Reticular structures and reticulospinal pathways participating in the initiation and inhibition of spino-bulbo-spinal activity

Reflex discharges in intercostal nerves and activity of reticulospinal fibers of the ventral and lateral funiculi, evoked by stimulation of the reticular formation and of the splanchnic and intercostal nerves were investigated in cats anesthetized with chloralose (50 mg/kg). Brain-stem neuronal structures participating in the "relaying" of spino-bulbo-spinal activity were shown to lie both in the medial zones of the medullary and pontine reticular formation and in its more lateral regions; they include reticulospinal neurons and also neurons with no projection into the spinal cord. Structures whose stimulation led to prolonged (300–800 msec) inhibition of reflex spino-bulbo-spinal activity were widely represented in the brain stem, especially in the pons. Analogous inhibition of this activity was observed during conditioning stimulation of the nerves. Reticulospinal fibers of the ventral (conduction velocity 16–120 m/sec) and lateral (17–100 m/sec) funiculi were shown to be able to participate in the conduction of spino-bulbo-spinal activity to spinal neurons. In the first case fibers with conduction velocities of 40–120 m/sec were evidently most effective. Evidence was obtained that prolonged inhibition of this activity can take place at the supraspinal level.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Institute of Normal and Pathological Physiology, Slovak Academy of Sciences, Bratislava, Czechoslovakia. Translated from Neirofiziologiya, Vol. 8, No. 4, pp. 373–383, July–August, 1976.     

Adaptive structures of the arteries of the heart participating in the regulation of coronary circulation

By means of a complex of anatomical, histological and histochemical methods cardiac vessels have been studied in 20 control dogs and in 84 dogs with experimentally produced circulatory disturbances peculiar for congenital heart diseases presented as an open arterial duct, coarctation of the aorta and the pulmonary trunk stenosis. The experimental animals have been observed for 6-12 months. In the animals with experimentally produced disturbances of the general and coronary hemodynamics hyperplasy in the coronary branches of the arteries appears, it is more pronounced in functionally loaded cardiac parts, as well as thickening of their walls at the expense of new formations and hyperthrophy of smooth muscle cells. In both control and experimental dogs in the coronary vessels at various branching levels certain formations are revealed; they are of compensatory-adaptive value: intimal and adventitial musculature, polypoid pulvinars, muscular-elastic constrictors, muscular cuffs and precapillary sphincters. They differ in structure, sources of their origin and in their functional value. Degree of their manifestation increases significantly after reproduction of the hemodynamic disturbances in the heart vascular system. The active role of these formations in regulation of the coronary circulation is demonstrated owing to a high content of ribonucleinic acid and glycogene in their smooth muscle cells and also an elevated succinate dehydrogenase, cytochromoxydase, acid and alcaline phosphatase activities.     

Morphologic aspects of local blood flow regulation in the myocardium

In 67 preparations of the human hearts at the first and second periods of mature age, spatial interrelations between blood vessels and cardiac muscle fibers in the ventricle myocardium have been studied. All the elements of the myocardial blood bed are oriented under a certain angle in relation to the cardiac muscle fibers. Regular arrangement of the arteries and sinusoid dilated veins under endocardium on the top of the papillary muscles and in the muscular trabecules is demonstrated. As proves the mathematical model, the slope orientation of the blood bed elements towards the cardiac muscle fibers ensures and adequate realization of the external influence of the contractile cardiomyocytes to the successive movement of blood along the intramural myocardial vessels. From morphological positions, a conclusion on the mechanism of the intracavitary pressure effect on blood movement along the intramural veins of the ventricular myocardium is argued. A conclusion is made on the leading role of the extravascular factors (intramyocardial and intercavitary pressure) in the local regulation of the blood stream in the myocardium and in development of working cardiac hyperemia.     

Quantitative analysis of pathways of methionine metabolism and their regulation in lemna

Individual rates of metabolism of the sulfur, methyl, and 4-carbon moieties of methionine were estimated in Lemna paucicostata Hegelm. 6746 growing under standard conditions, and used to quantitate pathways of methionine metabolism. Synthesis of S-adenosylmethionine (AdoMet) is the major pathway for methionine metabolism, with over 4 times as much methionine metabolized by this route as accumulates in protein. More than 90% of AdoMet is used for transmethylation. Methyl groups of choline, phosphatidylcholine, and phosphorylcholine are major end products of this pathway. Flux through methylthio recycling is about one-third the amount of methionine accumulating in protein. Spermidine synthesis accounts for at least 60% of the flux through methylthio recycling. The results obtained here, together with those reported for methionine-supplemented plants (Giovanelli, Mudd, Datko 1981 Biochem Biophys Res Commun 100: 831-839), indicate that methionine supplementation reduced methylneogenesis by no more than the small amount expected from the reduced entry of sulfate sulfur into methionine (Giovanelli, Mudd, Datko, 1985 Plant Physiol 77: 450-455). Methionine supplementation had no significant effect on transmethylation or methylthio recycling. The combined data provide the first comprehensive estimates of the quantitative relationships of major pathways for methionine metabolism and their control in plants.     

Role of calcium in volume regulation by dog red blood cells

Dog red blood cells (RBC) are shown to regulate their volume in anisosmotic media. Extrusion of water from osmotically swollen cells requires external calcium and is associated with net outward sodium movement. Accumulation of water by osmotically shrunken cells is not calcium dependent and is associated with net sodium uptake. Net movements of calcium are influenced by several variables including cell volume, pH, medium sodium concentration, and cellular sodium concentration. Osmotic swelling of cells increases calcium permeability, and this effect is diminished at acid pH. Net calcium flux in either direction between cells and medium is facilitated when the sodium concentrations is low in the compartment from which calcium moves and/or high in the compartment to which calcium moves. The hypothesis is advanced that energy for active sodium extrusion in dog RBC comes from passive, inward flow of calcium through a countertransport mechanism.     

On the pharmacology of venous smooth muscle from dog and man.

Changes in tension of spiral strips from canine and human veins induced by various drugs are compared with results from the literature on human veins. The order of potencies of alpha-adrenoceptor stimulating amines (adrenaline greater than noradrenaline greater than dopamine greater than isoprenaline) is similar in human and canine veins. Comparison of the affinities for alpha-adrenoceptors of pharmacologic drugs (thymoxamine, indoramine, clonidine, dihydroergotamine) suggest marked differences between the alpha-adrenoceptors in veins from man and dog. Venoconstriction mediating 5-HT receptors and a very small population of beta-adrenoceptors exist in both species. Human veins are always dilated by histamine, while canine femoral veins in vitro are relaxed by lower and contracted by higher histamine concentrations. Prostaglandin F2 alpha constricts both canine femoral and human hand veins. PGA2 and PGE2 increase the tension of canine and human veins in vitro but dilate human hand veins in situ. The order of potencies of ergot alkaloids in canine femoral veins is ergotamine greater than dihydroergovaline greater than dihydroergotamine = dihydroergostine greater than methysergide, whereas in human hand veins it is ergotamine = dihydroergovaline greater than methysergide greater than dihydroergotamine greater than dihydroergostine. In dogs the venoconstrictor effect of ergotamine is mediated by at least 3 mechanisms: stimulation of [1] alpha-adrenoceptors, [2] 5-HT receptors and [3] endogenous prostaglandin synthesis. Stimulation of alpha-adrenoceptors by dihydroergotamine and of 5-HT receptors by ergotamine was confirmed on human hand veins in situ. Prejunctional receptors at sympathetic nerve terminals are involved in the regulation of venous tone. Inhibitory alpha-adrenoceptors, dopamine and PGE2 receptors as well as facilitating beta-adrenoceptor existing at human vasoconstrictor nerves may be stimulated or blocked by pharmacologic drugs thereby modifying venous tone.