Neurochemical characterization of AMPA receptor-containing neurons in the mediolateral septal area of the rat

Abstract

 The lateral septum receives a massive innervation by excitatory amino acid-containing limbic cortical and hypothalamic afferents, and previous studies have described a wide distribution of α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptor-containing neurons in this area. The aim of this study was to determine whether different subtypes of AMPA receptors are expressed in the same neurons. Furthermore, considering the fact that a population of lateral septal cells, the ”somatospiny neurons,” are GABAergic calbindin-containing cells, the coexistence of each subtype of AMPA receptor with calbindin was also investigated. Colocalization experiments were performed on adjacent vibratome sections of the lateral septal area for GluR1 and GluR2/3 AMPA-receptor subunits, GluR1 and calbindin, GluR2/3 and calbindin, as well as GluR1 plus calbindin and GluR2/3 plus calbindin, using the ”mirror” colocalization technique. The results are summarized as follows: (1) GluR1 is present in the soma and most intensively expressed in dendrites and somatic and dendritic spines; while GluR2/3 is associated with the soma and proximal dendrites of the neurons. (2) Forty-one percent of the AMPA receptor-containing neurons cocontain GluR1 and GluR2/3. (3) Thirty-eight percent of GluR1- and 28% of GluR2/3-labeled cells express calbindin. (4) Sixty-two percent of the calbindin-immunoreactive neurons contain GluR1 and 51% of them express GluR2/3. (5) Half of the neurons expressing both GluR1 and GluR2/3 also contain calbindin. (6) The distribution of GluR1 plus GluR2/3-containing, GluR1 plus calbindin-containing, and GluR2/3 plus calbindin-containing neurons in the lateral septum are homogeneous. This study indicates the existence of multiple populations of AMPA receptor- and calbindin-containing neurons in the lateral septal area.