QUANTITATIVE HISTOCHEMISTRY OF γ-AMINOBUTYRIC ACID IN CAT SPINAL CORD WITH SPECIAL REFERENCE TO PRESYNAPTIC INHIBITION

Abstract— A method is described for quantifying the GABA distribution in cat spinal cord at 200–500 μn resolution. Isolated spinal cord (L5–S1) was frozen and sectioned at about 150 μm thickness. The frozen tissue section was cut into 200 or 500 μm square blocks. The GABA content of each square tissue block was determined by enzymic micromethods and GABA distribution was mapped quantitatively. Average GABA concentrations were: 0·4 mmol/l. in white matter, 1·2 mmol/l. in ventral horn and 1·7 mmol/l. in dorsal horn. The highest concentrations of GABA (2–3 mmol/l.) were found in the dorsolateral part of dorsal horn. In order to destroy the interneurons of dorsal horn, the blood vessels supplying the dorsal horn of the lumbar enlargement were unilaterally cauterized. Seven to 30 days after operation, both the size of dorsal root potential and the GABA level in the dorsal horn were markedly reduced on the cauterized side. These results suggest that GABA is highly concentrated in the interneurons of dorsal horn and functions as a transmitter of presynaptic inhibition.     

Glutamate Decarboxylase Activities in Single Vertebrate Neurons

An enzymatic microassay method for glutamate decarboxylase (GAD) and gamma-aminobutyric acid (GABA) was improved to a degree yielding high sensitivity and low blank. Single cell bodies of anterior horn cells and dorsal root ganglion cells were dissected out from the freeze-dried sections of rabbit and chicken spinal cords and Purkinje cell bodies from those of rabbit cerebellum. A minute amount of GABA, present in single neurons or synthesized by GAD in single neurons, was enzymatically converted to NADPH. The NADPH was amplified 10,000-350,000-fold and measured, using an enzymatic amplification reaction (NADP cycling). GAD was contained in all Purkinje cell bodies and its average activity was four- to fivefold higher than those of the molecular and granular layers of rabbit cerebellum. The GABA concentration was threefold higher in Purkinje cell bodies than in these layers. GAD activity, at a level similar to that in the cerebellar layers, was found in almost all the cell bodies of anterior horn cells from rabbit and chicken. GABA was detected in 40% of rabbit neurons and not in chicken neurons. Dorsal root ganglion cells from both species contained no measurable GAD or GABA.     

THE DISTRIBUTION OF GLYCINE, GABA, GLUTAMATE AND ASPARTATE IN RABBIT SPINAL CORD, CEREBELLUM AND HIPPOCAMPUS

The distribution of glycine, GABA, glutamate and aspartate was measured among about 60 subdivisions of rabbit spinal cord, and among the discrete layers of cerebellum, hippocampus and area dentata. A more detailed mapping for GABA was made within the tip of the dorsal horn of the spinal cord. Spinal ventral horn and dorsal root ganglion cell bodies were analyzed for the amino acids and for total lipid. The distribution of lipid and lipid-free dry weight per unit volume was also determined in spinal cord. Calculated on the basis of tissue water, glycine in the cord is highest in lateral and ventral white matter immediately adjacent to the ventral grey. The distribution of GABA is almost the inverse of that of glycine with highest level in the tip of dorsal horn. It is most highly concentrated in the central 75% of Rexed layers III and IV. Aspartate in the tip of ventral horn is 4-fold higher than in the tip of the dorsal horn and 3 times the average concentration in brain. Glutamate was much more evenly distributed and is relatively low in concentration with slightly higher levels in dorsal than in ventral grey matter. Large cell bodies in both ventral horn and dorsal root ganglion contained high levels of glycine. As reported by others, GABA was found to be high in cerebellar grey layers, area dentata, and regio inferior of hippocampus. Glycine was moderately high in cerebellar layers but moderate to low in hippocampus and area dentata.     

Spatial organization of inhibitory control of activity of vestibulospinal Deiters' neurons by Purkinje cells in the anterior lobe of the cerebellum

The topographical distribution of vestibulospinal neurons in Deiters' nucleus was investigated by a microelectrode method. By contrast with observations made in morphological experiments, the localization of antidromically identified vestibulocervical (C-neurons) and vestibulolumbar (L-neurons) cells was found not to be limited to the ventral middle and rostral third of the nucleus (the forelimb region) and caudodorsal part of the nucleus (hind limb region), but to include the whole of the ventral and dorsal half of the nucleus, respectively. The zones of localization of these two groups of neurons are not confined to a single layer: C-neurons are found in the dorsal half of the nucleus and L-neurons in its ventrocaudal part also. Analysis of the distribution of monosynaptic IPSPs arising in response to activation of Purkinje cells in the vestibulospinal neurons showed that C-neurons are controlled chiefly from the forelimb zone of the cerebellar cortex whereas L-neurons are controlled equally by inhibitory influences from the forelimb and hind limb zones of the anterior lobe of the cerebellar cortex.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 11, No. 1, pp. 54–64, January–February, 1979.     

Chromogranin A in neurons of the rat cerebellum and spinal cord: quantification and sites of expression.

Chromogranin A (CGA) is an abundant protein of dense-cored secretory vesicles in endocrine and neuronal cells. The present study, for the first time, compares CGA of neurons of the central nervous system with the CGA of adrenal origin. By S1 nucleus protection assay, we found that the 3' part of the CGA mRNA between exons 5-8 of the cerebellum and the spinal cord of the rat is homologous to that of the adrenal. In situ hybridization histochemistry revealed that CGA mRNA in the cerebellar cortex is present in cell bodies of Purkinje cells and in neurons of the deep cerebellar nuclei. The perikarya of these cells also exhibit CGA-like immunoreactivity. CGA mRNA and CGA-like immunoreactivity are also present in the motoneurons of the ventral, lateral, and dorsal horns of the rat spinal cord. The amounts of CGA, as determined by radioimmunoassay in cerebellum and spinal cord, were about one tenth of the amounts detected in the adrenal, adenohypophysis, or the olfactory bulb. The sites of CGA expression suggest that CGA may be involved in signal transduction in the motor system.     

Cerebello-vestibular connections of the anterior vermis. A retrograde tracer study in different mammals including primates

Purkinje cells were retrogradely labelled from large injections of wheatgerm-coupled horseradish peroxidase in the vestibular nuclei, including Deiters' nucleus. The labelled Purkinje cells were located in two parallel strips in the anterior vermis; the medial strip is located within the A-zone, the lateral strip corresponds to the B-zone. In the ventral part of the anterior lobe the two strips fuse into a single band, in the dorsal part of the anterior lobe they are separated by a wedge-shaped area, corresponding to the X-zone. The B-zone proceeds in the simple lobule, where it deviates laterally and where it terminates at the centre of the ansoparamedian lobule. Identical zonal patterns were observed in cat, rabbit, rat and monkey. The demarcation of the anterior vermis by the lateral border of the B-zone, and the differences in the projection of the A and B-zone are briefly discussed.     

Effects of GABA, THIP, and potassium on excitability of myelinated axons of isolated amphibian spinal roots

The effects of direct applications of GABA (gamma-aminobutyric acid) and the GABAA agonist, THIP (4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol) on the excitability of myelinated axons of individual dorsal and ventral spinal roots (lumbar VI and (or) VII) of the isolated bullfrog peripheral nerve are reported. Increases evoked by the GABA agonists (0.01-10 mM) in the amplitude of half-maximal A-fiber compound action potentials indicate the presence of depolarizing responses with apparently greater localization to the dorsal roots, and a sensitivity to GABA twofold greater than that for THIP. The changes evoked by GABA and THIP, as well as potassium have components that closely resemble those of sensory and motor fibers in the more distal, desheathed nerve bundle but are smaller and delayed, differences attributable to a closely attached root sheath that acts as a diffusion barrier. These results confirm the likely existence of GABAA receptors on both dorsal and ventral spinal roots.     

ENZYMES OF ENERGY-CONVERTING SYSTEMS IN INDIVIDUAL MAMMALIAN NERVE CELL BODIES1

Abstract— The activities of 7 enzymes (hexokinase, phosphofructokinase, glucose-6-P dehydrogenase, 6-P-gluconic dehydrogenase, NADP linked isocitric dehydrogenase, malic dehydrogenase and lactic dehydrogenase) were measured in individual nerve cell bodies of 8 different neuronal types: pyramidal cells from cerebral cortex and Amnion's horn, Purkinje cells, giant cells in the reticular formation, Deiters’nucleus cells, facial nucleus cells, anterior horn cells and dorsal root ganglion cells. Samples of similar size were analysed from the molecular layer of cerebellum. The cell bodies were dissected from frozen-dried tissue sections and weighed on quartz fibre balances. The weights ranged from 0–2 ng for the smallest pyramidal cells to 9 ng for the largest giant cells. The specific enzymatic reactions were carried out in small volumes (0–01–5 μl) under mineral oil (‘oil-well technique’). The NADPH₂ or NAD formed was amplified by‘enzymatic cycling’and measured fluorometrically. A new cycling method was used for measuring the NAD formed in three of the enzymatic methods. Double cycling was used to measure glucose-6-P and 6-P-gluconate dehydrogenases in the smallest cell bodies. Each type of neuron exhibited a unique enzyme pattern, but four general patterns could be distinguished. The most variable of the enzymes was glucose-6-P dehydrogenase which was nearly 10-fold higher in anterior horn cells than in pyramidal cells from the cerebral cortex. Malic dehydrogenase was the most constant, with a 3-fold range from the highest (Purkinje cells) to the lowest (dorsal root ganglion cells).     

The dorsomedial nuclear group of cranial nerves in the frog.

The dorsomedial motor nuclei were demonstrated by the cobalt-labeling technique applied to the so-called somatic motor cranial nerves. The motoneurons constituting these nuclei are oval-shaped and smaller than the motoneurons in the ventrolateral motor nuclei. They give rise to ventral and dorsal dendrite groups which have extensive arborization areas. A dorsolateral cell group in the rostral three quarters of the oculomotorius nucleus innervates ipsilateral eye muscles (m.obl.inf., m.rect.inf., m.rect.med.) and a ventromedial cell group innervates the contralateral m. rectus superior. Ipsilateral axons originate from ventral dendrites, contralateral axons emerge from the medial aspect of cell bodies, or from dorsal dendrites, and form a "knee" as they turn around the nucleus on their way to join the ipsilateral axons. A few labeled small cells found dorsal and lateral to the main nucleus in the central gray matter are regarded as representing the nucleus of Edinger-Westphal. The trochlearis nucleus is continuous with the ventromedial cell group of the oculomotorius nucleus. The axons originate in dorsal dendrites, run dorsally along the border of the gray matter and pierce the velum medullare on the contralateral side. A compact dendritic bundle of oculomotorius neurons traverse the nucleus, and side branches appear to be in close apposition to the trochlearis neurons. A dorsomedial and a ventrolateral cell group becomes labeled via the abducens nerve. The former supplies the m. rectus lateralis, while the latter corresponds to the accessorius abducens nucleus which innervates the mm. rectractores. Neurons in this latter nucleus are large and multipolar, resembling the neurons in the ventrolateral motor nuclei. Their axons originate from dorsal dendrites and form a "knee" around the dorsomedial aspect of the abducens nucleus. Cobalt applied to the hypoglossus nerve reaches a dorsomedial cell group (the nucleus proper), spinal motoneurons and sympathetic preganglionic neurons. Of the dorsomedial motor cells, the hypoglossus neurons are the largest, and a branch of their ventral dendrites terminates on the contralateral side. Some functional and developmental biological aspects of the morphological findings, such as the crossing axons and the peculiar morphology of the accessory abducens nucleus, are discussed.     

A comparison of microdistributions of taurine and cysteine sulphinate decarboxylase activity with those of GABA and L-glutamate decarboxylase activity in rat spinal cord and thalamus

Abstract— Distribution profiles of taurine and activity of cysteine sulphinate decarboxylase (CSD), the enzyme catalysing the formations of hypotaurine from cysteine sulphinate and of taurine from cysteate respectively, in the rat spinal cord and thalamus were studied in comparison with those of GABA and activity of l -glutamate decarboxylase (GAD), the rate limiting enzyme for GABA formation. In the spinal cord (L₂-L₃), it was found that taurine is fairly evenly distributed, whereas the activity of CSD is higher in the dorsal half of the spinal cord than in the ventral half. The highest CSD activity was found in the dorsal part of the dorsal horn. In the anterior part (A 5.4) of the thalamus, taurine and CSD activity were also distributed evenly and no areas having high taurine content and CSD activity were detected. In contrast with the even distributions of taurine and CSD activity, both GABA and GAD activity were distributed unevenly in the same CNS areas examined: The areas having high GABA content and GAD activity in the thalamus (A 5.4) coincided with the ventrolateral part of the ventral nucleus of thalamus (VM), entopeduncular nucleus (EP) and nucleus reuniens thalami (RE), whereas those in the spinal cord were found to be in the dorsal part of the dorsal horn and surrounding parts of the central canal, respectively. Considering a probable role of GABA in mammalian central nervous system (CNS) as an inhibitory neurotransmitter, it seems unlikely that taurine acts as an inhibitory neurotransmitter at least in the rat spinal cord and thalamus.     

Calcitonin gene-related peptide: detailed immunohistochemical distribution in the central nervous system

With the use of an antiserum generated in rabbits against synthetic human calcitonin gene-related peptide (CGRP) the distribution of CGRP-like immunoreactive cell bodies and nerve fibers was studied in the rat central nervous system. A detailed stereotaxic atlas of CGRP-like neurons was prepared. CGRP-like immunoreactivity was widely distributed in the rat central nervous system. CGRP positive cell bodies were observed in the preoptic area and hypothalamus (medial preoptic, periventricular, anterior hypothalamic nuclei, perifornical area, medial forebrain bundle), premamillary nucleus, amygdala medialis, hippocampus and dentate gyrus, central gray and the ventromedial nucleus of the thalamus. In the midbrain a large cluster of cells was contained in the peripeduncular area ventral to the medial geniculate body. In the hindbrain cholinergic motor nuclei (III, IV, V, VI, VII XII) contained CGRP-immunoreactivity. Cell bodies were also observed in the ventral tegmental nucleus, the parabrachial nuclei, superior olive and nucleus ambiguus. The ventral horn cells of the spinal cord, the trigeminal and dorsal root ganglia also contained CGRP-immunoreactivity. Dense accumulations of fibers were observed in the amydala centralis, caudal portion of the caudate putamen, sensory trigeminal area, substantia gelatinosa, dorsal horn of the spinal cord (laminae I and II). Other areas containing CGRP-immunoreactive fibers are the septal area, nucleus of the stria terminalis, preoptic and hypothalamic nuclei (e.g., medial preoptic, periventricular, dorsomedial, median eminence), medial forebrain bundle, central gray, medial geniculate body, peripeduncular area, interpeduncular nucleus, cochlear nucleus, parabrachial nuclei, superior olive, nucleus tractus solitarii, and in the confines of clusters of cell bodies. Some fibers were also noted in the anterior and posterior pituitary and the sensory ganglia. As with other newly described brain neuropeptides it can only be conjectured that CGRP has a neuroregulatory action on a variety of functions throughout the brain and spinal cord.     

γ-Aminobutyric acid system in isolated dorsal and ventral horn neurons from bovine spinal cord

In order to search for the relationship between the structure and the function of the nervous system, the spinal cord provides suitable material. We devised a procedure for isolation of large ventral and small dorsal horn neurons. Then we examined the -aminobutyric acid (GABA) system in both neurons isolated using our procedure. Glutamic decarboxylase (GAD) activity in dorsal horn neurons was much higher than that in ventral horn neurons. Further, GABA uptake activity by the dorsal horn neurons was also somewhat higher than that by the ventral horn neurons, although some properties of GABA uptake were found to be almost the same in both neuronal fractions. However, we could not find any difference of GABA--ketoglutarate transaminase (GABA-T) activity between the dorsal and ventral horn neurons. These results suggest that GAD and GABA uptake may be indicators for cell specificity to some extent.     

Immunohistochemical mapping of galanin-like neurons in the rat central nervous system

Using an antiserum generated in rabbits against synthetic galanin (GA) and the indirect immunofluorescence method, the distribution of GA-like immunoreactive cell bodies and nerve fibers was studied in the rat central nervous system (CNS) and a detailed stereotaxic atlas of GA-like neurons was prepared. GA-like immunoreactivity was widely distributed in the rat CNS. Appreciable numbers of GA-positive cell bodies were observed in the rostral cingulate and medial prefrontal cortex, the nucleus interstitialis striae terminalis, the caudate, medial preoptic, preoptic periventricular, and preoptic suprachiasmatic nuclei, the medial forebrain bundle, the supraoptic, the hypothalamic periventricular, the paraventricular, the arcuate, dorsomedial, perifornical, thalamic periventricular, anterior dorsal and lateral thalamic nuclei, medial and central amygdaloid nuclei, dorsal and ventral premamillary nuclei, at the base of the hypothalamus, in the central gray matter, the hippocampus, the dorsal and caudoventral raphe nuclei, the interpeduncular nucleus, the locus coeruleus, ventral parabrachial, solitarii and commissuralis nuclei, in the A1, C1 and A4 catechaolamine areas, the posterior area postrema and the trigeminal and dorsal root ganglia. Fibers were generally seen where cell bodies were observed. Very dense fiber bundles were noted in the septohypothalamic tract, the preoptic area, in the hypothalamus, the habenula and the thalamic periventricular nucleus, in the ventral hippocampus, parts of the reticular formation, in the locus coeruleus, the dorsal parabrachial area, the nucleus and tract of the spinal trigeminal area and the substantia gelatinosa, the superficial layers of the spinal cord and the posterior lobe of the pituitary. The localization of the GA-like immunoreactivity in the locus coeruleus suggests a partial coexistence with catecholaminergic neurons as well as a possible involvement of the GA-like peptide in a neuroregulatory role.     

Separate populations of primary sensory neurons project to the splanchnic nerve and thoracic spinal nerve rami of the rat. A fluorescent double labelling study

Using fluorescent double labelling technique with one tracer applied to the greater splanchnic nerve and a second to the ventral or dorsal spinal nerve ramus at the T9 level, it was shown that two separate populations of sensory nerve cell bodies in the T9 dorsal root ganglion were projecting to the splanchnic nerve and spinal rami, respectively. Only two double labelled cells were detected. The results support the theory that spinal and/or supraspinal interactions and not dichotomizing sensory axons are responsible for referred pain.     

Regional concentrations of transmitter amino acids after spinal cord ischaemia in the rabbit

Concentrations of Asp, Glu, Gly, GABA and Gln were studied in the ventral and dorsal horns of the rabbit spinal cord after ligation of the abdominal aorta. The most significant changes observed after 10, 20 and 40 min ischaemia were an increase in the Asp and GABA concentration in the ventral horns and an increase in the Asp, Gly and GABA concentration in the dorsal horns. These changes correspond to shifts in the relevant reactions under conditions of the altered redox equilibrium in the tissue during ischaemia. Four days after 10 min ischaemia, amino acid concentrations in the spinal cord were at the control levels. Four days after 20 and 40 min ischaemia Asp, Gly and GABA concentrations were decreased in the ventral horns and Asp, Gly, GABA and Glu concentrations in the dorsal horns. The percentually greater decrease in the concentration in the ventral horns may be associated with the greater morphological damage to these structures.     

Organization of the sensory and motor nuclei of the glossopharyngeal and vagal nerves in lampreys

Anterograde and retrograde transport of horseradish peroxidase was used to examine the afferent and efferent projections of the glossopharyngeal and vagal nerves in the lamprey, Lampetra japonica. Except for the ganglion cells and motoneurons, the distribution patterns of HRP-positive elements differed little between the two nerves. Afferent fibers mainly terminated in the ipsilateral cerebellar area, medial octavolateralis nucleus, and between the ventral octavolateralis nucleus and descending tract and nucleus of the trigeminal nerve (dV). In the cerebellar area, most of the labeled fibers were located in the molecular zone, but some penetrated into the granular zone. In the rostral part of the medial octavolateralis nucleus, labeled fibers coursed from the middle to the lateral area, and in the caudal part, they were localized in the dorsal area of the nucleus. In the area between the dV and ventral octavolateralis nucleus, labeled fibers coursed near the dorsal margin of the rostral part of the dV, and in the caudal part, they shifted dorsally. Ganglion cells and motoneurons of each nerve were also labeled.     

AMINO ACID AND SUBSTANCE P CONTENTS IN SPINAL CORD OF CATS WITH EXPERIMENTAL HIND-LIMB RIGIDITY PRODUCED BY OCCLUSION OF SPINAL CORD BLOOD SUPPLY

Abstract— Experimental hind-limb rigidity of spinal origin was produced in cats by temporary occlusion of thoracic aorta and internal mammary arteries. In the lumbar segments (L6- S1) of these rigid cats, the monosynaptic reflex recorded from ventral roots was enhanced whereas the polysynaptic reflexes as well as the dorsal root reflexes were almost abolished. On morphological examination of the lumbar spinal cord, the number of interneurons was greatly reduced, whereas the small sized cells, presumably glial cells, were increased by about two times. Ventral horn motoneurons were also reduced. The lumbar spinal cords of the rigid cats were analysed for amino acid and substance P contents. Four major amino acids, aspartate, glutamate, glycine and GABA, were definitely reduced in both grey and white matter except that the glutamate level in the dorsal white was within the normal range. Content and distribution pattern of substance P were not altered in the lumbar cord of the rigid cats. These results are consistent with the notions that GABA occurs in the dorsal horn interneurons subserving primary afferent depolarisation, and that substance P is concentrated in primary afferent fibre terminals. The implications of the decrease of aspartate, glutamate and glycine in the spinal cord of rigid cats are discussed.     

Primary projections of the trigeminal nerve in two species of sturgeon: Acipenser oxyrhynchus and Scaphirhynchus platorynchus

Horseradish peroxidase histochemical studies of afferent and efferent projections of the trigeminal nerve in two species of chondrostean fishes revealed medial, descending and ascending projections. Entering fibers of the trigeminal sensory root project medially to terminate in the medial trigeminal nucleus, located along the medial wall of the rostral medulla. Other entering sensory fibers turn caudally within the medulla, forming the trigeminal spinal tract, and terminate within the descending trigeminal nucleus. The descending trigeminal nucleus consists of dorsal (DTNd) and ventral (DTNv) components. Fibers of the trigeminal spinal tract descend through the lateral alar medulla and into the dorsolateral cervical spinal cord. Fibers exit the spinal tract throughout its length, projecting to the ventral descending trigeminal nucleus (DTNv) in the medulla and to the funicular nucleus at the obex. Retrograde transport of HRP through sensory root fibers also revealed an ascending bundle of fibers that constitutes the neurites of the mesencephalic trigeminal nucleus, cell bodies of which are located in the rostral optic tectum. Retrograde transport of HRP through motor root fibers labeled ipsilateral cells of the trigeminal motor nucleus, located in the rostral branchiomeric motor column.     

Morphology of lumbar-projecting lateral vestibulospinal neurons in the brainstem and cervical spinal cord in the squirrel monkey

The lateral vestibulospinal tract (LVST) is one of the major descending pathways controlling the extensor musculature of the body. To determine whether individual LVST neurons terminating in the lumbosacral spinal segments issue collaterals more rostrally to exert an influence of the cervical ventral horn intracellular recording and biocytin labeling techniques were used in the squirrel monkey. Only neurons monosynaptically related to the 8th nerve and antidromically identified to project below T12 were selected for study. The axon course through the brainstem and cervical spinal cord was examined in 37 LVST neurons. The average distance of recovered axon was 17.3 mm (4.5-31.7 mm). None could be antidromically activated from shocks applied to the rostral medial longitudinal fasciculus near the 3rd nuclei; and no collaterals were observed in the brainstem. Of the 37 neurons, only 1 axon issued a collateral to innervate the ventral horn, primarily in the region of the spinal accessory motoneurons; this single collateral provided a relatively minor input compared to that of LVST neurons terminating in the cervical cord. Thus, secondary, caudal-projecting LVST neurons represent a private, and mostly rapid, communication pathway between dorsal Deiters' nucleus and the motor circuits controlling the lower limbs and tail.     

Peptide YY-like immunoreactivity in the central nervous system of the rat

The concentration of peptide YY (PYY)-like immunoreactivity in rat brain and spinal cord was determined by radioimmunoassay. The highest concentrations were found in the cervical spinal cord (18.1 +/- 1.3 ng/g, mean +/- S.E.M.) and in the medulla oblongata (16.3 +/- 1.5 ng/g). Lower amounts were found in the pons and in the hypothalamus. Chromatographic analysis of the PYY-like immunoreactivity from various regions of the brain revealed 95% of the immunoreactive material to be indistinguishable from synthetic porcine PYY. PYY-immunoreactive nerve cell bodies could be demonstrated by immunocytochemistry in the medulla oblongata of colchicine-treated rats, the largest group of cells being found in the midline area between and partly in the raphe pontis and obscurus nuclei. Another large group of immunoreactive cells was detected more laterally in the medial parts of the gigantocellular reticular nucleus. A few cells, finally, were seen in the dorsal parts of the medulla, including the nucleus of the solitary tract. Varicose nerve fibers displaying PYY immunoreactivity were observed in many parts of the hypothalamus, pons, medulla and spinal cord.