Evan H. Goulding

Brain-derived neurotrophic factor regulates energy balance downstream of melanocortin-4 receptor

The melanocortin-4 receptor (MC4R) is critically involved in regulating energy balance, and obesity has been observed in mice with mutations in the gene for brain-derived neurotrophic factor (BDNF). Here we report that BDNF is expressed at high levels in the ventromedial hypothalamus (VMH) where its expression is regulated by nutritional state and by MC4R signaling. In addition, similar to MC4R mutants, mouse mutants that expresses the BDNF receptor TrkB at a quarter of the normal amount showed hyperphagia and excessive weight gain on higher-fat diets. Furthermore, BDNF infusion into the brain suppressed the hyperphagia and excessive weight gain observed on higher-fat diets in mice with deficient MC4R signaling. These results show that MC4R signaling controls BDNF expression in the VMH and support the hypothesis that BDNF is an important effector through which MC4R signaling controls energy balance.

Molecular cloning and single-channel properties of the cyclic nucleotide-gated channel from catfish olfactory neurons

We have cloned a functional cDNA encoding the cyclic nucleotide-gated channel selectively expressed in catfish olfactory sensory neurons. The cyclic nucleotide-gated channels share sequence and structural features with the family of voltage-gated ion channels. This homology is most evident in transmembrane region S4, the putative voltage sensor domain, and the H5 domain, thought to form the channel pore. We have characterized the single-channel properties of the cloned catfish channel and compared these properties with the channel in native catfish olfactory sensory neurons. The channel is activated equally well by cAMP and cGMP, shows only a slight voltage dependence of gating, and exhibits a pH- and voltage-dependent subconductance state similar to that observed for the voltage-gated L-type calcium channel.

Deletion of Mecp2 in Sim1-expressing neurons reveals a critical role for MeCP2 in feeding behavior, aggression, and the response to stress.

Rett Syndrome (RTT) is an autism spectrum disorder caused by mutations in the X-linked gene encoding methyl-CpG binding protein 2 (MeCP2). In order to map the neuroanatomic origins of the complex neuropsychiatric behaviors observed in patients with RTT and to uncover endogenous functions of MeCP2 in the hypothalamus, we removed Mecp2 from Sim1-expressing neurons in the hypothalamus using Cre-loxP technology. Loss of MeCP2 in Sim1-expressing neurons resulted in mice that recapitulated the abnormal physiological stress response that is seen upon MeCP2 dysfunction in the entire brain. Surprisingly, we also uncovered a role for MeCP2 in the regulation of social and feeding behaviors since the Mecp2 conditional knockout (CKO) mice were aggressive, hyperphagic, and obese. This study demonstrates that deleting Mecp2 in a defined brain region is an excellent approach to map the neuronal origins of complex behaviors and provides new insight about the function of MeCP2 in specific neurons.

Enhanced Locomotor, Reinforcing, and Neurochemical Effects of Cocaine in Serotonin 5-Hydroxytryptamine 2C Receptor Mutant Mice

Brain serotonin [5-hydroxytryptamine (5-HT)] systems substantially influence the effects of cocaine; however, the contributions of individual 5-HT receptor subtypes to the regulation of cocaine responses are unclear. A line of mutant mice devoid of 5-HT2C receptors was used to examine the contribution of this receptor subtype to the serotonergic modulation of cocaine responses. Mutants display enhanced exploration of a novel environment and increased sensitivity to the locomotor stimulant effects of cocaine. In an operant intravenous self-administration model under a progressive ratio schedule of reinforcement, mutants display elevated levels of lever pressing for cocaine injections, indicating that the drug is more reinforcing in these mice. Moreover, mutants exhibit enhanced cocaine-induced elevations of dopamine (DA) levels in the nucleus accumbens, a brain region implicated in the stimulant and rewarding properties of cocaine. In contrast, phenotypic differences in dorsal striatal DA levels were not produced by cocaine treatment. These findings strongly implicate 5-HT2C receptors in the serotonergic suppression of DA-mediated behavioral responses to cocaine and as a potential therapeutic target for cocaine abuse.

Exposure of Residues in the Cyclic Nucleotide–Gated Channel Pore: P Region Structure and Function in Gating

In voltage-gated ion channels and in the homologous cyclic nucleotide-gated (CNG) channels, the loop between the S5 and S6 transmembrane segments (P region) is thought to form the lining of the pore. To investigate the structure and the role in gating of the P region of the bovine retinal CNG channel, we determined the accessibility of 11 cysteine-substituted P region residues to small, charged sulfhydryl reagents applied to the inside and outside of membrane patches in the open and closed states of the channel. The results suggest that the P region forms a loop that extends toward the central axis of the channel, analogous to the L3 loop of bacterial porin channels. Furthermore, the P region, in addition to forming the ion selectivity filter, functions as the channel gate, the structure of which changes when the channel opens.

A robust automated system elucidates mouse home cage behavioral structure

Patterns of behavior exhibited by mice in their home cages reflect the function and interaction of numerous behavioral and physiological systems. Detailed assessment of these patterns thus has the potential to provide a powerful tool for understanding basic aspects of behavioral regulation and their perturbation by disease processes. However, the capacity to identify and examine these patterns in terms of their discrete levels of organization across diverse behaviors has been difficult to achieve and automate. Here, we describe an automated approach for the quantitative characterization of fundamental behavioral elements and their patterns in the freely behaving mouse. We demonstrate the utility of this approach by identifying unique features of home cage behavioral structure and changes in distinct levels of behavioral organization in mice with single gene mutations altering energy balance. The robust, automated, reproducible quantification of mouse home cage behavioral structure detailed here should have wide applicability for the study of mammalian physiology, behavior, and disease.

Behavioral indices of ongoing pain are largely unchanged in male mice with tissue or nerve injury-induced mechanical hypersensitivity

&NA; Despite the impact of chronic pain on the quality of life in patients, including changes to affective state and daily life activities, rodent preclinical models rarely address this aspect of chronic pain. To better understand the behavioral consequences of the tissue and nerve injuries typically used to model neuropathic and inflammatory pain in mice, we measured home cage and affective state behaviors in animals with spared nerve injury, chronic constriction injury (CCI), or intraplantar complete Freund’s adjuvant. Mechanical hypersensitivity is prominent in each of these conditions and persists for many weeks. Home cage behavior was continuously monitored for 16 days in a system that measures locomotion, feeding, and drinking, and allows for precise analysis of circadian patterns. When monitored after injury, animals with spared nerve injury and complete Freund’s adjuvant behaved no differently from controls in any aspect of daily life. Animals with CCI were initially less active, but the difference between CCI and controls disappeared by 2 weeks after injury. Further, in all pain models, there was no change in any measure of affective state. We conclude that in these standard models of persistent pain, despite the development of prolonged hypersensitivity, the mice do not have significantly altered “quality of life.” As alteration in daily life activities is the feature that is so disrupted in patients with chronic pain, our results suggest that the models used here do not fully reflect the human conditions and point to a need for development of a murine chronic pain model in which lifestyle changes are manifest. Mice with spared nerve injury, chronic constriction injury, and complete Freund’s adjuvant injection did not alter behavior in their home cage or a battery of affective tests.

Cellular Telephones Measure Activity and Lifespace in Community-Dwelling Adults: Proof of Principle

OBJECTIVES: To describe a system that uses off‐the‐shelf sensor and telecommunication technologies to continuously measure individual lifespace and activity levels in a novel way.

A Flexible Estimating Equations Approach for Mapping Function-Valued Traits

In genetic studies, many interesting traits, including growth curves and skeletal shape, have temporal or spatial structure. They are better treated as curves or function-valued traits. Identification of genetic loci contributing to such traits is facilitated by specialized methods that explicitly address the function-valued nature of the data. Current methods for mapping function-valued traits are mostly likelihood-based, requiring specification of the distribution and error structure. However, such specification is difficult or impractical in many scenarios. We propose a general functional regression approach based on estimating equations that is robust to misspecification of the covariance structure. Estimation is based on a two-step least-squares algorithm, which is fast and applicable even when the number of time points exceeds the number of samples. It is also flexible due to a general linear functional model; changing the number of covariates does not necessitate a new set of formulas and programs. In addition, many meaningful extensions are straightforward. For example, we can accommodate incomplete genotype data, and the algorithm can be trivially parallelized. The framework is an attractive alternative to likelihood-based methods when the covariance structure of the data is not known. It provides a good compromise between model simplicity, statistical efficiency, and computational speed. We illustrate our method and its advantages using circadian mouse behavioral data.

Treadmill gait speeds correlate with physical activity counts measured by cell phone accelerometers.

A number of important health-related outcomes are directly related to a persons ability to maintain normal gait speed. We hypothesize that cellular telephones may be repurposed to measure this important behavior in a noninvasive, continuous, precise, and inexpensive manner. The purpose of this study was to determine if physical activity (PA) counts collected by cell phone accelerometers could measure treadmill gait speeds. We also assessed how cell phone placement influenced treadmill gait speed measures. Participants included 55 young, middle-aged, and older community-dwelling men and women. We placed cell phones as a pendant around the neck, and on the left and right wrist, hip, and ankle. Subjects then completed an individualized treadmill protocol, alternating 1 min rest periods with 5 min of walking at different speeds (0.3-11.3 km/h; 0.2-7 mi/h). No persons were asked to walk at speeds faster than what they would achieve during day-to-day life. PA counts were calculated from all sensor locations. We built linear mixed statistical models of PA counts predicted by treadmill speeds ranging from 0.8 to 6.4 km/h (0.5-4 mi/h) while accounting for subject age, weight, and gender. We solved linear regression equations for treadmill gait speed, expressed as a function of PA counts, age, weight, and gender. At all locations, cell phone PA counts were strongly associated with treadmill gait speed. Cell phones worn at the hip yielded the best predictive model. We conclude that in both men and women, cell phone derived activity counts strongly correlate with treadmill gait speed over a wide range of subject ages and weights.