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D S Forman

Publications and source records attributed to D S Forman.

17 recordsLinked to original sources
PubMed1988

Organelle dynamics in lobster axons: anterograde and retrograde particulate organelles.

Particulate organelles in isolated axons from the walking legs of the lobster were detected with differential interference contrast optics and video microscopic techniques. The motion of the organelles was studied in normal axons, in axons whose surface membrane was rendered permeable with saponin, and in axoplasm extruded from the axons. In normal axons at 20-22 degrees C, organelles moved more rapidly in the anterograde direction than in the retrograde direction (respective mean velocities 1.73 micron/s and 0.63 micron/s). The instantaneous velocities of both sets of organelles were variable: those of the anterograde organelles varied less than those of retrograde organelles. The variation in instantaneous velocity was patterned; all organelles studied had velocities that fluctuated slowly with a major frequency at about 0.1 Hz. Some organelles oscillated about a fixed position at a similar major frequency. In axons with a permeabilized surface membrane there was no organelle motion unless adenosine 5'-triphosphate (ATP) was present in the bathing medium. Organelle motion reactivated with ATP was patterned in a way similar to that in normal intact axons. In extruded axoplasm in the presence of ATP, organelles moved along transport filaments that were assumed to be microtubules. Movement of organelles from one transport filament to another was not accompanied by changes in motion that could explain the normal fluctuation in velocity. The evidence indicates that the variable, or oscillatory, character of organelle motion in lobster axons is caused by an active component of the mechanisms of axonal transport.

Animals↗
PubMed1987

Organelle dynamics in lobster axons: anterograde, retrograde and stationary mitochondria.

Mitochondria in isolated motor axons from the walking legs of lobster were observed with differential interference contrast optics and video microscopic techniques. Movements of the mitochondria were analyzed in time-lapse videotape records. The mean velocity of transport in the retrograde direction (1.33 +/- 0.64 micron/s) was greater than the mean velocity of transport in the anterograde direction (0.72 +/- 0.26 micron/s). The mean lengths of the mitochondria moving in the retrograde and anterograde directions were only slightly different (6.9 microns and 5.5 microns, respectively). No correlation was found between mitochondrial length and average velocity or reciprocal velocity. The instantaneous velocities of mitochondria were distributed over a range of approximately 3 micron/s; both the anterograde and retrograde distributions contained a small proportion of values whose sign was opposite to the modal value. The variation in instantaneous velocity took place at frequencies close to 0.1 Hz. Some mitochondria displayed longitudinally oriented oscillatory movements of a similar low frequency. While the movement of most mitochondria was parallel to the axis of the axon, transverse deviations and complex circular paths were sometimes observed. Some mitochondria reversed their orientation and continued in the same direction, so that the end which had been the leading end became the trailing end. Many mitochondria immediately beneath the plasma membrane were stationary and adhered strongly to the plasma membrane when the axoplasmic structure was disrupted. In electron micrographs, fine strands connected peripheral mitochondria and the plasma membrane. These strands may anchor the stationary mitochondria to the plasma membrane.

Animals↗
PubMed1987

Polarity orientations of microtubules in squid and lobster axons.

Polarity orientations of microtubules in periaxolemmal and internal regions of squid and lobster axons were determined in order to test the hypothesis that regional differences in particle transport are produced by differentially distributed microtubule subclasses. Over 95% of the microtubules in all regions of the axons investigated were oriented with plus ends located distally, pointing away from axonal somata, and there were no significant differences in orientation ratios in periaxolemmal and internal axoplasm. In axonal sheath glial cells of lobsters, microtubules were found to be oriented parallel to axonal microtubules and to have approximately equally mixed polarities. The results for axonal microtubules did not support the possibility of subclasses of axonal microtubules.

Animals↗
PubMed1987

Morphology of astroglial cells is controlled by beta-adrenergic receptors.

Astroglial cells in vivo and in vitro respond to hormones, growth factors, and neurotransmitters by changing from an epithelial-like to stellate morphology. We have studied the temporal relationship between receptor activation, second messenger mobilization, and morphological changes using LRM55 astroglial cells. Maintenance of an altered morphology required continuous beta-adrenergic receptor activation. These changes appeared to be mediated by cAMP since they were elicited by its analogue, dibutyryl cAMP, and by forskolin, a direct activator of adenylate cyclase. Changes in cell morphology may require a relatively small increase in intracellular cAMP, since receptor-stimulated changes in cAMP levels were transient and peaked approximately 5 min after receptor activation while changes in morphology took at least 30 min to reach a new steady state. Time-lapse videomicroscopy and high voltage electron microscopy indicated that receptor activation resulted in a sequence of morphological events. Time-lapse observations revealed the development and enlargement of openings through the cytoplasm associated with cytoplasmic withdrawal to the perinuclear region and process formation. Higher resolution high voltage electron microscopy indicated that the transition to a stellate morphology was preceded by the appearance of two distinct cytoplasmic domains. One contained an open network of filaments and organelles. The other was characterized by short broad cytoplasmic filaments. The first domain was similar to cytoplasm in control cells while the second was associated with the development and enlargement of openings through the cytoplasm and regions of obvious cytoplasmic withdrawal.

Astrocytes↗
PubMed1986

Slow pulsatile movements of Schwann cells in vitro: a time-lapse cinemicrographic study.

Slow pulsatile movements of Schwann cells in vitro were studied quantitatively by using time-lapse cinemicrography. Schwann cells from peripheral nerves of 3-day-old rats were cultured in serum-free medium. Most Schwann cells showed intermittent episodes of pulsatile movement; each episode consisted of one or several contractile pulses. About half of the episodes consisted of a single pulse, and episodes with more than four pulses were rare. The average episode of activity lasted 2.6 min, while the average duration of a single pulse was 1.5 min. The mean quiescent interval between episodes of activity was 3.7 min. Some cells showed no pulsatile activity. Active cells averaged 6.6 episodes/h. The fraction of time which a Schwann cell spent in pulsatile activity varied widely, with an average of 28%. Behavior of Schwann cells in HEPES-buffered Hanks saline was generally similar to that in the complete medium. Raising K+ to 40 mM or Ca++ to 10 mM did not markedly affect the time course of the pulsatile motility, although the contractions were more vigorous in the high Ca++. Pulsatile movement was reversibly inhibited by cytochalasin B and appeared to be potentiated by drugs that disrupt microtubules.

Animals↗
PubMed1979

Rate of regeneration of sensory axons in transected rat sciatic nerve repaired with epineurial sutures.

Rat sciatic nerves were cut and the ends were rejoined using epineurial sutures. The most rapidly regenerating sensory axons, as measured by the pinch test, grew at a rate of 3.2 +/- 0.2 (SE) mm/day after a delay of 4.0 +/- 0.3 (SE) days. Regenerating axons began to grow beyond the site of injury about 2 days later in sutured nerves than in crushed nerves; this difference provides an estimate of the scar delay in sutured nerves. The rate of axonal outgrowth was slower in sutured nerves than in crushed nerves throughout the distal stump.

Animals↗
PubMed1978

Regeneration of motor axons in the rat sciatic nerve studied by labeling with axonally transported radioactive proteins.

Labeling regenerating axons with axonally transported radioactive proteins provides information about the location of the entire range of axons from the fastest growing ones to those which are trapped in the scar. We have used this technique to study the regeneration of motor axons in the rat sciatic nerve after a crush lesion. From 2 to 14 days after the crush the lumbar spinal cord was exposed by laminectomy and multiple injections of [3H]proline were made stereotactically in the ventral horn. Twenty-four hours later the nerves were removed and the distribution of radioactivity along the nerve was measured by liquid scintillation counting. There was a peak of radioactivity in the regenerating axons distal to the crush due to an accumulation of label in the tips of these axons. After a delay of 3.2 +/- 0.2 (S.E.) days, this peak advanced down the nerve at a rate of 3.0 +/- 0.1 (S.E.) mm/day. The leading edge of this peak, which marks the location of the endings of the most rapidly growing labeled fibers, moved down the nerve at a rate of 4.4 +/- 0.2 mm/day after a delay of 2.1 +/- 0.2 days; this is the same time course as that of the most rapidly regenerating sensory axons in the rat sciatic nerve, measured by the pinch test. Another peak of radioactivity at the crush site, presumed to represent the ends of unregenerated axons or misdirected sprouts, declined rapidly during the first week, and more slowly thereafter.

Animals↗
PubMed1977

Axonal transport of organelles visualized by light microscopy: cinemicrographic and computer analysis.

Rapid movements of intra-axonal organelles in acutely isolated single myelinated fibers from bullfrog sciatic nerve were visualized by dark-field microscopy. The movements were recorded by cinemicrography, and analyzed by computer-based methods. The movements are saltatory and bidirectional, but each particle moves mainly in a single direction. For more than 90% of the particles, the predominant movement direction is retrograde, i.e. toward the cell body. Quantitative measurements on a variety of parameters of the organelle movements are presented. Different particles in the same axon show a broad range of mean speeds. The average mean speed of movement in the retrograde direction at 28 degrees C was 1.08 micrometer/sec (S.D. - 0.41), equivalent to an axonal transport rate of 93 mm/day. Disperse distributions were also found for other parameters such as the instantaneous velocities of individual particles. Quantal velocities, periodic movement patterns, and specific 'channels' were not detected. When the data from a population of particles is treated statistically, the average mean speed, the distribution of velocities, and other statistical parameters are found to be similar in different axons studied at the same temperature. Direct microscopical observation of axonal organelle movement is a technique which provides information about axonal transport which is different from and complementary to that obtained from enzyme accumulation of radioactive tracer methods.

Animals↗
PubMedDate not supplied

Enkephalin and neuropeptide Y: two colocalized neuropeptides are independently regulated in primary cultures of bovine chromaffin cells.

We have found that Neuropeptide Y is colocalized with enkephalin in bovine adrenal chromaffin cells. The two peptides can be found in the same granules in those cells where they coexist. These cells correspond to the adrenergic subpopulation of chromaffin cells since they contain the epinephrine synthetic enzyme, phenylethanolamine N-methyltransferase. Despite their coexistence, production of the two peptides is independently regulated. Enkephalin levels are doubled after nicotinic depolarization (which increases enkephalin synthesis) or after treatment with reserpine (which increases enkephalin precursor processing). Neither of these treatments, acting by different mechanisms, has any effect on the levels of Neuropeptide Y.

Adrenal Glands↗