Distribution of the peptide Ala‐Pro‐Gly‐Trp‐NH₂ (APGWamide) in the nervous system and periphery of the snail lymnaea stagnalis as revealed by immunocytochemistry and in situ hybridization

Abstract

Immunocytochemistry and in situ hybridization were used to identify 200-250 central neurons that synthesize and contain the peptide APGWamide in the central nervous system of Lymnaea. The majority of these cells reside within the right anterior lobe of the cerebral ganglion and most appear to have projections to the ventral lobe of the ganglion. The neurites then branch to innervate the lobe and to send further projections into the penial nerve and to the PeIb cluster of the right pedal ganglion. The right ventral lobe also contains a cluster of about 30-40 somata, which apparently synthesize and contain APGWamide. Other populations of cells found in both the right and left anterior lobes project ipsilaterally to the pleural, parietal, and visceral ganglia. Prominent somata are also located in clusters in the visceral and right parietal ganglia. These cells project ipsilaterally into caudal neuropilar regions of the cerebral ganglia. Peripheral projections of central neurons form a dense plexus of varicose, APGWamide-containing fibres in superficial layers of the penis and preputium. Other peripheral projections were noted in the prostate and vas deferens. No peripherally located cell bodies appeared to contain or synthesize the peptide. The results show that APGWamide is widely present in the central nervous system and male reproductive organs and suggest that it plays a major role in control of reproduction.

Molecular cloning of a cDNA encoding the neuropeptides APGWamide and cerebral peptide 1: Localization of APGWamide-like immunoreactivity in the central nervous system and male reproductive organs ofAplysia

“…Immunocytochemical studies, using antibodies previously shown to selectively label cells that express APGWamide in Lymnaea (Croll and Van Minnen, 1992), confirmed and extended the Northern blot data. The general distribution of APGWamide-lir was, in some respects, strikingly similar to the distribution of immunoreactivity in other gastropod species (i.e., the pulmonate snails Lymnaea and Helix).…”

“…Sections of the central nervous system (CNS) of Lymnaea served as positive controls. These sections, which were processed in parallel with sections of tissue from Aplysia, exhibited the same pattern of staining described previously (Croll and Van Minnen, 1992).…”

“…Central ganglia and selected peripheral organs (large and small hermaphroditic ducts, ovotestis, and penis) were dissected from sexually mature specimens (Nϭ8), fixed in 4% paraformaldehyde for 16-20 hours and then processed for histology with procedures previously described to selectively label APGWamide-like immunoreactivity (APGWamide-lir) in Lymnaea (Croll et al, 1991b;Croll and Van Minnen, 1992). The fixed tissues were dehydrated through an ascending ethanol series, embedded in paraffin and then sectioned at 10 µm thickness.…”

“…The predicted precursor contains multiple copies of the sequence Ala-Pro-Gly-Trp-Gly (which is posttranslationally processed to generate Ala-Pro-Gly-Trp-amide [APGWamide]), four connecting peptide sequences, and a Cterminal anterior lobe peptide (CALP; Li et al, 1992). Neurons of the right anterior lobe constitute the major site of expression of the APGWamide gene in Lymnaea (Croll et al, 1991b;Croll and Van Minnen, 1992), suggesting that peptides derived from the precursor are secreted at or near the penial complex and are involved in the control of aspects of male mating behavior. The immunoreactive neurons also have central targets (Croll et al, 1991b;Smit et al, 1992).…”

Egg-Laying in the Cuttlefish Sepia officinalis

“…In the pond snail Lymnaea stagnalis, this tetrapeptide detected in the penile nerve regulates penis erection [12][13][14].…”