New photoresponses of phycomyces

The influence of light on asexual fruiting and mycelial growth of Phycomyces blakesleeanus Burgeff was studied by means of fruiting body counts and size measurements in cultures on solid media under varied incubation conditions. Five types of photoresponses were shown by ATCC Strain 8743a: (a) photoinduction of giant sporangiophores; (b) interference by light with an endogenous system that otherwise induces fruiting when the mycelium approaches the rim of the Petri dish; (c) inhibition of mycelial growth rates by light; (d) inhibition of dwarf sporangiophore induction by light; and (e) postponement by light of death in clones maintained by serial transfer at low temperature. A second strain, designated G5, showed responses comparable to (a), (b), and (d). The magnitudes of the responses were greatly affected by temperature of incubation and available nitrogen (asparagine) supply. The photoinduction of giant sporangiophores could be demonstrated with light of wavelengths between 380 and 480 nanometers but not with 520 nanometers or above. At 480 nanometers, light doses as small as 40 ergs per square centimeter were effective in inducing giant sporangiophores in strain 8743a.     

PHOTORESPONSES OF PHYCOMYCES BLAKESLEEANUS: INITIATION AND DEVELOPMENT OF SPORANGIOPHORE PRIMORDIA

Phycomyces blakesleeanus (Burgeff) produces both giant and dwarf sporangiophores from superficial and submerged hyphae. The morphogenesis of submerged primordia has been studied in cultures grown in petri dishes on a defined nitrogen-poor medium at low temperature under varied conditions of illumination. The primordia of dwarf and giant sporangiophores differed markedly in size, morphology, tropistic behavior, developmental plasticity, photosensitivity, and conditions required for initiation. Dwarf primordia, abundant only in dark-grown cultures, began as hyphal thickenings that later developed characteristic ramifications not seen in giant primordia. The formation of dwarf primordia was correlated spatially and temporally with termination of mycelial expansion near the rim of the dish and in local regions elsewhere. Illumination strongly suppressed the ramification process in existing primordia but did not prevent the maturation of dwarf sporangiophores that had already emerged from the nutrient surface. Giant primordia were prominent only in illuminated cultures. With continuous light from the time of inoculation, giant sporangiophores and giant primordia were found chiefly in midregions of the dish. If illumination was delayed until dwarfs had begun to form near the rim of the dish, the giant primordia were also concentrated near the rim. In that case about half of the giants were formed by conversion of a small fraction of the existing dwarf primordia and the rest were formed de novo from vegetative hyphae.     

Antioxidant defence system during exponential and stationary growth phases of Phycomyces blakesleeanus: Response to oxidative stress by hydrogen peroxide

An analysis of the components of the antioxidant defence system in exponential and stationary growth phases of filamentous fungus Phycomyces blakesleeanus and the response to the oxidative stress hydrogen peroxide were performed. There is a strong positive correlation between mycelial antioxidant capacity and the contents of gallic acid, d-erythroascorbate (d-EAA) or d-erythroascorbate monoglucoside (d-EAAG). These secondary metabolites are specifically synthesized by this fungus and reach maximal values in the stationary growth phase, suggesting that they can play some role in the antioxidant defence system of this fungus. There is a differential expression of the two more notable antioxidant activities, catalase (CAT) and superoxide dismutase (SOD), depending of the growth stage of P. blakesleeanus, CAT being expressed in the exponential and SOD in the stationary phase. Phycomyces blakesleeanus showed a high resistance to the oxidative stress caused by H₂O₂ (50 and 200 mM) which was higher in exponential phase. This higher resistance can be explained by the presence of CAT, glutathione peroxidase (GPx), and the probable contribution of glutathione-S-transferase (GST) and high levels of reduced form of glutathione (GSH). The transition to stationary phase was accompanied with a higher physiological oxidative damage illustrated by the higher protein carbonylation. In this growth stage the resistance of the fungus to the oxidative stress caused by H₂O₂ could be explained by the presence of SOD, GPx, and the probable contribution of GST as well as of secondary metabolites, mainly d-EAA and d-EAAG. These results highlight a specific response to oxidative stress by H₂O₂ depending on the growth phase of P. blakesleeanus.     

Rapid and repeated origin of insular gigantism and dwarfism in Australian tiger snakes

It is a well-known phenomenon that islands can support populations of gigantic or dwarf forms of mainland conspecifics, but the variety of explanatory hypotheses for this phenomenon have been difficult to disentangle. The highly venomous Australian tiger snakes (genus Notechis) represent a well-known and extreme example of insular body size variation. They are of special interest because there are multiple populations of dwarfs and giants and the age of the islands and thus the age of the tiger snake populations are known from detailed sea level studies. Most are 5000-7000 years old and all are less than 10,000 years old. Here we discriminate between two competing hypotheses with a molecular phylogeography dataset comprising approximately 4800 bp of mtDNA and demonstrate that populations of island dwarfs and giants have evolved five times independently. In each case the closest relatives of the giant or dwarf populations are mainland tiger snakes, and in four of the five cases, the closest relatives are also the most geographically proximate mainland tiger snakes. Moreover, these body size shifts have evolved extremely rapidly and this is reflected in the genetic divergence between island body size variants and mainland snakes. Within south eastern Australia, where populations of island giants, populations of island dwarfs, and mainland tiger snakes all occur, the maximum genetic divergence is only 0.38%. Dwarf tiger snakes are restricted to prey items that are much smaller than the prey items of mainland tiger snakes and giant tiger snakes are restricted to seasonally available prey items that are up three times larger than the prey items of mainland tiger snakes. We support the hypotheses that these body size shifts are due to strong selection imposed by the size of available prey items, rather than shared evolutionary history, and our results are consistent with the notion that adaptive plasticity also has played an important role in body size shifts. We suggest that plasticity displayed early on in the occupation of these new islands provided the flexibility necessary as the island's available prey items became more depauperate, but once the size range of available prey items was reduced, strong natural selection followed by genetic assimilation worked to optimize snake body size. The rate of body size divergence in haldanes is similar for dwarfs (h(g) = 0.0010) and giants (h(g) = 0.0020-0.0025) and is in line with other studies of rapid evolution. Our data provide strong evidence for rapid and repeated morphological divergence in the wild due to similar selective pressures acting in different directions.     

Hybrid dwarfness in crosses between wheat (Triticum aestivum L.) and rye (Secale cereale L.): a new look at an old phenomenon

The existence of hybrid dwarfs from intraspecific crosses in wheat (Triticum aestivum) was described 100 years ago, and the genetics underlying hybrid dwarfness are well understood. In this study, we report a dwarf phenotype in interspecific hybrids between wheat and rye (Secale cereale). We identified two rye lines that produce hybrid dwarfs with wheat and have none of the hitherto known hybrid dwarfing genes. Genetic analyses revealed that both rye lines carry a single allelic gene responsible for the dwarf phenotype. This gene was designated Hdw‐R1 (Hybrid dwarf‐R1). Application of gibberellic acid (GA₃) to both intraspecific (wheat–wheat) and interspecific (wheat–rye) hybrids showed that hybrid dwarfness cannot be overcome by treatment with this phytohormone. Histological analysis of shoot apices showed that wheat–rye hybrids with the dwarf phenotype at 21 and 45 days after germination failed to develop further. Shoot apices of dwarf plants did not elongate, did not form new primordia and had a dome‐shaped appearance in the seed. The possible relationship between hybrid dwarfness and the genes responsible for the transition from vegetative to generative growth stage is discussed.     

Effects of hyperbaric oxygen on the growth and properties of Pseudomonas aeruginosa

Growth of Pseudomonas aeruginosa in 2 atmospheres absolute of 100% oxygen at 37 degrees C produced two types of abnormal colonies--stunted, rough colonies, termed dwarfs, and large, domed, mucoid colonies, termed giants. The occurrence of these variants depended upon the partial pressure of oxygen and the inoculum size. Subculture of dwarf or giant colonies produced a mixture of both colony types after incubation in hyperbaric oxygen, and colonies of normal appearance after incubation in air. Electron micrographs of ultrathin sections showed that cells from dwarf colonies had a more clearly defined envelope region than cells from normal colonies. Giant colony and normal colony-derived cells were of similar appearance. Whole cells from giant colonies contained more carbohydrate, readily extractable lipid, neutral lipid and free fatty acid than cells from normal colonies; the two cell types showed similar contents of 2-keto,3-deoxyoctonic acid and total phospholipid, but different proportions of individual phospholipids. Cells from dwarf, giant and normal (air-grown) colonies were incubated in air on nutrient agar containing either polymyxin, tetracycline or phenoxyethanol. Relative to cells from normal colonies, cells from dwarf colonies showed enhanced resistance to all three agents and cells from giant colonies showed enhanced resistance to polymyxin and tetracycline only. The resistance of cells from variant colonies was lost following a single subculture in air in the absence of antibacterial agents. It was concluded that the envelopes of cells from dwarf and giant colonies differed both from each other and from those of normal cells. These differences, and the formation of variant colonies, appeared to result from bacterial adaptation to hyperbaric oxygen rather than from mutation.     

Coleoptile length,gibberellin sensitivity and concentrations in five non-allelic dwarf mutants of pearl millet — Pennisetum glaucum (L.) R. Br.

The concentrations of endogenous gibberellins (GAs) were determined by combined gas chromatography-mass spectrometry in shoots of five non-allelic dwarfs of pearl millet Pennisetum glaucum (L.) R. Br. One mutant (d3), with an extreme dwarf phenotype, was found to be deficient in all GAs measured; the others (d1, d2, d4 and the quantitatively inherited dwarf) had similar levels of GAs to the tall genotype. Only the GA-deficient dwarf recovered the tall phenotype in response to applying GA₃ up to the adult stage, while the others showed slight to moderate responses at the seedling stage, depending on the season, and no response at later stages. The d1, d3 and d4 dwarfs had short coleoptiles. A wide range of coleoptile lengths with a normal distribution pattern was observed in the tall, d2 and the quantitatively inherited dwarf, suggesting that there is polygenic control of this trait.     

Revised fusulinid biostratigraphy of the Middle–Late Permian of Jebel Tebaga (Tunisia)

Most carbonate series of Jebel Tebaga (Tunisia) are assigned to the Capitanian (last stage of the Middle Permian); however, their accurate correlation with the El Capitan stratotype in the USA and with contemporaneous Tethyan localities remains unclear. With the intent to establish more accurate lithostratigraphic and biostratigraphical divisions, (1) we re-sampled bed-by-bed the classical field sections of Jebel Tebaga; (2) we revised the lithostratigraphical units E-I to E-VI, and (3) we selected 9 fusulinids in order to characterize more precisely local bioevents. We have therefore studied 3 giant genera (Chusenella, Neoschwagerina and Yabeina), 3 medium-sized taxa (Dunbarula, Rauserella and Yangchienia), and 3 small size genera (Lantschichites, Codonofusiella and Reichelina). The first group was known to synchronously disappear at the time of the end-Guadalupian mass extinction. The thirth group was generally considered to be characteristic of the early Late Permian, after a Lilliput effect among the fusulinid groups, during which the dwarfs replaced the giants. Our data show that, in Jebel Tebaga, the so-called Wuchiapingian small forms Codonofusiella and Reichelina appear very early in the Late Capitanian. In some hills of the Tebaga area (i.e., Baten Beni Zid and Jebel Seikra), Codonofusiella and Reichelina even dominated the fusulinid assemblages during two short episodes. The first episode is located near the base of the Capitanian series; the second one, although located near its top, remains Capitanian in age, because it took place before the local disappearance of the three giants Neoschwagerina, Yabeina and Chusenella. As the sequence becomes sandier after this bioevent, the boundary with the Wuchiapingian (first stage of the Late Permian or Lopingian) cannot be well positioned. The end-Guadalupian event is only marked by this sedimentological modification. Because the Late Permian Cheguimi sandstone is entirely devoid of foraminifers and conodonts, no local subdivisions can be proposed in this series.     

Extant and extinct forms of arctic charr Salvelinus alpinus (L.) complex from the Leprindo lake system (Transbaikalia): Differentiation in life history, morphology, and genetics

Interconnected lakes Bol’shoe Leprindo and Maloe Leprindo in Transbaikalia hosted large (extinct) and dwarf charr forms. Rarely “small” individuals intermediate in size between these forms are caught. In order to assess morphological, ecological, and genetic differentiation of sympatric charr forms and parapatric charr populations we studied their meristic and morphometric characters, feeding, breeding, and growth; we also investigated variation at 8 microsatellite loci using DNA isolated both from contemporary and historic samples. Profound differences were found between large and dwarf charr in growth rate, feeding (piscivores and highly specialized zooplanktivores, respectively), spawning time, and morphology. Dwarf charr from the two lakes demonstrate minor differences in morphology and growth rate. “Small” individuals are morphologically similar with dwarf charr and spawn together with them, they are recruited from dwarf form in late ontogeny as the result of transition to piscivorous feeding and growth acceleration. Microsatellite analysis showed that: (1) large and dwarf charr forms display high degree of genetic differentiation and reproductive isolation; (2) dwarf charr from interconnected lakes belong to different isolted populations; (3) “small charr” are genetically identical with dwarfs. The degree of ecomorphological and genetic differentiation between large and dwarf forms places charr from Leprindo Lakes among the most strongly differentiated Arctic charr forms’ flocks known at the vast range of S. alpinus complex.     

Analysis of phenomena involved in the apical growth of<Emphasis Type="Italic"> Phycomyces blakesleeanus</Emphasis>

The effects of the Ca²⁺/H⁺ exchanger A23187 and the K⁺/H⁺ exchanger nigericin, the electrogenic membrane-potential depleters valinomycin and CCCP, and the calcium channel blockers ruthenium red, nifedipine, and nitrendipine on the apical growth of Phycomyces blakesleeanus were analyzed. While all of the compounds inhibited the growth of germlings in liquid medium, the Ca²⁺ channel blockers were the least effective. Chitin synthesis in vivo was also sensitive to the inhibitors; here again, the calcium channel blockers were less efficient, and their effect occurred after a lag phase, in contrast to the electroneutral ionophores whose effects were immediate. The ionophores rapidly inhibited protein secretion, and reduced the number of secretory vesicles and chitosomes in the hyphal apex of P. blakesleeanus. The results suggest that not only tip-to-base calcium gradients but also transmembrane ionic gradients and membrane potential have a role in the apical growth of P. blakesleeanus. They are probably involved in the formation, migration, and/or fusion with the plasmalemma of secretory vesicles and chitosomes.     

Phycomyces: electrical response to light stimuli

Electrical signals have been detected in response to light excitation of the fungus Phycomyces blakesleeanus. These signals are related to the wavelength and intensity of the stimulus and the growth stage of the fungus. A relationship between the signals and the possible photoreceptor-pigment system is explored.     

Phenotypic characterization of lettuce dwarf mutants and their response to applied gibberellins

Four monogenic, recessive dwarf mutants of lettuce (Lactuca sativa L.), previously isolated from a population induced by ethyl methanesulfonate, were compared with the normal genotype (E-1) for plant height, weight, leaf area, as well as hypocotyl length and root length. These nonallelic dwarfs (dwf1, dwf2, and dwf3) exhibited reduced hypocotyl length, smaller, dark green leaves, and reduced stem length. Another mutant, dwf2, allelic with dwf2, exhibited an intermediate phenotype. Epidermal cells on hypocotyls and mature leaves were counted for both normal E-1 and dwf2 plants. The total number of epidermal cells per unit area for hypocotyls and for leaves from these plants was very similar, implying the dwarf's smaller size was due to an inhibition of cell expansion and not due to decreased cell divisions. Both dwarf and normal hypocotyls elongated normally in response to exogenous gibberellin A₃ (GA₃). In the rosette stage, only E-1 and dwf2 responded similarly to lower concentrations of GA₃, while the other dwarfs required higher concentrations to respond. Hypocotyls of dwf2 and E-1 elongated equally with applied ent-kaurenol, ent-kaurenoic acid, GA₅₃-aldehyde, GA₅₃, GA₁₉, GA₂₀, and GA₁ indicating that the biochemical block in dwf2 occurs at a very early step in the GA-biosynthetic pathway.     

The sensitive period for light and temperature regulation of sporangiophore development inPhycomyces

Light and temperature markedly influence sporangiophore development inPhycomyces blakesleeanus. Under normal conditions in the dark, low temperature drastically stimulates the production of dwarf sporangiophores (microphorogenesis) and inhibits that of giant sporangiophores (macrophorogenesis). These effects of low temperature could still be observed if applied only for a short period before sporangiophore initiation. Continuous white illumination strongly inhibits microphorogenesis and slightly stimulates macrophorogenesis. Short exposures to white light noticeably inhibit microphorogenesis and stimulate macrophorogenesis when given to mycelia grown for between 90 and 160 h at 14° C or 150 h or more at 10° C. These results indicate the existence in the mycelium of developmental stages for the regulation of sporangiophorogenesis by environmental signals.     

Ecological and genecological distinctions of a high intertidal dwarf form of Fucus distichus (L.) Powell in New England

Morphological, ecological, and genetic distinctions of a high intertidal, dwarf, non-tide pool member of the Fucus distichus (L.) Powell complex were assessed at an exposed site in southern Maine, U.S.A. Variation in plant stature from typical F. distichus ssp. edentatus (De la Pylaie) Powell to the dwarf form is continuous. On the other hand, measurements of reproductively mature plants collected throughout the eulittoral zone showed a bimodal pattern, i.e., there was a high frequency of dwarf forms (4–8 cm) and F. distichus ssp. edentatus (13–28 cm). The two forms have distinct reproductive phenologies: the dwarf plant exhibiting a unimodal reproductive maximum (fall), while F. distichus ssp. edentatus has pronounced bimodal reproductive maxima (spring and fall). Differences in stature and reproduction between the dwarf form and F. distichus ssp. edentatus were maintained when their respective progeny were grown under common environmental conditions. Thus, the differences are heritable rather than environmentally induced.     

New sources of dwarfing genes in pearl millet (Pennisetum americanum)

Summary Thirteen naturally occurring dwarf lines of pearl millet [Pennisetum americanum (L.) Leeke], identified from the world collection, varied for several morphological and agronomic characters. Extreme dwarfs were characterized by a tufted growth habit which could be distinguished from the time of germination, while the other dwarf lines could be distinguished only after anthesis. The F₁ hybrids between the tall and dwarf genotypes were tall, indicating that dwarfness is a recessive trait. In 10 out of the 13 crosses, the F₂ segregation ratio was three tall to one dwarf (31) suggesting that the dwarfness is controlled by a single recessive gene, while the height differences in 3 of the dwarfs (IP 8056, IP 8210 and IP 8214) were controlled by more than one gene as they showed continuous variation for plant height in F₂. When the remaining 10 single gene dwarfs were crossed to either d ₁ (Tift 238) or d ₂ (Tift 23 DB) dwarfs, only 2 crosses produced tall F₂ hybrids and they segregated for height in F₂ indicating that these 2 dwarfs are non-allelic to d ₁ and d ₂. Reciprocal crosses of these 2 dwarfs produced tall F₁ hybrids and showed a dihybrid segregation of 934 in F₂ indicating that the dwarfing genes of these 2 parents are non-allelic to each other. These non-allelic dwarfs were assigned the gene symbols d ₃ (IP 10401), and d ₄ (IP 10402).Submitted as J.A. No. 429 by the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT)     

Exogenous GA3 Application Can Compensate the Morphogenetic Effects of the GA-Responsive Dwarfing Gene Rht12 in Bread Wheat

The most common dwarfing genes in wheat, Rht-B1b and Rht-D1b, classified as gibberellin-insensitive (GAI) dwarfing genes due to their reduced response to exogenous GA, have been verified as encoding negative regulators of gibberellin signaling. In contrast, the response of gibberellin-responsive (GAR) dwarfing genes, such as Rht12, to exogenous GA is still unclear and the role of them, if any, in GA biosynthesis or signaling is unknown. The responses of Rht12 to exogenous GA₃ were investigated on seedling vigour, spike phenological development, plant height and other agronomic traits, using F_2∶3 and F_3∶4 lines derived from a cross between Ningchun45 and Karcagi-12 in three experiments. The application of exogenous GA₃ significantly increased coleoptile length and seedling leaf 1 length and area. While there was no significant difference between the dwarf and the tall lines at the seedling stage in the responsiveness to GA₃, plant height was significantly increased, by 41 cm (53%) averaged across the three experiments, in the GA₃-treated Rht12 dwarf lines. Plant height of the tall lines was not affected significantly by GA₃ treatment (<10 cm increased). Plant biomass and seed size of the GA₃-treated dwarf lines was significantly increased compared with untreated dwarf plants while there was no such difference in the tall lines. GA₃-treated Rht12 dwarf plants with the dominant Vrn-B1 developed faster than untreated plants and reached double ridge stage 57 days, 11 days and 50 days earlier and finally flowered earlier by almost 7 days while the GA₃-treated tall lines flowering only 1–2 days earlier than the untreated tall lines. Thus, it is clear that exogenous GA₃ can break the masking effect of Rht12 on Vrn-B1 and also restore other characters of Rht12 to normal. It suggested that Rht12 mutants may be deficient in GA biosynthesis rather than in GA signal transduction like the GA-insensitive dwarfs.     

Physical Basis for Altered Stem Elongation Rates in Internode Length Mutants of Pisum

Biophysical parameters related to gibberellin (GA)-dependent stem elongation were examined in dark-grown stem-length genotypes of Pisum sativum L. The rate of internode expansion in these genotypes is altered due to recessive mutations which affect either the endogenous levels of, or response to, GA. The GA deficient dwarf L181 (ls), two GA insensitive semierectoides dwarfs NGB5865 and NGB5862 (Ika and Ikb, respectively) and the `slender' line L197 (la cry^[ill]), which is tall regardless of GA content, were compared to the wild-type tall cultivar, Torsdag. Osmotic pressure, estimated by vapor pressure osmometry, and turgor pressure, measured directly with a pressure probe, did not correlate with the differences in growth rate among the genotypes. Mechanical wall properties of frozen-thawed tissue were measured using a constant force assay. GA deficiency resulted in increased wall stiffness judged both on the basis of plastic compliance and plastic extensibility normalized for equal stem circumference. Plastic compliance was not reduced in the GA insensitive dwarfs, though Ika reduced circumference-normalized plasticity. In contrast, in vivo wall relaxation, determined by the pressure-block technique, differed among genotypes in a manner which did correlate with extension rates. The wall yield threshold was 1 bar or less in the tall lines, but ranged from 3 to 6 bars in the dwarf genotypes. The results with the ls mutant indicate that GA enhances stem elongation by both decreasing the wall yield threshold and increasing the wall yield coefficient. In the GA-insensitive mutants, Ika and Ikb, the wall yield threshold is substantially elevated. Plants possessing Ika may also possess a reduced wall yield coefficient.     

Random amplified polymorphic DNA (RAPD) detection of dwarf off-types in micropropagated Cavendish (Musa spp. AAA) bananas

Summary A RAPD marker specific to the dwarf off-type (hereafter known as dwarf) from micropropagation of Cavendish banana (Musa spp. AAA) cultivars New Guinea Cavendish and Williams was identified following an analysis of 57 normal (true-to-type) and 59 dwarf plants generated from several different micropropagation events. Sixty-six random decamer primers were used in the initial screen, of which 19 (28.8%) revealed polymorphisms between normal and dwarf plants. Primer OPJ-04 (5'-CCGAACACGG-3') was found to amplify an approx. 1.5 kb band which was consistently present in all normal but absent in all dwarf plants of both cultivars. Reliable detection of dwarf plants was achieved using this marker, providing the only available means ofin vitro detection of dwarfs. The use of this marker could facilitate early detection and elimination of dwarfs from batches of micropropagated bananas, and may be a useful tool in determining what factors in the tissue culture process lead to this off type production.Other micropropagation-induced RAPD polymorphisms were observed but were not associated with the dwarf trait.     

Immunocytochemical effects of thyroxine stimulation on the adenohypophysis of dwarf (dw) mutant mice

The effects of dietary thyroxine on the immunoreactivity of cells in the pars distalis of the adenohypophysis in dwarf (dw/dw) mice were determined by ultrastructural immunocytochemistry. In nontreated dwarfs only adrenocorticotropic hormone (ACTH) cells and luteinizing hormone (LH) cells showed positive reactions to their respective antibodies, whereas no cells showed immunoreactivity to antibodies to growth hormone (GH), thyroid-stimulating hormone (TSH), or prolactin (Prl). In dwarfs supplemented postnatally with dietary thyroxine for 9 wks, the treatment failed to produced immunoreactive GH, TSH or Prl cells. However, LH cells became more prominent and fully developed, with denser concentrations of immunoreactive particles overlying the secretory granules than occurred in nontreated dwarfs. In thyroxine-treated dwarfs, ACTH cells were similar in ultrastructural features and immunoreactivity to those in nontreated dwarfs.     

Hypothalamic catecholamine histofluorescence in dwarf mice

Summary Brains of growth hormone (GH)-and prolactin (PRL)-deficient Ames (df/df) and Snell (dw/dw) dwarf mice and normal mice of the same strains were examined for catecholamine (CA) histofluorescence, with particular emphasis upon the hypothalamic tuberoinfundibular (A12) (arcuate nucleus/median eminence) region, which plays a role in the regulation of both GH and PRL. Dwarfs and normal animals of both types also were treated with a drug regimen to deplete sequentially neuronal CA stores (reserpine), inhibit CA oxidation (nialamide) and load dopaminergic A12 cells with exogenous transmitter (norepinephrine), in order to test viability and axonal transport capacity of A12 neurons. In both types of dwarfs, compared with normals, fluorescence was markedly reduced in the zona externa of the median eminence, which is normally rich in terminals from A12 neurons. Fluorescence in the median eminence was particularly weak in Ames dwarfs, and A12 perikarya were difficult to discern in this group. Snell dwarfs showed reduced fluorescence of A12 perikarya when compared with the brightly fluorescent perikarya seen in normal mice. In supraoptic and paraventricular nuclei, and in the zona interna of the median eminence, CA fluorescence attributable to NE was comparable among dwarfs and normals; fluorescence of dopaminergic perikarya in substantia nigra was also unaffected in dwarfs. Exogenously administered NE effected enhanced fluorescence of A12 Perikarya in normal mice and in Snell dwarfs; NE treatment in the Ames dwarf, however, failed to increase significantly the faint fluorescence of A12 cell bodies. The results indicate that dopaminergic A12 neurons in Snell dwarf mice are present and viable. Reduction in DA in the median eminence in both genetic dwarfs and failure of CA uptake in Ames dwarfs may indicate altered axon morphology or transport capacity, and/or abnormal DA biosynthesis, which may be more severe in Ames than in Snell dwarfs. Thus, genetic alteration in differentiation of pituitary cells may play a significant role in development of the CA systems in the hypothalamus.Supported by PHS Grants HD 18243 (CP), NS15816 and AG00847 (JRS) and HS12671 (AB).