Effects of chronic antidepressant drug administration and electroconvulsive shock on activity of dopaminergic neurons in the ventral tegmentum: a reply to Chenu et al. (2011)

We have read the letter commenting on our article entitled ‘Effects of chronic antidepressant drug administration and electroconvulsive shock on activity of dopaminergic neurons in the ventral tegmentum’. We offer the following response. The authors of the letter direct attention to our mean spontaneous firing rate for dopaminergic neurons in the ventral tegmental area (VTA-DA neurons) being lower than typically found and particularly note that we included neurons with firing rates as low as 1.0 Hz. Our mean rates of firing are indeed somewhat lower than often reported by other investigators. We were clearly aware of this, specifically describing in our Methods section that we included slow-firing neurons. Our criteria for DA neurons in the VTA depended upon ( a ) stereotaxic location and then ( b ) the specific wave form of the unit as stated in the Procedure section, which is widely acknowledged for these neurons. Because we were recording multiple neurons in each animal, there was no way to mark individual neurons and identify their locations and/or characteristics histologically; consequently, we included neurons based on waveform. Given these criteria, we saw no basis for discarding neurons because their firing rate was slow and, consequently, such neurons were included. The writers of the letter call attention to an article by Ungless et al. (2004), who described differences between DA and non-DA neurons in the VTA. The writers noted that our mean spontaneous firing rate was closer to that of non-dopaminergic cells than dopaminergic cells. However, the main point of the article by Ungless et al. was that VTA-DA neurons were inhibited by aversive or stressful stimuli whereas non-DA neurons were excited by such stimuli; they reported 10 of 12 DA neurons were inhibited by 10-s foot pinch whereas four of six non-DA neurons were excited by this stimulus. We have examined the …