Occurrence and distribution of substance P-related immunoreactivity in the brain of adult lampreys, Petromyzon marinus and Entosphenus tridentatus.

The occurrence and distribution of substance P (SP)-related immunoreactivity were examined in the adult brains of two species of lampreys, Petromyzon marinus and Entosphenus tridentatus, by using the PAP technique and three different anti-SP sera (anti-SP#1, anti-SP#2, and anti-SP#3). In both species of lampreys, anti-SP#1 and anti-SP#2 yielded positive reactions in the brain, while there was no, or slight immunoreaction there to anti-SP#3. The positive reactions toward anti-SP sera in the lamprey brain were not eliminated, or insufficiently reduced by preabsorption with SP, but they were completely abolished by preabsorption with eledoisin-related peptide. Thus, SP-positive material in the lamprey brain is more closely related, in terms of immunological determinants, to eledoisin than to SP. In Petromyzon, SP-positive perikarya were found in the ventrolateral telencephalon and the ventral hypothalamus, whereas in Entosphenus they were found in the ventral thalamus, tegmentum motoricum mesencephali (two locations), and rostral rhombencephalon, as well as in the above-mentioned two regions. Nevertheless, the distributions of SP-positive fibers in the regions of the brain other than the neurohypophysis were very similar between the two species: SP-positive fibers were found at many locations of the brain, and were especially rich in the periventricular subependymal zone of the ventral telencephalon and in the diencephalon, preoptic area, hypothalamus, and interpeduncular nucleus. In Petromyzon, a heavy accumulation of positive fibers was observed in the rostral part of the anterior neurohypophysis, whereas in Entosphenus no such fibers were observed there. These results clearly suggest the presence of a neuronal system of unknown function containing a SP-related peptide in the brain of lampreys.