The glyoxylic acid fluorescence histochemical method: a detailed account of the methodology for the visualization of central catecholamine neurons

Localization of serotonin within tanycytes of the rat median eminence

Formaldehyde and glyoxylic acid histochemical methods were employed to examine monoamine fluorescence of the rat median eminence. Tanycytes of the median eminence contained a yellow histofluorescence which was verified with microspectrofluorometry as due to the presence of serotonin. Catecholamine-containing varicosities, arranged in linear profiles throughout the depth of the median eminence, were observed. These linear profiles appeared to follow the contours of serotonin-containing tanycytes. Organ-culture experiments supported the hypothesis that the serotonin associated with tanycytes is localized within the tanycytes and does not arise from an extrahypothalamic source of nerve terminals. These data provide evidence that a tanycytic catecholamine-indoleamine morphological juxtaposition occurs in a manner reminiscent of that of another circumventricular organ, the pineal.

Noradrenaline neuron innervation of the neocortex in the rat

Noradrenaline innervation of the rat neocortex is studied by glyoxylic acid histochemistry and radioisotopic biochemical analysis. The data indicate that all neocortical areas receive a noradrenergic innervation which is identical in organization but varies in density from area to area. Radioisotopic analysis of catecholamines in the cortical areas studied reveals only the presence of significant levels of noradrenaline. Unilateral locus coerulus ablation greatly diminishes ipsilateral noradrenaline content and fiber innervation in all neocortical areas studied. Detailed histochemical analysis reveals a diffuse plexus-like arrangement of noradrenaline fibers, with each cortical layer having a distinctive pattern of innervation. Single noradrenergic fibers enter layer VI of cortex and branch at all levels to undergo extensive collateralization. Terminal horizontal branching in the molecular layer results in the most dense fiber plexus of all cortical layers. This pattern of noradrenaline innervation is similar to that of other non-specific afferent systems innervating neocortex.

Innervation of scar tissue in the skin of the rat

In this study the reinnervation of scar tissue was investigated histochemically to demonstrate catecholamine fluorescence and nonspecific cholinesterase activity. The scarring was produced by healing and contraction of a defect in the dorsal skin of the rat. The first regenerating nerves showing nonspecific cholinesterase activity were observed in the scar four weeks postoperatively. Throughout the investigation period, that is up to twenty weeks after the operation, only free regenerated nerves were found in the scar; no encapsulated nerve endings were observed. No fluorescent adrenergic nerves were found in the dense collagenous part of the scar tissue. Regenerated fluorescent nerves were, however, observed in the loose regenerated connective tissue under the scar. Most of these nerves followed the course of blood vessels. In the present work a vigorous contraction of the scar tissue was noted and a poor innervation of the scar tissue with free nerves was observed. The role of these regenerated nerve endings in sensory discrimination, and the importance of different transmitters acting in the sensory system are discussed.

Comparative formaldehyde-induced and glyoxylic acid-induced fluorescence histochemical studies on the intrinsic adrenergic innervation of the intestine and the liver of normal and vagotomized cats

The inbuilt intrinsic adrenergic nervous apparatus of the intestine and liver of the cat was studied using 1. the formaldehyde-induced fluorescence histochemical method and 2. the glyoxylic acid-induced fluorescence histochemical method for serial microtome sections and whole mount tissue layers or smear preparations. In addition, the effect of I) total abdominal infra-diaphragmatic vagotomy with or without associated Finney-type gastro-duodenostomy and II) unilateral (left or right) and bilateral cervical vagotomy with or without tracheostomy on the intrinsic adrenergic innervation was tested. Fluorescing varicose axons, both "free" (i.e. unrelated to the blood vessels) and gathered to typical perivascular nerve plexuses were observed in all segments and all layers of the wall of the intestine. The density of the adrenergic innervation varied remarkably from an area to another, even in the same segment and tissue layer, which makes comparative estimations of the density of the innervation very difficult. However, the intrinsic adrenergic innervation of the circular muscle layer of the colon and the rectum seems to be consistently quite rich, and in the rectum, also the longitudinal muscle layer is relatively heavily innervated. It thus seems obvious that (in the cat) also the direct adrenergic innervation of the external smooth muscle layers is of considerable importance, specially in the rectum. In contrast, the results of the present study clearly indicate that the liver parenchyma (of the cat) is devoid of functional intrinsic adrenergic innervation. Vagotomies did not cause any changes in the intrinsic adrenergic innervation of the intestine and liver: even after complete vagotomy no reduction was observed in the number of fluorescing axons or in the intensity of the fluorescence. Consequently, the vagal contribution of adrenergic axons to the liver and the intestine must be negligible, at least in the cat. The use of the glyoxylic acid-induced fluorescence histochemical method and whole-mount tissue layers was found most suitable for mapping and comparative estimation of the density of the intrinsic adrenergic nerve net, and is therefore recommended for other similar or related studies.

Adrenergic innervation of the human gall bladder

Adrenergic innervation of the human gall bladder was studied using two specific fluorescence histochemical methods. Blue-green fluorescing varicose nerves were scarce and mostly followed the course of blood vessels as typical perivascular plexuses. However, some adrenergic nerves not associated with the vessels were occasionally seen, as well as structures suggestive of a pericellular arrangement of varicose adrenergic nerve terminals on non-fluorescing ganglion cells. A few enterochromaffin cells were seen in the epithelial lining, also in the deep invaginations obviously representing the Aschoff-Rokitansky sinuses. Occasionally, small rounded cells with a rounded, relatively large nucleus, and exhibiting a weak yellow-green to blue-green granular cytoplasmic fluorescence, were observed in the wall of the gall bladder. The possible functional and evolutionary significance of these neural and endocrine elements was discussed against the data on physiological and pharmacological studies obtained from the literature. It was concluded that their significance is, in all probability, secondary to the influence of the intestinal polypeptide hormones, vagal innervation and circulating catecholamines upon the normal function of the gall bladder. The glyoxylic acid-induced fluorescence histochemical method was found to be superior to the conventional formaldehyde technique in studies on human tissue.

Monoaminergic synapses, including dendro-dendritic synapses in the rat substantia nigra

Intraventricular administration of 1 or 2 mg of the osmiophilic "false transmitter" 5-hydroxydopamine (5-OHDA) was used to label monoamine storage and release sites in the rat substantia nigra. Vesicles containing unusually dense cores indicative of the presence of the marker were seen forming from the Golgi apparatus in the cell bodies of medium-sized neurons of the substantia nigra, pars compacta, and from smooth endoplasmic reticulum in the dendrites of those neurons and in small unmyelinated axons of unknown origin. In serial sections, both axons and dendrites containing synaptic vesicles marked with 5-OHDA were seen to form synapses "en passage" in pars compacta, and some presynaptic dendrites containing vesicles filled by the marker were also observed to form contacts with dendrites in pars reticulata. The only identified postsynaptic elements engaging in monoaminergic synapses in the substantia nigra were dendrites of medium-sized pars compacta neurons.

Simultaneous fixation and production of catecholamine fluorescence in central nervous tissue by perfusion with aldehydes

Perfusion with a mixture of formaldehyde (4%) and glutaraldehyde (0.5%) is shown both to fix central nervous tissue and to produce, with no further treatment, a fluorescence histochemical localization of catecholamines. After perfusion, serial sections can be readily taken through the whole brain with a Vibratome. Landmarks which are apparent at low power with white-light illumination can be seen when the sections are viewed in the fluorescence microscope. Catecholamine-containing nerve cell bodies, varicose axon terminals and non-varicose nerve fibres appear brightly fluorescent and well localized. The method has been applied to rats, guinea-pigs and rabbits and is ideally suited to the accurate mapping of central catecholamine neurons and their processes.

Different behavioral responses to L-DOPA after anterolateral or posterolateral hypothalamic injections of 6-hydroxydopamine

After bilateral microinjections of 6-hydroxydopamine (6-OHDA) into the anterolateral (AL) or posterolateral (PL) hypothalamus L-DOPA (1,3,4-dihydroxy-phenylalanine) produced running and rearing in AL6-OHDA rats and oral stereotypies in PL 6-OHDA rats. Since the same dose of L-DOPA had no behavioral effect in vehicle injected rats, the responses to L-DOPA of both AL and PL 6-OHDA rats are examples of behavioral supersensitivity. The different forms of behavioral supersensitivity correlated with different patterns of catecholamine (CA) denervation determined by fluorescent microscopy. The major regions of CA denervation in AL 6-OHDA rats were neocortex, hippocampus, limbic forebrain, anteromedial striatum and anterolateral hypothalamus. PL 6-OHDA had these same areas denervated and, in addition, had severe denervation of the entire striatum, parts of the amygdala and thalamus, and of the posterolateral hypothalamus. We conclude that the supersensitive behavioral response to a fixed dose of L-DOPA is determined by the pattern and/or extent of CA denervation.

A fluorescent histochemical study of changes in noradrenergic neurons following experimental cerebral infarction in the rat

Following surgical ligation of the middle cerebral artery in the rat, central catecholamine containing neurons were studied using the glyoxylic acid histochemical technique. By 5 days after the ischemic lesion, the density of fluorescent varicosities decreased in both uninjured cerebral cortex and the cerebellar cortex and the intensity of fluorescence of somata in the ipsilateral and contralateral locus coeruleus decreased as compared with controls. At 20 days afer lesioning, catecholamine containing neurons looked normal under fluorescence microscopic examination, except fine varicose fluorescent axons were present for the first time among the cellular debris of the lesion and appeared to have sprouted into the lesion site. However, by 40 days after surgery, there was a marked increase in the density of fluorescent varicosities in the uninjured ipsilateral cerebral cortex, in the contralateral cerebral cortex, and in the cerebellum. These observations confirm the view that an ischemic cortical lesion can lead to profound changes in cetecholamine containing neurons in distant areas of the brain which are uninjured by the local infarction.

Magnesium ions in catecholamine fluorescence histochemistry. Application to the cryostat and vibratome techniques

The effects of high concentrations of magnesium ions in the cryostat and Vibratome procedures for visualization of catecholamine fluorescence in the central nervous system have been investigated. In cryostat sections, obtained from specimens perfused with a formaldehyde and glyoxylic acid containing buffer, the addition of high concentrations of MgSO4 to the perfusion solution enhances the fluorescence intensity and reduces the unspecific background fluorescence and the diffusion of the catecholamine fluorophore. This improves the visualization of all portions of the central catecholamine-containing neurons. Similar effects are obtained in the formaldehyde-Vibratome technique by the introduction of an immersion bath containing MgSO4 after the sectioning procedure. The use of the magnesium perfusion or immersion steps furthermore increases the reproducibility of the Vibratome and cryostat techniques. The paper describes the improved Vibratome and cryostat techniques used in our laboratory.

Fluorescence histochemical demonstration of dopa thioethers by condensation with gaseous formaldehyde

The usefulness of the formaldehyde (FA) and glyoxylic acid (GA) methods for the fluorescence histochemical demonstration of dopa thioethers has been tested using protein droplet models. Similar fluorescence intensities were recorded from these compounds after either FA or GA treatment. Cysteinyldopa gave a high fluorescence yield similar to that obtained from dopamine and dopa in the FA reaction, whereas gluatitodopa showed a lower, although clearly visible fluorescence. Since the FA method seemed to be the most useful one for demonstration of catechol thioethers, the FA-induced fluorophores of these compounds were further characterized by microspectrofluorometry. The spectral characteristics of the thioether fluorophores (excitation maxima at 420 nm and emission maxima at 480-485 nm) distinguish these substances from dopa and other compounds fluorogenic in the Falck-Hillarp method. Dopa thioethers are proposed to form fluorophores with FA in a manner analogous to that of the primary catecholamines i.e. via low-fluorescent tetrahydroisoquinolines, along two different pathways, to strongly fluorescent 3,4-dihydroisoquinolines and 2-methyl-dihydroisoquinolinium compounds. These dihydroisoquinolines are in a pH-dependent tautomeric equilbrium with their quinoidal forms as reflected by a characteristic spectral shift upon acidification. The results of this study provide the guide-lines for the characterization of fluorogenic compounds in pigment-forming cells.

Water-stable fluorophores, produced by reaction with aldehyde solutions, for the histochemical localization of catechol- and indolethylamines

The properties of a new fluorescence histochemical method for arylethylamines based on reaction with a mixture of 4% formaldehyde and 0.5% glutaraldehyde in aqueous solution are described. At room temperature the aldehyde mixture produced a well-localized fluorescence reaction in tissues, which, when examined microscopically in aqueous solution, was sufficiently intense for fine terminal noradrenergic axons to be seen. If the tissue was subsequently dried, the fluorescence intensity increased. At the same time as inducing the fluorophores, the aldehyde mixture fixed the tissue to a standard well suited for electron microscopy. It thus proved possible to locate amine containing cells in the fluorescence microscope and subsequently examine their ultrastructure. In aqueous models, the aldehyde mixture formed fluorescent products with adrenaline, noradrenaline, dopamine, dopa, 5-hydroxytryptamine and 5-hydroxytryptophan, but not with histamine or octopamine. The fluorescence induced in the aldehyde mixture remained stable if the tissue was subsequently transferred to saline or distilled water and when it was dehydrated in ethanol and cleared with xylene, benzene, chloroform or acetone.

Central dual innervation of arterioles and capillaries in the brain

Fluorescence-and electron-microscopic studies were performed on nerve terminals close to intracerebral blood vessels in the rat. For the electron microscope subdural perfusion fixation with potassium permanganate was used. In the rat cerebral cortex deprived of the bilateral superior cervical ganglion some aminergic terminal boutons containing large and small core vesicles were observed contiguous to blood vessels. These terminals abutted on the capillary basement membrane. Since these terminals are found in the rat after bilateral superior cervical ganglion exision, they probably originate from central catecholaminergic neurons in the brain stem. These findings suggest that central aminergic neurons might play some role in cerebral blood flow regulation. In addition to aminergic terminal boutons, non-aminergic nerve terminals containing non-core vesicles also ended in the capillaries. Cerebral capillaries also have central dual innervation, aminergic and cholinergic, and dual peripheral innervation by sympathetic and parasympathetic fibers.

Studies of auricular catecholamines by fluorescence histochemistry in various heart diseases of man

A comparative histochemical and clinical study concerning the state of the intrinsic adrenergic innervation of the human atrial myocardium was carried out, using the glyoxylic acid-induced fluorescence histochemical method. Specimens from the right auricular appendage were obtained during open-heart surgery from patients suffering from 1. ischaemic heart disease (IHD), 2. atrial septal defect of the secundum type (ASD), and 3. left-sided univalvular or multivalvular heart disease (VHD) with or without congestive heart failure (CHF) experienced prior to surgery. In the IHD group the densities of both the perivascular and the "free" myocardial adrenergic nerve net were greater than in the ASD group and especially in the VHD/CHF group. Secondly, the intensity of fluorescence of the adrenergic structures was generally higher in the IHD group than that in the VDH/CHF group. Further, the average size of the varicosities, the number of varicosities per given length of axon, and the proportional share of the large varicosities were greater in the IHD group than in the ASD and VHD/CHF groups. The difference between the IHD and ASD groups was not great but was obvious in any case. In some patients with VHD/CHF fluorescing axons were observed only occasionally, and the tiny varicosities exhibited a hardly discernible fluorescence. Thus the amount of noradrenaline (NA) in the adrenergic fibres in the IHD group seems to be higher than in the ASD and especially VHD/CHF groups. The level of NA in the IHD group is assumed to constitute a contributory factor in both intracellular metabolic changes and the systemic changes typical of myocardial ischaemia and infarction. In one patient with IHD and in six patients with VHD/CHF with significantly higher heart volume (mean+/-SD) compared with the rest of the patients (P less than 0.001), huge local axonal accumulations of NA in the form of "droplet fibres" were found. These enlarged, bulging adrenergic axons are assumed to be a consequence of mechanical trauma with stretching or disruption of the axons due to myodegenerative processes. It is further assumed that these "droplet fibres" are relatively common in those patients with diseased myocardium. They may constitute an extra contributory factor to the tendency to arrhythmiility of non-atuomatic tissue.

Catecholamine histofluorescence using cryostat sectioning and glyoxylic acid in unperfused frozen brain: a detailed description of the technique

This paper presents a technique for glyoxylic acid-induced monoamine histofluorescence in the central nervous system. Unperfused rat brains are sectioned in a cryostat, immersed in 2% glyoxylic acid solution, warm-air dried and gassed at 100 degrees C. Intense, well-localized catecholamine fluorescence is produced and all known catecholamine-containing structures are demonstrated. The fluorescence obtained by this method was evaluated by a variety of agents and was shown to be catecholaminergic in origin. In contrast to the Vibratome-glyoxylic acid technique, this procedure reliably produces thin, whole-brain sections of even thickness and allows protracted use of the tissue block. Because unperfused tissue is used, the technique can be applied to a broad variety of material, such as post-mortem tissue or invertebrate preparations. Alternate sections can be prepared for a variety of techniques requiring unperfused tissue (e.g., enzymatic localization, chemical assay, anatomical techniques). The reasons for choosing each of the parameters in the technique are discussed.

Consecutive demonstration of nerves containing catecholamine and acetylcholinesterase in the rat cornea

The innervation of the cornea of newborn (two day old) and adult rats was investigated using glyoxylic-acid-induced fluorescence (GIF) for catacholamines and subsequent acetylcholinesterase reaction. Fluorescent nerve were observed around the limbal vessels and in the pericorneal nerve plexus, from which they branched towards the central parts of the cornea. The fluorescent corneal nerves were either nonvaricose or had varicosities at intervals of 10 micra. When the animals had been pretreated with nialamide, noradrenaline and propranolol, some fluorescent branching nerve terminals with numerous varicosities also appeared. All fluorescent nerves disappeared two days after ipsilateral superior cervical sympathectomy. When the acetylcholinesterase (AChE) reaction was performed subsequently to the GIF reaction the following nerve types could be identified: 1. nerves containing both catecholamine (CA) fluorescence and AChE, 2. Nerves containing only AChE.

Identification of catecholamine and luteinizing hormone-releasing hormone (LHRH)-containing neurons in primary cultures of dispersed cells of the basal hypothalamus

Primary cultures of dispersed cells were prepared from 3-5 mg pieces of basal hypothalami of 10-12-day-old rats. The tissue included median eminence, arcuate nucleus and variable amounts of adjacent hypothalamus and preoptic area. The dispersion procedure consisted basically of tissue trypsinization and mechanical dissociation of cells. They were cultured in a modified L-15 medium in an air atmosphere. Neurons survived approximately 3 months. On the basis of morphological characteristics, two basic cell types could be distinguished. One was a larger (50 mum diameter) multipolar cell; microspectrofluorometric analysis revealed that a small percentage of these neurons contained a catecholamine. A second type was smaller, fusiform or ovoid and generally bipolar; a significant number of these were immunoreactive for the releasing hormone LHRH.

Combined visualization of central catecholamine- and acetylcholinesterase-containing neurons: application of the glyoxylic acid and thiocholine histochemical methods to the same Vibratome section

This paper describes a procedure for demonstration of catecholamine- and acetylcholinesterase-containing neurons in the same section of central nervous tissue. The brains are first processed according to the glyoxylic acid (GA) fluorescence method for catecholamine neurons, i.e. perfused with an ice-cold GA solution, sectioned on a Vibratome instrument, immersed in a GA solution and dried under a stream of warm air. The unmounted sections are examined and photographed in the fluorescence microscope, and then stained for acetylcholinesterse according to Holmstedt's modification of the Koelle thiocholine method (incubation for 4-6 h with acetylthiocholine as substrate and Mipafox as inhibitor of non-specific cholinesterases). the sections are then examined in the light microscope, rephotographed, and the picture compared with that following the GA reaction. The present technique makes possible, for the first time, detailed light microscopical studies of themorphological relations between central catecholamine-and acetylcholinesterase-containing neurons in the same section.

Adrenergic innervation of large cerebral blood vessels of the rabbit studied by fluorescence microscopy. Absence of features that might contribute to non-uniform change in cerebral blood flow

The literature provides evidence for non-uniform regional changes in cerebral blood flow under a variety of circumstances. Possible causes of such changes were sought in the larger cerebral arteries of the rabbit prepared according to the glyoxylic acid fluorescence histochemical technique. The adrenergic innervation of the circle of Willis, the basilar artery and their main branches, although showing small differences, is essentially of uniform density. There is no evidence for collars of adrenergic nerves around the origin of small branches nor for cushions at their orifices. Innervation density appears to diminish as the pial vessels get smaller and all vessels seem to be innervated. Thus non-uniform alterations of cerebral blood flow cannot be accounted for by these factors.

Rectal mucosal adrenergic innervation and enterochromaffin cells in ulcerative colitis and irritable colon

Rectal mucosal biopsies of 13 patients suffering from ulcerative colitis, 7 patients presenting symptomatology typical of irritable colon, and 7 control persons were studied by the recently introduced glyoxylic-acid-induced fluorescence histochemical method. In ulcerative colitis, compared to control specimens: 1) the density of the adrenergic nerve network was significantly pronounced; 2) the mean diameter of the varicosities and the proportional share of large varicosities were increased, as well as the number of varicosities per a given length of an axon; 3) the intensity of the fluorescence of varicosities of comparable size was significantly increased; 4) the number of enterochromaffin cells was significantly decreased. In irritable colon, compared to control specimens, the number of enterochromaffin cells was significantly increased. These findings suggest that biogenic amines are somehow involved in both ulcerative colitis and irritable colon. The fluorescence histochemical method used was found sensitive, specific, and suitable for comparative studies on human clinical material.

Simultaneous demonstration of cholinesterases and glyoxylic acid-induced fluorescence of catecholamines in stretch preparations

A combined simultaneous method to demonstrate adrenergic nerves using glyoxylic acid-induced fluorescence and nerves showing cholinesterase activity using the thiocholine technique is described in whole-mount preparations. The subcutaneous fascia and the right atrium of the heart of the rat and guinea-pig were used as tissue specimens, and the innervation patterns of adrenergic and cholinergic nerves were demonstrated in UV and transmitted light. Technical points and the limitations of the method are discussed.

Facial vein in the rabbit. Neurogenic vasodilation mediated by beta-adrenergic receptors

A segment of the facial vein of the rabbit, that opposite the buccal cavity, responds to norepinephrine (NE) and opposite the buccal cavity, responds to norepinephrine (NE) and transmural nerve stimulation (TNS) by a brisk biphasic dilation. The dilation in response to both procedures is reveresed by prior exposure to propranolol (10(-6)M). Pretreatment with phenoxybenzamine (10(-5)M) increases the size of the neurogenic response and displaces the NE dose-relaxation curve to the left. Histamine causes a constrictor response exclusively. Sympathetic stimulation of a segment of the facial vein proximal to this buccal segment, and also of the external jugular vein, results in constriction. Light microscopy showed no fequtres which can account for the dilation, and fluorescence histochemistry using a modified Flack technique showed a dense adrenergic nerve plexus extending throughout the thickness of the media. We found that frequency-response characteristics and neuronal uptake of 3H-NE were consistent with findings for a blood vessel with a heavy medial innervation. Also, monoamine oxidase and catechol O-methyltransferase activities were similar to those found in other rabbit veins. Furthermore, these results are consistent with an adrenergic neuroeffector organization in which there is a predominance of beta- over alpha-adrenergic receptors. In conclusion, the presence of a dilator response in this buccal segment of the facial vein may be related to its location in the wall of the cheek, where it may be subjected to considerable stretch.

Uptake of infarct-imaging agents in reversibly and irreversibly injured myocardium in cultured fetal mouse heart

We studied the specificity of uptake of infarct-imaging agents for reversibly or irreversibly injured myocardium independently of blood flow by using intact beating fetal mouse hearts in organ culture. Reversible injury resulted from deprivation of oxygen and glucose for 4 hours at 37 degrees C; irreversible injury, from similar deprivation at 42 degrees C. At the end of the insult, uptake of 99mTc(Sc)-labeled pyrophosphate, glucoheptonate, or tetracycline was markedly increased in irreversibly damaged and, to a lesser degree, in reversibly injured hearts. After 24 hours of recovery, necrotic hearts accumulated even more pyrophosphate and tatracycline but less glucoheptonate. Uptake of radioiodinated tetracycline increased only in irreversibly injured hearts. Pyrophosphate uptake was not reduced in hearts cultured in calcium-free medium. These finding suggest that 99mTc(Sn)-labeled pyrophosphate, tetracycline, and glucoheptonate preferentially localize in irreversibly damaged myocardium; the 99mTc(Sn) complex modifies the specificity of uptake; and the uptake of 99mTc(Sn)-pyrophosphate appears unrelated to calcium uptake.

Histochemical fluorescence of tissue and brain mono amines: Results in 18 minutes using the sucrose-phosphate-glyoxylic acid (SPG) method

A rapid and sensitive modification of the glyoxylic acid method for the histofluorescent visualization of catecholamines and serotonin in mammalian brain, and other tissues, from cryostat sections is described. The procedure uses a phosphate-sucrose buffer solution combined with 1% glyoxylic acid. Tissues are reacted for 3 s at room temperature. Catecholaminergic cell bodies, pre-terminal, and terminal varicosities, well-localized and brightly fluorescent, are seen throughout cortical and subcortical structures. Serotoninergic cells show a weak fluorescence in rat and mouse brain but a strong fluorescence in dog and monkey brain.

[An improved histofluorescence procedure for freeze-dried paraffin-embedded tissue based on combined formaldehyde-glyoxylic acid perfusion with high magnesium content and acid pH]

A technique is described for highly sensitive and precise visualization of central catecholamine systems in paraffin sections of freeze-dried tissue. The procedure is based on perfusion of the animal with a solution containing formaldehyde and/or glyoxylic acid, in the presence of a very high magnesium content (40 g MgSO4/150 ml solution) and acid pH. The perfused tissue is rapidly frozen, freeze-dried, treated with formaldehyde vapours (at +80 degrees C for 1 h), embedded in parffin in vacuo, and finally sectioned. The present technique has a sensitivity for the dopamine- and noradrenaline-containing systems that is comparable with that of the glyoxylic acid-Vibratome technique, which utilizes fresh, glyoxylic acid-perfused tissue. Thus, the preterminal axon pathways become fluorescent throughout their full extent and the several new terminal systems, discovered with the glyoxylic acid-Vibratome method, are well demonstrable. The method is also highly useful for the study of the cell bodies and their dendritic processes. The catacholamine fibre systems are visualized without any signs of diffusion and with a richness in detail. In animals pretreated with L-tryptophan and MAO-inhibitor the technique is also useful for studies on central indolamine-containing systems.

A methodological approach to rapid and sensitive monoamine histofluorescence using a modified glyoxylic acid technique: the SPG method

A modified approach of the glyoxylic acid (GA) condensation reaction for the visualization of biogenic amines in tissue is described. Cryostat sections are used from brain or extracerebral tissue in dog, monkey, rat and mouse and exposed for 3 s to a room temperature solution containing sucrose-potassium phosphate-glyoxylic acid (SPG). The tissues are air dried and heated in an oven for 5 min. The complete precessing time from fresh tissue to microscopic examineation takes 18 min. Morphologically sharp and brightly fluorescent monoamine-containing neurons, pre- and terminal axons are seen against a dark parenchymal background without drug pre-treatment. The SPG method retains the high specific sensitivity for monoamines previously described in the original technique but is, in addition, more rapid and simple and is easily accissible as a research tool to investigators inexperienced in histofluoresecence techniques.

A method for studying glyoxylic acid induced fluorescence and ultrastructure of monoamine neurons

Inasmuch as precise correlations of light- and electronmicroscopy are crucial for understanding biostructure, it seemed necessary to bring together the advantages of the glyoxylic acid (GA) method (for inducing monoamine fluorescence) and electron microscopy. A combined fluorescence and electron microscope method using GA is introduced. The brain is perfused by 2% GA in Krebs-Ringer bicarbonate buffer (pH 7.0) and this solution is followed by 4% paraformaldehyde containing 0.5% glutaraldehyde in Sorensen's phosphate buffer (pH 7.4). Sections are cut by cryostat or by vitratome and incubated in 2% GA in phosphate buffer (pH 7.0). Using fluorescence microscopy, features of interest are sketched and/or photographed. Afterwards, the same or subsequent section is processed for electron microscopy. Since axons of catecholamine-containing neurons (as well as their perikarya and terminals) are visualized by GA, the recommended procedure expands the range of studies concerning monoamine neurons that can now be carried out effectively.