Amino acid neurotransmission between fimbria-fornix fibers and neurons in the lateral septum of the rat: A microiontophoretic study

Abstract

We investigated the nature of the excitatory amino acid and the type of amino acid receptor involved in the projection of fimbria-fomix (fi-fx) fibers on neurons in the lateral septal complex (LSC) of the rat. It appeared that neurons which were strongly orthodromically activated (SOA) by stimulation of fi-fx fibers were excited by glutamate (GLU) and aspartate (ASP) at much lower ejecting currents than neurons which were only weakly orthodromically excited. In addition, GLU was a stronger agent than ASP, particularly in SOA septal cells. Two amino acid antagonists tested, glutamic acid diethylester (GDEE) and 2-amino-S-phosphonovaleric acid (2-APV), selectively antagonized responses to the amino acid agonists quisqualate (QUIS) and N-methyl-D-aspartate (NMDA), respectively. They also depressed GLU-and ASP-induced responses, although in that case the antagonists frequently had to be expelled with currents higher than those needed to block QUIS-and NMDA-evoked excitations. Furthermore, GDEE frequently antagonized GLU-induced responses better than ASPevoked excitations, whereas 2-APV often blocked responses to ASP more effectively than those to GLU. It was observed that GDEE, ejected with currents that blocked responses to QUIS reversibly, decreased the number of synaptic responses induced in SOA cells by fi-fx stimuli. Synaptically induced excitation in these neurons was consistently una&cted by 2-APV, even when the antagonist was expelled with high currents. According to these results, LSC neurons, in particular the SOA neurons, are more Abbreviations: li-fx-fimbria-fomix; LSC-lateral septal complex; SOA, WOA-strongly, weakly orthodromically activated; GLU-glutamate; ASP-aspartate; GDEE-glutamic acid diethylester, 2-APV-2-amino%phosphonovaleric acid; QUIS-quisqualate; NMDA-N-methylDaspartate; KA-kainic acid.

Dynamic changes in extracellular release of GABA and glutamate in the lateral septum during social play behavior in juvenile rats: Implications for sex-specific regulation of social play behavior

“…GABA and glutamate, the principle inhibitory and excitatory neurotransmitters in the brain, largely modulate LS neuronal activity (Joëls & Urban, 1984a,b; Allaman-Exertier et al, 2007). GABA released in the LS likely derives from local LS neurons sending recurrent axon collaterals to neighboring neurons (Onteniente et al, 1987; Phelan et al, 1989; Jakab & Leranth, 1990; Risold & Swanson, 1997b), thereby inhibiting intraseptal neuronal activity.…”