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Title: Processing of mechanoreceptive input in crayfish : an in vivo and in vitro study of the role of the cuticular stress detectors in motor control
Author: Leibrock, Cornelia Sieglinde
Awarding Body: University of Glasgow
Current Institution: University of Glasgow
Date of Award: 1993
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Cuticular stress detectors (CSD1 and CSD2) are mechanoreceptors positioned in the proximal parts of the legs of decapod crustaceans. Using a reduced preparation consisting of the isolated thoracic central nervous system and a walking leg of either of the two crayfish species, Procambarus clarkii or Pacifastacus leniusculus, it has been possible to study by means of extracellular and intracellular techniques the physiological properties of the sensory fibres and the reflex responses in the four proximal muscle groups to mechanical and electrical stimulation of the receptor organs. The location of the CSD terminals within the thoracic ganglion was determined by anterograde fillings of the afferent fibres with biocytin. The anterograde fills also showed the absence of any cell bodies within the thoracic ganglion. Thus one can be certain that the CSD nerves contain no motorneurone axons and that all fibres within the CSD nerves belong to sensory cells. These have their cell bodies in the periphery; their orthodromic direction of conduction is from the periphery to the thoracic central nervous system. Most CSD fibres terminate, and branch extensively within the ganglion. Nevertheless, some CSD1 fibres were found to pass through the ganglion and continue rostrally within the ventral nerve cord. Intracellular recordings of impulses arriving in the central ganglion made it possible to identify the physiological properties of single receptor cells when stimulating the receptor organs mechanically. The recordings from CSD2 terminals were found to be in consensus with extracellular recordings from previous studies. CSD1 intracellular recordings revealed a class of sensory fibres not previously described. They were identified as 'high threshold' fibres, for large amplitude, high frequency stimuli were necessary for their activation. These CSD 1 fibres appear to be responsible for the occurrence of a reflex response reversal in anterior levator motorneurones. This is discussed with reference to a possible role of the CSD 1 receptor organ in the control of autotomy. Intracellular recordings from sensory terminals also revealed the presence of centrally coupled sensory afferents. Coupled units often had different conduction velocities, and 'on' units were sometimes coupled with 'off units. Lucifer Yellow usually filled two or more fibres when injected into a single cell. This is in support of central coupling, for the dye is known to cross gap junctions. Some sensory units showed antidromic spike conduction, i.e. from the ganglion to the sense organ, being always coupled to fibres firing orthodromically. It is suggested that the coupling provides a mechanism for amplification of the sensory signals, the antidromic spikes induced by impulses coming from coupled units. This is supported by the finding that stronger mechanical or electrical stimulation of the sensory fibres leads to an increased occurrence of antidromic spikes. Using a number of electrophysiological and pharmacological tests, it has been demonstrated that at least 32% of all the connections recorded between the CSDs and the motorneurones of the four proximal muscle groups are monosynaptic. The reflex responses within one motorneurone group varied. The importance of sensory feedback in shaping the final motor output was studied in preparations showing rhythmic, reciprocal activity in antagonistically operating muscle groups. Rhythmic CSD activity was shown to be able to entrain such fictive locomotor activity. CSD1 activity during normal walking behaviour was studied in an in vivo preparation. Thus, reflex responses could be discussed with knowledge of the natural activation of the CSDs and related to their functional significance in locomotion.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available