2006). In this case it needs to be confirmed, by EM, that counting somata does not underestimate the m2-immunoreactive population. Also of interest in the future would be a study of AChR expression by calbindin- and calretinin-immunoreactive cells in MT. These are critical populations to describe for the extrastriate cortex as the proportion of inhibitory cells that express calbindin and calretinin increases as one moves up through the visual pathway (DeFelipe et al. 1999) and into the prefrontal Inhibitors,research,lifescience,medical cortex (Conde et al. 1994). In V1, these classes comprise fewer than 5% of all neurons (Hendry et al. 1990; Van Brederode et al. 1990; Beaulieu et al. 1992;

Meskenaite 1997). Due to their low density, different

tissue sampling methods would have been required in order to include a comparison of these populations between MT and V1 in the present study. In conclusion, PV neurons in visual areas V1 and MT frequently express m1 AChRs, and in fact the majority of this class of neurons in both areas are m1 AChR immunoreactive. Inhibitors,research,lifescience,medical These data support the use of V1 as a model circuit for cholinergic modulation of PV neuron-mediated inhibition in the visual cortex. They also provide a possible mechanism for the particularly strong effects of attention on narrow-spiking neurons in the extrastriate cortex. Acknowledgments Tissue for this study was generously provided by the labs Inhibitors,research,lifescience,medical of E. Callaway and J. Gottlieb. Thanks to the Inhibitors,research,lifescience,medical staff at the Waitt Biophotonics imaging core at the Salk Institute for their technical support. Thanks also to C. Aoki for helpful comments on an earlier version of the manuscript. Conflict of Interest None declared.
Although the symptoms of nicotine withdrawal are primarily psychological, convention holds that drug withdrawal Inhibitors,research,lifescience,medical syndromes indicate physical dependence (PD). Perturbations in neural function provoked by a drug are thought to induce counter-posing homeostatic neural adaptations, which, in the absence of the drug, give rise to withdrawal symptoms. This model assumes that with physical dependence, homeostatic neural

Methisazone adaptations are always present in a latent state, and become manifest in a dynamic state during drug withdrawal. The purpose of this study is to identify neural correlates of the latent state of PD to nicotine, and the dynamic state of nicotine withdrawal. trans-isomer molecular weight craving is an important symptom of PD that manifests dynamically during withdrawal. (American Psychiatric Association 2000) Withdrawal-induced craving (WIC) is that which is triggered by abstinence and relieved by the administration of nicotine. WIC is triggered through different mechanisms than other forms of craving, such as cue-induced craving. Smokers describe three qualitatively distinct forms of WIC of increasing severity, and as PD develops, these three forms of WIC are experienced in the same set order. (DiFranza et al.