Potential pathways for intercellular communication within the calbindin subnucleus of the hamster suprachiasmatic nucleus.
In mammals, the suprachiasmatic nucleus (SCN) is the master circadian pacemaker. Within the caudal hamster SCN, a cluster of neurons containing the calcium binding protein, calbindin-D28K (CB), has been implicated in circadian locomotion. However, calbindin-immunoreactive (CB+) neurons in the calbindin subnucleus (CBsn) do not display a circadian rhythm in spontaneous firing [Eur J Neurosci 16 (2002) 2469]. Previously, we proposed that intercellular communication might be essential in integrating outputs from rhythmic (CB-) neurons and nonrhythmic (CB+) neurons to produce a circadian output in the intact animal. The primary aim of this study is to provide a neuroanatomical framework to better understand intercellular communication within the CBsn. Using reconstructions of previously recorded neurons, we demonstrate that CB+ neurons have significantly more dendrites than CB- neurons. In addition, CBsn neurons have dorsally oriented dendritic arbors. Using double-label confocal microscopy, we show that GABA colocalizes with CB+ neurons and GABA(A) receptor subunits make intimate contacts with neurons in the CBsn. Transforming growth factor alpha (TGFalpha), a substance shown to inhibit locomotion [Science 294 (2001) 2511], is present within the CBsn. In addition, neurons in this region express the epidermal growth factor receptor, the only receptor for TGFalpha. Lastly, we show that CB+ neurons are coupled to CB+ and CB- neurons by gap junctions. The current study provides a structural framework for synaptic communication, electrical coupling, and signaling via a growth factor within the CBsn of the hamster SCN. Our results reveal connections that have the potential for integrating cellular communication within a subregion of the SCN that is critically involved in circadian locomotion.
Jobst
E E
EE
Oregon National Primate Research Center, 505 Northwest 185th Avenue, Beaverton, OR 97006, USA. jobste@ohsu.edu
Robinson
D W
DW
Allen
C N
CN
D000818:Animals; D064026:Calbindins; D002450:Cell Communication / Q000502:physiology*; D006224:Cricetinae; D017629:Gap Junctions / Q000737:chemistry* / Q000502:physiology; D066298:In Vitro Techniques; D007365:Intercellular Junctions / Q000737:chemistry / Q000502:physiology; D008297:Male; D008647:Mesocricetus; D009434:Neural Pathways / Q000737:chemistry / Q000502:physiology; D011963:Receptors, GABA-A / Q000032:analysis / Q000502:physiology; D064030:S100 Calcium Binding Protein G / Q000032:analysis* / Q000502:physiology; D013493:Suprachiasmatic Nucleus / Q000737:chemistry* / Q000166:cytology / Q000502:physiology
D064026:Calbindins; D011963:Receptors, GABA-A; D064030:S100 Calcium Binding Protein G