F. De Smet

The presence of dopamine β-hydroxylase in the cerebrospinal fluid of rabbits and its increased concentration after stimulation of peripheral nerves and cold stress

The presence of dopamine beta-hydroxylase activity in the cerebrospinal fluid of rabbits has been shown using a sensitive radiochemical assay; the identity of the reaction product was confirmed by using thin layer chromatographic techniques. The enzyme found in this fluid has some properties (sedimentation and electrophoretic migration) in common with the best characterized preparation of dopamine beta-hydroxylase, that prepared from bovine adrenal chromaffin granules. It also has these properties in common with the enzyme present in the high-speed supernatants obtained from osmotically disrupted synaptosomes prepared from rabbit brain. When the sciatic nerves of rabbits under urethane anaesthesia were stimulated, or when shaved rabbits were subjected to cold stress, the level of dopamine beta-hydroxylase in the cerebrospinal fluid increased. The increase in response to nerve stimulation was gradual, starting within 90 min of stimulation and remained high for at least 3 h after the stimulation had ended, at which time it was 280% of the normal value. There was no equivalent increase in the protein concentration of the cerebrospinal fluid nor was there a change in the enzyme activity when sciatic nerves were exposed but not stimulated. The enzyme present in the cerebrospinal fluid during this period of high activity is identical in its sedimentation and electrophoretic properties to that present in normal fluid. It is suggested that the dopamine beta-hydroxylase activity in cerebrospinal fluid may be derived from noradrenergic neurons within the brain and that the enzyme is released together with noradrenaline.

The effect of drugs on the concentration of dopamine β-hydroxylase in the cerebrospinal fluid of rabbits

Abstract Systemic administration of each of the drugs studied (phenoxybenzamine, yohimbine, phentolamine, nicotine, physostigmine and pentylenetetrazol) caused an increase in the dopamine β-hydroxylase activity per unit volume of cerebrospinal fluid. The increase was gradual starting within 90 min after injection of the drug and remained high for at least 3 h. At that time the dopamine β-hydroxylase levels after treatment with phenoxybenzamine and yohimbine reached values of 600% and 580%, respectively, of the control. The increase in dopamine β-hydroxylase activity upon phenoxybenzamine treatment was dose dependent. Injection of pentylenetetrazol caused an increase in dopamine β-hydroxylase to 230% of the control value. Pretreatment of rabbits with an intracisternal injection of 6-hydroxydopamine not only caused a 68% decrease in the noradrenaline content and a 69% decrease in the dopamine β-hydroxylase levels in the brain, but also led to a 52% fall in the dopamine β-hydroxylase level of the cerebrospinal fluid. Upon injection of pentylenetetrazol into rabbits pretreated with 6-hydroxydopamine, the dopamine β-hydroxylase levels in the cerebrospinal fluid only reached a mean value of 0.98 units/ml compared with 2.62 units/ ml for control rabbits injected with pentylenetetrazol; the increase in the blood level of dopamine β-hydroxylase activity was, however, unaffected. Data derived from normal and 6-hydroxydopamine pretreated rabbits revealed a fairly good correlation between dopamine β-hydroxylase levels in the cerebrospinal fluid and the brain. From these experiments it is concluded that dopamine β-hydroxylase activity in the cerebrospinal fluid is derived from central noradrenergic neurons and that drugs which increase central noradrenergic activity also increase dopamine β-hydroxylase levels in the cerebrospinal fluid. It is further suggested that determination of dopamine β-hydroxylase activity in the cerebrospinal fluid may be a sensitive and relatively easy method to assess central noradrenergic activity.

The forward, backward and 90° deuteron photodisintegration between 7 and 19 MeV photon energy

Abstract The 0° and 180°, as well as the 90° differential cross sections for the 2 H(γ, p)n reaction have been measured at lab photon energies between 7 and 19 MeV. Special attention was paid to the accuracy, in particular by measuring the forward Compton electron yield. For the extreme angles, the statistical error on our results amounts to 4–5% (0°) and 7–8% (180°), respectively, while the systematic uncertainty is at most 3%. The data confirm the existence of a minimum in the forward cross section and indicate beyond any doubt that the fore/aft ratio is larger than unity. Comparison shows reasonable agreement with the results from recent “conventional” theoretical approaches, including meson exchange and relativistic corrections, although the description of the c -coefficient, appearing in the Partovi expansion of the differential cross section, remains unsatisfactory. A possible source for this discrepancy could be the inadequate description of the El and/or the E2 transition operator.

Search for the minimum in the forward2H(γ,p)n cross section

The forward2H(γ,p)n cross section was measured at 7.2 and 8.5 MeV photon energy. The new absolute values confirm the theoretically predicted presence of a minimum in this cross section. A discrimination is made between the results from various theoretical descriptions.

Determination of the random particle energy spectrum in tagged photon experiments

A new, improved method to define the random particle energy spectrum in tagged photon experiments is described. This procedure yields the random spectrum with very good statistical accuracy, and can be applied when no hard coincidence with the focal plane is required in order to accept events.

Biochemical evidence for two types of noradrenaline storage particles in rabbit iris

Centrifugation techniques were used to determine the subcellular distribution of noradrenaline (NA) and dopamine β-hydroxylase (DβH) in the rabbit iris. By application of isopycnic and differential gradient centrifugation methods 2 types of NA vesicles could be demonstrated. Of the total particle bound NA about 70% is associated with ‘light’ and about 30% with ‘heavy’ vesicles. For both types of vesicles the distribution of DβH reflected that of NA.

Molecular forms of dopamine beta-hydroxylase in rat superior cervical ganglion and adrenal gland

Dopamine beta-hydroxylase (DBH) enzyme activity was associated in rat superior cervical ganglion with tetrameric DBH-A (294,000 D) and dimeric DBH-B (147,000 D) and in rat adrenal gland with DBH-A and a novel molecular form of DBH, defined as DBH-C, with a molecular weight of 125,000 D. Pretreatment of the rats with cycloheximide markedly reduced DBH activity without altering the molecular heterogeneity.

Clustering in a network of mutually attracting agents

We introduce a model of mutually attracting agents in an arbitrary network, for which the long term behavior results in the emergence of several clusters. The cluster structure is independent of the initial condition and is characterized by a set of inequalities in the parameters of the model. With varying coupling strength, transitions between different cluster structures may take place. We illustrate the relation with the Kuramoto model on interconnected oscillators and we discuss an application on opinion formation.

IDENTIFICATION, ISOLATION AND PARTIAL CHARACTERIZATION OF TWO TYPES OF NA STORAGE VESICLES IN DOG SYMPATHETIC GANGLIA

Subcellular fractionation studies of dog coeliac ganglia revealed that about 50 % of noradrenaline (NA) is present in a particle bound form and is associated in equal amounts with “heavy” and “light” vesicles.

Area contraction of k-dimensional surfaces and almost global asymptotic stability

In this paper we will formulate sufficient conditions for the area contraction of k-dimensional surfaces under the flow of a set of differential equations. We discuss the connection with the Hausdorff dimension of invariant sets and show how the presence of first integrals of the system influences these results. We conclude with an application to almost global asymptotic stability.