Larval Lampreys Research Articles

Spinal cord injury induces changes in electrophysiological properties and ion channel expression of reticulospinal neurons in larval lamprey.

In larval lamprey, hemitransections were performed on the right side of the rostral spinal cord to axotomize ipsilateral reticulospinal (RS) neurons. First, at short recovery times (2-3 weeks), uninjured RS neurons contralateral to hemitransections fired a smooth train of action potentials in response to sustained depolarization, whereas axotomized neurons fired a single short burst or short repetitive bursts. For uninjured RS neurons, the afterpotentials of action potentials had three components: fast afterhyperpolarization (fAHP), afterdepolarizing potential (ADP), and slow AHP (sAHP) that was attributable to calcium influx via high-voltage-activated (HVA) (N- and P/Q-type) calcium channels and calcium-activated potassium channels (SKKCa). For axotomized RS neurons, the fAHP was significantly larger than for uninjured neurons, and the ADP and sAHP were absent or significantly reduced. Second, at relatively long recovery times (12-16 weeks), axotomized RS neurons displayed firing patterns and afterpotentials that were similar to those of uninjured neurons. Third, mRNA levels of lamprey HVA calcium and SKKCa channels in axotomized RS neurons were significantly reduced at short recovery times and restored at long recovery times. Fourth, blocking calcium channels in uninjured RS neurons resulted in altered firing patterns that resembled those produced by axotomy. We demonstrated previously that lamprey RS neurons in culture extend neurites, and calcium influx results in inhibition of neurite outgrowth or retraction. Together, these results suggest that the downregulation of Ca2+ channels in axotomized RS neurons, and the associated reduction in calcium influx, maintain intracellular calcium levels in a range that is permissive for axonal regeneration.

Condition assessment of lamprey populations in the Yorkshire Ouse catchment, north‐east England, and the potential influence of physical migration barriers

Abstract River lamprey (Lampetra fluviatilis) and sea lamprey (Petromyzon marinus) are designated features of the River Derwent Special Area of Conservation (SAC) and the Humber Estuary (a possible SAC). This study determined the condition of lamprey populations in the Yorkshire Ouse catchment by assessing the species composition, distribution, abundance and size‐structure of larval (ammocoete) populations in five major tributary rivers (Derwent, Swale, Ure, Nidd and Wharfe). According to EU condition assessment criteria, Lampetra populations (assumed to be mostly river lamprey) are at present in favourable condition, with site mean (±SE) densities ranging from 2.7 (±1.2) to 160.3 (±50.5) individuals m−2 (all river means >2 individuals m−2), and at least two size (≈age) classes present in optimal microhabitats. By contrast, no sea lamprey larvae were recorded, suggesting that populations of this species are in unfavourable condition. Actions to protect and enhance nationally or internationally important stocks must be implemented from at least a catchment perspective, because many of the issues affecting such species are not localized. With respect to lampreys, particular attention should be given to protecting spawning and nursery habitats, improving water quality, reducing impingement at abstraction points, preventing exploitation at spawning grounds and increasing passage at potential physical obstructions. Copyright © 2007 John Wiley & Sons, Ltd.

Toward Improved Assessment of Sea Lamprey Population Dynamics in Support of Cost-effective Sea Lamprey Management

Cost-effective integrated pest management of sea lampreys requires good assessment information. Assessment of sea lamprey populations is used to inform decisions about which control methods to use, as well as where and when to apply them. Additionally, assessment data are used to evaluate the performance of past management actions. This theme paper identifies key research questions that limit our understanding of sea lamprey population dynamics, as well as the quality of the assessment information currently used to inform management. The discussion is organized by dividing the sea lamprey life history into four stages—spawning, recruitment to age 1, larval, and parasitic—and examining the state of knowledge about population dynamics and assessment for each life stage. For spawning lamprey key research questions include migration timing, mating systems, and factors influencing spawning success. For recruitment to age 1, factors affecting recruitment variation and methods for age determination are critical needs. For larval lampreys, the primary target of control using lampricides, the key questions concern the accuracy of assessment methods used to guide lampricide treatment decisions and the effects of uncertainty on the utility of these methods. For parasitic lampreys, the main questions center on the nature of the host attack process and variation in survival during the parasitic phase. Finally, this review noted that the development of integrated models to evaluate control strategies remains a high priority for research. Because resources available for sea lamprey management are limited, high quality assessment information and good knowledge of sea lamprey population dynamics are key ingredients of a cost-effective control program.

Laboratory assessment of sea lamprey larvae burrowing performance

Abstract – To study the burrowing behaviour and performance of larval sea lamprey (Petromyzon marinus L.), 120 ammocoetes were collected and observed in the laboratory. Burrowing movements of ammocoetes placed in an aquarium with sediments of differing grain size were video recorded. The video was reviewed and, for each larva, the total time spent moving, the number of stops during the burrowing movement, the total time spent stopped and total time elapsed until complete withdrawal below the substrate surface was registered. Smaller ammocoetes had lower burrowing performance than larger individuals, across all substrate types, but the differences were greater in coarser substrates. Additionally, coarser sediment particles increased the time spent on burrowing regardless of larval size.

Laboratory assessment of sea lamprey larvae burrowing performance

Abstract – To study the burrowing behaviour and performance of larval sea lamprey (Petromyzon marinus L.), 120 ammocoetes were collected and observed in the laboratory. Burrowing movements of ammocoetes placed in an aquarium with sediments of differing grain size were video recorded. The video was reviewed and, for each larva, the total time spent moving, the number of stops during the burrowing movement, the total time spent stopped and total time elapsed until complete withdrawal below the substrate surface was registered. Smaller ammocoetes had lower burrowing performance than larger individuals, across all substrate types, but the differences were greater in coarser substrates. Additionally, coarser sediment particles increased the time spent on burrowing regardless of larval size.

An attempt to differentiate sympatricIchthyomyzonammocoetes using meristic, morphological, pigmentation, and gonad analyses

We assessed characters that could be used to differentiate ammocoetes of chestnut lamprey ( Ichthyomyzon castaneus Girard, 1858), northern brook lamprey ( Ichthyomyzon fossor Reighard and Cummins, 1916), and silver lamprey ( Ichthyomyzon unicuspis Hubbs and Trautman, 1937). We sampled ammocoetes of the three species from 25 streams around the Great Lakes. Existing genetic markers were used to identify chestnut lamprey for this study, but the lack of genetic markers for silver and northern brook lampreys forced our preliminary classification of these two species to be based on stream-specific catch records of adults. Comparison of ammocoete gonads was inconclusive as a technique to distinguish between these two species. Other characters examined (including pigmentation patterns, morphometric characters, body shape, and myomere counts) varied significantly among species, but were inadequate for use as diagnostic characters because of high intraspecific variation and overlapping ranges. Chestnut lamprey ammocoetes were sometimes distinguishable by their pigmented lateral line organs, but this character was not always apparent. The lack of distinguishing characteristics makes existing taxonomic keys misleading for identifying Ichthyomyzon lamprey larvae.

Characterization of Na+-Activated K+ Currents in Larval Lamprey Spinal Cord Neurons

Potassium channels play an important role in controlling neuronal firing and synaptic interactions. Na(+)-activated K(+) (K(Na)) channels have been shown to exist in neurons in different regions of the CNS, but their physiological function has been difficult to assess. In this study, we have examined if neurons in the spinal cord possess K(Na) currents. We used whole cell recordings from isolated spinal cord neurons in lamprey. These neurons display two different K(Na) currents. The first was transient and activated by the Na(+) influx during the action potentials, and it was abolished when Na(+) channels were blocked by tetrodotoxin. The second K(Na) current was sustained and persisted in tetrodotoxin. Both K(Na) currents were abolished when Na(+) was substituted with choline or N-methyl-D-glucamine, indicating that they are indeed dependent on Na(+) influx into neurons. When Na(+) was substituted with Li(+), the amplitude of the inward current was unchanged, whereas the transient K(Na) current was reduced but not abolished. This suggests that the transient K(Na) current is partially activated by Li(+). These two K(Na) currents have different roles in controlling the action potential waveform. The transient K(Na) appears to act as a negative feedback mechanism sensing the Na(+) influx underlying the action potential and may thus be critical for setting the amplitude and duration of the action potential. The sustained K(Na) current has a slow kinetic of activation and may underlie the slow Ca(2+)-independent afterhyperpolarization mediated by repetitive firing in lamprey spinal cord neurons.

Movements and Muscle Activity Initiated by Brain Locomotor Areas in Semi-Intact Preparations From Larval Lamprey

In in vitro brain/spinal cord preparations from larval lamprey, locomotor-like ventral root burst activity can be initiated by pharmacological (i.e., "chemical") microstimulation in several brain areas: rostrolateral rhombencephalon (RLR); dorsolateral mesencephalon (DLM); ventromedial diencephalon (VMD); and reticular nuclei. However, the quality and symmetry of rhythmic movements that would result from this in vitro burst activity have not been investigated in detail. In the present study, pharmacological microstimulation was applied to the above brain locomotor areas in semi-intact preparations from larval lamprey. First, bilateral pharmacological microstimulation in the VMD, DLM, or RLR initiated symmetrical swimming movements and coordinated muscle burst activity that were virtually identical to those during free swimming in whole animals. Unilateral microstimulation in these brain areas usually elicited asymmetrical undulatory movements. Second, with synaptic transmission blocked in the brain, bilateral pharmacological microstimulation in parts of the anterior (ARRN), middle (MRRN), or posterior (PRRN) rhombencephalic reticular nucleus also initiated symmetrical swimming movements and muscle burst activity. Stimulation in effective sites in the ARRN or PRRN initiated higher-frequency locomotor movements than stimulation in effective sites in the MRRN. Unilateral stimulation in reticular nuclei elicited asymmetrical rhythmic undulations or uncoordinated movements. The present study is the first to demonstrate in the lamprey that stimulation in higher-order locomotor areas (RLR, VMD, DLM) or reticular nuclei initiates and sustains symmetrical, well-coordinated locomotor movements and muscle activity. Finally, bilateral stimulation was a more physiologically realistic test of the function of these brain areas than unilateral stimulation.

Survival and Tag Retention of Pacific Lamprey Larvae and Macrophthalmia Marked with Coded Wire Tags

AbstractWe examined the survival, tag retention, and growth of Pacific lamprey Lampetra tridentata larvae and macrophthalmia marked with standard‐length decimal coded wire tags and exposed to two levels of handling stress. The survival of marked individuals did not differ from that of unmarked individuals at either life stage for the duration of the experiment (56 d). Tag retention was 100% for all treatment combinations except larvae that were handled frequently (93 ± 3%). The majority of tag loss occurred within 28 d of marking, and no tag loss was observed between 42 and 56 d after marking. The individuals that lost tags were among the smallest marked, and a logistic regression model indicated a relationship between larva length and the probability of tag retention. Size of larvae (length and mass) and macrophthalmia (mass) decreased over the duration of the experiment; however, changes in size were systematic among treatment combinations, indicating that factors other than tagging or handling affected growth. These data indicate that coded wire tags may be useful for field‐based studies of Pacific lamprey larvae and macrophthalmia.

Molecular cloning, tissue distribution, and developmental expression of lamprey transthyretins

We isolated and cloned full-length cDNAs of transthyretin (TTR) from 2 genera of lamprey, Petromyzon marinus and Lampetra appendix. These sequences represent the first report of TTR sequences in vertebrates basal to teleost fishes. The deduced amino acid sequence of lamprey TTR cDNAs showed 36–47% identity with those from other vertebrates; secondary structure predictions and homology-based modeling were both consistent with TTRs from other vertebrates, and these cDNAs lacked the signatures found in TTR-like sequences of non-vertebrates. Of evolutionary interest is the observation that the N-termini of the lamprey TTR subunits are nine amino acids longer than those of eutherian TTRs and four to six amino acids longer than those from all other vertebrates. Sequencing of intron 1 confirmed that this longer N-terminal region is a result of the position of the intron 1/exon 2 splice site, further supporting previous studies. TTR mRNA was detected in a variety of larval lamprey tissues, with the highest levels found in the liver. TTR mRNA was also readily detected by Northern blotting, in the livers of animals at all phases of the lifecycle and was significantly elevated during metamorphosis. The upregulation of lamprey TTR gene expression during a major developmental event is consistent with observations in other vertebrates. In all other vertebrates studied to date, the transient upregulation of TTR gene expression or some other thyroid hormone distributor protein coincides with, and is thought to facilitate, the surge in serum thyroid hormone concentrations required for normal development. However, in lampreys, the upregulation of TTR gene expression occurs when serum thyroid hormone concentrations are at their lowest.

Glutamate regulates neurite outgrowth of cultured descending brain neurons from larval lamprey

In larval lamprey, descending brain neurons, which regenerate their axons following spinal cord injury, were isolated and examined in cell culture to identify some of the factors that regulate neurite outgrowth. Focal application of 5 mM or 25 mM L-glutamate to single growth cones inhibited outgrowth of the treated neurite, but other neurites from the same neuron were not inhibited, an effect that has not been well studied for neurons in other systems. Glutamate-induced inhibition of neurite outgrowth was abolished by 10 mM kynurenic acid. Application of high potassium media to growth cones inhibited neurite outgrowth, an effect that was blocked by 2 mM cobalt or 100 microM cadmium, suggesting that calcium influx via voltage-gated channels contributes to glutamate-induced regulation of neurite outgrowth. Application of glutamate to growth cones in the presence of 2 microM omega-conotoxin MVIIC (CTX) still inhibited neurite outgrowth, while CTX blocked high potassium-induced inhibition of neurite outgrowth. Thus, CTX blocked virtually all of the calcium influx resulting from depolarization. To our knowledge, this is the first direct demonstration that calcium influx via ligand-gated ion channels can contribute to regulation of neurite outgrowth. Finally, focal application of glutamate to the cell bodies of descending brain neurons inhibited outgrowth of multiple neurites from the same neuron, and this is the first demonstration that multiple neurites can be regulated in this fashion. Signaling mechanisms involving intracellular calcium, similar to those shown here, may be important for regulating axonal regeneration following spinal cord injury in the lamprey.

Developmental differences in neuromodulation and synaptic properties in the lamprey spinal cord

Functional properties in the spinal cord change during development to adapt motor outputs to differing behavioral requirements. Here, we have examined whether there are also developmental differences in spinal cord plasticity by comparing the neuromodulatory effects of substance P in the larval lamprey spinal cord with its previously characterized effects in premigratory adults.The premigratory adult effects of substance P were all significantly reduced in larvae. As the adult effects of substance P depend on the N-methyl-d-aspartate (NMDA)-dependent potentiation of glutamatergic synaptic transmission, we examined if the developmental differences in neuromodulation were associated with differences in synaptic properties. We found that the amplitude, rise time, and half-width of excitatory postsynaptic potentials (EPSPs) from excitatory network interneurons were all significantly reduced in larvae compared with adults. These differences were associated with a reduction in the NMDA component of larval EPSPs, an effect that could have contributed to the reduced modulatory effects of substance P in larvae. In contrast to glutamatergic inputs, the amplitude, rise time, and half-width of inhibitory postsynaptic potentials (IPSPs) from ipsilateral inhibitory interneurons were all significantly increased in larvae compared with adults. Substance P also potentiated larval IPSP amplitudes, an effect not seen in adults. This increase in inhibition contributed to the reduced effects of substance P in larvae, as premigratory adult-like modulation could be evoked when inhibition was blocked with strychnine.These results suggest that opposite developmental changes in excitatory and inhibitory synaptic transmission and their modulation are associated with developmental differences in spinal cord neuromodulation.

Larval lampreys possess a functional lateral line system

Morphology of larval lampreys' neuromasts was found to be very similar to that of adults. Activity in the lateral line nerve, elicited by a vibrating ball, indicated a functional lateralis system. Analysis revealed at least two populations of afferents, responding to opposite directions of water flow, with adapting responses. The response magnitude increased monotonically with stimulus amplitude. Larval lampreys' neuromasts were less sensitive than those of teleosts. At low frequencies the response showed a phase lead of 200-220 degrees with respect to the maximum of the ball displacement and a gain that was approximately linearly proportional to frequency.

Comparison of Larval Sea Lamprey Life History Characteristics in a Lampricide‐Treated Tributary and Untreated Tributary System of Lake Champlain

AbstractControl of sea lampreys Petromyzon marinus in Lake Champlain and the Laurentian Great Lakes is dependent primarily on selective lampricides that reduce the density of sea lamprey larvae in tributary streams. After lampricide treatment, recolonized larval sea lampreys may experience enhanced growth from density‐dependent factors, which may lead to transformation at a larger size and younger age than would have occurred before treatment. In this study, the effects of lampricide treatments on larval sea lamprey life history characteristics were compared between Lewis Creek (Vermont), a treated stream, at 4–5 years posttreatment and the untreated Pike River–Morpion Stream system (Quebec, Canada). Sea lamprey habitat was measured in each stream at approximately 100 randomly selected transects, and larval density was determined using a backpack electrofishing unit during 1999 and 2000. Larval sea lamprey density was approximately threefold higher in Lewis Creek than in the Pike River and Morpion Stream in both years. Growth measured in length and weight indicated that neither treatment nor low density created conditions for faster growth. During 1999, transformers were, on average, shorter and younger in Lewis Creek (131 mm; 100% age 4) than in the Pike River–Morpion Stream (143 mm; 100% age 5). During 2000, the majority (75%) of transformers were age 5 in all streams. Weights of age‐4 transformers in Lewis Creek (1999 and 2000) and the Pike River (2000) were higher than those of age‐4 ammocoetes in those streams. Our results suggest that the first year‐class to become reestablished after lampricide application may transform at a younger age and smaller size than fish of the same age‐class in an untreated stream. Treatment intervals must adapt to changes in age at transformation to prevent transformers from leaving Lake Champlain and Great Lakes tributaries.

Dispersal of sea lamprey larvae during early life: relevance for recruitment dynamics

Dispersal is an important early life history process that influences fish population dynamics and recruitment. We studied larval sea lamprey (Petromyzon marinus) dispersal by combining spatially explicit field sampling, genetic methods, and laboratory experiments to investigate how far sea lamprey larvae can disperse away from nests during their first growing season; subsequent dispersal by age 1 of sea lamprey; and the effect of density on larval dispersal. In two study streams sea lamprey larvae were observed to have moved >150 m downstream from the most likely source nest within 2–3 weeks of hatching. Conversely, randomization trials suggested that for both streams age 0 larvae were found closer to full siblings than would be expected if dispersal was not constrained by distance. Restricted dispersal was also observed for age 1 larvae in five streams, although for this age class full siblings were more commonly found to be separated by >1,000 m. Laboratory experiments indicated a significant effect of density on the movement of larval sea lamprey, with more larval movement at higher densities. Temperature also affected movement significantly, with reduced larval movements at cooler temperatures. Our findings suggest that larval sea lamprey dispersal is sufficient to minimize the likelihood of strong density-dependent effects on recruitment, even with large population sizes.

Densities and Habitat of American Brook Lamprey (Lampetra appendix) Larvae in Minnesota

At least one formerly large population of American brook lamprey (Lampetra appendix) has been extirpated in Minnesota, but little is known about the species in the state. We examined densities and age structures of American brook lamprey larvae in several streams in southeastern Minnesota. Mean densities of lamprey larvae in the best habitats available in 13 streams varied from 0.33–5.78 larvae/m2. Seven of nine streams examined had missing age classes of larvae, with five streams missing two or more classes. Habitat use and length–weight relationships of larvae were similar to those reported previously for this and other species of lamprey. Many L. appendix populations in Minnesota are healthy, but others are susceptible to extirpation because of low densities and multiple missing age classes. The current status of many of these populations, and their susceptibility to further disturbance, need to be more thoroughly examined to better assess the need for legal protection for the species in Minnesota.

Effects of preservation on pigmentation and length measurements in larval lampreys

The effects of two methods of preservation (fixation and storage in 10% formalin, and fixation in 10% formalin followed by storage in 95% alcohol) on pigmentation and morphometric features used for identification of larval Ichthyomyzon lampreys were analysed. Both short‐term (3 weeks) and long‐term (6 months) studies were conducted using digital analysis of images of fresh and preserved lampreys. Six standard morphometric lengths and 10 areas of pigmentation were analysed. All measurements were significantly affected by preservation. Preservative type affected pigmentation and morphometric characteristics differently, and characters were affected to different degrees. Multiple measurements over time showed that almost all changes occurred within 3 weeks of preservation. Regression equations allowed for accurate correction of preservation effects on morphometric measurements, but the effects on pigmentation levels were less predictable. Effects of preservation on larval lampreys need to be considered when comparing fresh and preserved specimens because they influence critical identification features.

Fluorogold labeling of descending brain neurons in larval lamprey does not cause cell death

In our previous double-labeling studies, the fluorescent anatomical tracers Fluorogold (FG) and Texas red dextran amine (TRDA) were used to demonstrate that descending brain neurons, ∼80% of which are reticulospinal (RS) neurons, in spinal cord-transected larval lamprey regenerate their axons. However, the numbers of FG-labeled descending brain neurons decreased significantly with increasing recovery times, from 2 to 16 weeks. For some FG-labeled mammalian neurons, FG appears to degrade and/or be lost over time, while in other neurons this tracer can kill neurons. In the present study, these possibilities were examined in larval lamprey for FG-labeled descending brain neurons. As in our previous studies, FG was applied to the spinal cord at 40% body length (BL, relative distance from the head) to retrogradely labeled descending brain neurons, and after recovery times of 2, 8, or 16 weeks, HRP, a non-toxic retrograde tracer, was applied to the spinal cord at 20% BL to determine if the numbers of HRP-labeled neurons were reduced. At these three recovery times, the numbers of HRP-labeled descending brain neurons were not significantly different than the numbers of HRP-labeled neurons in control animals that were not labeled with FG. Furthermore, the size and morphology of cell bodies and dendritic trees were not noticeably different in descending brain neurons with and without FG. Thus, in larval lamprey, FG does not appear to kill these neurons, but some FG probably is degraded and/or lost from neurons with increasing recovery times.

Detection of Uncured Visible Implant Elastomer Tags in Larval Pacific Lampreys

AbstractLampreys in the Columbia River basin are a conservation concern, and understanding their status is a priority among managers. Many population assessment techniques depend on the ability to tag fish so that these tags are retained for the duration of the study with minimal effect on survival. There are several methods for tagging small fishes in streams, including passive integrated transponders, coded wire tags, and visible implant elastomer (VIE) tags. Of these, VIE tags have not been extensively tested on larval or juvenile lampreys. We evaluated the performance of uncured VIE tags on ammocoetes of Pacific lampreys Lampetra tridentata in a laboratory experiment to determine tag detection and the influences of color and tag position on detection. Additionally, we examined the effects of transformation (ammocoete to macrophthalmia) on tag detection. Though survival was not specifically tested, 0 of the 84 lampreys died as a result of tagging. Tag detection was 87% after 168 d in lampreys that did not transform; in those that did transform, however, tag detection was reduced to 38%. Tag position did not affect detection, but red and orange tags were detected more consistently than green tags. Overall, uncured VIE tags can be used effectively to tag larval lampreys; however, studies that depend on long‐term tag detection either should be conducted at a time when lampreys are not expected to transform or should only use ammocoetes that are not likely to transform during the study.

Glutamate regulates neurite outgrowth of cultured descending brain neurons from larval lamprey

Glutamate regulates neurite outgrowth of cultured descending brain neurons from larval lamprey