Abstract Not Available.

Abstract Not Available.

Over the last decade the tempo of research on the parathyroid gland and its relationship to metabolism has increased rapidly. As new advances in our knowledge of calcium and phosphorus metabolism are made, old ideas and theories must be re-evaluated and some modified, others discarded. New concepts of parathyroid function are being brought forth from the mass of literature which is accumulating. A reversal of thought is taking place regarding both the primary site of action of the parathyroid hormone and the mechanism of control of its secretion. For years it was stated that the primary action of the hormone was to regulate the kidney threshold for phosphorus excretion. In keeping with this idea, it was also felt that the phosphate level of the serum was the direct controlling agent of parathyroid hormone secretion. Enough evidence has now accumulated to show that the primary action of the parathyroid hormone is probably on bone rather than on the kidney. In addition, it is now widely accepted that the serum calcium level controls the secretion of the hormone. To date there has been a general lack of evidence for the exclusive control of hormone secretion by calcium. This is due, in large measure, to the lack of an adequate index of endogenous parathyroid activity. It has been heretofore difficult, if not impossible, to adequately assess the degree of parathyroid secretion under a number of physiological conditions. It is hoped that the work presented herein will prove helpful in providing additional evidence in support of the latter proposition.

Both electron microscopy and light microscope histochemistry have been used to describe the cytology of the hypodermis of the parasitic nematode, Capillaria hepatica. The hypodermis of the mid portion of the body of this species forms a complete cellular layer around the worm and may be divided into the following regions: the multicellular lateral and ventral chords; the interchordal hypodermis, apparently formed by flat processes of the cells of the multicellular chords; and the dorsal chord, probably formed by the internal reflection of the hypodermal cell processes which form the interchordal hypodermis. The cytology of the hypodermal gland cells which occur within the multicellular chords is described in detail. The elaboration of the infolded cell membrane of the gland cell forms a region of the cell termed the lamellar apparatus. This region is associated with a pore through the cuticle, but is separated from this pore by an area termed the pore chamber which contains a gel-like material. The outer margin of this material is marked by a boundary layer while diffuse, granular cap material is associated with the outer surface of this layer. No morphological evidence has been found to suggest that the cell is glandular in function, but the structure of the lamellar apparatus would be consistent with the suggestion that the cell may function in either osmotic or ionic regulation. Experiments in which the osmotic value of the external environment of the worms was altered offer no evidence either for or against such a function. The uptake of neutral red and colloidal gold by the hypodermis is similarly inconclusive, but shows that such materials are concentrated into vacuoles within the non-glandular hypodermal cells. Glycogen, the chief storage product of the body wall, occurs in the basal two-thirds of the non-glandular cells. The possible significance of the concentration of the most of the organelles of the non-glandular cells in the apical cytoplasm is discussed. The structure of the six-layered cuticle, and of the somatic musculature is described, and the relationship of the hypodermis to these tissues is discussed. No evidence has been found for the existence of pore canals extending from the hypodermis into the cuticle, nor of supportive fibrils extending from the muscle cell into the hypodermis.

The circadian rhythm (CR) of compound optic nerve potentials (CAPs) from the isolated eye of Aplysia californica can be phase shifted by 5-HT (serotonin). Data are presented in this thesis which suggest that 5-HT acts as a transmitter of temporal information to the circadian pacemaker (CP) in the Aplysia eye. Six h. 5-HT treatments produce both advance and delay phase shifts, are effective at low concentrations (10('-7)M), and alter both the spontaneous activity of the eye and the response of the eye to light. In addition, evidence is presented that the eye contains 5-HT (50ng/mg protein), can synthesis 5-HT from tryptophan, and that the 5-HT stored in the eye can be depleted by Hi-K('+) (depolarizing) treatments. The effects of 5-HT on the eye also show a degree of stereospecificity since three structurally related indoleamines, LSD, Br-LSD, and bufotenine acted as agonists of 5-HT when added to the eye, while other amines (5-hydroxytryptophan, tryptamine, 7-methyltryptamine, and others) and two putative neurotransmitters (Dopamine, Acetylcholine) did not mimic the effects of 5-HT. These results suggest that 5-HT may act as a neurotransmitter in the Aplysia eye. 5-HT appears to be producing its effects on the CR by acting either directly on the CR cell(s), or on cells electrotonically coupled to the CR cell(s), since treatments which block transmitter release (HiMg('2+)-LoCa('2+)-EGTA) do not inhibit phase shifting by 5-HT. The phase shifting effects of 5-HT may be mediated by changes in cellular cAMP, since 8-benzylthio-cAMP (2 x 10('-3)M), a cAMP analog, mimics 5-HT by producing both advance and delay phase shifts when given during the same phases as 5-HT. Papaverine (2 x 10('-4)M), which is a phosphodiesterase inhibitor that has been shown to increase cAMP levels in Aplysia tissue, also mimicked the phase shifting effects of 5-HT. IBMX (5 x 10('-4)M), another phosphodiesterase inhibitor, did not produce significant phase shifts when given alone, but did potentiate the phase shifting effects of subthreshold doses of 5-HT (10('-8)M). The results presented in this thesis are significant because 5-HT is the first endogenous substance shown to produce phase shifts in Aplysia and one of the few natural substances known to produce effects on the CR from any system. The data suggest that 5-HT may be part of a pathway which transmits entrainment information to the CP cell(s) in the eye, and that the effects of 5-HT may be mediated by changing levels of cAMP. 5-HT may provide a natural marker for investigating entrainment pathways and mechanisms in the Aplysia eye.

A semi-intact eye-cup preparation was developed which maintains visual responses and enables intracellular recordings to be made from the optic lobes of the crayfish compound eye. Sustaining fibers (SFs) were impaled with lucifer yellow electrodes near their entrance to the second optic ganglion or Medulla (where the SFs originate). Corneal receptive fields were determined and the SFs identified based on the previous work of Wiersma and Yamaguchi (1966). Following identification of each cell, the dendritic morphology was observed with lucifer yellow iontophoresis and subsequent fluorescence microscopy. An individual SF possesses a dendritic arborization restricted to that portion of the Medulla corresponding to its corneal receptive field. Therefore, the position of the dendritic tree combined with the retinotopic organization within the distal optic neuropils determine each SF's visual receptive field. Contour sensitivity maps were obtained for SF 019. The quantitative variation in sensitivity along a given arc in visual space was correlated with 019 dendritic density along the corresponding portion of the Medulla. The SFs' responses to various stimulus conditions were recorded intracellularly in their integrating segments. No synaptic interactions between SFs were observed. Bursting in response to broad-field intense illumination results from periodic excitatory synaptic input. Other visual interneurons were impaled and dye-filled. These included, (a) Phasic light-on cells, (b) Tonic light-off cells, (c) Phasic light-on and -off cells, (d) Optic tract motion detectors, (e) Nonspiking light-on neurons, (f) Lamina monopolar cells, and (g) Lamina tangential cells (TAN2). A group of neurosecretory cells analogous to the Medulla Externa X-Organ of other crustaceans was discovered in the crayfish. These neurosecretory cells are also interneurons possessing a modality specific (visual) synaptic input. They are inhibited by step increases in illumination and the response lasts for the duration of the stimulus. Transient off-inhibition is commonly present. The IPSPs reverse near resting membrane potentia and appear to be GABA mediated and chloride-dependent. These cells project axons to the proximal edge of the Lamina and have a vertical plane of dendrites in the same layer of the Medulla as the SFs. It is proposed that these cells are involved in the neurosecretory control of the circadian rhythm of screening pigment migration and/or photoreceptor sensitivity in the retina.

The crayfish Sustaining fibers (SFs) are used to analyze the functional organization of the second optic lobe, the Medulla. The SFs are tonic ON visual interneurons whose dendrites lie in a single plane in the Medullary neuropile, and whose axons project via the optic tract to the supraesophageal ganglion, or brain. The SF passive properties are remarkable linear. In the region of the primary neurite generally recorded from, these neurons show linear i-V, i-f and V-f functions. The SF dendrites appear to be entirely passive integrators of their synaptic inputs. The light-driven synaptic input to SFs is delivered by a retinotopic columnar array. The EPSP in response to a light stimulus is large (20-40 mV), and consists of two phases. The transient phase has a reversal potential approximately 50 mV above resting potential. The steady-state phase has a reversal potential about 37 mV above rest, and is associated with a steady-state input conductance which has a peak of about 120% of the resting value. A light-OFF hyperpolarization has a reversal potential 5 mV below rest and is associated with a conductance increase. Cable modelling of SFs revealed that the dendrites are electrotonically compact, about 0.5(lamda) in total width. Passive voltage attenuations in the dendrites are very small (average 6% proximal to distal, 35% distal to proximal). The synaptic parameters (reversal potential and conductance change) are used in conjunction with the model to accurately predict the EPSP voltage. A class of local, non-spiking amacrine (axon-less) cells is described. They are morphologically similar to the SF dendritic trees but with two distinct planes of dendrites and no axons. These neurons respond to light with a response like the SF EPSP but produce no action potentials. The amacrine cells strongly inhibit SF excitatory inputs without directly synapsing on the SFs. Similarities between amacrine cell properties and SF surround inhibition lead to the conclusion that the amacrine cells are directly involved in the formation of SF surround inhibition, and act on the columnar input pathway of the SFs.

Experiments were conducted to determine the currents involved in the pacemaker activity of aggregates and single cells from the embryonic chick heart. Two microelectrode voltage clamp studies of embryonic chick ventricular heart cell aggregates revealed two time-dependent current components in the pacemaker range of potentials ($-$60 to $-$120 mV). Barium (Ba, 5 mM) blocked the more negatively activated time-dependent component unmasking a component which remained inwardly directed for hyperpolarizing steps beyond the potassium equilibrium potential (E$ sb{ rm K}$). This component, which was blocked by cesium (Cs, 2 mM), is consistent with an inward current which activates upon hyperpolarization (the I, model) as proposed by DiFrancesco (1981a,b), for Purkinje fibers. / In order to minimize the problems associated with the accumulation/depletion of ions in the extracellular space during voltage clamp experiments, studies were carried out on single ventricular cells or small clusters of ventricular cells.

No description available.

Embryonic Xenopus muscle cells grown in culture develop patches of high acetylcholine receptor (AChR) density which can be visualized using fluorescent -bungarotoxin. In the present study it was found that these AChR patches often occur at sites of strong adhesion with the culture dish and remain in a fixed position, relatively unchanged for several days. Discrete patches of cholinesterase (ChE) also develop, often at the same sites as the AChR patches, even if the muscle cells have never been innervated in vivo. ChE, like AChRs, also becomes localized at sites of nerve-muscle contact in cultures grown with spinal cord cells whether or not neuromuscular transmission is blocked by curare. The results further indicate that in addition to directing AChR and ChE localization to the site of nerve-muscle contact, the nerve prevents the formation and reduces the survival of AChR and ChE patches elsewhere on the muscle cell.