Axons Of Neurosecretory Cells Research Articles

FEATURES OF STRUCTURAL REORGANISATION OF THE HYPOTHALAMIC SUPRAOPTIC NUCLEUS IN RATS DURING THE EARLY STAGES OF DIABETES DEVELOPMENT

The objective of the study – to ascertain the structural organisation of the hypothalamicsupraoptic nucleus in rats with streptozotocin- induced diabetes.Materials and Methods. Mature rats, modelled with streptozotocin- induced diabetes,were used in the experiment. On the 14th day of the experimental diabetes developmentin rats, quantitative cyto-myeloarchitecture parameters, histological and ultrastructuralchanges in the anterior hypothalamic supraoptic nucleus were determined.Results. After 14 days of the experiment modelling, the histological structure of thehypothalamic supraoptic nucleus remains practically unchanged and identical to the intactanimals. However, occasional occurrences of central chromatolysis were observed in thelight neurons of the supraoptic nucleus. The perikarya of the dark neurons were denselyfilled with Nissl substance. The ultrastructural feature of the dark neurosecretory cellsis the presence of highly developed granular endoplasmic reticulum in their peripheralzone, which was represented by flat elongated cisterns. These cisterns had a large numberof ribosomes on their surface. Additionally, free ribosomes and polysomes were present inthe hyaloplasm between the cisterns. A similar pattern has been observed in light neurons.Furthermore, an increase in the volumetric density of neurosecretory granules comparedto intact indicators of up to 2.36 ± 0.12 % (p ≤ 0.01) has been detected. In the neuropil of the hypothalamus, most of the axons were filled with neurosecretory granules (NG)of moderate electron density. Alongside axons that were expanded and filled withneurosecretory granules, axons of neurosecretory cells with usual structure containingmitochondria, synaptic vesicles, neurotubules, and neurofilaments have been observed.Conclusions. 1. The hypothalamic supraoptic nucleus contained light and darkneurosecretory cells with a well-developed protein synthesis apparatus. 2. Ultrastructuralchanges of the neuro-glio-capillary complexes in the investigated hypothalamic nuclei weredetected on the 14th day of the experimental streptozotocin- induced diabetes, indicatingthe activation of neurosecretion synthesis and the transport to the neurohypophysis. Anincrease in the volumetric density of neurosecretory granules compared to intact animalswas found to be 2.36±0.12 % (p≤0.01).

Ultrastructural studies on the neurosecretory cells in the pars intercerebralis of larvae of tasar silkworm, Antheraea mylitta (D) eco-race Bhandara (Lepidoptera: Saturniidae)

The cerebral neurosecretory cells (NSC) constitute four paired groups, medial (MNC), lateral (LNC-I, LNC-II) and posterior (PNC) in the brain of larvae of tasar silkworm Antheraea mylitta (D) Eco-race Bhandara. The MNC is the largest groups of peptidergic neurosecretory cells and are located in the pars intercerebralis region. The transmission electron microscopic (TEM), ultrastructure of the NSC confirmed the presence of mitochondria, endoplasmic reticulum, Golgi bodies, lysosomes and neurosecretory granules. The median neurosecretory cells shows secretory activity and release of secretory products, the neurosecretory granules (NSG) in the axons of NSC as well as the blood sinus.

Régulations aminergique et cholinergique du système caudal neurosécréteur de l'omble de fontaine, Salvelinus fontinalis, en relation avec l'osmo-iono-regulation

The innervation of the caudal neurosecretory system of the brook trout, Salvelinus fontinalis, was studied under light and electron microscopy in order to characterize its nature, distribution, and regulatory function over the activity of the caudal neurosecretory cells. A dual innervation of the cell bodies and axons of neurosecretory cells was disclosed. One type of axosomatic connection exhibited small lucent vesicles and large dense-cored granules. These boutons were identified as monoaminergic since they appeared depleted after reserpine treatment and they were selectively labeled with 5-OH-dopamine. In fish exposed to demineralized water, reserpine induced a condition that stimulated the synthetic activity of caudal neurosecretory cells, a clear reduction of this activity, according to morphometric (cell and nucleus diameters) and ultrastructural criteria (dimensions of the Golgi complex). By comparison, no significant variation of the synthetic activity was noted in freshwater-adapted trout treated with reserpine. A second type of innervation was also identified as cholinergic by histochemical localization of acetylcholinesterase. Electron microscopic analysis also revealed axosomatic and axoaxonic cholinergic synaptic connections with characteristic small 500-Å diameter lucent vesicles. The injection of fenitrothion, an anticholinesterase agent, enhanced discharge of neurosecretory material from axonal endings of caudal cells while the synthetic activity did not appear to be modified. Our findings suggest an important role of aminergic and cholinergic controls over the response of the caudal neurosecretory system of Salvelinus fontinalis during hyperosmotic adaptation.

Electrical activity of neurosecretory axons from the brain of Rhodnius prolixus: Relation of changes in the pattern of activity to endocrine events during the moulting cycle

Ongoing electrical activity was recorded from the axons of neurosecretory cells from the brain of 5th instar Rhodnius prolixus throughout the moulting cycle. Dramatic changes in both the frequency and pattern of electrical activity occur at specific times during the cycle, enabling the timing of release of neurohormones from the brain to be inferred. The level of transport of stainable secretion appears to be closely coupled to the electrical activity at all times. Activity is low in unfed Rhodnius, but within minutes of the insect taking a blood meal, there is a rapid appearance of bursting activity from a number of units, in conjunction with apparently continuous firing components. The bursting activity declines at about 2 h remaining low for the following 5 days, at which time there is a resurgence in the bursting pattern for a few hours. Both peaks of bursting activity immediately precede increases in haemolymph titer of ecdysones, suggesting that release of prothoracotropic hormone occurs on these two occasions. The continuously firing components initiated at feeding maintain a high level for 5 days indicating release of other brain neurosecretions. Intense electrical activity in the form of bursting activity and high apparently continuous pattern resumes shortly before ecdysis and continues until 12 h after. The relationship of neurohormone release at this time to bursicon and ecdysis behavior is discussed.

Ultrastructure of probable sites of release of neurosecretory materials in an insect, Calliphora stygia Fabr. (diptera)

The ultrastructure of some probable sites of release of materials from axons of neurosecretory cells is described. The sites comprise clusters of small pale vesicles adjacent to the plasma membrane with electron-dense material and neurosecretory granules associated with them. These sites were found in some axons in which the plasma membrane is adjacent to the basement membrane and in other axons in which the plasma membrane is contiguous with the plasma membrane of cells of the corpus allatum and with other axons containing neurosecretory granules.

The effect of photoperiodic stimulation on phosphatase activity in the hypothalamo-hypophysial system of the white-crowned sparrow, Zonotrichia leucophrys gambelii.

1. The metabolic activity of the hypothalamo-hypophysial neurosecretory system of the White-crowned Sparrow, Zonotrichia leucophrys gambelii, has been investigated by means of quantitative estimates of acid- and alkaline-phosphatase activity. The activities of samples from the median eminence, samples from the supraoptic region, the adenohypophyses, and the neurohypophyses of photosensitive and refractory birds, both subjected to short and long daily photoperiods, have been compared. Histochemical demonstrations of the distribution of acid- and alkaline-phosphatase activity have been effected to provide a better basis for interpretation of the quantitative data. 2. The photosensitive birds which were subjected to 20-hour daily photoperiods showed the typical photoperiodically induced testicular growth and fat deposition. There was an increase in acid-phosphatase activity in the supraoptic region. This increase in acid-phosphatase activity may be correlated with increased activity of the neurosecretory cells as indicated by cytologic criteria, including an increased rate of formation of aldehyde-fuchsin stainable material. No such increase in acid phosphatase occurred in refractory birds on 20-hour photoperiods. In photosensitive birds, there was also an increase in acid-phosphatase activity in the median eminence, an increase which appears to be attributable primarily to changes in activity of the axons in the glandular layer although a contribution by the nucleus tuberis cannot be excluded. The change in acid-phosphatase activity in the median eminence coincides well with the observed increase in rate of disappearance of aldehyde-fuchsin-positive granules from the axons. Neither an increase in acid phosphatase nor a decrease in granules occurred in the median eminences of refractory birds subjected to 20-hour daily photoperiods. The acid-phosphatase activity of the adenohypophyses of photosensitive birds was greater than in refractory birds although neither was affected by long daily photoperiods. These results are consistent with the hypothesis that the photoperiodic response in Zonotrichia leucophrys gambelii involves, in the supraoptic region, an increase in acid-phosphatase activity associated with increased synthesis of aldehyde-fuchsin-positive material in the neurosecretory cells, and, in the axons of the glandular layer of the median eminence, an essentially simultaneous increase in acid-phosphatase activity associated with a humoral transfer to the capillaries of the hypophysial portal system. Our data suggest that the higher rate of production of gonadotropins in the adenohypophysis by photosensitive birds involves a higher acid-phosphatase activity but that the photoperiodically induced increase in release of these gonadotropins, mediated by a humoral agent in the hypophysial blood, does not involve a detectable further increase in acid-phosphatase activity. 3. The data on alkaline phosphatase in supraoptic-region, median-eminence region, and adenohypophysis give no indication that this enzyme is involved in the photoperiodically induced activity of the hypothalamo-hypophysial system. 4. In agreement with previous investigations in this laboratory (Okscheet al., 1959), the data obtained in this investigation on phosphatase activity indicate no participation by the neurohypophysis in the photoperiodic response. 5. The histochemical observations indicate that the neurosecretory cells of the paraventricular and supraoptic nuclei have acid- and alkaline-phosphatase activities similar to those of ordinary neurones. The axons of neurosecretory cells, except in the median eminence, are not identifiable by histochemical demonstration of phosphatase activity. In the fibers of the glandular layer of the median eminence there is a pronounced acid-phosphatase, but no alkaline-phosphatase reaction, in these fibers. Also the nuclei and nucleoli of cells of the mammillary and tuberal nuclei have a fairly strong acid-phosphatase activity. In the adenohypophysis there is a conspicuous acid-phosphatase and a strong alkalinephosphatase reaction in the nuclei and nucleoli, but only slight activities in the cytoplasm.