Volume 16, Number 23,
Issue of December 1, 1996
pp. 7699-7710
Copyright ©1996 Society for Neuroscience
A Population of Supramammillary Area Calretinin Neurons
Terminating on Medial Septal Area Cholinergic and Lateral Septal Area
Calbindin-Containing Cells Are Aspartate/Glutamatergic
Received June 26, 1996; revised Sept. 12, 1996; accepted Sept. 19, 1996.
Csaba Leranth1 and
Jozsef Kiss2
1 Department of Obstetrics and Gynecology and Section
of Neurobiology, Yale University School of Medicine, New Haven,
Connecticut 06520-8063, and 2 Joint Research Organization
of the Hungarian Academy of Sciences and Semmelweis Medical University,
Neuroendocrine Unit, Budapest, Hungary
The excitatory amino acid, aspartate/glutamate content of septal
complex calretinin (CR)-, choline acetyltransferase plus substance P-,
and Leu-enkephalin (Leu-enk)-containing extrinsic afferents was
examined. Experiments were carried out using the transmitter-specific
[3H]-D-aspartate retrograde tracer technique
in combination with immunostaining for CR, choline acetyltransferase,
and Leu-enk. The extrinsic and intrinsic CR innervation of the same
brain areas were elucidated on control rats and on animals in which the
septum was surgically separated from its ventral afferents. Correlated light and electron microscopic double-immunostaining experiments were
used to determine the synaptic connections between CR axon terminals
and lateral septal area calbindin (CB)- and medial septal area choline
acetyltransferase-immunoreactive neurons. Furthermore, to determine the
synaptic power of supramammilloseptal aspartate/glutamatergic neurons
on the septal complex, semiquantitative analyses were performed in the
supramammillary area on retrogradely (1)
[3H]-D-aspartate-radiolabeled and (2)
HRP-labeled material.
The results demonstrated that a population of the extrinsic CR axons
originating in the supramammillary area are aspartate/glutamatergic. These fibers forming asymmetric synaptic contacts terminate on both CB
and cholinergic neurons. Intraseptal CR neurons, which establish
symmetric synapses, innervate only lateral septal area neurons,
including the CB-containing cells. These observations, together with
other published data, raise the possibility of a hippocampus-lateral
septal (GABAergic CB-containing neurons)-supramammillary area
(aspartate/glutamatergic cells)-medial septal (cholinergic neurons)-hippocampus signal loop, which might be involved in the generation and regulation of hippocampal theta rhythm activity.
Key words:
autoradiography;
Leu-enkephalin;
substance P;
acetylcholine;
calbindin;
double immunostaining;
theta rhythm