The Suprachiasmatic Nucleus and the Circadian Timing System - Progress in Molecular Biology and Translational Science - page 17

Input SCN Output

Hypothalamus - M SPVZ, POA, DMH
Hypothalamus - PVH
Basal forebrain - BST

Limbic cortex
Basal forebrain
Hypothalamus
Brainstem

Shell Shell

Ventral thalamus - zona incerta
Midline thalamus - PVT
Midline thalamus - PT, RE
Hypothalamus - PSCN. L SPVZ, VTA

Midline thalamus

Core Core

Basal forebrain - LSN

Visual input: Retina,
Intergeniculate leaflet,
Pretectal area

Figure 1.5 Diagram showing major connections of the SCN core and shell. BST, bed
nucleus of the stria terminalis; DMH, dorsomedial hypothalamic nucleus; LSN, lateral
septal nucleus; POA, preoptic area; PT, parataenial nucleus; PSCN, perisuprachiasmatic
nucleus; PVH, paraventricular hypothalamic nucleus; PVT, paraventricular thalamic
nucleus; RE, nucleus reuniens; LSPVZ, lateral subparaventricular area; MSPVZ, medial
subparaventricular area; VTA, ventral tuberal area; ZI, zona incerta.

The second method is immunocytochemistry. In material stained with
antisera for peptides, AVP þ axons are densely distributed over the medial
and dorsal portions of the SCN, extending laterally but largely sparing the ven-
tral region occupied by the VIP and GRP neurons. In contrast, the axonal
plexus produced by VIP and GRP neurons extends densely over the entire
SCN. 100-102 Commissural fibers were first noted by van den Pol. 72,103 Using
transynaptic transport of the swine herpes virus (pseudorabies virus; Ref. 97 ),
after injection of virus intomultiple areas outside the SCN, we found evidence
for a precise pattern of intrinsic and commissural connections that confirms and
extends the observations from normal material. First, neurons of the shell pro-
ject to contralateral shell and neurons of the core to contralateral core. Second,
neurons of the core project to shell on the ipsilateral side, but there is no evi-
dence for a commissural core to shell projection.

4.2. Afferent connections
4.2.1 Visual system projections
4.2.1.1 Retina
The first studies of RHT projections demonstrated a preponderance of
innervation to the ventral half of the SCN. 48-50 This has been confirmed
with increasingly sensitive techniques (Refs. 104,150 ) , and it is clear that
the RHT termination in the SCN is almost exclusively to the core, over-
lapping the distribution of VIP þ and GRP þ perikarya. The RHT