Modulatory actions of octopamine and serotonin on the contraction of buccal muscles in Rapana thomasiana--I. Enhancement of contraction in radula protractor

Isolation and characterization of a novel small cardioactive peptide-related peptide from the brain of Octopus vulgaris

A novel small cardioactive peptide (SCP)-related peptide (oct-SCPRP: Ser-Asn-Gly-Tyr-Leu-Ala-Leu-Pro-Arg-Gln-NH2) was isolated from the brain of the octopus (Octopus vulgaris). cDNA encoding this precursor protein was cloned. Oct-SCPRP was shown to evoke contraction in the radula protractor muscle, and the precursor protein was highly homologous to the SCP family in the Mollusk but did not encode a related peptide, SCPB. The expression of oct-SCPRP mRNA was present not only in the peripheral nervous system (PNS) which is a motor center for the control of feeding, but also in the central nervous system (CNS) which is capable of complex analysis, learning, and controls behaviors.

Isolation and characterisation of conomap-Vt, ad-amino acid containing excitatory peptide from the venom of a vermivorous cone snail

Cone snail venom is a rich source of bioactives, in particular small disulfide rich peptides that disrupt synaptic transmission. Here, we report the discovery of conomap-Vt (Conp-Vt), an unusual linear tetradecapeptide isolated from Conus vitulinus venom. The sequence displays no homology to known conopeptides, but displays significant homology to peptides of the MATP (myoactive tetradecapeptide) family, which are important endogenous neuromodulators in molluscs, annelids and insects. Conp-Vt showed potent excitatory activity in several snail isolated tissue preparations. Similar to ACh, repeated doses of Conp-Vt were tachyphylactic. Since nicotinic and muscarinic antagonists failed to block its effect and Conp-Vt desensitised tissue remained responsive to ACh, it appears that Conp-Vt contractions were non-cholinergic in origin. Finally, biochemical studies revealed that Conp-Vt is the first member of the MATP family with a d-amino acid. Interestingly, the isomerization of L-Phe to D-Phe enhanced biological activity, suggesting that this post-translational modified conopeptide may have evolved for prey capture.

Molecular and functional characterization of a novel gonadotropin-releasing-hormone receptor isolated from the common octopus (Octopus vulgaris)

GnRH (gonadotropin-releasing hormone) plays a pivotal role in the regulation of reproduction in vertebrates through interaction with a specific receptor. Previously, we isolated a GnRH homologue, oct-GnRH, from the common octopus (Octopus vulgaris). In the present study, we have identified a GnRH receptor (oct-GnRHR) specific for oct-GnRH from Octopus brain. Oct-GnRHR includes domains and motifs typical of vertebrate GnRH receptors. The intron-inserted positions are conserved between oct-GnRHR and the chordate GnRHR genes. The oct-GnRHR expressed in Xenopus (South African clawed frog) oocytes was responsive to oct-GnRH, but not to any other HPLC fractions of the Octopus brain extract. These results show that oct-GnRHR is an authentic receptor for oct-GnRH. Southern blotting of reverse-transcription PCR products revealed that the oct-GnRHR mRNA was widely distributed in the central and peripheral nervous systems and in several peripheral tissues. In situ hybridization showed that oct-GnRHR mRNA was expressed in some regions involved in autonomic functions, feeding, memory and movement. Oct-GnRH was shown to induce steroidogenesis of testosterone, progesterone and 17beta-oestradiol in Octopus ovary and testis, where oct-GnRHR was abundantly expressed. These results suggest that oct-GnRH, like its vertebrate counterparts, acts as a multifunctional neurotransmitter, neuromodulator and hormone-like factor, both in Octopus central nervous system and peripheral tissues, and that both structure and functions of the GnRH family are, at least partially, evolutionarily conserved between octopuses and chordates.

Serotonergic modulation of a voltage-gated calcium current in parapodial swim muscle from Aplysia brasiliana

Here we describe the effects of serotonin (5-HT) on dissociated parapodial muscle fibers from Aplysia brasiliana. 5-HT has previously been implicated as a modulatory transmitter at the parapodial neuromuscular junction. Exogenously applied or endogenously released 5-HT increases the amplitude of motoneuron-induced excitatory junctional potentials and contractions in parapodial muscle. Exogenously applied 5 microM 5-HT increases the amplitude of a voltage-gated inward calcium current in isolated muscle fibers by an average of 42% in response to a voltage step from -70 to -10 mV. The amplitude of the inward current was increased at all voltages tested, with the peak increase occurring between -30 and -20 mV. The dihydropyridine calcium channel antagonist nifedipine (10 microM) blocked this effect of 5-HT. The data indicate that 5-HT increases a previously identified calcium current in parapodial muscle fibers that is similar to the vertebrate L-type current. Although several types of K+ channels exist in these fibers, including Ca(2+)-dependent K+ channels, the results suggest that 5-HT has little effect on these currents. Parapodial muscle contractions during swimming behavior occur in response to bursts of motoneuron action potentials that produce graded muscle depolarizations that occur over a 1- to 2-s period rather than being instantaneous or rapid responses as might be produced by one or two action potentials or a brief voltage step. With the use of 1-s voltage ramps, we attempted to mimic physiological depolarization and demonstrate that 5-HT is able to increase the amplitude of the inward calcium current. The data presented in this paper provide evidence that 5-HT increases the Ca2+ current, which may be one mechanism by which 5-HT modulates muscle contractions during swim behavior.