Variable task switching in the feeding network of is a function of differential command input.

Command systems integrate sensory information and then activate the interneurons and motor neurons that mediate behavior. Much research has established that the higher-order projection neurons that constitute these systems can play a key role in specifying the nature of the motor activity induced, or determining its parametric features. To a large extent, these insights have been obtained by contrasting activity induced by stimulating one neuron (or set of neurons) to activity induced by stimulating a different neuron (or set of neurons).

Convergent effects of neuropeptides on the feeding central pattern generator of .

These experiments focus on an interneuron (B63) that is part of the feeding central pattern generator (CPG) in . Previous work has established that B63 is critical for program initiation regardless of the type of evoked activity. B63 receives input from a number of different elements of the feeding circuit.

The Complement of Projection Neurons Activated Determines the Type of Feeding Motor Program in .

Multiple projection neurons are often activated to initiate behavior. A question that then arises is, what is the unique functional role of each neuron activated? We address this issue in the feeding system of . Previous experiments identified a projection neuron [cerebral buccal interneuron 2 (CBI-2)] that can trigger ingestive motor programs but only after it is repeatedly stimulated, i.

An Anticipatory Circuit Modification That Modifies Subsequent Task Switching.

Modulators are generally expected to establish a network configuration that is appropriate for the current circumstances. We characterize a situation where the opposite is apparently observed. A network effect of a peptide modulator is counterproductive in that it tends to impede rather than promote the creation of the configuration that is appropriate when the modulator is released.

Synaptic mechanisms for motor variability in a feedforward network.

Behavioral variability often arises from variable activity in the behavior-generating neural network. The synaptic mechanisms underlying this variability are poorly understood. We show that synaptic noise, in conjunction with weak feedforward excitation, generates variable motor output in the feeding system.

Background calcium induced by subthreshold depolarization modifies homosynaptic facilitation at a synapse in Aplysia.

Some synapses show two forms of short-term plasticity, homosynaptic facilitation, and a plasticity in which the efficacy of transmission is modified by subthreshold changes in the holding potential of the presynaptic neuron. In a previous study we demonstrated a further interactive effect. We showed that depolarizing changes in the presynaptic holding potential can increase the rate at which facilitation occurs.

Network Degeneracy and the Dynamics of Task Switching in the Feeding Circuit in .

The characteristics of a network are determined by parameters that describe the intrinsic properties of the component neurons and their synapses. Degeneracy occurs when more than one set of parameters produces the same (or very similar) output. It is not clear whether network degeneracy impacts network function or is simply a reflection of the fact that, although it is important for a network to be able to generate a particular output, it is not important how this is achieved.

Persistent effects of cyclic adenosine monophosphate are directly responsible for maintaining a neural network state.

Network states are often determined by modulators that alter the synaptic and cellular properties of the constituent neurons. Frequently neuromodulators act via second messengers, consequently their effects can persist. This persistence at the cellular/molecular level determines the maintenance of the state at the network level.

Peptide Cotransmitters as Dynamic, Intrinsic Modulators of Network Activity.

Neurons can contain both neuropeptides and "classic" small molecule transmitters. Much progress has been made in studies designed to determine the functional significance of this arrangement in experiments conducted in invertebrates and in the vertebrate autonomic nervous system. In this review article, we describe some of this research.

Cellular Effects of Repetition Priming in the Feeding Network Are Suppressed during a Task-Switch But Persist and Facilitate a Return to the Primed State.

Many neural networks are multitasking and receive modulatory input, which configures activity. As a result, these networks can enter a relatively persistent state in which they are biased to generate one type of output as opposed to another. A question we address is as follows: what happens to this type of state when the network is forced to task-switch? We address this question in the feeding system of the mollusc This network generates ingestive and egestive motor programs.

Newly Identified Aplysia SPTR-Gene Family-Derived Peptides: Localization and Function.

When individual neurons in a circuit contain multiple neuropeptides, these peptides can target different sets of follower neurons. This endows the circuit with a certain degree of flexibility. Here we identified a novel family of peptides, the Aplysia SPTR-Gene Family-Derived peptides (apSPTR-GF-DPs).

Multifaceted Expression of Peptidergic Modulation in the Feeding System of Aplysia.

Neuropeptides are present in species throughout the animal kingdom and generally exert actions that are distinct from those of small molecule transmitters. It has, therefore, been of interest to define the unique behavioral role of this class of substances. Progress in this regard has been made in experimentally advantageous invertebrate preparations.

Discovery of leucokinin-like neuropeptides that modulate a specific parameter of feeding motor programs in the molluscan model, .

A better understanding of neuromodulation in a behavioral system requires identification of active modulatory transmitters. Here, we used identifiable neurons in a neurobiological model system, the mollusc , to study neuropeptides, a diverse class of neuromodulators. We took advantage of two types of feeding neurons, B48 and B1/B2, in the buccal ganglion that might contain different neuropeptides.

A clarifying method that improves imaging of Aplysia ganglia.

Improvements in the imaging of neural circuits are essential for studies of network function in both invertebrates and vertebrates. Therefore, CLARITY, a new imaging enhancement technique developed for mouse brains has attracted broad interest from researchers working on other species. We studied the potential of a modified version of CLARITY to enhance the imaging of ganglia in an invertebrate Aplysia.

Use of the feeding network to study repetition priming of an episodic behavior.

Many central pattern generator (CPG)-mediated behaviors are episodic, meaning that they are not continuously ongoing; instead, there are pauses between bouts of activity. This raises an interesting possibility, that the neural networks that mediate these behaviors are not operating under "steady-state" conditions; i.e.

A d-Amino Acid-Containing Neuropeptide Discovery Funnel.

A receptor binding class of d-amino acid-containing peptides (DAACPs) is formed in animals from an enzymatically mediated post-translational modification of ribosomally translated all-l-amino acid peptides. Although this modification can be required for biological actions, detecting it is challenging because DAACPs have the same mass as their all-l-amino acid counterparts. We developed a suite of mass spectrometry (MS) protocols for the nontargeted discovery of DAACPs and validated their effectiveness using neurons from Aplysia californica.

Consequences of degeneracy in network function.

Often distinct elements serve similar functions within a network. However, it is unclear whether this network degeneracy is beneficial, or merely a reflection of tighter regulation of overall network performance relative to individual neuronal properties. We review circumstances where data strongly suggest that degeneracy is beneficial in that it makes network function more robust.

Repetition priming of motor activity mediated by a central pattern generator: the importance of extrinsic vs. intrinsic program initiators.

Repetition priming is characterized by increased performance as a behavior is repeated. Although this phenomenon is ubiquitous, mediating mechanisms are poorly understood. We address this issue in a model system, the feeding network of Aplysia This network generates both ingestive and egestive motor programs.

Aplysia Locomotion: Network and Behavioral Actions of GdFFD, a D-Amino Acid-Containing Neuropeptide.

One emerging principle is that neuromodulators, such as neuropeptides, regulate multiple behaviors, particularly motivated behaviors, e.g., feeding and locomotion.

Functional Characterization of a Vesicular Glutamate Transporter in an Interneuron That Makes Excitatory and Inhibitory Synaptic Connections in a Molluscan Neural Circuit.

Understanding circuit function requires the characterization of component neurons and their neurotransmitters. Previous work on radula protraction in the Aplysia feeding circuit demonstrated that critical neurons initiate feeding via cholinergic excitation. In contrast, it is less clear how retraction is mediated at the interneuronal level.

Specificity of repetition priming: the role of chemical coding.

We investigate stimulus specificity of repetition priming in a tractable model system; the feeding network of Aplysia. Previous studies primarily focused on an aspect of behavior that is altered during ingestive priming, radula opening. Priming of radula opening occurs when two modulatory peptides [feeding circuit activating peptide (FCAP) and cerebral peptide-2 (CP-2)] are released from the cholinergic command-like neuron cerebral buccal interneuron 2.

Neuromodulation as a mechanism for the induction of repetition priming.

It is becoming apparent that the activity of many neural networks is shaped by effects of endogenous neuromodulators. Modulators exert second messenger-mediated actions that persist. We consider how this may impact network function and its potential role in the induction of repetition priming (increased performance when behavior is repeated).

Complementary interactions between command-like interneurons that function to activate and specify motor programs.

Motor activity is often initiated by a population of command-like interneurons. Command-like interneurons that reliably drive programs have received the most attention, so little is known about how less reliable command-like interneurons may contribute to program generation. We study two electrically coupled interneurons, cerebral-buccal interneuron-2 (CBI-2) and CBI-11, which activate feeding motor programs in the mollusk Aplysia californica.

PKC-mediated GABAergic enhancement of dopaminergic responses: implication for short-term potentiation at a dual-transmitter synapse.

Transmitter-mediated homosynaptic potentiation is generally implemented by the same transmitter that mediates the excitatory postsynaptic potentials (EPSPs), e.g., glutamate.