Extracellular matrix fibrils and cell contacts in the chick embryo

Summary The migration of neural crest and sclerotome cells and the extension of ventral root axons in chick embryos at stages 16–20 were studied by light microscopy as well as scanning and transmission electron microscopy at the leg bud level of fixed specimens. Extensive cellular movements take place in association with an extracellular matrix consisting of microfibrils. The neural crest and sclerotome cells migrate into the large matrix-filled extracellular space surrounding the neural tube and notochord, apparently using microfibril bundles as substratum. The cells exhibit pseudopodia which are closely associated with the matrix fibrils. The fibrils around the notochord show a spatial arrangement indicating that the sclerotome cells are contact-guided to their subsequent positions. Mutual cell contacts, including those established by cell processes, frequently show cytoplasmic electron dense plaques at adjacent membranes. These small plaque contacts might be correlated to contact inhibition of locomotion between the cells and participate in the guidance of cells. The growth cones of extending axons exhibit filopodia contacting both surrounding mesenchyme cells and extracellular fibrils. The orientation of the axons might thus be affected by contacts with cell surfaces as well as with extracellular material.Technical assistance was given by Mrs. Kerstin Ahlfors, Mrs. Charlotte Fällström, Mrs. Annika Kylberg and Mrs. Stine SöderströmSupported by grants from The Swedish Natural Science Research Council     

The fine structure of distal receptors on the labium of the aphid,Brevicoryne brassicae L. (Homoptera)

Summary Short peg receptors located at the distal tip of the aphid labium have the structure of mechanoreceptors. Each peg is innervated by a single sensory nerve which is anchored eccentrically to a basal cuticular tube and terminates in electron-dense material in the base of the peg. The arrangement and eccentric insertion of the eight pegs in the labial wall on one side of the stylet groove, with the eccentric insertions of their innervating neurones, provide a mirror image of the receptors on the opposite side. On the basis of a comparison of the structure of these receptors with that of tactile receptors for which electrophysiological data on sensitivity are available, it is possible to predict that the receptors detect both surface contact (pressure) and surface profile; and that the bilateral symmetry in the receptor arrangement facilitates the detection of vein contours which are preferred settling sites on the leaf. The structure of the dendritic terminal and its insertion is that of a well reinforced cytoskeleton designed to transmit tension to the cell membrane, in agreement with the concept that transduction is a membrane related phenomenon. The distal microtubules, fifty per-cent of which originate as well as terminate in the tubular body, are packed in electron-dense material which binds to the cell membrane. The membrane in turn is attached to cuticular components of the receptor. Abrupt changes in dimension of the dendritic outer segment may be designed to modulate the conduction of a membrane potential. On the other hand, lack of continuity in the microtubules makes these organelles poor candidates for the transduction of excitation from a distal site of stimulation to a proximal region.Supported by operating grants Nos. A 6063 and A 9856 from NRCC     

Morphological aspects of the hypothalamic-hypophyseal system

Summary The ultrastructure of the tanycyte ependyma in male 160–180 g Wistar albino rats was studied under normal conditions and in experiments involving long-term suppression of ACTH secretion and its long-term stimulation. The former was accomplished by daily (for 8 days) intraperitoneal administration of dexamethasone phosphate at low (5 g/100 g) and high (100 g/100 g) concentrations. The effectiveness of suppression of the hypothalamic-hypophyseal-adrenal system in the experimental animals was judged by their reaction to two-minute ether stress (determination of plasma corticosterone) and by the results of measurement of the adrenal weights. Stimulation of ACTH secretion was achieved by bilateral adrenalectomy; the animals were examined on days 8, 10, 14, and 22 following the operation. The results obtained were in agreement with the previously established fact that there is a negative correlation between tanycyte activity and hypophyseal adrenocorticotrophic function (Akmayev and Fidelina, 1974). They also testified to the predominant involvement of the median eminence tanycyte ependyma (beta-tanycytes according to the authors' nomenclature) in these relationships.It is supposed that these correlations are regulated by a feedback mechanism and attest to the involvement of beta-tanycytes in the inhibiting control of hypophyseal adrenocorticotrophic function. The mechanism of this control may be explained alternatively: either the tanycytes transport ACTH-suppressing substances (catecholamines, corticosteroids, ACTH) from the CSF to the hypophyseal portal system or they themselves secrete substances possessing ACTH-suppressive activity. The authors distinguish several types of vesicles in the beta-tanycytes, the number of which changed with experimentally induced shifts in hypophyseal adrenocorticotrophic function. These vesicles are discussed in connection with the transport and secretory activity of the tanycytes and are considered to be a possible substrate of the hypothalamic inhibiting effect on ACTH secretion.     

Immunocytochemical investigation of the hypothalamo-neurohypophysial system in birds

Summary The results of an immunohistochemical investigation of the hypothalamo-neurohypophysial system in several species of birds have shown that: (1) mesotocin and vasotocin are synthesized in separate neurons; (2) in all species investigated the distribution of mesotocinergic and vasotocinergic perikarya follows a common pattern; (3) the external zone of the avian anterior median eminence contains exclusively vasotocinergic nerve fibers, originating in supraoptic and ventral paraventricular regions; (4) the distribution of immunoreactive elements in the neural lobe shows a definite species-dependent pattern.     

Microtubules in myelinated and unmyelinated axons of rat sciatic nerve

Summary Tannic acid in glutaraldehyde was used to stain microtubules in myelinated and unmyelinated axons of rat sciatic nerve. In the majority of areas the tannic acid failed to penetrate the unmyelinated axons whilst penetrating neighbouring myelinated axons, suggesting a difference in the ability of the two types of nerves to exclude tannic acid. Where tannic acid had penetrated the unmyelinated axons the 13 protofilament substructure and size of the microtubules appeared identical to those seen in the myelinated axons.     

Comparative cellular localization of corticotropin and melanotropin in lerot adenohypophysis (Eliomys quercinus)

Summary Corticotropin and melanotropin producing cells were localized in the adenohypophysis of normal Lerots by using antibodies against synthetic corticotropins (anti 1–24 ACTH, anti 17–39 ACTH, anti 25–39 ACTH), and melanotropins (anti MSH, anti MSH). All the anticorticotropin sera stained the same cells both in the anterior lobe and in the intermediate lobe. The anti MSH serum only stained a few cells, exclusively located in the intermediate lobe. These MSH cells were not stained with anticorticotropin antibodies. The anti MSH serum revealed all the cells stained with anticorticotropin and anti MSH sera. Absorption tests showed that the 4–10 heptapeptide common to ACTH and MSH, is not responsible for the immunohistochemical staining. The staining of only some corticotrophs with the anti 4–10 ACTH serum might indicate the presence in these cells of a peptide with an accessible 4–10 site. These results are discussedWe thank A. Pillez for technical assistance (C.N.R.S.). This work was supported by a grant from U.E.R. III Lille 1976Attaché de Recherche INSERM     

Ciliary function of the frog oro-pharyngeal epithelium

Summary The palate epithelium of the frog was examined by scanning electron microscopy, light microscopy and high speed cine micrography. The cilia remain stationary for much of the time in the end-of-effective stroke position. Each beat cycle begins with a forwardly-directed recovery stroke lasting about 60 ms, followed by an effective stroke towards the oesophagus lasting about 12 ms. Activity can often be correlated with the presence of mucus, which is carried as strands on the tips of the ciliary effective strokes whilst the recovery strokes move beneath the mucus. Coordination of ciliary activity was very variable; local antiplectic metachrony of the recovery strokes could almost always be seen, and on very active epithelia effective strokes were associated with approximately diaplectic waves (either to left or right), but any particular pattern of coordinated activity was transient and quickly transformed to another pattern. Beating and coordination of these short cilia were compared with those of cilia propelling water.     

The topography of the caudal part of the paraventricular organ in Rana temporaria

Summary The results of a monoamine-fluorescence study of the hypothalamus of Rana temporaria show that the brain area corresponding with the nucleus infundibularis dorsalis (NID), as described in other species, does not differ, neither morphologically nor histochemically, from the paraventricular organ (PVO), with which it is anatomically continuous. It is concluded that a nucleus infundibularis dorsalis does not exist as a separate entity in this species.     

Linear and nonlinear models of the basilar membrane motion

A linear and a nonlinear transmission line model of the basilar membrane is described. The motion of the basilar membrane model has been simulated by numerical methods and compared with physiological data for several types of sound stimuli. It is shown that a linear model exhibits a frequency modulation in its impulse response that is in accordance with physiological data. The nonlinear model displays a sharpened frequency response for lower sound intensities. Futhermore, a nonlinear model explains why hearing damage imposed by short, high-intensity, sounds is extended to the low-frequency regions of the cochlea.     

Distribution and properties of NADPH-linked aldehyde reductases from rat brain synaptosomes

Studies on the subcellular distribution of NADPH-linked aldehyde reductase from rat brain showed that 10% of the total reductase activity is located in the mitochondrial-synaptosomal fraction. There are differences in the percentages of reductase activity found in the synaptosomes compared to cytosol in various regions of the brain. The NADPH-linked aldehyde reductase from the synaptosomal fraction exhibited a nonlinear Lineweaver-Burk plot. This nonlinearity is due to the presence of two distinct aldehyde reductases, which can be distinguished by Michealis constants forp-nitrobenzaldehyde of 4.1×10^–5 M and 2.6×10^–6 M. The two NADPH-linked aldehyde reductases isolated from synaptosomes were further characterized according to pH optima, andK _i values for inhibition by barbiturates. In addition regional distributions for the two enzymes were determined. TheK _i values for pentobarbital for the highK _m enzyme and the lowK _m enzyme were estimated to be 2×10^–5 M and 6×10^–5 M, respectively. It was concluded from the above studies that the lowK _m reductase is probably responsible for 3,4-dihydroxyphenylglycoaldehyde (derived from norepinephrine) reduction in brain and a role of the highK _m enzyme for protection of neurons from high concentrations of chemically reactive aldehydes was proposed.This work was supported in part by Grants from the National Institute of Mental Health, MH 18948 from the University of Colorado Council on Research and Creative Work and by an MBS Program Grant #081-39.This work was performed in partial fulfillment of the requirements for the Ph. D. thesis.