Biology Reference
In-Depth Information
Figure 1.2 Diagrams showing the location of lesions. The data interpretations are
shown in the table below the diagrams. Ref. 52 ; reprinted with permission, Elsevier.
rhythm. 68 An intriguing aspect of this is that the transplants are effective with-
out reestablishing connections to the host brain. 69 Taken together, these stud-
ies clearly established SCN function as a circadian pacemaker. What was not
entirely clear was the definition of “pacemaker” in this situation.
Nevertheless, these data formed the basis for continuing investigation of
the neural basis of circadian timing. I will review aspects of this in four con-
texts: (1) anatomical organization of the SCN including intrinsic organiza-
tion and the issue of subdivisions, (2) visual and nonvisual SCN afferents, (3)
efferent projections including issues of nonsynaptic communication, and (4)
functional organization of the SCN as a component of a brain CTS. The
review is not intended to be comprehensive but to present an overview
of the information that gradually has come available over the past 40 years
as this is interpreted by one who was “in at the beginning.”
3. ANATOMICAL ORGANIZATION OF THE SCN
3.1. General organization
In Nissl-stained material, the SCN is a compact nucleus of small cells situated
just above the medial optic chiasm and lateral to the periventricular nucleus
adjacent to the third ventricle. Dorsally and laterally, the SCN is bordered
by the anterior hypothalamic area. Caudally it extends into the rostral
 
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