Magnetic field changes activate the trigeminal brainstem complex in a migratory bird - PubMed (original) (raw)

Magnetic field changes induce ZENK activation in the trigeminal system. (A) Schematic illustration of the avian trigeminal sensory system; dorsal is up and anterior is left. Neuronal somata of all three branches of the trigeminal nerve are located in the trigeminal ganglion. Their afferents give rise to an ascending (TTA) and a descending tract (TTD), which terminate in PrV and SpV, respectively. (B) Quantification of ZENK activated neurons (black spots in D–F and L–N) in PrV, the optic tectum, and in medial and lateral SpV. Sham-sectioned birds experiencing changing magnetic field (CMF) conditions are shown in red; sham-sectioned birds experiencing zero magnetic field (ZMF) conditions are shown in green; and birds with sectioned V1 experiencing CMF conditions are shown in blue. **P < 0.01, ns, no significant difference. (C–F) Frontal brain sections show strongly increased nuclear ZENK expression in PrV, particularly in a crescent-shaped structure ventral (to) PrV, when the birds experienced CMF conditions and were tested with an intact ophthalmic branch of the trigeminal nerve (V1) (D). This activation disappeared when the magnetic field stimuli was removed in birds with an intact V1 (E) and in birds experiencing the CMF condition when V1 was cut (F). (G–N) Frontal brain sections through SpV at the level of the vestibulo-cochlear nerve (N. VIII) also show strongly increased ZENK expression in medial (SpVm) but not in lateral (SpVl) parts of SpV in birds with an intact ophthalmic nerve experiencing CMF conditions compared with the other two conditions. (H–J) Schematic illustration (original data supplied as

Fig. S1

) of ZENK expressing neurons (red dots). (K–N) Magnified detail of SpV (original data; black spots are ZENK-positive neurons). Quantified areas are encircled in red (D, H, and L; sham-sectioned, CMF), green (E, I, and M; sham-sectioned, ZMF), and blue (F, J, and N; V1-sectioned, CMF). Acetylcholinestarase (AChE) activity (C, G, and K) helped to define anatomical boundaries. (Scale bars, 200 μm.) Cb, cerebellum; LSO, lateral superior olivary nucleus; mlf, medial longitudinal fascicle; N.V, trigeminal nerve; N.VIII, vestibulo-cochlear nerve; OT, optic tectum; PrV, principal sensory nucleus of the trigeminal nerve; Rt, reticular formation; SpVl/m, spinal trigeminal nucleus, lateral/medial portion; Tel, telencephalon; TTA, ascending branch of the sensory trigeminal tract; TTD, descending branch of the sensory trigeminal tract; vPrV, ventral (to) PrV; XC, cochlear decussation.