Biomedical subjects

L Maler

Publications and source records attributed to L Maler.

At least 73 records · Page 4Linked to original sources

PubMed1987

The laminar distribution of amino acids in the caudal cerebellum and electrosensory lateral line lobe of weakly electric fish (Gymnotidae).

We have studied the distribution of the putative amino acid neurotransmitters glutamate, aspartate, gamma-aminobutyric acid (GABA), glycine, taurine and beta-alanine in the caudal cerebellar lobe and electrosensory lateral line lobe (ELL) of weakly electric gymnotid fish. In the caudal lobe of the cerebellum, the levels of the various amino acids in the granular and molecular layers are comparable to the levels in the rat cerebellum, with the exception of taurine which is present in greater amounts in the gymnotid. In the ELL, these amino acids are differentially distributed in the various layers of this structure. Glutamate and taurine are enriched in the molecular layer, whereas GABA, aspartate, and beta-alanine are enriched in the deep neuropil + granular layers. Glycine is slightly enriched in the pyramidal cell layer.

Amino Acids↗

PubMed1987

Ultrastructural studies of physiologically identified electrosensory afferent synapses in the gymnotiform fish, Eigenmannia.

Eigenmannia is a weakly electric fish that emits a constant-frequency electric organ discharge (EOD). Probability coder (P unit) and phase coder (T unit) electroreceptive afferents differentially encode changes in EOD amplitude and phase, respectively. physiologically identified T and P units were intracellularly labelled with HRP and their terminals were examined with electron microscopy to determine their postsynaptic targets. This technique reveals that phase and amplitude are relayed to first-order electrosensory neurons by two parallel but not independent pathways. P-type afferents terminate on granular interneurons, basilar pyramidals, and polymorphic cells, electrosensory lateral line lobe targets that monitor amplitude modulations, but P-type afferents do not contact spherical cells. T-type afferents relay phase information to spherical cells and thus form a separate afferent pathway. T unit terminals do not synapse directly on basilar pyramidal cells. Collateral branches from T-type afferents, however, were also found to terminate on granule and polymorphic cells, thereby adding phase information into the amplitude channel. P- and T-type afferents exhibit cellular specificity by forming synaptic junctions with different subsets of post synaptic targets in the deep neuropil. The afferent terminals make either asymmetric chemical or gap junction synapses depending on the identity of the post synaptic target. T units contacting granule cells or polymorphic cells had not been previously described. Two possible roles of adding phase to amplitude information are discussed in terms of electrolocation.

Animals↗

PubMed1987

Cytology and immunocytochemistry of the nucleus of the lateral line lobe in the electric fish Gnathonemus petersii (Mormyridae): evidence suggesting that GABAergic synapses mediate an inhibitory corollary discharge.

Knollenorgans, low-threshold electroreceptors found in mormyrid fish, are involved primarily, if not exclusively, in communication. The rhombencephalic nucleus of the lateral line lobe (nLLL) is the target nucleus of knollenorgan afferents. Cells in the nLLL receive a few medium size to large endings with round synaptic vesicles (classified as spoon; large club; small club-, and rodlet-shaped endings) with which they form nexus (gap junction) and asymmetrical chemical synapses associated with the round synaptic vesicles. In addition these endings emit thin collaterals which terminate as small boutons on nLLL neurons; these boutons also have round vesicles and make mixed (electrotonic and chemical) synapses. In addition, cells in the nLLL receive synaptic input from numerous small boutons containing pleomorphic vesicles and making symmetric synapses. We have not found any interneurons within nLLL. Our ultrastructural analysis suggests that boutons synapsing on nLLL neurons belong to only two afferent fiber systems and that the wiring diagram of nLLL is extremely simple. We have studied the immunolocalization in nLLL of glutamic acid decarboxylase (GAD), the enzyme essential for the synthesis of GABA that is also a useful marker for this widely distributed inhibitory neurotransmitter. GAD immunoreactivity was confined to the small boutons with pleomorphic vesicles. GAD was also found in a nucleus projecting to the nLLL, here named the sublemniscal nucleus (SL), which probably conveys corollary discharge signals to the nLLL. This GABAergic projection may be responsible for the potent inhibition associated with the electric organ discharge command that has been described in these cells.

Animals↗

PubMed1987

Cytology and immunocytochemistry of the nucleus extrolateralis anterior of the mormyrid brain: possible role of GABAergic synapses in temporal analysis.

Mormyrid fish use their electrosensory/electromotor system for both electrolocation and electrocommunication. One type of electroreceptor, the knollenorgan, has a low threshold and is used strictly for detecting a conspecific's electric organ discharge. Knollenorgan afferents terminate with mixed synapses (gap junctions and asymmetric chemical synapses) on neurons of the nucleus of the lateral line lobe (nLLL), which in turn projects to a midbrain nucleus--the nucleus extrolateralis anterior (ELa). ELa contains numerous granule cells, which are adendritic, and scattered larger neurons, here termed interstitial cells, which possess several branched dendrites. Because of the overall paucity of dendrites, the neuropil of ELa is scarcely developed and myelinated fibers predominate in between the cell bodies. Axons presumed to originate in nLLL make mixed synapses on both the interstitial and the granule cells. The interstitial neurons are immunoreactive for glutamic acid decarboxylase (GAD), the synthetic enzyme for the inhibitory neurotransmitter gamma-aminobutyric acid (GABA), while the granule cells are GAD-negative. Many GAD-positive synapses are found on each granule cell soma; at smaller densities, GAD-positive boutons also synapse on the cell bodies and dendrites of interstitial cells. The GAD-positive boutons have pleomorphic vesicles and make symmetric synapses. Such boutons presumably originate from a plexus of interstitial cell axons. Mormyrid fish use their knollenorgan afferents for precise temporal discriminations, and this information is needed for electrocommunication. The ELa, with its relatively simple neuronal circuitry, is the most likely site for precise temporal analysis in the knollenorgan afferent pathway, and we propose that the GABAergic synapses on the granule cells may be essential for accurate detection of specific time intervals.

Animals↗

PubMed1987

The organization of afferent input to the caudal lobe of the cerebellum of the gymnotid fish Apteronotus leptorhynchus.

The caudal lobe of the cerebellum of the high frequency gymnotid fish Apteronotus leptorhynchus is that region of the cerebellum lying lateral to the posterolateral sulcus. It consists of three granular masses--the eminentia granularis posterior pars lateralis, a transitional zone T, and the eminentia granularis posterior pars medialis--with their associated molecular layers. We have used the retrograde transport of wheat germ agglutinin conjugated horseradish peroxidase to study the afferent input to the various subdivisions of the caudal lobe. Each granular mass receives different types of input. Eminentia granularis posterior pars lateralis receives a massive bilateral input from an isthmic nucleus, nucleus praeeminentialis, concerned with descending control of the electrosensory system and from a rhombencephalic nucleus, the lateral reticular nucleus, which itself receives a major spinal input. In addition eminentia granularis posterior receives lesser input from other pretectal, (N. at base of dorsomedial optic tract, pretectal complex "B") mesencephalic (dorsal tegmental N., nucleus raphe dorsalis), isthmic (bed N. of praeeminentialis-cerebellaris tract, locus coeruleus) and rhombencephalic nuclei (lateral tegmental N., eurydendroid cells, octaval N., perihypoglossal N., paramedian reticular N., medullary reticular formation, medullary raphe, efferent octavolateralis N., inferior olive, and funicular N.). The input from nucleus praeeminentialis dorsalis is mapped topographically onto eminentia granularis posterior with respect to their rostro-caudal location. We could not define any topography in the mapping of the dorso-ventral body axis upon eminentia granularis posterior; small injections of WGA-HRP produced several small clusters of labeled cells within nucleus praeeminentialis dorsalis which does suggest a more complex organization of this projection. Zone T receives most of its input from the ipsilateral VIIIth nerve ganglion cells and certain pretectal nuclei, but it also receives a small input from nucleus praeeminentialis dorsalis. Eminentia granularis posterior pars medialis receives minor input from a small pretectal nucleus and a small ventral diencephalic nucleus, this region appears to receive its major input from eurydendroid cells of eminentia granularis posterior. The molecular layer associated with each granular mass receives contralateral input from separate clusters of inferior olivary cells. In addition the eurydendroid cells (cerebellar output neurons) of eminentia granularis posterior pars lateralis receive a substantial direct input from cells located in the medial aspect of nucleus praeeminentialis dorsalis.

Animals↗

PubMed1987

Inter-male aggressive signals in weakly electric fish are modulated by monoamines.

Apteronotus leptorhynchus is a gymnotid fish producing a constant high frequency electric organ discharge (EOD). Males of this species use transient increases in EOD frequency (chirps) as aggressive signals. They will also shift the frequency of their EOD away from the similar frequency of a nearby conspecific in order to protect their ability to electrolocate (jamming avoidance response, JAR). Monoamines have been implicated as modulatory agents for various sensorimotor and affective systems, including aggressive behaviour. Since these monoamines are present in the brain of this fish (unpublished observation), we have used these simple and quantifiable behaviours to study the role of monoamines, with special emphasis on possible specific effects on aggressive signalling (chirps). When serotonin (0.1 microgram) is injected directly into the ventricle of these fish it briefly inhibits chirping (aggression) without inhibiting the JAR; this is consistent with the hypothesis that, in mammals, serotonin inhibits aggressive behaviour. Noradrenaline (0.1 microgram) enhances both chirping and the JAR. Dopamine (0.1 microgram) enhances the JAR; it has powerful but inconsistent effects on chirping (inhibition or excitation).

Aggression↗

PubMed1986

A monoclonal antibody to mammalian neurofilament protein stains somata and dendrites in gymnotid fish.

Monoclonal antibody N210 (mabN210) recognizes the 210 kdalton neurofilament protein in mammals and gives characteristic immunocytochemical staining of neurofilament-rich processes. For example, in the cerebellum it recognizes myelinated axons and the calyx formed by basket cell axon collaterals. The distribution of mabN210 immunoreactivity was studied in the gymnotid brain (Apteronotus albifrons). In contrast to the mammalian distribution, mabN210 immunoreactivity was not found in most axons of the gymnotid brain. Instead, deposits of reaction product were present in the somata and dendrites of most neurons and were especially dense in those neurons with extensive dendritic trees, the Purkinje cells, pyramidal cells of the electrosensory lateral line lobe, the crest cells of the nucleus medialis and the pyramidal cells of the tectum. Electrosensory lateral line lobe pyramidal cells are known to contain few, if any, neurofilaments in their dendrites. Western blots of whole gymnotid brain proteins demonstrated that mabN210 recognizes two polypeptides apparent molecular weights 60 and 19 kdaltons. These proteins are thus antigenically similar to neurofilament protein and their expression in the gymnotid brain may be related to the peculiar dendritic branching pattern of Purkinje cells and similar cell types.

Afferent Pathways↗

PubMed1986

The optic tectum of gymnotiform teleosts Eigenmannia virescens and Apteronotus leptorhynchus: a Golgi study.

Golgi, Nissl, Bielschowsky and cholinesterase techniques have been used to analyze the optic tectum of the weakly electric teleost fish Eigenmannia virescens and Apteronotus leptorhynchus. Six layers are readily distinguished: a fairly thick stratum marginale, a narrow stratum opticum and stratum fibrosum et griseum superficiale, a well-developed stratum griseum centrale, a stratum album centrale and a compact stratum periventriculare. Fifty-six neuronal types are present. In regard to comparative aspects of tectal organization, it became apparent that although most neuronal types are similar to those reported in other teleostean fish, there are certain obvious differences such as: pyramidal cell somata not confined to stratum fibrosum et griseum superficiale, but also clustered in the adjacent stratum opticum, presenting stratified or diffuse basilar dendritic arbors; and a change from vertical to oblique and almost horizontal neuronal orientation in the ventral and caudal tectum. The presence of pyramidal cells with aligned and misaligned apical and basal dendritic fields. A cell of stratum griseum centrale with an ascending axon to stratum opticum. A special projection type of fusiform cell of stratum griseum centrale, with an efferent axon of somatic origin. A cell rich stratum griseum centrale, with a wider variety of multipolar and bipolar cell population than reported in other teleosts. Fourteen types of pyriform cells are present, four of which are efferent. Our observations are suggestive of regional differences in regard to the caudalmost tectum in Apteronotus: presumably this is related to the extremely sparse retinal input to this part of the tectum. A close functional correlation has been found between some multipolar and pyriform cells identified in our material with similar cells reported by Rose and Heiligenberg as multisensory cells, following recordings and horseradish peroxidase fillings of these cells. Based on the observation of patchy torus semicircularis input to stratum fibrosum et griseum superficiale, disjunct from the retinal input to this layer, it is proposed that perhaps this arrangement is the result of competition for synaptic targets during development.

Animals↗

PubMed1986

Retinofugal projections in a weakly electric gymnotid fish (Apteronotus leptorhynchus).

The eyes of weakly electric gymnotid fish are poorly developed in comparison to those of most diurnal teleosts. The tectum and pretectum, despite their usual association with the visual system, are large and well differentiated in gymnotids. We have studied retinal projections in gymnotids in order to define the visual components of the mesencephalon and diencephalon and thus allow comparison with other teleosts in which retinofugal fibers have been extensively mapped. Retinofugal projections reported in this work are based on the anterograde transport of conjugated wheat germ agglutinin horseradish peroxidase, following injection into the posterior chamber of the eye of Apteronotus leptorhynchus (brown ghost knife fish). The results show a remarkable similarity to those of non-electroreceptive teleosts. Although the optic nerves appear to cross completely at the optic chiasm, close scrutiny shows a slender recrossing fascicle which continues from the contralateral tractus opticus medialis through the rostroventral hypothalamus to reach the ipsilateral side, providing a scanty projection to the n. opticus hypothalamicus, n. anterior periventricularis, n. dorsolateralis thalami, and n. commissurae posterioris. A few fibers ascend via the tractus opticus dorsomedialis to the rostral dorsomedial part of the stratum fibrosum et griseum superficiale of the ipsilateral tectum. The main body of the retinal projections in Apteronotus are to the following contralateral target areas: preoptic area, n. opticus hypothalamicus, n. anterior periventricularis, n. dorsolateralis thalami, n. pretectalis, area pretectalis, n. corticalis, n. commissurae posterioris, n. geniculatus lateralis, area and n. ventrolateralis thalami, caudal dorsal tegmentum and the tectum opticum. The retinotectal projection is modest in comparison to that of more vision dependent fish and terminates mainly in the upper half of the stratum fibrosum et griseum superficiale; hardly any retinal fibers reach the caudalmost tectum.

Afferent Pathways↗

PubMed1986

Identification of a nucleus isthmi in the weakly electric fish Apteronotus leptorhynchus (Gymnotiformes).

The nucleus isthmi of teleost fish, amphibians, reptiles and birds, and its probable homologue, the nucleus parabigeminalis of mammals, share in common certain features such as location in the dorsal tegmentum and reciprocal connectivity with the optic tectum. In gymnotid fish the nucleus isthmi is located dorsolaterally in the brainstem tegmentum, ventral to the torus semicircularis and the lateral mesencephalic reticular area and dorsal to the rostral nucleus praeeminentialis. The nucleus isthmi has an ovoid shape, with a compact cellular part on its dorsal, medial and ventral aspects surrounding a hilar region with a sparse population of larger cells. Following wheat germ agglutinin-conjugated horseradish peroxidase injections into the optic tectum, anterogradely labeled fine terminals were observed leaving the tectobulbar tract and entering the ipsilateral nucleus isthmi via its laterally facing hilar region. Retrogradely labeled cells were present in the nucleus isthmi on both sides, indicating the presence of a bilateral isthmotectal projection similar to that reported in amphibians. The putative isthmal nucleus stains densely for acetylcholinesterase. Based on the similarity of its location, shape, cholinesterase histochemistry and reciprocal connectivity with the optic tectum, we identified this structure as the nucleus isthmi of gymnotids. An interesting observation of this study was that the nucleus isthmi, in addition to receiving fine terminals from the optic tectum, is also the recipient of a sparser population of thicker-caliber afferent fibers which terminate not only in the large-celled hilar region but also within the smaller-celled component of the nucleus; this projection appears to emanate from the torus semicircularis dorsalis.

Animals↗

PubMed1986

A time-comparison circuit in the electric fish midbrain. II. Functional morphology.

The weakly electric fish Eigenmannia is able to detect temporal disparities as small as 400 nsec between two signals from different parts of the body surface (Carr et al., 1986). The elements of this time-comparison circuit have been identified by EM reconstruction of its component cells. Information about the timing of the zero-crossing of signals on each area of the body surface is coded in phase-coder receptors, a subset of tuberous electroreceptors. Electroreceptors on the body surface are innervated by primary afferents with their central termination on the spherical cells of the medullary electrosensory lateral line lobe. These cells project to lamina VI of the midbrain torus, a structure similar to the inferior colliculus. Afferents entering lamina VI form a very restricted terminal arbor in which they synapse on the three cell types of this lamina. Each afferent makes gap-junction synapses on one or two giant cell somata and morphologically mixed synapses on the distal dendrites of two types of small cell. The afferent terminals thus encode the timing of the electric signal on a local patch of the body surface, forming a somatotopic map of the body surface in lamina VI. The giant cells are adendritic and their axonal arbor is such as to distribute timing information originating from one part of the body surface throughout lamina VI, so that each region of lamina VI receives information about the timing of zero-crossings from the entire body surface from giant cells, as well as information from a local portion of the body surface from the afferent terminals. The giant cells terminate exclusively on the cell bodies of the small cells of lamina VI, shown to be sensitive to small temporal disparities by Heiligenberg and Rose (1985). Thus, each small cell receives a single synapse on its soma from a giant cell that conveys phase-coding information from some portion of the body surface and receives local phase-coding input onto its dendrites from spherical cell afferents. The sensitivity of the small cells to temporal disparities appears to be conferred by their segregation of inputs from two different parts of the body surface onto dendrites and soma, respectively. We propose that the dendritic input acts as a delay line, and the small cell fires maximally when the inputs from the dendrites and the giant cell input onto the soma coincide.

Animals↗

PubMed1985

A Golgi study of the cell types of the dorsal torus semicircularis of the electric fish Eigenmannia: functional and morphological diversity in the midbrain.

The dorsal torus semicircularis (torus) of the gymnotiform fish Eigenmannia was examined in Golgi-impregnated material. These results were correlated with those of a previous HRP study which used retrograde labelling techniques to identify the efferent cell types of the torus (Carr et al., '81, J. Comp Neurol. 203:649-670). The torus is a laminated midbrain nucleus of the electrosensory system. It receives somatotopically ordered electrosensory input from the medulla and caudal lobe of the cerebellum, proprioceptive input from the descending nucleus of the trigeminal nerve, and input from the optic tectum. The torus projects to the nucleus praeeminentialis, the optic tectum, nucleus electro-sensorius, parts of the central posterior thalamus, the pretectum, the lateral mesencephalic reticular formation (LMRA), the reticular formation, and the inferior olive. The torus has 12 laminae and 48 cell types by Golgi criteria. There are three major orientations to the dendritic fields of the toral neurons: purely horizontal neurons with dendrites confined to a single lamina, multipolar neurons whose dendrites often do not respect laminar boundaries, and vertical cells with dendrites that travel in the vertical bundles of dendrites and axons which pierce the torus at regular intervals. There are four major groups of vertically oriented neurons. The first has a predominantly horizontal dendritic tree with one or two vertical dendrites which connect the cell to a distant lamina. The second consists of "U"-shaped neurons with a horizontal arbor and two major dendrites which ascend in adjacent vertical bundles. The third group is made up of bilaminar neurons which receive input from two vertically separated dendritic arbors, and the fourth group is purely vertical in orientation. A group of four tegmental cell types in the LMRA also send their dendrites into the efferent tracts of the torus, and into lamina IX. The torus is similar in complexity and number of cell types to the mammalian inferior colliculus. The large number of cell types in these midbrain sensory nuclei, compared to the number of afferent inputs (seven or more for the torus) is notable and may reflect the parcellation of function associated with the parallel processing of these inputs.

Afferent Pathways↗

PubMed1985

The effect of nerve activity on the distribution of synaptic vesicles.

Certain gymnotid fish (apteronotids) continuously emit a high-frequency electric-organ discharge and thus continuously drive their electroreceptor afferents at high rates. Electroreceptor afferents terminate in one lamina of the electrosensory lateral line lobe (ELL) and can be readily sampled. Normally these terminals have many small vesicles clustered adjacent to the presynaptic membrane. When afferent activity is blocked for 24 hr by an injection of tetrodotoxin (TTX) into the electroreceptor nerve, the density of vesicles adjacent to the synaptic membrane declines; the volume of the remaining vesicles increases. If the nerve of a TTX-treated fish is stimulated proximal to the injection site, these changes can be reversed. These results imply that the migration of vesicles toward the presynaptic membrane is influenced by the level of activity in the nerve.

Animals↗

PubMed1984

Localization of vitamin D-dependent calcium binding protein in the electrosensory and electromotor system of high frequency gymnotid fish.

Vitamin D-dependent calcium binding protein (D-CaBP) was localized in the brains of high frequency gymnotid fish. In birds and mammals this protein is seen in a variety of cell types including Purkinje cells, inferior olivary cells and CA1 pyramids of the hippocampus. This distribution has led us to speculate that D-CaBP may be important in buffering intracellular calcium, perhaps more specifically that calcium which enters the cell during dendritic calcium spikes. In the gymnotid fish D-CaBP was found in many of the same cell types in which it is also seen in birds and mammals. In addition, D-CaBP is specifically present in neurons which drive the electric organ (pacemaker and relay cells) and neurons within the electrosensory system which are phase-locked to the electric organ discharge (spherical and giant cells). Relay cells and giant cells have exceptionally high concentrations of D-CaBP. These cells do not exhibit calcium spikes and the role of their D-CaBP may be to regulate calcium released from intracellular stores.

Afferent Pathways↗

PubMed1983

Distribution of muscarinic receptors in the caudal cerebellum and electrosensory lateral line lobe of gymnotiform fish.

Muscarinic binding sites were found in the electrosensory lateral line lobe (ELLL) and vestibulo cerebellum (LC) of certain gymnotid fish; these binding sites were not present in significant numbers in the corpus cerebelli. Autoradiography of [3H]quinuclidinylbenzilate and [3H]propylbenzylcholine mustard binding confirmed these results and also demonstrated that, within the ELLL the region with muscarinic binding sites was coextensive with the region of cholinergic input. We did not find any evidence for nicotinic receptors (alpha-bungarotoxin binding) in ELLL, LC, or corpus cerebelli.

Animals↗

PubMed1983

The nucleus praeeminentialis: a Golgi study of a feedback center in the electrosensory system of gymnotid fish.

The cytoarchitecture of the dorsal nucleus praeeminentialis in two families of weakly electric fish (Eigenmannia viriscens and Apteronotus albifrons) was examined in both Nissl and Golgi material, and an attempt was made to correlate this information with our data from HRP studies on the afferent and efferent connections of this nucleus. The n. praeeminentialis is an isthmic structure located dorsolateral to the lateral lemniscus and anterior to the eminentia granularis--a subdivision of the archicerebellum of fish. The n. praeeminentialis can be divided into a large dorsal portion concerned with electroreception and a small ventral portion involved with the lateral line mechanoreception. The dorsal n. praeeminentialis consists of three parts: a pars medialis, a large pars principalis (p.P.) and a narrow pars lateralis. The p.P. presents three zones: a dorsal, a central, and a ventral zone, which are reciprocally and topographically connected with the zones of the electroreceptive lateral line lobe (ELLL), medial ELLL with ventral zone, central ELLL with central zone, and lateral ELLL with dorsal zone. Several types of projection cells are present in the n. praeeminentialis: (a) neurons that show preferential orientation of their long dendrites in relation to the afferent fiber systems, (b) cells with wide dendritic fields radiating in all directions, and (c) cells with small polarized dendritic fields toward the incoming ELLL afferents. Interneurons are also identified, showing different axonal ramification patterns. The afferent and efferent fiber systems linking the n. praeeminentialis to ELLL, lobus caudalis (L.C.), and torus semicircularis (T.S.d.) point to the important position of this nucleus in the feedback loop of the electrosensory pathway. The complex processing within this nucleus is reminiscent of the feedback loops in the auditory system.

Afferent Pathways↗

PubMed1982

Peripheral organization and central projections of the electrosensory nerves in gymnotiform fish.

The electrosensory system of weakly electric gymnotiform fish is described from the receptor distribution on the body surface to the termination of the primary afferents in the posterior lateral line lobe (PLLL). There are two types of electroreceptor(ampullary and tuberous) and a single type of lateral line mechanoreceptor (neuromast). Receptor counts in Apteronotus albifrons show that (1) neuromasts are distributed as in other teleosts; (2) ampullary receptors number 151 on one side of the head and 208 on one side of the body; (3) tuberous receptors were estimated to number 3,000-3,500 on one side of the head and 3,500-5,000 on one side of the body. The distribution of each receptor type is described. Each receptor is innervated by a single primary afferent. Electrosensory afferents have myelinated cell bodies in the ganglion of the anterior lateral line nerve (ALLN). The distribution of these ganglion cell diameters is strongly bimodal in Apteronotus and Eigenmannia: The smaller-diameter cells may be those which innervate ampullary electroreceptors, the larger-diameter tuberous electroreceptors. Transganglionic HRP transport techniques were used to determine the first-order connections of the anterior lateral line nerve in six species of gymnotiform fish. Small branches of the ALLN were labeled so as to determine the somatotopic organization in the PLLL. The PLLL is divided into four segments from medial to lateral, termed medial, centromedial, centrolateral, and lateral segments (Heiligenberg and Dye, '81). Representations of the head are found rostrally in each zone, and the trunk is mapped caudally in each zone. Thus there are four body maps in the PLLL. The medial segment receives ampullary input (Heiligenberg and Dye, '82) and maps the dorsoventral body axis mediolaterally, as does the tuberous centrolateral segment. The tuberous centromedial and lateral segments map the dorsoventral axis lateromedially. Thus the medial and centromedial segments meet belly to belly, the centromedial and centrolateral segments meet back to back, and the centrolateral and lateral segments meet belly to belly. Adjacent electrosensory maps within the PLLL are therefore always mirror images.

Afferent Pathways↗

PubMed1982

Efferent projections of the posterior lateral line lobe in gymnotiform fish.

The posterior lateral line lobe (PLLL) of gymnotoid fish has efferent projections to two midbrain regions: the nucleus praeeminentialis dorsalis (n.P.d.) and the torus semicircularis dorsalis (T.Sd.). Both ipsilateral and contralateral connections are present; the n.P. d. receives nearly equal input from both sides while the T.Sd. receives a stronger contralateral input. The PLLL projection to n.P.d. merely maps medial PLLL to ventral n.P.d. and lateral PLLL to dorsal n.P.d., thus preserving the separate topography and relative orientation of the four electrosensory maps found in the PLLL. Only PLLL pyramidal cells (basilar and nonbasilar pyramids) contribute to this projection. The four PLLL electrosensory maps converge onto T.Sd. so that they map the dorsal body surface onto medial T.Sd. and the ventral body surface onto lateral T.Sd. Pyramidal cells, spherical cells, and multipolar cells contribute to this projection. A small commissural connection links homologous segments of the PLLL; these fibers arise from polymorphic cells of the PLLL.

Animals↗