Immunocytochemical study of the development of vasotocin/mesotocin in the hypothalamo-hypophysial system of the chick embryo

Abstract

The hypothalamo-hypophysial system of the chick embryo has been studied with a monoclonal antibody which cross-reacts with arginine vasotocin and mesotocin, using thick (100 micron) sections in conjunction with a peroxidase-conjugated rabbit anti-mouse antibody. Although weakly stained perikarya occur occasionally in the tuberal region on embryonic days 6 and 7, the most consistent immunostaining of perikarya is found in the periventricular region of the caudal midhypothalamus at the level of the optic chiasm after embryonic day 8 1/2. Synthesis of peptides, therefore, takes place while the cells are close to their site of origin. Between embryonic days 9 and 10, beaded axons run along the anterior median eminence closely apposed to the adenohypophysis, thereby forming the anlage of the zona externa. The axons of the hypothalamo-neurohypophysial tract surround the neural lobe between embryonic days 11 and 12. The caudal to rostral wave of neuronal maturation that occurs during development appears to be due to a progressive differentiation of the periventricular zone, as well as the migration of perikarya. The early periventricular perikarya at embryonic day 8 1/2 send processes rostrally in a wing-shaped formation that extends both dorso- and ventrolaterally. From embryonic days 10 to 12, perikarya can be observed in the wing-like extensions, apparently migrating to rostral levels. The dorsolateral pathway gives rise at its midportion to the lateral cell group, whereas those perikarya migrating more laterally form the anlage of the external supraoptic nucleus. The ventrolateral wing-shaped extension of perikarya appears to be directed toward the ventral group and those lateral perikarya continuous with it. The location of mature neuronal cell groups is well established by embryonic day 17.

Embryonal Development of Arginine Vasotocin/Mesotocin Gene Expression in the Chicken Brain

“…Alternatively, the nonapep- tides discussed here may be directly involved in differentiation of their own or other cell populations or may support the onset and/or maintainance of cell migration (5). The synthesis of AVT/MT seems to start shortly after the last mitotic division (7).…”

“…The immunoreactive cells occur in three diencephalic regions, a ventral group, corresponding to the SON in mammals, a periventricular group, corresponding to the PVN and a dorsal/dorsolateral diencephalic area (6). Immunostaining with antibodies against AVT and M T failed to show clearly identifiable immunostainable perikarya before embryonal day (E) 8 (7). Earlier studies (8) were unable to visualize AVT immunoreactive cell bodies before E 14 though investigations using chromalum-haematoxylin staining d o indicate neurosecretory material as early as E4 (9), E l l (10) and E l 3 (11,12).…”

“…The differences may be due to various methods of fixation and staining. It is also unclear which hypothalamic nuclei first express the nonapeptides: staining has been reported first either in the median eminence (8), or in the cells of the SON (9, 1 I ) or the PVN (7,10).…”

Effects of Increased Levels of Prenatal Mesotocin on Postnatal Individual Recognition and Stress Responsiveness in Northern bobwhite quail (Colinus Virginianus)

“…The brains of 40 quail embryos were collected to determine the average endogenous levels of mesotocin present throughout the 23 days of prenatal development in Northern bobwhite quail eggs. Eggs were weighed prior to incubation and brain tissue was collected and weighed on embryonic days 8, 12, 16, and 20 (Charvet & Striedter, 2010;Milewski et al, 1989;Tennyson et al, 1986;Blähser & Heinrichs, 1982). An additional 13 embryos were used to verify the efficacy of the injection procedure once the baseline levels of MT were determined.…”

“…It is here that OT is bound to its' transporter protein neurophysin I and released into the blood stream when stimulated. Similarly, MT which differs from OT by only one amino acid (Jonaidi, Oloumi, & Denbow, 2003;Gimpl & Fahrenholz, 2001;Bons, 1980) has been shown to be produced and stored in the same relative brain structures as OT in humans and other mammal species (Ross & Young 2009;Tennyson, Nilaver, Hou-Yu, Valiquette, & Zimmerman, 1986). Research has also provided support for MT serving similar functional purposes as those of OT (Jonaidi et al, 2003;Milewski, Ivell, Grossman, & Ellendorff, 1989;Tennyson et al, 1986;Blähser & Heinrichs, 1982; discussed in further detail below).…”