Targeted Deletion of ERK5 MAP Kinase in the Developing Nervous System Impairs Development of GABAergic Interneurons in the Main Olfactory Bulb and Behavioral Discrimination between Structurally Similar Odorants

Abstract

ERK5 MAP kinase is highly expressed in the developing nervous system and has been implicated in promoting the survival of immature neurons in culture. However, its role in the development and function of the mammalian nervous system has not been established in vivo. Here, we report that conditional deletion of the erk5 gene in mouse neural stem cells during development reduces the number of GABAergic interneurons in the main olfactory bulb (OB). Our data suggest that this is due to a decrease in proliferation and an increase in apoptosis in the subventricular zone (SVZ) and rostral migratory stream (RMS) of ERK5 mutant mice. Interestingly, ERK5 mutant mice have smaller OB and are impaired in odor discrimination between structurally similar odorants. We conclude that ERK5 is a novel signaling pathway regulating developmental OB neurogenesis and olfactory behavior.

Inducible Activation of ERK5 MAP Kinase Enhances Adult Neurogenesis in the Olfactory Bulb and Improves Olfactory Function

“…Every eighth serial coronal section (30 m) containing the SVZ or every fifth section containing the entire olfactory bulb (30 m) was immunostained. Immunoreactivepositive cells (BrdU ϩ , NeuN ϩ , or double-BrdU ϩ /NeuN ϩ ) were counted with the experimenter blinded to mice genotypes or treatments as previously described (Pan et al, 2012a;Zou et al, 2012). For the SVZ, cells were counted manually and the resulting cell numbers were scaled relative to the number of sections per SVZ (Pan et al, 2012a).…”

“…For the SVZ, cells were counted manually and the resulting cell numbers were scaled relative to the number of sections per SVZ (Pan et al, 2012a). For the OB, stereology software (MBF Bioscience) was used as previously described to count cells (Zou et al, 2012). ImageJ was used for measuring Sox2 and TdTomato immunofluorescence intensity.…”

“…This was conducted as previously described (Pan et al, 2012a;Zou et al, 2012). Briefly, animals were pretrained with mineral oil-laced cotton swabs for four 60 s presentations with 2 min intervals to ensure that subsequent exposure to an odorantlaced cotton swab did not elicit a response due to object novelty.…”

“…The odor habituation/dishabituation tests were then conducted by presenting isoamyl acetate (IAA), citralva, and vanillin sequentially, with four presentations (60 s/presentation with 2 min intertrial interval) for each odorant. As we described previously, the duration of the animals' investigation (sniffing) of the cotton swab was recorded with a stopwatch (Pan et al, 2012a;Zou et al, 2012). The sniffing was defined as animals' noses approaching to and within 1 cm distance to the swabs (Pan et al, 2012a;Zou et al, 2012).…”

“…As we described previously, the duration of the animals' investigation (sniffing) of the cotton swab was recorded with a stopwatch (Pan et al, 2012a;Zou et al, 2012). The sniffing was defined as animals' noses approaching to and within 1 cm distance to the swabs (Pan et al, 2012a;Zou et al, 2012). A significant decrease in investigation time during subsequent presentations of the same odorant indicates odor recognition and habituation, and an increase in investigation of a new odorant indicates dishabituation (Pan et al, 2012a;Zou et al, 2012).…”