Romuald Nargeot and Alexis Bédécarrats
Behaviors of invertebrates can be modified by associative learning in a similar manner to those of vertebrates. Two simple forms of associative learning, Pavlovian and operant conditioning, allow animals to establish a predictive relationship between two events. Here we summarize five decades of studies of behavioral, cellular, and subcellular changes that are induced by these two learning paradigms in different invertebrate animal models. A comparative description of circuitry, neuronal elements, and properties that contribute to these conditioning procedures will be drawn to decipher common and distinguishing features of the learning processes. We will illustrate that similar circuits, synaptic and neuronal membrane plasticity, and similar molecular sites of detection of association are implicated in both forms of conditioning. However, evidence will also suggest that passively responding and endogenous dynamic properties of central networks and/or their constituent neurons might differentially contribute to Pavlovian and operant learning.
Yun Doo Chung and Jeongmi Lee
Hearing in invertebrates has evolved independently as an adaptation to avoid predators or to mediate intraspecific communication. Although many invertebrate groups are able to respond to sound stimuli, insects are the only group in which hearing is widely used. Therefore, we will focus here on the auditory systems of some well-known insect models. Appearance of the ability to perceive sound in insects is presumably a quite recent event in evolution. As a result of independent evolution, diverse types of hearing organs are evolved in insects. Here we will introduce basic features of insect ears and the mechanisms through which sound stimuli are converted into neuronal electric signals. We will also summarize our current understanding of neural processing of auditory information, including tonotopy, sound localization, and pattern recognition.
Changes in the Inferior Colliculus Associated with Hearing Loss: Noise-Induced Hearing Loss, Age-Related Hearing Loss, Tinnitus and Hyperacusis
Alan R. Palmer and Joel I. Berger
The inferior colliculus is an important auditory relay center that undergoes fundamental changes following hearing loss, whether noise induced (NIHL) or age related (ARHL). These changes may contribute to the induction or maintenance of phenomena such as tinnitus (phantom auditory sensations) and hyperacusis (increased sensitivity to sound). Here, we outline changes that can occur in the inferior colliculus following damage to the periphery and/or as a result of the ageing process, both immediate and long-term, and attempt to disentangle which changes relate to either tinnitus or hyperacusis, as opposed to solely hearing loss. Understanding these changes is ultimately important to reversing the underlying pathology and treating these conditions.
Reception of chemicals via olfaction and gustation are prerequisites to find, distinguish, and recognize food and mates and to avoid dangers. Several receptor gene superfamilies are employed in arthropod chemosensation: inverse 7-transmembrane (7-TM) gustatory and olfactory receptors (GRs, ORs), 3-TM ionotropic glutamate-related receptors (IRs), receptor-guanylyl cyclases, transient receptor potential ion channels, and epithelial sodium channels. Some of these receptor gene families have ancient origins and expanded in several taxa, producing very large, variant gene families adapted to the respectively relevant odor ligands in species-specific environments. Biochemical and electrophysiological studies in situ as well as molecular genetics found evidence for G-protein-dependent signal transduction cascades for ORs, GRs, and IRs, suggesting that signal amplification is paramount for chemical senses. In contrast, heterologous expression studies argued for primarily ionotropic transduction as a prerequisite to interstimulus intervals in the range of microseconds.
Important cnidarian contributions to our understanding of nervous system evolution may be found in the arrangement of conducting systems and their interactions. We see multiple, diffuse systems that interact to produce specific behaviors, the compression of conducting systems into compact directional or bidirectional conduction systems, and accumulation of multiple compressed conducting systems into integrating structures like nerve rings. We even see ganglion-like rhopalia that contain bilateral and directional conducting pathways. We now know that this compression and specificity of connections is controlled by conserved sets of genetic commands similar to those found in bilateral animals, and likely in common ancestors. This gradation in centralization is only limited in a directed pathway by the unique radial symmetry of cnidarians. Based on the compression of cnidarian conducting systems into integrating centers (nerve rings and rhopalia), the primary hurdle to cephalization is body symmetry. Medusoid cnidarians possess multiple “brains” connected by conducting systems that, by necessity, are nonpolarized.
Daniel Cattaert and Donald Hine Edwards
This chapter will consider the control of posture and walking in decapod crustaceans (crabs, lobsters, rock lobsters, and crayfish). The walking system of crustaceans is composed of five pairs of appendages, each with seven articulated segments. While crabs sideways walking relies on stereotyped trailing and leading leg movements, forward/backward walking in lobsters and crayfish is achieved by different movements in the different legs, depending on their orientation versus body axis. Largely independent neural networks, localized in each of the 10 hemi-segmental thoracic ganglia, control each leg during locomotion. Each of these networks is modularly organized, with a specific central pattern generator (CPG) controlling each joint. Although coordinating interneurons have been described, inter-joint and inter-leg coordination is largely maintained by sensory feedback. Recently, the key role of proprioceptive signals in motor command processing has been addressed thanks to hybrid system experiments and modelling.
Roy E. Ritzmann and Sasha N. Zill
This article discusses legged locomotion in insects. It describes the basic patterns of coordinated movement both within each leg and among the various legs. The nervous system controls these actions through groups of joint pattern generators coupled through interneurons and interjoint reflexes in a range of insect species. These local control systems within the thoracic ganglia rely on leg proprioceptors that monitor joint movement and cuticular strain interacting with central pattern generation interneurons. The local control systems can change quantitatively and qualitatively as needed to generate turns or more forceful movements. In dealing with substantial obstacles or changes in navigational movements, more profound changes are required. These rely on sensory information processed in the brain that projects to the multimodal sensorimotor neuropils collectively referred to as the central complex. The central complex affects descending commands that alter local control circuits to accomplish appropriate redirected movements.
Sally A. Marik and Charles D. Gilbert
The cerebral cortex is a learning engine. The ability to encode information about sensory experience or practiced movements is a universal property of all cortical areas. This capacity, known as cortical plasticity, is seen in experience dependent changes in the functional properties of cortical neurons and in the alteration of cortical circuits. Certain properties are mutable only during a short period in postnatal life, which is known as the critical period, while others retain the ability to change throughout life. The same changes associated with assimilating normal experiences can be implemented for functional recovery following lesions of the central nervous system.
Taesun Eom, Ilham A. Muslimov, Anna Iacoangeli, and Henri Tiedge
This chapter reviews current developments in the area of translational control in neurons. It focuses on the activity-dependent translational modulation by neuronal regulatory RNAs, including underlying interactions with eukaryotic initiation factors (eIFs), and on the role of such modulation in locally controlled protein synthesis in synapto-dendritic domains. It highlights the role of dendritic RNA targeting as a key prerequisite of local translation at the synapse and discusses the significance of these mechanisms in the expression of higher brain functions, including learning, memory, and cognition. The chapter concludes with discussion of anticipated future work to continue to elucidate these mechanisms and provide advances in the area of translational regulation in neurons and our understanding of how translational dysregulation contributes to neurological and cognitive disorders.
The complex architecture of the nervous system is the result of a stereotyped pattern of proliferation and migration of neural progenitors in the early embryo, followed by the outgrowth of nerve fibers along rigidly controlled pathways, and the formation of synaptic connections between specific neurons during later stages. Detailed studies of these events in several experimentally amenable model systems indicated that many of the genetic mechanisms involved are highly conserved. This realization, in conjunction with new molecular-genetic techniques, has led to a surge in comparative neurodevelopmental research covering a wide variety of animal phyla over the past two decades. This chapter attempts to provide an overview of the diverse neural architectures that one encounters among invertebrate animals, and the developmental steps shaping these architectures.