Behavioural Brain Research 93 (1998) 157 – 165 Research report Mild traumatic lesion of the right parietal cortex in the rat: Characterisation of a conditioned freezing deficit and its reversal by dizocilpine Sandy Hogg 1,a , David J. Sanger b , Paul C. Moser a, * a Synthe ´labo Recherche, 10 rue des Carrieres, 92500 Rueil -Malmaison, France b Synthe ´labo Recherche, 31 aenue Paul Vaillant -Couturier, 92220 Bagneux, France Received 26 May 1997; received in revised form 8 October 1997; accepted 8 October 1997 Abstract We have previously demonstrated that traumatic injury of the lateral aspect of the right parietal cortex results in reduced acquisition of the passive avoidance task but enhanced learning in an active avoidance procedure. In order to try to explain the apparent dichotomy between these findings a series of experiments examined the effect of fluid percussion-induced traumatic brain injury (FP-TBI) on the conditioned freezing response to a context previously paired with an aversive stimulus. Rats subjected to FP-TBI displayed less conditioned freezing than the sham-operated controls. This effect was particularly marked when the delay between context exposure and footshock was short ( 30 s) and was no longer significant when this delay was 3 min, indicating that the injured animals did not have an impaired freezing response per se. This phenomenon was enduring such that it could still be observed 2 months following the surgery. There was no significant freezing deficit after FP-TBI of the motor cortex, demonstrating that the site of injury is important and that the freezing deficit is not a general response to CNS trauma. The NMDA receptor antagonist dizocilpine (MK-801, 1 mg/kg i.v.) significantly reduced the trauma-induced freezing deficit when administered as a single bolus 15 min prior to the surgery, or as three repeated treatments (3 ×0.33 mg/kg) 15 min, and 6 and 24 h following lesion. The trauma-induced deficit in conditioned freezing can explain the differences in active and passive avoidance behaviours and appears to be specific to lesion of the lateral parietal cortex. In addition, the behavioural deficit can be attenuated using the neuroprotective agent dizocilpine, suggesting that it may prove useful as a sensitive and specific measure of cortical damage following traumatic injury. © 1998 Elsevier Science B.V. All rights reserved. Keywords: Cerebral trauma; Context; Conditioned emotional response; Dizocilpine; MK-801 1. Introduction Traumatic brain lesions in animals are widely re- ported to induce performance deficits in the Morris water maze task [16,25,46] or in passive avoidance [19,56]. These results are generally interpreted as reflect- ing a cognitive impairment induced by the lesion, al- though the presence of more generalised neurological deficits and high levels of mortality following the trau- matic lesion can complicate such interpretations. We have recently described the effects of mild fluid percus- sion-induced traumatic injury (FP-TBI) of the right parietal cortex in a variety of behavioural tasks [19], and reported a deficit in the avoidance of a previously shocked compartment in a step-through passive avoid- ance paradigm but an improvement in the acquisition of an active avoidance task. Both tasks are considered * Corresponding author. Tel.: +33 1 41391396; fax: +33 1 41391306 1 Present address: H. Lundbeck A/S, Ottiliavej 9, DK-2500 Copen- hagen-Valby, Denmark. 0166-4328/98/$19.00 © 1998 Elsevier Science B.V. All rights reserved. PII S0166-4328(97)00145-9