The hippocampi of species commonly used for in vitro physiologic studi
es were examined to determine if there were species-specific and regio
nal differences in somatostatin immunoreactivity. The distributions of
somatostatin-immunoreactive somata and fiber plexuses were determined
, and the concentration of somatostatin along the septotemporal axis o
f the hippocampus was measured using a radioimmunoassay. There are man
y similarities in the patterns of somatostatin immunoreactivity in the
hippocampi of mice, rats, guinea pigs, and rabbits. All species had a
relatively even distribution of somatostatin-positive perikarya acros
s three fields of the hippocampus (dentate gyrus, CA3, and CA1-2), a s
imilar distribution of somatostatin-immunoreactive perikarya across th
e strata of the CA1-2 field and the dentate gyrus; and more somatostat
in-positive cells in temporal than in septal hippocampus. However, the
re are species-specific differences in the distribution of somatostati
n-immunoreactive perikarya across the strata of CA3. In addition, unli
ke the other species examined, mice appeared not to have a somatostati
n-immunoreactive fiber plexus in the molecular layer of the dentate gy
rus. The functional signifi cance of these differences remains to be d
etermined. (C) 1994 Wiley-Liss, Inc.