Projections from the subparaventricular zone define four channels of output from the circadian timing system

• Published in: Journal of comparative neurology (1911) Vol. 523; no. 18; pp. 2714 - 2737
• Main Authors: Vujovic, Nina, Gooley, Joshua J., Jhou, Thomas C., Saper, Clifford B.
• Format: Journal Article
• Language: English
• Published: United States Blackwell Publishing Ltd 15.12.2015; Wiley Subscription Services, Inc
• Subjects: Animals; Biotin - analogs & derivatives; Biotin - metabolism; Brain Mapping; Cholera Toxin - metabolism; Circadian Rhythm - physiology; circadian timing; Dextrans - metabolism; Green Fluorescent Proteins - genetics; Green Fluorescent Proteins - metabolism; Male; Neural Pathways - physiology; neural projections; Neurons - metabolism; Rats; Rats, Sprague-Dawley; subparaventricular zone; Suprachiasmatic Nucleus - cytology; Suprachiasmatic Nucleus - physiology; Transduction, Genetic; Vasoactive Intestinal Peptide - metabolism; circadian timing; subparaventricular zone; neural projections
• ISSN: 0021-9967; 1096-9861
• DOI: 10.1002/cne.23812

The subparaventricular zone of the hypothalamus (SPZ) is the main efferent target of neural projections from the suprachiasmatic nucleus (SCN) and an important relay for the circadian timing system. Although the SPZ is fairly homogeneous cytoarchitecturally and neurochemically, it has been divided into distinct functional and connectional subdivisions. The dorsal subdivision of the SPZ (dSPZ) plays an important role in relaying signals from the SCN controlling body temperature rhythms, while the ventral subdivision (vSPZ) is critical for rhythms of sleep and locomotor activity (Lu et al. [] J Neurosci 21:4864–4874). On the other hand, the medial part of the SPZ receives input mainly from the dorsomedial SCN, whereas the lateral SPZ receives input from the ventrolateral SCN and the retinohypothalamic tract (Leak and Moore [] J Comp Neurol 433:312–334). We therefore investigated whether there are corresponding differences in efferent outputs from these four quadrants of the SPZ (dorsolateral, ventrolateral, dorsomedial, and ventromedial) by a combination of anterograde and retrograde tracing. We found that, while all four subdivisions of the SPZ share a similar backbone of major projection pathways to the septal region, thalamus, hypothalamus, and brainstem, each segment of the SPZ has a specific set of targets where its projections dominate. Furthermore, we observed intra‐SPZ projections of varying densities between the four subdivisions. Taken together, this pattern of organization suggests that the circadian timing system may have several parallel neural outflow pathways that provide a road map for understanding how they subserve different functions. J. Comp. Neurol. 523:2714–2737, 2015. © 2015 Wiley Periodicals, Inc. The subparaventricular zone (SPZ) has medial vs. lateral subdivisions, defined by vasopressin (AVP) vs. vasoacitve intestinal peptide (VIP) input from the suprachiasmatic nucleus. There are also dorsal vs. ventral SPZ subdivisions, which have distinct effects on circadian rhythms. Each of the four SPZ quadrants has distinct efferent output pathways.