The monoamine innervation of rat cerebral cortex: synaptic and nonsynaptic axon terminals

Hormonal control of behavior: amines and the biasing of behavioral output in lobsters

Hormones and neurohormones act on the nervous system to produce important changes in behavior. Amine actions in the lobster nervous system and their possible relations to aggressive behavior in lobsters were studied in order to explore how such changes might come about.

Neuropeptide Y-containing neurons in the rat striatum: ultrastructure and cellular relations with tyrosine hydroxylase- containing terminals and with astrocytes

The ultrastructural localization of neuropeptide Y (NPY) was comparatively examined in the dorsal (caudate-putamen) and ventral (nucleus accumbens) striatum using the peroxidase-antiperoxidase (PAP) method. In both striatal regions, NPY-like immunoreactivity (IR) was detected in perikarya, dendrites and axons. The labeled perikarya were 15-25 microns in a diameter and contained large, deeply and multiply indented nuclei and prominent Nissl bodies. The labeled dendrites contained a few large (80-150 nm) dense-core vesicles, lacked detectable spines and received few afferents. These morphological characteristics of NPY-IR neurons in both areas are in close accord with previous descriptions for the medium aspiny intrinsic neurons. Axon terminals with terminals with NPY-like IR contain primarily small clear round vesicles, as seen in single or serial sections. These terminals formed junctions that lacked recognizable pre- or post- synaptic densities, but showed parallel spacing between apposed plasmalemmas at presumed synaptic clefts. Targets of the axon terminals with NPY-like IR included unlabeled somata, unlabeled proximal dendrites and labeled and unlabeled distal dendrites. The NPY-IR neurons in the caudate-putamen differed from those in the nucleus accumbens in that (1) there were no recognized appositions between labeled dendrites and labeled terminals, and (2) fewer terminals contained large dense-core vesicles. These findings are consistent with the concept that in the nucleus accumbens, the excitability of the NPY-IR neurons may be more directly modulated by NPY or another transmitter co-existing in the terminals. Catecholamines are known to co-exist with NPY in certain rostrally projecting brainstem nuclei. Therefore, in the two striatal regions, we additionally sought to determine (1) whether the NPY-IR neurons might be modulated by catecholaminergic afferents and (2) whether NPY might co-exist with catecholamines in terminals. Goat antiserum against NPY and rabbit antiserum against tyrosine hydroxylase (TH), the catecholamine-synthesizing enzyme, were simultaneously localized in single sections by PAP and immunoautoradiographic methods, respectively. Quantitative analysis in dually labeled sections from both striatal areas revealed few, if any, direct synaptic contacts between TH-labeled terminals and dendrites containing NPY-like IR. However, there was convergence of separate NPY- and TH-IR terminals on unlabeled dendrites. A few terminals in the nucleus accumbens, but not in the dorsal striatum, showed immunoreactivity methods, to TH and also contained dense-core vesicles with NPY-like IR.(ABSTRACT TRUNCATED AT 400 WORDS)

Structural aspects, potassium stimulation and calcium dependence of nonsynaptic neuropeptide release by the egg laying controlling caudodorsal cells of Lymnaea stagnalis

The cerebral peptidergic caudodorsal cells of the freshwater snail Lymnaea stagnalis control egg laying and egg-laying behaviour by releasing peptides into (1) the haemolymph, from neurohaemal axon terminals in the periphery of the cerebral commissure and (2) the intercellular space of the central nervous system, from collaterals in the inner compartment of this commissure. Recently, it was shown that collateral release occurs from nonsynaptic release sites, which lack the morphological specializations that are characteristic of classical synapses. Probably, these sites enable the caudodorsal cells to communicate with central neurons in a nonsynaptic ("paracrine", "diffuse", "hormone-like") fashion. The structural and ionic bases of nonsynaptic release were studied using the tannic acid-Ringer incubation-method for the detection of exocytotic release of secretory granule contents in vitro. Elevation of the extracellular potassium concentration strongly stimulates exocytotic activity in the collaterals. No stimulation was found in the absence of extracellular calcium ions. Similar results have been obtained for the neurohaemal axon terminals. Electron-dense material occurs apposed at the cytoplasmic side of the axolemma of collaterals (ethanolic phosphotungstic acid method). This material appears homologous with the presynaptic dense projections forming the "vesicular grid" in classical synapses. Such projections are also present in the neurohaemal axon terminals. It is concluded that secretion from nonsynaptic release sites in caudodorsal cell collaterals shares fundamental characteristics with secretion from conventional neuronal release sites (neurohaemal axon terminals and classical synapses); release occurs by exocytosis of secretory granules, is associated with a vesicular grid, is stimulated by membrane depolarization, and depends on the presence of extracellular calcium ions.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of p-chlorophenylalanine on cerebral metabolism and biogenic amine content of traumatized brain

It was shown previously that focal cortical freezing lesions in rats cause widespread decrease in local cerebral glucose utilization (LCGU) in cortical areas of the lesioned hemisphere. This was interpreted as reflecting a depression of cortical activity. It was then demonstrated that cortical serotonin (5-HT) metabolism was increased throughout the lesioned hemisphere of a focally injured brain. To find out if the changes in the serotonergic system are of functional importance and mediate the observed changes in LCGU, the effects of the inhibition of 5-HT synthesis with p-chlorophenylalanine (PCPA) on cerebral metabolism and biogenic amine content in injured brain were studied. PCPA in doses up to 300 mg/kg had little, if any, effect on LCGU in intact brain and in doses up to 100 mg/kg did not modify the depressed LCGU in injured brain. In doses of 200 and 300 mg/kg, PCPA selectively increased cortical glucose utilization in the lesioned hemisphere where it was depressed following injury. PCPA decreased 5-HT levels in the cortical and raphe areas of both intact and injured brain in a dose-dependent manner. However, at doses of PCPA ineffective on LCGU (50 and 100 mg/kg), traumatization still resulted in increased 5-HT metabolism. Doses of PCPA that ameliorated the depression of LCGU in injured brain completely prevented increases in both 5-HT and its metabolite 5-hydroxyindoleacetic acid seen following traumatization in untreated animals. These results provide evidence that decreased LCGU in lesioned brain is due to an activation of the serotonergic system by traumatization. The data are in agreement with the postulated inhibitory role of serotonin in the cortex and its involvement in functional alterations associated with injury. They suggest that blockage of this neurotransmitter system may have a potential in the development of novel therapeutic approaches to brain injury.

Differential patterns of local cerebral glucose utilization in response to 5-hydroxytryptamine agonists

Local cerebral glucose utilization was measured in parallel groups of conscious rats following intravenous injection of either 1 mg/kg 8-hydroxy-2-(di-N-propylamino)tetralin (a 5-hydroxytryptamine 1A binding site agonist), 3 mg/kg 5-methoxy 3-(1,2,3,6-tetrahydro-4-pyridinyl)1H indole, succinate (a 5-hydroxytryptamine1B agonist), or saline alone, using the 2-deoxyglucose quantitative autoradiographic techniques (n = 5 in each of the three groups). Following both drugs, local rates of glucose use in the majority of the 72 brain areas analysed remained unaltered, but in some other regions either increases or decreases were observed. In keeping with the observed behavioural response to 8-hydroxy-2-(di-N-propylamino)tetralin there were marked increases in cerebellum (+56%) and motor cortex where a columnar arrangement of increased metabolism (+34%) contrasted with adjacent columns of decrease (-26%). Hippocampal areas showed moderate decreases in glucose use (-13 to -21%). All areas which increased following 8-hydroxy-2-(di-N-propylamino)tetralin also increased following 5-methoxy 3-(1,2,3,6-tetrahydro-4-pyridinyl)1H indole, succinate, but in the latter case all elements of the basal ganglia were also increased, including globus pallidus (+105%) and the striatum where the changes (+54%) were limited to a discrete dorsal region of the nucleus. In the hippocampus only dorsal dentate gyrus was decreased (-24%) whilst a moderate increase (+16%) was observed in dorsal subiculum. The complexity of these results contrasts with previous 2-deoxyglucose investigations where less specific 5-hydroxytryptamine receptor ligands were used, and suggests that certain aspects of brain function may be selectively targeted by systemic pharmacological manipulation of endogenous serotonergic systems.

Serotoninergic innervation of the cat cerebral cortex

Serotoninergic axons in the cat cerebral cortex were demonstrated immunohistochemically with a monoclonal antibody to serotonin (5-HT). Three types of 5-HT axons are distinguished at the light microscopic level by differences in their morphology. Small varicose axons are fine (less than 0.5 micron) and bear fusiform varicosities that are generally less than 1 micron in diameter. These axons extend throughout the width of the cortex and branch frequently, giving rise to widely spreading collaterals. Nonvaricose axons are smooth, show a relatively large and constant caliber (about 1 micron), travel in straight, horizontal trajectories, and branch infrequently. Large varicose axons are distinguished by large round or oval varicosities (1 micron or more in diameter) borne on fine-caliber fibers. These axons often form basket-like arbors around the somata of single neurons. In the simplest basket-like arbors, several large, round varicosities from a small number of axons contact the soma. In complex baskets intertwining collaterals contact the soma and apparently climb along and outline the cell's major dendrites. The patterns revealed by the climbing axons suggest that a variety of nonpyramidal cell types selectively receive dense 5-HT innervation. Serial reconstructions of the 5-HT axons within the cortex show that the large varicose axons arise as infrequent collaterals from the nonvaricose axons. A single nonvaricose parent axon gives rise to several large varicose axon collaterals that may contribute to different basket-like arbors. Conversely, a single basket-like arbor may be formed by large varicose axon collaterals from more than one nonvaricose parent axon. The small varicose axons do not appear to be related within the cortex to either the nonvaricose or large varicose axon types. The results support the hypothesis that the 5-HT projection to the cortex is organized into two subsystems, one of which may exert widespread influence in the cortex via highly divergent branches, while the other, with a more restricted distribution, acts on specific classes of cortical neurons.

Electron microscope immunocytochemical localization of thyrotropin-releasing hormone (TRH) prohormone in the rat hypothalamus

Using an antiserum to a synthetic peptide corresponding to the sequence Phe-178-Ser-199 of the precursor of thyrotropin-releasing hormone (pro-TRH), we have studied by immunoelectron microscopy the ultrastructural localization of pro-TRH in the rat hypothalamus. In the paraventricular nucleus neuronal cell bodies, dendrites and axons were labelled. The dense core vesicles were strongly immunoreactive. Immunostained cell bodies, dendrites and endings were frequently observed in contact with unidentified neuronal elements. In the median eminence, numerous endings containing positive dense core vesicles were detected. These results suggest that pro-TRH and/or fragment(s) of pro-tRH could play a neuromodulator/neurotransmitter role in the hypothalamus and could also be released into the pituitary portal plexus.

Ultrastructural features of dopamine axon terminals in the anteromedial and the suprarhinal cortex of adult rat

The ultrastructural features and synaptic relationships of dopamine (DA) axon terminals were examined in the prefrontal cortex of adult rat after immunocytochemical staining with a highly specific polyclonal antiserum directed against DA-glutaraldehyde-lysyl-protein conjugate (donated by M. Geffard). Single and serial ultrathin sections were obtained from the deep layers of the anteromedial and the suprarhinal DA fields. The DA axon terminals from both regions averaged 0.7 micron in diameter, contained a mixed population of small, round and clear synaptic vesicles associated with a few larger dense-cored or fully immunostained vesicles, and frequently exhibited synaptic contacts which were exclusively made on dendritic shafts and spines. These synapses were mostly of the symmetrical type (80%) and were more often seen on dendritic shafts than spines, particularly in the suprarhinal (89%) compared with the anteromedial cortex (62%). As estimated either by stereological extrapolation from single sections or by direct observation in serial sections, the synaptic incidence of these DA varicosities was significantly greater in the anteromedial than suprarhinal DA field. In the longest series of thin sections, a junctional complex could be observed on 93% of the DA varicosities from the anteromedial cortex but only on 56% in the suprarhinal cortex. Such an inter-regional disparity in the relational characteristics of the DA input will need to be taken into account in elucidating the role and properties of this monoamine in cerebral cortex.

Radioautographic method for quantifying regional monoamine innervations in the rat brain. Application to the cerebral cortex

Conditions leading to selective and complete labeling of the noradrenaline (NA) and serotonin (5-HT) innervations in rat cerebral cortex were sought by incubating 200-micron-thick whole hemisphere slices with various combinations of tritiated monoamines and uptake blockers at different concentrations in the presence of a monoamine oxidase inhibitor. After fixation with glutaraldehyde, post-fixation with osmium tetroxide and flat-embedding in Epon, 4-micron-thick sections of the entire slices were radioautographed by dipping in nuclear emulsion. As previously reported, dopamine (DA) terminals could be specifically visualized and counted following incubation with 1 micron [3H]DA and 5 microM desipramine (DMI) with or without 5 microM citalopram (CITAL). The number of NA terminals could thus be obtained by subtracting DA varicosities from the total number of sites labeled in adjacent slices incubated without DMI but in presence of CITAL to eliminate some interspecific labeling of 5-HT terminals. NA terminals could also be identified exclusively and counted after labeling with 1 microM [3H]NA in the presence of 10 microM benztropine. 5-HT terminals were specifically detected after incubation with 1 microM [3H]5-HT in the presence of 10 microM non-radioactive NA. The labeled varicosities were counted in areas FR1 and PAR1 of the frontal and the parietal neocortex, respectively, with the aid of a microcomputer-based image analysis system. DA varicosities were concentrated mainly in layer VI of these regions and were more numerous in the frontal than the parietal area. NA terminals were equally distributed in the two regions but approximately twice as numerous in layer I than subjacent layers. The 5-HT innervation also showed a comparable overall density in the two cortical regions but with a differing intracortical distribution. In the frontal area, 5-HT terminals were slightly more concentrated in layer I (1.3-fold) than underlying layers where they were rather uniformly distributed. In the parietal area, layer I was again the most densely innervated (1.8 times the average), but a second zone of higher density (1.5 times average) was present in the outer part of layer V. The remaining layers showed lower numbers of 5-HT terminals than in the frontal region. To obtain absolute estimates of these innervation densities, the number of detected varicosities was assessed experimentally as a function of radioautographic exposure time and of histological section thickness, and their 'equivalent circle diameter' was measured in electron microscope radioautographs.(ABSTRACT TRUNCATED AT 400 WORDS)

Neuropeptide Y in the rat nucleus accumbens: ultrastructural localization in aspiny neurons receiving synaptic input from GABAergic terminals

The ultrastructure, afferent input, and sites of termination of neurons containing neuropeptide Y-like immunoreactivity (NPY-LI) were examined in the adult rat nucleus accumbens by using the peroxidase-antiperoxidase (PAP) method. The NPY-LI was seen in sparsely distributed, spindle-shaped perikarya having cross-sectional diameters of 15-20 microns. These perikarya exhibited highly invaginated nuclear membranes and thin rims of cytoplasm containing Golgi lamellae, dense-core vesicles, and other organelles. A few large, principally aspiny, dendrites also showed NPY-LI. The dendrites received synaptic input from unlabeled terminals forming both symmetric and asymmetric junctions. Immunolabeling for NPY was evident in other processes that were not clearly differentiated as dendrites or axons. These were seen primarily near glial processes and the basal laminae of blood vessels. A few myelinated and many unmyelinated axons and axon terminals also were labeled for NPY. These terminals contained numerous, small (40-60 nm), clear and one or more large (80-100 nm) dense core vesicles. Forty-seven percent (27 out of 57) of the terminals containing NPY-LI formed symmetric junctions with unlabeled dendrites or dendritic spines. The remainder lacked recognizable densities within single planes of section. The neurons exhibiting NPY-LI in the nucleus accumbens were characterized further with respect to their afferent input from terminals labeled for the GABA-synthesizing enzyme, glutamic acid decarboxylase (GAD). Immunogold labeling of a rabbit antiserum against NPY and PAP labeling for a sheep antiserum to GAD were sequentially applied to the same sections. The GAD-labeled terminals formed symmetric junctions primarily with the more numerous unlabeled dendrites. However, a few synaptic junctions also were detected between the GAD-labeled terminals and dendrites showing immunogold labeling for NPY. We conclude (1) that in the rat nucleus accumbens, NPY-LI is found principally in neurons of the aspiny type and (2) that the output from these presumably intrinsic neurons to other neighboring neurons or blood vessels is at least partially modulated by GABA.

Noradrenaline- and vasoactive intestinal peptide-containing neuronal systems in neocortex: functional convergence with contrasting morphology

Neurotransmitter-specific anatomical techniques have provided a tool to define the morphological constraints within which a given neurotransmitter will exert its cellular actions. Biochemical and electrophysiological approaches have revealed the nature of these cellular actions for several neurotransmitters. Furthermore, by using purified preparations and tissue cultures a certain degree of resolution has been achieved by which the cell type, where a neurotransmitter's effect takes place, can be determined. In this article we review these aspects for noradrenaline and vasoactive intestinal peptide, two neurotransmitters of the cerebral cortex contained within neuronal systems that present strikingly different morphologies. Nevertheless, noradrenaline and vasoactive intestinal peptide share certain cellular actions and can interact synergistically. The experimental evidence accumulated to date indicates that noradrenaline- and vasoactive intestinal peptide-containing neurons can influence three general cell types of the cerebral cortex, i.e. (i) other neurons, (ii) astrocytes and (iii) cells of the vasculature. This diversity in cellular partners supports the notion that noradrenaline and vasoactive intestinal peptide can be released from neurons at conventional synapses as well as at extrasynaptic sites, thus suggesting the co-existence of two modes of release within the same neuron.

Serotonergic axons in the monkey's lateral geniculate nucleus

Axons containing serotonin (5-hydroxytryptamine, 5-HT) in the lateral geniculate nucleus of Macaca monkeys were stained using light or electron microscopic (EM) immunocytochemical labeling techniques. 5-HT labeled axons were sparsely and homogeneously distributed throughout the entire nucleus. Small varicosities were located irregularly along each axon giving them a beaded appearance. Examination of these axons at the EM level revealed that the varicosities contained synaptic vesicles that were variable in size and shape. Nearly all of the varicosities lacked synaptic contacts; only two out of over two hundred labeled varicosities appeared to form a synaptic contact, and serial sections through ten varicosities showed no discernible pre- or postsynaptic membrane specializations. 5-HT labeled axon varicosities were not observed to be preferentially located in proximity to any specific neuronal structures at either the light or EM level. 5-HT varicosities were estimated to form about 1% of the profiles containing synaptic vesicles in the neuropil of the lateral geniculate nucleus. We conclude that axons containing serotonin in the lateral geniculate nucleus release this neurotransmitter to act in a neuromodulatory manner throughout the neuropil, probably to set a general level of neuronal excitability.

Synaptic organization of dopaminergic interplexiform cells in the goldfish retina

The synaptic organization of dopaminergic interplexiform cells (DA-IPC) in the goldfish retina was studied by a combined double-label electron-microscopical (EM) immunocytochemical/autoradiographical study. DA-IPCs were labeled with antisera against tyrosine hydroxylase. The possibility of synaptic contact with GABAergic amacrine cells in the proximal inner plexiform layer (IPL) was studied by using 3H-GABA uptake. Most synaptic input and output from DA-IPC processes involved amacrine cell processes. In addition, synaptic interactions were observed between DA-IPC processes and bipolar cell terminals, other DA-IPC processes, very small dendrites in the IPL, ganglion cell and optic fiber layers (OFL), and cell bodies in the ganglion cell layer (GCL). Input and output synapses with GABAergic amacrine processes also were observed. Two-thirds of the DA-IPC boutons in the proximal IPL were involved in "junctional appositions," that is, the junctions appeared to be specialized but they were different than classical chemical synapses. The synaptic organization of DA-IPCs in the goldfish IPL appears to be far more complex than previously thought. Although earlier studies have attempted to explain the action of dopamine in terms of interaction only with amacrine cells, the present study shows that effects involving bipolar cells, other DA-IPCs, unidentified processes and cell bodies in the GCL and OFL must be considered as well.

Modified coeruleo-cortical noradrenergic neurotransmission after serotonin depletion by PCPA: electrophysiological studies in the rat

To detect eventual modifications in the efficacy of the noradrenergic (NA) coeruleo-cortical system after serotonin (5-HT) depletion by parachlorophenylalanine (PCPA), three electrophysiological parameters were investigated in urethane-anesthetized rats which were treated for 2 days with daily injections of this inhibitor of 5-HT synthesis. 1) The spontaneous activity of locus coeruleus (LC) noradrenergic neurons showed a significant increase in PCPA-treated compared to control rats (4.3 vs. 2.6 Hz). 2) The sensitivity of NA autoreceptors was measured in the LC by the effect of intravenous administrations of clonidine or microiontophoretic applications of NA on spontaneous neuronal firing. In treated rats, clonidine and NA induced a lesser reduction of LC neuron firing than in the controls (27 vs. 75% decreases and 1,367 vs. 280 nC, respectively). 3) The responsiveness of cortical neurons to electrical stimulation of the LC was assessed by peristimulus time histograms in the dorsal fronto-parietal cortex. Following stimulation at 2 or 4 Hz, a majority of spontaneously firing cortical units was inhibited by electrical stimulation of the LC, but the percentage of such units was reduced and showed a decreased responsiveness after PCPA treatment. These findings suggest that following 5-HT depletion by PCPA, cortical NA neurotransmission is markedly reduced in its efficacy in spite of some increase in the spontaneous activity of coeruleo-cortical NA neurons.

Ultrastructural localization of beta-adrenergic receptor-like immunoreactivity in the cortex and neostriatum of rat brain

We sought to quantitatively examine the processes containing beta-adrenergic receptor-like immunoreactivity (beta-AR-LI) in the cerebral cortex and neostriatum using a previously characterized rabbit antiserum to frog erythrocyte beta-ARs under optimized immunolabeling conditions. Quantitative assessments of the laminar distribution of beta-AR-LI in the cortex was achieved by computer-assisted image analysis of immunoautoradiographs and by quantitative electron microscopic analysis of peroxidase-antiperoxidase (PAP) labeling in aldehyde-fixed sections and unfixed synaptosomes. In the somatosensory and anterior cingulate cortical areas, light microscopy of aldehyde-fixed sections immunolabeled by the PAP method revealed small (0.5-1.0 micron) punctate processes in all layers. In the deeper layers, rims of immunoreactivity around the plasmalemma of a population of neuronal perikarya and processes were also observed. By immunoautoradiography, labeling was seen in distinct, laminar distributions resembling the reported autoradiographic patterns using radioligands. By electron microscopy, the immunoreactive profiles in all cortical layers were primarily thick and thin postsynaptic densities (PSDs), comprising 4% of all identifiable PSDs in fixed sections and 12% in unfixed synaptosomal preparations. Also labeled were saccules of smooth endoplasmic reticulum and pinocytotic vesicles in dendrites, glial processes and lightly myelinated axons. In the neostriatum, the density of autoradiographic immunoreactivity was equivalent to the heavily labeled laminae of the cerebral cortex. Immunoreactivity detectable by light microscopy included punctate processes and rims of perikarya, as was seen in the cerebral cortex. The PAP reaction was shown by electron microscopy to be localized to the cytoplasmic surface of plasmalemma of a few proximal dendrites, but was most prominently associated with PSDs of dendritic spines. Preadsorption of the antiserum with a partially purified beta-AR preparation abolished all detectable immunoreactivity. These results provide further support for the specificity of the antiserum for beta-ARs, and are the first quantitative ultrastructural evidence for association of beta-AR-LI with PSDs in the cerebral cortex. The neostriatum, whose major catecholaminergic innervation is dopaminergic, and not noradrenergic, is also confirmed to exhibit high levels of beta-AR-LI within subcellular structures analogous to those seen in the cerebral cortex.(ABSTRACT TRUNCATED AT 400 WORDS)

Ultrastructural organization of regenerated serotonin axons in the dorsomedial hypothalamus of the adult rat

The ultrastructural organization of regenerated serotonin (5-HT) axons was examined in the dorsomedial hypothalamus (DMH) of the adult rat using high-resolution radioautography after intraventricular infusion of [3H]5-HT. An analysis of the microenvironment of the [3H]5-HT-labelled terminals in the DMH was made 30 and 50 days after unilateral injection of 5,7-dihydroxytryptamine (5,7-DHT) or vehicle solution into the dorsolateral hypothalamus. In sham-treated animals [3H]5-HT-labelled axons were small, contained many small clear vesicles, one or more large granular vesicles, and showed only rare synaptic specializations. In 5,7-DHT-treated animals the internal organization of [3H]5-HT-labelled profiles resembled that of sham-treated animals. A tendency toward increased synaptic frequency was found for [3H]5-HT-labelled terminals in the 5,7-DHT-treated group 50 days post-lesion, and an increase in the number of [3H]5-HT-labelled terminals abutting unlabelled perikarya was found in both 30- and 50-day post-lesion groups as compared to sham-treated groups. No other differences in ultrastructural environment were found between sham- and 5,7-DHT-treated animals at either 30 or 50 days post-lesion. These results suggest that 5-HT fibres in the hypothalamus regenerate with a great deal of cellular specificity.

Light and electron microscopic immunocytochemical analysis of the serotonin innervation of the rat visual cortex

The serotonin afferents of the rat visual cortex were examined immunocytochemically at the light and electron microscopic levels. Immunoreactive fibres were typically thin, tortuous and varicose. Occasionally, some thicker fibres were found. The orientation of labelled axons varied according to laminar position, with fibres running parallel to the pial surface present mainly in layers I and VI, and radially oriented fibres prominent in layers II and III. Branches arising from horizontal or radially oriented fibres were seen to form irregularly shaped loops particularly in layers IV and V. The density of innervation and the prevailing axonal orientation in each cortical layer were similar in both coronal and parasagittal planes. The ultrastructural features of serotonin-labelled axon terminals were examined in single and serial ultrathin sections. While in single sections the majority did not exhibit synaptic specializations, extensive serial section analysis showed that virtually all of these terminals were engaged in junctional complexes. Postsynaptic elements were spines and dendritic shafts, including pyramidal cell apical dendrites, with both symmetrical and asymmetrical membrane specializations. In axospinous synapses, the labelled terminals were usually adjacent to unstained axon terminals contacting the same postsynaptic element.

The organization and hypothalamic projections of the tuberomammillary nucleus in the rat: an immunohistochemical study of adenosine deaminase-positive neurons and fibers

The intense immunohistochemical reaction for the enzyme adenosine deaminase displayed by neurons in the tuberomammillary nucleus in the rat was used to study the distribution and morphology of cells comprising this nucleus, their fiber fields within the posterior hypothalamus and their projection pathways from the hypothalamus. Neurons immunoreactive for adenosine deaminase were found along ventricular and basal aspects of the hypothalamus from the level of the dorsomedial nucleus to the caudal pole of the mammillary body. Approximately 4500 neurons were seen on each side of the brain. Positive neurons showed a complex distribution, largely avoiding nuclear boundaries within the posterior basal hypothalamus and mammillary body. This distribution is mapped in detail and a nomenclature based on topography is introduced so that different regions of the cell distribution may be discussed more easily. Reactive neurons showed a Golgi-like staining which allowed careful study of their morphology. In general, neurons were large, with major axes of from 22 to 30 micron, and bipolar in shape. A second, smaller cell type, 14-16 micron in diameter was also seen and, although often less intensely stained, it was considered a constituent of tuberomammillary nucleus of the hypothalamus as well. Stained dendritic arbours extended considerable distances from the parent cell bodies and branched regularly. Dendrites showed very sparse spines and had an apparently scalloped surface. Features suggestive of varicose segments of dendrites were also noted. The long, smooth dendrites of positive neurons were often seen to aggregate into bundles which avoided nuclear boundaries and tended to collect adjacent to basal and ventricular surfaces of the posterior hypothalamus. Varicose fibers immunoreactive for adenosine deaminase formed a dense network within the hypothalamus. These fibers were considered to derive from the positive neurons in the tuberomammillary nucleus and were similar to adenosine deaminase-immunoreactive fibers seen throughout much of the rest of the brain. The density of this type of positive fiber was, however, much greater within the hypothalamus. The region of the posterior basal hypothalamus also contained relatively sparse populations of adenosine deaminase-positive fibers, apparently distinct from this network. These consisted of a field of fine fibers in the median division of the medial mammillary nucleus and a few large varicosities in the dorsolateral part of the median eminence.(ABSTRACT TRUNCATED AT 400 WORDS)

Serotonergic axons form basket-like terminals in cerebral cortex

Serotonergic axons in the posterior cerebral cortex of the cat were demonstrated immunohistochemically using a monoclonal antibody to serotonin (5-HT). This technique reveals the presence of a dense serotonergic innervation of single cortical neurons at the light microscopic level. 5-HT axons with large varicosities (1-6 microns in diameter) form distinct, basket-like arrays around counterstained somata principally in layer I. In each basket one or more axons encircle and make repeated contact with the soma. Some axons extend from the soma and apparently climb along the dendrites of the target neuron. The climbing 5-HT axons form a stellate or horizontal pattern suggesting that the target cells are non-pyramidal neurons of the supragranular layers.

Electron microscopy of serotonin-immunoreactive neuron branches and terminals in the locust central nervous system

Using a pre-embedding peroxidase technique, we have investigated the ultrastructure of elements that react with antibodies to 5-hydroxytryptamine in the central nervous system of the locust. Reactive neuron profiles are widespread, and contain a variety of vesicle types: small lucent vesicles, some of which are stained only on their outer membranes while others are stained internally, and large dense granules that again differ in the staining properties of their cores. Some of the reactive profiles contain synaptic specializations, while others receive synaptic inputs from unlabelled elements. The heterogeneity of reactive profiles makes it impossible to define ultrastructural characteristics of putative serotonergic terminals that might be generally applicable. The differential reactivity both of small vesicles and of large dense granules may indicate functional differences within these categories.

Immunocytochemical localization of dopamine in the prefrontal cortex of the rat at the light and electron microscopical level

In the present study the dopaminergic innervation of the prefrontal cortex was studied by means of a recently developed anti-dopamine serum. This method can demonstrate endogenous dopamine in a specific way, and offers the opportunity to study the distribution of dopaminergic fibres in the cortex in detail in counterstained sections. Furthermore, dopaminergic nerve endings can be visualized at the electron microscopic level. Light microscopic observations demonstrated that the highest density of dopaminergic fibres in the frontal cortex is found in the prefrontal cortex and the infralimbic cortex. Within the prefrontal cortex, a good correlation is found between regional differences in distribution of dopaminergic fibres and the cytoarchitectonic parcellation of this part of the cortex. Outside the prefrontal cortex dopaminergic fibres were observed in adjacent frontal areas, the cortex surrounding the entire rhinal sulcus and the retrosplenial cortex. Electron microscopic observations demonstrated dopaminergic terminals through all cortical layers. The majority of dopaminergic terminals in the prefrontal cortex from synaptic contacts with dendritic processes. The synaptic profiles were usually symmetric and were characterized by the presence of many clear vesicles and an occasional dense-core vesicle.

Effects of injury on the indoleamines in cerebral cortex

It was shown previously that focal cortical freezing lesions in rats cause widespread depression of local cerebral glucose utilization (LCGU) in cortical areas of the lesioned hemisphere. This was interpreted as reflecting functional depression. The underlying mechanisms were postulated to involve alterations of biogenic amine systems. Accordingly, levels of serotonin (5-HT), its metabolite 5-hydroxyindoleacetic acid (5-HIAA), and its precursor tryptophan were determined by an HPLC method with electrochemical detection in frontoparietal cortical areas of both hemispheres at 4 h and 1, 3, 6, 8, and 10 days after a unilateral cortical freezing lesion. The 5-HT content was significantly lower than normal in the lesioned hemisphere only at 24 h, whereas the 5-HIAA level peaked at 24 h but was significantly elevated above normal values between 4 h and 6 days after lesioning. No changes were noted in 5-HT and 5-HIAA contents in the hemisphere contralateral to the lesion. These results indicate that cortical 5-HT metabolism is increased throughout the lesioned hemisphere of a focally injured brain. The increase in tryptophan content of the lesioned brain appeared to have a time course more closely related to previously demonstrated changes in cortical LCGU than to the increase in 5-HIAA content.

Monoaminergic fibers form conventional synapses in the cerebral cortex

The morphological characteristics of the monoaminergic axon-terminals in the mammalian cerebral cortex have been the subject of controversy in recent years. Systematic analysis of serial ultrathin sections, immunocytochemically stained with antibodies against noradrenaline and serotonin, has shown that nearly all stained terminals form synapses characterized by specialized junctional appositions. These results suggest that, contrary to the widely held view, monoamines in the cortex are released at specialized junctions.

Serotonin-containing structures in the nucleus raphe dorsalis of the cat: an ultrastructural analysis of dendrites, presynaptic dendrites, and axon terminals

In the nucleus raphe dorsalis of the cat, an electron microscopic immunocytochemistry method was used to identify the fine structure of serotoninergic dendritic profiles and axon terminals analyzed in serial sections. Two classes of serotoninergic dendrites were distinguished in the nucleus. The first class was constituted by conventional serotonin (5-HT) dendrites that were contacted by unlabeled axon terminals containing differing populations of synaptic vesicles. The second class consisted of serotoninergic dendrites that contained vesicles in their dendritic shafts. Such 5-HT dendrites were further subdivided into two groups according to their synaptic contacts. In some 5-HT vesicle-containing dendrites, the vesicles were densely packed in small clusters and were associated with a well-defined synaptic specialization. These dendrites were classified as serotoninergic presynaptic dendrites and established synaptic contacts with unlabeled and labeled dendrites and were contacted by unlabeled axon terminals. In other 5-HT vesicle-containing dendrites, extensive serial section examination showed that the vesicles could be observed near the membrane but were never found to be associated with any synaptic membrane specialization. Serotoninergic axon terminals that were presumed to be recurrent collaterals of 5-HT neurons were present in the nucleus. Some of them were observed in synaptic contact with dendrites or dendritic protrusions whereas others did not exhibit synaptic specializations. The existence of serotoninergic dendrodendritic synaptic contacts and axon terminals suggests direct local interactions between serotoninergic neurons within the nucleus raphe dorsalis.

Noradrenergic innervation of serotoninergic neurons in the myenteric plexus

The monoaminergic innervation of the guinea pig small intestine was investigated to determine if there is an anatomical basis for the hypothesis that serotoninergic and noradrenergic neurons physiologically interact in the enteric nervous system. Initial rates of uptake of tritiated 5-hydroxytryptamine (3H-5-HT) or norepinephrine (3H-NE) by segments of guinea pig small intestine were measured in order to estimate the regional density of the serotoninergic and noradrenergic innervation. No change was found in the uptake of 3H-5-HT as a function of distance between duodenum and ileum, whereas the relative uptake of 3H-NE declined. The pattern of serotoninergic elements demonstrated radioautographically was compared with that obtained by visualizing 5-HT immunoreactivity. Both methods revealed that a small number of serotoninergic neurons, located in 35.3% +/- 1.5% of myenteric ganglia, give rise to many fibers that form thick bundles in interganglionic connectives. Moreover, there was a pronounced heterogeneity in the serotoninergic innervation of individual myenteric neurons and ganglia. In material fixed with aldehydes and postfixed with NaMnO4, noradrenergic axon terminals were identified by their characteristic small dense-cored vesicles. Following incubation with 3H-NE only terminals with small dense-cored vesicles were radioautographically labeled, confirming that these terminals are noradrenergic. When 3H-5-HT was substituted for 3H-NE, noradrenergic terminals were not labeled, showing that nonspecific uptake of 3H-5-HT into noradrenergic axons did not occur in the presence of 5-hydroxydopamine. The combination of aldehyde-NaMnO4 fixation with the radioautographic localization of 3H-5-HT thus permitted the simultaneous identification of serotoninergic and noradrenergic neural elements. Serotoninergic varicosities were found to differ from noradrenergic varicosities in the size, appearance, and packing density of their synaptic vesicles. In addition, recognizable but rudimentary pre- and postsynaptic membrane specializations were associated with serotoninergic but not noradrenergic varicosities. Most serotoninergic neuronal cell bodies were contacted both by serotoninergic synapses and noradrenergic varicosities. Similar appositions of noradrenergic varicosities with nonserotoninergic neurons appeared to be rare. In view of earlier observations that sympathetic nerves affect the release of 5-HT from stimulated enteric serotoninergic neurons, it seems likely that the noradrenergic appositions with serotoninergic neurons are the anatomical substrate for this effect.(ABSTRACT TRUNCATED AT 400 WORDS)

Brainstem projections to lumbar motoneurons in rat--I. An ultrastructural study using autoradiography and the combination of autoradiography and horseradish peroxidase histochemistry

In 11 rats the descending projections from the ventrolateral medullary medial reticular formation, the medullary raphe nuclei and the area of the nucleus coeruleus and subcoeruleus to lumbar motoneuronal cell groups were studied by means of electron microscopical autoradiography after [3H]leucine injections in the respective brainstem areas. The distribution of the transported radioactivity in the autoradiographs was determined using the circle method [Williams (1977), in Practical Methods in Electron Microscopy, Vol. 6, pp. 85-173] which showed that the vast majority of the silver grains was located over terminal profiles. In the motoneuronal cell groups six different types of terminals were distinguished. After injections in the ventrolateral medial reticular formation the majority of the silver grains was located over F-type terminal profiles while many fewer silver grains were found over S- and G-types. After injections in the raphe nuclei and the adjoining medial reticular formation approximately equal numbers of silver grains were found over F- and G-type terminals while fewer were found over S-type. A small proportion of silver grains was present over C-type terminals and only after injections in the ventrolateral medial reticular formation. After [3H]leucine injections in the area of the nucleus coeruleus and subcoeruleus the majority of silver grains were located over E- and S-type terminals whereas relatively few were located over F-type terminals. The E-type terminal, which has not been described before in the motoneuronal cell groups, is characterized by the fact that it contains relatively small vesicles and occasionally elongated or canaliculi-like structures. In the three groups of experiments approximately 40-50% of the labelled S- and F-type terminal profiles established synaptic contacts, but only approximately 10% of the labelled E- and G-type terminal profiles did so. In all cases these synaptic contacts were established mainly with proximal dendrites. In the autoradiographs some of the silver grains were concentrated into clusters. The vast majority of these clusters, consisting of six or more silver grains, were centred over terminal profiles. The differential distribution of these clusters over the different types of terminal profiles in the various experiments was roughly the same as found by means of the circle method. In two rats [3H]leucine injections in the ventrolateral medial reticular formation were combined with horseradish peroxidase injections in the ipsilateral hindleg muscles, resulting in retrograde labelling of the corresponding motoneurons as visualized by means of the tetramethyl benzidine incubation method.(ABSTRACT TRUNCATED AT 400 WORDS)

A quantitative morphometric analysis of the neuronal and synaptic content of the frontal and temporal cortex in patients with Alzheimer's disease

A quantitative morphometric analysis was used to estimate neurone and synapse densities in cerebral cortical biopsy tissues from patients with dementia under 65 years of age and pathologically verified as suffering from Alzheimer's disease. Estimates of the numerical density of neurones and synapses were made in layers II-III and V of both frontal and temporal cortex. A greater loss of synapses than that of neurones was found in Alzheimer's disease, amounting to a minimum (uncorrected for atrophy) of 25% in layers II-III and 36% in layer V of the temporal cortex, and 27% in layer V of the frontal cortex. Values of synapse to neurone ratio also demonstrated this greater loss of synapses, there being on average 38% fewer synapses associated with each surviving neurone in layers II-III of the temporal cortex, 30% fewer in layer V, and a deficit of 14% in layer V of the frontal cortex. It is concluded that a major loss of synapses occurred in this group of patients with Alzheimer's disease, probably at an early stage of the disease, and that the loss is likely to form a fundamental part of the pathological process that underlies the cortical damage of this condition.

Change in the activity of cortical neurons under the influence of biogenic amines

Under the conditions of extracellular recording of action potentials, the influence of proposed neuromediators on the structure of background impulse activity of neurons of various regions of the cerebral cortex was studied. Computer analysis of the statistical parameters of impulse flows revealed the presence of a fundamental difference between the effects of neuromediators of cortical and subcortical origin. It was demonstrated that prolonged application of serotonin and noradrenalin evokes a change in structure of cortical neuron impulse activity more complex than the simple inhibition and excitation characteristic of acetylcholine or GABA. Different types were found of the reaction of neurons to the same monoaminergic stimulus, types whose characteristic feature is the dependence of the end result of the influence on the initial level of excitation in the neuron examined. The fundamental difference between the effects of preparations studied in the visual and sensorimotor regions of the cortex was not discovered. The data obtained are considered from the point of view of the modulating role of the biogenic amines in the regulation of the level of excitation of cerebral cortical neurons.

Opiate receptors in the human spinal cord: a detailed anatomical study comparing the autoradiographic localization of [3H]diprenorphine binding sites with the laminar pattern of substance P, myelin and nissl staining

The anatomical localization of opiate receptors in the human spinal cord has been examined in six cases aged 7-41 years using quantitative autoradiographic methods following the incubation of fresh, unfixed cryostat sections with [3H]diprenorphine. In order to precisely localize the distribution of receptors in the spinal cord, the laminar anatomy of the spinal grey was demonstrated at each spinal level examined using 50-microns sections stained for myelin, Nissl substance and substance P. In all cases, autoradiograms demonstrated that opiate receptors were distributed in a similar fashion in the grey matter of the cervical, thoracic, lumbar, sacral and coccygeal regions of the human spinal cord. At all 25 spinal levels examined, opiate receptors were mainly localized within the upper laminae of the dorsal horn (laminae I-III) and within the tract of Lissauer. The highest density of opiate receptors was localized within the inner segment of lamina II where the receptors formed a very dense band lying immediately dorsal to lamina III. The density of receptors in this inner region of lamina II (33 +/- 2 fmol/mg) was more than two-and-one-half times greater than that in the remaining upper laminae which showed moderate receptor densities: lamina I (12 +/- 4 fmol/mg) and outer lamina II (13 +/- 3 fmol/mg) both showed similar receptor densities which were higher than those in lamina III (10 +/- 3 fmol/mg) The tract of Lissauer (11 +/- 2 fmol/mg) also showed a moderate density of opiate receptors which was intermediate between the densities in laminae I/IIo and the density of lamina III. The density of receptors in the remaining laminae of the spinal cord varied from moderately low to virtually zero. Moderately low densities of receptors were found in laminae V, VI, VIII, IX and X with very low levels within laminae IV and VII. In particular, in lamina VII opiate receptors were unable to be detected above normal background levels in the dorsal nucleus of Clarke. These results show that, as in other mammalian species, opiate receptors in the human spinal cord are mainly concentrated in the upper laminae of the dorsal horn and in the tract of Lissauer. The possible role of these receptors in modulating spinal nociceptive information is discussed with respect to previous findings on the relationship of opiate receptors to primary afferent fibres in the spinal cord.

Distribution of biogenic amines and their catabolites in brains from patients with Alzheimer's disease

Norepinephrine, epinephrine, dopamine, serotonin and their major catabolites were measured in 17 regions of the left hemisphere of two brains obtained from two brothers with Alzheimer's disease with very early onset. The clinical diagnosis was confirmed by histological examination of the right hemispheres and brain stems. The quantitative data were compared with our values in normal brains. In the patient suffering from the less severe dementia, there was a severe reduction of the serotonin concentration in all examined neocortical areas and its concentration was even below the detection limit in the nucleus amygdalis, hippocampus, caudate nucleus, putamen, globus pallidus and substantia nigra. In the other patient, who suffered from a more pronounced dementia with myoclonus, the serotonin concentration was below the detection limit in all examined structures. In contrast with these findings, the noradrenergic, adrenergic and dopaminergic systems appeared to be relatively unaffected by the disease process. Focusing our attention on the nuclei wherein the monoamine transmitter systems originate, it appeared that neuronal losses and neurofibrillary tangles clearly predominated in the substantia grisea subependymalis, the nucleus centralis superior and the nucleus raphe dorsalis, origin of the main serotonergic system. The serotonin deficiency sheds light on possible mechanisms of myoclonus in Alzheimer's disease.

Opioid receptors in rat neostriatum: radioautographic distribution at the electron microscopic level

The distribution of mu-opioid receptors, selectively labeled in vitro with a monoiodinated Met-enkephalin analog [( 125I]FK 33-824), was analyzed by light and electron microscopic radioautography in sections from the neostriatum of the rat. In the light microscope, patches of high receptor densities were detected amidst a moderately labeled matrix. The number of silver grains, as counted in 1-micron thick plastic-embedded sections, was 3 times greater inside the patches than in the intervening matrix. In both compartments, the proportion of labeled binding sites associated with the neuropil was significantly higher (greater than 70%) than that associated with nerve cell bodies or myelinated fascicles. Quantitative analyses of electron microscopic radioautographs revealed that the majority of silver grains corresponding to specifically bound [125I]FK molecules originated from radioactive sources associated with apposed neuronal membranes. Of the total number of specific binding sites, 53% was associated with axodendritic, 18% with axoaxonic and 3% with axosomatic interfaces. The occurrence of multiple labeled foci along the plasma membrane of certain perikarya and dendrites suggested that some of the binding sites might be associated with somato/dendritic elements. The high incidence of labeling along axoaxonic interfaces indicated that others were linked to the membrane of axons and/or axon terminals. A major finding of the present study was that only a small proportion of specific FK binding sites (7% of total) was associated with synaptic junctions. Labeled synapses were primarily of the asymmetric type and were found predominantly on dendritic branches and spines. A few were observed on nerve cell bodies. Labeled symmetric synapses were rare and encountered exclusively on dendritic branches. The high frequency with which specifically labeled binding sites were found to be associated with neuronal interfaces involving axonal processes strongly suggests that even if non-junctional these binding sites correspond to functional receptors. Whether these receptors are activated by endogenous ligand molecules released by the labeled terminals themselves or from terminals located at a distance from the labeled interfaces remains to be determined.

Morphological basis for nonsynaptic communication within the central nervous system by exocytotic release of secretory material from the egg-laying stimulating neuroendocrine caudodorsal cells of Lymnaea stagnalis

The fine structure of the axons of the cerebral, egg-laying stimulating caudodorsal cells of the snail Lymnaea stagnalis has been studied with various light and electron microscope techniques. Special attention was paid to exocytotic release of secretory material (demonstrated with the tanic acid method) from nonsynaptic release sites in the cerebral commissure. This phenomenon has been compared with neurohaemal release. The commissure consists of two morphological compartments, separated by a sheath of glial cells. The outer compartment is formed by the neurohaemal area of the caudodorsal cells, the inner consists of thousands of, mainly unidentified, axons. Furthermore, ventral caudodorsal cells send axons through the inner compartment. These give rise to collaterals, which divide into smaller collaterals, forming an extensive network ("collateral system") throughout the inner compartment. Eventually, collaterals end blindly within the inner compartment. They contain the same three morphological types of secretory granule as the neurohaemal axon terminals. The collaterals never form synaptic contacts; exocytotic release of the contents of secretory granules takes place at nonsynaptic release sites. These sites occur rather dispersed and do not face one particular type of neighbouring neural element. As in the neurohaemal area, both single and multiple exocytoses occur. Widened intercellular spaces, filled with flocculent, electron-dense material, occur near highly active nonsynaptic release sites. The spaces are often bordered by glial cells and may facilitate diffusion of released secretory material through the inner compartment. Apparently, a ventral caudodorsal cell releases secretory material in two fashions: from neurohaemal axon terminals into the haemolymph, and nonsynaptically, from the collaterals into the intercellular space of the central nervous system. Possible functions of the glial sheath between the neurohaemal area and the inner compartment are proposed. Most likely, the collateral system enables the caudodorsal cells to communicate with targets within the central nervous system in a nonsynaptic fashion. A possible target is the cerebral Ring Neuron, which sends an axon branch through the inner compartment and, as was previously shown neurophysiologically, is controlled by the caudodorsal cells in a nonsynaptic fashion.

Serotonin containing neurons in the retina of the teleost Eugerres plumieri

The concentration and localization of serotonin was determined in the retina of the teleost Eugerres plumieri by using high performance liquid chromatography (HPLC) and immunohistochemical techniques. Serotonin and dopamine were measured simultaneously, their concentrations in the retina being 77 +/- 8 and 516 +/- 23 ng/mg tissue respectively. Treatment of the animals with pargyline significantly increased the levels of dopamine and serotonin. When retinas were treated with the neurotoxin 5,6-dihydroxytryptamine, the level of serotonin was reduced by more than 90% while the dopamine content only diminished by 20% when compared to controls. By using immunohistochemistry with a monoclonal anti-serotonin antibody it was possible to localize this amine in cell bodies of a population of amacrine cells with processes extending mainly into a thin layer of the most external lamina of the inner plexiform layer. Very few ramifications were seen projecting to the internal lamina of this layer. When visualized in flat mount preparations, dense arborization of fluorescent processes was observed. This is the first direct evidence that serotonin is apparently present in amacrine cells of the retina of E. plumieri with a distribution of the serotonergic terminals similar to goldfish but somewhat different when compared to other species.

Exocytosis from large dense cored vesicles outside the active synaptic zones of terminals within the trigeminal subnucleus caudalis: a possible mechanism for neuropeptide release

It has been hypothesized that chemical interactions between neurons in the central nervous system can occur in the absence of well defined synaptic complexes, but morphological correlates have been difficult to find. The present study demonstrates exocytotic release from large (70-130 nm) dense cored vesicles at structurally nonspecialized areas along the plasmalemma of structurally different categories of terminals and occasionally from dendrites and axons within the neuropil of the trigeminal subnucleus caudalis. In rats, the marginal (lamina I) and substantia gelatinosa (lamina II) layers contain the central terminals of primary afferent fibers from the infraorbital nerve that supply the skin and whiskers (vibrissae). Different types of interneurons are also present and may modify the input being relayed to higher centers. While exocytotic profiles were present in control animals, they increased significantly (P less than 0.01) on the ipsilateral side 1-24 h after a unilateral skin lesion in the vibrissae area. A second increase (P less than 0.001) occurred 14-15 days after the lesion. Virtually all examples of large vesicle exocytosis were observed at structurally nonspecialized sites while those at the active synaptic zones involved small clear vesicles. Substance P-like immunofluorescence, present in controls and on the ipsilateral side during the first 6 days, subsequently declined until 4 weeks after surgery when some recovery was noted. The increase in large vesicle exocytosis and the decrease in substance P are interpreted to reflect functional adjustments of different neurons in response to the lesion. The exocytosis involving large dense cored vesicles may serve to deliver transmitters and/or neuropeptide modulators to appropriate receptors in a wider area than release into a specialized synaptic cleft would allow.

Effect of serotonin and acetylcholine on electrical activity of the isolated rabbit cortex

Neuronal isolation of the rabbit cerebral hemisphere shifts the EEG spectrum in the direction of slower processes. Application of acetylcholine to the cortex brings about EEG activation and appearance of the theta rhythm. Initially serotonin application is accompanied by the appearance of theta rhythm periods; during subsequent administration of the drug these periods are gradually substituted by slow delta waves. Combined application of serotonin and acetylcholine to the isolated cortex brings about bursts of high amplitude activity, abruptly substituted by "silent" phases. In contrast to the intact cortex, where serotonin brought about prolonged and rhythmic alternation on the EEG of phases of high amplitude activity and of silent periods, in the isolated cortex the bursts of activity of about 1 min duration appeared only after application of acetylcholine to the serotonin-saturated cortex. Repeated phases of activation were either absent or of short duration and were rapidly extinguished.

Cholinergic innervation of the cat striate cortex: a choline acetyltransferase immunocytochemical analysis

In area 17 of adult cats the morphology, distribution, and synaptology of cholinergic elements were examined by immunocytochemical methods with a monoclonal antibody against choline acetyltransferase (ChAT). ChAT(+) fibers are present throughout the entire depth of the cortex but are particularly dense in layer I. Typically these fibers are very thin and possess numerous irregularly spaced varicosities. Except in layer I and deep layer VI, where the fibers tend to run parallel to the pial surface, they appear to be randomly oriented. At the electron microscope level, immunolabeling was present in unmyelinated fibers of irregular contour and diameter. Most of the ChAT(+) varicose profiles contained mitochondria and round vesicles. Synaptic complexes were relatively infrequent and tended to be of the symmetrical type. They were located mostly on dendritic shafts and only rarely on cell bodies and dendritic spines. Both pyramidal and nonpyramidal cells were found to be innervated by cholinergic afferents. These anatomical data are consistent with the known physiology of acetylcholine in the visual cortex, which indicates that it acts as a modulator of cortical excitability.

Morphological identification of serotonin-accumulating neurons in the living retina

Neurons that accumulate the transmitter serotonin have been identified in the living retina by being labeled with 5,7-dihydroxytryptamine (5,7-HT), an autofluorescent serotonin analog. Iontophoretic injection of Lucifer yellow into the labeled cells under microscopic control revealed that the serotonin-accumulating neurons in rabbit retina constitute two morphological types of amacrine cells, termed S1 and S2, whose distal dendrites are stratified at the inner margin of the inner plexiform layer. The dendritic overlap of the S1 type is extraordinarily large: each point on the retina is covered by the fields of 550 to 900 S1 amacrines, and 6 to 8 meters of their dendrites are packed into each square millimeter of retina. Such a pervasive neuropil may provide an effective substrate for diffuse transmitter release, as proposed for serotonergic fibers elsewhere in the central nervous system.

Cellular localization of adrenergic receptors in rat and human brain

The localization of adrenergic receptors in the central nervous system was studied in two physiological conditions of noradrenergic denervation, a 6-hydroxydopamine-induced lesion of the locus coeruleus in newborn rat, and a pathological related degeneration of the locus coeruleus in man, Parkinson's disease. The localization of these receptors in the synapse has been studied with the technique of subcellular fractionation by differential centrifugation. In lesioned rats, an increase in the density of alpha 1 and beta 1 receptors was observed in several brain regions, in contrast to alpha 2 receptors which were not modified. Subcellular fractionation in lesioned rats showed an increase in alpha 1 and beta 1 receptors in synaptosomal fractions. Similar results were found in parkinsonian patients: alpha 1 receptors increased in the synaptosomal fraction; beta receptors increased in synaptosomal and microsomal fractions. These results suggest that alpha 1 and beta 1 receptors may be located on non-noradrenergic nerve terminals in mammalian brain. alpha 2 and beta 2 receptors may be situated on glial cells or neuronal elements unrelated to noradrenergic input.

Immunocytochemical localization of serotonin in the rat dentate gyrus following raphe transplants

The ultrastructural features of the serotoninergic innervation of the rat dentate gyrus in normal adults and in animals receiving raphe nuclear area transplants was investigated using an antibody to serotonin (5-HT). Neonatal rats received a lesion of the fimbria-fornix and entorhinal cortex. Three days later, a portion of embryonic (E-16-18) raphe nuclear area was transplanted to the entorhinal cavity and the animals were allowed to survive for 60 days. Animals were processed for the immunocytochemical localization of 5-HT using the peroxidase-antiperoxidase method. Light microscopic observation showed that 5-HT-containing fibers from transplanted raphe neurons densely innervated the hilar and molecular zones of the dentate gyrus. Electron microscopic analysis showed that 5-HT immunoreactivity was contained only in axons and axon varicosities. There were no differences in the ultrastructural characteristics of axons and axon terminals between normal animals and those which had received raphe transplants. A mixture of both conventional synaptic junctions and non-synaptic axonal swellings were found in both groups.

Autoradiographic comparison of the distribution of the neutral endopeptidase "enkephalinase" and of mu and delta opioid receptors in rat brain

The neutral endopeptidase EC 3.4.24.11, also designated enkephalinase, has been visualized by in vitro autoradiography using the tritiated inhibitor [3H]-N-[(2RS)-3-hydroxyaminocarbonyl-2-benzyl-1-oxopropyl] glycine, ([3H]HACBO-Gly). Specific binding of [3H]HACBO-Gly (Kd = 0.4 +/- 0.05 nM) corresponding to 85% of the total binding to brain slices was inhibited by 1 microM thiorphan, a selective inhibitor of enkephalinase, but remained unchanged in the presence of captopril, a selective inhibitor of angiotensin-converting enzyme. Very high levels of [3H]HACBO-Gly binding were found in the choroid plexus and the substantia nigra. High levels were present in the caudate putamen, globus pallidus, nucleus accumbens, olfactory tubercle, and in the substantia gelatinosa of the spinal cord. Moderate densities were found in parts of the amygdala, the periaqueductal gray matter, the interpeduncular nucleus, and the molecular layer of the cerebellum. The distribution of enkephalinase was compared to that of mu and delta opioid receptors, selectively labeled with [3H]Tyr-D-Ala-Gly-MePhe-glycinol and [3H]Tyr-D-Thr-Gly-Phe-Leu-Thr, respectively. In the caudate putamen, [3H]HACBO-Gly binding overlapped the clustered mu sites but appeared more closely related to the diffusely distributed delta sites. High levels of enkephalinase and mu opioid binding sites were present at the level of the periaqueductal gray matter and in the substantia gelatinosa of the spinal cord, regions where only sparse delta opioid receptors could be detected. The association of enkephalinase with delta and mu opioid receptors in these areas is consistent with the observed role of the enzyme in regulating the effects of opioid peptides in striatal dopamine release and analgesia, respectively. Except for the choroid plexus and the cerebellum, the close similarity observed in numerous rat brain areas between the distribution of enkephalinase and that of mu and/or delta opioid binding sites could account for most of the pharmacological effects elicited by enkephalinase inhibitors.

Ultrastructural demonstration of nonsynaptic release sites in the central nervous system of the snail Lymnaea stagnalis, the insect Periplaneta americana, and the rat

Release of neuronal secretory products by exocytosis was studied ultrastructurally in the central nervous systems of three different species (the snail Lymnaea stagnalis, the cockroach Periplaneta americana and the rat). Tissues were fixed with: (1) a mixture of glutaraldehyde and osmium tetroxide, (2) the tannic acid-glutaraldehyde-osmium tetroxide (TAGO) method, and (3) the tannic acid-Ringer incubation (TARI) method. Especially after TARI-treatment, release of the contents of the secretory vesicles by exocytosis could be clearly demonstrated in: (1) synapses, (2) neurohaemal axon terminals (L. stagnalis), and (3) neuronal processes without morphological synaptic specializations (nonsynaptic release sites). Release from nonsynaptic release sites occurs in most cases over a large area of the plasma membrane of a neuronal process facing several neural elements. On the basis of the differences in morphology of the secretory vesicles at nonsynaptic release sites, it is proposed that various types of (peptidic) messenger are released from such sites. In some neurones of L. stagnalis nonsynaptic release sites have been found together with synapses, or with neurohaemal axon terminals (caudodorsal cells, light green cells and light yellow cells). The possibility that nonsynaptic release sites represent the morphological correlates of nonsynaptic communication in the central nervous system has been discussed.