Although prolactin has been shown to entrain hair growth cycles in seasonally responsive mammals, no comparable role has been identified in the age-dependent pelage replacement of rodents. Prolactin binds to dimerised membrane-associated prolactin receptors (PRLR) on target organs and initiates signalling via a number of intracellular pathways including the JAK-Stat5b pathway. The role of this pathway in murine hair growth was investigated by (i) PRLR gene disrupted mice, (ii) altered circulating prolactin profiles and (iii) impaired PRLR signal transduction with Stat5b gene-disrupted mice.
The long (PRLR-L), and two short (PRLR-S2 and PRLR-S3) forms of the prolactin receptor were shown by RT-PCR to be expressed in the skin. These receptors were immunolocalised to the outer root sheath of the follicle as well as the epidermis and sebaceous gland. The first hair replacement cycle in PRLR gene-disrupted mice was advanced by 4 days in males and 2 weeks in females compared to wild type controls. Similarly, bromocriptine suppression of prolactin secretion advanced hair replacement by four days, which could be reversed by administration of exogenous prolactin at 18-22 days of age. In contrast, hair replacement in Stat5b-disrupted mice was delayed by two weeks. The duration of anagen, measured as the period of fibre elongation, did not differ between treated and control groups in any of these experiments. Pelage structure, fibre length and fibre diameter was not substantially altered. Pelage renewal across the body was slower during pregnancy and pseudopregnancy, and halted completely during lactation. Only after weaning was follicle reactivation resumed. As a key gestational and lactation hormone, prolactin is a likely candidate as a modulator of hair cycling at this time. An inverse relationship between PRLR-L mRNA and prolactin mRNA demonstrates the high level of prolactin signal regulation in the skin during reproduction.
Hence, both reduced circulating prolactin levels and PRLR-deficiency results in a shorter telogen and hair renewal at a younger age. In contrast, when the signalling protein Stat5b is absent, follicle growth was retarded and new hair growth occurred later than in wild type mice. This could be explained by the altered pituitary feedback regulation of lactotrophs resulting in hyperprolactinemia in Stat5b-deficient mice. These results provide strong evidence that prolactin inhibits the activation of murine hair follicle growth.
The L2,3 edges of compounds containing tetrahedrally coordinated, isoelectronic d0 transition-metal oxyanions, TiO44-, VO43-, CrO42- and MnO4- have been measured using electron energy-loss spectroscopy (EELS). The general shape of the electron energy-loss near-edge fine structure (ELNES) is found to be remarkably similar for these oxyanions and arises from the atomic multiplet spectrum of the d0 transition-metal ion modified by the tetrahedral field due to the oxygen ligands. The observed structure is also discussed within the framework of molecular-orbital (MO) theory. The possibilities of using these spectra as fingerprints for d0 transition-metal ions in tetrahedral coordination is discussed. The structure observed at the O K edges is also commented upon in the light of these findings.
This paper reports on the applications of analytical electron microscopy to the study of cathodic arc deposited CrN coating on a Ti(6% Al, 4% V) substrate. Particular attention is given to analysis of the coating/substrate interface. Electron energy loss spectroscopy is used to show that the Cr sputter cleaning of the Ti(6% Al, 4% V) results in penetration of Cr into the substrate giving a bcc alloy layer whose composition varies from Ti(6% Al, 4% V) at the substrate interface to almost pure Cr at the coating interface. Subsequent deposition of CrN results in an initial deposition of sub-stoichiometric Cr2N followed by sub-stoichiometric CrN with a { 022} texture and a columnar structure. The degree of sub-stoichiometry of the nitrides depends on the substrate bias and the substrate orientation relative to the cathode.
'%3e%3cpath fill='%23012169' d='M0 0v30h60V0z'/%3e%3cpath stroke='%23fff' stroke-width='6' d='m0 0 60 30m0-30L0 30'/%3e%3cpath stroke='%23C8102E' stroke-width='4' d='m0 0 60 30m0-30L0 30' clip-path='url(%23b)'/%3e%3cpath stroke='%23fff' stroke-width='10' d='M30 0v30M0 15h60'/%3e%3cpath stroke='%23C8102E' stroke-width='6' d='M30 0v30M0 15h60'/%3e%3c/g%3e%3c/svg%3e)
'/%3e%3cuse xlink:href='%23a' transform='rotate(72 0 0)'/%3e%3cuse xlink:href='%23a' transform='rotate(-72 0 0)'/%3e%3cuse xlink:href='%23a' transform='scale(-1 1) rotate(72)'/%3e%3c/g%3e%3c/defs%3e%3cpath fill='%23012169' d='M0 0h1200v600H0z'/%3e%3cpath stroke='%23FFF' stroke-width='60' d='m0 0 600 300M0 300 600 0' clip-path='url(%23b)'/%3e%3cpath stroke='%23C8102E' stroke-width='40' d='m0 0 600 300M0 300 600 0' clip-path='url(%23c)'/%3e%3cpath stroke='%23FFF' stroke-width='100' d='M300 0v300M0 150h600' clip-path='url(%23b)'/%3e%3cpath stroke='%23C8102E' stroke-width='60' d='M300 0v300M0 150h600' clip-path='url(%23b)'/%3e%3cuse xlink:href='%23d' fill='%23FFF' transform='matrix(45.4 0 0 45.4 900 120)'/%3e%3cuse xlink:href='%23d' fill='%23C8102E' transform='matrix(30 0 0 30 900 120)'/%3e%3cg transform='rotate(82 900 240)'%3e%3cuse xlink:href='%23d' fill='%23FFF' transform='rotate(-82 519.022 -457.666) scale(40.4)'/%3e%3cuse xlink:href='%23d' fill='%23C8102E' transform='rotate(-82 519.022 -457.666) scale(25)'/%3e%3c/g%3e%3cg transform='rotate(82 900 240)'%3e%3cuse xlink:href='%23d' fill='%23FFF' transform='rotate(-82 668.57 -327.666) scale(45.4)'/%3e%3cuse xlink:href='%23d' fill='%23C8102E' transform='rotate(-82 668.57 -327.666) scale(30)'/%3e%3c/g%3e%3cuse xlink:href='%23d' fill='%23FFF' transform='matrix(50.4 0 0 50.4 900 480)'/%3e%3cuse xlink:href='%23d' fill='%23C8102E' transform='matrix(35 0 0 35 900 480)'/%3e%3c/svg%3e)