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

Structure and chemical organization of the accessory olfactory bulb in the goat

The structure and chemical composition of the accessory olfactory bulb (AOB) were examined in male and female goats. Sections were subjected to either Nissl staining, Klüver-Barrera staining, lectin histochemistry, or immunohistochemistry for nitric oxide synthase (NOS), neuropeptide Y (NPY), tyrosine hydroxylase (TH), dopamine beta-hydroxylase (DBH), and glutamic acid decarboxylase (GAD). The goat AOB was divided into four layers: the vomeronasal nerve layer (VNL), glomerular layer (GL), mitral/tufted (M/T) cell layer (MTL), and granule cell layer (GRL). Quantitative and morphometric analyses indicated that a single AOB contained 5,000-8,000 putative M/T cells with no sex differences, whereas the AOB was slightly larger in males. Of the 21 lectins examined, 7 specifically bound to the VNL and GL, and 1 bound not only to the VNL, but also to the MTL and GRL. In either of these cases, no heterogeneity of lectin staining was observed in the rostrocaudal direction. NOS-, TH-, DBH-, and GAD-immunoreactivity (ir) were observed in the MTL and GRL, whereas NPY-ir was present only in the GRL. In the GL, periglomerular cells with GAD-ir were found in abundance, and a subset of periglomerular cells containing TH-ir was also found. Double-labeling immunohistochemistry revealed that virtually all periglomerular cells containing TH-ir were colocalized with GAD-ir.

A field guide to the anterior olfactory nucleus (cortex)

While portions of the mammalian olfactory system have been studied extensively, the anterior olfactory nucleus (AON) has been relatively ignored. Furthermore, the existing research is dispersed and obscured by many different nomenclatures and approaches. The present review collects and assembles the relatively sparse literature regarding the portion of the brain situated between the olfactory bulb and primary olfactory (piriform) cortex. Included is an overview of the area's organization, the functional, morphological and neurochemical characteristics of its cells and a comprehensive appraisal of its efferent and afferent fiber systems. Available evidence suggests the existence of subdivisions within the AON and demonstrates that the structure influences ongoing activity in many other olfactory areas. We conclude with a discussion of the AON's mysterious but complex role in olfactory information processing.

Catecholaminergic projections onto spinal neurons destined to the pelvis including the penis in rat

In rats, the spinal cord contains proerectile autonomic motoneurons destined to the penile tissue and its vasculature, and somatic motoneurons destined to the perineal striated muscles. It receives dense catecholaminergic projections issued from the medulla and pons. In adult male rats, we evidenced the catecholaminergic innervation of spinal neurons controlling lower urogenital tissues and regulating penile erection. We combined retrograde tracing techniques and immunohistochemistry against synthetic enzymes of noradrenaline and adrenaline. Both sympathetic and parasympathetic preganglionic neurons, labeled from the major pelvic ganglion or from the corpus cavernosum, were apposed by catecholaminergic immunoreactive fibers. Motoneurons, retrogradely labeled from the striated muscles, were also apposed by catecholaminergic immunoreactive fibers. Synapses between these motoneurons and fibers were suggested by confocal microscopy and confirmed by electron microscopy in some cases. The results reinforce the hypothesis of a catecholaminergic control of autonomic and somatic motoneurons regulating penile erection at the spinal level.

Catecholamine systems in the brain of vertebrates: new perspectives through a comparative approach

A comparative analysis of catecholaminergic systems in the brain and spinal cord of vertebrates forces to reconsider several aspects of the organization of catecholamine systems. Evidence has been provided for the existence of extensive, putatively catecholaminergic cell groups in the spinal cord, the pretectum, the habenular region, and cortical and subcortical telencephalic areas. Moreover, putatively dopamine- and noradrenaline-accumulating cells have been demonstrated in the hypothalamic periventricular organ of almost every non-mammalian vertebrate studied. In contrast with the classical idea that the evolution of catecholamine systems is marked by an increase in complexity going from anamniotes to amniotes, it is now evident that the brains of anamniotes contain catecholaminergic cell groups, of which the counterparts in amniotes have lost the capacity to produce catecholamines. Moreover, a segmental approach in studying the organization of catecholaminergic systems is advocated. Such an approach has recently led to the conclusion that the chemoarchitecture and connections of the basal ganglia of anamniote and amniote tetrapods are largely comparable. This review has also brought together data about the distribution of receptors and catecholaminergic fibers as well as data about developmental aspects. From these data it has become clear that there is a good match between catecholaminergic fibers and receptors, but, at many places, volume transmission seems to play an important role. Finally, although the available data are still limited, striking differences are observed in the spatiotemporal sequence of appearance of catecholaminergic cell groups, in particular those in the retina and olfactory bulb.

Afferents to the rostral olfactory bulb in sheep with special emphasis on the cholinergic, noradrenergic and serotonergic connections

The olfactory bulb (OB) is involved in the processing of olfactory information particularly through the activation of its afferents. To localize their cell origin in sheep, a specific retrograde fluorescent tracer, Fluoro-Gold, was injected into the olfactory bulb of seven ewes. By using immunocytochemical techniques, retrogradely labeled neurons were colocalized with choline acetyltransferase, tyrosine hydroxylase, dopamine-beta-hydroxylase and serotonin to characterize cholinergic, noradrenergic and serotonergic Fluoro-Gold-labeled neurons. Most afferents originated from the ipsilateral side of the injection site. The OB received major inputs from the anterior olfactory nucleus (AON), the piriform cortex (PC), the olfactory tubercle, the diagonal band of Broca (DBB) and the amygdala. Other retrogradely labeled neurons were observed in the taenia tecta, the septum, the nucleus of the lateral olfactory tract, the preoptic area, the lateral hypothalamic area, the mediobasal hypothalamus, the lateral part of the premammillary nucleus, the paraventricular nucleus of the hypothalamus, the paraventricular thalamic nucleus, the central grey, the substantia nigra (SN), the ventral tegmental area (VTA), the lateral nucleus to the interpeduncular nucleus (IIP), the raphe and the locus coeruleus (LC). Contralateral labeling was also found in the AON, the PC, the SN compacta, the VTA, the IIP and the LC. Cholinergic Fluoro-Gold-labeled neurons belonged to the horizontal and vertical branch of the DBB. Noradrenergic afferents came from the LC and serotoninergic afferents came from the medial raphe nuclei and the 1IP. These data are discussed in relation with olfactory learning in the context of maternal behavior in sheep.

Structure and diversity in mammalian accessory olfactory bulb

The accessory olfactory bulb (AOB) is the first neural integrative center for the olfactory-like vomeronasal sensory system. In this article, we first briefly present an overview of vomeronasal system organization and review the history of the discovery of mammalian AOB. Next, we briefly review the evolution of the vomeronasal system in vertebrates, in particular the reptiles. Following these introductory aspects, the structure of the rodent AOB, as typical of the well-developed mammalian AOB, is presented, detailing laminar organization and cell types as well as aspects of the homology with the main olfactory bulb. Then, the evolutionary origin and diversity of the AOB in mammalian orders and species is discussed, describing structural, phylogenetic, and species-specific variation in the AOB location, shape, and size and morphologic differentiation and development. The AOB is believed to be absent in fishes but present in terrestrial tetrapods including amphibians; among the reptiles AOB is absent in crocodiles, present in turtles, snakes, and some lizards where it may be as large or larger than the main bulb. The AOB is absent in bird and in the aquatic mammals (whales, porpoises, manatees). Among other mammals, AOB is present in the monotremes and marsupials, edentates, and in the majority of the placental mammals like carnivores, herbivores, as well as rodents and lagomorphs. Most bat species do not have an AOB and among those where one is found, it shows marked variation in size and morphologic development. Among insectivores and primates, AOB shows marked variation in occurrence, size, and morphologic development. It is small in shrews and moles, large in hedgehogs and prosimians; AOB continues to persist in New World monkeys but is not found in the adults of the higher primates such as the Old World monkeys, apes, and humans. In many species where AOB is absent in the adult, it often develops in the embryo and fetus but regresses in later stages of development. Finally, new areas in vomeronasal system research such as the diversity of receptor molecules and the regional variation in receptor neuron type as well as in the output neurons of the AOB and their projection pathways are briefly discussed. In view of the pronounced diversity of size, morphologic differentiation, and phylogenetic development, the need to explore new functions for the vomeronasal system in areas other than sexual and reproductive behaviors is emphasized.

Serotonergic neurons are present and innervate blood vessels in the olfactory bulb of the laboratory shrew, Suncus murinus

The distribution and characteristics of serotonin-immunoreactivity in the olfactory bulb of the laboratory shrew (Suncus murinus, insectivore) was studied immunohistochemically. Serotonergic neurons were found only in the subependymal layer of the main olfactory bulb. These neurons were 8-12 microm in size and bipolar in shape. These serotonergic neurons had smooth nerve fibers which innervate blood vessels located mainly in the subependymal layer of the main olfactory bulb. On the other hand, other serotonergic nerve fibers with varicosities, which must be extrinsic, were detected in most olfactory layers except the olfactory nerve layer. This result suggests that intrinsic serotonergic neurons may control blood vessels and varicose serotonergic nerve fibers may act to modulate the olfactory transmission.

Central connections of the ovine olfactory bulb formation identified using wheat germ agglutinin-conjugated horseradish peroxidase

Pheromonal stimuli elicit rapid behavioral and reproductive endocrine changes in the ewe. The neural pathways responsible for these effects in sheep are unknown, in part, because the olfactory bulb projections have not been examined in this species. Using the anterograde and retrograde neuronal tracer, wheat germ agglutinin-conjugated horseradish peroxidase (WGA-HRP), we describe the afferent and efferent olfactory bulb connections of the Suffolk ewe. Injections of WGA-HRP limited to the main olfactory bulb resulted in retrograde labeling of cells in numerous telencephalic, diencephalic, and metencephalic regions. Terminal labeling was limited to layer la of ipsilateral cortical structures extending rostrally from the anterior olfactory nucleus (AON), piriform cortex, anterior-, and posterolateral-cortical amygdaloid nuclei to lateral entorhinal cortex caudally. Injections involving the accessory olfactory bulb and AON produced additional labeling of cells within the bed nucleus of the stria terminalis (BNST), medial nucleus of the amygdala, and a few cells in the posteromedial cortical nucleus of the amygdala. Terminal labeling included a small dorsomedial quadrant of BNST and also extended to the far lateral portions of the supraoptic nucleus. A clearly defined accessory olfactory tract and nucleus was not evident, perhaps due to limitations in the sensitivity of the method. With this possible exception, the afferent and efferent olfactory connections in the sheep appear similar to those reported for other species.

Oxytocin and vasopressin release in the olfactory bulb of parturient ewes: changes with maternal experience and effects on acetylcholine, gamma-aminobutyric acid, glutamate and noradrenaline release

Maternal behaviour and the ewe's ability to recognize her lamb depend on olfactory cues and parturition, and are facilitated by maternal experience. Parturition induces a variety of neurochemical changes in the brain and, in particular, oxytocin (OT) release. This peptide injected centrally induces maternal behaviour. Oxytocin release occurs in the olfactory bulb (OB) at parturition and yet this structure is involved in the process of selective bonding with lamb. The present study therefore investigated the possibility that oxytocin release in the OB might modulate the release of classical transmitters that are known to be important in controlling selective recognition and whether maternal experience has any effect on this. We have first used in vivo microdialysis to measure OT release, as well as that of the related peptide, arginine-vasopressin (AVP), in the OB of maternally experienced and inexperienced ewes during parturition. While OT release significantly increased in both primiparous and multiparous ewes at parturition this increase was significantly greater in multiparous ewes. No significant change of AVP release was observed in either group. However, vagino-cervical stimulation (VCS) performed at 6 h post-partum caused similar increases in OT but not AVP release in both primiparous and multiparous ewes suggesting that the first birth experience potentiates the ability of VCS to evoke OT release within 6 h of parturition. Using retrodialysis, either OT (10 microM) or AVP (10 microM) were infused into the OB of multiparous and nulliparous ewes and their effects on modulating acetylcholine (ACh), noradrenaline (NA), glutamate and gamma-aminobutyric acid (GABA) release were monitored. Both peptides produced an increase of ACh and NA in multiparous animals and this effect was either absent or less pronounced in nulliparous animals. OT, but not AVP, also increased GABA release equivalently in nulliparous and multiparous animals. Glutamate release was not altered in response to OT or AVP infusion. These results suggest that OT release in the OB at parturition may facilitate the recognition of lamb odours by modulating NA, ACh and GABA release which are of primary importance for olfactory memory. The reduced release of OT in the OB of primiparous ewes at parturition, together with its reduced ability to modulate NA and ACh release, might also partly explain why maternally inexperienced animals require a longer period to selectively bond with their lambs.

Preparation of an antiserum using a fusion protein produced by a cDNA for rat aromatic L-amino acid decarboxylase

Aromatic L-amino acid decarboxylase (AADC) decarboxylates L-DOPA and 5-hydroxytryptophan into dopamine and serotonin, respectively. Starting from a rat AADC cDNA clone isolated in our laboratory, we produced a beta-galactosidase-AADC fusion protein in E. coli. It was purified from inclusion bodies and injected into a rabbit. The antiserum identified AADC on a Western blot of extracts from rat organs as a unique 50 kDa band; it also strongly reacted by immunohistochemistry with dopaminergic and serotonergic neurons. This new beta-galactosidase-AADC fusion protein then constitutes a useful tool for producing AADC as an antigen free of contamination by mammalian proteins.

Neuronal projections to the medial preoptic area of the sheep, with special reference to monoaminergic afferents: immunohistochemical and retrograde tract tracing studies

The preoptic area contains most of the luteinizing hormone releasing hormone immunoreactive neurons and numerous monoaminergic afferents whose cell origins are unknown in sheep. Using tract tracing methods with a specific retrograde fluorescent tracer, fluorogold, we examined the cells of origin of afferents to the medial preoptic area in sheep. Among the retrogradely labeled neurons, immunohistochemistry for tyrosine hydroxylase, dopamine-beta-hydroxylase, phenylethanolamine N-methyltransferase, and serotonin was used to characterize catecholamine and serotonin fluorogold labeled neurons. Most of the afferents came from the ipsilateral side to the injection site. It was observed that the medial preoptic area received major inputs from the diagonal band of Broca, the lateral septum, the thalamic paraventricular nucleus, the lateral hypothalamus, the area dorsolateral to the third ventricle, the perimamillary area, the amygdala, and the ventral part of the hippocampus. Other numerous, scattered, retrogradely labeled neurons were observed in the ventral part of the preoptic area, the vascular organ of the lamina terminalis, the ventromedial part of the hypothalamus, the periventricular area, the area lateral to the interpeduncular nucleus, and the dorsal vagal complex. Noradrenergic afferents came from the complex of the locus coeruleus (A6/A7 groups) and from the ventro-lateral medulla (group A1). However, dopaminergic and adrenergic neuronal groups retrogradely labeled with fluorogold were not observed. Serotoninergic fluorogold labeled neurons belonged to the medial raphe nucleus (B8, B5) and to the serotoninergic group situated lateral to the interpeduncular nucleus (S4). In the light of these anatomical data we hypothesize that these afferents have a role in the regulation of several functions of the preoptic area, particularly those related to reproduction. Accordingly these afferents could be involved in the control of luteinizing hormone releasing hormone (LHRH) pulsatility or of preovulatory LHRH surge.

Morphological relationships between tyrosine hydroxylase-immunoreactive neurons and dopamine-beta-hydroxylase-immunoreactive fibres in dopamine cell group A15 of the sheep

Double immunocytochemical labelling with antibodies raised against tyrosine hydroxylase (TH) and dopamine-beta-hydroxylase was used on semi-thin sections of sheep hypothalamus to investigate possible morphological relationships between dopamine neurons of group A15 and noradrenaline afferents to this area. Dopamine-beta-hydroxylase-immunoreactive (IR) fibres were found in the close proximity of dendrites of TH-IR neurons. At electron microscopic level, single immunocytochemical staining with TH antibodies revealed the presence of synaptic contacts between labelled or unlabelled axon terminals and anti-TH labelled dendrites. These observations suggest that in the sheep, TH-IR neurons of group A15 are controlled by non-catecholaminergic and catecholaminergic afferents. Catecholamine inputs could contain either dopamine or noradrenaline. The hypothesis of noradrenaline inputs to A15 is strongly supported by the results obtained after double labelling on semi-thin sections. Tyrosine hydroxylase-immunoreactive perikarya and dendrites often seemed to be partly surrounded by glial processes. This latter observation suggests that the synaptic investment of these neurons might be controlled by glial cells.

Autoradiographic detection of vasopressin binding sites, but not of oxytocin binding sites, in the sheep olfactory bulb

Oxytocin facilitates maternal behaviour in sheep. In the present study, we searched for the presence of oxytocin and vasopressin binding sites in the sheep olfactory bulb, a brain area which is thought to be involved in specific bond formation between the ewe and its lamb. Using in vitro autoradiography, we observed binding of tritiated vasopressin to the glomerular layer of the olfactory bulb. Competition studies performed with structural analogues and the use of a 125I-labelled linear vasopressin antagonist suggested that sites which bind vasopressin are V1 type receptors. In contrast, specific binding sites for oxytocin in the olfactory bulb could be detected neither in control females, nor in ovariectomized females treated with estradiol nor in postparturient ewes, although such sites were present in the uterus.

Norepinephrine-containing glomus cells in the rabbit carotid body. II. Immunocytochemical evidence of dopamine-beta-hydroxylase and norepinephrine

The presence of noradrenergic glomus cells in the rabbit carotid body was investigated at the light and electron microscope levels, using dopamine-beta-hydroxylase and norepinephrine immunocytochemistry as well as the chromaffin reaction. Frozen and semi-thin plastic sections showed some dopamine-beta-hydroxylase immunoreactive glomus cells either isolated in the connective tissue or, more frequently, mixed with unreactive cells. At the ultrastructural level immunopositive cells differed from immunonegative ones by the larger size of most of their dense-cored vesicles. Similar observations were made after using anti-norepinephrine antibodies. Immunoreactive cells to anti-dopamine-beta-hydroxylase and anti-norepinephrine antibodies were relatively few although their number varied from carotid body to carotid body. The immunolabelling intensity was very variable from cell to cell. Consecutive frozen sections processed for norepinephrine- and dopamine-immunocytochemistry showed many cell clusters containing both norepinephrine and dopamine-immunoreactive glomus cells. Some chromaffin glomus cells were clearly identifiable by the very strong electron opacity of their dense-cored vesicles; most of these vesicles were characterized by their large size, as the dense-cored vesicles observed in dopamine-beta-hydroxylase- and norepinephrine-immunopositive cells. These results demonstrated that dopamine-beta-hydroxylase and norepinephrine-immunopositive, as well as chromaffin cells, were identical to the cells which take up exogenous norepinephrine, described in part I of this study. However, many intermediate levels were found between norepinephrine-immunonegative and strongly norepinephrine-immunopositive glomus cells, suggesting that the distinction between these two kinds of cells is not clearcut.

Catecholamine-containing neurons in the sheep brainstem and diencephalon: immunohistochemical study with tyrosine hydroxylase (TH) and dopamine-beta-hydroxylase (DBH) antibodies

The present study describes the distribution and morphological characteristics of neurons and nerve fibers containing the catecholamine-synthesizing enzymes, tyrosine hydroxylase and dopamine-beta-hydroxylase, in the sheep brainstem and diencephalon on the basis of immunohistochemical procedures. Neurons and fibers were considered to be dopaminergic if they showed anti-tyrosine hydroxylase immunoreactivity, without corresponding anti-dopamine-beta-hydroxylase immunoreactivity. The structures labeled with both antisera were considered noradrenergic or adrenergic. The distribution of catecholaminergic neurons corresponds to that described by other authors with similar methods in the rat and in primates. The noradrenergic neurons belong to cell groups A1 to A7 and the dopaminergic neurons to cell groups A8 to A15. In almost all studied areas, the catecholaminergic innervation is similar to that observed in the other species. However, the central catecholaminergic systems of the sheep showed some specific characteristics: (1) groups A3 and A4, described in the rat, were not found, (2) group A14 contains fewer neurons than in the rat, (3) group A15 does not contain a dorsal but only a ventral portion, (4) there is a larger dispersion of neurons within each group, especially A6 and A7, than in rodents, and (5) there is a larger noradrenergic innervation of the catecholaminergic groups than in the other species.

Adrenergic neurons in sheep brain demonstrated by immunohistochemistry with antibodies to phenylethanolamine N-methyltransferase (PNMT) and dopamine-beta-hydroxylase (DBH): absence of the C1 cell group in the sheep brain

Using immunohistochemistry with specific antisera against dopamine-beta-hydroxylase and phenylethanolamine N-methyltransferase, we present the first description of the adrenergic structures of the sheep medulla oblongata. Dopamine-beta-hydroxylase-immunoreactive perikarya in the sheep brain are localized as described in the rodents (A1 and A2 groups) but their distribution is characterized by only one phenylethanolamine N-methyltransferase immunoreactive cell body group, found in the nucleus tractus solitarius. This group corresponds to the C2 group previously described in the rat, but neither group C1 nor group C3 are found in the sheep with our method. Compared with rodents or primates, this animal presents a different pattern of central adrenergic innervation and could be an alternative model to study the central role of adrenaline in various physiological functions as different as swallowing or reproduction.