Abstract
The organization of the serotonergic system, one of the most important neurotransmitter systems in the brain, has been carefully analyzed in most vertebrate groups, and major shared characteristics have been described, although traits particular to each vertebrate class have also been found. The present study is the first that provides a comprehensive and detailed map of the serotonergic structures in the brain of two representative species of lungfishes, the African lungfish (Protopterus dolloi) and the Australian lungfish (Neoceratodus forsteri), as revealed by immunohistochemistry against serotonin (5-HT). Lungfishes are currently considered the closest living relatives of tetrapods and represent an interesting group for the study of evolutionary traits in the transition from fishes to tetrapods. Distinct groups of serotonin immunoreactive cells were observed in the preoptic area, nucleus of the periventricular organ, pretectum, optic tectum and the long column of the raphe. Fiber labeling was widely distributed in all main brain subdivisions but was more abundant in regions such as the striatum, septum, amygdaloid complex, preoptic area, suprachiasmatic nucleus, lateral hypothalamic area, prethalamus, thalamus, mesencephalic tegmentum and rhombencephalic reticular formation. Comparison of these results with those from other classes of vertebrates highlights numerous common traits shared by most groups of fishes but also reveals that the serotonergic system in lungfishes largely resembles those of amphibians and other tetrapods.
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Abbreviations
- a:
-
Cerebellar auricle
- ac:
-
Anterior commissure
- aol:
-
Octavolateral area
- BST:
-
Bed nucleus of the stria terminalis
- cCb:
-
Corpus cerebelli
- Cbc:
-
Cerebellar commissure
- cc:
-
Central canal
- CeA:
-
Central amygdala
- D:
-
Dorsal part of the thalamus
- DCN:
-
Dorsal column nucleus
- DF:
-
Dorsal funiculus
- Dp:
-
Dorsal pallium
- E:
-
Epiphysis
- flm:
-
Fasciculus longitudinalis medialis
- fr:
-
Fasciculus retroflexus
- GCL:
-
Ganglion cell layer of the retina
- gl:
-
Glomerular layer of the olfactory bulb
- Hb:
-
Habenula
- hc:
-
Habenular commissure
- Hyp:
-
Hypophysis
- igl:
-
Internal granular layer of the olfactory bulb
- INL:
-
Inner nuclear layer of the retina
- Ip:
-
Interpeduncular nucleus
- IPL:
-
Inner plexiform layer of the retina
- Ipn:
-
Interpeduncular neuropile
- Is:
-
Isthmic nucleus
- Jc:
-
Juxtacommissural pretectal nucleus
- LA:
-
Lateral amygdala
- Lc:
-
Locus coeruleus
- LDT:
-
Laterodorsal tegmental nucleus
- LF:
-
Lateral funiculus
- lfb:
-
Lateral forebrain bundle
- Lp:
-
Lateral pallium
- Ls:
-
Lateral septum
- M:
-
Median part of the thalamus
- Ma:
-
Mammillary region
- MC:
-
Mauthner cell
- MCa:
-
Mauthner cell axon
- MeA:
-
Medial amygdala
- ml:
-
Mitral layer of the olfactory bulb
- Mp:
-
Medial pallium
- Mpd:
-
Dorsal part of the medial pallium
- Mpv:
-
Ventral part of the medial pallium
- Ms:
-
Medial septum
- nVII:
-
Facial nerve
- N.f:
-
Neoceratodus forsteri
- nlla:
-
Anterior nerve of the lateral line
- NPv:
-
Nucleus of the periventricular organ
- nso:
-
Spino-occipital nerve
- Nsol:
-
Nucleus of the solitary tract
- nX:
-
Vagal nerve
- ob:
-
Olfactory bulb
- oc:
-
Optic chiasm
- ONL:
-
Outer nuclear layer of the retina
- OT:
-
Optic tectum
- Pa:
-
Pallium
- PA:
-
Pallidum
- PC:
-
Purkinje cells of cerebellum
- Pc:
-
Precommissural pretectal nucleus
- P.d:
-
Protopterus dolloi
- p 1–3:
-
Prosomeres 1–3
- PO:
-
Preoptic area
- PT:
-
Pretectum
- PTh:
-
Prethalamus
- r 0–8:
-
Rhombomeres 0–8
- Rai:
-
Inferior raphe nucleus
- Ram:
-
Median raphe nucleus
- Ras:
-
Superior raphe nucleus
- Ri:
-
Inferior reticular nucleus
- RID:
-
Dorsal infundibular recesses
- RIDi:
-
Inferior dorsal infundibular recesses
- RM:
-
Retromammillary region
- Rm:
-
Median reticular nucleus
- Rs:
-
Superior reticular nucleus
- S:
-
Septum
- SC:
-
Suprachiasmatic nucleus
- sco:
-
Subcommissural organ
- sg:
-
Granular layer of the cerebellum
- sgc:
-
Stratum griseum centrale of the mesencephalic tectum
- sgp:
-
Stratum griseum periventriculare of the mesencephalic tectum
- Smn:
-
Somatomotor neurons of spinal cord
- sm:
-
Molecular layer of the cerebellum
- sn:
-
Superficial nucleus
- SN:
-
Substantia nigra
- so:
-
Spino-occipital motor nucleus
- sol:
-
Solitary tract
- sop:
-
Stratum opticum of the mesencephalic tectum
- SPa:
-
Subpallium
- SPV:
-
Supraoptoparaventricular nucleus
- Str:
-
Striatum
- Tegm:
-
Tegmentum
- Th:
-
Thalamus
- Tor:
-
Torus semicircularis
- TP:
-
Posterior tubercle
- Tub:
-
Tuberal hypothalamus
- V:
-
Ventral part of the thalamus
- v:
-
Ventricle
- VF:
-
Ventral funiculus
- VP:
-
Ventral pallium
- VTA/SN:
-
Ventral tegmental area/substantia nigra complex
- III:
-
Oculomotor nucleus
- IV:
-
Trochlear nucleus
- Vm:
-
Trigeminal motor nucleus
- VIIm:
-
Facial motor nucleus
- IXm:
-
Glossopharyngeal motor nucleus
- Xm:
-
Vagal motor nucleus
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Acknowledgments
We deeply thank Dr. Glenn R. Northcutt for providing the brains of Neoceratodus forsteri and for his continuous help and advise during many phases of the research. This research was supported by the Spanish Ministry of Science and Technology (Grant numbers: BFU2009-12315/BFI and BFU2012-31687).
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The authors declare that they have no conflict of interest.
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López, J.M., González, A. Comparative analysis of the serotonergic systems in the CNS of two lungfishes, Protopterus dolloi and Neoceratodus forsteri . Brain Struct Funct 220, 385–405 (2015). https://doi.org/10.1007/s00429-013-0661-0
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DOI: https://doi.org/10.1007/s00429-013-0661-0