Size Of Dense-core Vesicles Research Articles

Estradiol regulates large dense core vesicles in the hippocampus of adult female rats

Previous work has shown that the steroid hormone estradiol facilitates the release of anticonvulsant neuropeptides from inhibitory neurons in the hippocampus to suppress seizures. Because neuropeptides are packaged in large dense core vesicles, estradiol may facilitate neuropeptide release through regulation of dense core vesicles. In the current study, we used serial section electron microscopy in the hippocampal CA1 region of adult female rats to test three hypotheses about estradiol regulation of dense core vesicles: (1) Estradiol increases the number of dense core vesicles in axonal boutons, (2) Estradiol increases the size of dense core vesicles in axonal boutons, (3) Estradiol shifts the location of dense core vesicles toward the periphery of axonal boutons, potentially lowering the threshold for neuropeptide release during seizures. We found that estradiol increases the number and size of dense core vesicles in inhibitory axonal boutons, consistent with increased neuropeptide content, but does not shift the location of dense core vesicles closer to the bouton periphery. These effects were specific to large dense core vesicles (>80nm) in inhibitory boutons. Estradiol had no effects on small dense core vesicles or dense core vesicles in excitatory boutons. Our results indicate that estradiol suppresses seizures at least in part by increasing the potentially releasable pool of neuropeptides in the hippocampus, and that estradiol facilitation of neuropeptide release involves a mechanism other than mobilization of dense core vesicles toward sites of release.

Fine structure of the free-living parakeet pineal in relation to the breeding cycle.

Seasonal changes in the ultrastructure of the free-living Rose-Ringed Parakeet Psittacula krameri pineal were examined in relation to the sub-tropical environment and seasonal reproduction. Dark and light pinealocytes of the presumptive neuroendocrine cell line predominated, while supporting cells, ependymal cells, myelinated and non-myelinated nerve fibers with nerve endings, and regressed photoreceptor elements were also observed. Unlike in pineals of many animals, particularly mammals, the presence of dense-core vesicles (DCVs) with varying core density, and absence of clear vesicles and vacuoles with flocullent material, indicate the involvement of DCVs in the synthesis and secretion of pineals principle/s. In November (pre-breeding) when the day length registered a drop to LD 10:14, pinealocytes showed significantly decreased and smaller DCVs and mitochondria, nuclei with heterochromatin, and greater distribution of glycogen and lipid droplets, all indicating low pineal metabolic activity. During the shortest day regime from December to March, when the birds peaked breeding, the number and size of DCVs and mitochondria increased, and Golgi body-endoplasmic reticulum-lysosome complex (GERL) was very well defined. Images of DCVs suggested possible secretion of pineal principle/s by dissolution, and exocytosis. Coincidence of these features with peak gonadotrophic (circulating LH) and spermatogenic and testicular endocrine activity described previously suggested an active turnover of pineal products during this short day length regime when parakeets breed. In contrast, during the post-breeding season (April onwards), when the day-length increased to LD 13:11 and hypophyseal-gonadal function was down, nuclei and RER continued to show active profile, the Golgi body and associated complex were moderately seen, and the DCVs and mitochondria were significantly smaller and lesser. It is therefore probable that the pineal is an important relay to translate cues related to less drastic sub-tropical environmental change into DCV-linked neurohormones that in turn may be involved in modulating seasonal breeding in parakeets.

Hypophysiotrophic neurons are capable of altering the ratio of co-packaged neurohormones

Neuronal dense-core vesicles provide a mechanism whereby peptide messengers are secreted in discrete quanta. Here we report on the capacity of rat hypophysiotrophic corticotropin releasing factor-41 neurons to alter the peptide content as well as the size of dense-core vesicles after removal of glucocorticoid negative feedback by adrenalectomy. We demonstrate, using quantitative immunoelectron microscopy, that long-term adrenalectomy induces a progressive increase in the ratio of vasopressin to corticotropin releasing factor-41-immunoreactive sites in the dense-core vesicle compartment. The intravesicular concentration of vasopressin appeared to be the variable parameter while that of the corticotropin releasing factor-41 remained stable at all survival times after adrenalectomy. Moreover, observations for up to 5 weeks indicate that adrenalectomy results in a progressive increase in the mean volume of dense-core vesicles to about three times normal. These results suggest that the quantal size and the composition of dense-core vesicles are subject to long-term modulation. The capacity of corticotropin releasing factor-41 neurons to alter dense-core vesicles could enhance or diminish the efficacy of the hypothalamohypophyseal communication underlying physiological adaptation to stress, as well as pathological changes.

The neurons containing dense core vesicles in the mouse hypothalamic arcuate nucleus: distribution and influence of ovarian activity.

The hypothalamic arcuate nucleus (ARC) was electron microscopically studied in diestrous (D) and estrous (E) mice, and mice ovariectomized (OX) 3 weeks before. In the middle region of the ARC (mARC), the number of dense core vesicles (DCVs) appearing in a section of each neuronal perikaryon was examined, and the location of the neurons containing DCVs was mapped. About 10% of the neurons in the mARC contained many (5 or more) DVCs in the perikarya in a section. These neurons mainly localized in the ventromedial portion of the mARC, which shows that the cytoarchitecture of the mouse ARC is heterogeneous. The localization and the frequency of these neurons were not influenced by the variance of ovarian activity. A DCV was composed of an electron-dense core and a membrane halo, and was likely to be formed in the cisternae of the Golgi apparatus. The size of DCVs was estimated at 100 nm as the median diameter and was stable independent of the ovarian activity. However, the formation of DCVs was likely influenced by the ovarian activity, because DCVs in D mice were more intimately associated with the Golgi apparatus than in E or OX mice. In the neuronal perikarya of the ventromedial portion of the mARC, Nissl bodies developed in OX mice and nucleolus-like bodies developed in E mice. These results suggest that the neurons of the ventromedial portion of the mARC change their function according to the variance of ovarian activity and, therefore, are involved in the estrogen feedback mechanism.

Topography of the neurons responding to estrogen in the hypothalamic arcuate nucleus of immature female mice

The neurons in the hypothalamic arcuate nucleus (ARC) of 20-day-old female mice were examined by electron microscopy. The administration of estradiol-17 beta during 20 days from the day of birth resulted in the increase of dense-core vesicles (DCVs) in some neuronal perikarya of the middle region of the ARC (middle ARC), while, in the posterior region of the ARC (posterior ARC), the increase of DCVs was less marked. Topographical studies revealed that the neuronal perikarya containing few DCVs were assembled in the ventromedial area of the middle ARC in both control mice and mice given estrogen. Those containing 5 or more DCVs were found predominantly in the ventromedial area of the middle ARC in mice given estrogen. In the posterior ARC, however, the neuronal perikarya containing DCVs seemed to be scattered. The distribution patterns of the diameter of DCVs were significantly different between control mice and mice given estrogen. The administration of estrogen seem to bring about the enlargement in the size of DCVs. These results indicate that the neurons responding to estrogen are present in the ventromedial area of the middle ARC, and suggest that this area is a significant focus in estrogen feedback mechanisms.

Monoamine storage sites in the rat superior cervical ganglion following synthesis inhibition.

Monoamine storage sites in paraganglionic (PG-) cells of the rat superior cervical ganglion were investigated by electron and fluorescence microscopy following treatment with p-chlorophenylalanine (pCPA), disulfiram or guanethidine respectively. Dense core vesicles in PG-cells are significantly decreased (p less than 0.001) in number following pCPA, and in the majority of these cells following disulfiram and guanethidine. However in a minor portion of PG-cells the latter agents cause an increase in number and in size of dense core vesicles, in parallel with structural alterations. In agreement with these electron microscopic findings fluorescence microscopic and cytophotometric evaluations reveal a general decrease in catecholamine content with few cells showing an increase. The findings provide a morphological basis for the assumption, that monoamine storage sites in PG-cells can be decreased by inhibition of monoamine synthesis, following administration of pCPA, disulfiram and guanethidine. However the two types of responses of PG-cells which occur after disulfiram and guanethidine demonstrate a functional heterogeneity of this cell system in the rat superior cervical ganglion which is discussed.