Enhanced novelty-induced activity, reduced anxiety, delayed resynchronization to daylight reversal and weaker muscle strength in tenascin-C-deficient mice Fabio Morellini and Melitta Schachner Zentrum fu ¨ r Molekulare Neurobiologie, Universita ¨ t Hamburg, Falkenried 94, D-20251 Hamburg, Germany Keywords: circadian activity, ethology, exploration, extracellular matrix, learning, memory, passive avoidance Abstract Tenascin-C (TNC) is an extracellular matrix protein with multiple and important functions during development and in the adult. We here present a study on the behaviour of TNC-deficient (knockout, KO) mice. Longitudinal experiments including tests for circadian activity, exploration, state and trait anxiety, motor coordination and cognition were performed. KO mice showed increased reactivity to explore a novel environment and decreased anxiety. Spontaneous circadian activity was unaffected, but KO mice showed delayed resynchronization to daylight reversal. TNC deficiency caused weaker muscle strength, whereas gait, coordination and motor learning were unaltered. Short- and long-term memory in the fear conditioning task and working memory in the spontaneous alternation test were normal in KO mice. KO mice showed impaired memory recall in the step-down, but not in the step-through, passive avoidance task. Ethological observation of mice behaviour and principal component analyses indicated that the higher novelty- and stress-induced active responses of KO mice account for their poorer performance in passive avoidance tasks, whereas cognitive abilities are unaltered. The present study extends and corrects previous results, and is an example of how an ethological approach allows a precise description and interpretation of the behavioural alterations of mutant mice. Introduction Tenascin-C (TNC) is an extracellular matrix glycoprotein highly conserved during evolution. It is most prominently expressed during development in the nervous system and in non-neuronal tissues (Jones & Jones, 2000). In the nervous system, TNC is mainly synthesized and secreted by astroglial cells and expressed in various regions during early development. It is downregulated after matura- tion, but persists in restricted areas of the adult brain (Bartsch et al., 1992, 1994; for review, see also Bartsch, 1996). TNC is upregulated in the hippocampus undergoing plastic events, such as after induction of long-term potentiation in mice in vivo (Nakic et al., 1998), during epileptogenesis in a murine model of temporal lobe epilepsy (Heck et al., 2004) and in kainic acid-treated rats (Nakic et al., 1996). Conversely, depletion of TNC in the adult brain leads to reduced plasticity of cortical whisker representation after vibrissectomy (Cybulska-Klosowicz et al., 2004). The observation that TNC expression is upregulated when the CNS responds to stimulation suggests that it might also be involved when behavioural responses are regulated to best adapt to the environment. To investigate the functions of TNC in vivo, two TNC-deficient mouse mutants have been independently generated and showed to develop normally (Saga et al., 1992; Steindler et al., 1995; Forsberg et al., 1996). However, more detailed studies of the mutant from Saga et al. (1992) revealed subtle biochemical and behavioural abnormal- ities (Cifuentes-Diaz et al., 1998, 2002; Nakao et al., 1998; Kiernan et al., 1999), although the interpretation of these results is complicated by the debate on the overall expression of abnormal TNC fragments in this mutant (Mitrovic & Schachner, 1995; Steindler et al., 1995; Settles et al., 1997). We generated a constitutive TNC knockout (KO) mouse that lacks detectable levels of TNC protein or truncated forms thereof as judged from immunoblot experiments that revealed at least less than 0.05% of the amount of TNC protein normally expressed in wild type (WT) mice (Evers et al., 2002). These KO mice from our group showed subtle but significant morphological alterations in the cerebral cortex (Irintchev et al., 2005), and reduced long-term potentiation and long-term depression in the CA1 region of the hippocampus as compared with WT littermates (Evers et al., 2002). Despite these physiological alterations, hippocampus-dependent learning, relearning and long-term memory in the water maze task were normal in KO mice (Evers et al., 2002). However, KO mice showed impaired memory in the step-down passive avoidance task (Strekalova et al., 2002). In the present work, we extended the behavioural analysis of TNC KO mice by performing longitudinal studies that allowed us to correlate parameters related to different systems such as circadian activity, novelty-induced exploration, anxiety, motor function, and learning and memory. For a better interpretation of the results, experiments were designed and analysed using an ethological perspective taking into account the social and environmental condi- tions in which animals were tested as well as the adaptive functions of the behaviours analysed. Correspondence: Dr F. Morellini, as above. E-mail: fmorell@zmnh.uni-hamburg.de Received 8 August 2005, revised 25 November 2005, accepted 16 December 2005 European Journal of Neuroscience, Vol. 23, pp. 1255–1268, 2006 doi:10.1111/j.1460-9568.2006.04657.x ª The Authors (2006). Journal Compilation ª Federation of European Neuroscience Societies and Blackwell Publishing Ltd