Biology Reference
In-Depth Information
CHAPTER ONE
The Suprachiasmatic Nucleus
and the Circadian Timing System
Robert Y. Moore
Department of Neurology, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
Contents
1.
Introduction
2
2. The Emergence of a Circadian Neurobiology
5
3. Anatomical Organization of the SCN
9
3.1 General organization
9
3.2 Neurochemical organization
11
3.3 SCN organization in the rat brain
11
3.4 SCN organization in the human brain
13
3.5 The subdivision view of SCN organization
13
4. Afferent and Efferent Connections
16
4.1 Intrinsic and commissural connections
16
4.2 Afferent connections
17
4.3 Efferent organization
19
5. Conclusions
20
6. Reprise
22
References
22
Abstract
The circadian timing system (CTS) in mammals may be defined as a network of inter-
connected diencephalic structures that regulate the timing of physiological processes
and behavioral state. The central feature of the CTS is the suprachiasmatic nucleus (SCN)
of the hypothalamus, a self-sustaining circadian oscillator entrained by visual afferents,
input from other brain and peripheral oscillators. The SCN was first noted as a distinct
component of the hypothalamus during the late nineteenth century and recognized
soon after as a uniform feature of the mammalian and lower vertebrate brain. But, as
was true for so many brain components identified in that era, its function was unknown
and remained so for nearly a century. In the latter half of the twentieth century, numer-
ous tools for studying the brain were developed including neuroanatomical tracing
methods, electrophysiological methods including long-term recording in vivo and
in vitro, precise methods for producing localized lesions in the brain, and molecular neu-
robiology. Application of these methods provided a body of data strongly supporting
the view that the SCN is a circadian pacemaker in the mammalian brain. This chapter
