Somatostatin-14-like immunoreactive neurons and fibres in the human olfactory bulb

Summary This study describes the morphological features and the distribution pattern of neurons in the human olfactory bulb which are immunoreactive for an antiserum against the neuropeptide somatostatin-14.Immunoreactive nerve cell bodies were mainly found in the white matter surrounding the cell clusters of the anterior olfactory nucleus. Some immunoreactive neurons were also found scattered throughout the anterior olfactory nucleus and the deeper parts of the inner granule cell layer. Only a few immunoreactive neurons were localized in the glomerular layer and the outer granule cell layer.Immunoreactive fibres were found in all layers of the olfactory bulb. In addition, an impressive number of coiled and kinked immunoreactive fibres were localized within the anterior olfactory nucleus forming a dense plexus. Accumulations of twisted and coiled branches of immunoreactive fibres were rarely found either surrounding or within the olfactory glomerula.The characteristics of somatostatin-14 immunoreactive neurons as seen in the combined pigment-Nissl preparation were studied after decolourizing the chromogen and restaining the preparations with aldehydefuchsin in order to demonstrate the lipofuscin pigment and gallocyanin chrome alum for Nissl material. About 90% of the immunoreactive neurons studied in this manner turned out to be devoid of lipofuscin granules. The remaining 10% displayed different patterns of pigmentation.These findings suggest the presence of different types of somatostatin-14-like immunoreactive neurons in the olfactory bulb of the human adult.     

Localization of C-PON immunoreactivity in the rat main olfactory bulb. Demonstration that the population of neurons containing endogenous C-PON display NADPH-diaphorase activity

The presence of the neuropeptide C-terminal flanking peptide of neuropeptide-Y, C-PON, has been investigated in the main olfactory bulb of the rat using conventional fluorescence and peroxidase-antiperoxidase immunocytochemical techniques. The distribution of immunoreactive structures to C-PON was examined in both horizontal and coronal sections. Endogenous C-PON was localized within two types of short-axon cells including (1) superficial short-axon cells in the glomerular layer and (2) deep short-axon cells lying in the deepest portion of the granule cell layer and in the adjacent white matter. In addition, varicose immunoreactive processes were detected in all layers, although they were more numerous in the deepest portion of the granule cell layer. Immunoreactive cell bodies and processes were also observed in the nucleus olfactorius anterior and in the intrabulbar portion of the anterior commissure. Nevertheless, immunoreactive structures were not localized in the lateral olfactory tract. The indirect immunofluorescence technique to detect endogenous C-PON in combination with the enzyme histochemical demonstration of NADPH-diaphorase activity, in single sections, showed that the NADPH-diaphorase procedure is a reliable marker for these C-PON positive cells. Also, indirectly, that, in the rat main olfactory bulb, C-PON and neuropeptide-Y are contained in the same cell types. Many glomeruli were stained following the NADPH-diaphorase procedure, but they were not C-PON immunoreactives. Results of this study provide evidence suggesting that C-PON may influence polysynaptically the function of mitral cells and, therefore, the olfactory bulb output.     

Central connections of the olfactory bulb in the american opossum (didelphys virginiana): A light microscopic degeneration study

Destructive lesions were made in the right olfactory bulb of 16 adult opossums. Following postoperative survival periods of 4 to 31 days, the animals were sacrificed and perfused with 10% Formalin. Frozen sections of the brain were cut in either the coronal, horizontal, or sagittal plane and processed by the Fink-Heimer II method. Degenerating axons of olfactory bulb neurons were traced caudally in the ipsilateral lateral olfactory tract (LOT). Small lesions revealed a topographic representation of the olfactory bulb within the LOT. The dorsal, lateral, and ventral parts of the bulb were, respectively, represented in the dorsal, intermediate, and ventral parts of the LOT. Terminal degeneration was observed in the superficial half of the molecular layer ipsilaterally in the following structures: anterior olfactory nucleus, anterior hippocampal rudiment, olfactory tubercle, piriform cortex, ventrolateral frontal neocortex, lateral entorhinal cortex, nucleus of the LOT, and the lateral aspect of the cortical amygdaloid nucleus. No degeneration was observed in the anterior limb of the anterior commissure. Dorsal and lateral parts of the olfactory bulb projected to the anterolateral aspect of the olfactory tubercle, whereas the ventral part projected heavily to the entire tubercle. There was no evidence of topographic projections to other olfactory structures. The observations of the present investigation indicated that the olfactory bulb projections in the opossum, a primitive mammal, are essentially comparable with those of placental mammals.     

Neuropeptide Y in the olfactory system, forebrain and pituitary of the teleost, Clarias batrachus

Distribution of neuropeptide Y (NPY)-like immunoreactivity in the forebrain of catfish Clarias batrachus was examined with immunocytochemistry. Conspicuous immunoreactivity was seen in the olfactory receptor neurons (ORNs), their projections in the olfactory nerve, fascicles of the olfactory nerve layer in the periphery of bulb and in the medial olfactory tracts as they extend to the telencephalic lobes. Ablation of the olfactory organ resulted in loss of immunoreactivity in the olfactory nerve layer of the bulb and also in the fascicles of the medial olfactory tracts. This evidence suggests that NPY may serve as a neurotransmitter in the ORNs and convey chemosensory information to the olfactory bulb, and also to the telencephalon over the extrabulbar projections. In addition, network of beaded immunoreactive fibers was noticed throughout the olfactory bulb, which did not respond to ablation experiment. These fibers may represent centrifugal innervation of the bulb. Strong immunoreactivity was encountered in some ganglion cells of nervus terminalis. Immunoreactive fibers and terminal fields were widely distributed in the telencephalon. Several neurons of nucleus entopeduncularis were moderately immunoreactive; and a small population of neurons in nucleus preopticus periventricularis was also labeled. Immunoreactive terminal fields were particularly conspicuous in the preoptic, the tuberal areas, and the periventricular zone around the third ventricle and inferior lobes. NPY immunoreactive cells and fibers were detected in all the lobes of the pituitary gland. Present results describing the localization of NPY in the forebrain of C. batrachus are in concurrence with the pattern of the immunoreactivity encountered in other teleosts. However, NPY in olfactory system of C. batrachus is a novel feature that suggests a role for the peptide in processing of chemosensory information.     

Zincergic innervation from the anterior olfactory nucleus to the olfactory bulb displays plastic responses after mitral cell loss

Zinc ions are selectively accumulated in certain neurons (zinc-enriched neurons). The mouse olfactory bulb is richly innervated by zinc-enriched terminals. Here, the plasticity of the zincergic system was studied in the olfactory bulb of the Purkinje Cell Degeneration mutant mouse, an animal with specific postnatal neurodegeneration of the main projection neurons of the olfactory bulb. The analysis focused particularly on the anterior olfactory nucleus since most centrifugal afferents coming to the olfactory bulb arise from this structure. Zinc-enriched terminals in the olfactory bulb and zinc-enriched somata in the anterior olfactory nucleus were visualized after selenite injections. Immunohistochemistry against the vesicular zinc transporter was also carried out to confirm the distribution pattern of zinc-enriched terminals in the olfactory bulb. The mutant mice showed a clear reorganization of zincergic centrifugal projections from the anterior olfactory nucleus to the olfactory bulb. First, all zincergic contralateral neurons projecting to the olfactory bulb were absent in the mutant mice. Second, a significant increase in the number of stained somata was detected in the ipsilateral anterior olfactory nucleus. Since no noticeable changes were observed in the zinc-enriched terminals in the olfactory bulb, it is conceivable that mitral cell loss could induce a reorganization of zinc-enriched projections coming from the anterior olfactory nucleus, probably directed at balancing the global zincergic centrifugal modulation. These results show that zincergic anterior olfactory nucleus cells projecting to the olfactory bulb undergo plastic changes to adapt to the loss of mitral cells in the olfactory bulb of Purkinje Cell Degeneration mutant mice.     

Zincergic innervation from the anterior olfactory nucleus to the olfactory bulb displays plastic responses after mitral cell loss

Zinc ions are selectively accumulated in certain neurons (zinc-enriched neurons). The mouse olfactory bulb is richly innervated by zinc-enriched terminals. Here, the plasticity of the zincergic system was studied in the olfactory bulb of the Purkinje Cell Degeneration mutant mouse, an animal with specific postnatal neurodegeneration of the main projection neurons of the olfactory bulb. The analysis focused particularly on the anterior olfactory nucleus since most centrifugal afferents coming to the olfactory bulb arise from this structure. Zinc-enriched terminals in the olfactory bulb and zinc-enriched somata in the anterior olfactory nucleus were visualized after selenite injections. Immunohistochemistry against the vesicular zinc transporter was also carried out to confirm the distribution pattern of zinc-enriched terminals in the olfactory bulb. The mutant mice showed a clear reorganization of zincergic centrifugal projections from the anterior olfactory nucleus to the olfactory bulb. First, all zincergic contralateral neurons projecting to the olfactory bulb were absent in the mutant mice. Second, a significant increase in the number of stained somata was detected in the ipsilateral anterior olfactory nucleus. Since no noticeable changes were observed in the zinc-enriched terminals in the olfactory bulb, it is conceivable that mitral cell loss could induce a reorganization of zinc-enriched projections coming from the anterior olfactory nucleus, probably directed at balancing the global zincergic centrifugal modulation. These results show that zincergic anterior olfactory nucleus cells projecting to the olfactory bulb undergo plastic changes to adapt to the loss of mitral cells in the olfactory bulb of Purkinje Cell Degeneration mutant mice.     

Distribution of nerve growth factor receptor-like immunoreactivity in the adult rat central nervous system. Effect of colchicine and correlation with the cholinergic system--I. Forebrain

Nerve growth factor receptor, as recognized by the monoclonal antibody 192-IgG, was localized to multiple regions of the adult rat forebrain. Immunoreactive cell bodies and fibers were seen in both sensory and motor regions which are known to contain cholinergic and non-cholinergic neurons. Specifically, nerve growth factor receptor immunoreactivity was present in cells lining the olfactory ventricle, rostral portion of the lateral ventricle, in basal forebrain nuclei, caudate putamen, globus pallidus, zona incerta and hypothalamus. Immunoreactive cells which were situated subpially along the olfactory ventricle and anterior portions of the lateral ventricle, and in the arcuate nucleus resembled neuroglia but could not definitively identified at the light microscopic level. Animals pretreated with intracerebroventricular colchicine displayed significantly increased nerve growth factor receptor immunoreactivity in all previously positive neurons and particularly in the medial preoptic area and ventral premammillary nucleus of the hypothalamus. In such animals, receptor immunoreactivity also appeared in previously non-immunoreactive cells of the hippocampal CA3 region and polymorph layer of the dentate gyrus as well as in the mitral cell layer of the olfactory bulb. Nerve growth factor receptor-immunoreactive fibers and varicosities were seen in the olfactory bulb, piriform cortex, neocortex, amygdala, hippocampus, thalamus, olivary pretectal nucleus and hypothalamus. In most regions, such fiber-like immunoreactive structures likely represented axon terminals, although in some areas, neuroglial or extracellular localizations could not be excluded. In this context, diffuse, non-fibrillar receptor immunoreactivity occurred in the lateral habenular nucleus and medial terminal nucleus of the accessory optic tract. Furthermore, intense nerve growth factor receptor immunoreactivity occurred along certain regions of the pial surface on the ventral surface of the brain. The distribution of nerve growth factor receptor-immunoreactive cell bodies and fibers in multiple sensory and motor nuclei suggests wide-spread influences of nerve growth factor throughout the adult rat forebrain. There is a high degree of overlap with regions containing choline acetyltransferase immunoreactivity. However, significant disparities exist suggesting that certain nerve growth factor receptor-containing non-cholinergic neurons of the rat forebrain may also be affected by nerve growth factor.     

Central olfactory connections in the microsmatic marmoset monkey (Callithrix jacchus)

The mammalian primary olfactory system consists of a set of different telencephalic structures, including paleo-, archi-, periarchi- and mesocortical components. We present the first characterisation of the normal and connectional anatomy of the primary olfactory cortex of the common marmoset, a microsmatic simian species increasingly used in primate research. The centrifugal and centripetal bulbar projections were determined by injections of the anterograde and retrograde tracer wheat germ agglutinin-conjugated horseradish peroxidase and fluorescent dyes into the ipsilateral main olfactory bulb. The efferent projections of the marmoset bulb are organised entirely ipsilaterally and are established via a rudimentary medial olfactory tract and the dominant lateral olfactory tract. Target areas are the anterior olfactory nucleus, the entire prepiriform cortex, ventral tenia tecta, periamygdaloid cortex and the rostral part of the entorhinal cortex. The bulbar axons predominantly terminate in the outer part of layer I. The anterior olfactory nucleus receives a weak additional input within layer II and III, which is not found in macrosmatic rodents. Further anterograde labelling was found in the endopiriform nucleus deep under the prepiriform cortex and within an anterolateral strip of the olfactory tubercle. However, control injections into the olfactory tubercle suggest that the marmoset olfactory tubercle receives a bisynaptic olfactory input only. Retrograde labelling after bulb injections revealed that, except for the olfactory tubercle, all primary olfactory cortices contributed to an ipsilateral bulbopetal feedback projection. Like in rodents, the only bulbopetal projection organised bilaterally in the marmoset is maintained by the anterior olfactory nucleus. With few exceptions, the projections of the marmoset olfactory brain are organised similarly to that of the macaque monkey or those of macrosmatic species.     

Tyrosine hydroxylase immunoreactive structures in the aged human olfactory bulb and olfactory peduncle

We studied the anatomical distribution of dopaminergic structures in the normal, aged, human olfactory bulb and olfactory peduncle with a monoclonal antibody against tyrosine hydroxylase. Three different tyrosine hydroxylase containing cell groups are present in the olfactory bulbs: (1) a group of round, medium-sized cells within and around the glomeruli; (2) cells in the external plexiform layer; and (3) cells that are scattered in the stratum album. Occasionally, a few labeled neurons can be observed in the granule cell layer. In the olfactory peduncle a few labeled cells are present in the superficial layers just underneath the pia. Tyrosine hydroxylase containing terminal-like structures are present in the glomerular layer and the external plexiform layer. In a few cases dense terminal labeling is also observed in the cell groups that constitute the anterior olfactory nucleus. In the olfactory peduncle scattered labeled fibers are present. In addition, the present study makes clear that quantitative differences exist between the individual cases for which no explanation could be found.     

Ontogenesis of the axonal circuitry associated with the olfactory system of the rat embryo.

The prenatal development of axonal connections in the rat olfactory system was studied using DiI. On day 16 (E16), the olfactory and vomeronasal nerves extended from the olfactory epithelia to the olfactory bulb (OB), the terminal nerve to the telencephalic septum, while axons of mitral and tufted cells reached the anterior olfactory nucleus (AO). Axons from the AO were also seen in the anterior commissure. On day E16(8) (at 16 days, 8 h), axons were anterogradely followed from the dorsal OB through the lateral olfactory tract (lo) to the bed nucleus of the accessory olfactory tract. At E18(0), crystals implanted in the olfactory epithelium labeled the mitral cell layer and the lo.     

The bilateral bulbar projections of the primary olfactory neurons in the frog

Summary Whether or not the frog olfactory neuroreceptor cells project bilaterally to the olfactory bulb is still a debated question. We therefore decided to ascertain whether bilateral projections of the primary olfactory input exist and if so to investigate their extent. Reproducible extracellular bilateral bulbar potentials were recorded in the frog following electrical stimulation of dorsal or ventral olfactory nerve bundles. The general features of the contralateral evoked responses were very similar to those of the ipsilateral response. The contralateral response disappeared after transection of the rostral part of the olfactory interbulbar adhesion but not following transection of the habenular or anterior commissures. Horseradish peroxidase labelling showed that the fiber terminations of the olfactory nerve bundle was not restricted to the ipsilateral olfactory bulb but included the medial aspects of the contralateral bulb. The intertelencephalic sections increased the magnitude of the ipsilateral evoked responses. Olfactory bulb isopotential maps revealed a rough topographical correspondence between the olfactory neuroepithelium and bulb along the medio-lateral axis as well as along the dorso-ventral axis. In addition, a projection of the medial and central part of the olfactory sac to the medial part of the contralateral olfactory bulb through the interbulbar adhesion was confirmed. These findings suggest first, that the fibers from the neuro-receptors located in either the ventral or the dorsal olfactory mucosae project to both olfactory bulbs, and second, that the left and right bulbs exert a constant inhibition on each other via the habenular commissure.Abbreviations AON anterior olfactory nucleus - ax olfactory neuroreceptor axon - BA bulbar adhesion - D_I latero-dorsal olfactory nerve bundle - D_II centro-dorsal olfactory nerve bundle - D_III mediodorsal olfactory nerve bundle - EPL external plexiform layer - GL glomerular layer - gl glomerulus - GRL granular cell layer - MOB main olfactory bulb - m mitral cell - MBL mitral cell body layer - ON olfactory nerve - V lateral ventricule - V_I latero-ventral ol-factory nerve bundle - V_II centro-ventral olfactory nerve bundle - V_III medio-ventral olfactory nerve bundle - VN vomero-nasal nerve     

Trajectory and terminal distribution of single centrifugal axons from olfactory cortical areas in the rat olfactory bulb

The olfactory bulb receives a large number of centrifugal fibers whose functions remain unclear. To gain insight into the function of the bulbar centrifugal system, the morphology of individual centrifugal axons from olfactory cortical areas was examined in detail. An anterograde tracer, Phaseolus vulgaris leucoagglutinin, was injected into rat olfactory cortical areas, including the pars lateralis of the anterior olfactory nucleus (lAON) and the anterior part of the piriform cortex (aPC). Reconstruction from serial sections revealed that the extrabulbar segments of centrifugal axons from the lAON and those from the aPC had distinct trajectories: the former tended to innervate the pars externa of the AON before entering the olfactory bulb, while the latter had extrabulbar collaterals that extended to a variety of targets. In contrast to the extrabulbar segments, no clear differences were found between the intrabulbar segments of axons from the lAON and from the aPC. The intrabulbar segments of centrifugal axons were mainly found in the granule cell layer but a few axons extended into the external plexiform and glomerular layer. Approximately 40% of centrifugal axons innervated both the medial and lateral aspects of the olfactory bulb. The number of boutons found on single intrabulbar segments was typically less than 1000. Boutons tended to aggregate and form complex terminal tufts with short axonal branches. Terminal tufts, no more than 10 in single axons from ipsilateral cortical areas, were localized to the granule cell layer with varying intervals; some tufts formed patchy clusters and others were scattered over areas that extended for a few millimeters. The patchy, widespread distribution of terminals suggests that the centrifugal axons are able to couple the activity of specific subsets of bulbar neurons even when the subsets are spatially separated.     

Immunocytochemical demonstration of the presence of catecholamine and serotonin neurons in the sheep olfactory bulb

The catecholamine and serotonin innervation of the sheep olfactory bulb was studied using immunocytochemistry. Specific antisera raised against tyrosine hydroxylase, dopamine beta-hydroxylase, phenylethanolamineN-methyl transferase and serotonin were used. Tyrosine hydroxylase-positive cell bodies were present in all cell layers except in the anterior olfactory nucleus, the greatest number being found in the glomerular layer. Neither dopamine β -hydroxylase-positive nor serotonin-positive cell bodies were observed. Dopamine β-hydroxylase-positive fibers were widely distributed in the granule cell layer but less widely in other layers. The glomerular layer contained the greatest distribution of serotonergic positive fibers, but such fibres were also visualized in other cell layers. No phenylethanolamineN-methyl transferase-positive structures were found in this investigation.     

Tyrosine hydroxylase-like immunoreactive neurons in the olfactory bulb of the snake,Elaphe quadrivirgata,with special reference to the colocalization of tyrosine hydroxylase- and GABA-like immunoreactivities

Summary The distribution and structural features of tyrosine hydroxylase-like immunoreactive (TH-LI) neurons were studied in the olfactory bulb of a snake, Elaphe quadrivirgata, by using pre-and post-embedding immunocytochemistry at the light microscopic level. In contrast to rodent olfactory bulbs previously reported, many TH-LI neurons were seen not only in the main olfactory bulb (MOB) but also in the accessory olfactory bulb (AOB). With regard to the TH-like immunoreactivity, there appeared no appreciable differences between MOB and AOB. As in mammalian MOB, the majority of TH-LI neurons were clustered in the periglomerular region and appeared to send their dendritic branches into glomeruli, which as a whole make an intense TH-LI band in the glomerular layer (GML). In the external plexiform/mitral cell layer (EPL/ML) of MOB and AOB as well as in the outer sublamina of the internal plexiform layer (OSL) of AOB, an appreciable number of TH-LI neurons were scattered, extending dendritic processes which appeared to make a loose meshwork. TH-LI neurons in EPL/ML (including OSL) appeared to consist of at least two morphologically different types. The first had a small perikaryon and one or two smooth dendrites which usually extended to GML and were frequently confirmed to enter into glomeruli. The second had a larger perikaryon and 2–3 dendrites which branched into several varicose processes extending in EPL/ML/OSL but appeared not to enter into glomeruli. The TH-like immunoreactivity was rarely seen in the internal plexiform layer and internal granule cell layer. The colocalization of GABA-like and TH-like immunoreactivities was further studied. Almost all TH-LI neurons in both EPL/ ML/OSL and GML contained GABA-like immunoreactivity irrespectively of the type of TH-LI cells.Abbreviations in Figures AOB accessory olfactory bulb - MOB main olfactory bulb - Hem hemisphere - ON olfactory nerve layer - VN vomeronasal nerve layer - GM glomerular layer - EP/M external plexiform layer/Mitral cell layer - IP internal plexiform layer - IG internal granular layer - OS outer sublamina of the IPL of AOB - MS middle sublamina of the IPL of AOB - IS inner sublamina of the IPL of AOB     

Neuronal nitric oxide synthase in the olfactory system,forebrain, pituitary and retina of the adult teleost Clarias batrachus

Immunocytochemical application of antibodies against nNOS to the brain sections of Clarias batrachus revealed intense immunoreactivity in several olfactory receptor neurons (ORNs), in their axons over the olfactory nerve, and terminals in the olfactory glomeruli. Several basal cells in the olfactory epithelium showed NOS immunoreactivity. Application of post-embedding immunoelectron microscopy showed nNOS labeled gold particles in apical cilia, dendrites and soma of the ORNs and also in the axon terminals in the glomeruli of the olfactory bulb. nNOS containing fibers were also encountered in the medial olfactory tracts (MOTs). Bilateral ablation of the olfactory organ resulted in total loss of nNOS immunoreactivity in the fascicles of the olfactory nerve layer and also in the MOT. nNOS immunoreactivity was seen in several cells of the nucleus preopticus (NPO) and their axons that innervate the pituitary gland. Some cells in the floor of the tuberal area were stained positive with nNOS antibodies. nNOS immunolabeled cells were seen in all the three components of the pituitary gland with light as well as post-embedding immunoelectron microscopy. While several nNOS immunoreactive fibers were seen in rostral pars distalis, a much limited fiber population was seen in the proximal pars distalis. In addition, conspicuous immunoreactivity was noticed in some ganglion cells in the retina and in some fibers of the optic nerve traceable to the optic tectum. The NO containing system in this fish appears to be similar to that in other fishes.     

Small cholinergic neurons within fields of cholinergic axons characterize olfactory-related regions of rat telencephalon.

Small immunoreactive cholinergic neurons were detected in the main and accessory olfactory bulbs of the rat with choline acetyltransferase immunocytochemistry. Such cells were also found in additional forebrain regions that received direct efferent innervation from the main olfactory bulb, such as the anterior olfactory nucleus, two subdivisions of the olfactory amygdala (nucleus of the lateral olfactory tract and anterior cortical nucleus), and the cortical-amygdaloid transition zone. Cholinergic neurons located in these olfactory-related regions were similar to each other morphologically and to those previously described by other investigators in the cerebral cortex, the hippocampus, and the basolateral amygdala. Somal measurements indicated that choline acetyltransferase-positive cells in olfactory-related regions were all essentially the same size, measuring 13-14 by 8-9 microns in major and minor diameters, respectively. In addition, these small cells were commonly bipolar in form with thin, smooth dendrites, and such characteristics have generally been associated with intrinsic, local circuit neurons in the forebrain. Depending on their location, however, these small cholinergic neurons differed from each other with regard to their frequency and dendritic orientation within planar sections. Choline acetyltransferase-immunoreactive cells in most cortical regions were relatively numerous and usually exhibited long, planar dendrites oriented perpendicularly to the pial surface. In contrast, dendrites of cholinergic neurons found in "cortical-like" regions (e.g. olfactory bulbs or nucleus of the lateral olfactory tract) were relatively sparse in number and appeared to be distinctly non-planar and randomly oriented. Despite these differences, the small choline acetyltransferase-positive cells had many features in common, including their distribution within forebrain regions that contained substantial terminal networks of choline acetyltransferase-positive axons thought to be derived primarily from the basal forebrain complex. In the rat, at least, the presence of small cholinergic interneurons within forebrain regions innervated by the large cholinergic projection neurons of the basal forebrain seems to be developing as a general principle of telencephalic organization. However, differences in both the size and the distribution of the terminal fields derived from each source imply a functional diversity between the intrinsic and extrinsic cholinergic systems of the forebrain.     

Spreading depression in the olfactory bulb of rats: reliable initiation and boundaries of propagation

Spreading depression in the olfactory bulb of rats is an elusive phenomenon, the demonstration of which requires specific conditioning procedures. The present paper describes a simple technique for reliable initiation of bulbar spreading depression with microinjections of potassium acetate. Adult hooded rats were anesthetized with pentobarbital (50 mg/kg) and slow potential changes accompanying spreading depression were recorded with capillary microelectrodes stereotaxically inserted into the olfactory bulb and adjacent forebrain structures. KCl microinjection (0.5-1.0 microliter, 0.134-0.670 mol/l) into the olfactory bulb elicited local depolarization which only exceptionally developed into a propagating spreading depression. Potassium acetate (0.5-1.0 microliter, 0.15 mol/l) injected into the rostral olfactory bulb evoked a negative slow potential wave (amplitude of around 25 mV and duration 30-50 s) propagating at a rate of 3-4 mm/min through all the olfactory bulb layers. Low positive (5 mV) instead of negative waves were recorded in the superficial olfactory nerve layer with reversal in the glomerular layer (200-300 micron). The slow potential decreased in the rostrocaudal direction and expired at the caudal boundary of the olfactory bulb. Bulbar spreading depression never spread to neocortex, and cortical spreading depression never entered into the olfactory bulb but stopped in the anterior olfactory nucleus 7 mm rostral to bregma. Repeated potassium acetate injections into the olfactory bulb occasionally elicited a series of spreading depression waves recurring at regular intervals, probably reflecting reverberation of scroll-shaped waves around the rostrocaudal axis of the olfactory bulb.(ABSTRACT TRUNCATED AT 250 WORDS)     

Distribution of neuropeptide Y-like immunoreactivity in the rat central nervous system--II. Immunohistochemical analysis

The distribution of neuropeptide Y-like immunoreactivity in the rat brain and spinal cord was investigated by means of the peroxidase-antiperoxidase procedure of Sternberger using a rabbit anti-neuropeptide Y serum. A widespread distribution of immunostained cells and fibres was detected with moderate to large numbers of cells in the following regions: olfactory bulb, anterior olfactory nucleus, olfactory tubercle, striatum, nucleus accumbens, all parts of the neocortex and the corpus callosum, septum including the anterior hippocampal rudiment, ventral pallidum, horizontal limb of the diagonal band, amygdaloid complex. Ammon's horn, dentate gyrus, subiculum, pre- and parasubiculum, lateral thalamic nucleus (intergeniculate leaflet), bed nucleus of the stria terminalis, medial preoptic area, lateral hypothalamus, mediobasal hypothalamus, supramammillary nucleus, pericentral and external nuclei of the inferior colliculus, interpeduncular nucleus, periaqueductal central gray, locus coeruleus, dorsal tegmental nucleus of Gudden, lateral superior olive, lateral reticular nucleus, medial longitudinal fasciculus, prepositus hypoglossal nucleus, nucleus of the solitary tract and spinal nucleus of the trigeminal nerve. In the spinal cord cells were found in the substantia gelatinosa at all levels, the dorsolateral funiculus and dorsal gray commissure in lumbosacral cord. The pattern of staining was found to be similar to that observed with antisera to avian and bovine pancreatic polypeptide, but to differ in some respects from that observed with antisera to molluscan cardioexcitatory peptide. The presence of neuropeptide Y immunoreactive fibres in tracts such as the corpus callosum, anterior commissure, lateral olfactory tract, fimbria, medial corticohypothalamic tract, medial forebrain bundle, stria terminalis, dorsal periventricular bundle and other periventricular areas, indicated that in addition to the localisation of neuropeptide Y-like peptide(s) in interneurons in the forebrain, neuropeptide Y may be found in long neuronal pathways throughout the brain.     

The distribution of taurine,cysteinyl sulphinilic acid decarboxylase and crysteinyl sulphinlic acid α-ketoglutarate transaminase in the rat olfactory bulb and olfactory nucleus

Taurine, a putative neurotransmitter, cysteinyl sulphinlic acid α-ketogluraric acid transaminase (CSA-T) and cysteinyl sulphinlic acid decarboxylase (CSA-D) were measured in the different structures of the rat olfactory bulb and olfactory nucleus. It appears there are significant differences between the level of taurine in internal layers (mitral cells, plexiform) and external layer such as fibrorum. The CSA-T and CSA-D activities followed approximately the distribution of taurine in the different areas of the rat olfactory bulb and nucleus.A very high activity of CSA-T was present in all areas studied and a role for the enzyme is proposed. The cellular distribution of CSA-T, CSA-D and taurine is compared with the distribution in retina.