Systems of chemoperception in Decapod crayfish

The review presents data on some peripheral and central structures in the system of perception of chemical stimuli in crayfish and other Decapoda. The hair receptors on chelipeds, antennas, and antennules are innervated by mechano- and chemoreceptor neurons. Antennules are crayfish specialized chemoreceptor organs whose surface contains groups of exteroceptors. On claws of ambulatory feet (AF), antennas, antennules, and other mobile appendages there is a regular disposition of exteroceptor receptive fields in the form of receptor hair bushes. Behavioral experiments have shown sensitivity of crayfish to odor of individuals of their gender and sex partners as well as the presence in crayfish of pheromones providing connection of female with offspring at the initial stages of their life cycle. Individual chemosensory cells innervating hair bushes on the crayfish AF respond to amino acids, amines, nucleotides, and sugars. Minimal thresholds of reaction of the studied Decapoda chemoreceptors in response to some chemical compounds correspond to 0.1–1.0 μM. For some chemoreceptors, dose-dependent effects have been shown. Alongside with monomodal chemoreceptors, the crayfish have bimodal receptors perceiving mechanical and chemical stimuli. The efficient response of crayfish chemoreceptors can be obtained to the substance that has amino group with hydrogen bridge to carboxyl group, contains no more that 3 carbon atoms in the chain, is characterized by a certain stereoform. Among chemoreceptors there are fast and slow adapting cells. Efficiency of response of individual chemoreceptors depends on temperature of medium. In crayfish, chemoreceptors responding to ecdysterons have been revealed. Ecdysterons play a great role in intra- and inter-species communications in Crustacea. Based on the study of efferent responses of interneurons of the first and higher orders in the first thoracic crayfish ganglion to stimulation of the own receptive fields, a concept has been put forward of the structural-functional organization of afferent projections at the segmental level. Peculiarities of afferent projections from antennule chemoreceptors are considered. The data are presented on connections of these chemoreceptors with antennular, olfactory, and accessory lobules, various cell groups, interneurons of the first, second, and third orders located in various brain parts. An attention has been drawn to connections of serotonin neurons in glomeruli with endings of chemoreceptor neurons and projections of interneurons of the higher orders, which are located in the internal medulla of the crayfish eyestalks. Several principles of integration of the chemoreceptor information in central parts of the crayfish nervous system are discussed. The giant serotonin neurons revealed in crayfish glomeruli most likely participate in formation of memory to certain chemical actions. Polymodal receptor signals in the central chain of the perception system activate autonomic centers, and the changes of the animal functional state can be evaluated from the heart responses. These responses recorded by novel noninvasive methods allow detection of the initial and other phases of the stress state at changes of the medium chemical quality. Progress of the current biochemical and electrophysiological methods of study chemoreceptors allow hoping for learning of fine chemoperception mechanisms in invertebrate and vertebrate animals.