RT Journal Article
SR Electronic
T1 Connectome of the Suprachiasmatic Nucleus: New Evidence of the Core-Shell Relationship
JF eneuro
JO eNeuro
FD Society for Neuroscience
SP ENEURO.0205-18.2018
DO 10.1523/ENEURO.0205-18.2018
VO 5
IS 5
A1 Shruti Varadarajan
A1 Mary Tajiri
A1 Rashi Jain
A1 Rebecca Holt
A1 Qanetha Ahmed
A1 Joseph LeSauter
A1 Rae Silver
YR 2018
UL http://www.eneuro.org/content/5/5/ENEURO.0205-18.2018.abstract
AB A brain clock, constituted of ∼20,000 peptidergically heterogeneous neurons, is located in the hypothalamic suprachiasmatic nucleus (SCN). While many peptidergic cell types have been identified, little is known about the connections among these neurons in mice. We first sought to identify contacts among major peptidergic cell types in the SCN using triple-label fluorescent immunocytochemistry (ICC). To this end, contacts among vasoactive intestinal polypeptide (VIP), gastrin-releasing peptide (GRP), and calretinin (CALR) cells of the core, and arginine vasopressin (AVP) and met-enkephalin (ENK) cells of the shell were analyzed. Some core-to-shell and shell-to-core communications are specialized. We found that in wild-type (WT) mice, AVP fibers make extremely sparse contacts onto VIP neurons but contacts in the reverse direction are numerous. In contrast, AVP fibers make more contacts onto GRP neurons than conversely. For the other cell types tested, largely reciprocal connections are made. These results point to peptidergic cell type-specific communications between core and shell SCN neurons. To further understand the impact of VIP-to-AVP communication, we next explored the SCN in VIP-deficient mice (VIP-KO). In these animals, AVP expression is markedly reduced in the SCN, but it is not altered in the paraventricular nucleus (PVN) and supraoptic nucleus (SON). Surprisingly, in VIP-KO mice, the number of AVP appositions onto other peptidergic cell types is not different from controls. Colchicine administration, which blocks AVP transport, restored the numbers of AVP neurons in VIP-KO to that of WT littermates. The results indicate that VIP has an important role in modulating AVP expression levels in the SCN in this mouse.