Establishment of microscale vegetation pattern in maritime chaparral after fire

We quantified microscale pattern in vegetation and seed assemblages along a 24 m transect before and for two years following a controlled burn in chamise (Adenostoma fasciculatum) chaparral in central coastal California. Our objective was to document scale-dependent correlation between pre-burn seed assemblages, pre-burn canopy cover, microtopography, soil temperatures during burning, post-burn seed assemblages and post-burn vegetation. Scale-dependent correlations among pre- and post-burn seed densities, maximum soil temperatures during burning, microtopography and post-burn vegetation were measured based on two-term local covariance analysis.Seed distribution varied among species prior to fire, with seeds of some annual species concentrated in gap areas. Maximum soil temperatures during burning ranged from less than 50 °C to 225 °C, and were generally lowest in gaps in the pre-burn canopy. These gaps were associated with local topographic depressions. After burning, readily germinable seeds were concentrated in or near gaps in the pre-burn canopy. Germination of different species was variously enhanced, diminished or unchanged by the passage of fire. Post-burn vegetation was very patchy, with some areas nearly devoid of seedlings and other areas, especially pre-burn canopy gaps, supporting numerous seedlings. Seedling recruitment patterns in the second year were generally highly correlated with patterns in pre-burn seed banks and first year vegetation. Although many species exhibited similar recruitment patterns, several different mechanisms may have been responsible for the origin of those patterns.     

Heterozygotes for cystic fibrosis: models for study of airway and autonomic reactivity

Airway reactivity to cold air and methacholine, alpha-adrenergic and cholinergic reactivity measured as pupillary responses to phenylephrine and carbachol, respectively, and beta-adrenergic reactivity assessed by lymphocyte adenosine 3',5'-cyclic monophosphate (cAMP) response to isoproterenol were compared in 108 parents of patients with cystic fibrosis (CF) and 133 healthy adult controls. No differences were found between CF parents and controls in airway response to cold air or methacholine or in lymphocyte cAMP response to isoproterenol. Significant differences were found, however, in the response of the pupils to both phenylephrine and carbachol. Heterozygotes for CF have more reactive pupils; i.e., they require smaller doses of agonist for a 10% change in pupil size. In control subjects, the response of the pupils to phenylephrine and carbachol is highly correlated (r = 0.45, P less than 0.001), whereas in CF heterozygotes, the correlation is not significantly different from zero (r = -0.02). In controls, the pupil response to carbachol has a significant negative correlation with cold air response (r = 0.39, P less than 0.05), indicating that those whose pupils were most sensitive to carbachol had the greatest airway reactivity to cold air, but in CF heterozygotes the correlation is not significant (r = 0.10). A significant correlation exists between lymphocyte cAMP response and airway cold air response in CF heterozygotes (r = -0.32, P less than 0.05) (those whose beta-adrenergic responsiveness is low have greater airway reactivity), but not in controls. The CF parents with the most reactive airways tend to have lower beta-adrenergic responses.(ABSTRACT TRUNCATED AT 250 WORDS)     

Regionalized adaptations and muscle fiber proliferation in stretch-induced enlargement

The relative contribution of increases in fiber area to stretch-induced muscle enlargement was evaluated in the slow tonic fibers of the anterior latissimus dorsi of adult Japanese quails. A weight corresponding to 10% of the bird's body mass was attached to one wing. Thirty days of stretch in 34 birds averaged 171.8 +/- 13.5% increase in muscle mass and 23.5 +/- 0.8% increase in muscle fiber length. The volume density of noncontractile tissue increased in middle and distal regions of stretch-enlarged muscles. Mean fiber cross-sectional area increased 56.7 +/- 12.3% in the midregion of stretched muscles. Further analysis indicated slow beta-fiber hypertrophy occurred in proximal, middle, and distal regions; however, fast alpha-type fiber hypertrophy was limited to middle regions of stretched muscles. Stretched muscles had a significant increase in the frequency of slow beta-fibers that were less than 500 microns 2 in all regions and fast alpha-type fibers in middle and distal regions. Total fiber number was determined after nitric acid digestion of connective tissue in 10 birds. Fiber number increased 51.8 +/- 19.4% in stretched muscle. These results are the first to clearly show that muscle fiber proliferation contributes substantially to adult skeletal muscle stretch-induced enlargement, although we do not know whether the responses of the slow tonic anterior latissimus dorsi might be similar or different from mammalian twitch muscle.     

Intracranial self-stimulation motivates treadmill running in rats.

Most animal running models have traditionally used aversive motivators to induce exercise tasks. This study demonstrates treadmill running motivated by reinforcement of intracranial self-stimulation (ICSS), providing an alternative model with which to study physiological responses to exercise. Twenty-nine male Sprague-Dawley rats were stereotaxically implanted with bipolar electrodes aimed at the ventral tegmental area of the brain. After 7 days of operant lever-press training for ICSS, rats that pressed at least 50 presses/min were randomly divided into three conditions: exercise-reinforcing brain stimulation (Ex-St), exercise-aversive shock (Ex-Sh), and sedentary controls (C). Ex-St and Ex-Sh ran for 30 min at 25 m/min at 5% grade for 2 wk with ICSS and electric shock as the motivator, respectively, while C did not run. At the end of 2 wk, Ex-St and Ex-Sh performed an endurance run. Results show that Ex-St ran longer than Ex-Sh [63 +/- 10 vs. 42 +/- 10 (SD) min; P less than 0.05]. HR was higher in Ex-St than in C (P less than 0.05). Rectal temperature increased similarly in both exercise groups. This model provides a highly effective method to motivate treadmill running in rats and as such can be used to characterize physiological responses to exercise without the potentially confounding influence of stress associated with an aversive shock motivator.     

Definition of subchromosomal intervals around the myotonic dystrophy gene region at 19q

The localization to 19q of the gene causing myotonic dystrophy (DM) has been defined more precisely by refinement of the physical location of several linked markers. A somatic cell hybrid mapping panel from cells with t(1;19), t(12;19), and t(X;19) translocation products was constructed to define five different intervals across 19q. In addition, we have derived a series of cell hybrids by irradiation of a der(19)-only hybrid to further subdivide the cen-q13.1 region. Using an array of 36 cloned genes, anonymous DNAs, and enzyme markers, we have tested the location of the panel breakpoints and refined the regional assignment of several of these markers. All markers tightly linked to DM are localized mainly within 19q13.2, thus suggesting that the DM gene is also close to this region.     

Mutational analysis of a lactogenic hormone reveals a role for lactogen-specific amino acid residues in receptor binding and mitogenic activity

Mutant forms of mouse placental lactogen-II (PL-II) have been generated to assess the role of specific amino acid residues and protein regions in binding to the PRL receptor and in mitogenic activity. Conversion of any of three lactogen-specific residues significantly reduced both of these hormone functions; mutation of the two other lactogen-specific amino acids revealed only minimal effects unless these changes were coupled with a second mutation. Deletions within the PL-II protein all resulted in a complete loss of function, but switching regions between PL-II and proliferin, another member of the prolactin family in the mouse, did yield a chimeric protein with some PRL-like activity. This activity was increased substantially by conversion of one amino acid residue in the proliferin region to the corresponding lactogen-specific residue. The locations of the amino acids that have been found to affect hormone function are predicted to be closely apposed in the folded protein, suggesting that this region may be the site of interaction of this lactogenic hormone with the PRL receptor.     

AF1, a sequenced bioactive neuropeptide isolated from the nematode Ascaris suum

An FMRFamide-like neuropeptide, named AF1, was isolated from head extracts of the nematode Ascaris suum using five steps of HPLC. AF1 is a heptapeptide with the amino acid sequence Lys-Asn-Glu-Phe-Ile-Arg-Phe-NH2. Synthetic AF1 (10(-9) to 10(-7) M) rapidly and reversibly abolished slow membrane potential oscillations of identified ventral and dorsal inhibitory motoneurons and selectively reduced their input resistances. Synaptic transmission was not blocked. In intact Ascaris, AF1 inhibited locomotory movements. This study indicates a potential physiological role for an endogenous neuropeptide in nematodes.     

Expression of beta-amyloid precursor protein in reactive astrocytes following neuronal damage

Although the beta-amyloid peptide is an established core component of neuritic plaques that accumulate in Alzheimer's disease, the mechanisms responsible for its deposition are not well understood. We now report that lesions of rat hippocampal neurons cause a time-dependent, long-lasting elevation of immunoreactivity for the beta-amyloid precursor protein (APP) in neighboring astrocytes, a cell type not normally containing the protein. The increase represents astroglial expression of the protein rather than a scavenging of APP released by damaged neurons. Immunoelectron microscopy confirmed that APP-containing cells are reactive astroglia, both surrounding capillaries and within the neuropil. These results demonstrate that neuronal damage stimulates APP expression in adult brain and suggest that reactive astrocytes may be a source of the beta-amyloid that forms neuropathological plaques in Alzheimer's disease.     

Altered expression of keratin and vimentin in human retinal pigment epithelial cells in vivo and in vitro.

Actively proliferating human retinal pigment epithelial (RPE) cells grown in tissue culture possess keratin-containing intermediate filaments that react with a combination of AE1 and AE3 anti-keratin monoclonal antibodies. Antibody reactivity is lost, however, from RPE cells as the cell population ceases to proliferate when it approaches confluence and attains morphological characteristics more similar to those in vivo. In contrast, clone 8.13 anti-keratin antibody stains all cells in the culture at all stages of the growth cycle and cell densities. These findings were reflected in vivo using retinal pigment epithelium taken directly from the eye. Normal non-proliferating RPE cells bound 8.13 antibody to cytoskeletal structures, as judged by indirect immunofluorescence, but did not bind AE1/AE3 antibodies. However, proliferating dedifferentiated RPE cells from the vitreous humor of patients with proliferative vitreoretinopathy possess filaments that bind both AE1/AE3 and 8.13 antibodies. Thus it appears that structures detected by AE1/AE3 antibodies only occur in actively growing RPE cells in vitro and in vivo. Keratins produced by RPE cells were identified using Western blotting. Species with molecular masses of 54 (keratin 7), 52 (keratin 8), 42 (keratin 18), and 40 (keratin 19) kiloDaltons were the most abundant in proliferating cultured cells, but cells isolated directly from the eye were found to lack keratin 7 and 19. Keratin 19 was, however, observed in proliferating RPE cells from some patients with proliferative vitreoretinopathy. The latter findings explain the differential staining observed with AE1/AE3 antibodies in cells in culture and isolated directly from the eye since these antibodies interact primarily with keratin 19 which is absent from non-proliferating RPE cells. In contrast to the presence of keratin-containing intermediate filaments in human RPE cells in vivo, there are apparently no detectable vimentin-containing cytoskeletal structures. However, all RPE cells cultured in vitro develop filaments composed of vimentin which persist in cells that have reached confluence.