Brain Research 865 (2000) 45–58 www.elsevier.com / locate / bres Research report Postnatal development of a GABA deficit and disturbance of neural functions in mice lacking GAD65 a, a a a ,1 b * Oliver Stork , Feng-Yun Ji , Koichi Kaneko , Simone Stork , Yuko Yoshinobu , b b a Takahiro Moriya , Shigenobu Shibata , Kunihiko Obata a Laboratory of Neurochemistry, National Institute for Physiological Sciences, Okazaki, Japan b Department of Pharmacology, School of Human Sciences, Waseda University, Tokorazawa, Japan Accepted 23 February 2000 Abstract The 65-kDa isoform of glutamic acid decarboxylase (GAD65) is believed to play an essential role for GABA synthesis in the central 2 / 2 nervous system. Using mice with targeted disruption of the GAD65 gene (GAD65 mice) we investigated the contribution of GAD65 to GABA synthesis in different brain areas during postnatal development and in adulthood. In the amygdala, hypothalamus and parietal 1 / 1 cortex of GAD65 mice an increase of GABA levels was observed during postnatal development, most prominently between the first 1 / 2 and second month after birth. This increase appeared to be dependent on GAD65, as it was delayed by 2 months in GAD65 mice and 2 / 2 2 / 2 was not observed in GAD65 mice. Likely as a consequence of their GABA deficit, adult GAD65 mice showed a largely abnormal neural activity with frequent paroxysmal discharges and spontaneous seizures. They furthermore displayed increased anxiety-like behaviour in a light / dark avoidance test and reduced intermale aggression, as well as a reduced forced-swimming-induced immobility 1 / 2 indicative of an antidepressant-like behavioural change. Adult GAD65 mice did not show behavioural disturbances except for a 2 / 2 reduced aggressive behaviour that was comparable to that in GAD65 mice. We conclude that GAD65-mediated GABA synthesis may be crucially involved in control of emotional behaviour and indispensable for a tonic inhibition that prevents the development of hyperexcitability in the maturating central nervous system. Aggressive, and possibly other social behaviour may be especially prone to regulation through GAD65-mediated GABA synthesis.  2000 Elsevier Science B.V. All rights reserved. Themes: Neurotransmitters, modulators, transporters, and receptors Topics: GABA Keywords: Amygdala; Hypothalamus; Seizure; Emotional behaviour; Knock out mouse 1. Introduction g-Aminobutyric acid (GABA), the major inhibitory neurotransmitter in the vertebrate central nervous system Abbreviations: ANOVA, analysis of variance; CNS, central nervous system; EEG, electroencephalogram; EMG, electromyogram; GABA, (CNS), is produced in a large, heterogeneous population of g-aminobutyric acid; GAD65, 65-kDa isoform of glutamic acid decarbox- GABAergic neurons that can be found throughout the ylase; GAD67, 67-kDa isoform of glutamic acid decarboxylase; PBS, brain [39]. GABA released from these cells plays im- phosphate-buffered saline; PCR, polymerase chain reaction; PLSD, portant roles in a variety of behavioural functions such as protected least-significant difference control of motor activity, circadian rhythm, and emotional *Corresponding author. Present address: Institute of Physiology, School of Medicine, Otto-von-Guericke University of Magdeburg, Leip- behaviour. It is, furthermore, involved in structural and ziger Str. 44, 39120 Magdeburg, Germany. Tel.: 149-391-611-7130; fax: functional organisation and re-organisation processes of 149-391-671-5819. the CNS during development, synaptic plasticity and the E-mail address: oliver.stork@medizin.uni-magdeburg.de (O. Stork) 1 development of epileptic activity [5,41,53]. GABA is Present address: Institute of Physiology, School of Medicine, Otto-von- generated through a-decarboxylation of glutamic acid by Guericke University of Magdeburg, Leipziger Str. 44, 39120 Magdeburg, Germany. the enzyme glutamic acid decarboxylase, two isoforms of 0006-8993 / 00 / $ – see front matter  2000 Elsevier Science B.V. All rights reserved. PII: S0006-8993(00)02206-X