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Studies on the function of the ampullae of Lorenzini in sharks

Studies on the function of the ampullae of Lorenzini in sharks

Zeit Vergl Physiol 47(4): 438-456

By previous experimentation, an "ampullary" type of lateral-line organ is proposed. This would serve as a detector of weak local potential changes. The behavioral responses of Scyliorhinus canicula to local stimulation of the head with trains of electric impulses (frequency: 5 cycles per second) are described. In intact animals, threshold strength amounts to about 3 [mu]V/cm, both when the posterior part of the head (area between spiracle and gill-slits) and the anterior part (rostrum) are stimulated. Cutting the n. max. V + bucc. VII, puts all Lorenzinian ampullae having their openings between spiracle and gill-slits out of action, whereas the lateral canal organs and all other skin receptors in the same area remain untouched. After unilateral transection of this nerve, electrical stimulation of the area involved at the operated side yields a tenfold increased threshold value; at the intact side, however, the threshold is just as unchanged as it is on stimulation of the rostrum at either side. Thus the ampullae of Lorenzini involved had been acting before as electroreceptors, responding to the potential changes at their openings. After bilateral transection of the nerve, stimulation of the area involved at either side yields a hundredfold increased threshold value as compared with the threshold of the intact animal. On stimulation of the rostrum, however, the threshold is only slightly increased. Additional elimination of the rostral ampullae by transection of both nn. ophth. sup. V + VII puts all ampullae of Lorenzini out of action (except the mandibular groups at the lower jaw) and abolishes all responses to electrical stimulation at both sides of the head up to the maximal stimulus intensity available of 2000 [mu]V/cm. With regard to these responses, the few mandibular ampullae are apparently of minor importance. Since neither the ordinary lateral-line organs nor other skin receptors respond to weak electrical stimuli within the range involved, it is concluded that the ampullae of Lorenzini represent the sole electroreceptors. The electro-receptive function of the ampullae of Lorenzini has been demonstrated for the first time by using artificial stimuli in behavior experiments. Whether[long dash]and in which way[long dash]this ability is used under natural cir -cumstances is still unknown and will be the subject of future investigation.

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