A quantitative ultrastructural investigation of tyrosine hydroxylase-immunoreactive axons in the hairy skin of the guinea pig

Abstract

Besides its thermoregulatory role, the sympathetic innervation of the skin is involved in a modulation of sensory processing and trophic functions that has not been fully characterized. To investigate possible sites at which such sympathosensory interactions might occur, a quantitative ultrastructural study of the sympathetic innervation of the skin was attempted. The hairy skin of the guinea pig was studied because the sympathetic and sensory nerve axons in this species can easily be discriminated by the presence of immunoreactivity to the catecholamine-synthesizing enzyme, tyrosine hydroxylase (TH). The thermoregulatory role of the sympathetic skin innervation was highlighted by the almost exclusive sympathetic innervation of piloarrector muscles which contained 62% (n = 195) of randomly selected TH-immunoreactive (TH-IR) axon profiles. Of TH-IR pilomotor axons, 53% were filled with vesicles. Vesicle-containing axonal profiles were equally frequent around dermal arterial blood vessels (partly associated with mast cells), hair follicles, and within nerve fibre bundles surrounded by a perineural sheath, in each case accounting for about 3% of all dermal TH-IR axonal profiles. In contrast to piloarrector muscles, at these locations TH-IR (sympathetic) and non-reactive (sensory) axons were found in close association. These findings are in line with the previously reported inhibitory influence of sympathetic stimulation upon hair follicle afferents and perivascular sensory nerve terminals. In addition, they point to a yet underestimated target of sympathetic axon terminals, i.e. preterminal nerve fibre bundles.

The existence of a linear system consisting of sympathetic endings in rat skin

“…This is in partial agreement with the results of Roberts and Levitt (1982), Roth and Kummer (1994), Waris and Rechardt (1977), who described the sympathetic innervation of hairy skin were mainly localized within AP muscles. The SSLs in the skin and the hair follicles or AP muscles, presumably play an unknown vital role in the function of the rat body.…”

“…The fluorescent catecholamine fibers were not found everywhere throughout the dermis, but were most commonly localized within hair follicles, AP muscles, and arterioles. Roth and Kummer (1994) investigated the sympathetic innervation of hairy skin with quantitative ultrastructural methods in guinea pig. They concluded that this innervation targeted AP muscles almost exclusively.…”

Expression of tyrosine pathway enzymes in mice demonstrates that homogentisate 1,2‐dioxygenase deficiency in the liver is responsible for homogentisic acid‐derived ochronotic pigmentation

“…Th was expressed mainly in the brain, involved in the production of catecholamine neurotransmitters, adrenaline, noradrenaline and dopamine, which are essential for normal brain function, control of physical movement and emotional behavior 31 . TH has been previously identified in the retina, 32 heart 33 and kidney 34 of mice, and intestine 35 and skin 36 of guinea pigs, due to association with the sympathetic nerves 37 within these tissues. Th was observed to a lesser degree in some of the tissues studied here, but not detected in cartilage.…”

Expression of the High-Affinity Choline Transporter, CHT1, in the Neuronal and Non-neuronal Cholinergic System of Human and Rat Skin

“…The arrector pili muscle is innervated by nerve ®bers that originate from sympathetic ganglia. In the guinea-pig and the rat, practically all of these ®bers are immunoreactive for the ratelimiting enzyme in norepinephrine synthesis, tyrosine hydroxylase, and therefore these axons are noradrenergic (Gibbins, 1991;Roth and Kummer, 1994;Bergner et al, 2000); however, ®bers innervating the human piloarrector muscle showed CHT1 immunoreactivity that has been demonstrated in cholinergic ®bers Lips et al, 2002). CHT1 in non-neuronal cells The mRNA for CHT1 was detected in human and rat skin specimens and in HaCaT cells.…”