Evidence against differential release of noradrenaline, neuropeptide Y, and dopamine‐β‐hydroxylase from adrenergic nerves in the isolated perfused sheep spleen

Abstract

The subcellular storage and release of noradrenaline (NA), dopamine-beta-hydroxylase (D beta H), and neuropeptide Y (NPY) was studied in the isolated perfused sheep spleen. Subcellular distribution studies showed a bimodal distribution for NA which was well reflected by D beta H and indicated the occurrence of two types of NA storage vesicles. The most dense, presumably large dense-cored vesicles (LDV), contain both membrane-bound and soluble D beta H; the less dense presumably corresponds to small dense-cored vesicles (SDV) and at least does not contain soluble D beta H. The distribution of NPY is extended but shows a peak only at the position of LDV, indicating that LDV contain NPY. Continuous electrical stimulation of the splenic nerve at 2 Hz, 5 Hz, 10 Hz, and 20 Hz or at 20 hz with bursts induced the release of NA, NPY, and D beta H. The ratio among these components was constant. The fractional release of D beta H and NA was comparable at all frequencies used; that of NPY was 10-20 times lower, suggesting the occurrence of a large nonreleasable NPY pool. The present data argue against a high frequency stimulation or intermittent stimulation-induced preferential release of NPY from adrenergic neurons and question the concept of frequency-dependent chemical coding of sympathetic transmission in general. The simplest interpretation of our data is that NA and NPY are released at all frequencies from a single pool. The present finding might signify that only large dense-cored vesicles are involved in the sympathetic stimulation-evoked secretion of catecholamines from adrenergic nerve terminals of the isolated sheep spleen.

Neuropeptide Y Is Released from Human Mammary and Radial Vascular Biopsies and Is a Functional Modulator of Sympathetic Cotransmission

“…An almost linear relation was observed between the frequency of nerve depolarization and the amount of extracellular NPY detected, in support of the classical studies by Lundberg et al [2, 39]. The dogma that cotransmitter peptides are only released by high-frequency nerve depolarization is questionable, since with more sensitive techniques, it is possible to detect the release of NPY with lower frequencies than previously deemed necessary [19, 40]. …”

Peptidergic Innervation of Blood Vessels and Interstitial Cells in the Testis of the Cat

“…This response could be influenced by simultaneous release of NPY, as suggested by the large number of perivascular NPY-ir fibers. NPY and CPON derive from the same precursor messenger RNA, show full co-localization in nerve terminals (Hauser-Kronberger et al, 1993) and are co-released with norepinephrine from sympathetic nerves (De Potter et al, 1995). Most likely, the NPY/CPON-ir nerve supply in male genitalia partially corresponds to the catecholaminergic innervation, because guanethidine treatment reduces or abolishes both the tyrosine hydroxylaseir and NPY-ir nerves in the rat (Carvalho et al, 1986).…”

The vesicular monoamine transporter 2 is present in small synaptic vesicles and preferentially localizes to large dense core vesicles in rat solitary tract nuclei.

“…There is extensive physiological (20,21) and anatomical (22) evidence that peripheral sympathetic neurons modulate visceral responses through the slow, nonsynaptic release of monoamines from DCVs in axon terminals. In addition, it has been shown that monoamines can be released from dendrites (23,24) and that dendritic exocytosis sometimes occurs from DCVs (25).…”