Kai C. Nielsen

Contractile response and amine receptor mechanisms in isolated middle cerebral artery of the cat

Abstract On the basis of previous histochemical investigations demonstrating a rich adrenergic and cholinergic nerve supply to the main pial arteries, the contractile response of the feline middle cerebral artery to various vasoactive amines was studied in vitro . A 4 mm long segment of the artery was mounted in a rigid system allowing the registration of even very small circular contractions by a force-displacement transducer. The preparation was maintained in an aerated and thermostatically controlled (37° C) Krebs-Ringer buffer solution at pH 7.35–7.45. Dose-response curves are presented for 5-hydroxytryptamine, acetylcholine, histamine, adrenaline, noradrenaline and isoprenaline; a contractile response up to approximately 350 dyn being obtained. The contraction induced by 5-hydroxytryptamine, acetylcholine and histamine was blocked by the respective specific antagonists. From experiments with adrenergic blocking agents it was concluded that the catecholamine-induced contraction of the pial artery is mediated through a combination of alpha- and beta-adrenergic receptors.

Cholinergic Mechanisms in Pial Vessels

SummaryPlexuses of cholinergic nerve terminals were demonstrated (acetylcholinesterase staining) in pial arteries (down to a diameter of about 15μ) at the base of the brain and on the brain convexities of mice, rats, rabbits, hamsters, guinea-pigs, and cats. The pial veins were less well supplied than the arteries. Consecutive formaldehyde gas treatment (to visualize adrenergic nerves) and acetylcholinesterase staining revealed that the adrenergic and cholinergic plexuses followed each other closely, the axon terminals running together in the same Schwann cell strands. This was confirmed by electron microscopy after KMnO4 fixation or 5-hydroxydopamine treatment. The varicosities of cholinergic and adrenergic axons were sometimes seen as close as 250 Å. In the neuro-effector area, the terminals of both nerve types (naked or surrounded by an incomplete Schwann cell covering) approached the smooth muscle cells as close as 800–1100 Å, and they were separated from the latter only by the fused neuronal and muscular basement membranes. In this area axo-axonal contacts were observed. The adrenergic, but not the cholinergic, nerves disappeared after bilateral removal of the superior cervical sympathetic ganglia. Isolated cat middle cerebral artery contracted strongly with acetylcholine, and the effect was inhibited by atropine.With regard to the cholinergic neural control of the intracranial arteries, it may have particular functional implications: (1) that these vessels do have a cholinergic parasympathetic innervation in contrast to most other vascular systems, for example, in the mesenterium, (2) that this cholinergic nerve supply was found to be about equally prominent as the adrenergic (sympathetic) innervation which, in some pial vessels, is even better developed than in the mesenteric arteries, and (3) that the adrenergic and cholinergic systems in the intracranial arteries may interact, even at the level of the neuro-muscular contacts, a complex situation which may be partly responsible for the previous difficulties in defining the autonomic neural influence on the brain circulation.

Ultrastructure of the autonomic innervation apparatus in the main pial arteries of rats and cats

The autonomic nerve supply, particularly its terminal portion, was studied by electron microscopy of the anterior and middle cerebral arteries of rats and cats. In agreement with previous histochemical information, the arteries received a considerable number of non-myelinated axons that were enclosed in a Schwann cell plasmodium. Close to the vascular wall, varicosed terminals were found together with smooth preterminal fibres. In KMnO4-fixed material from untreated animals, about half of the terminals contained an abundance of dense-cored, 50 nm synaptic vesicles, whereas the synaptic vesicles in the remainder of the terminals were empty. In terminals of both types, a smaller number of larger electron-dense vesicles of 100 nm was present. After treatment of the animals with 5-hydroxydopamine followed by glutaraldehyde and osmium fixation, dense-cored vesicles with a diameter of 50 nm up to 80 nm appeared in about the same number of terminals as were previously found to contain the electron-dense synaptic vesicles. The rest of the axon terminals remained unchanged. It is concluded that the terminals with dense-cored vesicles belonged to adrenergic nerves, whereas those with the empty 50 nm vesicles were cholinergic. Near the vessel, the Schwann cell sheath of the terminals was usually incomplete, and varicosities of either the same or different (i.e., adrenergic/cholinergic) type came in close apposition to each other with a distance between adjacent membranes of approximately 25 nm. This arrangement offers a structural possibility for an interaction mechanism between the two types of axon terminals. In the adventitia the terminals had either an incomplete Schwann cell sheath, or were completely naked. Varicosities of the terminals of both types of axons approached the outer muscular layer of the media with a distance of about 100 nm. In this neuro-effector area, axo-axonal appositions were also found. The pial arteries possessed a neuro-effector apparatus that fulfilled the criteria of a true autonomic innervation in the same way as with arterial vessels in various peripheral organs.

Autonomic Neuroreceptor Mechanisms in Brain Vessels

Intracranial vessels are well innervated by both adrenergic and cholinergic nerves. They possess adrenergic and cholinergic receptors. A contractile response can be provoked by various amines, and nor

Anastomosing adrenergic nerves from the sympathetic trunk to the vagus at the cervical level in the cat

Summary The origin, course, and relative contribution of postganglionic sympathetic nerves was investigated in the cervical vagus and in the sympathetic trunk of the cat by the direct fluorescence microscopic demonstration of the adrenergic transmitter. In order to allow a better tracing of the axons, the level of norepinephrine in the preterminal portion was increased through axotomy at a level about 4 cm below the nodose ganglion. Numerous adrenergic fibres were found in the cervical vagus proper. They seemed to arise in the superior cervical ganglion, from which they partly passed in an anastomotic fashion through the adjacent nodose ganglion and partly entered the vagus trunk below this ganglion. Besides preterminal postganglionic sympathetic nerves passing through the ganglion, a few adrenergic terminals of probably vascular nature were also seen to run among the ganglion cells. Also the cervical sympathetic trunk contained postganglionic sympathetic fibres which seem to originate from ganglion cells present in the most caudal pole of the superior cervical ganglion and/or from scattered ganglion cells located below this ganglion. At least part of the adrenergic fibres presently demonstrated in the vagus and in the sympathetic trunk terminate in the heart: superior cervical ganglionectomy produced a significant decrease, 22–27%, in cardiac norepinephrine.

Control of ventricular fibrillation during induced hypothermia in cats after blocking the adrenergic neurons with bretylium

Abstract Ventricular fibrillation is usually the terminal event preceding death in homeothermic mammals subjected to progressive cooling, and it is the major risk severly limiting the use of induced hypothermia under various clinical conditions. The results of a series of investigations on hibernators, and on cats subjected to certain pharmacological treatments, have strongly indicated that adrenergic mechanisms are involved in the development of hypothermic ventricular fibrillation, and this heart failure has been successfully prevented by interfering with such mechanisms. In the present study on cats it has been shown that bretylium, which blocks the transmitter release from peripheral adrenergic neurons, significantly lowered the body temperature at which ventricular fibrillation develops, when given in a dose of 10 or 20 mg/kg. Blood pressure was maintained with angiotensin, which affects the vascular smooth muscles without involving the adrenergic receptors. Adrenalectomy did not further improve the outcome of the results. When given in a dose of 30+50 mg/kg, bretylium was able to prevent the development of ventricular fibrillation in 11 out of 12 animals, which were cooled down to 17.7 - 16.6°C rectal temperature and subsequently rewarmed to normothermia without complications. Control animals receiving no pretreatment regularly developed ventricular fibrillation at about 21°C rectal temperature. The ventricular fibrillation could be reversed into regular heart activity by D(-)-INPEA (N-isopropyl- p -nitrophenylethanolamine), a specific β-adrenergic blocking agent; the L(+) -form of INPEA, having only minimal receptor blocking activity, was without effect. The results offer further evidence in favour of the view that the adrenergic nervous system, probably in the heart, is an important factor for the production of hypothermic ventricular fibrillation.

Regional variation in the presence of mast cells in the mammalian brain.

Competitive inhibition of H M T by standard antihistamines has been reported earlier [4] and presently extended to burimamide. Finally, it appears that the marked effects of antihistamines on brain H A metabolism are restricted to this class since they could not be observed with other psychotropic agents (imipramine, chlorpromazine, phenobarbital, chlordiazepoxyde, scopolamine), showing one or more of their pharmacological properties. References [1] J. C. SCHWARTZ, H. POLLARD, S. BISCHOFF, M. C. REHAULT and M. VERDIERE-SCHUGUE, Eur. J. Pharmac. 16, 326 (1971). [2] J. W. BLACK, W. A. M. DUNCAN, C. J. DURANT, C. R. GANELLIN and E. M. PARSONS, Nature 236, 385 (1972). [3] K. KRHJEWd and J. W. PHILLIS, Br. J. Pharmac. 20, 471 (1963). [4] K. J. NETTER and K. BODENSCHATZ, Biochem. Pharmac. 16, 1627 (1967).

Control of Ventricular Fibrillation during Induced Hypothermia in Cats after Differential Depletion of Cardiac Catecholamine Stores with Prenylamine (Segontin)

The role of adrenergic mechanisms for the development of ventricular fibrillation during induced hypothermia was studied in cats. Prenylamine (60 mg/kg) caused a disappearance of the adrenergic transmitter in the muscular nerves; those to the vessels were only slightly affected. Thus pretreated, animals can be cooled to 17.8 to 17°C rectal temperature, and subsequently rewarmed, without developing ventricular fibrillation. Blood pressure was maintained with metaraminol. Without pretreatment the animals constantly develop ventricular fibrillation at 23 to 18.6°C. When prenylamine was given in a dose (20 mg/kg) that does not overtly affect the norepinephrine content of the cardiac adrenergic nerves, ventricular fibrillation was not prevented. In one group of animals receiving 60 mg/kg of prenylamine, norepinephrine instead of metaraminol was infused to maintain the blood pressure during cooling. These animals developed ventricular fibrillation (or cardiac standstill). Fluorescence microscopy showed that the infusion had restored the norepinephrine content in the cardiac nerves previously depleted of their endogenous transmitter by prenylamine. The incidence of ventricular fibrillation seems to be related to the number of intact adrenergic nerves present in relation to the cardiac muscles. Hypothermia caused a distinct release of transmitter from the cardiac adrenergic nerves.

Differential amine depletion from cardiac adrenergic nerves by Segontin

Selbst bei hohen Dosen von Segontin wird eine beachtliche Menge von Noradrenalin im Herz zurückgehalten. Fluoreszenzhistochemische Untersuchungen nach verschiedenen Dosen von Segontin machen wahrscheinlich, dass dieser Aminrest in den Gefässnerven enthalten ist, während der vollständige Schwund der Überträgersubstanz in den Muskelnerven beobachtet wird.

Increase in Kaolin-Induced Intracranial Hypertension after Decentralization of the Superior Cervical Sympathetic Ganglia in Rabbits

Intracranial hypertension, used here as an experimental model to exaggerate changes in ventricular fluid pressure (VFP), was produced in rabbits by cisternal injection of kaolin, which impairs the out