Fine structure of a sensory organ in the arista of Drosophila melanogaster and some other dipterans

Summary The arista, a characteristic appendage of dipteran antennae, consists of 2 short segments at the base and a long distal shaft. A small sensory ganglion, from which arises the aristal nerve, is located proximally in the shaft. The fine structure of the aristal sensory organ was studied in detail in the fruitfly (Drosophila) and for comparison in the housefly (Musca) and the blowfly (Calliphora). In Drosophila, the aristal sense organ consists of 3 identical sensilla that terminate in the hemolymph space of the aristal shaft, and not in an external cuticular apparatus. Each sensillum comprises 2 bipolar neurons and 2 sheath cells; a third sheath cell envelops the somata of all six neurons of the ganglion. The neurons have long slender dendrites with the usual subdivision into an inner and an outer segment. One of the outer segments is highly lamellated and bears small particles (BOSS-structures) on the outside of its cell membrane; the other outer segment is unbranched and has a small diameter. The fine structure of the first dendrite is strongly reminiscent of thermoreceptors known from the antennae of other insects. These thermoreceptors are often coupled with hygroreceptors; however, we can only speculate whether the second dendrite of the aristal organ also has this function. Our present results argue against mechanoreceptive functions, as formerly postulated. The aristal sense organs in Musca and Calliphora are similar to those in Drosophila, but contain more sensilla (12 in Musca, 18 in Calliphora).     

Stereological and functional investigations on isolated adrenocortical cells: Zona fasciculata/reticularis cells of chronically ACTH-treated rats

Summary The morphology and function of isolated inner (zona fasciculata/reticularis) adrenocortical cells of rats pretreated with ACTH for 3, 6, 9 or 12 days were investigated. ACTH treatment induced a notable time-dependent enhancement in the steroidogenic capacity (corticosterone production) and growth of inner cells. The volumes of cells, mitochondrial compartment, membrane space [the cellular space occupied by smooth endoplasmic reticulum (SER) membranes] and lipid-droplet compartment, as well as the surface area of mitochondrial cristae and SER tubules, were increased in relation to the duration of ACTH pretreatment, and showed a highly significant positive linear correlation with both basal and stimulated corticosterone production. The acute exposure of isolated cells to ACTH provoked a striking lipid-droplet depletion, the extent of which was linearly and positively correlated with stimulated corticosterone secretion. The hypertrophy of the mitochondrial compartment and SER are interpreted as the morphological counterpart of the enhanced steroidogenic capacity of inner adrenocortical cells, inasmuch as the enzymes of steroid synthesis are located in these two organelles, and it is well known that chronic ACTH exposure stimulates the de novo synthesis of many of them in vivo. The rise in the number of lipid droplets, in which cholesterol is stored, is interpreted as being due to the fact that, under chronic ACTH treatment, the processes leading to cholesterol accumulation in adrenocortical cells (exogenous uptake and endogenous synthesis) exceed those of its utilization in basal steroid secretion. Cholesterol accumulated in lipid droplets as a reserve material may be rapidly utilized after acute ACTH exposure to meet the needs of the enhanced steroidogenic capacity of adrenocortical cells.     

Characterization of the follicles in the intermediate lobe of the pituitary gland of the Mongolian gerbil (Meriones unguiculatus)

Summary The Mongolian gerbil (Meriones unguiculatus) contains abundant follicles throughout the intermediate lobe (IL) of the pituitary gland in the adult animal. The mode of follicle formation, the nature of the follicle building cells and the distribution of follicles were investigated in semithin sections of the gerbil IL. The sections were stained conventionally, or immunohistochemically with antibodies directed against -melanocyte stimulating hormone (- MSH). Follicular cells were constantly -MSH-negative, and resembled the marginal cells lining the hypophyseal cleft with regard to their cytological and immunohistochemical properties. Moreover, follicular cells appeared to be derived from strands of marginal cells that regularly invaginated deep into the IL. Both follicular and marginal cells often made up cellular clusters. This process coincided with follicle formation and the generation or transport of the colloidal content found inside follicles and the hypophyseal cleft. Although the non-secretory cells of the IL obviously constituted one major source of pituitary colloid in the gerbil, -MSH-positive secretory cells, which occasionally were found to be discharged into the cleft cavity, might contribute to the colloidal contents.     

Morphological changes in the junctional complex of cells in the arachnoid layer of the rat after cold injury

Summary The junctional complexes of cells in the outer arachnoid layer overlying the cerebral cortex of 2-week-old rats were examined with freeze-fracture electron microscopy up to 60 min after transcranial cold injury to the dorsal surface of the brain. Within 30 min after injury, areas of gap and tight junctions with morphological features characteristic of junction formation and/or junction disruption were found scattered among normal junctional complexes in some arachnoid cells. Within 60 min after injury, tight junctions with features typical of less leaky zonulae occludentes were present in all arachnoid cells examined. These morphological features include increases in the number of tight junctional strands and the number of strand-to-strand anatomoses. Gap junctions were interspersed among the tight junctional strands, and many were completely encircled by the strands. The increase in the number and complexity of the tight junctional strands in response to brain injury may be the morphological basis for the maintenance of the cerebrospinal fluid-blood dural barrier.This study was supported by the National Institute of Neurological and Communicative Disorders and Stroke Grant NS20590. The opinions or assertions contained herein are the private ones of the authors and are not to be construed as official or reflecting the views of the DoD or the USUHS. The experiments reported herein were conducted according to the principles set forth in the Guide for Care and Use of Laboratory Animals, Institute of Laboratory Animal Resources, National Research Council, DHEW Pub. No. (NIH) 78-23     

Abnormal expression ofα-L-fucosidase in lymphoid cell lines of fucosidosis patients

Fucosidosis is an autosomal recessive lysosomal storage disease due to a deficiency of-L-fucosidase activity in tissues and body fluids. Exponentially growing lymphoid cell cultures from four fucosidosis patients had 2.7-fold to 15.6-fold less extracellular-L-fucosidase protein and 28.8-fold to 144.0-fold less intracellular-L-fucosidase protein with negligible catalytic activity, compared to the mean of 19 control cultures. The percentage of total-L-fucosidase protein released extracellularly by cultures from the four patients was 64 to 85%, compared to 35±9% for control cultures. Intracellular and extracellular enzyme forms in fucosidosis and control cell lines were glycoproteins containing polypeptide chains ofM _r=52,000. During a 1.5-hr pulse-label with³⁵S-methionine,-L-fucosidase was synthesized by control cells and two fucosidosis cell lines as an intracellular form withM _r=58,000. During a subsequent 21-hr chase with unlabeled methionine, mutant enzyme was almost entirely processed to an extracellular form withM _r=62,000. In contrast, only 25–30% of control enzyme was processed to an extracellular form (M _r=62,000), with the remainder retained intracellularly (M _r=60,000). In the other two fucosidosis cell lines,-L-fucosidase was synthesized as an intracellular form withM _r=56,000 that was processed to an extracellular form withM _r=60,000. In summary, the fucosidosis mutation(s) affected the catalytic activity, quantity, and extracellular release of-L-fucosidase as expressed by lymphoid cells.This work was funded by NIH Grants DK 32161 to R. A. DiCioccio and GM 28428 to J. K. Darby.     

Properties of calcium channels in cardiac muscle and vascular smooth muscle

The voltage-dependent slow channels in the myocardial cell membrane are the major pathway by which Ca²⁺ ions enter the cell during excitation for initiation and regulation of the force of contraction of cardiac muscle. The slow channels have some special properties, including functional dependence on metabolic energy, selective blockade by acidosis, and regulation by the intracellular cyclic nucleotide levels. Because of these special properties of the slow channels, Ca²⁺ influx into the myocardial cell can be controlled by extrinsic factors (such as autonomic nerve stimulation or circulating hormones) and by intrinsic factors (such as cellular pH or ATP level). The slow Ca²⁺ channels of the heart are regulated by cAMP in a stimulatory fashion. Elevation of cAMP produces a very rapid increase in number of slow channels available for voltage activation during excitation. The probability of a slow channel opening and the mean open time of the channel are increased. Therefore, any agent that increases the cAMP level of the myocardial cell will tend to potentiate I_si, Ca²⁺ influx, and contraction. The myocardial slow Ca²⁺ channels are also regulated by cGMP, in a manner that is opposite to that of CAMP. The effect of cGMP is presumably mediated by means of phosphorylation of a protein, as for example, a regulatory protein (inhibitory-type) associated with the slow channel. Preliminary data suggest that calmodulin also may play a role in regulation of the myocardial slow Ca²⁺ channels, possibly mediated by the Ca²⁺-calmodulin-protein kinase and phosphorylation of some regulatory-type of protein. Thus, it appears that the slow Ca²⁺ channel is a complex structure, including perhaps several associated regulatory proteins, which can be regulated by a number of extrinsic and intrinsic factors.VSM cells contain two types of Ca²⁺ channels: slow (L-type) Ca²⁺ channels and fast (T-type) Ca²⁺ channels. Although regulation of voltage-dependent Ca²⁺ slow channels of VSM cells have not been fully clarified yet, we have made some progress towards answering this question. Slow (L-type, high-threshold) Ca²⁺ channels may be modified by phosphorylation of the channel protein or an associated regulatory protein. In contrast to cardiac muscle where cAMP and cGMP have antagonistic effects on Ca²⁺ slow channel activity, in VSM, cAMP and cGMP have similar effects, namely inhibition of the Ca²⁺ slow channels. Thus, any agent that elevates cAMP or cGMP will inhibit Ca²⁺ influx, and thereby act to produce vasodilation. The Ca²⁺ slow channels require ATP for activity, with a K_0.5 of about 0.3 mM. C-kinase may stimulate the Ca²⁺ slow channels by phosphorylation. G-protein may have a direct action on the Ca²⁺ channels, and may mediate the effects of activation of some receptors. These mechanisms of Ca²⁺ channel regulation may be invoked during exposure to agonists or drugs, which change second messenger levels, thereby controlling vascular tone.     

Thymic nurse cells: morphological study during their isolation from murine thymus

Summary Thymic nurse cells (TNC), which are multicellular complexes composed of epithelial cells and thymocytes, were obtained from C3H-mice thymuses. They were described by means of light and electron microscopy. The morphology of epithelial cells forming isolated TNC compared to that of small tissue fragments obtained by enzymatic digestion revealed that TNC could be derived from all parts of the thymus: cortex, corticomedullary junction and medulla, the cortex being their principal source. This variety of origin, the presence of several epithelial cells inside a single TNC, the presence of non-lymphoid cells, and the various locations of eleaved desmosomes confirmed that their aspect in vitro as round and sealed structures can be considered to be an artifact due to the isolation technique used. Indeed, during this procedure, they are formed by a process of wrapping of the epithelial cytoplasm around the tightly associated thymocytes. All three epithelial cell types: cortical reticular cells, medullary reticular cells, and medullary globular cells can form TNC.A portion of this work was presented at the first Thymus Workshop. Rolduc, Netherlands, April, 1988     

Correlation of spinule dynamics and plasticity of the horizontal cell spectral response in cyprinid fish retina: quantitative analysis

Summary A negative feedback interaction between luminosity type horizonatal cells (HCs) and green-sensitive cones generates the long-wavelength-sensitive depolarizing response in biphasic chromaticity type HCs. This interaction is suppressed in the dark and is potentiated by light adaptation of the retina. HCs are morphologically plastic; during light adaptation, their dendritic terminals within cone pedicles extend, giving rise to spinules. This paper examines whether there is a quantitative correlation between the time course of light-dependent formation of the spinules and enhancement of the feedback interaction. The strength of the feedback interaction in isolated retinac of the roach was determined as the neutral wavelength at which reversal of spectral response polarity occurred in biphasic HCs. A good correlation was found between the neutral wavelength and the spinule/ribbon ratios of retinae. Biphasic HCs were intracellularly stained with horseradish peroxidase and the correlative ultrastructure of the contacted pedicles was examined. Neutral wavelength was found to be correlated with the spinule number, weighted according to the number of synaptic contacts mediating feed-forward transmission. The latter was estimated from the total number of labelled C_b/H2 HC processes (central and lateral) at synaptic triads. A model in which spinules mediate the negative feedback interaction of HCs in the retina of cyprinid fish is presented.     

Localization of vasopressin,serotonin and angiotensin II in endothelial cells of the renal and mesenteric arteries of the rat

Summary The localization of vasopressin, serotonin and angiotensin II in the endothelial cells of renal and mesenteric arteries was investigated using the pre-embedding peroxidase-antiperoxidase technique for electron microscopy. Vasopressin-and serotonin-positive endothelial cells were present in both renal and mesenteric arteries while angiotensin II-positive cells were observed in the mesenteric artery exclusively. Both arteries showed less than 10% immunoreactive cells. The lack of angiotensin II in the endothelial cells of the renal artery suggests that there may be subtle physiological differences between the renal and mesenteric arteries with respect to the local control of blood flow.     

Atrophy of compartments of rat lymph nodes related to an entry of lethally altered lymphocytes

Summary This paper reports the occurrence of an accumulation of lethally altered lymphocytes in the subcapsular sinus of a compartment or compartments of some lymph nodes, an unusual feature best developed in nodes of the mesenteric site in aging athymic animals. Many of these cells are rod-like. In other compartments, similar lymphocytes occurred at various depths in the nodal parenchyma. This was accompanied by the disappearance of a compartment's populations of normal lymphoid cells. The observations reveal that lymphocytes, altered in a tissue, may reach the subcapsular sinus of the draining node compartment and migrate into its parenchyma which then undergoes atrophy. The likely involvement of mast cells is discussed.This work was funded by the Medical Research Council of Canada.