Hitoshi Teranishi

Isolation and Identification of a Novel Fish Substance P and Its Effect on Retinal Cell Responses

Abstract A novel bioactive peptide was isolated from the brain of the Japanese crucian carp, Carassius auratus langsdorfii, by using the intestine of the fish as the bioassay system. The primary structure of the peptide was determined to be KPRPHQFIGLMamide. The sequence was found to be highly homologous to the fish substance P-related peptides isolated from Atlantic cod and rainbow trout. We designated the peptide Carassius Substance P (Caa-SP). Caa-SP was identical with the peptide whose presence was inferred from a cDNA analysis by other investigators. Caa-SP exerted an excitatory effect on visceral muscle tissues of fish with the threshold at about 3 × 10−9 M. The peptide enhanced the ERG b-wave, depolarized the dark membrane potential and slightly decreased the amplitude of S-potentials of the L-type horizontal cells in the carp retina.Sperm displacement is a sperm competition avoidance mechanism that reduces the paternity of males that have already mated with the female. Direct anatomical sperm removal or sperm flushing is known to occur in four insect orders: Odonata, Orthoptera, Coleoptera and Hymenoptera. In a fifth order, Dermaptera (earwigs), I found that the virga (the elongated rod of the male genitalia) of Euborellia plebeja seems to be used to remove rival sperm from the spermatheca (a fine-tubed female sperm storage organ). In this species, copulation lasted on average 4.6 minutes, during which time the male inserted the virga deep into the spermatheca, and then extracted it ejaculating semen from the opening of the virgal tip. The extraction of virgae (with its brim-like tip) appeared to cause removal of stored sperm in the spermatheca. The virga was as long as the body length of males, and the spermatheca was twice the female body length. The long length of the spermatheca and the possible removal function of the virga may select for virgal elongation.