K. A. West

Identification and terminal distribution of the tubero-hypophyseal monoamine fibre systems in the rat by means of stereotaxic and microspectrofluorimetric techniques.

Summary The monoamine-containing fibres to the median eminence and the neurointermediate lobe have been studied by fluorescence microscopy in combination with microknife lesions. The origin and the course of the fibres were evaluated on the basis of monoamine accumulation proximal to the lesion and monoamine disappearance distal to the lesion. The nature of the monoamines stored in the various fibre systems was characterized with microspectrofluorimetry. Five groups of monoamine-containing axons were seen to enter the median eminence: (a) A large group of dopamine axons which originated in cells of the arcuate nuclei and the ventral parts of the anterior periventricular nuclei; they entered the fibre layer of the median eminence close to the infundibular recess. (b) A large group of noradrenaline axons which originated in areas outside the mediobasal hypothalamus; they entered the anterior median eminence from the lateral side, close to the brain surface, and intermingled with the arcuato-hypophyseal dopamine fibres in the internal layer and the deeper part of the external layer of the median eminence. (c) Two minor groups of catecholamine axons: one reached the median eminence from the anterior side, with an antero-posterior direction, probably mingled with the axons of the supraoptico-hypophyseal tract; the other ran into the arcuate nucleus with a dorso-ventral course along and close to the third ventricle; the fibres could not be traced further. (d) A small group of scattered axons containing an unidentified fluorigenic substance which differed microspectrofluorimetrically from the catecholamines and 5-hydroxytryptamine. Judging from the disappearance of monoamines distal to the lesion and from the chemical and microspectrofluorimetric analyses of the catecholamines in the median eminence and the neuro-intermediate lobe, the following conclusions concerning the terminal ramifications of the catecholamine fibre systems could be drawn: The arcuato-hypophyseal dopamine neurones give rise to one part of the terminals in the zona externa of the median eminence and to most, possibly all, terminals in the zona interna. The tubero-hypophyseal noradrenaline fibres also have their terminals in the zona externa, and they contribute to the catecholamine innervation of the neuro-intermediate lobe. Many studies on the functional role of aminergic mechanisms in the hypothalamic regulation of the pituitary functions have focussed on the presence of dopamine in the median eminence. The present investigation has demonstrated two prominent neurone systems in the hypothalamo-pituitary complex: one containing dopamine, the other containing noradrenaline. Moreover, the results suggest the involvement of a third neurone system, probably containing an indole derivative.

Evidence for regenerative axon sprouting of central catecholamine neurons in the rat mesencephalon following electrolytic lesions

Abstract By means of histochemical fluorescence techniques, evidence has been obtained for regenerative sprouting of axons from catecholamine neurons in the rat mesencephalon 1–7 weeks after electrolytic destruction of the substantia nigra and part of the ventromedial midbrain tegmentum. Three days after the lesion, accumulations of catecholamine occurred in coarse, beaded and distorted fibers on the borders of the lesion within the ascending catecholamine fiber tracts. Such catecholamine accumulations in proximal portions of severed axons or axon collaterals are well known; these accumulations showed a progressive decrease after approximately 1 week. In the present study an additional phenomenon was discovered between 7 and 19 days after lesion, namely the appearance of numerous, densely packed, fine, varicose, fluorescent fibers, probably identical with sprouts from catecholamine neurons. These fibers had an abnormal distribution outlining the lesion border and the electrode tracks, sometimes coursing through the lesion and even invading the walls of blood vessels penetrating, or situated close to, the lesion. These numerous newly appearing fluorescent fibers, including those invading the blood vessel walls, were equally prominent in animals with their intracranial arteries sympathectomized by bilateral removal of the superior cervical ganglia. Hence, these fibers were of central origin. The fluorescence of the newly formed fibers was characteristic for catecholamines, and the presence of noradrenaline could be established by means of microspectrofluorometric analysis in fibers invading sympathectomized vascular walls. Although the catecholamine fluorescence in the abnormal fibers on the border of the lesion had decreased at 7 weeks, it persisted in the new fibers invading the vessel walls, which may thus constitute a terminal area of distribution for the regenerating central catecholamine neurons. The phenomenon of regenerative sprouting in the central nervous system has previously been demonstrated, but this is the first direct evidence of regeneration of central monoamine fibers.

Development and growth of axonal sprouts from noradrenaline and 5-hydroxytryptamine neurones in the rat spinal cord

Summary Compressions of, or transplantations to, the rat spinal cord were studied with the Falck-Hillarp fluorescence method for monoamines. Newly formed axon sprouts were observed from the severed preterminal axons of both noradrenaline and 5-hydroxytryptamine (5-HT) neurones in the white matter. The first traces of delicate newly formed fibres were observed after 2–3 days, and they rapidly increased in number during the first two weeks. The sprouting fibres were seen to grow into the necrosis. In the transplanted animals the catecholamine-containing fibre sprouts grew across a necrotic zone and reached the transplanted tissue, where they arranged themselves in a pattern resembling that of the normal adrenergic innervation of the transplanted tissue. Although the 5-HT-containing neurones showed abundant sprouting into the necrosis around the transplanted tissue, such fibres were never seen to grow into or on the surface of the transplant.

Peripheral sympathetic innervation and serotonin cells in the habenular region of the rat brain

SummaryThe pineal gland of the rat is located near the brain surface and is via a slender stalk connected to lamina intercalaris which constitutes a cell formation between the habenular and posterior commissures, continuing to the subcommissural organ. The stalk and lamina intercalaris, like the pineal proper, exhibited a yellow, formaldehyde-induced fluorescence which showed the histochemical and pharmacological properties of 5-HT. All these structures were richly supplied with catecholamine-fluorescent nerves which could be further followed rostrally from lamina intercalaris, mixing with the non-fluorescent commissural fibres and stria terminalis, into the medial habenular nucleus in which they extensively supplied both blood vessels and non-fluorescent nerve cells. Cytospectrofluorometric and chemical analysis suggested that the fluorescent nerves stored noradrenaline. This was supported by the finding that they disappeared after bilateral cervical sympathectomy (as did the fluorescent nerves in the pineal complex). In the medial habenular nucleus also catecholamine-containing and 5-HT-containing nerves of central origin were present.The occurrence of a rich, peripheral sympathetic innervation in the medial habenular nucleus of the brain offers possibilities for a previously not observed sympathetic influence on this nucleus. Also the arrangement, and the apparent continuity of the sympathetic innervation in the pineal gland, the lamina intercalaris, and the medial habenular nucleus, suggests some functional interconnection or coordination between these structures.

Effect of superior cervical sympathectomy on experimentally induced intracranial hypertension.

Summary The effect of cervical sympathectomy on intracranial pressure was studied in rabbits. The pressure was recorded in conscious animals via a specially devised cannula inserted into the left cerebral ventricle. Intracranial hypertension was induced by intracisternal injection of kaolin, which produced about a 5-fold increase in the ventricular fluid pressure as measured 2 days after the injection. In contrast to this, the ventricular fluid pressure was found to be at approximately the same level as in the untreated controls if the superior cervical ganglia had been removed bilaterally about a week before kaolin treatment. Sham operation had no effect on the kaolin-induced intracranial hypertension. The results are discussed with regard to the possibility of a sympathetic influence on intracranial pressure regulation.

LEAKAGE AS A SOURCE OF ERROR IN MEASUREMENT OF THE CEREBROSPINAL FLUID PRESSURE BY LUMBAR PUNCTURE

Leakage of CSF to the extradural space has long been supposed to be a cause of complications after lumbar puncture. Sicard in 1902 assumed post puncture headache to be due to leakage and Ingvur in 1923 produced strong evidence that leakage may continue for several days after the puncture with later complications, including strangulation of the medulla in the foramen magnum, as a result. Decrease of the CSFP while the lumbar needle is still in situ has been a,scribed to leakage by a few investigators (Roseman et al. 1941, Ferris 1941, Ecker 1955). The significance of such a leakage in routine measurements of the CSFP appears to have escaped attention. Our interest in this phenomenon was aroused when, some years ago, we tried to record spontanous variations of the increased intracranial pressure (so called plateau waves, Lundberg 1960) after lumbar puncture. Shortly after the puncture, the plateau waves decreased in magnitude and in most cases disappeared completely.

Influence of Sympathetic Denervation on Intracranial Pressure

The cerebral blood volume (CBV) and the formation of cerebrospinal fluid (CSF) are two factors influencing the intracranial pressure. Anatomical requirements exist for a sympathetic neurogenic control of both factors. Thus, the pial arteries and arterioles, intracerebral arterioles, as well as the venous system of the brain receive sympathetic fibres demonstrable by fluorescence histochemistry, and the nerve terminals fulfill ultrastructural criteria for a true innervation of the vascular smooth muscles (1). Numerous sympathetic nerves also supply the choroid plexuses where they run in close relation to the blood vessels as well as to the epithelial cells (2). All these nerves originate in the superior cervical sympathetic ganglia (1,2). As a functional approach to the possible influence of sympathetic nerves on intracranial pressure, changes in ventricular fluid pressure (VFP) were correlated with changes in CBV and plexus carbonic anhydrase (CA) activity — which is directly correlated with the rate of CSF production — at various stages after preor postganglionic sympathetic denervation.

Sympathetic influence on cerebral blood volume: Time-dependent effect of decentralization of the superior cervical ganglia in mice

Neue Befunde über die Neuronale Regulation der Hirndurchblutung. Durchschneidung der präganglionären Fasern des Hals-Sy. verursachen eine starke Initiale und eine etwas weniger ausgeprägte dauerzunahme der Durchblutung, was durch Unterbechung der innervation und Sensitivierung der Rezeptoren erklärt 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

Effects of Intracranial Hypertension, Low-Pressure Hydrocephalus and Subsequent Ventriculo-Peritoneal Shunting on Monoamine Neurons in Rabbit Brain

Intracranial hypertension and hydrocephalus may produce functional disturbances in the brain which, to a certain extent, are manifested in neurological symptoms. The damage to the brain parenchyma can also be estimated in terms of alterations in certain biochemical parameters, but it is difficult to distinguish to which extent such alterations are associated with the neurons or with other components of the brain. More specifically, the neuronal injury can be studied by morphological approaches, either at the level of optical or electron microscopy. However, it should be born in mind that a neuronal impairment which is demonstrable by morphological techniques, has already reached a fairly advanced stage.