Volume 16, Number 12,
Issue of June 15, 1996
pp. 3991-4004
Copyright ©1996 Society for Neuroscience
Expression of NGF and NT3 mRNAs in Hippocampal Interneurons
Innervated by the GABAergic Septohippocampal Pathway
Received Dec. 19, 1995; revised March 18, 1996; accepted March 21, 1996.
Nativitat Rocamora1,
Marta Pascual1,
Laszlo Acsàdy2,
Luís de
Lecea3,
Tamàs F. Freund2, and
Eduardo Soriano1
1 Department of Animal and Plant Cell Biology, Faculty
of Biology, University of Barcelona, Barcelona 08028, Spain,
2 Institute of Experimental Medicine, Hungarian Academy of
Sciences, H-1450 Budapest, Hungary, and 3 Department of
Molecular Biology, The Scripps Research Institute, La Jolla, California
92037
We used in situ hybridization for the detection of nerve
growth factor (NGF), brain-derived neurotrophic factor (BDNF), and
neurotrophin 3 (NT3) mRNAs combined with immunocytochemistry against
the calcium-binding proteins parvalbumin (PARV), calbindin 28k (CALB),
and calretinin (CALR) to determine the expression of neurotrophins in
functionally distinct subsets of hippocampal interneurons. Most
PARV-immunoreactive neurons in the hippocampus were NGF mRNA-positive
(82%), which corresponds to 71% of NGF-positive neurons in the
hippocampus proper and in the dentate gyrus (excluding granule cells).
In contrast, only a subset of CALB- and CALR-immunoreactive
interneurons (24% and 23%, respectively) displayed hybridization
signals for NGF. Small subsets of PARV- and CALR-positive cells
expressed NT3 mRNA, but we did not find hippocampal interneurons
expressing BDNF mRNA. These results show that NGF and NT3 genes are
differentially regulated in distinct subsets of GABAergic cells, and
these interneurons are a major source of NGF production in the
hippocampus.
We also addressed whether hippocampal interneurons expressing
neurotrophins were targets of the GABAergic septohippocampal pathway.
We developed a triple-labeling method that combines anterograde tracing
of this pathway by means of Phaseolus vulgaris
leucoagglutinin injections, with in situ hybridization for
the detection of neurotrophins, and immunocytochemistry for
calcium-binding proteins. Virtually every PARV-positive neuron
innervated by GABAergic septohippocampal baskets expressed NGF mRNA
(86%), whereas 39-59% of CALR- and CALB-positive interneurons that
were contacted by GABAergic septohippocampal axons showed NGF gene
expression. A small subset of NT3 mRNA-expressing interneurons was also
innervated by septohippocampal baskets. These findings show that the
GABAergic septohippocampal pathway preferentially terminates on
interneurons expressing NGF mRNA, suggesting that this neurotrophic
factor might be involved in the specification of this connection and in
its maintenance and normal function in the adult brain.
Key words:
rat hippocampus;
GABAergic interneurons;
neurotrophic
factor expression;
nerve growth factor;
neurotrophin 3;
calcium binding
proteins;
septohippocampal connections;
cholinergic afferents