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

Abstract

Social play is a motivated and rewarding behavior that is displayed by nearly all mammals and peaks in the juvenile period. Moreover, social play is essential for the development of social skills and is impaired in social disorders like autism. We recently showed that the lateral septum (LS) is involved in the regulation of social play behavior in juvenile male and female rats. The LS is largely modulated by GABA and glutamate neurotransmission, but their role in social play behavior is unknown. Here, we determined whether social play behavior is associated with changes in the extracellular release of GABA and glutamate in the LS and to what extent such changes modulate social play behavior in male and female juvenile rats. Using intracerebral microdialysis in freely behaving rats, we found no sex difference in extracellular GABA concentrations, but extracellular glutamate concentrations are higher in males than in females under baseline conditions and during social play. This resulted in a higher glutamate/GABA concentration ratio in males vs. females and thus, an excitatory predominance in the LS of males. Furthermore, social play behavior in both sexes is associated with significant increases in extracellular release of GABA and glutamate in the LS. Pharmacological blockade of GABA-A receptors in the LS with bicuculline (100 ng/0.5 μl, 250 ng/0.5 μl) dose-dependently decreased the duration of social play behavior in both sexes. In contrast, pharmacological blockade of ionotropic glutamate receptors (NMDA and AMPA/kainate receptors) in the LS with AP-5+CNQX (2mM+0.4mM/0.5 μl, 30 mM+3mM/0.5 μl) dose-dependently decreased the duration of social play behavior in females, but did not alter social play behavior in males. Together, these data suggest a role for GABA neurotransmission in the LS in the regulation of juvenile social play behavior in both sexes, while glutamate neurotransmission in the LS is involved in the sex-specific regulation of juvenile social play behavior.

Keywords: GABA; glutamate; lateral septum; microdialysis; sex difference; social play.

Fig. 1

Schematic drawing of the LS (bregma 0.20 mm; adapted from Paxinos and Watson, 1998) and representative enlargements of photomicrographs of Nissl-stained coronal sections of the rat brain indicating with a bracket the location and extend of the semipermeable membrane of a microdialysis probe placement unilaterally in the LS (left) and indicating with an arrow the microinjection location in the medial part of the LS using charcoal as marker (right). Correct placements were considered at bregma 0.20 mm ± 0.2 mm using the brain atlas by Paxinos and Watson (1998). The microinjection location was different compared to the microdialysis probe placement to allow the drugs to reach both sides of the LS.

Fig. 2

Extracellular GABA (A) and glutamate (B) released in the LS of male and female juvenile rats. Five consecutive dialysates were taken: Dialysates 1 and 2 are taken under baseline condition, dialysate 3 includes exposure to the 10-min social play test (play), and dialysates 4 and 5 are taken after exposure to the social play test under undisturbed conditions. Data represent mean + SEM. Extracellular concentrations: *p < 0.05, ^#p < 0.05 vs. baseline, two-way ANOVA followed by one-way ANOVA. Percentage release: *p < 0.05 vs. dialysates 1, 2, 4, 5 (males), vs. dialysates 1, 2, 5 (females in A), vs. dialysates 1, 2, 4 (females in B), two-way ANOVA for repeated measures followed by one-way ANOVA for repeated measures and LSD posthoc test.

Fig. 3

Glutamate/GABA concentration ratio in the LS of male and female juvenile rats under baseline condition and during social play. Data represent mean + SEM. *p < 0.05, # p = 0.098, two-way ANOVA for repeated measures followed by one-way ANOVA.

Fig. 4

Effects of pharmacological blockade of GABA-A receptors (A) or ionotropic glutamate receptors (B) in the LS on social play behavior in male and female juvenile rats. The GABA-A receptor antagonist bicuculline was injected in a dose of 100 ng/0.5 µl or 250 ng/0.5 µl. The NMDA receptor antagonist AP-5 and the AMPA/kainate receptor antagonist CNQX were concurrently injected in a dose of 2 mM+0.4 mM/0.5 µl or 30 mM+3 mM/0.5 µl. The duration of social play behavior is expressed as percentage of total time. Data represent mean + SEM. *p < 0.01, two-way ANOVA followed by one-way ANOVA (A) or Bonferroni posthoc test (B).