0043 INVESTIGATION OF THE DEVELOPMENTAL ORIGIN OF FOREBRAIN GABAERGIC NEURONS INVOLVED IN SLEEP-WAKE CONTROL USING A FATE-MAPPING APPROACH

Abstract

GABAergic neurons located in the basal forebrain (BF) play important roles in promoting wakefulness and cortical activation. The developmental origin of these neurons is unknown. Here we use a fate-mapping approach to investigate BF GABAergic neurons derived from the medial ganglionic eminence (MGE) which express the transcription factor, Lim homeobox 6 (Lhx6). Previously validated mice expressing Cre Recombinase (Cre) under the control of the Lhx6 promoter region were purchased from Jackson Laboratories (Bar Harbor, ME). A cross with a Cre-reporter strain expressing the red fluorescent protein, tdTomato, allowed us to investigate the location of MGE-derived neurons. Immunostaining was used to identify parvalbumin neurons. Adeno-associated viral vectors expressing excitatory receptors (hM3Dq) activated exclusively by the designer drug, clozapine-N-oxide (CNO), were injected bilaterally into BF to test the effect on sleep-wake states. Neurons specified by Lhx6 were widely distributed throughout the BF. They included BF parvalbumin-containing projection neurons involved in promotion of wakefulness and cortical gamma-band oscillations. 575/1071 PV neurons counted in the BF of one Lhx6-Cre-tdTomato mouse contained tdTomato. However, only 13.7 % of tdTomato neurons were PV+, suggesting that Lhx6 also specifies other types of BF GABA neurons. Chemogenetic activation of Lhx6-derived BF neurons strongly increased wakefulness and gamma band power for >1 hr after i.p. injection of CNO (0.3 mg/kg) at ZT2. CNO treated mice had 83 ± 3 % wakefulness whereas saline-treated mice had only 30 ± 1 % (n=2) in the period 20–80 min following injection. Saline-injected mice also had increased wakefulness but only in the 20 min immediately following the injection. Wakefulness-promoting BF GABAergic neurons are derived from MGE progenitor cells expressing Lhx6. Cortical interneurons implicated in schizophrenia and other neurodevelopmental disorders are derived from the same pathway suggesting a potential involvement of BF Lhx6-derived neurons in the sleep-wake disturbances observed in these disorders. This work was supported by the US Veterans Administration, VA CDA 1IK2BX002130 (JMM) and NIH: NINDS R21 NS093000 (REB) & NIMH R03 MH107650 (CY). JTM received partial salary compensation and funding from Merck MISP, but has no conflict of interest with this work.