Strike feeding behavior in the muskellunge, Esox masquinongy: contributions of the lateral line and visual sensory systems.

The muskellunge, Esox masquinongy, is a predatory esocid fish with well-developed visual and lateral line systems. The purpose of this study was to determine the relative roles of these two sensory modalities in organizing the strike behavior of the animal. Subadult muskellunge were videotaped in a test arena while feeding on fathead minnows (Pimephales promelas). Animals were tested under five conditions: (i) control animals in which the visual and lateral line systems were intact; (ii) animals with lateral line afference suppressed by immersion for 12-24 h in 0.1 mmol l(-1) CoCl2; (iii) animals blinded by bilateral optic nerve transection; (iv) animals that had been unilaterally blinded; and (v) animals in which the lateral line system had been unilaterally denervated. The feeding behavior of the muskellunge consists of two phases: a slow stalk of the prey with minimal body movement followed by an explosive C- or S-start lunge at the prey. Quantitative comparisons of animals in the five test groups indicate that, although vision is used in the initial acquisition of the prey, both vision and the lateral line system play important roles in determining the initiation of the rapid strike. The lateral line system may play a critical role in the final capture of the prey at the end of the strike. In addition, lateral-line-suppressed muskellunge strongly alter their approaches to more distant prey. Bilaterally blinded muskellunge do not stalk their prey, but will lunge only at prey that are at close range. Unilaterally blinded or denervated muskellunge also alter their detection of and approach to prey, attending to a wider region of the intact sensory hemisphere. Our data suggest not only that the visual and lateral line systems play complementary roles in the feeding behavior sequence but also that each system plays a more or less dominant role during consecutive phases of the behavior.

Multimodal sensory integration in the strike-feeding behaviour of predatory fishes.

The search for useful model systems for the study of sensory processing in vertebrate nervous systems has resulted in many neuroethological studies investigating the roles played by a single sensory modality in a given behaviour. However, behaviours relying solely upon information from one sensory modality are relatively rare. Animals behaving in a complex, three-dimensional environment receive a large amount of information from external and internal receptor arrays. Clearly, the integration of sensory afference arising from different modalities into a coherent 'gestalt' of the world is essential to the behaviours of most animals. In the last several years our laboratory team has examined the roles played by the visual and lateral line sensory systems in organizing the feeding behaviour of two species of predatory teleost fishes, the largemouth bass, Micropterus salmoides, and the muskellunge, Esox masquinongy. The free-field feeding behaviours of these fishes were studied quantitatively in intact animals and compared to animals in which the lateral line and visual systems had been selectively suppressed. All groups of animals continued to feed successfully, but significant differences were observed between each experimental group, providing strong clues as to the relative role played by each sensory system in the organization of the behaviour. Furthermore, significant differences exist between the two species. The differences in behaviour resulting when an animal is deprived of a given sensory modality reflect the nature of central integrative sensory processes, and these behavioural studies provide a foundation for further neuroanatomical and physiological studies of sensory integration in the vertebrate central nervous system.

Reasons for relinquishment of companion animals in U.S. animal shelters: selected health and personal issues.

In personal interviews, people surrendering their dogs and cats to 12 animal shelters in 4 regions of the country discussed their reasons for relinquishing their companion animals and answered questions about their own characteristics and those of their pet. The interviews identified 71 reasons for relinquishment. Personal issues lead the class of reasons for relinquishment of cats and ranked 3rd among those given for relinquishment of dogs. The top 3 health and personal issues cited for giving up cats were allergies of a family member to cats, owner's personal problems, and anew baby. For dogs, the top 3 reasons cited were lack of time for the dog, owner's personal problems, and allergies. Analysis of these health and personal issues suggests that education and counseling before and after acquisition of a pet, as well as the availability of temporary accommodations for pets during times of personal crisis, may reduce relinquishments.

Descending neural projections to the spinal cord in the channel catfish, Ictalurus punctatus.

Retrograde transport of horseradish peroxidase was used to determine the descending projections to the spinal cord in an otophysan fish, the channel catfish, Ictalurus punctatus. The majority of cells projecting to the spinal cord are located in the reticular formation, which is organized into rhombomeric segments. Vestibulospinal neurons are located in the descending, magnocellular, and tangential octaval nuclei, as well as in the medial octavolateralis nucleus of the lateral line system. Cells in the facial lobe project to the spinal cord. Additionally, axons of cells of the trigeminal system and the nucleus of the lateral lemniscus project caudally into the spinal cord. In the midbrain, descending spinal projections arise from cells of the medial longitudinal fasciculus and the red nucleus. More rostrally, cells of the ventrolateral thalamus, dorsal periventricular hypothalamus, central pretectal and magnocellular preoptic nuclei also project to the cord. The results of this study indicate that there are a number of homologies in the descending systems of bony fishes and other vertebrate taxa, including tetrapods. We also provide further evidence that a red nucleus is present in the brains of bony fishes and is therefore a primitive vertebrate character antedating the evolution of tetrapods.

Afferent and efferent connections of nucleus praeeminentialis in the channel catfish: a reevaluation.

Nucleus praeeminentialis (nPr) is an isthmic nucleus that has been described in the brains of electrosensory teleost fishes and a single non-electrosensory species. The nucleus receives axon collaterals of ascending medullary sensory lemniscal neurons. Axons of nPr neurons project in turn back down onto those same populations of medullary projection neurons via a descending parallel fiber system (the molecular layer or cerebellar crest). Thus nPr forms a link in a sensory feedback loop that modulates the activity of neurons that relay information from medulla to midbrain. The purpose of this study is to investigate the nature of the afferent and efferent connections of the nPr with the specific aim of investigating other sources of input into this modulatory circuit. Transport of neuronal tracers (horseradish peroxidase, DiI and dextran amines) revealed that nPr has extensive interconnections with nuclei in the basal metencephalon, cerebellum, octavolateralis column and basal medulla. A previously described source of afference, the torus semicircularis in the mesencephalon, was not indicated by our studies. Our studies suggest that in addition to regulating the sensitivity and resolution of electrosensory and mechanosensory lateral line systems, the nPr may play a role in the resolution of signal ambiguities posed by auditory or vestibular stimulation of the saccular endorgan of the inner ear.

Sensitivity and response dynamics of elasmobranch electrosensory primary afferent neurons to near threshold fields.

Elasmobranch fishes localize weak electric sources at field intensities of < 5 eta V cm-1, but the response dynamics of electrosensory primary afferent neurons to near threshold stimuli in situ are not well characterized. Electrosensory primary afferents in the round stingray, Urolophus halleri, have a relatively high discharge rate, a regular discharge pattern and entrain to 1-Hz sinusoidal peak electric field gradients of < or = 20 eta V cm-1. Peak neural discharge for units increases as a non-linear function of stimulus intensity, and unit sensitivity (gain) decreases as stimulus intensity increases. Average peak rate-intensity encoding is commonly lost when peak spike rate approximately doubles that of resting, and for many units occurs at intensities < 1 microV cm-1. Best neural sensitivity for nearly all units is at 1-2 Hz with a low-frequency slope of 8 dB/decade and a high-frequency slope of -23 dB/decade. The response characteristics of stingray electrosensory primary afferents indicate sensory adaptations for detection of extremely weak phasic fields near 1-2 Hz. We argue that these properties reflect evolutionary adaptations in elasmobranch fishes to enhance detection of prey, communication and social interactions, and possibly electric-mediated geomagnetic orientation.

Human and animal factors related to relinquishment of dogs and cats in 12 selected animal shelters in the United States.

Since the 1940s, perceived companion animal overpopulation in the United States has been an important issue to the animal welfare community (Moulton, Wright, & Rinky, 1991). This surplus of animals has resulted in millions of dogs and cats being euthanized annually in animal shelters across the country. The nature and scope of this problem have been notoriously difficult to characterize. The number of animal shelters in the United Stares, the demographics of the population of animals passing through them, and the characteristics of per owners relinquishing animals are poorly understood. What portion of these animals are adopted or euthanized, why they are relinquished, and their source of acquisition are all questions for which there have been little data. Consequently, we are no closer to answering the fundamental question of how and why many animals are destroyed each year in shelters (Arkow, 1994).

The evolution of vertebrate electrosensory systems.

Sensory systems that detect weak electric fields initially evolved as a primitive vertebrate character and have subsequently been lost and 're-evolved' a number of times in various taxa. As such, they provide unique examples of evolutionary parallelism and convergence in vertebrate sensory systems. Electrosensory systems have additionally proven to be admirable models for investigating the fundamental strategies by which nervous systems interpret environmental signals as the basis for organizing behaviors.

Cytoarchitecture of the medial octavolateralis nucleus in the goldfish, Carassius auratus.

The medial octavolateralis nucleus (MON) is the principal first-order medullary lateral line sensory nucleus found in the majority of anamniotic vertebrates. Although its presence has been confirmed in numerous taxa, the cytoarchitecture of this region has not been extensively studied in any species. The purpose of this study was to examine in detail the cytoarchitecture of the MON in the goldfish using Golgi staining and HRP histochemical techniques. The results of this study demonstrated the presence of a number of cell types with distinct cellular morphologies, several of which strongly resemble those described in octavolateralis nuclei dedicated to audition and electroreception. The most prominent of these MON neurons included crest cells of two varieties, either possessing or lacking basilar dendrites. Additionally, we described stellate and cristal interneurons and granule-like cells in the molecular layer, and lateral interneurons and granule-like neurons in deeper MON layers. These morphological similarities together with similarities in functional organization, and the probable close phyletic relationships of this "family" of hair cell sensory systems, argue for parallels in mechanisms of sensory processing and analysis in strongly divergent sensory modalities.

Electric organ discharge and electrosensory reafference in skates.

Skates possess bilateral electric organs that produce intermittent, weak discharges of relatively long duration compared to the discharges of other weakly electric fish. They, like all elasmobranchs, also have an electrosensory system capable of detecting weak, low-frequency electric fields. Several studies have suggested that the discharge is used in some type of social communication. This study measured the strength and nature of the response of the skate electrosensory system to electric organ discharge. Electric organ discharge (EOD) was elicited via electrical stimulation of the medullary command nucleus in two species of skates. The temporal structure and power spectra of the EODs demonstrated that they should be effective stimuli for the skate electrosensory system. The responses of electrosensory afferent fibers in the anterior lateral line nerve (ALLN) to EODs were variable depending upon the location and orientation of the receptor. The responses of most ALLN fibers were very weak compared to the strong reafference produced by the skate's ventilatory activity. Unlike the common-mode ventilatory reafference, EOD reafference was variable in terms of excitation or inhibition, depending upon receptor orientation. Despite the low signal-to-noise ratio observed in ALLN responses to EODs, it is likely that EODs serve as a communicative signal over moderate distances.

Central topography of anterior lateral line nerve projections in the channel catfish, Ictalurus punctatus.

Electroreception evolved in the catfishes probably as a specialization of the mechanosensory lateral line system. Fibers of the anterior lateral line nerve in catfishes innervate electrosensory ampullary organs and mechanosensory neuromasts of the head lateral line system. The purpose of this study is to determine the projection patterns of the major principal branches of the ALLN and to investigate the topography within the various nuclei of the terminal fields of these different branches. Fibers of the superficial ophthalmic, buccal and hyomandibular branches of the anterior lateral line nerve terminate in a somatotopic fashion within medullary and cerebellar nuclei. These fibers project to, and terminate within, several discrete nuclei in the medulla and cerebellum, notably the electrosensory lateral line lobe, the medial and caudal octavolateralis nuclei, and portions of a nuclear complex in the cerebellum called the eminentia granularis. Furthermore, the dorsoventral somatotopy in the medullary electrosensory nucleus is a reversed or 'mirror' image of that in the mechanosensory nucleus. This reversed map is similar to that observed in other electrosensory systems and suggests that there may be a common mechanism for the copying and preservation of spatial information as new systems are evolved from primitive sensory pathways.

Event-related potentials in the retina and optic tectum of fish.

1. Compound field potentials were recorded with up to 18 microelectrodes in comb, brush, or spear arrays on and in the optic tectum and with suction electrodes from the distal stump of the cut optic nerve and from the optic nerve head in the opened eye in elasmobranchs and teleosts. Diffuse light flashes of different durations and submaximal intensities were delivered in trains with regular or irregular interstimulus intervals (ISI). 2. Event-related potentials (ERPs) are visible in single trials and begin at 50-200 ms after an "oddball" flash, especially one that is slightly weaker, briefer, or delayed by as little as 6% of ISI, compared with the more frequent stimulus. ERPs to the opposite condition are not of the same form or size. 3. One or more stimuli were omitted from a train or the train terminated after various conditioning times. Deflections occur beyond the expected visual-evoked potentials (VEPs) to the last flash and are called omitted-stimulus potentials (OSPs). They occur on schedule--approximately 100 ms after the next flash would be due--almost independent of intensity, duration, or conditioning time. They are considered to be ERPs without any necessary implication or denial of a temporally specific expectation. 4. Three components of OSP occur alone or in combination: an initial fast peak, a slow wave, and an oscillatory spindle up to ls or more in duration. This resembles the OFF response to steady light. 5. All these components are already present in the retina with optic nerve cut. 6. The same mean ISI with a high proportion of jitter gives OSPs with only slightly longer latencies and smaller amplitudes; the OSP acts as though the retina makes an integrated prediction of ISI, intensity, and duration. 7. During a conditioning train the equilibrium between excitation and inhibition after each flash changes according to frequency, intensity, duration, and conditioning time; the VEP reflects this in a shape unique to the ISI; inhibition increases rapidly after each flash and then decays slowly according to the recent mean ISI. This allows rebound disinhibition after missing, weak, or delayed flashes (OSP or ERP) or causes an altered VEP after a longer or stronger oddball. 8. It seems unlikely that the OSP or oddball ERP in fish tectum is equivalent to mammalian ERPs under the same regime or signals higher cognitive events, because they are already present in the retina, require flash frequencies greater than 1 Hz, and grow with frequency up to and beyond flicker fusion.(ABSTRACT TRUNCATED AT 400 WORDS)

Medullary electrosensory processing in the little skate. I. Response characteristics of neurons in the dorsal octavolateralis nucleus.

1. Ampullary electroreceptors in elasmobranchs are innervated by fibers of the ALLN, which projects to the dorsal octavolateralis nucleus (DON). The purpose of this study is to examine the response characteristics of ALLN fibers and DON neurons to weak D.C. and sinusoidal electric field stimuli presented as local dipole fields. 2. ALLN fibers respond to presentation of D.C. fields with a phasic burst, followed by a more slowly adapting period of firing. Ascending efferent neurons (AENs) in the DON respond to stimuli with a similar initial burst, which adapts more quickly. 3. Type 1, 2, and 3 neurons are possible local interneurons or commissural DON neurons. Type 1 neurons demonstrate response properties similar to those of AENs. Type 2 cells demonstrated slowly adapting responses to excitatory stimuli, the duration of the response increased with the amplitude of the stimulus. Type 3 neurons demonstrated an increased rate of firing, but the response lacked any specific temporal characteristics. 4. ALLN fibers typically have receptive fields consisting of a single ampulla. The receptive field sizes of DON neurons exhibited varying degrees of convergence for different cell types. 5. Responses of ALLN fibers and DON neurons to weak sinusoidal stimuli demonstrated very similar frequency response characteristics for all cell types. The peak sensitivity of electrosensory neurons was between 5-10 Hz.

Medullary electrosensory processing in the little skate. II. Suppression of self-generated electrosensory interference during respiration.

1. Previous studies have demonstrated that the resting activity of electrosensory ALLN fibers is modulated by the animal's own respiratory activity and that all fibers innervating a single ampullary cluster are modulated with the same amplitude and phase relationship to ventilation. We demonstrate that ALLN fibers in the skate are modulated in this common-mode manner bilaterally, regardless of receptor group, orientation, or position of the receptor pore on the body surface (Fig. 2). 2. Ascending efferent neurons (AENs), which project to the electrosensory midbrain from the DON, are modulated through a much smaller portion of their dynamic range. AENs give larger responses to an extrinsic local electric field than to the respiratory driving, indicating that a mechanism exists for suppressing ventilatory electrosensory reafference. 3. In paralyzed animals no modulation of resting activity or of responses of extrinsic electric fields could be observed with respect to the animal's respiratory motor commands in the absence of electrosensory reafference. 4. Cells of the dorsal granular ridge (DGR) project to medullary AENs via the DON molecular layer. A majority of proprioceptive DGR neurons are modulated by ventilatory activity, however, in a given fish the modulation is not in the same phase relationship to ventilation among DGR units. 5. The modulation of AENs during respiration was increased following transection of the contralateral ALLN (Fig. 9). Resting activity and responses to excitatory stimuli were inhibited by simultaneous stimulation of the transected contralateral ALLN indicating that a common-mode rejection mechanism is mediated via the commissural interconnections of the DONs.

Dynamic properties of visual evoked potentials in the tectum of cartilaginous and bony fishes, with neuroethological implications.

We have extended the study of Bullock ('84), who reported on visually evoked potentials (VEP) in the tectum of 10 species of elasmobranchs, by adding further stimulus regimes, multichannel recording, and additional taxa, particularly addressing the question of flicker fusion frequency by electrophysiological signs in central processing centers. Using principally the guitarfish, Platyrhinoidis and Rhinobatos, and the bass, Paralabrax, with some additional data from 32 other species, the findings support the following conclusions: 1. Latency of the first main VEP peak, a sharp surface negativity, to a diffuse white flash of submaximal intensity while the eye is moderately light adapted varies from less than 20 ms in some teleosts to greater than 120 ms in agnathans, holocephalans, and some rays. Among the elasmobranchs tested, the sharks are generally faster than the rays. Among the teleosts tested, some species are at least three times slower than others. There is little overlap between the fastest elasmobranchs and the slowest teleosts. 2. After the first VEP peak, later components are more diverse than the classic descriptions of one late surface-negative hump; they may include also sharp peaks, slow humps, and oscillatory waves extending out to greater than 1 s postflash. These are highly labile, variable and similar to OFF responses after a long light pulse. All these components occur already in the retina, whether the optic nerve is intact or cut. Many records do not show the late components; in the same preparation, some tectal loci may and others may not. 3. Ongoing activity (the micro-EEG, over all frequency bands) is depressed between early and late waves after a flash as well as during a long light pulse. 4. Repeated flashes above a few per second do not so much cause fatigue of the VEPs as reduce or prevent them by a sustained inhibition; large late waves are released as a rebound excitation any time the train of flashes stops or is delayed or sufficiently weakened. 5. Repeated flashes depress first the early waves; later waves follow 1:1 up to an upper following frequency (UFF) of approximately 13 Hz in the guitarfishes at optimal intensity and light adaptation (15-17 degrees C). A transition zone of gradual fusion from 15 to 30 Hz is marked by sputtering or irregular sharp VEPs; above a lower fusion frequency (LFF) of 30-40 Hz, the flash train becomes equivalent to steady light.(ABSTRACT TRUNCATED AT 400 WORDS)

Segregation of electroreceptive and mechanoreceptive lateral line afferents in the hindbrain of chondrostean fishes.

The anterior lateral line nerve (ALLN) in the chondrostean fishes (sturgeon and paddlefishes) consists of both fibers innervating ampullary electroreceptors and fibers innervating the mechanoreceptive neuromasts of the cephalic lateral line system. The fibers of the posterior lateral line nerve (PLLN) innervate only mechanoreceptive neuromasts on the body trunk. The ALLN enters the medulla via dorsal and ventral roots; the dorsal root projects to the dorsal octavolateralis nucleus (DON), whereas the ventral root and the PLLN project principally to the medial octavolateralis nucleus (MON). Previous studies in elasmobranchs have demonstrated that fibers of the dorsal root of the ALLN convey electrosensory information, and fibers of the ventral root are concerned with mechanoreceptive information. Electrophysiological and neuroanatomical methods are employed in this study in order to determine if there exists a similar segregation of electroreceptive and mechanoreceptive lateral line afferents within the chondrostean medulla. In specimens of shovelnose, Scaphirhynchus platorynchus, and Atlantic sturgeon, Acipenser oxyrhynchus, and paddlefish, Polyodon spathula, evoked potentials recorded from the hindbrain and elicited by electric fields reached maximum amplitude within the DON and decreased in amplitude through the cerebellar crest. Evoked potentials elicited by stimulation of the posterior lateral line nerve achieved maximum amplitude within the MON. Single and multiple unit recordings revealed that units within the DON responded only to electric field stimulation, whereas units recorded in the MON responded only to mechanical stimulation. Horseradish peroxidase implanted beneath isolated patches of ampullae in Polyodon revealed fibers innervating electroreceptors projecting to the DON via the dorsal root of the ALLN. These results demonstrate a segregation of electroreceptive and mechanoreceptive lateral line afferent fibers in the chondrostean hindbrain, similar to that seen in elasmobranchs. This supports the contention that the electrosensory systems of elasmobranchs and chondrosteans are homologous, and are derived from the common ancestor of elasmobranch and actinopterygian fishes.

Primary projections of the trigeminal nerve in two species of sturgeon: Acipenser oxyrhynchus and Scaphirhynchus platorynchus.

Horseradish peroxidase histochemical studies of afferent and efferent projections of the trigeminal nerve in two species of chondrostean fishes revealed medial, descending and ascending projections. Entering fibers of the trigeminal sensory root project medially to terminate in the medial trigeminal nucleus, located along the medial wall of the rostral medulla. Other entering sensory fibers turn caudally within the medulla, forming the trigeminal spinal tract, and terminate within the descending trigeminal nucleus. The descending trigeminal nucleus consists of dorsal (DTNd) and ventral (DTNv) components. Fibers of the trigeminal spinal tract descend through the lateral alar medulla and into the dorsolateral cervical spinal cord. Fibers exit the spinal tract throughout its length, projecting to the ventral descending trigeminal nucleus (DTNv) in the medulla and to the funicular nucleus at the obex. Retrograde transport of HRP through sensory root fibers also revealed an ascending bundle of fibers that constitutes the neurites of the mesencephalic trigeminal nucleus, cell bodies of which are located in the rostral optic tectum. Retrograde transport of HRP through motor root fibers labeled ipsilateral cells of the trigeminal motor nucleus, located in the rostral branchiomeric motor column.

Central projections of the lateral line nerves in the shovelnose sturgeon.

Primary projections of the anterior ( ALLN ) and posterior ( PLLN ) lateral line nerves were traced in the shovelnose sturgeon by means of horseradish peroxidase (HRP) histochemistry and silver degeneration. The trunk of the ALLN divides into dorsal and ventral roots as it enters the medulla. Fibers of the dorsal root form ascending and descending branches that terminate within the ipsilateral dorsal octavolateralis nucleus and the dorsal granular component of the lateral eminentia granularis. Fibers of the ventral root of the ALLN , as well as fibers of the PLLN , enter the medulla ventral to the dorsal root of the ALLN where some of the fibers terminate among the dendrites of the magnocellular octaval nucleus. The bulk of the fibers form ascending and descending branches that terminate within the ipsilateral medial octavolateralis nucleus. A portion of the ascending fibers continue more rostrally and terminate in the ipsilateral eminentia granularis and bilaterally in the cerebellar corpus. Some fibers of the descending rami of both the ALLN and PLLN extend beyond the caudal limit of the medial octavolateralis nucleus to terminate in the caudal octavolateralis nucleus. The HRP cases also revealed retrogradely filled large neurons whose axons course peripherally in the lateral line nerve and are likely efferent to the lateral line organs.