Caenorhabditis elegans explores its environment by interrupting its forward movement with occasional turns and reversals. Turns and reversals occur at stable frequencies but irregular intervals, producing probabilistic exploratory behaviors. Here we dissect the roles of individual sensory neurons, interneurons, and motor neurons in exploratory behaviors under different conditions. After animals are removed from bacterial food, they initiate a local search behavior consisting of reversals and deep omega-shaped turns triggered by AWC olfactory neurons, ASK gustatory neurons, and AIB interneurons. Over the following 30 min, the animals disperse as reversals and omega turns are suppressed by ASI gustatory neurons and AIY interneurons. Interneurons and motor neurons downstream of AIB and AIY encode specific aspects of reversal and turn frequency, amplitude, and directionality. SMD motor neurons help encode the steep amplitude of omega turns, RIV motor neurons specify the ventral bias of turns that follow a reversal, and SMB motor neurons set the amplitude of sinusoidal movement. Many of these sensory neurons, interneurons, and motor neurons are also implicated in chemotaxis and thermotaxis. Thus, this circuit may represent a common substrate for multiple navigation behaviors.chemosensation ͉ exploratory behavior ͉ neural circuit A s an animal travels through its environment, its nervous system detects sensory cues, evaluates them based on context and the experience of the animal, and converts this information into adaptive movement. For simple behaviors, sensory neurons sometimes communicate directly with motor neurons, but, in more complex behavioral circuits, several layers of interneurons integrate sensory information and relay it to motor neurons. The path from sensory input to motor output has been defined in only a few cases, including circuits for crustacean feeding (1) and circuits for rapid escape in fish, flies, and nematodes (2-4). In the nematode Caenorhabditis elegans, the escape circuit was defined by using a complete synaptic wiring diagram of the 302 neurons in its nervous system (4, 5). Six mechanosensory neurons that detect noxious stimuli synapse onto four pairs of interneurons called forward and backward command neurons. The command neurons synapse in turn onto motor neurons responsible for forward and backward locomotion, leading to rapid withdrawal from the stimulus. The definition of the escape circuit has enabled analysis of its development, regulation, and modification by experience (6-11). The C. elegans wiring diagram provides an opportunity to define many complete neuronal paths from sensory stimulus to behavior.In contrast with the escape circuit, the neuronal control of locomotion during exploratory behavior is poorly characterized. C. elegans navigates to favorable conditions by chemotaxis, thermotaxis, and aerotaxis. In these sensory behaviors and in exploratory behaviors in the absence of informative sensory cues, the animal moves forward and occasionally changes its direction of move...

SynopsisThe paper examines the theory of the 2-stage voltage transformer and shows that it not only provides a very accurate primary/secondary voltage ratio but also increases the effective input impedance of one of its primary windings to a very high value. It is shown theoretically and experimentally that these characteristics enable inductive voltage dividers to be made which have extremely small errors of voltage division within individual decades and in which the errors due to interconnecting the decades are virtually eliminated. Single-decade dividers having in-phase errors of less than 5 parts in 10 9 of the input over the frequency band 40-400Hz have been constructed.

No abstract

No abstract