Possible role of brain norepinephrine in the hypothalamic hypophyseal adrenal system.

Intracisternal injection of bethanidine in rats decreased brain norepinephrine turnover without affecting its endogenous level, and increased both cardiac norepinephrine turnover and serum corticosterone level. A negative correlation was observed between brain norepinephrine turnover rate and serum corticosterone level. On the other hand, when cardiac norepinephrine turnover was suppressed by intraperitoneal injection of bethanidine, serum corticosterone did not change significantly. Next, ether inhalation was added after intracisternal injection of bethanidine. Then, serum corticosterone increased more even brain norepinephrine turnover was suppressed only slightly. These data may indicate that serum corticosterone increases by selective decrease in brain norepinephrine turnover via the humoral route; from the hypothalamus down to the adrenal cortex. Inversely, intracisternal injection of corticosterone increased brain norepinephrine turnover. These results suggest that brain norepinephrine may play an inhibitory role in the tonic regulation of CRF-ACTH secretion in the higher center than the hypothalamus and there may be a closed-loop feedback system between brain norepinephrine and serum corticosterone.     

Effector innervation of melanophores of the arteries of the base of the brain]

Melanophores in the arteries of the base of the brain of kittens displayed pronounced variations in size and shape in response to the peripheral electrical stimulation of the vagus and the sympathetic nerves. These melanophores changed their size and shape under the influence of acetylcholine and noradrenaline solutions in vitro too. The present experiments showed melanophores to have a double effector innervation.     

Adrenergic and cholinergic components of the innervation of the arteries of the base of the bird brain

By means of Falck's and Koelle's methods adrenergic and cholinergic structures were studied in the arteries in the cerebral basis of blue rock pigeons and of hens, white leghorn stock. The number of nerve transmitters was estimated per 1 mm2 of the vessel surface. The arteries of the basis in pigeon brain are surrounded with developed adrenergic and cholinergic nerve plexuses, their density decreasing in the following order: nasal branch of the internal carotid artery, middle, nasal cerebral and basilar arteries. A little more cholinergic transmitters occur on the middle cerebral artery, while on the other vessels, concentration of cholinergic and adrenergic fibers is equal. In hens, the density in the arrangement of adrenergic nerve transmitters is higher in the nasal branch of the internal carotid and in the nasal cerebral arteries than in the basilar artery. At the same time, chromaffin cells forming numerous conglomerations in some places are found on the latter. In pigeons, the density of adrenergic fibers arrangement on the arteries of the cerebral basis is higher than in hens.     

Cholinergic and adrenergic innervation of the arteries of the base of the brain in certain lower vertebrates]

The arteries in the encephalon base have been investigated by Koelle's and Falck's methods in Teleostei (Anarhichas lupus, Eleginus navaga, Leuciscus brandti, Pelingas), amphibians (Rana temporaria, Rana semiplicata, Bufo bufo) and in reptiles (Testudo horsfieldi, Trionyx chinensis). Cholin- and adrenergic nerve fibres of the encephalic arteries have been revealed in all the vertebrates studied, but their concentration is far from being equal. In fishes and reptiles neural conductors from scarse plexus with wide loops. Concentration of effector neural fibres only in Bufo bufo exceeds that of fishes. In some cases, the arteries of frogs have equal or less density of cholin- and adrenergic neural conductors as compared with those of Pelingas. Certain individual peculiarities are noted in distribution of the effector neural fibres of the encephalic arteries of the vertebrates. In reptiles, the neural apparatus of the encephalic blood vessels reaches a considerable development; it is definitely differentiated into two plexuses - superficial and deep, having a close interconnection. The development of the effector vascular plexus in vertebrates corresponds to increasing mass of the brain and the vascular diameters. Taking into consideration structural peculiarities of the neural conductors and their concentration, it should be recognized that the role of the neural factor in regulation of the cerebral circulation increases in the following order: fishes - amphibians - reptiles.     

Ultrastructural characteristics of branch sphincters and precortical arteries in the rabbit pial arterial system

Structural peculiarities of pial arteries and their active microvascular segments-sphincters in offshoots and precortical arteries have been investigated, using electron and light microscopy. Our studies have revealed that these vascular segments, which can independently change their lumen, possess multiple myoendothelial junctions, as well as neuro-muscular contacts. This gives evidence of their independent responses that might be determined by structural peculiarities and innervation of their walls.     

The structure of the arteries at the base of the brain in young and adult dwarf goats. 2. Age-associated changes

Age-associated changes in cerebral arteries of 6 years old pygmy goats were investigated quantitative-histologically. No atherosclerotic alterations could be observed. But age-related thickenings of the subendothelial lamina till to 7 microns were present. Beside a significant increases of the intima, also an increase of the media as also of some lumina could be seen. In relation to the increase of the arterial lumen, the increase of the media was more rapid. Apparently more intercellular substance is formed by the smooth muscle cell during age. These studies confirm only weak intimal thickenings of the cerebral arteries during ageing. They do not effect the blood supply of the brain.     

The origin of free brain malonate

Rat brain contains substantial concentrations of free malonate (192 nmol/g wet weight) but origin and biological importance of the dicarboxylic acid are poorly understood. A dietary source has been excluded. A recently described malonyl-CoA decarboxylase deficiency is associated with malonic aciduria and clinical manifestations, including mental retardation. In an effort to study the metabolic origin of free malonate, several labeled acetyl-CoA precursors were administered by intracerebral injection. [2-¹⁴C]pyruvate or [1,5-¹⁴C]citrate produced radioactive glutamate but failed to label malonate. In contrast, [1-¹⁴C]acetate, [2-¹⁴C]acetate, and [1-¹⁴C]butyrate were converted to labeled glutamateand malonate after the same route of administration. The intracerebral injection of [1-¹⁴C]--alanine as a precursor of malonic semialdehyde and possibly free malonate did not give rise to radioactivity in the dicarboxylate. The labeling pattern of malonic acid is compatible with the reaction sequence: acetyl-CoAmalonyl-CoAmalonate. The final step is thought to occur by transfer of the CoA-group from malonyl-CoA to succinate and/or acetoacetate. Labeling of malonate from acetate is most effective at the age of 7 days when the net concentration of the dicarboxylic acid in rat brain is still very low. At this age, butyrate was a better precursor of malonate than acetate. It is proposed that fatty acid oxidation provides the acetyl-CoA which functions as the precursor of free brain malonate. Compartmentation of malonate biosynthesis is likely because the acetyl-CoA precursors citrate and pyruvate are ineffective.Presented before the 12th Biennial Meeting of the International Society for Neurochemistry, Algarve, Portugal, April 24, 1989.     

The resonance of the arterial system

The arterial system is assumed to consist of two elastic chambers connected by a conducting channel. It is assumed that a current of fluid enters one chamber, whereas the other chamber is drained by a pipe with a certain peripheral resistance. The continuity of the fluid is described by a differential equation for each chamber. The inertia resistance of the conducting channel is taken into consideration. It is shown that the system may possess a resonance frequency. The latter, if it exists, as well as the damping coefficients are expressed in terms of the elastic moduli of the chambers, the conductivity of the channel, and the peripheral resistance. It is shown that with plausible values of the latter variables the resonance frequency as determined theoretically has the right order of magnitude as found experimentally.     

The origin and evolution of the nervous system

The nervous systems of animals as diverse as flies and mice share many conserved features, suggesting that such features were already present in their last common ancestor. As our knowledge of neural development increases, so does the list of conserved features, pointing to the existence of a highly sophisticated, single species as the origin of most extant nervous systems. Possible reasons for this unexpected monophyly are discussed, leading to the conclusion that the appearance of very different life forms, lifestyles and habitats requires the previous attainment of a neural circuitry that is sufficiently robust to cope with large changes without losing its overall coherence.     

Totally tubular: the mystery behind function and origin of the brain ventricular system

A unique feature of the vertebrate brain is the ventricular system, a series of connected cavities which are filled with cerebrospinal fluid (CSF) and surrounded by neuroepithelium. While CSF is critical for both adult brain function and embryonic brain development, neither development nor function of the brain ventricular system is fully understood. In this review, we discuss the mystery of why vertebrate brains have ventricles, and whence they originate. The brain ventricular system develops from the lumen of the neural tube, as the neuroepithelium undergoes morphogenesis. The molecular mechanisms underlying this ontogeny are described. We discuss possible functions of both adult and embryonic brain ventricles, as well as major brain defects that are associated with CSF and brain ventricular abnormalities. We conclude that vertebrates have taken advantage of their neural tube to form the essential brain ventricular system.     

Plasminogen-activator of the arterial wall in occluded arteries

The plasminogen activator in 117 specimen of 20 coronary and 29 pulmonary arteries occluded completely by thrombi or emboli within the adventitia and intima was studied using TODD's histochemical method. 39 cadavers were used, 1--18 hours post mortem from subjects aged from 45 to 88 years. In occluded arteries both coronary and pulmonary the plasminogen activator activity was decreased in comparison with normal and atherosclerotic patients. In coronary and pulmonary arterial thrombi a low grade focal activity of plasminogen activator was detected. It is assumed that the decrease of plasminogen activator in the occluded human arterial wall is due to the impaired oxygen supply of the vessel wall and to the consumption of the plasminogen activator for thrombus lysis. These mechanisms are likely to influence the plasminogen activator for a certain and prolonged time, since there were no changes of fibrinolysis within the vessel wall of arteria carotis in rats where an acute thrombosis was elicited by means of an electric current.