Elsevier

Neuroscience

Volume 160, Issue 2, 5 May 2009, Pages 284-294
Neuroscience

Behavioural Neuroscience
Research Paper
Anxiety-like behavior is modulated by a discrete subpopulation of interneurons in the basolateral amygdala

https://doi.org/10.1016/j.neuroscience.2009.01.083Get rights and content

Abstract

The basolateral amygdala (BL) is a putative site for regulating anxiety, where inhibition and excitation respectively lead to decreases and increases in anxiety-like behaviors. The BL contains local networks of GABAergic interneurons that are subdivided into classes based on neurochemical content, and are hypothesized to regulate unique functional responses of local glutamatergic projection neurons. Recently it was demonstrated that lesioning a portion of the BL interneuronal population, those interneurons that express neurokinin1 receptors (NK1r), resulted in anxiety-like behavior. In the current study, these NK1r expressing cells of the BL are further phenotypically characterized, demonstrating approximately 80% co-expression with GABA thus confirming them as GABAergic interneurons. These NK1r interneurons also colocalize with two distinct populations of BL interneurons as defined by the neuropeptide content. Of the NK1r positive cells, 41.8% are also positive for neuropeptide Y (NPY) and 39.7% of the NK1r positive cells are also positive for cholecystokinin (CCK). In addition to enhancing the phenotypic characterization, the extent to which the NK1r cells of amygdala nuclei contribute to anxiety-like responses was also investigated. Lesioning the NK1r expressing interneurons, with a stable form of substance P (SSP; the natural ligand for NK1r) coupled to the targeted toxin saporin (SAP), in the anterior and posterior divisions of the BL was correlated to increased anxiety-like behaviors compared to baseline and control treated rats. Furthermore the phenotypic and regional selectivity of the lesions was also confirmed.

Section snippets

Animals

Male Wistar rats (Harlan Sprague-Dawley, Indianapolis, IN, USA) between 325 and 350 g were individually housed with free access to food and water. The room temperature was maintained at 72 °F (22 °C) on a 12-h light/dark schedule. All studies were conducted in accordance with the NIH Guidelines for the Care and Use of Laboratory Animals (NIH Publication no. 80-23) revised 1996 and the guidelines of the Indiana University Pudrdue University Indianapolis Institutional Animal Care and Use

Phenotypic characterization of BL interneurons

It is has been reported that NK1r expressing cells of the BL co-localize with interneurons containing NPY, SOM and CB, but do not overlap with PV or CR containing interneurons. However, NK1r co-expression with GABA and CCK within the same interneurons has not been examined. Here we used dual labeling immunofluorescence to determine the extent to which NK1r-IR cells were also GABA-IR, CCKL-IR [defined as large (L) CCK-IR cells with a soma diameter >10 μm; Mascagni and McDonald, 2003], and NPY-IR

Discussion

As observed in previous studies utilizing this, or similar targeted toxin (Truitt and Coolen 2002, Levita et al 2003), SSP-SAP injections ablate approximately 80% of the NK1r expressing cells in a regionally selective and cell-type specific manner. Specifically, NK1r-IR cells lesions were primarily restricted to the BL without significantly reducing NK1r-IR cells in adjacent CeA as well as not significantly reducing the total number of neurons (NeuN-IR) or even interneurons (GABA-IR). This

Conclusion

In conclusion, we have demonstrated that a small population of GABAergic cells, the NK1r interneurons, in the BL is capable of regulating anxiety-like behaviors. These cells are likely to modulate behaviors by their action within the context of the BL local circuit, and loss of these cells results in exaggerated levels of anxiety-like responses. Furthermore, this study also demonstrates that the targeted toxin approach is a valid tool in the assessment of the functional roles of local circuit

Acknowledgments

The authors would like to acknowledge Pam Kelley for blinded scoring of the SI behavior. This work was supported by PHS grants RO1s MH065702 and MH52619 to A.S.

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