== A1

== A1. Thus, in addition to well described long-loop pathways, it is possible that AGR is involved in integration and pattern regulation directly in the STG. == Introduction == Sensory feedback from muscle receptors shapes motor neuron activity in mono- and disynaptic (short-loop) stretch or resistance reflexes. In addition, most reflex pathways have polysynaptic (long-loop) components that are crucial to adapt reflexes to different behavioral states. In fact, phase-specific sensory feedback to vertebrate and invertebrate motor neurons during rhythmic motor activity can cause reflexes to reverse or become a component of the rhythm-generating networks themselves [1-7]. The underlying mechanisms of sensory integration during reflex modification are not fully understood. However, many functional aspects of feedback integration, such as presynaptic inhibition and antidromic spiking, can be linked to the structures of motor or sensory neurons [8]. Examining the morphology of a neuron in detail opens the door to interesting questions. How variable are the structures of identified neurons across individual animals? Which parameters must be preserved to maintain consistent function within a network? These questions are particularly hard to address in large networks in which cell type identification is ambiguous and exacerbated by PF-8380 complicated branching structures. There is a large body of evidence for distinct rules that govern aspects of cell morphology during network development. The distribution of attractant and repellent molecules and the respective receptors in the developing spinal cord can determine the position of the soma, axon growth cone guidance, and midline crossing of the axon [9-13]. The shape and position of the same neuron however often vary from animal to animal, as seen in the crustacean stomatogastric ganglion (STG) where only some features of neuron morphology are shared across animals [14-16]. To better understand these aspects of neuron morphology, here we examine a sensory neuron in the STG that is involved in a rich set of reflex pathways but has a relatively simple branching structure. Rhythmically active networks in the stomatogastric nervous systems (STNS) control movement PF-8380 of the crustacean stomach muscles. During gastric mill activity, protraction and retraction of the stomach teeth is controlled by coordination of the gastric mill network [17]. As in lobsters and crayfish, the Anterior Gastric Receptor (AGR) inC. borealishas a bipolar soma that is located in the in the dorsal ventricular nerve (dvn) or, less often, in the posterior part of the STG and projects to the PF-8380 dorsal gastric nerve (dgn) [18]. Bilateral dendrites project into the two gastric mill 1 (gm1) muscles where spikes are initiated close to thegm1muscles [19]. The AGR axon projects in a long-loop pathway through the STG and makes excitatory and inhibitory connections in the anterior paired commissural ganglia (CoGs) with projection neurons that feed back to the STG motor circuits [17,20-24]. The single AGR is a muscle force receptor in thegm1muscles. The AGR neuron integrates proprioceptive information from both sides of the animal but also functions similarly to an interneuron by influencing gastric and pyloric network Rabbit polyclonal to ACTR5 activity, independent of its receptor properties [25]. Multiple dendritic and axonal spike initiation zones respond to different neuromodulators [21,24-27]. Moreover, neuropeptides switch PF-8380 AGR firing between tonic spiking mode or bursting mode, which each activate a different gastric motor pattern [28]. Recent work has shown that the actions of AGR are influenced by other sensory neurons (Barriere et al., 2008) and that the effects of AGR firing depend on when it is active during gastric mill rhythms (Smarandache et al., 2008). Thus far, all of these physiological actions on gastric and pyloric network activity have been attributed to the long-loop polysynaptic reflex pathway through the anterior CoGs. No detailed study of the AGR morphology within the STG exists and, so far, projections in the STG neuropil have not been described. We now provide anatomical descriptions of.