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L Maler

Publications and source records attributed to L Maler.

At least 55 records · Page 3Linked to original sources
PubMed1992

Zebrin II distinguishes the ampullary organ receptive map from the tuberous organ receptive maps during development in the teleost electrosensory lateral line lobe.

In weakly electric gymnotiform teleosts, monoclonal antibody anti-zebrin II recognizes developing pyramidal cells in the ampullary organ-receptive medial segment of the medullary electrosensory lateral line lobe (ELL) and in the mechanoreceptive nucleus medialis. Developing pyramidal cells in the remaining three tuberous organ-receptive lateral ELL segments are unreactive. These results suggest that certain biochemical features of the ELL ampullary organ-receptive medial segment are more similar to the nucleus medialis than to the tuberous organ-receptive ELL segments, and support the hypothesis that the ampullary system evolved from mechanosensory precursors.

Animals↗
PubMed1992

Anatomical organization of the hypophysiotrophic systems in the electric fish, Apteronotus leptorhynchus.

The organization of afferents to the pituitary was investigated by applying DiI crystals to the pituitary or pituitary stalk of the gymnotiform electric fish, Apteronotus leptorhynchus. Most hypophysiotrophic cells were found in the hypothalamus and were distributed throughout its rostrocaudal extent: nucleus preopticus periventricularis, pars anterior and posterior; suprachiasmatic nucleus; anterior, dorsal, ventral, lateral, and caudal hypothalamic nuclei; and nucleus tuberis lateralis, pars anterior and posterior. In addition a small number of retrogradely labeled cells were found in the ventral telencephalon (area ventralis, pars ventralis) and, most surprisingly, in a thalamic nucleus (nucleus centralis posterioris). The nucleus preopticus periventricularis pars posterior and the anterior hypothalamic nucleus appear to correspond to the parvicellular and magnocellular divisions of the nucleus preopticus of other teleosts. Integration of these results with immunohistochemical localization of monoamines and neuropeptides in the apteronotid brain suggests many homologies between the hypophysiotrophic nuclei of teleosts and other vertebrates, including mammals. Apteronotus communicates electrically during agonistic and sexual interactions. There are numerous anatomical links between the hypophysiotrophic systems and the brain areas related to electrocommunication.

Animal Communication↗
PubMed1992

Distribution of zebrin II in the gigantocerebellum of the mormyrid fish Gnathonemus petersii compared with other teleosts.

Immunocytochemistry has demonstrated unexpected heterogeneity among cerebellar Purkinje cells. For example, monoclonal antibody Mab anti-zebrin II reveals parasagittal bands of immunoreactive Purkinje cells in the mammalian cerebellum, but reveals a non-sagittal cerebellar compartmentation pattern in goldfish and gymnotiform fish. The present paper investigates the cerebellar compartmentation pattern, as reflected in the zebrin II distribution, in two other teleosts, the electric mormyrid fish Gnathonemus petersii with its large and regularly built gigantocerebellum, and the electrosensory osteoglossomorph teleost Xenomystis nigri, by using light as well as electron microscopic immunohistochemical techniques. Zebrin II is expressed only in Purkinje cells, where it is present in the cytoplasm of all neuronal compartments, including spines, distal and proximal dendrites, the cell body, and the initial part, as well as terminal boutons of the axon. Other types of cerebellar neurons, including the eurydendroid projection neurons, are zebrin II-negative. In Gnathonemus, zebrin II-positive Purkinje cells are present in the large caudolateral part of the valvula, in lobes C2, C3, and C4 of the corpus, and in the anterior as well as the posterior part of the caudal cerebellar lobe. Zebrin II-negative Purkinje cells are present in a continuous region encompassing the rostromedial part of the valvula, the lobus transitorius, lobe C1 and the ventral part of lobe C2, and in a small, lateral zone of the posterior part of the caudal lobe. In Xenomystis, all Purkinje cells, including those in the medial valvula and the posterior part of the caudal lobe, appear to react with mab anti-zebrin II. This more widespread distribution may be due to the presence of a second antigenic polypeptide in this species. On the basis of the present findings, it is concluded that the mormyrid lobus transitorius, lobe C1, and the ventral part of lobe C2 probably belong to the valvula, while the corpus is restricted to the dorsal part of lobe C2, lobe C3, and lobe C4. The functional significance of zebrin II expression for different subsets of teleostean Purkinje cells remains unclear, since comparisons of different teleosts reveal no general correlation with particular afferent or efferent connections, nor with special morphological features such as a dendritic palisade pattern or different arrangements of the Purkinje cell bodies. A comparison between mammals and teleosts suggests that a distinct parasagittal cerebellar zonation in teleosts is absent, and the major part of the teleostean cerebellum may be considered as a single (midsagittal) cerebellar zone, with about the same width as one mammalian parasagittal zone.

Animals↗
PubMed1991

Somatostatin-like immunoreactivity in the region of the prepacemaker nucleus in weakly electric knifefish, Eigenmannia: a quantitative analysis.

The diencephalic prepacemaker nucleus (PPn) is a bilateral cluster of neurons that controls frequency modulations of the otherwise very regular electric organ discharge cycle in weakly electric knifefish, Eigenmannia. Ultrastructural evidence had suggested that the action of excitatory and inhibitory synapses contacting PPn neurons is modulated by neuropeptides. In this investigation, we examined the distribution of somatostatin-like immunoreactive (S-IR) structures in the region of the PPn. In transverse sections, we found 5 bilateral S-IR structures in the region of the PPn: a 'dorsohorizontal stripe'; a 'lateral cell group'; a 'diagonal stripe'; a 'tubercular stripe'; and a 'hypothalamic stripe'. The dorsohorizontal stripe, consisting of S-IR fibers, terminals, and roughly 200 cell bodies unilaterally, stretches from the edge of the third ventricle at the thalamic dorsal-posterior nucleus and the central posterior nucleus approximately 400 microns laterally to the PPn. S-IR cell bodies show a distinct pattern of distribution within this stripe. Almost half of the somata are located within 50 microns of the ventricle. These ventricular cells are small and often densely clustered. Laterally, towards the PPn, the number of labelled cells decreases, whereas their size gradually increases. The lateral cell group consists of roughly 20 somata in the medial region of the subelectrosensorius nucleus. Fibers of the diagonal stripe travel from the hypothalamus dorsalis to the PPn. Fibers of the tubercular stripe originate from S-IR cell bodies in the medial zone of the periventricular nucleus of the posterior tuberculum and merge with the diagonal stripe. Fibers of the hypothalamic stripe connect the hypothalamus lateralis and the diagonal stripe. The density of immunolabelling in the hypothalamic stripe is significantly higher in mature than in immature females.

Animals↗
PubMed1991

Zebrin II immunoreactivity in the rat and in the weakly electric teleost Eigenmannia (gymnotiformes) reveals three modes of Purkinje cell development.

Monoclonal antibody (mab) anti-zebrin II recognizes a single 36-kD polypeptide in Purkinje cells in the rat and fish cerebellum. In the adult rat, zebrin II+ Purkinje cells form, in each hemicerebellum, seven parasagittal bands interposed by zebrin II- bands. We show that, in rats, immunoreactivity first appears caudally at postnatal day 5 and spreads; all Purkinje cells are labelled by postnatal day 12. Subsequently, immunoreactivity is selectively lost so that by day 18 the adult pattern of zebrin II+/-immunoreactive bands is created. This pattern indicates two types of Purkinje cells according to developmental trajectory, zebrin II-/+/-. In the adult gymnotiform teleost Eigenmannia, Purkinje cells in the corpus cerebelli (CCb), lateral valvula cerebelli (VCbl), and eminentia granularis anterior (EGa) are zebrin II+. Purkinje cells in the eminentia granularis posterior (EGp) and medialis (EGm) and the medial valvula cerebelli (VCbm) are zebrin II-. Zebrin II antigenicity is first present at 6 days postspawning (P6) in the EGa and at P8 in the CCb. In the valvula, labelling does not appear until P29. Immunoreactivity in the CCb, VCBl, and the EGa persists in the adult, whereas in the VCbm Purkinje cells become zebrin II- before reaching adulthood. These developmental histories (zebrin II-/+ and zebrin II-/+/-) correspond to the patterns of Purkinje cell development in mammals. Additionally, Eigenmannia has a third class of Purkinje cells, in the EGp and EGm, that never express zebrin II immunoreactivity, indicating that zebrin II expression is not an obligatory feature of Purkinje cell development in all vertebrates.

Animals↗
PubMed1991

In situ hybridization of putative somatostatin mRNA in the brain of electric gymnotiform fish.

The distribution of somatostatin mRNA in the brain of Apteronotus leptorhynchus, a weakly electric gymnotiform fish, has been mapped by employing in situ hybridization with an oligodeoxynucleotide probe corresponding to nucleotides 1-26 of catfish somatostatin mRNA; this probe was end-labelled with digoxigenin. Most labelled cell groups were found in the telencephalon, followed by the diencephalon. This distribution is in good agreement with previous immunohistochemical investigations. In the complex of the diencephalic central-posterior/prepacemaker nucleus, a cluster of neurons controlling electrocommunicatory behavior, somatostatin mRNA could be detected only in lateral aspects, although many medial cells also stain positively with immunohistochemical techniques. This difference may be related to the growth of these neurons during adulthood.

Animals↗
PubMed1990

Development of the electrosensory nervous system of Eigenmannia (gymnotiformes): II. The electrosensory lateral line lobe, midbrain, and cerebellum.

The somatotopically and functionally organized electrosensory system of gymnotiform teleosts provides a model for the study of the formation of ordered nerve connections. This paper describes the development of the major electrosensory nuclei within the hind- and midbrain. All three main electrosensory nuclei--the electrosensory lateral line lobe (ELL), dorsal torus semicircularis (torus), and tectum--grow by adding cells at their caudolateral borders. Toral and tectal germinal zones arise from lateral ventricular outpocketings that either completely or partially close by maturity. In the ELL before day 5 postspawning, germinal cells form from an initial periventricular germinal zone, then migrate to the caudolateral border of the hindbrain and begin dividing. The ELL grows from two main germinal zones, one for the medial segment, and one for the three lateral tuberous segments. Within each ELL germinal zone, newly formed cells arise from two areas: granular cells arise from a ventral subzone, pyramidal cells are generated more dorsally. Granular cells remain in situ, whereas pyramidal cells may migrate rostromedially. Cells begin differentiating as soon as they are formed. Spherical and pyramidal cells send ascending axons into the internal plexiform layer by day 14-18 and the ELL gradually begins to assume its mature laminar appearance. The ELL grows caudally, preceding the caudal lobe of the cerebellum, which will eventually lie over and fuse with it. Primary electrosensory afferents enter the ELL by day 6; incoming afferents form four fascicles within the ELL, suggesting the formation of separate ELL segments. Unlabelled projections between labelled fields from a single nerve branch filled with HRP on day 7 suggest that somatotopic order is already present at this early age. In the periphery, receptor addition is unordered, occurring along nerve branch pathways. Meanwhile the ELL adds cells in an orderly fashion at its caudolateral border. This suggests that primary afferents shift position caudally with growth to maintain their somatotopic relationships. Because all three central nuclei are in topographic register and grow by adding cells caudally, during growth ELL efferents to the torus and toral efferents to the tectum may utilize passive mechanisms, such as fiber-fiber interactions, to guide axons.

Animals↗
PubMed1990

Interspecific variation in the projection of primary afferents onto the electrosensory lateral line lobe of weakly electric teleosts: different solutions to the same mapping problem.

We demonstrate that preterminal axons composing the primary afferent projection onto the four somatotopically organized electrosensory lateral line lobe (ELL) segments in weakly electric gymnotiform teleosts course in fundamentally different directions in the most commonly studied species. Afferents enter the deep fiber layer (dfl) of the ELL and course in variable, but species-specific, directions within a horizontal plane before turning dorsally to terminate within the deep neuropil layer of the ELL (dnl). Among the species considered here, apteronotids exhibit the tightest projection pattern. Afferents enter the rostral ELL from the anterior lateral line nerve ganglion (ALLNG) in a nonsomatotopic fashion. As they course horizontally, these fibers undergo a rostrocaudal somatotopic sorting along the ventrolateral border of the dfl, then turn within a horizontal plane to course medially across the ELL segments. These medially coursing horizontal fibers are sorted: they form sublaminae according to the nerve branch containing their peripheral axon. Horizontal axons then turn dorsally, form fascicles, and terminate within the dnl. Within the dorsal fascicles, axons run directly into the dnl with little deviation, and their terminal fields exhibit no appreciable spread. In sternopygids, dfl horizontal fibers course in directions orthogonal to those in apteronotids. Fibers enter the rostral ELL and course medially across segments before turning caudally within segments. Unlike apteronotids, sternopygid horizontal fibers do not sort tightly by nerve branch. As horizontal axons turn dorsally they also form tight fascicles. But rather than terminating directly and without spreading, as in apteronotids, sternopygid fibers disperse from these fascicles and become sorted horizontally a second time prior to terminating in the dnl.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Structural and functional organization of a diencephalic sensory-motor interface in the gymnotiform fish, Eigenmannia.

The diencephalic nucleus electrosensorius (nE) of gymnotiform fish comprises a series of finely tuned neuronal filters for control of the jamming avoidance response (JAR) and probably other electromotor tasks as well. The nE receives electrosensory input from the dorsal torus semicircularis (TSd) and octavolateral input from the ventral torus (TSv). The nE, in turn, projects to various hypothalamic and thalamic nuclei, including the prepacemaker nucleus (PPn), which can modulate the frequency of electric organ discharges (EODs) via its unique input to the medullary pacemaker nucleus. Four subdivisions of the nE can now be recognized: 1) The beat-related area (nEb)--a rostral cluster of tightly packed cells which receives TSd input and projects to the inferior lobe, anterior tuberal nucleus, anterior thalamic nucleus, central posterior thalamic nucleus, and PPn. The nEb contains neurons responsive to beat patterns caused by jamming stimuli. Stimulation of the nEb with L-glutamate, however, fails to induce any EOD-frequency shift. 2) The area causing EOD-frequency rises (nE increases)--a horizontal band of cells at the dorsal aspect of the caudal nE which receives TSd input and projects to the PPn and vicinity and to the cerebellum; nE increases stimulation induces slow EOD-frequency rises characteristic of the JAR. Responses of these cells to jamming stimuli are not yet known. 3) The area causing EOD-frequency falls (nE decreases)--a horizontal band of cells at the ventral aspect of the caudal nE which receives TSd input and projects only to the PPn and vicinity; nE decreases stimulation induces slow EOD-frequency falls characteristic of the JAR. The responses of these cells to jamming stimuli are not yet known. 4) The acousticolateral region (nEar)--a complex medial region of the nE which receives input predominantly from the ventral torus and projects to the inferior lobe, anterior tuberal nucleus, central posterior thalamic nucleus, PPn, and cerebellum; the sensory and motor properties of this region are not known in detail, although auditory and mechanosensory responses have been recorded here. Projections to the PPn and its vicinity suggest direct control of electromotor behaviors by the nE, whereas thalamic and hypothalamic projections may provide a substrate for electrosensory influences on neuroendocrine and motivational control centers. The optic tectum projects strongly to the pretectum and various other diencephalic nuclei in the vicinity of the nE, but it does not innervate the nE itself. Accordingly, ablation of the tectum does not affect the performance of the JAR.

Animals↗
PubMed1990

Catecholaminergic systems in the brain of a gymnotiform teleost fish: an immunohistochemical study.

The localization of catecholamines (CA) in the brain of Apteronotus leptorhynchus was studied with immunohistochemical techniques using antibodies to the enzymes tyrosine hydroxylase (TH), dopamine B-hydroxylase (DBH), phenylethanolamine-N-methyltransferase (PNMT), and the neurotransmitter dopamine (DA). Telencephalic TH and DA immunoreactive (ir) neurons were located in the following structures: olfactory bulb, area ventralis telencephali partes ventralis, centralis, dorsalis, and intermediate. Diencephalic TH ir neurons were distributed in: nucleus preopticus periventricularis pars anterior, floor of preoptic recess, n. suprachiasmaticus, n. preopticus periventricularis pars posterior, n. anterior periventricularis, area ventralis lateralis, rostral region of posterior periventricular nucleus (paraventricular organ of other authors), periventricular nucleus of posterior tuberculum, n. recessus lateralis, n. tuberis lateralis pars anterior, and n. tuberis posterior. Although most diencephalic TH ir structures were also DAir, the posterior periventricular nucleus, n. recessus lateralis pars medialis, n. recessus posterioris, and ventral region of nucleus lateralis tuberis pars anterior showed differences in the distribution of TH and DA immunoreactivity. The rhombencephalic structures contained cell groups with different combinations of catecholamines as follows: TH and DBH ir neurons in the isthmic tegmentum (locus coeruleus); TH and DBH ir cells in the rostral medullary tegmentum ventral to VIIth nerve; TH and PNMT ir cells in the sensory nucleus of the vagus nerve; TH, DBH, and PNMT ir cells in the dorsal medullary tegmentum, TH and DBH ir cells in the dorsomedian postobecular region, ventral to the descending trigeminal tract and lateral to the central canal at medullospinal levels. This study shows that: (1) with few exceptions TH and DA ir coincides, (2) gymnotiforms possess similar DBH ir rhombencephalic groups, but additional telencephalic and rhombencephalic TH ir groups, and PNMT ir cells that were not reported previously in teleosts, and (3) the presence of CAergic fibers in the electrosensory system supports findings of their modulatory function in communication and aggression.

Animals↗
PubMed1990

Zebrin II: a polypeptide antigen expressed selectively by Purkinje cells reveals compartments in rat and fish cerebellum.

Monoclonal antibody mab-zebrin II was generated against a crude homogenate of cerebellum and electrosensory lateral line lobe from the weakly electric fish Apteronotus leptorhynchus. On Western blots of fish cerebellar proteins, mab-zebrin II recognizes a single polypeptide antigen of apparent molecular weight 36 kD. Immunocytochemistry of apteronotid brains reveals that zebrin II immunoreactivity is confined exclusively to Purkinje cells in the corpus cerebelli, lateral valvula cerebelli, and the eminentia granularis anterior. Other Purkinje cells, in the medial valvula cerebelli and eminentia granularis posterior, are not zebrin II immunoreactive. Immunoreactive Purkinje cells are stained completely, including dendrites, axons, and somata. The antigen seems to be absent only from the nucleus. A similar distribution is seen in catfish, goldfish, and a mormyrid fish. Zebrin II immunoreactivity is also found in the rat cerebellum. Western blotting of rat cerebellar proteins reveals a single immunoreactive polypeptide, with apparent molecular weight 36 kD, as in the fish. Also as in the fish, staining in the adult rat cerebellum is confined to a subset of Purkinje cells. Peroxidase reaction product is deposited throughout the immunoreactive Purkinje cells with the exception of the nucleus. No other cells in the cerebellum express zebrin II. At higher antibody concentrations, a weak glial cross reactivity is seen in most other brain regions: we believe that this is probably nonspecific. Zebrin II+ Purkinje cells are clustered together to form roughly parasagittal bands interposed by similar nonimmunoreactive clusters. In all there are 7 zebrin II+ and 7 zebrin II- compartments in each hemicerebellum. One immunoreactive band is adjacent to the midline; two others are disposed laterally to each side in the vermis; there is a paravermal band; and finally three more bands are identified in each hemisphere. Both in number and position, these compartments correspond precisely to the bands revealed by using another antibody, mabQ113 (anti-zebrin I). In both fish and rat the compartmentation revealed by zebrin II immunocytochemistry is related to the organization of cerebellar afferent and efferent projections and may provide clues as to the fundamental architecture of the vertebrate cerebellum.

Animals↗
PubMed1989

Gap junction protein in weakly electric fish (Gymnotide): immunohistochemical localization with emphasis on structures of the electrosensory system.

Electrotonic transmission via gap junctions appears to be essential for both the relay and integration of information in nuclear groups involved in the electrolocation and electrocommunication systems of weakly electric fish. An affinity-purified antibody against the 27 kD gap-junctional polypeptide (GJP) from rat liver was used to determine immunohistochemically the distribution of GJP-immunoreactivity (GJP-IR) in electrosensory structures and some other brain regions of the gymnotiform fish, Apteronotus leptorhynchus. At the ultrastructural level, immunolabelling with this antibody was localized, in part, to neuronal and glial gap junctions where it was assumed to recognize a junctional polypeptide. By light microscopy, the vast majority of immunoreactive elements appeared either as fine puncta or as varicosities along fibers that exhibited immunostained intervaricose segments. Diffuse immunoreactivity within cell bodies was rare, being most evident in giant relay neurons and presumptive glial cells within the pacemaker nucleus and in neurons within the posterior raphe nucleus. The distribution of punctate and fibrous GJP-IR was remarkably heterogeneous with respect to density; large areas of the forebrain and most major fiber tracts were nearly devoid of immunoreactivity, whereas concentrations of puncta delineating patches within the inferior lobe of the hypothalamus and the vagal sensory nucleus were so dense as to appear as uniform deposition of immunoperoxidase reaction product at low magnification. Some structures known to be associated with the electrosensory system, including the nucleus electrosensorius and nucleus praeeminentialis, were among the brain regions containing the highest concentrations of immunoreactivity. At the cellular level, expected patterns of GJP-IR were observed in the pacemaker nucleus, torus semicircularis, and electrosensory lateral line lobe. In each of these structures punctate immunoreactivity was seen in apposition to cell bodies or dendrites of neurons known to receive gap junction contacts. In addition, the dendrites of neurons within the prepacemaker nucleus were laden with a striking array of puncta, suggesting that interactions via gap junctions may be a significant feature of these neurons. These immunohistochemical results are consistent with previous electrophysiological and ultrastructural observations pointing to the importance of electrotonic communication in the electrosensory system of weakly electric fish, and suggest that gap junctions may also contribute to neural transmission in central nervous system related to other functions in these teleosts.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1989

Ganglion cell arrangement and axonal trajectories in the anterior lateral line nerve of the weakly electric fish Apteronotus leptorhynchus (Gymnotiformes).

To determine the organizational principles underlying the peripheral electrosensory nervous system of weakly electric gymnotiform teleosts we labelled each of the four anterior lateral line nerve branches with HRP. We determined the position of labelled cell bodies within the ganglion and followed anterogradely filled fibers to their termination sites in one of the four somatotopic maps in the electroreceptive lateral line lobe (ELL). Within the ganglion, cell bodies exhibit a loose somatotopy based on nerve branch position: trunk electroreceptors have their cell bodies located in the caudal ganglion; cell bodies to the head receptors are rostral. Cell bodies to the head exhibit a rough dorsoventral polarity, supraorbital cells tend to be located dorsally, infraorbital cells centrally, and mandibular cells ventrally. Despite this general somatotopy there is substantial overlap (up to 30%) of cell bodies among regions. There appears to be no rostrocaudal topography within nerve branch regions. Iontophoretic WGA-HRP injected into the medial segment of the ELL retrogradely labelled cell bodies that innervate ampullary organs. These cell bodies were dispersed throughout the ganglion, indicating that cell bodies do not cluster by receptor type. Peripherally directed axons from the ganglion appear to undergo an active reorganization in order to form the nerve branches. Within nerve branches, axons to a particular area of skin do not cluster together. Centrally from the ganglion, axons retain the position of their cell body until they reach the ELL border. Once in the ELL, fibers become sorted in the deep fiber layer according to receptor type and the map they terminate in. This reorganization involves rearrangement of fascicles and axons within fascicles. In toto, proceeding from peripheral to central, the electrosensory periphery loses at least a portion of its receptor topography in the distal nerve and ganglion and then acquires both a functional and somatotopic organization after reaching the ELL; conceptually it is torn down and rebuilt again. From an ontogenetic perspective, axonal growth occurs from the ganglion outward; the fact that ganglion cell bodies are not highly organized while the receptors they innervate and their central processes are suggests that active axonal guidance mechanisms are involved.

Animals↗
PubMed1989

Receptor position, not nerve branch, determines electroreceptor somatotopy in the gymnotiform fish (Apteronotus leptorhynchus).

The supraorbital (SO) nerve branch of some weakly electric teleosts innervates electroreceptors on the entire rostral snout and therefore excludes the infraorbital (IO) branch. A ventral twig of SO innervates the ventral snout (normally IO territory) and projects into the electroreceptive lateral line lobe in an IO pattern. This suggests that afferents to adjacent snout receptors can take widely divergent pathways (different nerve branches) to the electrosensory lateral line lobe (ELL) yet retain somatotopy centrally. We conclude: (1) that there is intrabranch somatotopy within these nerves, and (2) that receptor position, not nerve branch, determines ELL somatotopy.

Animals↗
PubMed1989

GABAergic inhibition shapes temporal and spatial response properties of pyramidal cells in the electrosensory lateral line lobe of gymnotiform fish.

1. The amplitude-coding pyramidal neurons of the first-order nucleus in weakly electric gymnotiform fish (Eigenmannia), the electrosensory lateral line lobe (ELL), exhibit 2 major physiological transformations of primary afferent input. Pyramidal cells rapidly adapt to a step change in amplitude, and they have a center/surround receptive-field organization. This study examined the physiological role of GABAergic inhibition on pyramidal cells. GABAergic synapses onto the somata of pyramidal cells primarily originate from granule-cell interneurons along with descending input. 2. Pyramidal cells fall into two physiologically distinct categories: E units, which are excited by a rise in stimulus amplitude, and I units, which are inhibited by a rise in stimulus amplitude. Microiontophoretic application of bicuculline methiodide onto both types of pyramidal cells increased the time constant of adaptation, defined as the time required for the neuron's response to decay to 37% of its maximum value, by 70-90%. The peak firing rate of E units to a step increase in stimulus amplitude increased by 49%, while the firing rate of I units did not change significantly. 3. Bicuculline application demonstrated that GABAergic inhibition may contribute to the strict segregation of E and I response properties. In the presence of bicuculline, many E units (normally excited only by stimulus amplitude increases) became excited by both increases and decreases; many I units (normally excited only by amplitude decreases) also became excited to increases. 4. The size of the excitatory receptive-field of E units was not affected by bicuculline, although response magnitude increased. The inhibitory surround increased in spatial extent by 175% with bicuculline administration. Neither the size of the I unit receptive-field center nor the response magnitude changed in the presence of bicuculline. The antagonistic surround of I units, however, increased by 49%. 5. The anatomy of the ELL is well understood (see Carr and Maler 1986). The physiological results obtained in this study, along with the results of Bastian (1986a, b), further our understanding of the functional role of the ELL circuitry. Our results suggest that spatial and temporal response properties of pyramidal cells are regulated by different but interacting inhibitory interneurons, some of which use GABA as a neurotransmitter. The activity of these interneurons is in turn controlled by descending feedback systems.

Action Potentials↗
PubMed1988

Anatomical and functional organization of the prepacemaker nucleus in gymnotiform electric fish: the accommodation of two behaviors in one nucleus.

The diencephalic prepacemaker nucleus (PPn) of gymnotiform electric fish projects to the medullary pacemaker nucleus and modulates its regular firing frequency. Each firing of the pacemaker, in turn, drives an electric organ discharge (EOD). Two types of PPn neurons were retrogradely labeled from the pacemaker with HRP in Eigenmannia and Apteronotus. In both species, smaller ovoidal cells were found in the dorsomedial part of the PPn (PPn-G), and larger multipolar cells were found in the ventrolateral part of the PPn (PPn-C). This morphological distinction between the two subnuclei in the PPn was paralleled by a functional dichotomy. Microiontophoresis of L-glutamate in the PPn-G of both species elicited slow and gradual accelerations of EOD frequency characterized by a time constant on the order of seconds. The elicited frequency modulations were similar to those observed during the jamming avoidance response and during courtship. Glutamate stimulation of the PPn-C, in contrast, produced fast and abrupt frequency modulations characterized by a time constant on the order of milliseconds. These abrupt modulations resembled "chirps" observed during courtship and aggression. Similar behavior was produced by intracellular current injection into a PPn-C neuron of Apteronotus, and intracellular labeling of this neuron with Lucifer Yellow revealed a multipolar PPn-C neuron similar to those retrogradely labeled with HRP.

Action Potentials↗
PubMed1988

Morphological and electrophysiological properties of a novel in vitro preparation: the electrosensory lateral line lobe brain slice.

An in vitro brain slice preparation of the electrosensory lateral line lobe (ELL) of weakly electric fish was developed. The morphology of this slice was studied and revealed that most ELL neurons and synapses retained their normal appearance for at least 10 h in vitro. The electrophysiological characteristics of the main ELL output neurons, the pyramidal cells, were measured. Extracellular electrode recordings demonstrated that pyramidal cells are capable of spontaneous, rhythmic spike activity. Intracellular recordings showed that intrinsic oscillations in membrane potential underlie the bursting behavior. The majority of pyramidal cells respond to depolarizing current pulses with an initial lag in spike firing followed by a non-accommodating, higher frequency spike train. Time and voltage-dependent properties of pyramidal cell responsiveness, as well as the effects of pharmacological blocking agents indicated that rhythmic activity and repetitive firing are dominated by a persistent, subthreshold sodium conductance (gNa) which activates at depolarizing levels and is the driving force behind the membrane potential oscillations and the sustained (non-accommodating) spike firing. In addition, a transient, outward potassium conductance (gA) is responsible for the lag in spike firing by acting as a 'brake' during the initial 50-200 ms of a depolarizing stimulus. Calcium currents and calcium-dependent potassium conductance add to the interval between spontaneous bursts but appear insufficient for spike frequency accommodation. The in vitro behaviour of pyramidal cells differs substantially from the behaviour of the same cell type in vivo. These observations raise possibilities that intrinsic membrane properties together with local synaptic interactions may regulate pyramidal cell responsiveness.

Action Potentials↗