Neural network modulation; motor pattern selection from multifunctional
networks; local, presynaptic influences; neuropeptide function,
cotransmission, sensory influence on central neuronal networks.
Intrasomatic and intra-axonal recordings, extracellular recordings,
intracellular dye injections, neurotransmitter immunocytochemistry;
exogenous application of modulatory transmitters; confocal microscopy.
We aim to understand how the nervous system selects and generates
distinct motor patterns from multifunctional neural networks.
The current set of issues that we are addressing include (1) the
cellular mechanisms underlying how different identified modulatory
projection and sensory neurons elicit distinct outputs from the
same neural circuits, including the role of coreleased small molecule
and neuropeptide transmitters in this process, and (2) how distinct
but related neural circuits interact to generate a coordinated
output. We use a small model system, the stomatogastric nervous
system (STNS), which is an extension of the CNS in decapod crustaceans
that controls the rhythmic movements of different regions of the
foregut underlying various aspects of feeding. The STNS consists
of 4 ganglia, containing several distinct but interacting rhythmically
active circuits that control the different foregut regions. The
two motor patterns that we study (called the pyloric and gastric
mill rhythms) are generated by overlapping sets of neurons located
in the stomatogastric ganglion (STG), which contains only 26 neurons
in our experimental animal, the crab Cancer borealis. There are
many advantages to studying this preparation for obtaining a cellular-level
understanding of neuronal circuit function. All of the STG neurons
are readily recorded intracellularly, they are all physiologically
identified, their intraganglionic synapses and many of their membrane
properties are known, and so are their neurotransmitters. More
than a dozen modulatory transmitters have been localized as inputs
to the STG from the other STNS ganglia. When individually bath
applied, many of these transmitters elicit distinct pyloric and
gastric mill rhythms. Individual activation of different projection
and sensory neurons also elicits distinct rhythms. We are using
a set of identified projection and sensory neurons to study the
above-mentioned issues. We are also assessing the relationship
between the circuit response to bath application of individual
modulatory transmitters and to activation of modulatory neurons
containing the same transmitter. Our analysis also includes identifying
and determining the function of "presynaptic inputs"
occurring on the STG terminals of these projection neurons. These
presynaptic inputs are electrically invisible in the ganglion
of origin of these neurons, so we study them by recording from
these neurons intra-axonally, at the entrance to the STG. Results
from work with the STNS has led to general principles of neural
circuit dynamics that have been extended to many other systems,
ranging from other invertebrates to the mammalian systems.
KEY WORDS: Neuromodulation; neural networks; neuropeptides;
identified neurons; cotransmission.
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Beenhakker MP, Nusbaum MP (2004) Mechanosensory activation of
a motor circuit by coactivation of two projection neurons. J Neurosci
24:6741-6750.
Wood DE, Manor Y, Nadim F, Nusbaum MP (2004) Inter-circuit control
via rhythmic regulation of projection neuron activity. J Neurosci, 24:7455-7463.
Beenhakker MP, Blitz DM, Nusbaum MP (2004) Long-lasting activation
of rhythmic neuronal activity by a novel mechanosensory system
in the crustacean stomatogastric nervous system. Journal of Neurophysiology
91:78-91.
Christie AE, Stein W, Quinlan JE, Beenhakker MP, Marder E, Nusbaum
MP (2004) Actions of a histaminergic/peptidergic projection neuron
on rhythmic motor patterns in the stomatogastric nervous system
of the crab Cancer borealis. Journal of Comparative Neurology
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Nusbaum MP (2002) Regulating peptidergic modulation of rhythmically
active neural circuits. Brain Behavior and Evolution 60:378-387.
Wood
DE, Nusbaum MP (2002) Extracellular peptidase activity tunes motor
pattern modulation. J Neurosci 22:4185-4195.
Nusbaum MP, Beenhakker MP (2002) A small-systems approach to
motor pattern generation. Nature 417:343-350.
Nusbaum MP, Blitz DM, Swensen AM, Wood DE, Marder E (2001) The
roles of cotransmission in neural network modulation. Trends Neurosci
24:146-154.
Swensen AM, Golowasch J, Christie AE, Coleman MJ, Nusbaum MP,
Marder E (2000) GABA and GABA responses in the stomatogastric
ganglion of the crab. Cancer borealis. J Exp Biol, 203:2075-2092.
Meyrand P, Faumont S, Simmers J, Christie AE, Nusbaum MP (2000)
Species-specific modulation of pattern-generating circuits. European
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Wood DE, Stein W, Nusbaum MP (2000) Projection neurons with shared
cotransmitters elicit different motor patterns from the same neural
circuit. J Neurosci 20:8943-8953.
Blitz DM, Christie AE, Coleman MJ, Norris BJ, Marder E, Nusbaum
MP (1999) Different proctolin neurons elicit distinct motor patterns
from a multifunctional neuronal network. J Neurosci 19:5449-5463.
Bartos M, Manor Y, Nadim F, Marder E, Nusbaum MP (1999) Coordination
of fast and slow rhythmic neuronal circuits. J Neurosci 19:6650-6660.
Blitz DM, Nusbaum MP (1999) Distinct functions for cotransmitters
mediating motor pattern selection. J Neurosci 19:6774-6783.
