Substance P Immunoreactivity in the Rat Adrenal Gland during Postnatal Development

Abstract

ABSTRACT. Substance P (SP)-immunoreactive nerve fibers in the adrenal medulla was very few during postnatal day 0-5, indicating that its synthesis in the neurons and the transport to nerve endings was incomplete by the end of this period. Since the number of SP-immunoreactive nerve fibers gradually increased during postnatal week 1-2, it was hypothesized that SP was not fully transported to nerve endings until postnatal week 1-2. At postnatal week 3, numerous SP-immunoreactive nerve fibers contacted some noradrenaline (NA) cells but not adrenaline (A) cells in the medulla. From postnatal week 3 onward, the abundance and expression patterns of SP-immunoreactive nerve fibers in the medulla were similar to those in adults. At postnatal week 3, the innervation with SP-immunoreactive nerve fibers was completed indicating the possibility that SP affected on the secretory activity of NA cells but not of A cells in the medulla. The medullary SP-immunoreactive nerve fibers contacting the chromaffin cells possessed a few dense-cored vesicles in their endings at postnatal week 8. Very few SP-immunoreactive chromaffin cells were found in the medulla from postnatal day 0 onward, and SP immunoreactivity was primarily observed in granular cores of the cells suggesting that SP and catecholamine synthesized in the chromaffin cells were released from the granules by adequate stimuli. Very few or a few SP-immunoreactive nerve fibers, acting as a vasomotor effect were found around blood vessels in the superficial cortex from postnatal day 0 onward. It is well known that substance P (SP), an undecapeptide, is widely distributed in the central and the peripheral nervous tissues [5], acts as a neurotransmitter in primary sensory neurons [22] as well as a hormone in endocrine tissues [3,12,16], suggesting its important effects on the nervous and endocrine systems.Adrenal medulla is an endocrine organ that synthesizes and releases a large amount of catecholamines-noradrenaline (NA) and adrenaline (A)-via preganglionic cholinergic nerve fibers [31]. It has been reported that the chromaffin cells and nerve fibers in the adrenal gland of various mammals contain a variety of peptides and enzymes such as Leuenkephalin (Leu-ENK) [2], Met-enkephalin (Met-ENK) [23,26], nitric oxide synthase (NOS) [3], neuropeptide tyrosine (NPY) [13,18], pituitary adenylate cyclase activating polypeptide (PACAP) [7], and vasoactive intestinal polypeptide (VIP) [10]. Furthermore, they contain SP [3,12,16] and calcitonin gene related peptide (CGRP) [14] as markers of sensory neurotransmitters, suggesting that these nerve fibers were recognized as a sensory innervation in the adrenal gland [4,34]. Recently, we demonstrated that SPimmunoreactive nerve fibers in the adult rat adrenal gland innervated NA cells, but not A cells, co-localizing with CGRP, choline acetyltransferase (ChAT), NOS, and PACAP [20]. However, thus far, studies have not elucidated during postnatal development when the expression of SP in chromaffin cells and nerve fibers in the rat adrenal gland...

Cholinergic and peptidergic neurotransmission in the adrenal medulla: A dynamic control of stimulus‐secretion coupling

“…23 Similarly, the abundance of substance P (SP)-immunoreactive fibers is low at birth, and gradually increases during the first postnatal weeks to reach a density similar to that found in adults at postnatal week 3. 82 Regarding PACAP, a few weakly immunopositive nerve fibers are detected in the medulla of newborn rats, contrasting with the dense network of PACAP-immunoreactive fibers in adult animals. 75 Along similar lines, it is noteworthy that the postnatal peptide expression in nerve fibers invading the adrenal medulla is under regulation of the sympathetic preganglionic splanchnic nerve innervation.…”

“…In particular, enkephalin‐immunopositive nerve fibers increase in number and staining intensity during the postnatal period, while calcitonin gene‐related peptide (CGRP)‐ and galanin‐expressing fibers are almost fully grown at P2 . Similarly, the abundance of substance P (SP)‐immunoreactive fibers is low at birth, and gradually increases during the first postnatal weeks to reach a density similar to that found in adults at postnatal week 3 . Regarding PACAP, a few weakly immunopositive nerve fibers are detected in the medulla of newborn rats, contrasting with the dense network of PACAP‐immunoreactive fibers in adult animals .…”