A Brainstem Neural Substrate for Stopping Locomotion.

Locomotion occurs sporadically and needs to be started, maintained, and stopped. The neural substrate underlying the activation of locomotion is partly known, but little is known about mechanisms involved in termination of locomotion. Recently, reticulospinal neurons (stop cells) were found to play a crucial role in stopping locomotion in the lamprey: their activation halts ongoing locomotion and their inactivation slows down the termination process. Intracellular recordings of these cells revealed a distinct activity pattern, with a burst of action potentials at the beginning of a locomotor bout and one at the end (termination burst). The termination burst was shown to be time linked to the end of locomotion, but the mechanisms by which it is triggered have remained unknown. We studied this in larval sea lampreys (Petromyzon marinus; the sex of the animals was not taken into account). We found that the mesencephalic locomotor region (MLR), which is known to initiate and control locomotion, stops ongoing locomotion by providing synaptic inputs that trigger the termination burst in stop cells. When locomotion is elicited by MLR stimulation, a second MLR stimulation stops the locomotor bout if it is of lower intensity than the initial stimulation. This occurs for MLR-induced, sensory-evoked, and spontaneous locomotion. Furthermore, we show that glutamatergic and, most likely, monosynaptic projections from the MLR activate stop cells during locomotion. Therefore, activation of the MLR not only initiates locomotion, but can also control the end of a locomotor bout. These results provide new insights onto the neural mechanisms responsible for stopping locomotion.SIGNIFICANCE STATEMENT The mesencephalic locomotor region (MLR) is a brainstem region well known to initiate and control locomotion. Since its discovery in cats in the 1960s, the MLR has been identified in all vertebrate species tested from lampreys to humans. We now demonstrate that stimulation of the MLR not only activates locomotion, but can also stop it. This is achieved through a descending glutamatergic signal, most likely monosynaptic, from the MLR to the reticular formation that activates reticulospinal stop cells. Together, our findings have uncovered a neural mechanism for stopping locomotion and bring new insights into the function of the MLR.

Differences in short and long sleep durations between blacks and whites attributed to emotional distress: analysis of the National Health Interview Survey in the United States.

OBJECTIVES: The current study examined the role of emotional distress in explaining racial/ethnic differences in unhealthy sleep duration. DESIGN: Data from the 2004-2013 National Health Interview Survey were analyzed using SPSS 20. SETTING: Data were collected through personal household interviews in the United States. PARTICIPANTS: Of the total 261,686 participants (age≥18 years), 17.0% were black, 83.0% were white, and the mean age was 48 years (SE=0.04). MEASUREMENTS: To ascertain total sleep duration, participants were asked, "How many hours of sleep do you get on average in a 24-hour period?" Sleep duration was coded as short sleep (<7hours), average sleep (7-8hours), or long sleep (>8hours). Emotional distress-feeling sad, nervous, restless, hopeless, worthless, and burdened over a 30-day period-was measured using Kessler-6, a 6-item screening scale. RESULTS: Of the participants reporting significant emotional distress (4.0% black, 3.5% white), χ2 analyses revealed that a higher percentage of blacks, compared with whites, reported unhealthy sleep durations. Relative to Whites, Blacks had increased prevalence of short sleep (prevalence ratio=1.32, P<.001) or long sleep (odds ratio =1.189, P<.001). The interaction between race/ethnicity and emotional distress was significantly associated with short (prevalence ratio=0.99, P<.001) and long sleep (odds ratio=0.98, P<.001) durations. CONCLUSIONS: Individuals of the black race/ethnicity or those reporting greater levels of emotional distress are more likely to report short or long sleep duration. Emotional distress might partially explain racial/ethnic differences in unhealthy sleep duration between blacks and whites.