Roger P Croll

Dalhousie University | Dal · Department of Physiology and Biophysics

The intracardiac nervous system represents the final common pathway for autonomic control of the vertebrate heart in maintaining cardiovascular homeostasis. In teleost fishes, details of the organization of this system are not well understood. Here we investigated innervation patterns in the heart of the goldfish, a species representative of a larg...

Odor molecules are transduced by thousands of olfactory sensory neurons (OSNs) located in the nasal cavity. Each OSN expresses a single functional odorant receptor protein and projects an axon from the sensory epithelia to an olfactory bulb glomerulus, which is selectively innervated by only one or a few OSN types. We used whole-mount immunocytoche...

FMRFamide-related peptides (FaRPs) are involved in numerous neural functions across the animal kingdom and serve as important models for understanding the evolution of neuropeptides. Gastropod molluscs have proved to be particularly useful foci for such studies, but the developmental expression of FaRPs and the evolution of specific transcripts for...

The peripheral nervous system in gastropods plays a key role in the neural control of behaviors, but is poorly studied in comparison with the central nervous system. Peripheral sensory neurons, although known to be widespread, have been studied in a patchwork fashion across several species, with no comprehensive treatment in any one species. We att...

Catecholaminergic neurons are abundant in molluscs and are involved in a variety of behaviors such as feeding, respiration, learning, and locomotion. However, previous identification of these neurons has relied almost exclusively on immunohistochemistry using antibodies, which have not been fully validated for use in molluscs. We employed tissue‐sp...

A wide variety of human diseases have been modelled in zebrafish, including various types of cancer, cardiovascular diseases and neurodegenerative diseases like Alzheimer’s and Parkinson’s. Recent reviews have summarized the currently available zebrafish models of Parkinson’s Disease, which include gene-based, chemically induced and chemogenetic ab...

Developmental programmes for many marine invertebrates include the assembly of muscular systems appropriate to the functions of swimming and feeding in pelagic larvae. Upon metamorphosis, that musculature is often radically re‐organized to meet very different demands of post‐larval life. To investigate the development and fate of musculature in the...

Cardiac excitation originates in the sinoatrial node (SAN), due to the automaticity of this distinct region of the heart. SAN automaticity is the result of a gradual depolarisation of the membrane potential in diastole, driven by a coupled system of transarcolemmal ion currents and intracellular Ca ²⁺ cycling. The frequency of SAN excitation determ...

The cover image is based on the Research Article FMRF‐NH2‐related neuropeptides in Biomphalaria spp., intermediate hosts for schistosomiasis: Precursor organization and immunohistochemical localization by Solymar Rolón‐Martínez et al., https://doi.org/10.1002/cne.25195.

Freshwater snails of the genus Biomphalaria serve as intermediate hosts for the digenetic trematode Schistosoma mansoni, the etiological agent for the most widespread form of intestinal schistosomiasis. As neuropeptide signaling in host snails can be altered by trematode infection, a neural transcriptomics approach was undertaken to identify peptid...

Each zebrafish olfactory bulb contains ~ 140 glomeruli that are distinguishable based on size, location, neurochemistry and function. Here we examine the mitral cell innervation of differently sized glomeruli in adult zebrafish. Type 1 glomeruli had diameters of 80.9 ± 8.1 μm and were innervated by 5.9 ± 0.9 mitral cells. The Type 1 mediodorsal glo...

Freshwater snails of the genus Biomphalaria serve as obligatory hosts for the digenetic trematode Schistosoma mansoni, the causative agent for the most widespread form of intestinal schistosomiasis. Within Biomphalaria, S. mansoni larvae multiply and transform into the cercariae form that can infect humans. Trematode development and proliferation i...

Vasoactive Intestinal Peptide (VIP) is the major physiological agonist of the Cystic Fibrosis Transmembrane conductance Regulator (CFTR) chloride channel activity. VIP functions as a neuromodulator and neurotransmitter secreted by neurons innervating all exocrine glands. VIP is also a potent vasodilator and bronchodilator that regulates exocrine gl...

Infection with trematodes produces physiological and behavioural changes in intermediate snail hosts. One response to infection is parasitic castration, in which energy required for reproduction of the host is thought to be redirected to promote development and multiplication of the parasite. This study investigated some reproductive and biochemica...

Cephalopods are radically different from any other invertebrate. Their molluscan heritage, innovative nervous system, and specialized behaviors create a unique blend of characteristics that are sometimes reminiscent of vertebrate features. For example, despite differences in the organization and development of their nervous systems, both vertebrate...

Recent years have led to increased effort to describe and understand the peripheral nervous system and its influence on central mechanisms and behavior in gastropod molluscs. This study revealed that an antibody raised against keyhole limpet hemocyanin (KLH) cross-reacts with an antigen(s) found extensively in both the central and the peripheral ne...

Peptide hormones and neurotransmitters involved in reproduction and growth have been studied extensively in certain gastropod molluscs, such as Lymnaea stagnalis and Aplysia californica. The present study employs antisera that have been used to study peptidergic neurons in those species to probe the central nervous system of another gastropod, Biom...

Our understanding of the multiorgan pathology of cystic fibrosis (CF) has improved impressively during the last decades, but we still lack a full comprehension of the disease progression. Animal models have greatly contributed to the elucidation of specific mechanisms involved in CF pathophysiology and the development of new therapies. Soon after t...

CHARGE syndrome is linked to autosomal dominant mutations in the CHD7 gene and results in a number of physiological and structural abnormalities, including heart defects, hearing and vision loss and gastrointestinal (GI) problems. Of these challenges, GI problems have a profound impact throughout an individual's life, resulting in increased morbidi...

Cephalopods are non-traditional but captivating models of invertebrate neurobiology, particularly in evolutionary comparisons. Cephalopod olfactory systems have striking similarities and fundamental differences with vertebrates, arthropods, and gastropods, raising questions about the ancestral origins of those systems. We describe here the organiza...

Within a common body plan, echinoid planktotrophic larvae are morphologically diverse, with variations in overall size, the length, and number of arms and the presence or absence of epidermal structures. In this report, we are interested in variation in larval arm-flexing behavior and correlated differences in larval musculature. Larvae of the cida...

Objective Globally, more than 200 million people live at risk of the neglected tropical disease schistosomiasis (or snail fever). Larval schistosomes require the presence of specific snail species that act as intermediate hosts, supporting their multiplication and transformation into forms that can infect humans. This project was designed to genera...

Terrestrial animals must support their bodies against gravity, while aquatic animals are effectively weightless because of buoyant support from water. Given this evolutionary history of minimal gravitational loading of fishes in water, it has been hypothesized that weight-responsive musculoskeletal systems evolved during the tetrapod invasion of la...

The simpler nervous systems of certain invertebrates provide opportunities to examine colocalized classical neurotransmitters in the context of identified neurons and well defined neural circuits. This study examined the distribution of γ‐aminobutyric acid‐like immunoreactivity (GABAli) in the nervous system of the panpulmonates Biomphalaria glabra...

Zebrafish are emerging as a novel model for studying learning and memory due to the accessibility of molecular tools, rich repertoire of behaviours, relatively simple neuronal circuits, reasonable cost, and usefulness for high-throughput screens. However, the number of behavioural paradigms that minimize handling stress and are well suited to the s...

In addition to their intended clinical actions, all general anesthetic agents in common use have detrimental intra- and post-surgical side effects on organs and systems including the heart. The major cardiac side effect of anesthesia is bradycardia, which increases the probability of insufficient systemic perfusion during surgery. These side effect...

Hermissenda crassicornis is a model for studying the molecular and cellular basis for classical conditioning, based on its ability to associate light with vestibular stimulation. We used confocal microscopy to map histamine, FMRF-amide, and GABA immunoreactivity in the central nervous system (CNS), eyes, optic ganglia and statocysts of the nudibran...

Several lines of evidence suggest that serotonin (5-HT) has a regulatory role in cardiovascular function from embryogenesis through adulthood. However, the reported actions of 5-HT are often contradictory and include bradycardia or tachycardia, hypotension or hypertension, and vasodilation or vasoconstriction. Clarifying such cardiac effects requir...

Zebrafish are emerging as a novel model for studying learning and memory due to the accessibility of molecular tools, rich repertoire of behaviours, relatively simple neuronal circuits, reasonable cost, and usefulness for high-throughput screens. However, the number of behavioural paradigms that minimize handling stress and are well suited to the s...

Invertebrates comprise the vast majority of animal species on Earth and exhibit a diverse range of body forms which arise through different developmental programs. This chapter focuses on evolutionary relationships between different animal groups. It organizes into a scheme which groups the simplest animals, the diploblasts, and divides the more co...

In many marine invertebrates, larval metamorphosis is induced by environmental cues that activate sensory receptors and signalling pathways. Nitric oxide (NO) is a gaseous signalling molecule that regulates metamorphosis in diverse bilaterians. In most cases NO inhibits or represses this process, although it functions as an activator in some specie...

This article provides supporting data for the research article “A simple automated system for appetitive conditioning of zebrafish in their home tanks” [1]. In that article, we described overall movements of zebrafish toward a food source as a response to auditory or visual cues as conditioned stimuli in a novel learning paradigm. Here, we describe...

The cardiac pacemaker sets the heart’s primary rate, with pacemaker discharge controlled by the autonomic nervous system through intracardiac ganglia. A fundamental issue in understanding the relationship between neural activity and cardiac chronotropy is the identification of neuronal populations that control pacemaker cells. To date, most studies...

BACKGROUND: CHARGE syndrome has been linked to mutations in the CHD7 gene and results in a number of physiological and structural abnormalities. The estimated incidence in the Atlantic Provinces is 1 in 8500 births. Challenges include eating problems, which have a profound impact throughout a child’s life and can lead to complications and even deat...

For many biologists the nervous system is a particularly fascinating organ system. The nervous system is involved in or is even responsible for many features that are regarded as being characteristic of animals in general. Since the last comprehensive work was published about 50 years ago, the time has probably come to provide a new review on recen...

Gastropods comprise the second largest class in the Animal Kingdom with 60,000 to 80,000 living species occupying ecological niches covering the globe. Anatomy, behaviour and development vary significantly between the five clades of Patellogastropoda, Vetigastropoda,Neritimorpha, Caenogastropoda and Heterobranchia. Generally, the central nervous sy...

Histamine appears to be an important transmitter throughout the Animal Kingdom. Gastropods, in particular, have been used in numerous studies establishing potential roles for this biogenic amine in the nervous system and showing its involvement in the generation of diverse behaviours. And yet, the distribution of histamine has only previously been...

The siphon of Aplysia californica has several functions, including involvement in respiration, excretion and defensive inking. It also provides sensory input for defensive withdrawals that have been studied extensively to examine mechanisms that underlie learning. To better understand the neuronal bases of these functions, we used immunohistochemis...

Imaging calcium transients associated with neuronal activity has yielded important insights into neural physiology. Genetically encoded calcium indicators (GECIs) offer conspicuous potential advantages for this purpose, including exquisite targeting. While the catalogue of available GECIs is steadily growing, many newly developed sensors that appea...

In the vertebrate heart the intracardiac nervous system is the final common pathway for autonomic control of cardiac output, however the neuroanatomy of this system is not well understood in any vertebrate. In this study we investigated the innervation of the heart in a model vertebrate, the zebrafish. We used antibodies against acetylated tubulin,...

Embryonic cuttlefish can first respond to a variety of sensory stimuli during early development in the egg capsule. To examine the neural basis of this ability, we investigated the emergence of sensory structures within the developing epidermis. We show that the skin facing the outer environment (not the skin lining the mantle cavity, for example)...

Planorbid snails of the genus Biomphalaria are major intermediate hosts for the digenetic trematode parasite Schistosoma mansoni. Evidence suggests that levels of the neurotransmitter dopamine (DA) are reduced during the course of S. mansoni multiplication and transformation within the snail. This investigation used immunohistochemical methods to l...

In this study, we present a morphological description of the fine structure of the tissues composing the caudal tip of the adult zebrafish swim bladder and an immunochemical survey of the innervation at this site. The internal aspect of the caudal tip is lined by an epithelium specialized to secrete surfactant into the lumen as evinced by the exocy...

Trichoplax adhaerens is an enigmatic basal animal with an extraordinarily simple morphological organization and surprisingly complex behaviors. Basic morphological, molecular and behavioral work is essential to better understand the unique and curious life style of these organisms. We provide basic instructions on how Trichoplax can be cultured and...

Although our understanding of neuronal development in Trochozoa has progressed substantially in recent years, relatively little attention has been paid to the bivalve molluscs in this regard. In the present study, the development of FMRFamide-, serotonin- and catecholamine-containing cells in the mussel, Mytilus trossulus, was examined using immuno...

The distribution of serotonin-like immunoreactivity was determined in whole-mounted ganglia of the central nervous system of the prosobranch snail, Littorina littorea, with the goal of establishing a basis for cellular comparisons between different gastropod nervous systems. While general similarities appear to exist with other species, the nervous...

SUMMARY The frequency of respiratory pumping in Aplysia increases when CO2 is bubbled through the bathing sea water. Air, O2 and N2 do not have this effect. The sensitivity to CO2 may be mediated by receptors which are sensitive to pH changes within the range encountered during hypercapnia. In addition to the frequency change during hypercapnia, in...

Previous studies have suggested an involve- ment of catecholamines in the control of several larval behaviors, such as feeding, locomotion, and induction of settling and metamorphosis. In the present study we employed aldehyde-induced, blue-green fluorescence to indicate catecholamines in cells within representatives of two bivalve families, the Pe...

We characterized the expression of sall4, a gene encoding a zinc finger transcription factor involved in the maintenance of embryonic stem cells, in taste buds of zebrafish (Danio rerio). Using an enhancer trap line (ET5), we detected enhanced green fluorescent protein (EGFP) in developing and adult transgenic zebrafish in regions containing taste...

To investigate whether mechanoreception is used in non-visual feeding, the ontogeny of superficial neuromasts along the lateral line was described using the vital stain FM1-43FX and fluorescent microscopy. The number of neuromasts visible along one flank increased from 11 at first feeding (5 to 7 days post-hatch, dph) to >150 by the juvenile stage...

Introduction Gastropoda are guided by several sensory organs in the head region, referred to as cephalic sensory organs (CSOs). These CSOs are innervated by distinct nerves. This study proposes a unified terminology for the cerebral nerves and the categories of CSOs and then investigates the neuroanatomy and cellular innervation patterns of these c...

Olfactory glomeruli are innervated with great precision by the axons of different olfactory sensory neuron types and act as functional units in odor information processing. Approximately 140 glomeruli are present in each olfactory bulb of adult zebrafish; these units consist of either highly stereotypic large glomeruli or smaller anatomically indis...

The cover image shows the paired olfactory bulbs of an adult female zebrafish (Danio rerio). The image was obtained through a novel in toto immunohistochemistry protocol explained in Braubach, Fine and Croll in this issue. The tissue was labeled with antibodies against the molluscan blood protein, keyhole limpet hemocyanin (red), and the calcium bi...

The swimbladder of teleost fishes is the primary organ for controlling whole-body density, and thus buoyancy. The volume of gas in the swimbladder is adjusted to bring the organism to near neutral buoyancy at a particular depth. Swimbladder morphology varies widely among teleosts, but all species are capable of inflating and deflating this organ un...

The zebrafish is a widely used model vertebrate for research in molecular and developmental biology. Recently this species has been used for studies of the effects of microgravity on fundamental biological processes. Zebrafish, being small in size, develop rapidly to sexual maturity and produce relatively large numbers of transparent embryos, so ar...

Many teleosts use gas-filled swimbladders to control buoyancy and influence three-dimensional orientation (pitch and roll). However, swimbladder volume, and its contributions to these functions, varies with depth-related pressure according to Boyle's law. Moreover, the swimbladder volume at a given depth also depends on the compliance of the swimbl...

The gas-filled swimbladder of teleost fishes provides hydrodynamic lift which counteracts the high density of other body tissues, and thereby allows the fish to achieve neutral buoyancy with minimal energy expenditure. In this study, we examined whether the absence of a constant direction gravitational vector affects the ontogeny of the swimbladder...