Biomedical subjects

R D Fernald

Publications and source records attributed to R D Fernald.

At least 37 records · Page 2Linked to original sources

PubMed1997

Effect of social rank on brain monoaminergic activity in a cichlid fish.

In Haplochromis burtoni, an African cichlid fish, male sexual maturation is regulated via social interactions, and these effects are mediated by gonadotropin-releasing-hormone (GnRH)-containing neurons in the preoptic area of the brain. Since brain monoaminergic systems are known to be involved in the regulation of GnRH release, and the activity of these systems is influenced by agonistic interactions, we analyzed the effect of social status on brain monoaminergic activity in H. burtoni. Animals were either (1) in normal social groups consisting of two males and four females or (2) in groups of one male and five females. Quantitative behavioral observations were made on each group of animals and, following sacrifice several physiological measurements were made. Concentrations of serotonin (5-HT), 5-hydroxyindoleacetic acid (5-HIAA, the main 5-HT metabolite) and tryptophan (TRP, the amino acid precursor of 5-HT), dopamine (DA) and 3,4-dihydroxyphenylacetic acid (DOPAC, the main DA metabolite) were measured. The 5-HIAA/5-HT and DOPAC/DA ratios were calculated and used as indexes of 5-HT and DA activity, respectively. In addition, the gonadosomatic index was calculated from body and gonadal weights and used as an index of reproductive status. Concentrations of 5-HIAA as well as 5-HIAA/5-HT ratios were significantly higher in the brainstem of non-territorial males than in that of territorial males, and similar trends were seen in the telencephalon and hypothalamus. Moreover, TRP concentrations in the telencephalon and brainstem were significantly lower in non-territorial males. In this species, sexual maturation in females is not socially regulated, and there was no significant correlation between measured antagonistic behavior and biochemical indices. These results suggest a fundamental difference in the neurochemical responses between male and female H. burtoni.

Agonistic Behavior↗

PubMed1997

The evolution of eyes.

Eyes are the preeminent source of sensory information for the brain in most species, and many features of eyes reflect evolutionary solutions to particular selective pressures, both from the nonbiological environment and from other animals. As a result, the evolution of eyes, among all the sense organs, has attracted considerable attention from scientists. Paired eyes in the three major phyla, vertebrates, arthropods and mollusks, have long been considered to be classic examples of evolutionary convergence. At the macroscopic level, this must be true since they arise from different tissues and have evolved radically different solutions to the common problem of collecting and focusing light. However, opsin, the light-absorbing receptor protein, has a significant amount of shared DNA sequence homology across the phyla, and recently it has been discovered that some part of ocular development in different phyla is coordinated by a homologous, gene, Pax-6. So, although eyes from diverse phyla are clearly not homologous, neither can they be viewed as resulting solely from convergence. Instead, this shows that homology at the molecular level of organization does not predict homology at the organ or organismic level. The presence of homologous constituent molecules in nonhomologous structures reminds us that molecules are not eyes.

Animals↗

PubMed1997

Changing through doing: behavioral influences on the brain.

It seems self-evident that the brain controls behavior but does behavior also "control" the brain? This chapter examines evidence that behavior can and does influence specific aspects of brain structure and function. Evidence for such influence is easily obtained on an evolutionary time scale, since the selective forces found in the ecological niche of the animal are typically reflected in its sensory and motor activities as well as its body shape and behavioral habits. Similarly, during development, there is ample evidence that the behavior acts in concert with the environment to establish structural changes in the brain that last a lifetime. Perhaps most surprisingly there is now evidence that social behavior can cause changes in the brain in adult animals and that these changes are reversible. The changes caused by behavioral interactions can be dramatic and typically are related to reproductive behavior. Understanding the mechanisms responsible for dynamic changes in the nervous systems of adult animals is a major challenge and the discovery that it can occur may lead to insights about other systems where behavior sculpts the brain.

Animals↗

PubMed1996

Nonuniform distribution of cell proliferation in the adult teleost retina.

Teleost fish continue to grow throughout life, and their eyes enlarge correspondingly. Within the eye, the retina grows by stretching existing tissue and adding new cells. Cell addition occurs in two ways: First, all cell types except rod photoreceptors are added circumferentially at the edge of the eye where the retina meets the iris; second, rod photoreceptors are generated from a population of rod progenitor cells which divide throughout the outer nuclear layer (ONL). To determine the spatial distribution of rod progenitor cells across the teleost retina, we labeled dividing cells with an antibody to proliferating cell nuclear antigen (PCNA) throughout a 24 h period. We found a significantly higher density of dividing rod precursor cells at the nasal and temporal margins than in the central retina throughout the 24 h cycle. At night, the density of dividing cells is significantly greater at the nasal pole of the eye. The difference between cell division at the center and the margin was reduced at night when the density of cell division in the central retina increased significantly. Taken together, these data suggest that the eye grows asymmetrically, with more cells added at the nasal pole. Possible developmental causes and functional consequences of the reported distribution of cell divisions in time and location are presented.

Analysis of Variance↗

PubMed1996

Characterization of two new preproGnRH mRNAs in the tree shrew: first direct evidence for mesencephalic GnRH gene expression in a placental mammal.

Reproductive maturation and regulation is centrally orchestrated by gonadotropin-releasing hormone (GnRH). GnRH produced in the vertebrate hypothalamus acts on the pituitary to regulate gonadotropins. In nonplacental mammalian species, it has recently been shown that a second GnRH gene is expressed in mesencephalic cells. Here, we report the cDNA sequences and expression patterns for two distinct genes encoding the hypothalamic and mesencephalic GnRH forms in the brain of a placental mammal, the tree shrew (Tupaia glis belangeri). The novel mammalian GnRH form, designated here as [His5Trp7Tyr8]GnRH (often called chicken GnRH II), is expressed in neurons of the mesencephalon and is the first nonhypothalamic form to be isolated from a mammal. Its peptide sequence is identical to the form previously reported in fish, amphibians, reptiles, and birds, revealing that it has remained unchanged for 500 million years. In contrast, the sequences of the hypothalamic GnRH decapeptides vary by as much as 50% across vertebrate species. The remarkable sequence conservation of mesencephalic GnRH suggests that it has been highly constrained throughout evolution, perhaps indicating an important, conserved nongonadotropic role. The discovery and localization of two mRNAs encoding distinct GnRH forms in an advanced mammal suggest that other mammals, including primates, may also have a second GnRH gene with expression localized in the midbrain.

Amino Acid Sequence↗

PubMed1996

Androgen regulation of hypothalamic neurons containing gonadotropin-releasing hormone in a cichlid fish: integration with social cues.

Reproduction in vertebrates is regulated by internal signals such as hormone levels and by external signals such as social interactions. In an African cichlid fish, Haplochromis burtoni, the effect of social interactions is evident in the hypothalamo-pituitary-gonadal (HPG) axis of males. Territorial males, characterized by aggressive and reproductive activity, have significantly larger hypothalamic gonadotropin-releasing hormone (GnRH)-containing neurons and larger testes than nonterritorial males. Furthermore, a switch in the social status of an adult male causes a corresponding change in GnRH neuron size and testis size. Here we show that the GnRH-containing neurons in the hypothalamus of adult territorial males are also influenced by gonadal hormones. Castration of territorial males caused GnRH neurons to increase in size. This neuronal hypertrophy in castrated animals was prevented either by testosterone (T) or 11-ketotestosterone (KT) treatment. Estradiol (E2) treatment did not reduce GnRH cell size in castrated animals. These results suggest that androgens reduce the size of GnRH cells through negative feedback. Since E2 had no effect, androgen influence on GnRH cell size appears to be independent of aromatization. These data are consistent with the hypothesis that the setpoint for hypothalamic GnRH cell size is determined by social cues and that this setpoint is maintained by negative feedback from gonadal androgens.

Androgens↗

PubMed1995

Three gonadotropin-releasing hormone genes in one organism suggest novel roles for an ancient peptide.

Gonadotropin-releasing hormone (GnRH) is known and named for its essential role in vertebrate reproduction. Release of this decapeptide from neurons in the hypothalamus controls pituitary gonadotropin levels which, in turn, regulate gonadal state. The importance of GnRH is underscored by its widespread expression and conservation across vertebrate taxa: five amino acids are invariant in all nine known forms, whereas two others show only conservative changes. In most eutherian mammals, only one form, expressed in the hypothalamus, is thought to exist, although in a recent report, antibody staining in developing primates suggests an additional form. In contrast, multiple GnRH forms and expression loci have been reported in many non-mammalian vertebrates. However, evidence based on immunological discrimination does not always agree with analysis of gene expression, since GnRH forms encoded by different genes may not be reliably distinguished by antibodies. Here we report the expression of three distinct GnRH genes in a teleost fish brain, including the sequence encoding a novel GnRH preprohormone. Using in situ hybridization, we show that this form is found only in neurons that project to the pituitary and exhibit changes in soma size depending on social and reproductive state. The other two GnRH genes are expressed in other, distinct cell populations. All three genes share the motif of encoding a polypeptide consisting of GnRH and a GnRH-associated peptide. Whereas the GnRH moiety is highly conserved, the GnRH-associated peptides are not, reflecting differential selective pressure on different parts of the gene. GnRH forms expressed in nonhypothalamic regions may serve to coordinate reproductive activities of the animal.

Amino Acid Sequence↗

PubMed1995

Primary structure of solitary form of gonadotropin-releasing hormone (GnRH) in cichlid pituitary; three forms of GnRH in brain of cichlid and pumpkinseed fish.

GnRH is a decapeptide family with at least nine distinct structures. Vertebrates, except for most placental mammals, have more than one of these GnRH forms within the brain. We report chromatographical and immunological evidence that three forms of GnRH are in the brains of both cichlid (Haplochromis burtoni) and pumpkinseed (Lepomis gibbosus) fishes. We argue that the three forms correspond to those previously described as sea bream GnRH (sbGnRH), chicken GnRH-II and salmon GnRH. In contrast, only one GnRH form was present in the pituitary of the cichlid and is identified as sbGnRH by amino acid sequence. This is the first report in which the primary structure of GnRH is determined from pituitary tissue. The N-terminus was identified by monitoring the digestion of the peptide by pyroglutamate aminopeptidase with matrix assisted laser desorption/ionization (MALDI) mass spectrometry (MS). The amidation of the C-terminus was established using an esterification procedure for monitoring with MALDI-MS. This report supports the idea that three forms of GnRH within one species is widespread in the order Perciformes. The present study establishes sbGnRH as the third GnRH form in H. burtoni and predicts that sbGnRH is synthesized in preoptic neurons, then transported to the pituitary in the preoptic-hypophyseal axons for the release of one or both gonadotropins.

Amino Acid Sequence↗

PubMed1995

Daily rhythm of cell proliferation in the teleost retina.

To determine whether the number of cell divisions in the teleost retina exhibited a regular daily variation, we labeled dividing cells with an antibody to proliferating cell nuclear antigen. The number of dividing rod precursor cells in the outer nuclear layer of the retina were counted in retinas from the telost fish Haplochromis burtoni, sacrificed at 4-h intervals during a standard light-dark cycle and in constant darkness. These rod precursor cells exhibited a striking rhythm of cell division. The highest number of cell divisions (acrophase) was found to occur at night when it was approximately 3 times higher than during the day. The observed rhythm persisted in animals held in constant darkness. We suggest that this endogenous 24-h rhythm of rod precursor cell division may be controlled by a circadian clock. Although there are several examples of continuously proliferating cell populations which exhibit circadian or diurnal rhythms, this appears to be the first documentation of a rhythm of division in cells destined to become neurons.

Animals↗

PubMed1995

New rods move before differentiating in adult teleost retina.

To understand the cellular context of neuronal differentiation in the vertebrate retina, we analyzed the behavior of a class of progenitor cells in the outer nuclear layer of the teleost retina which divide throughout the animal's life and generate only rod photoreceptors. We present evidence that these progenitors reside adjacent to the outer limiting membrane of the retina during all phases of cell cycle. After final cell division, postmitotic cells move inward, toward the vitreal boundary of the outer nuclear layer, before they give rise to new rods. This movement is remarkable because it occurs in the mature, functioning retina. We hypothesize that only one of the two progenitor daughter cells moves while the other remains adjacent to the outer limiting membrane to divide again.

Animals↗

PubMed1995

A novel, rapid flat-mounting technique for visualizing antibody labeling in the retina.

Complete analysis of retinal tissue is difficult because it consists of a thin neural tissue spread across the back of a hemispheric surface. Conventional sectioning in a plane parallel to a central axis of symmetry produces a large number of samples, each containing only a small amount of the tissue of interest. Consequently, quantitative comparison of any feature of interest typically uses a small fraction of the sections from each retina, because analysis of the entire collection of sections is too time consuming. Such a sampling process can lead to misleading or erroneous conclusions. We present a new method which allows complete analysis of the retina using a small number of samples produced by sectioning flattened retinas. This procedure is straightforward as illustrated using an antibody against proliferating cell nuclear antigen (PCNA) to locate dividing cells in the teleost fish retina. Immunocytochemical staining on flat-sectioned retinas was quantified using a computer-based image analysis system. When the cells of interest are randomly distributed, conventional sampling procedures can seriously under- or over-estimate their number. The new technique presented allows significantly more efficient examination and quantification of the entire retina as compared to conventional techniques.

Animals↗

PubMed1995

Social control of cell size: males and females are different.

Successful animals survive because they modify their behavior in response to changes in their physical and social environments. Some responses such as fleeing or fighting, are immediate and can be understood or at least described by their proximate causes. Other modifications occur in animals over a longer time frame because they require tissue growth (or loss), changes in responsiveness to signalling molecules, or other alterations in the regulation of physiological systems. There are numerous examples of the short-term cause-effect relationships which are known in some detail. In contrast, less is known about how long-term changes result from environmental or social signals. Since reproduction is arguably the single most important aspect of an animal's life, reproductive behaviors offer a unique chance to study such change. Reproduction requires exquisite coordination of physiological state and behavioral acts. Many aspects of reproductive behavior occur only under natural conditions so it is imperative to analyze naturally occurring behaviors in real animals, preferably in the natural habitat. We have been studying an African cichlid fish in natural and semi-natural conditions because the connection between physiology and behavior can be easily seen. Moreover, the consequence of social success can be traced directly to changes in the brain, both in the short and long term. In this species, territorial males inhibit sexual maturation of nonterritorial males during development. Even after a male becomes sexually mature and territorial, being defeated causes his gonads to regress rapidly.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1995

The population of GnRH-containing neurons showing socially mediated size changes project to the pituitary in a teleost, Haplochromis burtoni.

Reproductive function in all vertebrates is controlled by the brain-pituitary-gonadal axis. In teleost fish, endocrine cells within the adenohypophysis are grouped together and each collection of cells is innervated by specific neuropeptide fibers. An important regulatory step in reproductive control is gonadotropin-releasing hormone (GnRH), whose delivery to the pituitary is responsible for its release of gonadotropins. The hormone GnRH has been shown to play a critical role in the social control of reproduction in a teleost fish, Haplochromis burtoni. However, there has been no direct evidence that the preoptic area GnRH neurons project to the pituitary. In this study, we used a retrograde tracer and immunohistochemistry to identify those GnRH containing neurons that project to the adenohypophysis. We compared reproductively active territorial males with quiescent non-territorial males to discover whether the connectivity of the preoptic area GnRH neurons depends on the reproductive status of the male. We found that, irrespective of reproductive status, most GnRH neurons in the preoptic area project to the pituitary and that all of these GnRH neurons show the soma size change that has been associated with reproductive status in Haplochromis burtoni. Based on these data, we propose that there is a single population of GnRH containing cells in the preoptic area that change size as a function of reproductive state and that this entire population projects to the pituitary. This is the first direct demonstration that this essential circuit, linking GnRH neurons in the preoptic area to the pituitary, exists.

Agonistic Behavior↗

PubMed1994

Ontogeny of gonadotropin releasing hormone-containing neurons in the teleost brain.

We investigated changes in two gonadotropin releasing hormone (GnRH)-containing neuronal populations during juvenile development in the African teleost, Haplochromis burtoni. Juveniles were sampled at weekly intervals and GnRHir neurons were identified through immunocytochemistry (ICC), then counted and measured on computer-captured video images. Soma size of GnRH neurons in the preoptic area (POA), which regulate gonadotropin release from the pituitary, is socially modulated in adults. Here we show that in juveniles the soma size of these neurons increases as a linear function of body weight. Terminal nerve (TN) GnRHir neurons, in contrast, are not involved in pituitary regulation and their soma size is not socially modulated in adults. In juveniles, soma size of these neurons is a quadratic function of body size and the covariance of soma size and body size is much less than in the POA GnRHir neurons. In both populations, GnRHir neuronal number covaries with body size or age only in the earliest juvenile stages. Analysis of the development of these two distinct GnRHir neuronal populations provides insight into their functional differentiation in adults.

Aging↗

PubMed1994

A second gene for gonadotropin-releasing hormone: cDNA and expression pattern in the brain.

In vertebrates, the gonadotropin-releasing hormone (GnRH) decapeptide is secreted from hypothalamic nerve terminals to regulate reproduction via control of synthesis and release of pituitary gonadotropins. Only one GnRH peptide has been found in mammals, with one exception, although numerous other vertebrate species express more than one of the eight known decapeptide forms as shown by immunocytochemical labeling of distinct cell groups in the brain. However, neither the functional nor the evolutionary relationships among these GnRH forms are clear, because only one preprohormone gene sequence from any species has been reported. The most ubiquitous alternative form of GnRH is [His5,Trp7,Tyr8]GnRH (also referred to as chicken-II), which differs from the mammalian sequence at amino acids 5, 7, and 8. This peptide has been shown to have the most potent releasing-hormone activity, although immunocytochemical staining has suggested it is synthesized only in the mesencephalon. Here we report the cloning and expression pattern of the gene for the precursor of this form from the teleost fish Haplochromis burtoni. This is the second GnRH-encoding gene to be characterized in this species. The newly discovered preprohormone gene differs from that previously reported in two ways. First, whereas the original gene predicts only a single associated peptide, this one predicts two associated peptides, both of which appear to be unique. Second, the gene for [His5,Trp7,Tyr8]GnRH is expressed in only one cell group in the mesencephalon. In contrast, the previously reported gene is expressed only in the terminal nerve. The striking differences between the preprohormone structure and localization suggest that the genes coding for the two known GnRH forms in H. burtoni did not arise from a recent duplication event. Interestingly, neither of the two genes found to date in this species is expressed in cells which project from the hypothalamus to the pituitary, suggesting that yet a third gene coding for GnRH may exist.

Amino Acid Sequence↗

PubMed1994

Regulation of eye growth in the African cichlid fish Haplochromis burtoni.

Fish were reared in 6 conditions: broad spectrum white light, total darkness, scotopic illumination, and 3 monochromatic colors matched to the absorption spectra of the three cone types to study the influence of the light regime on the regulation of eye growth in the African cichlid fish Haplochromis burtoni. Fish reared in total darkness showed high variability in naso-temporal diameter and axial length of the eye. Animals reared in darkness and in scotopic illumination had significantly larger eyes relative to lens size in comparison to fish reared in white light. Eye size and shape was nearly identical in fish reared in monochromatic and in white light. Because of overlap in the absorption spectra of the three cone types of H. burtoni it could not be resolved whether the regulatory mechanism receives input from all three cone types or only from the green (523 nm) sensitive cones. It is clear from our results, however, that neither the blue (455 nm) nor the yellow sensitive (562 nm) cones alone are responsible for eye size regulation. It seems equally unlikely that all three cone types have to act in concert for normal growth of the eye.

Adaptation, Ocular↗

PubMed1994

Refractive index distribution and spherical aberration in the crystalline lens of the African cichlid fish Haplochromis burtoni.

Refractive index distribution in the teleost crystalline lens was measured with a nondestructive method in freshly excised lenses of the African teleost fish Haplochromis burtoni. Independently, spherical aberration was measured in a parallel set of lenses. The measured refractive index profiles show a continual decrease of refractive index from the center to the surface of the lens. The H. burtoni lens is of high optical quality and slightly overcorrected for spherical aberration. Details of the small residual spherical aberration were accurately predicted by ray-tracing model calculations based on the measured refractive index profile. The refractive index profile and the spherical aberration both show more complex characteristics than suggested by earlier measurements and lens models.

Animals↗

PubMed1993

Regulation of cell division and rod differentiation in the teleost retina.

We tested the effects of several growth factors on the proliferation and differentiation of cells in the teleost retina which typically become rod photoreceptors to understand their regulation. Using organotypic slice cultures of differentiated teleost fish retinal tissue, we found that insulin and insulin-like growth factor I (IGF-I) stimulate proliferation of rod precursor cells whereas basic fibroblast growth factor (bFGF) does not. In the presence of bFGF, however, a greater proportion of the cells that had divided expressed a rod photoreceptor-specific phenotype than did control slices. This suggests insulin and the related IGF-I can influence the regulation of neuronal cell division whereas bFGF promotes the differentiation of neuronal stem cells into rod photoreceptors in retinal slice culture. These results support the idea that cell division and differentiation are differentially regulated and diffusible factors play a role in this process.

Animals↗