Peripheral innervation patterns and central distribution of fin chromatophore motoneurons in the cuttlefish Sepia officinalis

Exploration of chemosensory ionotropic receptors in cephalopods: the IR25 gene is expressed in the olfactory organs, suckers, and fins of Sepia officinalis

While they are mostly renowned for their visual capacities, cephalopods are also good at olfaction for prey, predator, and conspecific detection. The olfactory organs and olfactory cells are well described but olfactory receptors-genes and proteins-are still undescribed in cephalopods. We conducted a broad phylogenetic analysis of the ionotropic glutamate receptor family in mollusks (iGluR), especially to identify IR members (Ionotropic Receptors), a variant subfamily whose involvement in chemosensory functions has been shown in most studied protostomes. A total of 312 iGluRs sequences (including 111 IRs) from gastropods, bivalves, and cephalopods were identified and annotated. One orthologue of the gene coding for the chemosensory IR25 co-receptor has been found in Sepia officinalis (Soff-IR25). We searched for Soff-IR25 expression at the cellular level by in situ hybridization in whole embryos at late stages before hatching. Expression was observed in the olfactory organs, which strongly validates the chemosensory function of this receptor in cephalopods. Soff-IR25 was also detected in the developing suckers, which suggests that the unique « taste by touch » behavior that cephalopods execute with their arms and suckers share features with olfaction. Finally, Soff-IR25 positive cells were unexpectedly found in fins, the two posterior appendages of cephalopods, mostly involved in locomotory functions. This result opens new avenues of investigation to confirm fins as additional chemosensory organs in cephalopods.

Neural pathways in the pallial nerve and arm nerve cord revealed by neurobiotin backfilling in the cephalopod mollusk Octopus vulgaris

Here, we report the findings after application of neurobiotin tracing to pallial and stellar nerves in the mantle of the cephalopod mollusk Octopus vulgaris and to the axial nerve cord in its arm. Neurobiotin backfilling is a known technique in other molluscs, but it is applied to octopus for the first time to be best of our knowledge. Different neural tracing techniques have been carried out in cephalopods to study the intricate neural connectivity of their nervous system, but mapping the nervous connections in this taxon is still incomplete, mainly due to the absence of a reliable tracing method allowing whole-mount imaging. In our experiments, neurobiotin backfilling allowed: (1) imaging of large/thick samples (larger than 2 mm) through optical clearing; (2) additional application of immunohistochemistry on the backfilled tissues, allowing identification of neural structures by coupling of a specific antibody. This work opens a series of future studies aimed to the identification of the neural diagram and connectome of octopus nervous system.

Cephalopod Brains: An Overview of Current Knowledge to Facilitate Comparison With Vertebrates

Cephalopod and vertebrate neural-systems are often highlighted as a traditional example of convergent evolution. Their large brains, relative to body size, and complexity of sensory-motor systems and behavioral repertoires offer opportunities for comparative analysis. Despite various attempts, questions on how cephalopod 'brains' evolved and to what extent it is possible to identify a vertebrate-equivalence, assuming it exists, remain unanswered. Here, we summarize recent molecular, anatomical and developmental data to explore certain features in the neural organization of cephalopods and vertebrates to investigate to what extent an evolutionary convergence is likely. Furthermore, and based on whole body and brain axes as defined in early-stage embryos using the expression patterns of homeodomain-containing transcription factors and axonal tractography, we describe a critical analysis of cephalopod neural systems showing similarities to the cerebral cortex, thalamus, basal ganglia, midbrain, cerebellum, hypothalamus, brain stem, and spinal cord of vertebrates. Our overall aim is to promote and facilitate further, hypothesis-driven, studies of cephalopod neural systems evolution.

Neural Control of Dynamic 3-Dimensional Skin Papillae for Cuttlefish Camouflage

The color and pattern changing abilities of octopus, squid, and cuttlefish via chromatophore neuromuscular organs are unparalleled. Cuttlefish and octopuses also have a unique muscular hydrostat system in their skin. When this system is expressed, dermal bumps called papillae disrupt body shape and imitate the fine texture of surrounding objects, yet the control system is unknown. Here we report for papillae: (1) the motoneurons and the neurotransmitters that control activation and relaxation, (2) a physiologically fast expression and retraction system, and (3) a complex of smooth and striated muscles that enables long-term expression of papillae through sustained tension in the absence of neural input. The neural circuits controlling acute shape-shifting skin papillae in cuttlefish show homology to the iridescence circuits in squids. The sustained tension in papillary muscles for long-term camouflage utilizes muscle heterogeneity and points toward the existence of a "catch-like" mechanism that would reduce the necessary energy expenditure.

Guidelines for the Care and Welfare of Cephalopods in Research -A consensus based on an initiative by CephRes, FELASA and the Boyd Group

This paper is the result of an international initiative and is a first attempt to develop guidelines for the care and welfare of cephalopods (i.e. nautilus, cuttlefish, squid and octopus) following the inclusion of this Class of ∼700 known living invertebrate species in Directive 2010/63/EU. It aims to provide information for investigators, animal care committees, facility managers and animal care staff which will assist in improving both the care given to cephalopods, and the manner in which experimental procedures are carried out. Topics covered include: implications of the Directive for cephalopod research; project application requirements and the authorisation process; the application of the 3Rs principles; the need for harm-benefit assessment and severity classification. Guidelines and species-specific requirements are provided on: i. supply, capture and transport; ii. environmental characteristics and design of facilities (e.g. water quality control, lighting requirements, vibration/noise sensitivity); iii. accommodation and care (including tank design), animal handling, feeding and environmental enrichment; iv. assessment of health and welfare (e.g. monitoring biomarkers, physical and behavioural signs); v. approaches to severity assessment; vi. disease (causes, prevention and treatment); vii. scientific procedures, general anaesthesia and analgesia, methods of humane killing and confirmation of death. Sections covering risk assessment for operators and education and training requirements for carers, researchers and veterinarians are also included. Detailed aspects of care and welfare requirements for the main laboratory species currently used are summarised in Appendices. Knowledge gaps are highlighted to prompt research to enhance the evidence base for future revision of these guidelines.

Molecular cloning, expression analysis and cellular localization of an LFRFamide gene in the cuttlefish Sepiella japonica

Neuropeptides are important regulators of physiological processes in metazoans, such as feeding, reproduction, and heart activities. In this study, an LFRFamide gene was identified from the cuttlefish Sepiella japonica (designated as SjLFRFamide). The full-length sequence of SjLFRFamide cDNA has 841bp, and the open reading frame contains 567bp encoding 188 amino acids, which shared high similarity with precursor SOFaRP2 from Sepia officinalis. The deduced SjLFRFamdie precursor protein contains a signal peptide and four different FLPs (FMRFamide-like peptides): one pentapeptide (TIFRFamide), two hexapeptides (NSLFRFamide and GNLFRFamide) and one heptapeptide (PHTPFRFamide). Multiple sequence alignment showed that SjLFRFamide contains rather conserved mature peptides, which all ended in FRF. The phylogenetic analysis suggests that SjLFRFamide belongs to the LFRFamide subfamily. The tissue distribution analysis through quantitative real-time PCR method showed that SjLFRFamide mRNA is significantly expressed in the brain, and slight trace are detected in female nidamental gland and accessory nidamental gland. In situ hybridization assay of the brain indicated that SjLFRFamide is transcribed in several different functional lobes, suggesting SjLFRFamide might associate with multiple physiological regulations, such as feeding, chromatophore regulation and reproduction. This is the first study describing LFRFamide in S. japonica, which might have great importance for cuttlefish artificial breeding.

Characterization of homeobox genes reveals sophisticated regionalization of the central nervous system in the European cuttlefish Sepia officinalis

Cephalopod mollusks possess a number of anatomical traits that often parallel vertebrates in morphological complexity, including a centralized nervous system with sophisticated cognitive functionality. Very little is known about the genetic mechanisms underlying patterning of the cephalopod embryo to arrive at this anatomical structure. Homeodomain (HD) genes are transcription factors that regulate transcription of downstream genes through DNA binding, and as such are integral parts of gene regulatory networks controlling the specification and patterning of body parts across lineages. We have used a degenerate primer strategy to isolate homeobox genes active during late-organogenesis from the European cuttlefish Sepia officinalis. With this approach we have isolated fourteen HD gene fragments and examine the expression profiles of five of these genes during late stage (E24-28) embryonic development (Sof-Gbx, Sof-Hox3, Sof-Arx, Sof-Lhx3/4, Sof-Vsx). All five genes are expressed within the developing central nervous system in spatially restricted and largely non-overlapping domains. Our data provide a first glimpse into the diversity of HD genes in one of the largest, yet least studied, metazoan clades and illustrate how HD gene expression patterns reflect the functional partitioning of the cephalopod brain.

Cephalopods in neuroscience: regulations, research and the 3Rs

Cephalopods have been utilised in neuroscience research for more than 100 years particularly because of their phenotypic plasticity, complex and centralised nervous system, tractability for studies of learning and cellular mechanisms of memory (e.g. long-term potentiation) and anatomical features facilitating physiological studies (e.g. squid giant axon and synapse). On 1 January 2013, research using any of the about 700 extant species of "live cephalopods" became regulated within the European Union by Directive 2010/63/EU on the "Protection of Animals used for Scientific Purposes", giving cephalopods the same EU legal protection as previously afforded only to vertebrates. The Directive has a number of implications, particularly for neuroscience research. These include: (1) projects will need justification, authorisation from local competent authorities, and be subject to review including a harm-benefit assessment and adherence to the 3Rs principles (Replacement, Refinement and Reduction). (2) To support project evaluation and compliance with the new EU law, guidelines specific to cephalopods will need to be developed, covering capture, transport, handling, housing, care, maintenance, health monitoring, humane anaesthesia, analgesia and euthanasia. (3) Objective criteria need to be developed to identify signs of pain, suffering, distress and lasting harm particularly in the context of their induction by an experimental procedure. Despite diversity of views existing on some of these topics, this paper reviews the above topics and describes the approaches being taken by the cephalopod research community (represented by the authorship) to produce "guidelines" and the potential contribution of neuroscience research to cephalopod welfare.

Expression of the SOFaRP2 gene in the central nervous system of the adult cuttlefish Sepia officinalis

FMRFamide-related Peptides (FaRPs) are involved in a variety of physiological processes, including reproduction, feeding, development, body patterning and osmoregulation in vertebrates and invertebrates. Here we investigate the expression pattern of cuttlefish Sepia officinalis FaRP2 gene in the brain by in situ hybridization. The SOFaRP2 gene was found to be expressed most intensively in the posterior chromatophore lobe, vasomotor lobe and subvertical lobe. In addition, positive staining was also found in the fin lobe, brachial lobe, anterior chromatophore lobe, anterior, dorsal and lateral basal lobes, inferior and superior frontal lobes, and optic lobe. The expression pattern of SOFaRP2 suggests its involvement in chromatophore regulation, feeding behavior, and learning and memory.

Molecular analysis of a novel FMRFamide-related peptide gene (SOFaRP(2)) and its expression pattern in the brain of the European cuttlefish Sepia officinalis

FMRFamide-related peptides (FaRPs) are among several neurotransmitters known to regulate the chromatophore function in the European cuttlefish Sepia officinalis. Here we report the cloning and sequencing of a novel S. officinalis FaRP gene (SOFaRP(2)). The complete 835-base pair cDNA sequence of the SOFaRP(2) gene contains an open reading frame of 567 base pairs encoding 188 amino acids and four putative FaRPs, NSLFRFamide, GNLFRFamide, TIFRFamide and PHTPFRFamide. All except TIFRFamide cause chromatophore expansion when assayed in an in vitro chromatophore bioassay. To investigate the expression pattern of SOFaRP(2) gene in the cuttlefish brain, in situ hybridization was performed using a full length RNA probe. The SOFaRP(2) gene was expressed primarily in the posterior chromatophore, anterior chromatophore, lateral basal and optic lobes among other brain locations. The SOFaRP(2) gene appears to be expressed in all brain regions involved in chromatophore regulation. These data suggests that some or all of the four FaRPs encoded by SOFaRP(2) might be involved in controlling chromatophore activity in cuttlefish.

FaRP cell distribution in the developing CNS suggests the involvement of FaRPs in all parts of the chromatophore control pathway in Sepia officinalis (Cephalopoda)

The FMRFamide-related peptide (FaRP) family includes a wide range of neuropeptides that have a role in many biological functions. In cephalopods, these peptides intervene in the peculiar body patterning system used for communication and camouflage. This system is particularly well developed in the cuttlefish and is functional immediately after hatching (stage 30). In this study, we investigate when and how the neural structures involved in the control of body patterning emerge and combine during Sepia embryogenesis, by studying the expression or the production of FaRPs. We detected FaRP expression and production in the nervous system of embryos from the beginning of organogenesis (stage 16). The wider FaRP expression was observed concomitantly with brain differentiation (around stage 22). Until hatching, FaRP-positive cells were located in specific areas of the central and peripheral nervous system (CNS and PNS). Most of these areas were implicated in the control of body patterns, suggesting that FaRPs are involved in all parts of the neural body pattern control system, from the 'receptive areas' via the CNS to the chromatophore effectors.

Signaling to the enemy? Body pattern expression and its response to external cues during hunting in the cuttlefish Sepia officinalis (Cephalopoda)

Cuttlefish can rapidly alter their appearance by using neurally controlled chromatophore organs. This ability may provide a window into their cognitive capacity. We test whether the changes in body pattern that occur during hunting depend on context. If they do, then it may be possible to use these changes to study cephalopod cognition while the animal is engaged in ecologically relevant tasks. We found consistent individual differences in the tendency of cuttlefish to hunt with the first two arms raised. We also found that cuttlefish usually darken their skin after they seize a prey item. This darkening is observed regardless of the identity of the prey (fish, crab, or shrimp), prey context (buried in sand, in a bare tank, or on top of a rock pile), or the presence of a sudden stimulus. The sudden stimulus was created by presenting an overhead model bird to the cuttlefish. The model induced components of the Deimatic Display, which is a form of antipredator behavior, suggesting that the model was perceived as a potential threat. Passing Cloud displays and the Darkening of the arms were significantly reduced after exposure to the model bird. The effect of a potential predator on body pattern expression during hunting suggests it may be possible to use these changes as a sensitive indicator of ecologically relevant learning.

Central distribution and three-dimensional arrangement of fin chromatophore motoneurons in the cuttlefish Sepia officinalis

Cephalopod body patterning is a most complex invertebrate behavior. Generated primarily by pigment-containing chromatophore organs, this behavior enables rapid alteration of body coloration as a result of direct innervation of chromatophores by motoneurons. This study focuses on location and arrangement of fin chromatophore motoneurons in the cuttlefish Sepia and investigates the possibility of central topography. Retrograde labeling of topographically arranged fin nerve branches in the periphery revealed the posterior subesophageal mass (PSEM) of the brain as the primary location of fin chromatophore motoneurons; within this region, most cells were located in the posterior chromatophore and fin lobes. Additionally, a small percentage of labeled motoneurons occurred in the anterior subesophageal mass and the stellate ganglia. Data from three-dimensional reconstructions of PSEMs showed the arrangement of labeled motoneurons within individual lobes; these data suggest no obvious topographic arrangement. Further, electrical stimulation of the PSEM generated chromatophore activity on the fin and mantle. These stimulation results, coupled with the retrograde labeling, suggest that chromatophore motoneurons are located across multiple PSEM lobes.