Peripheral projections of nervus terminalis LHRH-containing neurons in the tiger salamander,Ambystoma tigrinum

The peripheral projections of the nervus terminalis (NT) have been difficult to examine due to the weak immunoreactivity of the processes to various antibodies. We performed two experimental manipulations in the tiger salamander in an attempt to increase the luteinizing hormone-releasing hormone-immunoreactive (LHRH-ir) labelling in the peripheral processes of the NT: 1) the NT was sectioned centrally, or 2) a 100 mg melatonin pellet was embedded subcutaneously for 3 days prior to sacriffice. Following these manipulations, animals were sacrifficed and tissue was processed with standard immunocytochemical techniques for the analysis of the distribution of LHRH-ir processes. In the nasal cavity, LHRH-ir fibers were observed projecting 1) into the rostral olfactory epithelium, 2) to Bowman's glands in the lamina propria of the rostromedial olfactory mucosa and ventrolateral mucosa between the main nasal cavity and Jacobson's organ, 3) into the naris constrictor muscle, and 4) along the palatine nerves and ganglia. These lesion and hormone manipulations have enabled the detection of peripheral projections of the NT not observed previously with immunocytochemical procedures alone. The wide distribution of LHRH-ir NT processes in the nasal cavity and cranium suggests that this nerve may influence many different cranial structures during appropriate pheromonal or neuroendocrine events.     

Central projections of the nervus terminalis in the bichir,Polypterus palmas

Summary Central pathways of the nervus terminalis (n.t.) in the bichir, Polypterus palmas, were studied with the use of tracing techniques. After application of horseradish peroxidase to the unilateral olfactory mucosa labeled n.t. fibers were traced in seven distinct bundles through the subpallium. Projection areas are found in the precommissural ventral nucleus of the area ventralis telencephali ipsilaterally, the anterior commissure and commissural parts of the periventricular preoptic nucleus bilaterally; few n.t.-fibers cross via the anterior commissure to the contralateral side; no fibers were observed to turn rostrally to the contralateral olfactory bulb. Major targets of the n.t. include a restricted ventral part of the periventricular preoptic nucleus at the level of the optic chiasma bilaterally, and the periventricular nuclei located between the thalamic nuclei and the hypothalamus bilaterally. N.t. fibers continue their course through the ipsilateral hypothalamus and are traced as far as the mesencephalic tegmentum ipsilaterally. N.t. terminations are found consistently within the boundaries of periventricular cell nuclei, suggesting axosomatic synaptic contacts. We propose a differentiation of the n.t. ganglion cells into a distal (mucosal) and proximal (bulbar) type regarding the peripheral cell processes. Our findings are compared with those of other reports on the n.t. system.     

The nervus terminalis also exists in cyclostomes and birds

Summary The terminal nerve has been described in all vertebrate classes, with the exception of cyclostomes and birds. With regard to this question, we have examined representatives of these two classes using tracer techniques, and found a terminal nerve in larval lampreys and young domestic mallards. Horseradish peroxidase or cobaltous lysine was injected into the olfactory mucosa, which is known to be innervated by peripheral branches of the terminal nerve. The brains were then searched for labeled, centrally directed fibers of the terminal nerve that project further caudally than the glomerular layer of the olfactory bulb. In larval lampreys, centrally projecting fibers of the terminal nerve were found in the tel-, diand mesencephalon. Termination of labeled fibers was observed in the hypothalamus. Some fibers of the terminal nerve cross to the contralateral side via the commissure of the posterior tuberculum. In young ducks, the terminal nerve projects ipsilaterally along the medial edge of the telencephalon.     

Tracing of single fibers of the nervus terminalis in the goldfish brain

Summary Central projections of the nervus terminalis (n.t.) in the goldfish were investigated using cobalt- and horseradish peroxidase-tracing techniques. Single n.t. fibers were identified after unilateral application of cobalt chloride-lysine to the rostral olfactory bulb. The central course and branching patterns of individual n.t. fibers were studied in serial sections. Eight types of n.t. fibers are differentiated according to pathways and projection patterns. Projection areas of the n.t. include the contralateral olfactory bulb, the ipsilateral periventricular preoptic nucleus, both retinae, the caudal zone of the periventricular hypothalamus bilaterally, and the rostral optic tectum bilaterally. N.t. fibers cross to contralateral targets in the anterior commissure, the optic chiasma, the horizontal commissure, the posterior commissure, and possibly the habenular commissure. We propose criteria that differentiate central n.t. fibers from those of the classical secondary olfactory projections. Branching patterns of eight n.t. fiber types are described. Mesencephalic projections of the n.t. and of secondary olfactory fibers are compared and discussed with regard to prior reports on the olfactory system of teleosts. Further fiber types for which the association with the n.t. could not be established with certainty were traced to the torus longitudinalis, the torus semicircularis, and to the superior reticular nucleus on the ipsilateral side.     

A light- and electron-microscopic study of mesencephalic neurons projecting to the ganglion of the nervus terminalis in the goldfish

Summary After application of various neuronal tracers (horseradish peroxidase, cobalt-chloride lysine, true blue) to the ganglion of the nervus terminalis a small number of neurons was retrogradely labeled in the mesencephalon. As revealed by combined horseradish peroxidase and catecholamine-fluorescence techniques these neurons are located in the isthmic area immediately rostral to, but not within the locus coeruleus. Cobalt-labeled axons of the mesencephalic neurons were traced individually in serial sections. Neurons projecting contralaterally cross in the horizontal commissure. Tracing of single fibers provided no evidence for axon collaterals within this pathway. Retrograde labeling reveals two different types of isthmic neurons afferent to the ganglion of the nervus terminalis: One smaller-sized type is located bilaterally and consists of four to six neurons; another type possessing many dendritic processes was consistently found as only one single cell located contralateral to the side of injection. The existence of two types of neurons was confirmed by their cytological differences: The small-sized type receives only sparse perisomatic input, while the large-sized type shows heavy somatic and dendritic, probably monoaminergic innervation.     

Retinofugal projections in salamanders of the family Plethodontidae

Summary A comparison of the retinofugal projections in 14 species of plethodontid salamanders by means of the horseradish peroxidase (HRP) technique revealed almost identical contralateral projections. In all species studied three optic tracts were found. Behind the chiasma opticum the basal optic tract runs to the peduncle region, there forming the basal optic neuropil. The marginal optic tract courses from the chiasma over the thalamus to the tectum opticum where it covers the entire surface. In the anterior thalamus the marginal optic tract innervates the neuropil Bellonci-pars lateralis and the corpus geniculatum thalamicum, and more caudally the neuropil posterior thalami. The medial optic tract supplies the neuropil Bellonci-pars lateralis and pars medialis in the anterior thalamus from where it runs medial to the marginal optic tract as a separate tract to the uncinate field in the posterior thalamus.The ipsilateral projections show differences among the species studied, although the global organization remains constant. The differences mainly concern the marginal optic tract which varies from being weakly labeled and restricted to the rostral part of the tectum opticum, to being heavily labeled and innervating the entire tectum to its caudal edge. Species with the heaviest ipsilateral projections all belong to the plethodontid tribe Bolitoglossini, all of which show direct development, a highly projectile tongue, rather frontally oriented eyes and excellent depth perception. In these species the thalamic ipsilateral projection areas are equal in size and shape to the contralateral one. The ipsilateral projections to the tectum show two distinct layers, a superficial and a deep one, which intermingle with the contralateral projections. The two other ipsilateral tracts do not differ significantly among the plethodontid species: the medial optic tract is always heavily and the basal optic tract always weakly labeled.     

Distribution of FMRFamide-like immunoreactivity in the brain,retina and nervus terminalis of the sockeye salmon parr,Oncorhynchus nerka

Summary Neurons displaying FMRFamide(Phe-Met-Arg-Phe-NH₂)-like immunoreactivity have recently been implicated in neural plasticity in salmon. We now extend these findings by describing the extent of the FMRF-like immunoreactive (FMRF-IR) system in the brain, retina and olfactory system of sockeye salmon parr using the indirect peroxidase anti-peroxidase technique. FMRF-IR perikarya were found in the periventricular hypothalamus, mesencephalic laminar nucleus, nucleus nervi terminalis and retina (presumed amacrine cells), and along the olfactory nerves. FMRF-IR fibers were distributed throughout the brain with highest densities in the ventral area of the telencephalon, in the medial forebrain bundle, and at the borders between layers III/IV and IV/V in the optic tectum. High densities of immunoreactive fibers were also observed in the area around the torus semicircularis, in the medial hypothalamus, median raphe, ventromedial tegmentum, and central gray. In the retina, immunopositive fibers were localized to the inner plexiform layer, but several fiber elements were also found in the outer plexiform layer. The olfactory system displayed FMRF-IR fibers in the epithelium and along the olfactory nerves. These findings differ from those reported in other species as follows: (i) FMRF-IR cells in the retina have not previously been reported in teleosts; (ii) the presence of FMRF-IR fibers in the outer plexiform layer of the retina is a new finding for any species; (iii) the occurrence of immunopositive cells in the mesencephalic laminar nucleus has to our knowledge not been demonstrated previously.     

Causes of larval drift of the fire salamander,Salamandra salamandra terrestris,and its effects on population dynamics

Summary The larval drift of the fire salamander was investigated over a period of three years in a mountain brook (Niederbergisches Land, F.R. Germany), as well in a laboratory water channel. The rate of larval drift fluctuated between 19% and 41% of the total population of larvae in a defined section of the brook during these three years. Most (83%) of the drifting larvae were hatchlings or very young stages. The drift was dependent on the strength of the current, the number of spawning females, the presence of suitable hiding places, sufficient space and adequate food. Hungry larvae drifted more often than satiated animals. The drift behaviour of hatchlings differed distinctly from that of older larvae. The significance of ecological factors on larval drift is discussed. It is evidently a more important factor in selection than has hitherto been recognized.     

Substance P-, F8Famide-, and A18Famide-like immunoreactivity in the nervus terminalis and retina of the goldfish Carassius auratus

We re-investigated the occurrence of substance P-like immunoreactivity in the retina of the goldfish Carassius auratus using antisera to substance P and other tachykinins. Most antisera labelled a previously described single class of mono-stratified amacrine cells arborizing in layer 3 of the inner plexiform layer. Preabsorption experiments showed that these amacrine cells contained at least one tachykinin-like peptide. One antiserum (INC 353) to substance P labelled not only these amacrine cells but also fibres in layer 1 of the inner plexiform layer and fibres in the optic nerve. These fibres were identified as retinopetal projections of the nervus terminalis, in part because of colocalized labelling with antisera against gonadotropin-releasing hormone and FMRFamide. Preabsorption experiments showed that the substance P-immunoreactive material in the nervus terminalis was not substance P or any other typical tachykinin. Labelling of the nervus terminalis with INC 353 was blocked by preabsorption with two bovine FMRFamide-like peptides, F8Famide and A18Famide, which contain a substance P(4–7)-like region. Antisera to F8Famide and A18Famide strongly labelled ganglia of the nervus terminalis and retinopetal fibres. We suggest that labelling of the nervus terminalis by antisera to substance P and FMRFamide occurs because of homologies between these antigens and a non-tachykinin, endogenous peptide that is similar to F8Famide and A18Famide.     

Pheromone detection and olfactory pathways in the brain of the female African catfish,Clarias gariepinus

Summary The olfactory tract of the African catfish, Clarias gariepinus, consists of two tracts, the medial and lateral olfactory tract. Ovulated female catfish are attracted by male steroidal pheromones. Attraction tests with catfish in which the medial and lateral olfactory tract have been selectively lesioned show that the effects of these pheromones are mediated by the medial olfactory tract. The central connections of the medial and lateral olfactory tract have been studied by retro- and anterograde transport techniques using horseradish peroxidase as a tracer. Upon entering the forebrain, the medial olfactory tract innervates the posterior pars ventralis and pars supracommissuralis of the area ventralis telencephali and the nucleus preopticus periventricularis, the nucleus preopticus and the nucleus recessus posterioris. Application of horseradish peroxidase to the olfactory epithelium shows that part of the innervation of the area ventralis telencephali and the nucleus preopticus periventricularis can be attributed to the nervus terminalis, which appears to be embedded in the medial olfactory tract. The lateral olfactory tract sends projections to the same brain areas but also innervates the nucleus habenularis and a large terminal field in the area dorsalis telencephali pars lateralis ventralis. Furthermore, the medial olfactory tract carries numerous axons from groups of perikarya localized in the area dorsalis telencephali. Contralateral connections have been observed in the olfactory bulb, telencephalon, diencephalon and mesencephalon. It is suggested that processes of the medial olfactory tract innervating the preoptic region may influence the gonadotropin-releasing hormone system and in doing so may lead to behavioral and physiological changes related to spawning.     

Central projections of the pineal complex in the silver lamprey Ichthyomyzon unicuspis

Summary The central projections of the pineal complex of the silver lamprey Ichthyomyzon unicuspis were studied by injection of horseradish peroxidase. The pineal tract courses caudally along the left side of the habenular commissure, and a few fibers penetrate the brain through the caudalmost portion of this commissure. Most of the fibers, however, continue caudally and enter the brain through the posterior commissure. The pineal tract projects bilaterally to the subcomissural organ, the superficial and periventricular pretectum, the posterior tubercular nucleus, the dorsal and ventral thalamus, the dorsal hypothalamus, the optic tectum, the torus semicircularis, the midbrain tegmentum, and the oculomotor nucleus. A few fibers decussate in the tubercular commissure, but the course of these decussate fibers could not be followed owing to the bilateral nature of the projections. No retrogradely labeled cells were found in the brain. With the exception of the projections to the optic tectum and torus semicircularis, the pineal projections in the silver lamprey are similar to those reported in other anamniote vertebrates.     

Distribution of GABA-immunoreactive neurons in the brain of adult and developing salamanders (Pleurodeles waltli,Triturus alpestris)

The distribution of GABAergic neurons in brains of the family Salamandridae (Pleurodeles waltli, Triturus alpestris) has been investigated immunohistochemically with an antibody against gamma-aminobutyric acid (GABA). In adult animals, immunoreactive neurons, fibers, and terminals are abundantly labeled. In the telencephalon, pallial areas contain fewer GABAergic neurons and fibers than basal forebrain areas. The amygdalar complex and the habenulae have a complex pattern of GABA-immunoreactivity that is especially pronounced within the neuropil. The pretectal and basal optic systems are provided with GABAergic neurons, corroborating electrophysiological results. The dorsal thalamus and parts of the torus semicircularis are almost completely devoid of GABA-immunoreactive neurons. In the torus, magnocellular neurons known to project to the contralateral counterpart are distinctly GABA-immunoreactive. During ontogeny, GABAergic neurons arise early when the first reflexive movements occur after mechanical stimulation. At stage 28, cells are labeled initially near the nucleus of the medial longitudinal fasciculus, which is the first supraspinal tract to appear in ontogeny. At stage 30 (still before hatching), GABAergic neurons are found in the pretectum, immunoreactive neurons arising in the dorsal tegmentum slightly later. Both systems are known to mediate basic reflexes in gaze stabilization. The commissura posterior is GABAergic at early stages suggesting an important functional role in homonymous inhibition between both sides. Thus in salamanders, the neurotransmitter GABA displays a complex distribution, similar to that in other vertrebrates. This pattern emerges early in ontogeny.     

Fine structure and primary sensory projections of sensilla located in the sacculus of the antenna of Drosophila melanogaster

Sensilla lining the inner walls of the sacculus on the third antennal segment of Drosophila melanogaster were studied by light and transmission electron microscopy. The sacculus consists of three chambers: I, II and III. Inside each chamber morphologically distinct groups of sensilla having inflexible sockets were observed. Chamber I contains no-pore sensilla basiconica (np-SB). The lumen of all np-SB are innervated by two neurons, both resembling hygroreceptors. However, a few np-SB contain one additional neuron, presumed to be thermoreceptive. Chamber II houses no-pore sensilla coeloconica (np-SC). All np-SC are innervated by three neurons. The outer dendritic segments of two of these neurons fit tightly to the wall of the lumen and resemble hygroreceptor neurons. A third, more electron-dense sensory neuron, terminates at the base of the sensillum and resembles a thermoreceptor cell. Chamber III of the sacculus is divided into ventral and dorsal compartments, each housing morphologically distinct grooved sensilla (GS). The ventral compartment contains thick GS₁, and the dorsal compartment has slender sensilla GS₂. Ultrastructurally, both GS₁ and GS₂ are doublewalled sensilla with a longitudinal slit-channel system and are innervated by two neurons. The dendritic outer segment of one ofthe two neurons innervates the lumen of the GS and branches. On morphological criteria, we infer this neuron to be olfactory. The other sensory neuron is probably thermoreceptive. Thus, the sacculus in Drosophila has sensilla that are predominantly involved in hygroreception, thermoreception, and olfaction. We have traced the sensory projections of the neurons innervating the sacculus sensilla of chamber III using cobaltous lysine or ethanolic cobalt (II) chloride. The fibres project to the antennal lobes, and at least four glomeruli (VM₃, DA₃ and DL_2-3) are projection areas of sensory neurons from these sensilla. glomerulus DL₂ is a common target for the afferent fibres of the surface sensilla coeloconica and GS, whereas the VM₃, DA₃ and DL₃ glomeruli receive sensory fibres only from the GS.     

Retinofugal and retinopetal projections in the teleost Channa micropeltes (Channiformes)

Summary Retinofugal and retinopetal projections were investigated in the teleost fish Channa micropeltes (Channiformes) by means of the cobaltous lysine and horseradish peroxidase (HRP) tracing techniques. Retinofugal fibers cross completely in the optic chiasma. A conspicious lamination is present in those parts of the optic tract that give rise to the marginal branches of the optic tract. This layering of optic fibers continues in the marginal branches to mesencephalic levels. Retinal projections to the preoptic and hypothalamic regions are sparse; they are more pronounced in the area of pretectal nuclei. The medial pretectal complex and the cortical pretectal nucleus are more fully differentiated than in other teleostean species. Further targets include the thalamus and the optic tectum. The course of major optic sub-tracts and smaller fascicles is described. Retinopetal neurons are located contralaterally in a rostral and a caudal part of the nucleus olfactoretinalis, and in a circumscribed nucleus thalamoretinalis. The present findings are compared with reports on other teleost species.     

黑斑蛙嗅器和犁鼻器的组化及超微结构特征

嗅感受器主要感知外界环境中化学信号分子.本文采用银染、NADPH-组化染色和电镜技术来观察黑斑侧褶蛙(Petophylax nigromaculatus)的嗅器和犁鼻器的功能差异及细胞组成.银染法可对嗅上皮和犁鼻上皮的细胞进行分类及区分.其中,支持细胞胞核深染成黑色,嗅细胞胞核银染为花斑状.细胞计数显示,犁鼻上皮的嗅神经细胞含量百分比显著高于嗅上皮.组化结果显示,黑斑侧褶蛙嗅上皮和犁鼻上皮对NADPH-d表达模式差异显著,前者表达明显高于后者.电镜结果显示,黑斑侧褶蛙嗅上皮和犁鼻上皮的支持细胞由两种类型的细胞组成,分别为纤毛型和颗粒型支持细胞.     

Central connections of the olfactory bulb in the bichir,Polypterus palmas,reexamined

Summary Central connections of the olfactory bulb of Polypterus palmas were studied with the use of horseradish peroxidase and cobalt-tracing techniques. The olfactory bulb projects to subpallial and palliai areas in the ipsilateral telencephalon; a projection to the contralateral subpallium is noted via the habenular commissure. A further target of secondary olfactory fibers is a caudal olfactory projection area in the ipsilateral hypothalamus. No labeling was seen in the anterior commissure and in the contralateral olfactory bulb. The medial and the lateral pallium receive secondary olfactory fibers in distinct areas. Neurons projecting to the bulb are found in the ipsilateral subpallium, mainly in one dorsal longitudinal nucleus. The main connection with the tel- and diencephalon is mediated via the medial olfactory tract. This tract also contains fibers to the contralateral telencephalon, and to the hypothalamus. The smaller lateral olfactory tract mediates fibers to the lateral pallium. The organization of pathways of secondary olfactory fibers in the telencephalon is described. The present findings are compared to those obtained in species possessing an inverted forebrain.This investigation was supported by grants from the Deutsche Forschungsgemeinschaft to DLM     

Central projections of labellar taste hairs in the blowfly,Phormia regina Meigen

Summary We have traced the central projections of the receptor neurons associated with each of the eleven largest taste hairs on the labellum of the blowfly, Phormia regina (Meigen), by staining them with cobaltous lysine. The eleven hairs fall into three groups which reflect their peripheral locations and their branching patterns in the subesophageal ganglion. Group 1, consisting of the anterior hairs (numbers 1 and 2) and Group 3, consisting of the posterior hairs (numbers 9–11) project bilaterally, while Group 2, consisting of the middle hairs (numbers 3–8) projects primarily ipsilaterally. The central projections of the hairs within a single group are similar. Each hair houses four chemoreceptors, which have differing chemical sensitivities and behavioral roles, and one mechanoreceptor. In some cases, there were indications that the different cells within a single hair have different central branching patterns. For some hairs, however, it was clear that a single central branching region and pattern was shared by more than one receptor cell. We failed to find either a continuous somatotopic representation of a hair's position on the periphery, or an anatomical segregation of receptors coding for different modalities. Behavioral experiments indicate that the fly is informed both of the identity of the hair stimulated and of the chemical nature of the stimulus. Our results suggest that this information is not represented on a gross anatomical level.     

An accessory olfactory pathway in Lepidoptera: the labial pit organ and its central projections in Manduca sexta and certain other sphinx moths and silk moths

Summary In the hawkmoth, Manduca sexta, the third segment of each labial palp contains a pit, which houses a densely packed array of sensilla. We have named this structure the labial pit organ (LPO). The sensilla within the pit are typical of olfactory receptors, characterized by a grooved surface, wall pores, and pore tubules. Axons arising from receptor cells that innervate these sensilla project bilaterally to a single glomerulus in each antennal lobe. We have compared this central projection with that in three other species of Manduca (M. quinquemaculata, M. dilucida, and M. lanuginosa) and in the silkmoths Antheraea polyphemus and Bombyx mori. A bilateral projection to a single glomerulus in each antennal lobe is present in all cases. We suggest that the LPO serves as an accessory olfactory organ in adult Lepidoptera.     

Genetic drift and rapid evolution of viviparity in insular fire salamanders (Salamandra salamandra)

Continental islands offer an excellent opportunity to investigate adaptive processes and to time microevolutionary changes that precede macroevolutionary events. We performed a population genetic study of the fire salamander (Salamandra salamandra), a species that displays unique intraspecific diversity of reproductive strategies, to address the microevolutionary processes leading to phenotypic and genetic differentiation of island, coastal and interior populations. We used eight microsatellite markers to estimate genetic diversity, population structure and demographic parameters in viviparous insular populations and ovoviviparous coastal and interior populations. Our results show considerable genetic differentiation (F(ST) range: 0.06-0.27), and no clear signs of gene flow among populations, except between the large and admixed interior populations. We find no support for island colonization by rafting or intentional/accidental anthropogenic introductions, indicating that rising sea levels were responsible for isolation of the island populations approximately 9000 years ago. Our study provides evidence of rapid genetic differentiation between island and coastal populations, and rapid evolution of viviparity driven by climatic selective pressures on island populations, geographic isolation with genetic drift, or a combination of these factors. Studies of these viviparous island populations in early stages of divergence help us better understand the microevolutionary processes involved in rapid phenotypic shifts.     

Isolation and characterization of polymorphic tetranucleotide microsatellite loci in the Fire salamander Salamandra salamandra (Amphibia: Caudata)

Ten tetranucleotide and one dinucleotide polymorphic microsatellite loci were cloned and characterized for the Fire salamander (Salamandra salamandra) from 34 populations in Germany. A high genetic diversity (5–22 alleles per locus) and heterozygosity (40.6–95.2%) were observed for these markers. Chord distances for population comparisons of the western evolutionary recolonization lineage in the area near Cologne ranged from 0.139 to 0.366, whereas population comparisons between the western and eastern lineage ranged from 0.541 to 0.670. When compared with classical isolation methods, a sufficient number of polymorphic microsatellites can be obtained for the Fire salamander only from specially enriched sublibraries.