Appearance of 5-hydroxytryptamine and an unidentified pharmacologically active lipid acid in effluent from perfused cerebral ventricles

Simultaneous comparison of cerebral dialysis and push-pull perfusion in the brain of rats: a critical review

Over the last 30 years, studies of the in vivo activity of neurotransmitters and other endogenous factors in the brain have comprised a major effort in the neurosciences. Historically, the technology of push-pull perfusion was utilized as a major approach to investigations in this field. In the last 10 years, cerebral dialysis has been used as an alternative method essentially for the same scientific purpose, since the perfusion technique was viewed as difficult and excessively damaging to tissue. This review considers the representative literature in which both systems have been used to study local neurochemical responses to a drug or other chemical factor, a physiological condition or other situation. In addition, new experiments have been undertaken to compare, in the same animal and at the same time, the utility and properties inherent in the techniques of push-pull perfusion and cerebral dialysis in terms of the profile of a neurotransmitter activity and their local histopathological effects. A miniaturized 33/26 ga push-pull needle and a 24 ga dialysis probe were implanted simultaneously in the left and right caudate nuclei, respectively, in the anesthetized rat. An artificial cerebrospinal fluid (CSF) was perfused simultaneously through both devices at a rate of 10 microliters/min in the push-pull cannula and at 1.0 or 2.0 microliters/min in the dialysis probe. Within a series of 8-10 successive perfusions, excess K+ ions in a concentration of either 30 or 60 mM were incorporated in the CSF and delivered simultaneously to both the push-pull cannula and dialysis probe. Samples of perfusate and dialysate were assayed chromatographically by coulometric HPLC detector and quantitated in terms of the pg/min efflux of dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA) and 5-hydroxyindoleacetic acid (5-HIAA). The results showed that the resting level of DA was almost undetectable in dialysate samples from either structure; in push-pull perfusates the recovery of DA ranged between 7.0 to 10.0 pg/min, which was increased threefold by excess K+ ions. The recovery of DA and the three metabolites in samples of push-pull perfusate was two to four times that in samples of dialysate during the condition of excess K+ ions. Post-mortem histological analysis of the sites of perfusion and dialysis revealed little or no differences in the cytological damage induced by either the perfusion needle or dialysis probe. Finally, the advantages and limitations of each of these two experimental approaches to in vivo analysis of neurotransmitter efflux are reviewed in relation to the selection of an open or closed system for the on-line study of in vivo neurochemical events.

Prostaglandins and hypothalamic neurotransmitter receptors involved in hyperthermia: a critical evaluation

The role of a prostaglandin of the E series (PGE) in the hypothalamic mechanisms underlying a fever continues to be controversial. This paper reviews the historical literature and current findings on the central action of the PGEs on body temperature (Tb). New experiments were undertaken to examine the local effect of muscarinic, nicotinic, serotonergic, alpha-adrenergic, or beta-adrenergic receptor antagonists at hypothalamic sites where PGE1 caused a rise in Tb of the primate. Guide tubes for microinjection were implanted stereotaxically above sites in and around the anterior hypothalamic, preoptic area (AH/POA) of male Macaque monkeys. Following postoperative recovery, 30-100 ng of PGE1 was micro-injected unilaterally in a volume of 1.0-1.5 microliter at sites in the AH/POA to evoke a rise in Tb, and once identified, pretreated with a receptor antagonist. PGE1 hyperthermia was significantly reduced by microinjections of the muscarinic and nicotinic antagonists, atropine, or mecamylamine, at PGE1 reactive sites in the AH/POA. The serotonergic antagonist, methysergide, injected at PGE1 sensitive sites in the ventromedial hypothalamus also attenuated the rise in Tb. However, the 5-HT reuptake blocker, fluoxetine, and the beta-adrenergic receptor antagonist, propranolol, injected in the AH/POA failed to alter the PGE1 hyperthermia. In contrast, the alpha-adrenergic antagonist, phentolamine, potentiated the increase in Tb at all PGE1 reactive sites in the hypothalamus. An updated model is presented to explain how the concurrent actions of aminergic neurotransmitters acting on their respective receptors in the hypothalamus can interact with a PGE to elicit hyperthermia. Finally, an evaluation of the current literature including recent findings on macrophage inflammatory protein (MIP-1) supports the conclusion that a PGE in the brain is neither an obligatory nor essential factor for the expression of a pyrogen fever.

Fenfluramine administered systemically or locally increases extracellular serotonin in the lateral hypothalamus as measured by microdialysis

Microdialysis was used to monitor serotonin, 5-hydroxyindoleacetic acid (5-HIAA) and the metabolites of dopamine, dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) in the perifornical lateral hypothalamus (PFH) of freely moving rats. Systemically administered d-fenfluramine (d-FEN) increased extracellular serotonin, DOPAC and HVA, while decreasing serotonin's metabolite 5-HIAA. Local application of d-FEN directly to the hypothalamic terminal region caused large increases in extracellular serotonin and had a tendency to decrease all 3 metabolites. This effect was confirmed when d-FEN was infused locally by reverse dialysis. These results provide direct evidence that the anorectic drug d-FEN can increase extracellular serotonin in the hypothalamus in vivo and suggest a serotonergic action in the perifornical region. This finding is consistent with our report that a meal also increases serotonin in this region.

Feeding increases extracellular serotonin in the lateral hypothalamus of the rat as measured by microdialysis

Microdialysis probes inserted into chronically implanted guide shafts allowed the collection of serotonin and 5-hydroxyindoleacetic acid (5-HIAA) from the lateral hypothalamus of rats during feeding behavior. After the collection of baseline samples, animals were offered a palatable diet that they could only see and smell for 60 min, then they were allowed access to the food for an hour. An additional three samples were collected after food was removed. Extracellular serotonin increased during the first half hour of access when the animals actually ate the food, and then returned to baseline level throughout the remainder of the test. 5-HIAA decreased gradually with no increase during feeding. These data suggest that eating a meal of palatable food causes a short-term increase in extracellular serotonin in the lateral hypothalamus. This increased serotonin may play a role in the control of lateral hypothalamic feeding and reward.

Immunocytochemical and radioautographic study of serotonin projections to cerebral ventricles of perinatal rats

Anatomical relationships between serotoninergic (5-HT) fibers and cerebral ventricles were studied in rats from the 16th fetal day until the 9th postnatal day with immunocytochemistry and radioautography. In the last case, 5-HT neuronal elements were detected according to their specific uptake of intraventricularly injected [3H]5-HT. At the 16th fetal day, occasional 5-HT fibers first spread from the main place of their origin in the raphe nuclei to the dorsocaudal portion of the 3rd ventricle and aqueduct. Two days later, a more extensive network of 5-HT fibers appeared around the dorsal portion of the 3rd ventricle whereas fibers only rarely penetrated toward its ventral portion. By the 9th postnatal day, extensive networks of supraependymal fibers became noticeable in the lateral ventricles and in the dorsal portion of the 3rd ventricle. In addition, a number of 5-HT fibers surrounded the infundibular and preoptic recesses and sometimes penetrated to the ventricular cavity. The functional significance of hypothalamic and ventricular 5-HT as a modulator of either the growth and differentiation of the developing brain or of some specific neuroendocrine functions is discussed.

Evoked release of proteins from central neurons in vivo

Push-pull cannulae were implanted in both substantiae nigrae and caudate nuclei of the halothane-anesthetized cat. The release of total protein, acetylcholinesterase, and nonspecific cholinesterases was examined. Following direct application of potassium to one substantia nigra, changes occurred in the local release of total protein and acetylcholinesterase, but not nonspecific cholinesterases; changes also were observed in both caudate nuclei and the contralateral substantia nigra. The local evoked release of acetylcholinesterase and of total protein differed in the extent to which they were calcium-dependent. Control studies suggest that release of these compounds, both spontaneous and evoked, is related, at least in part, to neuronal activity. The significance of the neuronal release of proteins is discussed.

Serotonin axons of the ependyma and circumventricular organs in the forebrain of the guinea pig. An immunohistochemical study

The distribution of supraependymal nerve fibers (SEF) containing serotonin (5-HT) was investigated immunohistochemically in the forebrain of the guinea pig. The highest densities of immunoreactive axons were found in the pars centralis and the inferior horn of the lateral ventricle and also in the superior part of the third ventricle. Because of the special development of the choroid plexus in these ventricular regions, it is suggested that 5-HT SEF might be involved in the regulation of the composition of the cerebrospinal fluid. The ependyma lining the circumventricular organs located in the forebrain, was not observed to receive a significant 5-HT-SEF innervation. In the pituitary gland, a loose but constant network of 5-HT axons, resembling those which course in the anterobasal hypothalamus, arcuate nucleus and internal layer of the median eminence, was observed in the neural lobe. In the epiphysis, immunoreactive 5-HT was detected in all pinealocytes (the entire cell was filled with reaction product) and in fibers running between them.

Radiation and brain calcium: a review and critique

Serious controversy pervades the scientific study of radio-frequency (RF) radiation and its biological effects. The issues range broadly from international differences in safe exposure standards to questions pertaining to the neurological symptoms purportedly induced by electromagnetic radiation. In a more specialized vein, there is great concern in the discipline about the influence of different sources of radiation on the activity of calcium in the brain. A principal and very realistic reason for this concern stems from the pivotal importance of calcium ions in the normal functioning of the brain in all of its myriad complexity. The purpose of the review is to critically evaluate from an unbiased and "non-involved" viewpoint the major findings on the possible interaction between calcium ions and various radiation sources. Background information is also considered as it relates even indirectly to hypothetical mechanisms that might be used to explain any possible shift in Ca++ ion kinetics. Finally, an inclusive critique is presented which deals with the bench-top methods and strategy used in the conduct of calcium-radiation experiments.

Stimulation of the rat dorsal raphe in vivo releases labeled serotonin from the parietal cortex

In vivo release of labeled serotonin ([3H]5-HT) from the parietal cortex was investigated by cortical cup technique and electrical stimulation of midbrain raphe in rats anesthetized with pentobarbital sodium. The spontaneous efflux of tritium from the parietal cortex preload with [3H]5-HT followed a multiphasic exponential course. After 120 min, the rate of efflux appeared to fit the single exponential function (slow phase). Imipramine (10(-6)-10(-3) M) produced a dose-dependent increase in the spontaneous release. When pargyline in concentrations ranging from 10(-4) to 10(-3) M were added to the medium in the cup, the unchanged [3H]5-HT significantly increased in a dose-dependent manner and the slow declining coefficient of tritium efflux significantly decreased in the presence of 10(-4) pargyline. Stimulation of the rostral two-thirds of the dorsal raphe and the lateral 5-HT bundle originating from the dorsal raphe significantly increased the release of [3H]5-HT and its metabolites while stimulation of the caudal one-third of the dorsal raphe did not produce a significant increase in the release of [3H]5-HT and its metabolites. Stimulation of the medium raphe produced no or only a slight increase in the release of [3H]5-HT and its metabolites. These findings are a direct demonstration of the in vivo release of [3H]5-HT from the parietal cortex with stimulation of the dorsal raphe, particularly the rostral two-thirds of the nucleus and provide the neurochemical evidence for the dorsal raphe-cortical 5-HT pathway via the lateral 5-HT bundle.

Prolonged stimulation of respiration by a new central neural mechanism

The inspiratory responses to stimulation by peripheral chemoreceptor, central chemoreceptor and calf muscle afferents were studied in anesthetized, or decerebrate, paralyzed cats whose end-tidal PCO2 was servo-controlled and kept constant. All stimuli were associated with immediate increases of inspiratory (phrenic) activity and at offset were followed by a respiratory afterdischarge lasting approximately five minutes. The level of inspiratory activity following decay of the afterdischarge was the same as the prestimulation control after central chemoreceptor and calf muscle stimulation. However, after peripheral chemoreceptor afferent stimulation the stable level of inspiratory activity following the afterdischarge had increased over the prestimulation level and remained elevated for as long as it was followed, up to 90 min. Decerebration, vagotomy, and section of the spinal cord at C--T1 did not prevent this long-lasting increase in respiration. We conclude that we have demonstrated a new ponto-medullary neural mechanism which is uniquely activated by peripheral chemoreceptor afferent input; once activated, this mechanism sustains respiration at an increased level for a long period of time.

Changes in body temperature after administration of amino acids, peptides, dopamine, neuroleptics and related agents

Drugs may alter body temperature by acting on any component of the thermoregulatory system. These components include heat production, heat conservation and heat loss effectors and their efferent pathways, thermosensors and their afferent pathways and neurons within the central nervous system that coordinate thermoregulatory effector activities. A thermostat is often thought to be involved although thermoregulation can be explained by models that do not incorporate a thermostat. An action on a particular component can be assessed by determining the effect of a drug on body temperature over a range of environmental temperatures and by observation and measurement of associated changes in effector activities. A scheme for such assessment is presented along with examples of its use. The study of drug-induced changes in body temperature has expanded greatly within the past decade. The primary purpose of this review is to provide a readily available source of information on interactions between certain drugs and the thermoregulatory system. Extensive tables are presented of body temperature changes after administration of amino acids, peptides, dopamine and related agents, phenothiazine neuroleptics and also phenothiazines that lack neuroleptic activity, butyrophenones, diphenylbutylpiperidines such as pimozide and miscellaneous neuroleptics. The information tabulated includes the species used, route of administration and dose of drugs, the environmental temperature at which the experiments were performed, the number of tests, the direction and magnitude of body temperature change and remarks on the presence of special conditions, such as age or lesions, or on the influence of other drugs, such as antagonists, on the response to the primary drug. Most of the cited literature was published since 1965.

Effect of nerve activity on the in vivo release of [3H]serotonin continuously formed from L-[3H]tryptophan in the caudate nucleus of the cat

A new isotopic approach has been developed to study the in vivo release of serotonin (5-HT). 'Encéphale isolé' cats were implanted with a push-pull cannula in the ventrocaudal part of the head of the caudate nucleus to estimate the release of [3H]5-HT continuously synthesized from L-[3H]tryptophan. Both [3H]5-HT and [3H]tryptamine were found in superfusates. Resting steady state in the release of [3H]indoleamines was observed as soon as 20 min after the beginning of the superfusion with L-[3H]tryptophan; the levels of [3H]5-HT in superfusates were 2.5 times those of [3H]tryptamine and about 6 times the blank value. They were markedly enhanced in the presence of fluoxetine (5 x 10(-6)M), a blocker of the 5-HT uptake process. A marked increase in the release of [3H]5-HT was seen during the local depolarization of 5-HT terminals with potassium chloride (60 mM) or batrachotoxin (10(-6)M) or during the stimulation of 5-HT cell bodies in the nucleus raphe dorsalis with L-glutamic acid (5 x 10(-5)M). These treatments did not enhance the efflux of [3H]tryptamine. The potassium-evoked release of [3H]5-HT was reduced by LSD (10(-5)M). LSD added alone in the superfusing fluid was without effect. The batrachotoxin-evoked release of [3H]5-HT was inhibited in the presence of tetrodotoxin (9 x 10(-6)M). The spontaneous release of [3H]5-HT and [3H]tryptamine was markedly reduced in the presence of a calcium-free medium containing cobalt (10 mM). A transient slight reduction in the spontaneous release of [3H]5-HT was observed in the presence of tetrodotoxin (9 x 10(-6)M). The local cooling of 5-HT cell bodies with a cryoelectrode induced a slight reversible decrease in [3H]5-HT release. These last two treatments were without significant effect on [3H]tryptamine efflux in superfusates. These results indicate that the release of [3H]5-HT endogenously formed from [3H]tryptophan is dependent on nerve activity and that this is not the case for [3H]tryptamine. The advantages of the isotopic approach for in vivo studies on the release of 5-HT are discussed.

In vivo voltammetry: monitoring of dopamine metabolites in CSF following release by electrical stimulation

An in vivo electrochemical system which continuously records the concentration of metabolites of biogenic amines in small animal CSF is described. A small electrode, immersed in lateral ventricle CSF through a guide cannula, measures the amine metabolites by voltammetric oxidation. The detailed results of HVA release following electrical stimulation of the nigrostriatal pathway in rats are presented and compared with previous perfusion data. All the electrochemical results are verified by independent liquid chromatographic (chemical) analysis.

Ultrastructural localization of radiolabelled L-dopa in the endocrine hypothalamus of the rat

Light and electron microscopic autoradiography has been employed to define the neuroanatomical patterns of uptake and binding of radiolabelled L-dopa in the endocrine hypothalamus of the rat. A dorsomedial continuum of arcuate and periventricular neurons selectively sequester 3HL-dopa 20 min following its intraventricular infusion. By 40 and 60 min following the infusion labelling of neurons is minimal and supports the notion of rapid degradation. Other cell compartments such as tanycytes demonstrate uptake of 3H L-dopa. The ultrastructural localization and distribution of radiolabelled L-dopa (or its metabolites) in the rodent hypothalamus is discussed with respect to mechanisms and cell compartments involved in neuroendocrine regulatory processes.

Increase in vivo of unesterified fatty acids, prostaglandin F2 alpha but not thromboxane B2 in rat brain during drug induced convulsions

The amount of free arachidonic acid and prostaglandin F2 alpha in rat cerebral hemispheres was increased following convulsions induced by carbachol and metrazol. The level of thromboxane B2 was not affected and prostaglandin endoperoxides could only be "trapped" after a very short convulsive period. Unesterified fatty acid levels at 2 minutes post-mortem were decreased by 50% in the cerebral hemispheres of phenytoin treated rats. Under the same conditions, phenobarbital and diazepam had little effect on the levels of free fatty acids in rat brain.

Effects of intracerebroventricular prostaglandins E2 and F2alpha on the urine outflow, and a possible role of pgE2 as a modulator

Effects of intracerebroventricularly (i.c.v.) injected PGE2 and PGF2alpha on the urine outflow were studied in ethanol-anesthetized rats. PGE2 and PGF2alpha, when injected i.c.v., caused diuresis which was followed by antidiuresis. Phentolamine, when perfused i.c.v., was an antidiuretic and inhibited the diuretic and antidiuretic effects of PGE2. Diphloretin phosphate inhibited both effects of PGE2. Polyphloretin phosphate (PPP) and propranolol blocked completely the PGE2-induced diuresis and consequently remarkable antidiuresis was observed after the combined treatments with PGE2 and PPP or propranolol. When PGE2 was perfused i.c.v., a sustained diuresis was obtained and antidiuretic effects of noradrenaline, gamma-aminobutyric acid and L-glutamate were potentiated, inhibited and unaffected by the perfusion with PGE2, respectively. It was indicated that the antidiuretic effect of PGE2 could be dissociated from the diuretic effect and that both effects were mediated through adrenergic mechanisms. The present result also suggested that central PGE2 might act as a modulator of some neurotransmitters involved in water metabolism.

Effects of centrally affecting drugs on the diuretic and antidiuretic actions of intracerebroventricular prostaglandin E2

Effects of centrally affecting drugs on the diuretic and antidiuretic actions of intracerebroventricularly (i.c.v.) injected prostaglandin (PG) E2 in ethanol-anaesthetized rats were studied. PGE2, when injected i.c.v. at a dose of 1 nmole, produced diuresis followed by antidiuresis. When morphine (0.1 mM) was perfused i.c.v., urine outflow decreased and neither diuretic nor antidiuretic effects of i.c.v. PGE2 was apparent. The perfusions with picrotoxin, gamma-aminobutyric acid and L-glutamate inhibited either the diuretic or the antidiuretic effect of PGE2. On the other hand, when pentobarbital, diazepam, isoniazid and strychnine were perfused i.c.v., the diuretic action of PGE2 was diminished and antidiuresis in response to PGE2 remained unchanged. These results suggested that the diuretic and antidiuretic effects of PGE2 could be separated. The developed of the diuretic effect of PGE2 was completely blocked by amitriptyline and antidiuresis was increased. In rats pretreated i.c.v. with reserpine, the diuretic effect of PGE2 was prolonged and antidiuresis in response to PGE2 was not observed. An antidiuretic action of i.c.v. norepinephrine was not varied by reserpine. Mechanisms for both effects of PGE2 are discussed.

The blood-brain barrier to horseradish peroxidase under normal and experimental conditions

This review paper deals with the transport of the protein tracer horseradish peroxidase across cerebral vessels under normal and various experimental conditions. Electronmicroscopical investigations have revealed that, under normal conditions, a minor vesicular transfer of intravenously injected peroxidase occurs across the endothelium in segments of arterioles, capillaries and venules, especially in arterioles with a diameter about 15-30 mu. This normally occurring vesicular transport is susceptible to various experimental conditions. Thus the transfer of tracer increases when a hypertonic solution is injected into the internal carotid artery presumably due to vesicular transport. Extensive acute hypertension of short duration also increases the vesicular transfer of peroxidase from blood to brain. Identical observations are obtained when the hypertension is evoked by intravenous injection of phentolamine and by electrically induced seizures. During the postischemic period, one hour after release of the occlusion of an internal carotid artery in the Mongolian gerbil the vesicular transport of peroxidase is increased across the endothelium of cerebral vessels. The explanation may be release of serotonin from blood platelets during the occlusion. The serotonin could then increase the blood pressure locally in the brain resulting in an enhanced permeability. Serotonin, after perfusion through the cerebral ventricular system, is also able to increase the normally occurring vesicular transfer. The most likely mechanism behind this phenomenon seems at the moment to be local hypertension evoked by serotonin-induced vasoconstriction of arterioles. Finally, the enhanced vesicular transport across cerebral endothelium caused by porto-caval anastomosis is mentioned and the possible role of disturbances in the metabolism of amines as responsible for the extravasation is discussed.

Mechanisms of the flare reaction in human skin

The diffuse area of arteriolar vasodilation surrounding a region of recently injured human skin (axon reflex flare) is dependent upon the integrity of nerve fibers with cell bodies located in dorsal root ganglia. Evidence is presented to indicate that a vasodilator peptide similar to a kinin, neurotensin, or substance P, is implicated in the chain of biochemical events responsible for the transient shift in vascular tonus observable as the flare reaction.

The primate median eminence. II. Correlative high-voltage transmission electron microscopy

The ultrastructure of the normal median eminence of the male rhesus monkey (Macaca mulatta) is described using high-voltage electron microscopy. Surface specializations of ependymal cells lining the infundibular recess included cilia, apical extrusions, and microvilli. Supraependymal cells were predominantly macrophage-like, but examples of lymphocytic types were also seen. Tanycytes had long, branching, basal processes filled with numerous microtubules, some lipid droplets, and granules. The zona interna was composed of large unmyelinated neurosecretory fibers. A few myelinated fibers were also seen, but their character as neurosecretory fibers could not be established. The zona externa was composed of densely-packed profiles of neuro secretory fibers of small diameter, was well-vascularized and contained the terminations of tanycytes. Perivascular glial cells, vesiculated elements, pituicytes, and cellular elements common to connective tissue were observed. The intricate relationships between both the cellular and fibrous elements of the median eminence can be appreciated with the capability of high-voltage electron microscopy to discern ultrastructure in sections 10 times thicker than those used for low-voltage electron microscopy. The median eminence of this primate species has an ultrastructural organization similar to that described for most other species.

Serotonin axons in the supra- and subependymal plexuses and in the leptomeninges; their roles in local alterations of cerebrospinal fluid and vasomotor activity

Extensive plexuses of serotonin axons form a supra- and subependymal system in the walls of the ventricles, in the arachnoid sheath around major cerebral blood vessels, and in the pia over the spinal cord. These have been demonstrated by autoradiography after continuous intraventricular perfusions of exogenous [3H]5-HT in rats and monkeys. The axons accumulate 5,6-DHT rendering them electron opaque, but have no uptake systems for [3H]NE. After treatment with MAO inhibitors and [3H]5-HT, the axonal boutons contain large (70nm) variably dense synaptic vesicles, and small (35 nm) vesicles each equipped with a dense dot. The latter vesicles are not seen in untreated controls. Electrical stimulation in the raphe nuclei causes significant increases in axonal [3H]5-HT uptake indicating that the fibers originate in the raphe. Quantitatively, the supraependymal plexus is variable, profuse over the dorsal and ventral aqueductal surfaces, sparse over the lateral aspects. Individual raphe neurons have their specific uptake affinities for [3H]5-HT that are independent of tracer concentration or diffusion gradient. It is suggested that raphe neurons with low 5-HT uptake may utilize other neurotransmitters. Two new functional roles are proposed: (1) the serotonin ventricular and pial axons are probably important modifiers of local cerebrospinal fluid (CSF) composition so that regional CSF variations in 5-HT and its metabolites are highly probable; (2) the subarachnoid plexus around major cerebral vessels may contribute to local vasomotor action, thus affecting the cerebral blood flow. The possible significance of these serotonin systems for an understanding of certain neurological entities such as migraine and hemodynamic regulation in cerebral vascular disease is indicated.

In vivo release of 5-HT in the lateral ventricle of the rat: effects of 5-hydroxytryptophan and tryptophan

The in vivo release of 5-HT was examined in the rat brain. For this purpose, the left lateral ventricle was perfused at a constant rate with an artificial CSF for several hours in animals anaesthetized with halothane. 5-HT was estimated in serial 1-h collected fractions. The amine was first isolated by adsorption on a Sephadex G-10 column and then assayed using the radioenzymatic method of Saavedra et al.37, slightly modified to improve its sensitivity. The quantity of 5-HT released spontaneously during the first hour fraction was 296 pg, it was lower (99 pg/h) in the following fractions. 5-HT released into the CSF may in great part originate from serotoninergic terminals localized in structures surrounding the ventricle. This was suggested by experiments in which exogenous [3H]5-HT or [3H]tryptophan were perfused through the lateral ventricle during a few hours. [3H]5-HT taken up or synthetized was mainly localized in structures surrounding the ventricular space. The acute injection of 5-hydroxytryptophan (100 mg/kg) induced an immediate important and long lasting increase of 5-HT release. In contrast the acute injection of tryptophan (100 mg/kg) led to a transient and moderate elevation of 5-HT release which was only detected during the second hour of perfusion. Curiously a similar pattern of transmitter release was observed following the constant intravenous infusion of the amino acid (70 mg/kg/h) except that the increase in 5-HT release was much more pronounced during the second hour than after the acute injection. Parallel experiments were made to determine the time course of the changes of free and total tryptophan levels in plasma and of those of tryptophan, 5-HT, and 5-hydroxyindoleacetic-acid (5-HIAA) in brain tissues, induced by the acute and long term administrations of tryptophan. Moreover the rate of 5-HT synthesis was estimated using the monoamine oxidase inhibition method 2 and 5 h after both tryptophan treatments in halothane anaesthetized rats. 5-HT levels and the synthesis rate of the transmitter were increased at 2 h (when both tryptophan treatments stimulated 5-HT release). Despite the presence of high tryptophan levels in plasma and tissues and of high 5-HT and 5-HIAA levels in tissues, the synthesis rate of 5-HT (as the 5-HT release) was similar to that of controls 5 h after the onset of tryptophan infusion. These results suggest that some relationships occurred between the changes in 5-HT SYNTHESIs and release after the first hour of perfusion. The absence of effects of tryptophan treatments on 5-HT release during the first hour of perfusion are also discussed.

The primate median eminence. I. Correlative scanning-transmission electron microscopy

A combined scanning/transmission electron microscopic (SEM/TEM) technique was used to analyze the third cerebral ventricle and underlying tissue of the median eminence of 6 mature rhesus monkeys. The same sample of the ventricular wall was subjected to both SEM and TEM. This technique demonstrates two basic subpopulations of supraependymal cells on the surface of the supraoptic, infundibular and mammillary recesses. Type 1 cells are definitely neuron-like in their surface configuration and internal fine structural organization. Type 2 cells are more similar to histiocytes and are not as numerous as type 1 cells. The functional capacity of type 1 cells is discussed in the context of their potential role as a neuronal network that may serve as a short loop autoregulatory mechanism controlling the synthesis of releasing hormones or biogenic amines.

Cerebral arterial spasm. 1. In vitro contractile activity of vasoactive agents on canine basilar and middle cerebral arteries

✓ In vitro experiments were performed using a small volume chamber to determine the contractile activity of various vasoactive agents on the canine basilar and middle cerebral arteries. Cumulative dose-response curves were obtained for most of the agents tested including serotonin and three different prostaglandins; many of these curves were found to be similar for segments from both arteries. It was concluded from these curves, and the known concentrations in blood, that serotonin is probably the agent in blood responsible for the cerebral arterial spasm that often follows a subarachnoid hemorrhage. This in vitro method is capable of detecting serotonin concentrations as low as 10−12 gm/ml and may prove useful as a quantitative and well-controlled method for studying the etiology of spasm and the receptor mechanisms present in the cerebral arteries.

Analysis of the effects on body temperature of intracerebroventricular injection in anaesthetized dogs of gamma-aminobutyric acid

1 The cerebral ventricles of dogs under intravenous pentobarbitone sodium anaesthesia, were perfused with artificial cerebro-spinal fluid (CSF) at a rate of 0.4-0.5 ml/min from the ventricular to the aqueductal cannulae. The effluent was collected from the aqueductal cannula in 20 min samples. The animals' temperatures were recorded from the rectum.2 gamma-Aminobutyric acid (GABA) 0.1-5 mg when injected into the ventricles produced variable temperature effects. Doses of 0.1 and 0.5 mg always produced hyperthermia and 1 and 5 mg doses sometimes produced hyperthermia and sometimes hypothermia.3 Intraventricular perfusion with 2-bromolysergic acid diethylamide (BOL) and hyoscine did not block hyperthermia. Tests on the rat isolated stomach strip or the guinea-pig isolated superfused ileum for the possible release, respectively, of 5-hydroxytryptamine or acetylcholine by GABA were negative.4 When tested for the presence of prostaglandin E(PGE)-like substances on the isolated rat stomach strip, both the control effluent and the GABA effluent showed activity, the latter being much more potent. There was a temporal correlation between this effect and hyperthermia. Intraventricularly administered sodium salicylate converted the GABA-induced hyperthermia to hypothermia and blocked the release of PGE-like substances.5 Hypothermia induced by GABA alone or in the presence of sodium salicylate was associated with the release of noradrenaline into the effluent.6 Intraventricular administration of GABA in reserpinized dogs produced hyperthermia and not hypothermia. Similar results were obtained with phentolamine perfusion in normal dogs.7 Perfusion with calcium-free solution blocked both the noradrenaline-releasing and hypothermic actions of GABA.8 It is concluded that hyperthermia associated with intraventricular injections of GABA is due to the release of PGE-like substance and hypothermia is due to the release of noradrenaline.

Release of transmitters into the perfused third cerebral ventrical of the cat

1. The third cerebral ventricle of cats treated with nialamide and anaesthetized with chloralose was perfused, and the effluent was tested for 5-hydroxytryptamine (5-HT) and also for acetylcholine (ACh) when the perfusion fluid contained neostigmine.2. Under ;resting' conditions a 25 min sample of effluent contained from < 1 to 6 ng 5-HT; the release remained steady during many hours of perfusion. It was necessary to watch out for traces of blood which might contribute to the 5-HT content and which were only visible after centrifugation.3. A number of regions in the ventral mid-brain and hind-brain were stimulated, including the two most anterior nuclei of the raphe, nucleus linearis rostralis and intermedius. Release of 5-HT (rarely more than 2 ng) was only obtained on stimulation of these two nuclei, whereas ACh was released by stimulating many points, such as the reticular formation or the decussation of the superior cerebellar peduncles, but not the two raphe nuclei.4. Low frequencies of stimulation were more effective at releasing 5-HT, and high frequencies at releasing ACh.5. Since the amount of 5-HT released on stimulation was rarely more than 2 ng, a powerful re-uptake process was suspected and confirmed by the use of chlorimipramine. Intravenous, intraperitoneal and intraventricular use of this drug temporarily increased the basal release to values ranging from 20 to 50 ng in 25 min samples, and about trebled the release on stimulation of either of the linear nuclei.6. Intravenous administration of chlorimipramine (10 mg/kg) caused the disappearance of electrical responses evoked in the brain stem by afferent sensory stimuli.

Prosaglandin E1 fever induced in rabbits

1. Micro-injections of prostaglandin E(1) (PGE(1)) into the anterior hypothalamus of the rabbit produced fever which was nearly immediate in onset. The prostaglandin sensitive region appears to be identical to that described as being fever sensitive to leucocytic pyrogen.2. Micro-injections of PGE(1) into the posterior hypothalamus and midbrain reticular formation of the rabbit did not produce fever.3. The febrile response to PGE(1) injected into the anterior hypothalamus was dose dependent over a range of 20-1000 ng.4. Ambient temperature influenced the thermoregulatory mechanism by which PGE(1) fever evolved. In the cold, PGE(1) fever was due to increased heat production while during heat exposure both evaporative and dry heat losses were reduced without significant changes in heat production. Vasoconstriction, confined mainly to the ears, was effective in producing fever in standard room environments (24-25 degrees C) along with a small increase in heat production.5. The preoptic anterior hypothalamic area retained its thermosensitivity during PGE(1) fever; heating this area attenuated, while cooling augmented the fever.6. The results support the view that PGE(1) is a mediator of pyrogen induced fever.