Behavior and Neurology of Lizards 
N. Greenberg and P. D. MacLean, eds. 
NIMH, 1978. 
A Working Concept of the Organization of the Anterior 
Dorsal Ventricular Ridge* 
Philip S. Ulinski 
Department of Anatomy 
University of Chicago 
SUMMARY. The anterior dorsal ventricular ridge (ADVR) is a large, subcortical structure 
which is present in the brains of all reptiles and birds. It is a major destination of ascending 
sensory systems (Northcutt, 1978) and is, therefore, likely to be involved in determining im- 
portant aspects of the behavior of these organisms. This contribution summarizes a series of 
investigations which I have conducted on the ADVR of snakes with a variety of neuro- 
anatomical techniques. Each technique provides a different piece of information about the 
neurons present in the structure. Together, they provide the first concept of the organization of 
snake ADVR. 
THE NEURONS PRESENT IN 
SNAKE ADVR 
Figure 1 shows a transverse section 
through the brain of a water snake (Natrix 
sipedon). The inset is a sketch of a water 
snake brain indicating the plane of the sec- 
tion which appears in the main part of the 
figure. The ADVR is a large structure lying 
inside the lateral ventricle and separated 
from the subjacent striatum (ST) by a thin, 
but distinct, cell-poor area. Neurons are dis- 
tributed fairly homogeneously throughout 
the ADVR. This snake (and probably most 
snakes) thus resembles the lizards designated 
Type II by Northcutt (1978) on the basis 
of ADVR structure. Figure 2 shows a sector 
of ADVR depicted at a higher magnification. 
There are subtle, important differences in 
the distribution of these neurons which 
permit division of snake ADVR into four 
zones lying concentric with the ventricle. 
These zones are labeled A through D, and 
each contains a characteristic population of 
neurons. 
Zone A neurons (Fig. 3) are embedded 
in the ependyma. Their dendrites extend 
through the 30/u, width of the cell-poor zone A 
and into the subjacent zone B. Some of the 
cells have a fairly heavy covering of den- 
dritic spines while others bear only a few 
spines. Nothing is known about the axons of 
zone A neurons. 
Zone B neurons (Fig. 4) tend to form 
clusters of up to six or seven neurons which 
have their somatic membranes closely ap- 
posed. The areas of contact are interrupted 
by membrane specializations which involve a 
thickening of the plasma membranes for 
about 0.25/1. and an electron lucent inter- 
cellular gap of about 50 A (Ulinski, 1976a). 
Since the specializations generally resemble 
gap junctions, it is tempting to speculate that 
these cell clusters are multicellular units of 
electrotonically coupled neurons. Similar 
clusters are present in the ADVR in many 
lizards (Northcutt, 1978) and birds (Saini 
and Lepellsack, 1977). Zone B neurons have 
dendrites which extend in all directions, 
forming roughly spherical dendritic trees and 
bearing a heavy cover of dendritic spines. 
Their axons typically course radially into 
zone A where they form branches which 
follow the curvature of the ventricle for 
long distances. A few of the neurons send 
axons centrally into zone C. 
Zone C neurons (Fig. 5) tend to occur in 
isolation. Although clusters of touching 
neurons occasionally do occur, they involve 
only a few neurons. They have dendritic trees 
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