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1. Serotonin (5-hydroxytryptamine) immunohistochemistry was used to locate and anatomically describe a set of four muscle receptor cells in the stomatogastric nervous system of the crabs Cancer borealis and Cancer irroratus. We found that these sensory cells, which we named gastropyloric receptor (GPR) cells, are the sole source of serotonergic inputs to(More)
1. Neuromodulation has previously been shown to be intrinsic to the central pattern generator (CPG) circuit that generates the escape swim of the nudibranch mollusk Tritonia diomedea; the dorsal swim interneurons (DSIs) make conventional monosynaptic connections and evoke neuromodulatory effects within the swim motor circuit. The conventional synaptic(More)
Heterosynaptic enhancement of transmitter release is potentially very important for neuronal computation, yet, to our knowledge, no prior study has shown that stimulation of one neuron directly enhances release from an interneuron. Here, we demonstrate that in the marine mollusk Tritonia diomedea, the serotonergic dorsal swim interneurons (DSIs)(More)
Motor circuits are often thought to be physically separate from their neuromodulatory systems. We report here a counter example, where neurons within a circuit appear to modulate synaptic properties of that same circuit during its normal operation. The dorsal swim interneurons (DSIs) are members of the central pattern generator circuit for escape swimming(More)
1. The gastropyloric receptor (GPR) cells, which are described in the preceding paper, are a set of proprioceptive cells in the crabs Cancer borealis and Cancer irroratus that contain serotonin (5-hydroxytryptamine, 5-HT) and choline acetyltransferase. These cells have a variety of synaptic effects on cells in the stomatogastric ganglion (STG). We used(More)
This study provides evidence that a neuron can exhibit differences in activity-dependent transmitter release at two synaptic sites due to variations in the properties of its presynaptic terminals. Two muscles in the stomatogastric system of the lobster Homarus americanus are innervated by a single motor neuron but respond differently to that motor neuron's(More)
For the mollusc Tritonia diomedea to generate its escape swim motor pattern, interneuron C2, a crucial member of the central pattern generator (CPG) for this rhythmic behavior, must fire repetitive bursts of action potentials. Yet, before swimming, repeated depolarizing current pulses injected into C2 at periods similar those in the swim motor program are(More)
The nervous system is evolutionarily conservative compared to the peripheral appendages that it controls. However, species-specific behaviors may have arisen from very small changes in neuronal circuits. In particular, changes in neuromodulatory systems may allow multifunctional circuits to produce different sets of behaviors in closely related species.(More)
There are two sources of neuromodulation for neuronal circuits: extrinsic inputs and intrinsic components of the circuits themselves. Extrinsic neuromodulation is known to be pervasive in nervous systems, but intrinsic neuromodulation is less recognized, despite the fact that it has now been demonstrated in sensory and neuromuscular circuits and in central(More)