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    870—Sensory Systems and Behavior

    Wednesday, November 13, 2013, 1:00 pm - 5:00 pm

    870.04: Avian magnetoreception: A putative map/signpost sense associated with the trigeminal system

    Location: Halls B-H

    ">*D. HEYERS1, D. KISHKINEV2, N. LEFELDT1, N. CHERNETSOV3, H. MOURITSEN1;
    1AG Neurosensorik, Carl-von-Ossietzky-Univ. Oldenburg, Oldenburg, Germany; 2Dep. of Integrative Biol., University Guelph, ON, Canada; 3Biol. Station Rybachy, Rybachy, Russian Federation

    Abstract Body: Numerous experiments have shown that birds can use the Earth´s magnetic field as a reference system for orientation. Behavioral experiments, supported in recent years by molecular biology, anatomy, chemical analyses and neurobiology, have given evidence for the existence of
    1) a magnetic "compass" sense associated with the visual system, probably providing directional information and
    2) a second magnetic sense with unknown biological function involving the ophthalmic branch of the trigeminal nerve (V1).
    Latter theory was based on the finding of iron-mineral-based structures in the upper beak, but has been seriously challenged by a study, suggesting that the previously described iron-accumulations are macrophages, not magnetosensitive nerve endings.
    Using behavioral molecular mapping, we could show that trigemino-recipient brainstem structures were activated when birds were exposed to strongly changing magnetic fields and that this activation significantly dropped when either the magnetic stimulus was removed or when V1 was ablated.
    Additionally, we could show that migratory birds were able to determine their position by compensating for a 1.000 km displacement through changing their migratory direction to reach their breeding grounds. These birds did not compensate for the displacement after sectioning V1.
    Although the nature and exact location of a putative magnetosensor associated with the trigeminal system remains elusive, V1 seems to innervate a magnetosensor. Furthermore, V1 seems to carry “map”-related information which migratory birds need to determine their approximate geographical position.

    Lay Language Summary: Nature´s GPS: a vision-based “compass” and a beak-based “map” in birds?
    Imagine being kidnapped and released again in the middle of nowhere. You better have two pieces of equipment in your pockets to navigate home: a “map” to determine your own position and a “compass” to set a direction accordingly.
    Could the Earth´s magnetic field provide these two types of information? Although migratory birds have been shown to use the Earth´s magnetic field for orientation on their fascinatingly precise journeys between breeding and wintering grounds, the question, how they sense and use it, is barely understood.
    Multidisciplinary research including chemical, biophysical, molecular and neurobiological approaches indicates at least two different sensory systems probably being involved in magnetoreception. A magnetic “compass” has been suggested to be associated with vision: when light hits a bird’s eye, light-sensitive molecules located in the retina, called “cryptochromes”, generate free radicals, i.e. molecules with unpaired electrons. Depending on the relative orientation of these sensor molecules to the magnetic field lines, the resulting amounts of radical pairs might modulate neuronal signals originating from the photoreceptors, thereby “translating” directional information into a visual pattern. On the brain level, recent studies suggest that magnetic compass information is processed in a visual fore-brain area called “Cluster N”. This brain structure, which has been shown to receive retinal input, shows strongly increased neuronal activation during magnetic compass orientation behavior and makes migratory birds, when inactivated, unable to use their magnetic compass: they go random!
    The upper beak was suggested to contain a second magnetosensor based on iron-rich cells linked to the trigeminal nerve. Although a new study identified most iron-rich cells in the upper beak as macrophages - immune not magnetosensitive cells, some studies nevertheless suggest that some kind of magnetoreceptor located in or near the upper beak does exist: by mapping brain activation following magnetic stimulation we could show that trigeminal hindbrain nuclei, which receive sensory information from the beak, show strong activation when birds were exposed to randomly changing magnetic fields. This activation significantly dropped when either the magnetic stimulus was removed or when the trigeminal nerve was cut. Thus, although the structure and exact location of the beak magnetoreceptor remains elusive, these results clearly suggest that the upper beak indeed contains a magnetosensor and that this information is transmitted through the trigeminal nerve. Might this magnetoreceptor be involved in a “map” sense?
    Whereas testing a compass sense has successfully been transferred to the lab, the investigation of a “map” sense bears multiple methodological problems. We established an experimental setup, in which we combined microsurgical approaches with a long-distance displacement: migratory birds caught on their spring migration in the Eastern Baltic were tested for their normal migratory direction which points towards northeast - their breeding grounds in southern scandinavia. Half of the birds underwent trigeminal nerve ablation, whereas in the other half the nerves were left intact. All birds were displaced 1.000 km eastward to Moscow region, now being southeast of their breeding grounds and tested for their migratory direction again. Whereas birds with intact trigeminal nerves changed their orientation towards northwest to adjust for the displacement in order to reach their breeding areas, the trigeminally ablated birds showed the same northeastern orientation as they were showing at the capture site: they did not notice the displacement! These data suggest that the trigeminal nerve carries map-related information, which migratory birds need to determine their own position.

    Information from Lay-Language Summaries is Embargoed Until the Conclusion of the Scientific Presentation

    870—Sensory Systems and Behavior

    Wednesday, November 13, 2013, 1:00 pm - 5:00 pm

    870.04: Avian magnetoreception: A putative map/signpost sense associated with the trigeminal system

    Location: Halls B-H

    ">*D. HEYERS1, D. KISHKINEV2, N. LEFELDT1, N. CHERNETSOV3, H. MOURITSEN1;
    1AG Neurosensorik, Carl-von-Ossietzky-Univ. Oldenburg, Oldenburg, Germany; 2Dep. of Integrative Biol., University Guelph, ON, Canada; 3Biol. Station Rybachy, Rybachy, Russian Federation

    Abstract Body: Numerous experiments have shown that birds can use the Earth´s magnetic field as a reference system for orientation. Behavioral experiments, supported in recent years by molecular biology, anatomy, chemical analyses and neurobiology, have given evidence for the existence of
    1) a magnetic "compass" sense associated with the visual system, probably providing directional information and
    2) a second magnetic sense with unknown biological function involving the ophthalmic branch of the trigeminal nerve (V1).
    Latter theory was based on the finding of iron-mineral-based structures in the upper beak, but has been seriously challenged by a study, suggesting that the previously described iron-accumulations are macrophages, not magnetosensitive nerve endings.
    Using behavioral molecular mapping, we could show that trigemino-recipient brainstem structures were activated when birds were exposed to strongly changing magnetic fields and that this activation significantly dropped when either the magnetic stimulus was removed or when V1 was ablated.
    Additionally, we could show that migratory birds were able to determine their position by compensating for a 1.000 km displacement through changing their migratory direction to reach their breeding grounds. These birds did not compensate for the displacement after sectioning V1.
    Although the nature and exact location of a putative magnetosensor associated with the trigeminal system remains elusive, V1 seems to innervate a magnetosensor. Furthermore, V1 seems to carry “map”-related information which migratory birds need to determine their approximate geographical position.

    Lay Language Summary: Nature´s GPS: a vision-based “compass” and a beak-based “map” in birds?
    Imagine being kidnapped and released again in the middle of nowhere. You better have two pieces of equipment in your pockets to navigate home: a “map” to determine your own position and a “compass” to set a direction accordingly.
    Could the Earth´s magnetic field provide these two types of information? Although migratory birds have been shown to use the Earth´s magnetic field for orientation on their fascinatingly precise journeys between breeding and wintering grounds, the question, how they sense and use it, is barely understood.
    Multidisciplinary research including chemical, biophysical, molecular and neurobiological approaches indicates at least two different sensory systems probably being involved in magnetoreception. A magnetic “compass” has been suggested to be associated with vision: when light hits a bird’s eye, light-sensitive molecules located in the retina, called “cryptochromes”, generate free radicals, i.e. molecules with unpaired electrons. Depending on the relative orientation of these sensor molecules to the magnetic field lines, the resulting amounts of radical pairs might modulate neuronal signals originating from the photoreceptors, thereby “translating” directional information into a visual pattern. On the brain level, recent studies suggest that magnetic compass information is processed in a visual fore-brain area called “Cluster N”. This brain structure, which has been shown to receive retinal input, shows strongly increased neuronal activation during magnetic compass orientation behavior and makes migratory birds, when inactivated, unable to use their magnetic compass: they go random!
    The upper beak was suggested to contain a second magnetosensor based on iron-rich cells linked to the trigeminal nerve. Although a new study identified most iron-rich cells in the upper beak as macrophages - immune not magnetosensitive cells, some studies nevertheless suggest that some kind of magnetoreceptor located in or near the upper beak does exist: by mapping brain activation following magnetic stimulation we could show that trigeminal hindbrain nuclei, which receive sensory information from the beak, show strong activation when birds were exposed to randomly changing magnetic fields. This activation significantly dropped when either the magnetic stimulus was removed or when the trigeminal nerve was cut. Thus, although the structure and exact location of the beak magnetoreceptor remains elusive, these results clearly suggest that the upper beak indeed contains a magnetosensor and that this information is transmitted through the trigeminal nerve. Might this magnetoreceptor be involved in a “map” sense?
    Whereas testing a compass sense has successfully been transferred to the lab, the investigation of a “map” sense bears multiple methodological problems. We established an experimental setup, in which we combined microsurgical approaches with a long-distance displacement: migratory birds caught on their spring migration in the Eastern Baltic were tested for their normal migratory direction which points towards northeast - their breeding grounds in southern scandinavia. Half of the birds underwent trigeminal nerve ablation, whereas in the other half the nerves were left intact. All birds were displaced 1.000 km eastward to Moscow region, now being southeast of their breeding grounds and tested for their migratory direction again. Whereas birds with intact trigeminal nerves changed their orientation towards northwest to adjust for the displacement in order to reach their breeding areas, the trigeminally ablated birds showed the same northeastern orientation as they were showing at the capture site: they did not notice the displacement! These data suggest that the trigeminal nerve carries map-related information, which migratory birds need to determine their own position.