Immunocytochemical analysis of putative allatostatin receptor (DAR-2) distribution in the CNS of larval Drosophila melanogaster

Allatostatins (ASTs) are a family of neuropeptides that inhibit the biosynthesis of juvenile hormone in cockroaches and related insects, but not in flies. Two receptors for allatostatins, DAR-1 and DAR-2, with sequence similarity to mammalian galanin receptors have previously been cloned in Drosophila melanogaster. To study the distribution of the predicted DAR-2 protein by immunocytochemistry, antisera were raised against a synthetic peptide corresponding to part of the amino terminus of the receptor sequence. In the brain of larval Drosophila, immunoreactivity appeared to be associated with glial septa surrounding neuropil compartments. In the ventral ganglion, immunoreactive cell bodies appeared to reside in the cortex of the ganglion, surrounding the central neuropil and neurohemal organs. In addition, double labeling immunocytochemistry revealed a substantial superposition between distribution of AST-like immunoreactivity and the putative DAR-2 protein in at least five cell bodies in the region of the ring gland corresponding to the corpora cardiaca.     

Distribution of five peptides, three general neuroendocrine markers, and two synaptic-vesicle-associated proteins in the spinal cord and dorsal root ganglia of the adult and newborn dog: an immunocytochemical study

This study describes the immunocytochemical distribution of five neuropeptides (calcitonin gene-related peptide [CGRP], enkephalin, galanin, somatostatin, and substance P), three neuronal markers (neurofilament triplet proteins, neuron-specific enolase [NSE], and protein gene product 9.5), and two synaptic-vesicle-associated proteins (synapsin I and synaptophysin) in the spinal cord and dorsal root ganglia of adult and newborn dogs. CGRP and substance P were the only peptides detectable at birth in the spinal cord; they were present within a small number of immunoreactive fibers concentrated in laminae I-II. CGRP immunoreactivity was also observed in motoneurons and in dorsal root ganglion cells. In adult animals, all peptides under study were localized to varicose fibers forming rich plexuses within laminae I-III and, to a lesser extent, lamina X and the intermediolateral cell columns. Some dorsal root ganglion neurons were CGRP- and/or substance P-immunoreactive. The other antigens were present in the spinal cord and dorsal root ganglia of both adult and newborn animals, with the exception of NSE, which, at birth, was not detectable in spinal cord neurons. Moreover, synapsin I/synaptophysin immunoreactivity, at birth, was restricted to laminae I-II, while in adult dogs, immunostaining was observed in terminal-like elements throughout the spinal neuropil. These results suggest that in the dog spinal cord and dorsal root ganglia, peptide-containing pathways complete their development during postnatal life, together with the full expression of NSE and synapsin I/synaptophysin immunoreactivities. In adulthood, peptide distribution is similar to that described in other mammals, although a relative absence of immunoreactive cell bodies was observed in the spinal cord.     

The distribution of putative neurotransmitters in the nervous system of the dipteran Chironomus tentans insect larva: An immunohistochemical study using antisera to 5-hydroxytryptamine,tyrosine hydroxylase,methionine-enkephalin,proctolin and bombesin

Using the indirect immunofluorescence technique, the localization and distribution of transmitters, transmitter-related enzymes and neuropeptides was studied in the larvae of the dipteran species Chironomus tentans. Immunoreactivity could be seen for 5-hydroxytryptamine, tyrosine hydroxylase (the rate-limiting enzyme in the catecholamine synthesis), and the neuropeptides methionine-enkephalin (met-enk), proctolin and bombesin. The immunoreactivity was confined both to cell bodies as well as to nerve fibers within ganglia and along the alimentary canal. Furthermore, tyrosine hydroxylase immunoreactivity could also be seen in epithelial cells locally distributed along a short, middle part of the alimentary tract. These latter cells were regarded as endocrine-like cells. No immunoreactivity could be found with certainty for the enzyme phenylethanolamine-N-methyltransferase (PNMT) nor for the peptides vasoactive intestinal polypeptide (VIP), dynorphin, substance P, somatostatin, thyrotropin releasing hormone (TRH), neuropeptide Y (NPY), peptide histidine isoleucine amide (PHI), neurotensin, galanin and cholecystokinin (CCK).     

Glutamic acid decarboxylase (GAD)-like immunoreactivity in the pedal ganglion of Mytilus galloprovincialis

Summary A substance immunologically related to vertebrate glutamic acid decarboxylase (GAD) has been visualized in the pedal ganglion of Mytilus with the pre-embedding peroxidase-antiperoxidase method, by use of an antiserum raised in sheep against rat brain GAD. The results show that GAD-like immunoreactivity is present both in neuronal perikarya and in nerve fibers. Positive neurons are located mainly among the fibers of the ganglion neuropil at the commissural level, and more rarely close to unreactive cortical cell bodies. Immunoreactive nerve fibers are observed throughout the neuropil and also in cerebropedal and pedal nerves.Supported by Ministero Pubblica Istruzione (40%)     

Colocalization of neuropeptides and NADPH-diaphorase in the intra-adrenal neuronal cell bodies and fibres of the rat

Colocalization of vasoactive intestinal peptide, neuropeptide Y, calcitonin gene-related peptide, substance P, and tyrosine hydroxylase, respectively, with NADPH-diaphorase staining in rat adrenal gland was investigated using the double labelling technique. All vasoactive intestinal peptide- and some neuropeptide Y-immunoreactive intrinsic neuronal cell bodies seen in the gland were double stained with NADPH-diaphorase. Double labelling also occurred in some nerve fibres immunoreactive to vasoactive intestinal peptide and neuropeptide Y in the medulla and cortex. No colocalization of calcitonin gene-related peptide, substance P or tyrosine hydroxylase immunoreactivity with NADPH-diaphorase staining was observed. However, nerve fibres with varicosities immunoreactive for all the neuropeptides examined were closely associated with some of the NADPH-diaphorase-stained neuronal cell bodies. Thus, in rat adrenal gland, nitric oxide is synthesized in all ganglion cells containing vasoactive intestinal peptide and in some containing neuropeptide Y, but not in those containing calcitonin gene-related peptide, substance P or tyrosine hydroxylase.     

Plasticity in expression of calcitonin gene-related peptide and substance P immunoreactivity in ganglia and fibres following guanethidine and/or capsaicin denervation

Summary This study was designed to investigate the effects of multiple denervation procedures on calcitonin gene-related peptide- and substance P-immunoreactive neurons in sympathetic and sensory cranial ganglia and in selected targets. Sympathectomy by long-term guanethidine treatment induced a pronounced increase in calcitonin gene-related peptide-immunoreactive and substance P-immunoreactive nerve fibres in all the tissues investigated, in contrast to a significant reduction of immunoreactive cell bodies. Neonatal capasaicin treatment abolished substance P immunoreactivity in many targets and caused a dramatic reduction of substance P-immunoreactive sensory nerve cell bodies; calcitonin gene-related peptide-immunoreactive nerve density was decreased, but the number of immunoreactive nerve cell bodies was unchanged. Guanethidine treatment of capsaicin-injected rats reversed the loss of calcitonin gene-related peptide-immunoreactive nerves, but not that of substance P-immunoreactive neurons. In the iris, capsaicin treatment had little effect on calcitonin gene-related peptide- and substance P-immunoreactive nerves, suggesting that in rats the majority of these fibres originate from capsaicin-insensitive neurons. The results suggest that the denervation procedures used in this study alter the synthesis and transport of neuropeptides in sensory neurons in conjunction with changes in the number of nerve fibres.     

Mapping of tachykinins in the cat spinal cord

Using an indirect immunoperoxidase technique, the location of cell bodies and fibers containing substance P, neurokinin A and neurokinin B was studied in the cat spinal cord. The former two neuropeptides showed a widespread distribution throughout the whole spinal cord, whereas the distribution of neurokinin B was more restricted. Neurokinin A-immunoreactive structures showed a more widespread distribution and a higher density than the immunoreactive structures observed to contain substance P. In the cat spinal cord, we observed cell bodies containing neurokinin A, but no cell bodies containing neurokinin B or substance P were found. These cell bodies were located in laminae V (sacral 1 and 2 levels), VI (sacral 1 and 3), VII (lumbar 7, sacral 1 and 3, caudal 1) and X (sacral 1). Laminae I and II showed the highest density of immunoreactive fibers for each of the three tachykinins studied, being in general lamina IV who showed the lowest number of immunoreactive fibers containing substance P, neurokinin A or B. The anatomical distribution of the three tachykinins studied in the cat spinal cord indicates that the neuropeptides could be involved in the neurotransmission and/or in the neuromodulation of nociceptive information, as well as in autonomic and affective responses to pain. Moreover, the involvement of substance P, neurokinin A or B in other functions unrelated to the transmission of pain is also possible (autonomic and motor functions). The distribution of the neuropeptides studied in the cat is compared with the location of the same neuropeptides in the spinal cord of other species. The possible origin of the tachykinergic fibers in the cat spinal cord is also discussed.     

Distinct distribution of CGRP-, enkephalin-, galanin-, neuromedin U-, neuropeptide Y-, somatostatin-, substance P-, VIP- and serotonin-containing neurons in the two submucosal ganglionic neural networks of the porcine small intestine

Summary In addition to differences between the two submucosal ganglionic neural networks, i.e., the plexus submucosus externus (Schabadasch) and the plexus submucosus internus (Meissner), with respect to the occurrence and distribution of serotonin as neurotransmitter, immunocytochemistry also revealed a distinct distribution for various neuropeptides in these two plexuses. Immunoreactivity for galanin, vasoactive intestinal polypeptide, calcitonin gene-related peptide, substance P, neuromedin U, enkephalin, somatostatin and neuropeptide Y was found in varicose and non-varicose nerve fibres of both submucosal ganglionic plexuses, albeit with a distinct distributional pattern. The difference in neurotransmitter and/or neuromodulator content between both neural networks became even more obvious when attention was focussed on the immunoreactivity of the nerve cell bodies for these substances. Indeed, neuropeptide Y, enkephalin-and somatostatin-immunoreactive neuronal perikarya as well as serotonergic neuronal cell bodies appear solely in the plexus submucosus externus. Neuromedin U-immunoreactive perikarya, mostly coexisting with substance P, are observed in large numbers in the plexus submucosus internus, whilst they are rare in the plexus submucosus externus. Double-labelling immunostaining for substance P with CGRP and galanin revealed a different coexistence pattern for the two submucosal ganglionic plexuses. The differing chemical content of the neuronal populations supports the hypothesis that the existence of the two submucosal ganglionic plexuses, present in most large mammals including man, not only reflects a morphological difference but also points to differentiated functions.     

Peripheral axotomy of the rat mandibular trigeminal nerve leads to an increase in VIP and decrease of other primary afferent neuropeptides in the spinal trigeminal nucleus

In the vasoactive intestinal polypeptide (VIP)-rich lumbosacral spinal cord, VIP increases at the expense of other neuropeptides after primary sensory nerve axotomy. This study was undertaken to ascertain whether similar changes occur in peripherally axotomised cranial sensory nerves. VIP immunoreactivity increased in the terminal region of the mandibular nerve in the trigeminal nucleus caudalis following unilateral section of the sensory root of the mandibular trigeminal nerve at the foramen orale. Other primary afferent neuropeptides (substance P, cholecystokinin and somatostatin) were depleted and fluoride-resistant acid phosphatase activity was abolished in the same circumscribed areas of the nucleus caudalis. The rise in VIP and depletion of other markers began 4 days postoperatively and was maximal by 10 days, these levels remaining unchanged up to 1 year postoperatively. VIP-immunoreactive cell bodies were absent from trigeminal ganglia from the unoperated side but small and medium cells stained intensely in the ganglia of the operated side after axotomy. These observations indicate that increase of VIP in sensory nerve terminals is a general phenomenon occurring in both cranial and spinal sensory terminal areas. The intense VIP immunoreactivity in axotomised trigeminal ganglia suggests that the increased levels of VIP in the nucleus caudalis are of peripheral origin, indicating a change in expression of neuropeptides within primary afferent neurons following peripheral axotomy.     

Substance P-like immunoreactivity in the trigeminal sensory nuclei of an infrared-sensitive snake,Agkistrodon blomhoffi

Summary With the peroxidase-antiperoxidase immunohistochemical method we ascertained the presence of substance P-like immunoreactivity (SPLI) in fibers and cell bodies of the trigeminal sensory system of the pit viper, Agkistrodon blomhoffi. There are a few SPLI fibers each in the principal sensory nucleus and the main neuropil of the lateral descending nucleus (i.e., the infrared sensory nucleus); a moderate number in the descending nucleus; and a large number in the caudal subnucleus, the medial edges of the interpolar subnucleus, and the marginal neuropil of the lateral descending nucleus. About 30% of the cell bodies in the ophthalmic and maxillo-mandibular ganglia show SPLI, and of the two craniocervical ganglia, the proximal ganglion has many more cells with SPLI than the distal ganglion. The SPLI distribution in the common trigeminal sensory system is similar to that of mammals, and suggests that the function of this system is also similar. In the infrared sensory system, the differing distribution in the main and marginal neuropils suggests separate functions for these two structures in the system.     

Tyrosine hydroxylase in the cerebral ganglia of the American cockroach (Periplaneta americana L.): an immunohistochemical study

We have investigated the distribution of tyrosine-hydroxylase-like immunoreactivity in the cerebral ganglia of the American cockroach, Periplaneta americana. Groups of tyrosine-hydroxylase-immunoreactive cell bodies occur in various parts of the three regions of the cerebral ganglia. In the protocerebrum, single large neurons or small groups of neurons are located in the lateral neuropil, adjacent to the calyces, and in the dorsal portion of the pars intercerebralis. Small scattered cell bodies are found in the outer layers of the optic lobe, and clusters of larger cell bodies can be found in the deutocerebrum, medial and lateral to the antennal glomeruli. Thick bundles of tyrosine-hydroxylase-positive nerve fibers traverse the neuropil in the proto- and deutocerebrum and innervate the glomerular and the nonglomerular neuropil with fine varicose terminals. Dense terminal patterns are present in the medulla and lobula of the optic lobe, the pars intercerebralis, the medial tritocerebrum, and the area surrounding the antennal glomeruli, the central body and the mushroom bodies. The pattern of tyrosine-hydroxylase-like immunoreactivity is similar to that previously described for catecholaminergic neurons, but it is distinctly different from the distribution of histaminergic and serotonergic neurons.     

Immunohistochemical Localization of Neuropeptides and Neurotransmitters in the Nucleus Solitarius

The nucleus tractus solitarii (NTS), which receives visceralafferent information from the cardiovascular, respiratory, gastrointestinaland taste systems, contains multiple neurotrasmitters and neuropeptidesthroughout its rostral to caudal extent. The neurotransmittersand neuropeptides immunoreactivity is located predominatelyin varicose fibers and small puncta throughout the neuropil.In addition, immunoreactive NTS neurons for a variety of neurotransmittersand neuropeptides are present in subnuclear regions. The neuroactive substances localized immunohistochemically inthe NTS include acetylcholine, the neuropeptides, substanceP, methionine- and leucine-enkephalin, ß-endorphin,cholecystokinin, neurotensin, galanin, calcitonin gene-relatedpeptide, somatostatin, FMRMamide, neuropeptide Y, angiotensinII, vasoactive intestinal polypeptide, vasopressin, oxytocin,thyrotropin-releasing hormone, luteinizing hormone-releasinghormone, atrial natriuretic peptide, the catecholamines, dopamine,norepinephrine, epinephrine, serotonin, histamine and the aminoacids, GABA and glutamate. The pattern of innervation for eachneurotransmitter and neuropeptide is not homogeneously distributedthroughout the NTS. Each substance has a unique pattern withinthe NTS as each subnuclear region contains different immunohistochemicalstaining patterns and densities of fibers. At the ultrastructural level both neurotransmitters and neuropeptidesare present in synaptic terminals that are in contact with differentparts of the neuronal membranes. Typically, the labeled terminalscontain both small, clear vesicles and large, dense core vesicleswith the exception of synaptic terminals containing acetylcholine,GABA and glutamate which do not typically have the large, densecore vesicles. The most frequent post-synaptic target are dendritesand spinous processes. Less frequently, synaptic contacts arepresent on the cell soma. Chem. Senses 21: 367–376, 1996.     

The distribution of NADPH diaphorase activity and immunoreactivity to nitric oxide synthase in the nervous system of the pulmonate mollusc Helix aspersa

Enzyme histochemistry and immunocytochemistry were used to determine the distribution of neurons in the snail Helix aspersa which exhibited nicotinamide adenine dinucleotide phosphate (NADPH) diaphorase activity and/or immunoreactivity to nitric oxide synthase (NOS). NADPH diaphorase-positive cells and fibres were distributed extensively throughout the central and peripheral nervous system. NADPH diaphorase-positive fibres were present in all neuropil regions of the central and peripheral ganglia, in the major interganglionic connectives and in peripheral nerve roots. NADPH diaphorase-positive cell bodies were found consistently in the eyes, the lips, the tentacular ganglia and the procerebral lobes of the cerebral ganglia; staining of cell bodies elsewhere in the nervous system was capricious. The distribution of NOS-like immunoreactivity differed markedly from that of NADPH diaphorase activity. Small clusters of cells which exhibited NOS-like immunoreactivity were present in the cerebral and pedal ganglia; fibres which exhibited NOS-like immunoreactivity were present in restricted regions of the neuropil of the central ganglia. The disjunct distributions of NADPH diaphorase activity and NOS-like immunoreactivity in the neurvous system of Helix suggest that the properties of neuronal NOS in molluscs may differ sigificantly from those described previously for vertebrate animals.     

Immunocytochemical and electron-microscopic study of the elasmobranch nucleus sacci vasculosi

Summary The elasmobranch nucleus sacci vasculosi was studied by means of electron microscopy (in the dogfish) and immunocytochemistry (in the dogfish and the skate) by using antibodies against tyrosine hydroxylase, alpha-melanocyte-stimulating hormone, somatostatin, serotonin, and substance P. Ultrastructural study of the dogfish nucleus sacci vasculosi shows the presence of medium-sized cells that possess numerous mitochondria but that have no dense-core vesicles in the cytoplasm or in cell processes. Fibres of the conspicuous tractus sacci vasculosi have a beaded appearance and form conventional synapses with dendrites and cell perikarya of the nucleus sacci vasculosi. The perikarya of this hypothalamic nucleus were not immunoreactive to any of the antibodies tested, and fibres immunopositive to tyrosine hydroxylase, alpha-melanocyte-stimulating hormone, somatostatin, serotonin, and substance P were scarce within this nucleus, in both the dogfish and the skate. Dorsal to the nucleus sacci vasculosi, there are numerous positive neuronal processes in addition to many small neurons that show immunoreactivity to alpha-melanocyte-stimulating hormone, somatostatin and tyrosine hydroxylase. Two types of neuron occur in this dorsal region, displaying dense-core vesicles of either 100–160 nm or 60–100 nm diameter in their cytoplasm; they were identified as peptide-containing and monoamine-containing neurons, respectively. The neuropil of this region has a significantly different ultrastructure from that of the nucleus sacci vasculosi, with many processes containing dense-core vesicles. This group of neurons, located dorsal to the nucleus sacci vasculosi and showing (a) immunoreactivity to neuropeptides or to monoamine-synthesizing enzyme, and (b) cytoplasm with dense-core vesicles, was considered not to be a part of the nucleus sacci vasculosi but rather part of the nucleus tuberculi posterioris. These results support the non-peptidergic and non-aminergic character of the nucleus sacci vasculosi.     

Tachykinin-related neuropeptide in the crayfish olfactory midbrain

Immunoreactivity indicative of tachykinin-related peptide (TRP) was detected in the olfactory midbrain of the crayfish Pacifastacus leniusculus when using an antiserum to the insect neuropeptide locustatachykinin I (LomTK-I). A monoclonal antibody to the mammalian tachykinin substance P was shown in double-labeling experiments to label structures in the crayfish brain identical to those labeled with the LomTK antiserum. Within the midbrain LomTK-like immunoreactive (LomTK-LI) material was observed in a limited population of neuronal somata and their varicose processes. A single pair of large interneurons gave rise to numerous varicose LomTK-LI processes innervating a cluster of cell bodies (cluster 10) as well as the olfactory neuropils. The latter neuropil was also innervated by a population of LomTK-LI globuli cells with cell bodies in cluster 9. Radioimmunoassay (RIA), utilizing the LomTK antiserum, and reverse-phase high-performance liquid chromatography (HPLC) were used to partially characterize the immunoreactive material in extract of the portion of the midbrain that houses the olfactory (OL) and accessory (AL) lobes and cell clusters 9 and 10 on the one hand, and in extract of the remaining parts of the brain on the other. Approximately the same amounts of LomTK-LI material were observed for the two extracts. RIA showed that the immunoreactive material of both extracts diluted roughly in parallel to synthetic LomTK-I and HPLC analysis of the extracts revealed immunoreactive material in both tissues which eluted with retention times in the range of synthetic LomTK-I and LomTK-II. These results suggest that TRPs similar to LomTKs are present in the olfactory midbrain of Pacifastacus. The distribution of immunolabeled neuronal structures suggests that in the crayfish, peptide(s) closely related to insect TRPs may act as a neuroactive substance released from nerve fibers in olfactory neuropil areas and at certain neuronal cell bodies.     

Immunohistochemical localisation of cholinergic markers in putative intrinsic primary afferent neurons of the guinea-pig small intestine

Antibodies against choline acetyltransferase (ChAT) and the vesicular acetylcholine transporter (VAChT) were used to determine whether neurons that have previously been identified as intrinsic primary afferent neurons in the guinea-pig small intestine have a cholinergic phenotype. Cell bodies of primary afferent neurons in the myenteric plexus were identified by their calbindin immunoreactivity and those in the submucous plexus by immunoreactivity for substance P. High proportions of both were immunoreactive for ChAT, viz. 98% of myenteric calbindin neurons and 99% of submucosal substance P neurons. ChAT immunoreactivity also occurred in all nerve cell bodies immunoreactive for calretinin and substance P in the myenteric plexus, but in only 16% of nerve cells immunoreactive for nitric oxide synthase. VAChT immunoreactivity was in the majority of calbindin-immunoreactive varicosities in the myenteric ganglia, submucous ganglia and mucosa and also in the majority of the varicosities of neurons that were immunoreactive for calretinin and somatostatin and that had been previously established as being cholinergic. We conclude that the intrinsic primary afferent neurons are cholinergic and that they may release transmitter from their sensory endings in the mucosa.     

The distribution and colocalization of neuropeptides and catecholamines in nerves supplying the gall bladder of the toad,Bufo marinus

The indirect immunofluorescence technique was used to determine the distribution of peptide-containing axons in the gall bladder of the cane toad, Bufo marinus. In addition, the adrenergic innervation of the gall bladder was examined by use of immunoreactivity to the catecholamine-synthesizing enzyme, tyrosine hydroxylase, and glyoxylic acid-induced fluorescence. On the basis of peptide coexistence, two intrinsic populations of neurones and their projecting fibres could be distinguished substance P neurones and vasoactive intestine peptide neurones. Neither of these two types of neurones contained any other colocalized neuropeptides. Four populations of nerve fibres arising from cell bodies outside the gall bladder were identified: nerves containing colocalized galanin, somatostatin and vasoactive intestinal peptide; nerves containing colocalized calcitonin gene-related peptide and substance P; adrenergic nerves containing neuropeptide Y; and nerves containing only adrenaline.     

Neurokinin A-like immunoreactivity in rat primary sensory neurons; coexistence with substance P

Rat spinal cord, dorsal root ganglia and skin were investigated employing immunohistochemical technique with specific antisera to neurokinin A and substance P. Neurokinin A-like immunoreactivity was detected in the spinal dorsal horn and skin with a similar distribution pattern as that of substance P-like immunoreactivity. After dorsal root transection a parallel decrease of neurokinin A and substance P-like immunoreactivity was observed in the dorsal horn. Using colchicine pretreatment a population of neurokinin A positive cell bodies was seen in the dorsal root ganglia, and by comparison of consecutive sections of the same cells stained for substance P it was revealed that these neurons also display substance P-like immunoreactivity. However, substance P-, but not neurokinin A-, immunoreactive cells were also observed. It is concluded that neurokinin A- and substance P-like immunoreactivity coexist in a population of rat primary sensory neurons.     

Autoradiographic localization of 3H-histamine accumulation by the visual system of the locust

Summary The uptake of [³H]-histamine into the retina and optic lobe of the locust, Schistocerca americana gregaria was studied by means of autoradiography at the light- and electron-microscopic levels. Light-microscopic autoradiography showed a significant accumulation of [³H]-histamine in several regions of the optic lobe. Dense accumulations of silver grains were concentrated along the medial border of the medullary neuropil and around the entire periphery of the lobula. No significant accumulations of grains were present within the retina or the neuropil zones of the lamina, medulla or lobula.Electron-microscopic autoradiography showed histamine-accumulating cells along the border of the medulla to exhibit electron density and morphology typical of glial cells. Labelled histamine was present within both glial cell bodies and their processes. In the region surrounding the neuropil of the lobula, [³H]-histamine was concentrated within fine glial processes wrapped around neuronal cell bodies and their axons. No neuronal cell bodies or axons showed accumulation of silver grains above background.These results are consistent with previous studies showing the glial uptake of amino acid and biogenic amine putative neurotransmitters. However, the lack of a demonstration of a specific uptake of histamine in neuropil zones makes it difficult to assess the role of histamine uptake in the inactivation of neurally released histamine in the locust visual system.