Ultrastructural changes in adrenaline- and SGC-cells after morphine coincide with alterations of adrenaline and dopamine levels

Regulation of large dense-core vesicle volume and neurotransmitter content mediated by adaptor protein 3

Adaptor protein 3 (AP-3) is a vesicle-coat protein that forms a heterotetrameric complex. Two types of AP-3 subunits are found in mammalian cells. Ubiquitous AP-3 subunits are expressed in all tissues of the body, including the brain. In addition, there are neuronal AP-3 subunits that are thought to serve neuron-specific functions such as neurotransmitter release. In this study, we show that overexpression of neuronal AP-3 in mouse chromaffin cells results in a striking decrease in the neurotransmitter content of individual vesicles (quantal size), whereas deletion of all AP-3 produces a dramatic increase in quantal size; these changes were correlated with alterations in dense-core vesicle size. AP-3 appears to localize in the trans-Golgi network and possibly immature secretory vesicles, where it may be involved in the formation of neurosecretory vesicles.

Mouse chromaffin cells have two populations of dense core vesicles

The quantal hypothesis states that neurotransmitter is released in discrete packages, quanta, thought to represent the neurotransmitter content of individual vesicles. If true, then vesicle size should influence quantal size. Although chromaffin cells are generally thought to have a single population of secretory vesicles, our electron microscopy analysis suggested two populations as the size distribution was best described as the sum of two Gaussians. The average volume difference was fivefold. To test whether this difference in volume affected quantal size, neurotransmitter release from permeabilized cells exposed to 100 microM Ca2+ was measured with amperometry. Quantal content was bimodally distributed with both large and small events; the distribution of vesicle sizes predicted by amperometry was extremely similar to those measured with electron microscopy. In addition, each population of events exhibited distinct release kinetics. These results suggest that chromaffin cells have two populations of dense core vesicles (DCV) with unique secretory properties and which may represent two distinct synthetic pathways for DCV biogenesis or alternatively they may represent different stages of biosynthesis.

Nitric oxide modulates evoked catecholamine release from canine adrenal medulla

Nitric oxide has various actions, acting in a neurotransmitter-like role and also as a paracrine messenger between vascular endothelial and smooth muscle cells. This study was done to determine whether endogenous nitric oxide has a role in modulating evoked catecholamine release from the canine adrenal medulla. Isolated adrenal glands were perfused with Krebs-Ringer solution as a control, or with Krebs-Ringer solution containing either N(G)-monomethyl-L-arginine (L-NMMA; 3x10(-4) M) to non-selectively inhibit nitric oxide synthase or 7-nitroindazole (10(-4) M), a relatively selective inhibitor of neuronal nitric oxide synthase. Catecholamine release was evoked using the nicotinic cholinergic agonist 1,1-dimethyl-4-phenylpiperazinium iodine. From the collected perfusate epinephrine, norepinephrine, and dopamine were measured by high performance liquid chromatography. Previous studies have shown that in the presence of L-NMMA, basal releases of epinephrine, norepinephrine and dopamine are increased. 7-Nitroindazole had no effect on basal catecholamine release, suggesting that nitric oxide from an endothelial source was responsible for the inhibition of basal catecholamine release from the adrenal medulla. Epinephrine and norepinephrine releases were augmented when either of the nitric oxide synthase inhibitors was added during submaximal nicotinic stimulation, indicating that endogenous nitric oxide inhibited release of epinephrine and norepinephrine. Both neuronal and endothelial nitric oxide synthases appeared to be responsible for this inhibition. In summary, these studies suggest that nitric oxide, from both neuronal and endothelial sources, modulates evoked catecholamine release from canine adrenal medulla, while nitric oxide from an endothelial source is most likely responsible for modulation of catecholamine release under basal conditions.

Electron microscopic evidence for multiple types of secretory vesicles in bovine chromaffin cells

It has been previously shown that the neuron-like chromaffin cells from the bovine adrenal medulla are heterogeneous. Among other differences, the cells also differed in secretory vesicles represented in their cytoplasm. The present study investigates the types of secretory vesicles in bovine chromaffin cells by electron microscopy. Morphometric analysis revealed five types of electron-dense secretory vesicles in chromaffin cells. These were as follows: elementary large catecholamine-storing chromaffin granules of rounded shape, large dense core vesicles of ovoid and rod-like shapes, small dense core vesicles as well as ribosome-coated vesicles of intermediate density. Among the electron-lucent vesicles there were small synaptic-like microvesicles, endocytotic clathrin-coated vesicles, growth cone vesicles, and emptied large light core vesicles. The structural and functional backgrounds of different types of secretory vesicles are described, focusing on their formation and potential role.

Catecholamine release and excretion in rats with immunologically induced preganglionic sympathectomy

Plasma and urinary catecholamines were quantified to assess global sympathoadrenal function in rats with preganglionic lesions caused by antibodies to acetylcholinesterase (AChE). Rats were given intravenous injections of normal mouse IgG or murine monoclonal anti-acetylcholinesterase IgG (1.5 mg). Five or 16 days afterward, basal blood samples were taken through indwelling arterial cannulate. A few hours later, the rats were immobilized for 10 min in padded restrainers, and another blood sample was drawn. HPLC determinations showed low basal levels of norepinephrine and epinephrine (< 0.2 ng/ml in all rat plasma samples). In control rats, immobilization stress increased levels of plasma catecholamines up to 35-fold. In rats tested 5 days after injection of antibody, the norepinephrine response was much smaller (15% of control), and the epinephrine response was nearly abolished (5% of control). There was some recovery at 16 days after antibody treatment, but stress-induced catecholamine release was still markedly impaired. Reduced stress-induced release was not accompanied by major changes in tissue epinephrine or norepinephrine (heart, spleen, adrenal glands, and brain), although adrenal dopamine content dropped by 60%. Urinary excretion was studied in parallel experiments to gain insight into the effects of AChE antibodies on basal sympathoadrenal activity. Epinephrine, norepinephrine, dopamine, and selected metabolites were quantified in 24-h urine samples collected at frequent intervals for 30 days after antibody injection. No statistically significant changes were detected in the urinary output of dopamine, 3-methoxytyramine, normetanephrine, or 3-methoxy-4-hydroxyphenylglycol. On the other hand, epinephrine and norepinephrine output increased sharply at the time of antibody injection and then fell significantly below control levels. Norepinephrine output returned to normal after 2 weeks, but epinephrine output remained depressed. These results are consistent with previous evidence of widespread and persistent antibody-mediated damage to the preganglionic sympathetic system.

Rough endoplasmic reticulum in the adrenaline and noradrenaline cells of the adrenal medulla: effects of intracranial surgery and pinealectomy

Adrenal medullas in 53-day-old rats of the nonoperated (NO) group (n = 31), the sham-operated (SPX) group (n = 35) and the pinealectomized (PX) group (n = 38) were examined electron microscopically 14 days after surgery. Cell profiles showing solitarily and sparsely distributed rough endoplasmic reticulum (RER) were most frequent in the PX group (daily mean: 66.9%, 427/638), less in the NO (56.0%, 336/600), and least in the SPX (48.5%, 297/612) in adrenaline (A) cells (chi 2-test: P less than 0.001), while most frequent in the NO group (68.8%, 340/494), less in the PX (64.3%, 303/471), and least in the SPX (57.4%, 256/446) (P less than 0.005) in noradrenaline (N) cells. Individual variation was less in A cells than in N cells. Cell profiles showing a large accumulation of RER was more frequent in A cells (NO:8.5%, SPX:13.1%, PX:7.7%) than in N cells (NO:2.8%, SPX:4.5%, PX:4.7%) (controls: P less than 0.001). Sham pinealectomy increased a large accumulation of RER in A cells (P less than 0.02) and a small aggregation of RER in N cells (P less than 0.005) with opposite effects of pinealectomy (P less than 0.005, P less than 0.025). Pinealectomy decreased a small aggregation of RER without effects of sham pinealectomy in A cells (P less than 0.001).

CONCLUSIONS

(1) Accumulation or aggregation of RER in adrenomedullary chromaffin cells was influenced from the pineal gland either as or without effects of intracranial surgery, and (2) RER in adrenomedullary chromaffin cells showed differences due to cell types.

Dopamine release from bovine adrenal medullary cells in culture

The present study tested whether release of dopamine from isolated bovine adrenal medullary cells in culture could be stimulated or inhibited by secretagogues and modulators known to affect noradrenaline and adrenaline release from adrenal medullary chromaffin cells. K+ depolarization or activation of voltage-sensitive Na+ channels by veratridine both stimulated dopamine release. Ca2+-dependent dopamine release was also stimulated by the mixed nicotinic-muscarinic agonist, carbachol. Carbachol-induced dopamine release was inhibited by a nicotinic but not by a muscarinic antagonist and dopamine release was also stimulated by a selective nicotinic agonist, 1,1-dimethyl-4-phenyl-piperazinium. Carbachol-induced dopamine release was inhibited by substance P and by neuropeptide Y. Histamine also stimulated dopamine release, while angiotensin II and glutamate produced no significant stimulation of dopamine release. Noradrenaline and adrenaline were released in response to the above agents with a profile almost identical to that of dopamine. The results indicate that dopamine can be directly released from adrenal medullary cells in response to stimulation of those cells and suggest that the dopamine release originates from chromaffin cells similar or identical to those storing noradrenaline and adrenaline. A possible role for dopamine, released from adrenal chromaffin cells, in modulating catecholamine release from the chromaffin cells and/or contributing to circulating plasma dopamine is discussed.

Differential distribution of neuropeptides and serotonin in pig adrenal glands

A differential distribution of vasoactive neuropeptides and serotonin in chromaffin cells and nerve fibers within the adrenal glands of the pig (Sus scrofa) was found using immunohistochemical methods. Met- and leu-enkephalins, present at high levels in the medulla (measured by radioimmunoassay), occurred in adrenaline storing cells, some of which contained calcitonin gene-related peptide. Islets of chromaffin cells beneath the capsule also contained enkephalins and calcitonin gene-related peptide. Nerve fibers with enkephalin-like immunoreactivity were sparse, but many varicose fibers in the inner cortex and medulla showed calcitonin gene-related peptide immunofluorescence in a pattern similar to vasoactive intestinal polypeptide. Neuropeptide Y was mainly associated with perivascular fibers and neither neuropeptide Y nor vasoactive intestinal polypeptide immunoreactive chromaffin cells were detected. In contrast to the neuropeptides, most serotonin-like immunoreactivity coincided with noradrenaline histofluorescence. It is concluded that the distribution of nerve fibers with calcitonin gene-related peptide and vasoactive intestinal polypeptide would allow interactions between chromaffin and inner cortical cells. Stimuli activating noradrenaline chromaffin cells could release serotonin while stimulation of adrenaline storage cells would release enkephalin and, to a lesser extent, calcitonin gene-related peptide. Met-enkephalin, which occurs 3 4:1 over leu-enkephalin, is the most likely of the co-released peptides to reach distant receptors via the venous outflow.

Quantitative ultrastructural analysis of differences in exocytosis number in adrenomedullary adrenaline cells of golden hamsters related to time of day, pinealectomy, and intracellular region

This research analyzed differences mainly in the incidence of exocytotic figures in adrenaline cells (A-cells) in pinealectomized (PX), sham-operated (SPX), and non-operated (NO) adult male golden hamsters, with the aim of determining whether these parameters change with the time of day and following pinealectomy, and whether intracellular regional differences exist in such changes. Animals acclimated to a standardized light:dark (LD) 12:12 photoperiod were sacrificed at 11 h after the onset of light (L-11h) and 1 h after the onset of darkness (D-1h) (8 animals/group/time) at 28 days postoperation. The adrenal medullas were examined and analyzed morphometrically by electron microscopy. The number of exocytoses per unit length (NEL) and the exocytosis index (a rough index of the number of exocytoses per cell) were measured in PF (perivascular-space-facing) and non-PF plasma membranes. NEL increased from L-11h (NO: 0.040 +/- 0.010, mean +/- SE) to D-1h (0.078 +/- 0.012) in all three experimental groups (ANOVA: P less than 0.005), showing over fourfold higher levels in PF than in non-PF membranes. NEL in PF membranes in PX animals showed higher levels than those in NO and SPX animals (P less than 0.025), but in non-PF membranes, no differences owing to time of day or surgery were seen. Exocytosis indices were (1) higher at D-1h than at L-11h in all three experimental groups (P less than 0.005), (2) similar in PF and non-PF membranes in control groups, and (3) higher in PF membranes in the PX group than in either non-PF membranes or PF membranes in control groups. In conclusion, the exocytosis number in A cells changes in relation to time of day, rising in early dark phase, and its rise following pinealectomy can be seen only in PF membranes.