Axonal pathways of giant neurons identified in the right parietal and visceral ganglia in the suboesophageal ganglia of an African giant snail (Achatina fulica Férussac)

• 1.1. The axonal pathways of thirteen giant neurons identified in the right parietal and the visceral ganglia, found in the suboesophageal ganglia of an African giant snail (Achatina fulica Férussac), were investigated by intracellular injections of Lucifer Yellow, with regard to their axonal projections into the following six peripheral nerves: lap n (left anterior palliai nerve), lpp n (left posterior palliai nerve), int n (intestinal nerve), anal n (anal nerve), rpp n (right posterior palliai nerve) and rap n (right anterior palliai nerve).
• 2.2. These projections were confirmed by the recording of the axonal responses from the nerves.
• 3.3. On the dorsal surface of the right parietal ganglion, the following four giant neurons were identified: PON (periodically oscillating neuron), TAN (tonically autoactive neuron), RAPN (right anterior palliai neuron), and d-RPLN (dorsal-right parietal large neuron).
• 4.4. The PON axonal pathways projected into int n; those of TAN into all of the nerves examined; those of RAPN into lap n, lpp n, int n, anal n and rap n.; and those of d-RPLN into pd nn (pedal nerves) through the pedal ganglia, lpp n, anal n, rap n and sometimes lap n.
• 5.5. On the dorsal surface of the visceral ganglion, the following four giant neurons were also identified: VIN (visceral intermittently firing neuron), FAN (frequently autoactive neuron), INN (intestinal nerve neuron) and d-VLN (dorsal-visceral large neuron).
• 6.6. The VIN axonal pathways, which had no branch into the six nerves examined, went to both the right and the left pedal ganglia, sending a branch into the cerebro-pleural connective; those of FAN projected into lap n, anal n and rap n, and sometimes into lpp n and rpp n; those of INN into int n; and those of d-VLN into pd nn, lap n, lpp n, anal n and rap n.
• 7.7. On the ventral surface of the right parietal ganglion, v-RPLN (ventral-right parietal large neuron) was identified. The axonal pathways went to pd nn, lap n, lpp n, anal n and rap n.
• 8.8. On the ventral surface of the visceral ganglion, the four giant neurons, v-VNAN (ventral-visceral noisy autoactive neuron), v-VLN (ventral-visceral large neuron), r-VMN (right-visceral multiple spike neuron) and 1-VMN (left-visceral multiple spike neuron) were identified.
• 9.9. The axonal pathway of v-VNAN projected into rpp n and rap n; those of v-VLN into pd nn, lap n, anal n, rap n and sometimes to lpp n; those of r-VMN into int n and rpp n; and those of 1-VMN also into int n and rpp n.
• 10.10. The present morphologial investigations of the giant neurons confirmed well the identifications of the neurons previously studied. The axon of the neurons examined here, except for VIN, projected into some of the peripheral nerves, while the VIN axon extended into the cerebro-pleural connective.
• 11.11. The five neurons, PON, TAN, v-VNAN, r-VMN and 1-VMN, formed fine axonal arborizations terminating at the neuropile, while the arborizations of the other neurons were not clearly observed.
• 12.12. Although the anatomical structures of the portion examined of the suboesophageal ganglia are asymmetrical, three pairs of symmetrically-situated neurons, d-RPLN and d-VLN, v-RPLN and v-VLN, and r-VMN and 1-VMN, were found, indicating the existence of symmetrical components in the ganglia.

     

Role of microtubules in milk secretion — Action of colchicine on microtubules and exocytosis of secretory vesicles in rat mammary epithelial cells

Summary Effect of colchicine on microtubules was studied in mammary epithelial cells treated both in vivo and in vitro with the alkaloid. Three hours after the intramammary infusion of colchicine, secretory activity of mammary epithelia ceased, milk constituents accumulated and were randomly distributed within the cytoplasm, sometimes leaking into the perialveolar connective tissue, and autophagic vacuoles were prevalent. It appeared that an accelerated involutionary process was occurring. No microtubules were observed after this treatment. In vitro treated cells appeared to be less affected by the alkaloid. Although numerous casein-containing secretory vesicles accumulated in the cytoplasm, lipid droplet accumulation was less, and fewer autophagic vacuoles were observed, although lysosomes were commonly observed. Occasionally, obliquely sectioned microtubules were found in cells treated with low concentrations of colchicine but were absent at higher colchicine concentrations; however, paracrystalline inclusions (tubulin aggregates) were observed in some cells at all concentrations of the drug. These observations provide evidence that drugs which interfere with microtubule integrity reduce the secretory activity in mammary epithelia. This evidence is consistent with the concept of an association of the microtubular system and the secretory process.     

“Insulin-like” effects of palmitate compromise insulin signalling in hypothalamic neurons

Journal of Comparative Physiology B - Saturated fatty acids are implicated in the development of metabolic diseases, including obesity and type 2 diabetes. There is evidence, however, that...     

Evidence for three “classes” of microtubules in the interpolar space of the mitotic micronucleus of a ciliate and the participation of the nuclear envelope in conferring stability to microtubules

Exposure of Nyctotherus ovalis to low temperatures or vinblastine caused similar reactions of classes of microtubules (mt) present in the mitotic micronucleus of this ciliate towards both treatments. However, differences of sensitivity between certain classes of mt at individual mitotic stages exist. Unlike the kinetochore mt (kmt) of most other eukaryotic cells, kmt in Nyctotherus completely disassemble after incubation at 6–8 ° C (60 min) and most disappear after prolonged exposure to vinblastine (10^–5 M, 16 h). The depolymerization of kmt causes the collapse of the spindle and a dislocation of chromosomes at metaphase, yet the reduced number of kmt after vinblastine-treatment still allows an alignment of composite complexes at the spindle equator. The data suggest that three individual sets of mt exist in the interpolar spindle region during ana- and telophase: 1) interpolar mt (int mt), which are assembled during anaphase, are cold- and vinblastine sensitive; 2) manchette mt (ma mt), which are first observed underneath the nuclear envelope during mid-anaphase, are cold-stable and insensitive to vinblastine treatment (10^–5 M); after prolonged treatment (16 h) they form spiral structures; 3) stembody mt (st mt), comprising the interpolar region of the nucleus during telophase, are cold- and vinblastine insensitive. Paracrystalline structures resembling a stembody are formed in telophase-like division stages after prolonged vinblastine exposure (16 h, 10^–5 M). Since kmt and int mt possess the same sensitivity under depolymerizing conditions, they probably have a similar composition. Thus the idea that the int mt in this organism arise by elongation of kmt is supported. However, st mt apparently do not originate from an extension of preexistent int mt, but appear to represent a new set of stable mt. This is emphasized not only by their greater stability compared to the int mt but also by the distribution of cold-stable mt in late anaphase micronuclei. The ma mt may be an intermediary step in formation of st mt since their stability resembles that of the st mt. A comparison of the substructure of vinblastine-induced paracrystals in Nyctotherus with those observed in in vitro systems with known composition suggests that a turnover of MAPs may be responsible for the different stability of mt and thus could specify and regulate mt sensitivity and function. Another organelle, possibly involved in conferring stability to mt, is the nuclear membrane. The assumption that the nuclear envelope possesses an intrinsic property to nucleate mt and thus aid in the alignment of mt is supported.     

What generates flux of tubulin in kinetochore microtubules?

Summary. We discuss models for production of tubulin flux in kinetochore microtubules. Current models concentrate solely on microtubules and their associated motors and enzymes. For example, in some models the driving force for flux is enzymes at the poles and the kinetochores; in others the driving force is motor molecules that are associated with a stationary spindle matrix. We present a different viewpoint, that microtubules are propelled poleward by forces arising from the spindle matrix, that the forces on the microtubules “activate” polymerising and depolymerising enzymes at kinetochores and poles, that matrix forces utilise actin, myosin, and microtubule motors, and that the matrix itself may not necessarily be static. Correspondence: A. Forer, Biology Department, York University, 4700 Keele Street, Toronto, ON M3J 1P3, Canada.     

Glial localization of interleukin-1α in invertebrate ganglia

1. Mytilus pedal ganglion contains a small population of glial cells that are immunopositive for interleukin-1 alpha. Positively stained fibers can also be seen in the neuropil of these sections. 2. The marine worm Nereis diversicolor also exhibits positive neural immunostaining for interleukin-1 alpha. 3. Both organisms contain hemocytes that contain immunoactivity for interleukin-1 alpha. The study suggests interleukin-1 alpha to be an ancient cytokine given its presence in organisms that evolved significantly earlier than mammals.     

Mechanisms of corticofugal control of the activity of “vagal” viscerosensory neurons in theNucleus tractus solitarii

In experiemnts on cats under chloralose-nembutal anesthesia, we studied viscerosensory neurons in thenucl. tractus solitarii identified by their responses to stimulation of then. vagus. The responses of these cells to stimulation of the secondary sensorimotor cortex (zoneS2) and dorsal regions of field 25 of the limbic cortex (DLC) were recorded. A substantial part of the “vagal” viscerosensory units demonstrated convergent properties and responded toS2 and DLC stimulations by phasic responses. The short latencies of these responses were indicative of oligosynaptic and, in some cases, even monosynaptic transmission of corticofugal influences on a considerable part of such neurons. Using paired stimulation allowed us to demonstrate that the effects of stimulation of the visceral afferent fiber undergo long-lasting suppression exerted by descending corticofugal volleys. The mechanisms of cortical control of the activity of bulbar viscerosensory neurons are discussed.     

Pharmacological characteristics of four giant neurons identified in the cerebral ganglia of an African giant snail (Achatina fulica Férussac)

Two giant neurons, d-RCDN (dorsal-right cerebral distinct neuron) and d-LCDN (dorsal left cerebral distinct neuron), with a diameter of about 100 microns, were found symmetrically on the dorsal surface of the cerebral ganglia of an African giant snail (Achatina fulica Férussac). They showed spontaneous spike discharges at a stable frequency. Two giant neurons, v-RCDN (ventral-right cerebral distinct neuron) and v-LCDN (ventral-left cerebral distinct neuron), (diameter, approx. 150 microns) were identified on the ventral surface of the same ganglia. No spontaneous spike discharges were evident. Both d-RCDN and d-LCDN were equally inhibited by dopamine, octopamine, 5-hydroxytryptamine and histamine. Acetylcholine sometimes showed inhibitory effects, but they were not so stable. No substance having excitatory effects on the neurons was found. Both v-RCDN and v-LCDN were equally excited by octopamine, 5-hydroxytryptamine, GABA and acetylcholine and inhibited by dopamine and beta-hydroxy-L-glutamic acid.     

Effects of synthetic peptides on giant neurons identified in the ganglia of an African giant snail (Achatina fulica Férussac)--II

Thirteen synthetic biologically-active peptides, which were classified into the peptides proposed as neurotransmitters in mammals and invertebrates and neural venom peptides, were investigated for their effects on the following six identifiable giant neurons of an African giant snail (Achatina fulica Férussac): RAPN (right anterior pallial neuron), INN (intestinal nerve neuron), RPeNLN (right pedal nerve large neuron), LPeNLN (left pedal nerve large neuron), d-LPeLN (dorsal-left pedal large neuron) and d-LPeCN (dorsal-left pedal constantly firing neuron). Oxytocin and proctolin at 10(-4)M excited the RAPN membrane potential, whereas FMRFamide at the same concentration inhibited the same neuron. FMRFamide at 10(-4)M markedly inhibited the d-LPeLN membrane potential, sometimes produced inhibition of RPeNLN and LPeNLN, showed varied effects (excitatory or inhibitory) on INN, and had no effect on d-LPeCN. The other peptides examined had almost no effect on any of the neurons tested.     

Input output curves of aggregates of “simple counter” neurons

The refractory periods of an aggregate of simple “counter” neurons are assumed distributed according to some probability frequency. The output of the aggregate is computed for rectangular and triangular distributions. In particular, it is shown that the maximum output of an aggregate with any triangular distribution cannot exceed the maximum output of its average neuron by a factor greater than 2 ln 2. This puts an upper bound on the amount of departure from the behavior of the average neuron which an aggregate characterized by a certain type of distribution can show. Next, the aggregate is supposed to be subjected to regularly spaced stimuli. Under these conditions, a single neuron will give a discontinuous output curve. If, however, the refractory periods are distributed according to some frequency, the output curve may be “smoothed out.” A general condition on the distribution is derived which makes the output monotone increasing with the input. The condition is applied to some special cases.     

Posttranslational acetylation of α-tubulin constrains protofilament number in native microtubules

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Highlights? α-TAT mutants have short microtubules and variable protofilament number ? α-tubulin K40 acetylation promotes interprotofilament salt bridges ? α-tubulin K40 acetylation is a key constraint on protofilament number in vivo     

Pharmacological characteristics of the two largest neurons symmetrically situated in the suboesophageal ganglia of an African giant snail (Achatina fulica férussac)

1. Pharmacological characteristics of the two largest neurons, r-PLN (right-parietal large neuron) and d-VLN (dorsal-visceral large neuron), situated symmetrically on the anterior-dorsal surface in the suboesophageal ganglia of an African giant snail (Achatina fulica Férussac), were determined.2. Of the catecholamines examined, dopamine (DA) showed marked but complex effects on the two neurons. DA produced a transient excitation followed by either hyperpolarization or depolarization of the neuromembranes. L-Norepinephrine produced a slight depolarization of the neurons.3. 5-Hydroxytryptamine (5-HT) produced marked excitation of both neurons. Bufotenine showed the same effects, but they were weaker than those of 5-HT.4. Histamine showed inhibatory effects on the two neurons examined, whereas L-histidine had rather slight or no excitatory effects.5. Of the amino acids examined, L-homocysteic acid (L-HCA) and erythro-β-hydroxy-L-glutamic acid had marked excitatory effects on r-PLN and d-VLN. L-Homocysteine sulfinic acid also showed the excitatory effects, but they were weaker than those of L-HCA. Glycine and L-methionine had slight excitatory effects on both neurons, whereas L-aspartic acid, L-glutamic acid and GABA had none.6. Acetylcholine (ACh) exhibited marked and complex effects on r-PLN and d-VLN. In trials, ACh produced either excitation or inhibation of both neurons. Propionylcholine and butyrycholine had slightly less effect, producing a slight inhibation of r-PLN and either excitation or inhibation of d-VLN in trials.     

Twist (and rotation?) of central-pair microtubules in flagella ofPoterioochromonas

Summary The chrysoflagellate algaPoterioochromonas bears two unequal flagella. There is a short naked one and a long flagellum with mastigonemes. Ultrastructural investigation reveals that the centralpair microtubules in both flagella have no fixed position with respect to the flagellar base and root system, or the mastigoneme rows in the long flagellum. The central-pair microtubules are twisted several times along the length of the flagellum. This might indicate active or passive rotation of the central-pair microtubules during flagellar beat.     

“SIF” cells in the sympathetic ganglia of the bullfrog,Rana catesbeiana: variety in population and innervation

Summary Small intensely fluorescent (SIF) cells appeared singly or, more frequently, in variably-sized clusters in the sacroccygeal 8th and 9th sympathetic ganglia of the bullfrog. Smaller clusters containing only two to nine SIF cells accounted for 61% of 1773 clusters examined. The largest cluster contained 283 cells. The number of cells in individual ganglia also varied from 21 to 3332. SIF cells, solitary as well as in smaller clusters, received no distinct form of the synaptic contact. In contrast, the cells in larger clusters were frequently innervated by nerve endings that were similar in vesicular constitution to the nerve endings on principal ganglion (PG) cells. No synaptic contact was found between SIF cells and PG cells. SIF cells were also characterized by their location in the vicinity of blood capillaries with a continuous endothelium. p]Our observation seems to suggest that larger clusters of SIF cells receiving nerve endings are linked to a paracrine and/or endocrine system. Chemical influence via the blood stream and intraganglionic milieu for non-innervated SIF cells in the solitary or smaller clusters is a subject for speculation. An interneuronal role of SIF cells to relay stimuli to PG cells seems unlikely. The possible functions here assigned to SIF cells could be variable in efficiency depending on their population and density.     

Is the preprophase band of microtubules a marker of organization in suspension cultures?

Summary To date it has been accepted that preprophase bands of microtubules (PPBs) either do not precede cell division or do so inconsistently in suspension cultures, the assumption being that such cultures proliferate in an unorganized state in which placement of cell plates is not regulated by the PPB system that is widespread in organized tissues. Using indirect immunofluorescence microscopy with antitubulin, the relative frequency of occurrence of PPBs in enzymatically separated cells from root tips and suspension cultures of carrot and tobacco, was quantified by taking the ratio of the number of PPBs: phragmoplast. This ratio was termed the PPB index.One carrot suspension culture proliferated in a medium containing 2,4-Dichlorophenoxyacetic acid (2,4-D), and recognizable stages in somatic embryogenesis formed when 2,4-D was removed from the medium. Another carrot suspension culture was nonembryogenic and removal of 2,4-D resulted in a reduction of cell division and increase in cell elongation. The tobacco culture was a cytokinin habituated cell line and also required 2,4-D to maintain cell division. It ceased proliferation, and cell elongation took place if 2,4-D was removed.The PPB index in the root tips from both species, and in both types of carrot suspension culture was approximately the same but was approx. 15-fold lower in the tobacco suspension. PPBs in the tobacco suspension were atypical in structure as well as sparse in numbers. The PPB index allows quantitative comparisons between different tissues to be made. The low PPB index and the irregular PPBs in the tobacco suspension correlates with its inability to undergo organized morphogenesis and generate spatially defined cell lineages upon 2,4-D removal. In contrast, the high PPB index in the carrot suspension cultures correlates with their potential for organized embryo formation, whether or not that potential is realized by withdrawal of 2,4-D. However, their high PPB index is not obligatorily coupled to embryogenesis.     

The distribution of microtubules in differentiating cells of Micrasterias denticulata bréb.

Summary As an extension of earlier cytophysiological and morphological studies on differentiating cells of Micrasterias denticulata, a fine structural investigation of glutaraldehyde-osmium tetroxide fixed material has been made. Special emphasis has been placed on the distribution of cytoplasmic microtubules and on their possible role in the processes of growth and differentiation. Four distinct systems of microtubules were found: (a) a band in the cortical protoplasm of the isthmus region which surrounds the nucleus; (b) several bands in the cortical protoplasm of the old half cells, with rod-like cross bridges between individual microtubules and between the microtubules and the plasmalemma; (c) clusters of microtubules near the posttelophase nucleus, some separated by intertubular structures possibly fibrils; and (d) microtubules in the internal and cortical protoplasm of differentiating half cells.This work was supported by a National Science Foundation Senior Foreign Scientist Fellowship to Dr. Oswald Kiermayer,and by funds of Training Grant 5-T1-GM-707-06 to Dr. Keith R. Porter.     

“CLASPing” tungsten's effects on microtubules with “PINs”

Tungsten, supplied as sodium tungstate, inhibits root elongation in Arabidopsis thaliana, which has been attributed to a diminishing of PIN2 and PIN3 auxin efflux carriers. In this work, we sought to analyze the effect of tungsten on cortical microtubules and CLASP (Cytoplasmic Linker Associated Protein), which are also involved in the anisotropic cell expansion of root cells. Seedlings grown in a tungsten-free substrate for 4 d and then transplanted into a tungsten-containing substrate exhibited randomly oriented microtubules in a time-dependent manner. While tungsten had no effect on roots treated for 3 h, microtubule alignment was obviously affected in the transition and elongation zones after a 6, 12, 24, 48 h tungsten treatment, at prolonged tungsten administrations and in seedlings grown directly in the presence of tungsten. This change in microtubule orientation may be associated with the reduction of CLASP protein expression induced by tungsten, as evidenced in experiments with plants expressing the CLASP-GFP protein. A possible mechanism, by which the coordinated functions of CLASP, PIN2 and microtubules are affected, as revealed by inhibited root growth, is discussed.