Biomedical subjects

R L Meyer

Publications and source records attributed to R L Meyer.

At least 55 records · Page 3Linked to original sources

PubMed1991

Antiserum to an inhibin alpha-chain peptide neutralizes inhibin bioactivity and increases ovulation rate in sheep.

A synthetic fragment representing the N-terminal 25 amino acid residues of the alpha-subunit of ovine inhibin (alpha-IF) was coupled to human alpha-globulin (h alpha-G) and used as an antigen. In Exp. 1, ovine antiserum generated against alpha-IF-h alpha-G was shown in vitro to neutralize inhibin bioactivity contained in ovine follicular fluid. In Exp. 2, 18 lambs were immunized with .3, .6 and 1.2 mg alpha-IF-h alpha-G or equivalent doses of h alpha-G. Antibody titer to alpha-IF was detected only in serum from lambs immunized against alpha-IF-h alpha-G and was first detected 27 +/- 2 d after primary immunization. Thereafter, antibody titers increased steadily. The degree of antibody responses was unrelated to antigen dose and differed among lambs. Plasma FSH concentrations were unchanged, whereas LH concentrations were lower (P less than .001) in sheep immunized against alpha-IF-h alpha-G. Ovulation rate was increased (3.5 +/- .5 vs 1.5 +/- .1; P less than .01) in lambs immunized against alpha-IF-h alpha-G. Ovulation rate was similar among animals receiving different antigen doses and increased with time after primary immunization (P less than .01). At estrous periods occurring approximately 34, 50, 74 and 107 d after primary immunization, respective ovulation rates were 157, 169, 207 and 450% of control values. Ovulation rate and antibody titer were correlated positively (pooled r = .95; P less than .01) within lambs. In Exp. 3, three lambs were immunized with .25 mg unconjugated alpha-IF; this was nonantigenic. In conclusion, the use of a synthetic fragment of the alpha-subunit of ovine inhibin as a hapten elicits an antibody capable of neutralizing inhibin bioactivity in vitro and increasing ovulation rate in vivo.

Alpha-Globulins↗

PubMed1990

Pharmacologic evidence for NMDA, APB and kainate/quisqualate retinotectal transmission in the isolated whole tectum of goldfish.

The optic tectum of goldfish with intact optic and toral marginal fiber tracts was isolated in a perfusion chamber where the effectiveness of antagonists was tested on synaptic field potential responses to stimulation of each afferent system. There were 3 main conclusions about excitatory synapses. First, monosynaptic activation of retinotectal synapses was not detectably antagonized by D-tubocurarine, implying there is no nicotinic cholinergic component to optic transmission nor strong cholinergic gating of optic terminals. Second, a significant component of retinotectal transmission was shown to be mediated by kainate and quisqualate receptors since 6,7-dinitroquinoxaline-2,3-dione and kynurenate strongly suppressed the optic field potential. In addition, activation of these synapses involves two previously undescribed N-methyl-D-aspartate (NMDA) and APB receptor subtypes since optic field potentials were partially suppressed by 2-amino-5-phosphonovalerate (APV), 2-amino-4-phosphonobutyrate (APB) and MK-801. This is the first evidence that APB receptors exist in the visual system central to the retina. Together, these results are consistent with the possibility that retinal ganglion cells use multiple glutamate receptor subtypes. Third, the optic tectum contains a population of intrinsic glutaminergic synapses activated by a non-optic input, the marginal fibers, which can be suppressed by both APV and kynurenate. The existence of tectal NMDA receptors which are not at primary optic synapses implies that APV used to interfere with rearrangement of optic fibers during development may act not only at afferent synapses but also at a more central component of the circuit.

Afferent Pathways↗

PubMed1990

Ocular dominance stripe formation by regenerated isogenic double temporal retina in Xenopus laevis.

In lower vertebrates such as frogs and fish, long ocular dominance stripes with anterior-posterior (A-P) orientation can be produced by causing both eyes to innervate one optic tectum during the course of development. Similar experiments on adult animals usually produce patches rather than stripes. During development, new retinal fibers from the nasal retina segregate into appropriate stripes at the growing edge of the posterior (P) tectum while new temporal fibers segregate at the non-growing anterior (A) tectal edge. Fiber segregation into long A-P oriented stripes might depend upon a template produced by new nasal fibers initiating stripe orientation in the vicinity of new tectal cells; new nasal fibers would orient to the nascent (posterior) edge of the template while temporal fibers would orient to the anterior (non-growing) end of the template. To test the dependence of stripe formation on the matching of nascent retinal cells with nascent tectal cells, we compared stripe orientation in animals with isogenic double nasal innervation and isogenic double temporal innervation of the tectum. In double nasal innervation, the oldest retinal cells innervate the anterior tectum; new fibers from the entire retinal periphery always innervate the newest tectal cells at the posterior tectum. Stripes are oriented A-P, consistent with a maturation front model. In contrast, the oldest retinal cells innervate the newest (posterior) tectal cells in double temporal innervation of the tectum; the growing retinal periphery innervates the non-growing anterior tectum. Stripes are also oriented A-P, indicating that the production of long stripes does not depend upon maturation front matching of nascent retinal fibers and nascent tectal cells.

Animals↗

PubMed1990

Rapid initiation of neurite outgrowth onto laminin from explants of adult mouse retina induced by optic nerve crush.

One optic nerve of an adult mouse was crushed in the orbit. After 8 days, both retinas were explanted onto laminin-coated coverslips. Within 24 h, neurites grew out onto this substrate from explants with prior crush and by 48 h two-thirds of explants had neurites. On polylysine or plain glass, outgrowth was generally not seen until 48 h and this was significantly reduced compared to laminin. Explants without optic nerve crush did not extend neurites until about 5 days later. We suggest that axotomy induces a time-dependent regenerative response in adult mammalian retinal ganglion cells which includes the expression of laminin responsiveness.

Animals↗

PubMed1989

Glutamate-immunoreactivity in the retina and optic tectum of goldfish.

Glutamate was immunohistochemically localized in the goldfish retina and tectum at the light and electron microscopic (E.M.) levels using double affinity purified antisera against glutaraldehyde conjugated L-glutamate. In retina, glutamate-immunoreactivity (Glu+) was observed in cone inner segments, cone pedicles, bipolar cells, a small number of amacrine cells and the majority of cells in the ganglion cell layer. The latter were shown to be ganglion cells by simultaneous retrograde labeling. Centrally, Glu+ was observed in axons in the optic nerve and tract, and in stratum opticum and stratum fibrosum et griseum superficialis (SFGS) of the tectum. The Glu+ in the optic pathway disappeared four days after optic denervation and was restored by regeneration without affecting the Glu+ of intrinsic tectal neurons. In tectum, Glu+ was also observed in torus longitudinalis granule cells, toral terminals in stratum marginale, some pyramidal neurons in the SFGS, multipolar and fusiform neurons in stratum griseum centrale, large multipolar and pyriform projection neurons in stratum album centrale, and many periventricular neurons. Glu+ was also localized within unidentified puncta throughout the tectum and within radially oriented dendrites of periventricular neurons. At the E.M. level, a variety of Glu+ terminals were observed. Glu+ toral terminals formed axospinous synapses with dendritic spines of pyramidal neurons. Ultrastructurally identifiable Glu+ putative optic terminals formed synapses with either Glu+ or Glu- dendritic profiles, and with Glu- vesicle-containing profiles, presumed to be GABAergic. These findings are consistent with the hypothesis that a number of intrinsic and projection neurons in the goldfish retinotectal system, including most ganglion cells, may use glutamate as a neurotransmitter.

Animals↗

PubMed1989

The growth of axons in three-dimensional astrocyte cultures.

The environment of the adult central nervous system (CNS) does not support axon regeneration. We have been unable to replicate this behaviour using monolayer cultures of glia, so we have developed a technique for three dimensional culture of glial cells. We have examined the growth of axons from embryonic and postnatal retina and dorsal root ganglia (DRG's) through purified three-dimensional astrocyte cultures. Neither postnatal DRG's nor adult retina were able to grow axons through astrocytes from cultures 3 weeks or more old, although some DRG axons grew in astrocyte cultures which were 10 days or less old. However axons from embryonic DRG's and retina grew axons profusely into even elderly astrocyte cultures. All the tissues grew axons into three-dimensional Schwann cell cultures. The behaviour of axons in three-dimensional glial cultures therefore reproduces the behaviour of axons in vivo.

Age Factors↗

PubMed1989

Normal numbers of retinotectal synapses during the activity-sensitive period of optic regeneration in goldfish: HRP-EM evidence implicating synapse rearrangement and collateral elimination during map refinement.

Optic and nonoptic fibers and synapses were counted in the primary optic innervation layer (S-SO-SFGS) in anteromedial tectum in normal goldfish and in fish 30, 60, and 240 d after the optic nerve was crushed. A newly developed "cold-fill" HRP-labeling protocol was used to label optic afferents for electron microscopy, and counts were then made on EM photomontages of columns through the HRP-labeled S-SO-SFGS. Normal numbers of retinotectal synapses were present at 30 d regeneration, at a time when activity-dependent refinement of the optic projection is incomplete. Normal numbers were also found at 60 and 240 d, when refinement is largely completed. In contrast to this constancy in optic synapse numbers, there was nearly 10 times the normal number of optic fibers in the SFGS at 30 d, and these were reduced by 50% at 60 d, remaining over 4 times normal at 240 d. These findings imply extensive rearrangement of optic synapses during map refinement. They also indicate that synapse rearrangement is associated with the elimination of optic collaterals.

Animals↗

PubMed1989

Impulse blockade by intraocular tetrodotoxin during optic regeneration in goldfish: HRP-EM evidence that the formation of normal numbers of optic synapses and the elimination of exuberant optic fibers is activity independent.

Optic fibers and synapses labeled with HRP were counted in the primary optic innervation layer of tectum after continuously blocking visual impulse activity with TTX during regeneration. Normal numbers of optic and nonoptic fibers and synapses were found at both 30 and 60 d, and key ultrastructural features of optic afferents such as fiber fasciculation, myelination, terminal clustering, synaptogenesis onto different classes of postsynaptic targets and general morphology were not notably affected by impulse blockade. These findings indicate that during regeneration the normal proliferation and elimination of optic fibers and the formation of normal numbers of optic synapses are not regulated by activity and are consistent with a pattern formation role for impulse activity rather than a trophic one.

Animals↗

PubMed1988

Laminar and sublaminar ultracytochemical localization of cytochrome oxidase in the optic tectum of normal goldfish.

Distinct laminae and sublaminae in the goldfish optic tectum exhibit substantial differences in cytochrome oxidase (C.O.) reactivity. To determine whether these differences are associated with differential reactivity of different neuronal profiles, each tectal sublamina was examined at the ultrastructural level following C.O. treatment. The greatest abundance of darkly reactive mitochondria was found in the optically innervated layers within both pre- and postsynaptic profiles in correspondence with the most intense staining of these layers at the light microscopic level. Many reactive mitochondria were localized within terminals that were presumed to be optic on the basis of cytological criteria or were shown to be optic by filling optic fibers with HRP and processing so as to simultaneously demonstrate both mitochondrial C.O. reactivity and HRP labeling. These optic terminals tended to differ from each other in size and level of reactivity. The largest terminals were located within sublamina d of the stratum fibrosum et griseum superficials (SFGSd), and these were the most intensely reactive and contained the greatest number of darkly reactive mitochondria. Medium-sized terminals were found within sublaminae SFGSa, SFGSb, and a and c of the stratum album centrale (SACa,c). These were also darkly reactive but contained fewer mitochondria. Other medium-to-small optic terminals were found in stratum opticum a and b (60a,b), SFGSb, SFGSc, and stratum griseum centrale c (SGCc). These typically contained fewer mitochondria that also tended to be relatively less reactive, although darkly reactive mitochondria were also present. We suggest that the metalbolic differences within optic terminals of different size and sublaminar stratification arise from different ganglion cell classes and that the different optic layers of tectum are functionally substratified. As expected, darkly reactive mitochondria were most abundant in th intensely stained sublaminae, which included the optic lamina SFGS and nonoptic sublamina SGCa, and they were found not only within optic terminals but also within dendrites, presynaptic dendrites, and nonoptic terminals as well. Glial processes tended to contain less reactive mitochondria. The most prominent of the nonoptic terminals were the large-diameter P1 terminals, which contained pleomorphic vesicles and formed symmetric (presumed inhibitory) synapses. In stratum marginale most of the darkly reactive mitochondria were localized within dendrites. In the rest of the tectal layers most of the darkly reactive mitochondria were found in both presynaptic terminals and dendrites.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1988

Laminar histochemical and cytochemical localization of cytochrome oxidase in the goldfish retina and optic tectum in response to deafferentation and during regeneration.

Cytochrome oxidase (C.O.) histochemistry and cytochemistry were used to examine the effects of optic denervation and subsequent optic fiber regeneration on oxidative metabolism in the retina and optic tectum of the goldfish. In the tectum, there was a dramatic and rapid decrease in C.O. activity within the optic layers 3-4 days after contralateral eye removal or optic nerve crush. At the E.M. level this was correlated with an initial decrease in mitochondrial reactivity within optic terminals followed by the subsequent degradation of mitochondria and phagocytosis of optic terminals. By 1 month after optic nerve crush, the entire tectum was reinnervated. However, the normal dark reactivity of the stratum fibrosum et griseum superficialis (SFGS), the main optic innervation layer, was not restored until after 3-4 months postcrush. The normal intense reactivity of the large-diameter optic axons and terminals at the bottom of the SFGS required an even longer period, about 7-8 months, for full recovery. The delayed restoration of C.O. reactivity was not due to a delay in synaptogenesis or in mitochondrial accumulation within optic terminals but to a delay in the maturation of mitochondrial reactivity. Following regeneration, the normal sublaminar stratification of C.O. bands was reestablished, suggesting that metabolically distinct classes of optic fibers may reinnervate at their original sublaminae. By using a distinct and persistent C.O. reactive sublamina, a of stratum griseum centrale (SGCa), just subjacent to the SFGS, it was possible to measure the thickness of the SFGS following optic denervation and subsequent reinnervation. At 1 week after optic nerve crush, the SFGS shrank by 35%. During regeneration, the thickness of the SFGS gradually increased to about 23% above normal at 2 months postcrush and this was maintained indefinitely. In the retina, ganglion cells were hypertrophic by 1 month postcrush and exhibited elevated levels of C.O. during the same period of time when optic terminals were unreactive. This indicates that oxidative metabolic activity within perikarya and axon terminals of the same neuron may be locally and independently regulated. It also suggests that in spite of the well-known elevation of axonal transport during the initial period of axon elongation and synaptogenesis, that oxidative metabolic energy production within the optic fibers is less than that of the mature projection.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1988

Normal and regenerating optic fibers in goldfish tectum: HRP-EM evidence for rapid synaptogenesis and optic fiber-fiber affinity.

The distribution of normal and regenerating retinal fibers and synapses was studied on tectum in goldfish by light (LM) and electron microscopy (EM). Since labeling of the early regenerating fibers was previously reported to be difficult, a new 'cold-fill' HRP labeling protocol was developed, which labeled regenerating optic fibers and terminals on tectum as early as 14 days after nerve crush when they first arrive on tectum. In order to characterize the laminar distribution of optic afferents in normal fish and in fish regenerating for 14-240 days, EM photomontages of areas 14 microns wide by 160 microns deep through the HRP-labeled primary optic innervation layer (S-SO-SFGS) were constructed. The time points in regeneration that were examined spanned the period in which others have shown that an initially diffuse retinotopic map becomes spatially restricted. At the LM level regenerating optic fibers were restricted to the optic lamina. They reinnervated tectum in an anterior to posterior sequence as previously seen with autoradiography. In addition, at 14 days, some "pioneer" optic fascicles were found to have already grown to posterior tectum where they gave rise to branches with boutonlike terminations and growth-cone-like processes. Form the ultrastructural analysis it was clear that optic fibers and terminals observed strict laminar boundaries as they partitioned themselves in the optic laminae (S, SO and SFGS) in both normal and regenerating fish. The behavior of optic fibers was lamina specific with respect to synapse formation and the orientation of fiber outgrowth. As early as 14 days regeneration, optic fibers made synapses onto the four types of postsynaptic profiles observed in normal fish. Numerous optic terminals were labeled at 14 days, and there appeared to be no waiting period between fiber ingrowth to the SO and synapse formation in the S and SFGS. At 14-60 days, atypical synaptic contacts which appear to be nascent synapses were made by labeled optic fibers in fascicles and by growth-cone-like processes. By 21-30 days, the density of optic terminals was high and there were many more fasciculated optic fibers in the SFGS than normal as late as 350 days. These findings suggest that optic fiber lamination is highly constrained by tectal cues, that fibers rapidly regenerate many synaptic terminals before retinotopic map refinement is complete, and that fibers have a strong affinity for each other.

Animals↗

PubMed1988

Optic synapse number but not density is constrained during regeneration onto surgically halved tectum in goldfish: HRP-EM evidence that optic fibers compete for fixed numbers of postsynaptic sites on the tectum.

The number of optic synapses in the half tectum of goldfish was counted by using an improved HRP-labeling protocol and a columnar sampling method that spanned the entire optic innervation layer, S-SO-SFGS. It was previously found by using this procedure in intact tectum that the normal number of optic synapses was regenerated by 30 days and maintained thereafter even in the absence of impulse activity. This suggested that the number of synapses in this system was intrinsically fixed. In order to examine whether this limit was imposed by optic fibers or by target cells, optic synapses were counted in surgically halved tecta which received compressed optic projections consisting of regenerating optic fibers from the entire retina. We reasoned that if synapse number is a function of the number of afferents, then there should be twice the normal number of optic synapses per column; on the other hand, if their number is fixed by target, then their number per column should be normal. We found that the number of optic (labeled) synapses was normal in sample columns from fish at 70 days and 160 days after optic nerve crush. Thus, retinal ganglion cells, on average, formed half as many synapses on the half tectum compared to intact tectum, indicating the number of optic synapses was limited by the tectum. The number of nonoptic (unlabeled) synapses was also found to be normal. By contrast, the S-SO-SFGS was found to be 88-103% thicker compared to normal fish, apparently because of a 20-fold increase in the number of optic fibers. As a result, the density of synapses was about half normal in half tecta, and so, in contrast to synapse number, synaptic density is not constrained during regeneration. We infer from these data that optic fibers compete for limited numbers of postsynaptic sites during regeneration and suggest that this competition promotes neural map refinement and the various plasticities described for this projection.

Animals↗

PubMed1988

Locally correlated activity in the goldfish tectum in the absence of optic innervation.

Despite a substantial literature on the role of correlated presynaptic activity in the patterning of nerve connections during synaptogenesis in the central nervous system, few studies have focuses on postsynaptic activity during this process. To address the possibility that the target exhibits correlated activity independently of presynaptic activity, extracellular activity was recorded from the main optic innervation layer stratum fibrosum et griseum superficiale (SFGS) in goldfish in which the optic nerve was crushed or the eye removed. At about 2 weeks after denervation, multiunit recordings revealed phasic temporally correlated discharge between different tectal units. Auto-correlation analysis of these trains showed a broad peak 75-100 ms wide confirming temporal correlation. Using cross-correlation analysis of two simultaneous recordings at different distances across tectum, this correlation was shown to be local. Strong positive correlations were detected over about 200 micron and decrease with greater distances disappearing beyond about 400 micron. These correlograms showed a broad symmetrical peak about 75-100 ms wide. This pattern of activity persisted from the day following nerve crush into the period of activity dependent reinnervation at 1 month. When the eye was removed, the pattern could be demonstrated for up to 3 months of denervation indicating the circuitry responsible for the correlated activity was quite stable in the absence of optic innervation. We conclude that tectal elements are capable of locally correlated discharge independently of optic innervation. We propose that locally correlated discharge represents cooperative groups of tectal cells and that these groups, rather than single cells, are the target of the activity dependent synaptic rearrangement such as ocular dominance columns which occurs during synaptogenesis.

Animals↗

PubMed1988

Histochemical localization of cytochrome oxidase in the retina and optic tectum of normal goldfish: a combined cytochrome oxidase-horseradish peroxidase study.

Cytochrome oxidase (C.O.) was histochemically localized in the normal retina and optic tectum of goldfish in order to examine the laminar and cellular oxidative metabolic organization of these structures. In the optic tectum, C.O. exhibited a distinct laminar, regional, and cellular distribution. The laminae with highest C.O. levels were those that receive optic input, suggesting a dominant role for visual activity in tectal function. This was demonstrated by colocalizing C.O. and HRP-filled optic fibers in the same section. However, the distribution of C.O. within the optic laminae was not uniform. Within the main optic layers, the SFGS, four metabolically distinct sublaminae were distinguished and designated from superficial to deep as sublaminae a, b, c, and d. The most intense reactivity was localized within SFGSa and SFGSd, followed by SFGSb, then SFGSc. In SFGSd, intense reactivity was found to occur specifically within a class of large diameter axons and terminals that were apparently optic since these were also labeled with HRP and cobaltous lysine applied to the optic nerve. Regional C.O. differences across the tectum were also noted. Low levels were found in neurons and optic terminals along the growing immature medial, lateral, and posterior edges of tectum, but were higher at the more mature anterior pole and central regions of tectum. This suggests that the oxidative metabolic activity is initially low in newly formed tectal neurons and optic axons, but gradually increases with neuronal growth and functional axon terminal maturation. Most C.O. staining was localized within neuropil, whereas the perikarya of most tectal neurons were only lightly reactive. Only a few neuron classes, mostly the relatively larger projection neurons, had darkly reactive perikarya. In the retina, intense C.O. reactivity was localized within the inner segments of photoreceptors, the inner and outer plexiform layers, and within certain classes of bipolar and ganglion cells. The large ganglion cells in particular were intensely reactive. Like the large diameter optic terminals in SFGSd, the large ganglion cells were preferentially filled with HRP, suggesting that they may project to tectum and are the source of the darkly reactive large diameter axons and terminals in sublamina SFGSd. We propose a new scheme to describe tectal lamination that integrates laminar differences in C.O. reactivity with classical histological work.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1988

Retinotopically inappropriate synapses of subnormal density formed by surgically misdirected optic fibers in goldfish tectum.

Selected optic fibers were surgically deflected from one tectum onto the opposite host tectum which was denervated by eye enucleation. At 6-8 months, deflected fibers were labeled with horseradish peroxidase and the retinotopically inappropriate part of tectum was examined using electron microscopy. Numerous (labeled) optic synapses were found in the primary optic innervation layer of the 'wrong' part of tectum but they were about half the normal density. The number and density of non-optic synapses was not found to be affected. These findings indicate optic fibers compete with each other but not with non-optic fibers for synaptic sites in tectum.

Animals↗

PubMed1987

Intratectal targeting by optic fibers in goldfish under impulse blockade.

Regenerating optic fibers in goldfish were tested for their capacity to grow from an inappropriate region of the tectum to their appropriate part of the tectum when silenced by periodic intraocular injections of tetrodotoxin. For this, fibers normally innervating the lateral posterior quadrant of one tectum were surgically redirected into the medial anterior end of the opposite host tectum. This starting position corresponds to the path normally taken by fibers to innervate the medial tectum. For comparison, fibers normally innervating the medial posterior quadrant of the opposite tectum were surgically redirected into this same position in the host tectum. To prevent cueing with resident optic fibers, host fibers were eliminated by removing the eye supplying the host tectum. The innervation by these deflected fibers was determined autoradiographically using quantitative microdensitometry. Electrically silent fibers were found to navigate toward their appropriate region just as well as fibers with impulse activity. Thus, the capacity of fibers to read positional tectal cues and to bypass foreign tectal regions was not detectably regulated by impulse activity.

Animals↗

PubMed1987

Compression and expansion without impulse activity in the retinotectal projection of goldfish.

The capacity of regenerating optic fibers to undergo retinotopic compression and expansion in the absence of impulse activity was tested by eliminating activity with periodic intraocular injections of tetrodotoxin (TTX) during regeneration. To test for compression, the posterior half of tectum was removed and the optic nerve crushed. For expansion, the temporal half of retina was ablated and the nerve also crushed. The projection was then subsequently examined with electrophysiological mapping and autoradiographic tracing. Like electrically active fibers, silent fibers formed a retinotopically ordered projection that was compressed onto the anterior half tectum. Similarly, TTX-treated fibers from a nasal half retina formed a retinotopic projection that was expanded across the entire tectum. Except for some enlargement of receptive fields produced by the TTX, the topography was equivalent to that formed by active fibers. Thus, fibers can apparently maintain relative positions irrespective of absolute tectal position without the benefit of activity-dependent ordering. This implies the existence of an activity-independent mechanism for relative positioning that may operate across larger distances than the activity-dependent ordering responsible for fine topography and ocular dominance columns.

Action Potentials↗

PubMed1987

Tests for relabelling the goldfish tectum by optic fibers.

The temporal half of retina was removed in goldfish and the optic nerve was crushed. Electrophysiological recordings at 1-2 months revealed a retinotopic expansion of the nasal half retina across nearly the entire tectum. In other fish, an abnormal innervation of nasal fibers in anterior tectum was induced and allowed to persist for 51 months. When fibers were then crushed, nasal fibers innervated posterior tectum at 1-2 months showing no preference for anterior tectum. Apparently, fibers did not relabel tectum.

Animals↗