Feedforward Compensation Mediated by the Central and Peripheral Actions of a Single Neuropeptide Discovered Using Representational Difference Analysis

Abstract

Compensatory mechanisms are often used to achieve stability by reducing variance, which can be accomplished via negative feedback during homeostatic regulation. In principle, compensation can also be implemented through feedforward mechanisms where a regulator acts to offset the anticipated output variation; however, few such neural mechanisms have been demonstrated. We provide evidence that an Aplysia neuropeptide, identified using an enhanced representational difference analysis procedure, implements feedforward compensation within the feeding network. We named the novel peptide "allatotropin-related peptide" (ATRP) because of its similarity to insect allatotropin. Mass spectrometry confirmed the peptide's identity, and in situ hybridization and immunostaining mapped its distribution in the Aplysia CNS. ATRP is present in the higher-order cerebral-buccal interneuron (CBI) CBI-4, but not in CBI-2. Previous work showed that CBI-4-elicited motor programs have a shorter protraction duration than those elicited by CBI-2. Here we show that ATRP shortens protraction duration of CBI-2-elicited ingestive programs, suggesting a contribution of ATRP to the parametric differences between CBI-4-evoked and CBI-2-evoked programs. Importantly, because Aplysia muscle contractions are a graded function of motoneuronal activity, one consequence of the shortening of protraction is that it can weaken protraction movements. However, this potential weakening is offset by feedforward compensatory actions exerted by ATRP. Centrally, ATRP increases the activity of protraction motoneurons. Moreover, ATRP is present in peripheral varicosities of protraction motoneurons and enhances peripheral motoneuronelicited protraction muscle contractions. Therefore, feedforward compensatory mechanisms mediated by ATRP make it possible to generate a faster movement with an amplitude that is not greatly reduced, thereby producing stability.

Complementary Interactions between Command-Like Interneurons that Function to Activate and Specify Motor Programs

“…CP2 antibody (rabbit) was a gift from Dr. P. Lloyd (Phares and Lloyd, 1996). FCAPb (ALDSLGGFQVHGW, ALDSLGGFQVHGW; Protein Core Facility, University of Illinois, Urbana, IL) was used to generate the antibodies in rabbits as described previously (Furukawa et al, 2001;Jing et al, 2010). Briefly, the antigen was prepared by coupling synthetic peptide to BSA (catalog #A0281; Sigma-Aldrich) using 1-ethyl-3-(dimethylaminopropyl)carbodiimide (catalog #E7750; Sigma-Aldrich).…”

“…Immunocytochemistry combined with dye injection was performed as described previously (Furukawa et al, 2001;Jing et al, 2010). CBI-11 was identified based on morphology and electrophysiological characteristics and injected with carboxyfluorescein .…”

“…In other experiments, retraction was monitored by the sustained depolarization of the radula closing motor neuron B8 after protraction. In contrast to the phase invariance of the protraction-retraction sequence, the timing of radula opening-closing depends on the type of program Chiel, 1993a, 1993b;Church and Lloyd, 1994;Nargeot et al, 1997;Jing and Weiss, 2001;Morgan et al, 2002;Jing et al, 2010;Wu et al, 2010). Briefly, when B8 fires predominantly during retraction and thus (in the intact animal) helps bring food into the buccal cavity, the program is considered to be ingestive.…”

“…However, research on other multifunctional networks questions the generality of this scheme. Under different circumstances, one neuron drives different behaviors in cricket, leech, and Aplysia (Nolen and Hoy, 1984;Jing and Weiss, 2001;Esch et al, 2002;Morgan et al, 2002;Jing et al, 2004). Therefore, the latter studies suggest that command-like neurons, especially those that drive programs reliably, may function preferentially to trigger programs, rather than to specify their nature.…”

Small-Volume Analysis of Cell–Cell Signaling Molecules in the Brain

“…Groundbreaking research, as reviewed by Li et al (2000), demonstrated that neuronal circuits can be studied by MALDI MS at the single-cell level, and their chemical content correlated to animal behavior and to specific physiological states. Combined with molecular biology and electrophysiology, single-cell MS is effective for examining neuronal architecture, and for delineating neuronal circuits that regulate physiology and control of instinctive and learned behaviors (Jarecki et al, 2010;Jing et al, 2010;Vilim et al, 2010). Investigations of signaling peptides and their involvement in neural plasticity, learning, memory, complex behavior, and various physiological functions at the level of the individual cell have been successful in invertebrate models (Jimenez et al, 1994;Christie et al, 2010;Li and Smit, 2010;Neupert and Predel, 2010;.…”