are made on a system with constant parameters, and hence, are amenable to off-line analysis.

Integral manifolds of slow adaptation

Conditions are given under which an integral manifold ("slow manifold") exists for a nonlinear system representing a broad class of adaptive algorithms. The parameter update equation restricted to the manifold is an exact description of the slow adaptation process which can be approximately analyzed by averaging. Stability properties of the slow motion in the manifold are extended off the manifold by a set of conditions under which the manifold is shown to be attractive. This two-time-scale analysis provides a geometrical visualization of instability phenomena observed in adaptive systems and generalizes earlier local stability results.

Reversibility of the lactate dehydrogenase isozyme shift induced by low oxygen tension

The shift of the lactate dehydrogenase (LDH) isoenzymes in experimental animals under hypoxia from B (aerobic) to A (anaerobic) is confirmed and its reversibility after removal of the animals to room air is reported. These experiments are interpreted as further supportive evidence of a physiological adaptive role for the lactate dehydrogenase enzyme system. The slow adaptive process observed in this experimental situation presumably requires de novo enzyme synthesis, however, in the emergency of a sudden deprivation of oxygen the liberation of preformed A LDH could be a link in the rapid chain of events resulting in depressed cardiac muscle contractility which follows myocardial infarction. A recently proposed comprehensive explanation of the role of LDH isozymes is thus extended.