Thereby confirming the important role of p53 in PA-2 induced apoptosis and growth arrest. The effect of PA-2 on apoptosis and p53 can be attenuated by co-incubation with NAC, an antioxidant, suggesting that it occurs downstream of oxidative stress induction. Induction of oxidative stress also has repercussions on the activity of NF-kB, which is strongly inhibited by PA-2 administration. The lateral habenula is a small epithalamic structure that projects via the fasciculus retroflexus to the midbrain. The LHb is known to modulate midbrain dopamine neurons, including inhibition of ventral tegmental area neurons via glutamatergic excitation of the GABAergic rostromedial tegmental nucleus and possible excitation of these neurons via a direct projection. The LHb has been implicated in a variety of functions including motor suppression, cognition, pain, stress, and reward, as well as regulation of reproductive behaviour, circadian rhythms and metabolism. Of particular interest to the experiments reported here is the claim that LHb is important for BAY 73-4506 aversive motivational value and punishment. Two primary lines of evidence have typically been invoked to support this possibility. First, recording studies in rhesus monkeys have shown that LHb and RMTg neurons are phasically excited by unexpected aversive events and reward omissions, as well as by cues that predict those outcomes. These phasic excitations are closely followed by a phasic inhibition of midbrain DA neuronal firing. These results have been interpreted as LHb neuronal coding of aversive outcome values and consequently suppressing motor behavior and reward seeking. Second, focal electrical or optogenetic stimulation of the LHbRMTg-VTA pathway is aversive and can act as a punisher. For example, Stamatakis and Stuber reported that ChR2 stimulation of LHb terminals in the RMTg supported both active and passive place avoidance learning in mice, and negatively reinforced as well as positively punished nosepoking behaviour in mice. These findings show that activity in LHb and the LHb-RMTg pathway is correlated with, and is sufficient to support, punishment learning. However, it is not immediately clear whether LHb is necessary for punishment. Although recent studies support this possibility broadly for LHb encoding of aversive motivational value, showing for example that lesions of the rat LHb/fasciculus retroflexus attenuate the aversive motivational properties of cocaine as well as ethanol and that reversible inactivations of LHb impair avoidance learning, the requirement of LHb for the acquisition and expression of punishment behaviour remains unknown. The aim of this experiment was to study the role of the LHb in the acquisition and expression of punishment in rats. Rats received bilateral cannulation of the LHb permitting reversible inactivation using the AMPA/kainate receptor antagonist NBQX. NBQX was used due to previous findings showing that aversion-related signals are conveyed to the LHb from the basal ganglia and that transmission.