Bennett Model Research Articles

Hamiltonian circuits determining the order of chromosomes

According to Bennett's model of cytogenetics the spatial order in haploid chromosome complements is based on a similarity relation which gives rise to a multigraph G which is the edge disjoint union of two of its subgraphs G 1 and G 2 . If the number of chromosomes is even, the order of the chromosomes is determined by a Hamiltonian circuit of G which is alternating in the edges of G 1 and G 2 . However, contrary to assumptions made by biologists, such an Hamiltonian circuit does not exist in general. In this paper we study modifications of the underlying similarity relation (which are in agreement with the biological context) which guarantee that, under certain conditions, Hamiltonian circuits of the mentioned type do always exist, i.e. the rules in Bennett's model become consistent.

Systemic Lidocaine Blocks Nerve Injury-induced Hyperalgesia and Nociceptor-driven Spinal Sensitization in the Rat

Repetitive C-fiber stimulation induces a state of facilitated processing of sensory information in the dorsal horn, while chronic nerve compression gives rise to a hyperalgesic state, characterized by spontaneous neuronal activity generated by voltage-sensitive sodium channels, as well as spinal facilitation. This study investigates the effects of systemic local anesthetic on thermal hyperalgesia evoked by chronic nerve compression and on the pain behavior responses to subcutaneous formalin. The effects of intravenous lidocaine were evaluated in rats with (1) the formalin test, a model of acute pain and centrally mediated delayed sensory sensitization, and (2) a model of chronic sciatic nerve compression leading to a neurogenic thermal hyperalgesia. Groups of rats (300 g) undergoing formalin testing were given intravenous lidocaine in doses of: 3 mg plus 25 micrograms/min infusion (yielding serum levels of 6.3 +/- 1.0 micrograms/ml) or 1.5 mg plus 12.5 micrograms/min infusion (yielding serum levels of 3.6 +/- 0.3 micrograms/ml) beginning 5 min before the subcutaneous injection of formalin in the left hind paw. In other studies, a group of six animals were rendered hyperalgesic in one hind limb by the placement of compressive ligatures about the left sciatic nerve (Bennett model) 3-5 days before these studies. These rats were treated with 0.6 mg intravenous lidocaine followed by an infusion of lidocaine at a rate of 5 micrograms/min (yielding serum levels of 1.0 +/- 0.1 micrograms/ml). Lidocaine had no significant effect on the first phase of the formalin test or on thermal response latencies in normal limbs. However, at a high dose, lidocaine significantly reduced phase 2 flinching behavior and at a low dose, reversed the thermal hyperalgesia produced by sciatic nerve ligation during 30 min of infusion for a period of 3 h after the infusion was discontinued. Intravenous lidocaine acts by distinct mechanisms to diminish the hyperesthetic state induced by peripheral nerve injury and to reduce the degree of spinal sensitization induced by C-afferent fiber activation.

Electrical communication between glomus cells of the rat carotid body

Glomus cells of rat carotid bodies can be electrotonically coupled. This was determined by simultaneous intracellular recording and stimulation of two neighboring cells. Voltage applied into one cell ( V 1 ), was detected in the other cell as E 2 . The ratio E 2/V 1 or coupling coefficient ( K C , varied from 0.003 to 1. R 0 or input resistance (24.1–3,500 MΩ), was calculated from the voltage elicited in the injected cell by current injection ( V 1/I 1 ). The coupling resistance ( R C ) was estimated by using Bennett's model 2 and was inversely related to K C . It ranged from 8.5 to 46,112 MΩ. Values for K C are provisional since we may not have always recorded from immediately adjacent cells. Similarly, calculations of R 0 and R C may not be accurate since, in all probability, there is a multicellular network. Stimulation by hypoxia (100% N 2 or Na 2S 2O 4), acidity (lactic acid or 100% CO 2), dopamine, ACh, nicotine and bethanechol depolarized the majority of glomus cells, their input resistance decreased and cells became uncoupled. Fewer cells were either unaffected or coupling increased. There was a significant and negative correlation between changes in coupling coefficient and in coupling resistance.

Geometrical constraints on Bennett's predictions of chromosome order.

Two aspects of the Bennett model are of interest from a mathematical point of view. First there is the question whether Bennett's "ranking method" for predicting the order of chromosomes will always work. The answer depends on the number n of chromosomes: if n is odd, predictions (being not necessarily unique) are possible in most cases. Secondly there is Bennett's procedure for determining the arrangement of chromosomes. It is shown that the method of minimising the perimeter of the polygon obtained by connecting the centromeres is only applicable if the positions of the n centromeres do not deviate too much from an arrangement along a regular n-gon.

Evaluation of an extension hotline using the bennett model

Evaluation of an extension hotline using the bennett model

Comments on Bennett's model of somatic chromosome disposition

Bennett's model predicting specific spatial chromosomal arrangements of haploid genomes has been examined. The rationale is found to be obscure and the prima facie case unconvincing. A posteriori evidence does not withstand close scrutiny.

The spatial distribution of chromosomes in metaphase neuroblast cells from subspecific F1 hybrids of the grasshopper Caledia captiva

The spatial distribution of chromosomes has been analysed in radial metaphase neuroblast cells in F1 hybrid embryos generated by crossing individuals of the Moreton and Torresian (TT) chromosomal taxa of the grasshopper Caledia captiva. The Moreton individuals were of two kinds depending on whether they carried an acrocentric X (MAX) or a metacentric X (MMX). No significant associations were detected between any pair of homologous chromosomes in either male or female (MAX x TT) and (MMX x TT) F1 hybrids. This result was supported by data which showed that the mean separation between homologues is greater, although not significantly so, than the mean separation between non-homologous chromosomes within the two Moreton genomes. Indeed, in a number of cases, genome separation was clearly observed in radial metaphase preparations from these F1 hybrids. By comparison the analysis of pairwise associations between non-homologous chromosomes within the MMX and MAX Moreton genomes revealed a number of significant associations and dissociations which strongly suggests that at least some chromosomes in these genomes are organised non-randomly at metaphase. Of particular interest was the highly significant X-5 association in the MMX genome since in a previous study X-5 rearrangements were found to occur repeatedly among different backcross progeny involving Moreton x Torresian F1 hybrids. Additionally a comparison of the organisation of chromosomes in the MAX and MMX genomes, which differ primarily by the type of X chromosome, revealed that in a number of cases pairs of chromosomes are arranged very differently with respect to each other. The distribution of chromosomes on the hollow spindle was also analysed to investigate whether a specific spatial ordering of chromosomes exists within these Moreton genomes based on the association of pairs of short arms and pairs of long arms of most similar length (the Bennett model). The twelve chromosomes in both genomes were uniquely ordered in a single chain. However, because of computing limitations, only the ordered arrangement of chromosomes 1–10 was investigated. An analysis of 48 cells in the MMX and 38 cells in the MAX genomes showed that the predicted order in the ten chromosome sub-set in each genome did not rank in the top 20% of the 181,440 possible orders. This suggests that, although there is a good evidence that some non-homologous chromosomes may be associated non-randomly at metaphase in these genomes, they do not appear to show a specific, ordered arrangement as predicted by the Bennett model. The significance of the observed non-random organisation of chromosomes in the MMX and MAX genomes is discussed in relation to the generation of novel chromosome rearrangements in Moreton x Torresian F1 hybrids and the evolution of the Moreton and Torresian genomes.

Tidal Volumes and Volume Ventilators

In response to Graybar's 1 Graybar GS The most advanced respiratory life support system available. Chest. 1979; 75 (letter to editor): 106-107 Abstract Full Text Full Text PDF PubMed Scopus (1) Google Scholar communication entitled “‘The Most Advanced Respiratory Life Support System Available,’” the differences in set and delivered values for tidal volume (TV) need further clarification. We do not disagree that the values of TV delivered by the particular ventilator (Puritan-Bennett MA-1) were exactly as reported by Graybar; 1 Graybar GS The most advanced respiratory life support system available. Chest. 1979; 75 (letter to editor): 106-107 Abstract Full Text Full Text PDF PubMed Scopus (1) Google Scholar however, all volume ventilators are designed to produce a set TV. The difference between the set and delivered values for TV is then influenced by the compliance factor of the tubing used. The operating instructions 2 Operating Instructions: Bennett Model MA-1 Respiration Unit (form 5030 Y) . Santa Monica, Calif, Puritan-Bennett Corp, 1976 Google Scholar for the particular ventilator (Puritan-Bennett MA-1) state: “To read patient tidal volume, correction must be made to the spirometer volume. The tube system captures approximately 3 ml of gas volume for every 1 cm H2O pressure” and “The patient and the tube system join in exhalation of the just delivered volume, part of which reached the patient, and part of which was compressed in the tube system.”

A realistic structural model of glassy iron

The Ichikawa model with k = 2.0 (the Bennett model) for iron was relaxed using Johnson's potential and the potential by Pak and Doyama. The relaxed models reproduce the experimental pair-distribution function and structure sensitive intensity and have high packing fractions.

Inhalation of varying concentrations of oxygen in the treatment of severe pulmonary insufficiency.

Acute pulmonary insufficiency in chronic pulmonary disease is a medical emergency. Its therapy is difficult, and the mortality isgreat.A number of approaches to the problem have been employed, including the use of antibiotics, corticosteroids, oxygen, tracheotomy, and various mechanical devices to improve respiration. The physiologic derangement seen in this condition is relatively constant although it may occur in a wide variety of diseases. There is severe arterial hypoxia and hypercapnia. Associated with the persistent hypercapnia is a decreased sensitivity of the respiratory center to the stimulus of carbon dioxide. The sole remaining stimulus to respiration is the hypoxia. When the arterial oxygen is increased above physiologic levels, such as occurs during breathing of 100 per cent oxygen, this stimulus is lost, alveolar ventilation decreases, arterial hypercapnia increases, the pH of the arterial blood decreases, and death ensues. In order to decrease the hypercapnia or minimize its increase and, at the same time, prevent severe hypoxia, oxygen in concentrations of less than 100 per cent was used in the treatment of this condition. The sensitivity of the medullary respiratory center to Pco2 may thus be gradually increased. What role the increased arterial oxygen plays in this improvement is unknown.’ The observations obtained from this form of therapy are the subject of this report. Methods All patients evaluated had chronic pulmonary disease, but of different etiologies. They were acutely ill with severe pulmonary insufficiency at the time of these observations. Studies were performed with the patients breathing ambient air, 100 per cent of oxygen by nasal catheter, and varying concentrations of oxygen administered by IPPB/I (intermittent positive pressure breathing, inspiratory). Arterial blood samples were obtained and analyzed for oxygen and carbon dioxide tensions by the Riley bubble technique.2 Admittedly, this is not the most accurate procedure available, but with a well-trained biochemist, periodically checked by tonometer studies, the physician at the bedside can quickly obtain valuable clinical information which win give an objective approach to further treatment. Varying concentrations of inspired oxygen were obtained by mixing compressed air and 100 per cent oxygen in the nebulizer of a Bennett Model PR-lA Respirator. *}�m the Cardiopulmonary Laboratory and the Medical Service, Veterans Administration Hospital, Hines, Illinois. tDirector, Cardiopulmonary Laboratory, Saint Joseph Infirmary, Louisville, Kentucky.