Peptidergic peripheral nervous systems in the mammalian pineal gland

Abstract

The distribution and density of tyrosine hydroxylase (TH) and neuropeptide Y (NPY)-immunoreactive, sympathetic fibers and calcitonin gene-related peptide (CGRP)-, substance P (SP)-, and vasoactive intestinal polypeptide (VIP)-immunoreactive, non-sympathetic fibers in the pineal gland, the effects of superior cervical ganglionectomy (SCGX) on these fibers, and the location of their terminals in the pineal gland were compared between rodents and non-rodents. A dense network of TH/NPY-positive fibers is present all over the pineal gland. A less dense network of CGRP/SP- or VIP-positive fibers occurs in the whole pineal gland of non-rodents, but these fibers are usually confined to the superficial pineal gland in rodents. After SCGX, some TH/NPY-fibers remain only in the deep pineal gland in rodents, whereas considerable numbers of these fibers persist throughout the gland in non-rodents. Thus, the remaining fibers, probably originating from the brain, may be more numerous in non-rodents. Since CGRP-, SP- or VIP-immunoreactive fibers in the pineal capsule can be traced to those in the gland, and since these fibers are ensheathed by Schwann cells, it is concluded that these fibers belong to the peripheral nervous system. However, the existence of SP-positive central fibers cannot be denied in some species. In the superficial pineal gland of rodents, sympathetic terminals are mostly localized in perivascular spaces, whereas the parenchymal innervation by sympathetic fibers in the pineal gland is more dense in non-rodents than in rodents. Synapses between sympathetic nerve terminals and pinealocytes occur occasionally in non-rodents, but only rarely in the superficial pineal gland of rodents. The occurrence of the synapses may depend on the frequency of intraparenchymal sympathetic terminals.

The anatomy and innervation of the mammalian pineal gland

“…However, it is important to note that the central innervation in most rodents terminates in the deep pineal gland and the pineal stalk (Matsushima et al 1999;Møller 1999).…”

“…However, in several species, few NPY-immunoreactive nerve fibers persist in the gland after superior cervical ganglionectomy. In some species, for example the rat, these fibers are predominantly located in the deep pineal gland (Matsushima et al 1999;Mikkelsen and Møller 1999), which suggests an origin of these fibers from perikarya in the brain.…”

Tachykinins and tachykinin‐receptors in the rat pineal gland

“…Thus, SP has previously been detected by immunohistochemistry in nerve fibers in the pineal gland of the several species, e.g. Sprague–Dawley (Rønnekleiv & Kelly, 1984; Reuss, 1999) and cotton rats (Matsushima et al ., 1994), Chinese hamster (Matsushima et al ., 1999), tree shrew (Kado et al ., 1999), gerbil (Shiotani et al ., 1986), monkey (Rønnekleiv, 1988), pig (Przybylska‐Gornowicz et al ., 2000) and cow (Møller et al ., 1993).…”

“…The perikaryal origin of SP‐immunoreactive nerve fibers in the mammalian pineal is not the superior cervical ganglion, because immunoreactive fibers remain after superior cervical ganglionectomy (Matsushima et al ., 1999). Retrograde tracings from the pineal gland combined with immunohistochemistry have shown an origin of most of these nerve fibers of the gerbil (Shiotani et al ., 1986) and rat (Reuss, 1999) to originate from the trigeminal ganglion.…”

Neuropeptide Y as a presynaptic modulator of norepinephrine release from the sympathetic nerve fibers in the pig pineal gland

“…In addition to the sympathetic innervation, the pineal gland receives also nerve fibers from other peripheral ganglia and from the brain (Mzller et al 1996, 1999, Matsushima et al 1999.…”