Xcitability of DMH cholinergic neurons was dependent on neural network activity since TTX completely abolished the observed synaptic changes. Based on these data, we suggest that cholinergic neurons in the DMH readily detect and respond to changes in nutrient status through GABAergic presynaptic inputs. We propose that reduced inhibitory tone and the consequent enhancement of excitability of cholinergic neurons may be an important factor driving feeding in mice. Central cholinergic neurons are found gathered together in nuclei such as in the basal forebrain and brainstem regions, or dispersed as interneurons throughout brain areas such as the striatum [24]. The distribution of cholinergic neurons in the hypothalamus is rather scattered [24,25]. The Chat-positive cells in the DMH are small- and medium-sized bipolar cells or relatively large triangular shaped cells [25], consistent with our findings that cholinergic neurons were subdivided into two populations on the basis of their morphology. In addition, a cluster of Chat-positive neurons are found in the DMH and DH [20,24]. Using transgenic Chat-tauGFP mice [22], we found that a subset of the DMH neurons were indeed Chat-positive cells but that the DMH cholinergic neurons within the DMH totaled only ,200 cells/animal, in contrast with the relative abundance of neuropeptide-expressing neurons in the hypothalamus, such as POMC neurons (,3000 neurons) 
[26,27]. Importantly, we noted that the Chat positive neurons were strictly confined to the DMH and/orDH. Hence, cholinergic neurons can be used as a nucleus-specific, albeit low abundance, marker for the DMH. There is considerable evidence demonstrating that the DMH plays an important regulatory role in the maintenance of overall energy balance. For example, lesions of the DMH induce anorexigenic effects (see for review [9]). Deletion of brain-derived neurotrophic factor (BDNF) in the DMH results in hyperphagic behaviors [13] and knock-down of NPY expression in the DMH (-)-Indolactam V web reduces body adiposity and food intake, but enhances thermogenesis by promoting the development of brown adipocytes [5]. A recent study further shows that DMH neurons co-release retrograde signaling molecules, such as endocannabinoids and nitric oxide, that are regulated by fasting [28?0]. Thus a subpopulation of DMH neurons, perhaps including the DMH cholinergic neurons, appears to participate in the control of ingestive behavior. It is well known that nicotine acts as a strong anorexigenic substance [16]. A recent elegant study by Picciotto and colleagues shows the cellular mechanisms that underlie the anorexigenic effects of nicotine [17]. Nicotine activates a3b4-containing nicotinic receptors on POMC neurons and thereby, reduces energy intake. In line with these findings, POMC neurons in the arcuate are innervated by cholinergic inputs [18], which suggests that not only nicotine but its endogenous counterpart, acetylcholine, affects feeding behavior via the melanocortinergic system. Interestingly, the activation of muscarinic receptors, in 4 IBP site particular type 3, induces opposing effects on feeding behavior. For instance, M3-deficient mice exhibit decreased food intake as well as body weight [19]. Furthermore, deletion of the M3 
muscarinic receptor alters the POMC: AgRP ratio and interferes with the ability of AgRP to stimulate food intake [19]. Thus the relative activation of nicotinic vs. muscarinic cholinergic receptors in the hypothalamus may be an important determinant of.Xcitability of DMH cholinergic neurons was dependent on neural network activity since TTX completely abolished the observed synaptic changes. Based on these data, we suggest that cholinergic neurons in the DMH readily detect and respond to changes in nutrient status through GABAergic presynaptic inputs. We propose that reduced inhibitory tone and the consequent enhancement of excitability of cholinergic neurons may be an important factor driving feeding in mice. Central cholinergic neurons are found gathered together in nuclei such as in the basal forebrain and brainstem regions, or dispersed as interneurons throughout brain areas such as the striatum [24]. The distribution of cholinergic neurons in the hypothalamus is rather scattered [24,25]. The Chat-positive cells in the DMH are small- and medium-sized bipolar cells or relatively large triangular shaped cells [25], consistent with our findings that cholinergic neurons were subdivided into two populations on the basis of their morphology. In addition, a cluster of Chat-positive neurons are found in the DMH and DH [20,24]. Using transgenic Chat-tauGFP mice [22], we found that a subset of the DMH neurons were indeed Chat-positive cells but that the DMH cholinergic neurons within the DMH totaled only ,200 cells/animal, in contrast with the relative abundance of neuropeptide-expressing neurons in the hypothalamus, such as POMC neurons (,3000 neurons) [26,27]. Importantly, we noted that the Chat positive neurons were strictly confined to the DMH and/orDH. Hence, cholinergic neurons can be used as a nucleus-specific, albeit low abundance, marker for the DMH. There is considerable evidence demonstrating that the DMH plays an important regulatory role in the maintenance of overall energy balance. For example, lesions of the DMH induce anorexigenic effects (see for review [9]). Deletion of brain-derived neurotrophic factor (BDNF) in the DMH results in hyperphagic behaviors [13] and knock-down of NPY expression in the DMH reduces body adiposity and food intake, but enhances thermogenesis by promoting the development of brown adipocytes [5]. A recent study further shows that DMH neurons co-release retrograde signaling molecules, such as endocannabinoids and nitric oxide, that are regulated by fasting [28?0]. Thus a subpopulation of DMH neurons, perhaps including the DMH cholinergic neurons, appears to participate in the control of ingestive behavior. It is well known that nicotine acts as a strong anorexigenic substance [16]. A recent elegant study by Picciotto and colleagues shows the cellular mechanisms that underlie the anorexigenic effects of nicotine [17]. Nicotine activates a3b4-containing nicotinic receptors on POMC neurons and thereby, reduces energy intake. In line with these findings, POMC neurons in the arcuate are innervated by cholinergic inputs [18], which suggests that not only nicotine but its endogenous counterpart, acetylcholine, affects feeding behavior via the melanocortinergic system. Interestingly, the activation of muscarinic receptors, in particular type 3, induces opposing effects on feeding behavior. For instance, M3-deficient mice exhibit decreased food intake as well as body weight [19]. Furthermore, deletion of the M3 muscarinic receptor alters the POMC: AgRP ratio and interferes with the ability of AgRP to stimulate food intake [19]. Thus the relative activation of nicotinic vs. muscarinic cholinergic receptors in the hypothalamus may be an important determinant of.
