A Group of Descending Glutamatergic Neurons Activated by Stress in Corticolimbic Regions Project to the Nucleus Accumbens

Abstract

The nucleus accumbens (NAc) is the major component of the ventral striatum that regulates stress-induced depression. The NAc receives dopaminergic inputs from the ventral tegmental area (VTA), and the role of VTA-NAc neurons in stress response has been recently characterized. The NAc also receives glutamatergic inputs from various forebrain structures including the prelimbic cortex (PL), basolateral amygdala (BLA), and ventral hippocampus (vHIP), whereas the role of those glutamatergic afferents in stress response remains underscored. In the present study, we investigated the extent to which descending glutamatergic neurons activated by stress in the PL, BLA, and vHIP project to the NAc. To specifically label the input neurons into the NAc, fluorescent-tagged cholera toxin subunit B (CTB), which can be used as a retrograde neuronal tracer, was injected into the NAc. After two weeks, the mice were placed under restraint for 1 h. Subsequent histological analyses indicated that CTB-positive cells were detected in 170~680 cells/mm 2 in the PL, BLA, and vHIP, and those CTB-positive cells were mostly glutamatergic. In the PL, BLA, and vHIP regions analyzed, stress-induced c-Fos expression was found in 20~100 cells/mm 2 . Among the CTB-positive cells, 2.6% in the PL, 4.2% in the BLA, and 1.1% in the vHIP were co-labeled by c-Fos, whereas among c-Fos-positive cells, 7.7% in the PL, 19.8% in the BLA, and 8.5% in the vHIP were co-labeled with CTB. These results suggest that the NAc receives a significant but differing proportion of glutamatergic inputs from the PL, BLA, and vHIP in stress response.

Insular Cortex Projections to Nucleus Accumbens Core Mediate Social Approach to Stressed Juvenile Rats

“…This approach allowed tract-specific control by directly infusing the hM3Dq and hM4Di agonist CNO to the terminals of IC neurons in NAc (see pharmacological manipulations). For retrograde tracing, 300 nl of cholera toxin B conjugated to Alexa Fluor 488 (CTb 488 ; Thermo Fisher, catalog #C34775) were microinjected to the right hemisphere NAc as previously (Dong et al, 2017;Park et al, 2018) at a rate of 100 nl/min and allowed 4 min for diffusion. After surgery, rats were administered meloxicam (1 mg/kg, Eloxiject; Henry Schein) and the antibiotic penicillin (12,000 units, Combi-pen; Henry Schein) and allowed 2 to 3 weeks to recover before behavioral testing as described below.…”

“…To test this hypothesis, 12 experimental rats received unilateral microinjections of the retrograde tracer CTb 488 in the left hemisphere NAc (Fig. 2 A, B) as previously (Dong et al, 2017;Park et al, 2018) so that neurons that project from IC to NAc can be identified for cell counting ( Fig. 2E).…”

Insular Cortex Projections to Nucleus Accumbens Core Mediate Social Approach to Stressed Juvenile Rats

“…For retrograde tracing, 300nl of Cholera Toxin B conjugated to AlexaFluor 488 (CTb 488 , Thermo Fisher, Cat. No: C34775) were microinjected to the right hemisphere NAc as previously (Dong et al, 2017;Park et al, 2018) at a rate of 100nl/minute and allowed 4 min for diffusion. After surgery, rats were administered meloxicam (1mg/kg, Eloxiject, Henry Schein) and the antibiotic penicillin (12,000 Units, Combi-pen, Henry Schein) and allowed 2 to 3 weeks to recover before behavioral testing as described below.…”

“…To test this hypothesis, 12 experimental rats received unilateral microinjections of the retrograde tracer CTb 488 in the left hemisphere NAc ( Fig. 2a and b) as previously (Dong et al, 2017;Park et al, 2018) so that neurons that project from IC to NAc can be identified for cell counting (Fig. 2e).…”