Graphical Abstract Highlights d Most dopaminergic lamprey SNc/VTA neurons express glutamate d Individual co-expressing SNc/VTA neurons project to both striatum and optic tectum d SNc/VTA fibers in the striatum release both dopamine and glutamate d SNc/VTA fibers in the optic tectum release dopamine, but not glutamate erez-Ferná ndez Correspondence sten.grillner@ki.se In Brief von Twickel et al. show that most dopaminergic neurons in the lamprey SNc/VTA co-express glutamate and individual co-expressing neurons project to both the striatum and optic tectum.Remarkably, glutamate co-release is restricted to striatum, indicating differential neurotransmitter release depending on target area.

Whereas our understanding of the dopaminergic system in mammals allows for a distinction between ventral tegmental area (VTA) and substantia nigra pars compacta (SNc), no clear evidence for separate structures in anamniotes has been presented to date. To broaden the insight into the organization and regulation of neuromodulatory systems in anuran amphibians, tracing and immunohistochemical investigations were performed in the Oriental fire-bellied toad, Bombina orientalis. Topographically organized catecholaminergic "nigrostriatal," "mesolimbic," "mesocortical," and spinal cord projections arising from the posterior tubercle and mesencephalic tegmentum were identified. We compared these results with published data from lampreys, chondrichthyes, teleosts, amphibians, reptiles, birds, and mammals. Based on the pattern of organization, as well as the differential innervation by the habenular nuclei, domains gradually comparable to the mammalian paranigral VTA, ventral tier of the SNc, interfascicular nucleus of the VTA, and supramamillary/retromamillary area were identified. Additionally, we could demonstrate topographic separate populations of habenula neurons projecting via a direct excitatory or indirect GABAergic pathway onto the catecholaminergic VTA/SNc homologs and serotonergic raphe nuclei. The indirect GABAergic habenula pathway derives from neurons in the superficial mamillary area, which in terms of its connectivity and chemoarchitecture resembles the mammalian rostromedial tegmental nucleus. These results demonstrate a much more elaborate interconnection principle of the anuran dopaminergic system than previously assumed. Based on the data presented it seems that most features of the Abbreviations: Accnucleus of the ventral tegmental area; IP, interpeduncular nucleus; IR, infundibular recess; l.DlHb, left dorsolateral habenula; l.DmHb, left dorsomedial habenula; l.VHb, left ventral habenula; LHb, lateral habenula; Mam, mamillary area; med, medulla oblongata; MHb, medial habenula; NMLF, nucleus of the medial longitudinal fasciculus; NPv, nucleus of the periventricular organ; p.s., partial habenula septum; r, rostral; r.DHb, right dorsal habenula; r.VHb, right ventral habenula; RaCS, superior central raphe nucleus; RaD, dorsal raphe nucleus; RaM, nucleus raphe magnus; Rm, retromamillary area; RMTg, rostromedial tegmental nucleus; Sm, superficial mamillary area; SNc, substantia nigra pars compacta; SNr, substantia nigra pars reticulata; Str, striatum; TP, posterior tubercle; TPc, caudal part of the posterior tubercle; TPdl, dorsolateral nucleus of the posterior tubercle; TPdm, dorsomedial nucleus of the posterior tubercle; Tub, tuberomamillary nucleus; v, ventral; VH, ventral hypothalamus; VHb, ventral habenula; vMAM, ventral mamillary region; VTA, ventral tegmental area; VTApn, paranigral VTA; Zip, periventricular nucleus of the zona incerta.Wolfgang Walkowiak and Arndt von Twickel contributed equally to this work.

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Since the resolution of the ANA grade [Amborellales, Nymphaeales, Austrobaileyales] as sister to all other flowering plants, a few comparative studies of root structure have suggested that some of their anatomical traits could be of importance to understanding root evolutionary development and angiosperm phylogeny. However, there is still a paucity of information on root structure and apical meristems (RAMs) in these lineages and especially the sister to all other Austrobaileyales, Austrobaileya scandens. We used microtome sections and bright field, epifluorescence, laser confocal, and scanning electron microscopy to study adventitious root RAMs and tissues of A. scandens. Our results indicate that root structure is relatively simple in A. scandens. The epidermis has a thick cuticle and lacks root hairs. The stele is typically diarch, or some modification thereof, and surrounded by a cortex differentiated into a uniseriate endodermis, a middle region sometimes packed with starch, some oil cells, and colonized by arbuscular mycorrhizal fungi, and a multiseriate exodermis. Secondary growth produced many vessel elements in the secondary xylem and scattered sclerenchymatous fibers in secondary phloem. The absence of distinct patterning within the RAM and between the RAM and derivative differentiating tissues shows that the RAM is open and characterized by common initials. Roots structure and anatomy of A. scandens are thus essentially similar to some previously described in Amborella or Illicium in the ANA grade and many magnoliids, and suggest that the first woody flowering plants likely had an open RAM with common initials. Their functional and evolutionary significance in woody early-diverging and basal lineages of flowering plants and gymnosperms remains unclear, but they are clearly ancestral traits.

Recent comparative studies of billfishes (Istiophoridae and Xiphiidae) have provided evidence of differences in the form and function of the rostra (bill) among species.Here, we report the discovery of a new structure, lacuna rostralis, on the rostra of sailfish Istiophorus platypterus, which is absent on the rostra of swordfish Xiphias gladius, striped marlin Kajikia audax and blue marlin Makaira nigricans. The lacunae rostralis are small cavities that contain teeth. They were found on the ventral rostrum surface of all I. platypterus specimens examined and dorsally in half of them. Ventrally, the lacunae rostralis were most prominent in the mid-section of the rostrum. Dorsally, they occurred closer to the tip. The density of lacunae rostralis increased towards the rostrum tip but, because they are smaller in size, the percentage of rostrum coverage decreased. The teeth located within the lacunae rostralis were found to be different in size, location and orientation from the previously identified micro-teeth of billfish.We propose two potential functions of the lacunae rostralis that both relate to the use of the bill in feeding: mechanoreception of prey before tapping it with the bill and more efficient prey handling via the creation of suction, or physical grip.