Fiber Connections of the Corpus Mamillare in a Percomorph Teleost, Tilapia <i>Oreochromis niloticus</i>

Abstract

The hypothalamus and perhaps its function appear to be similar among vertebrates. Thus, studying the teleostean hypothalamus could be a good model for understanding common neural circuits and mechanisms retained through the vertebrates. However, connections of the inferior lobe, which is considered the hypothalamus in teleosts, is poorly known. The corpus mamillare (CM) is a nucleus of the inferior lobe named after the mammalian mamillary body based on similarities in external morphology. Afferent connections of the CM have been reported only in cypriniform teleosts. These include projections from the nucleus pretectalis superficialis pars magnocellularis, a nucleus lacking in percomorph teleosts, and projections from the secondary gustatory nucleus. Efferent connections of the CM have not been reported in teleosts. In the present study, the CM and its subdivisions and the connections of these subnuclei were identified in isolated and maintained brains of tilapia Oreochromis niloticus by local DiI and biocytin injection. Afferent connections confirmed by reciprocal injections were from the nucleus diffusus lobi inferioris (NDLI) and the nucleus diffusus tori lateralis (NDTL). Efferent connections of each CM subnuclei were also reciprocally confirmed. These connections were to the area dorsalis pars medialis of the telencephalon, the nucleus ventromedialis (NVM) of the thalamus, the tectum opticum (TO), and the nucleus posterioris periventricularis. Because the NDLI is known to receive gustatory information in tilapia, the CM could relay gustatory inputs to multisensory areas, the TO and NVM, for which there are no current reports regarding gustatory inputs.

Fiber Connections of the Nucleus isthmi in the Carp <i>(Cyprinus carpio)</i> and Tilapia <i>(Oreochromis niloticus)</i>

“…of these labeled neurons agreed with those of NR neurons in the filefish and tilapia [Shimizu et al, 1999;Sawai et al, 2000].…”

“…However, the present study clearly demonstrates that the percomorph NR and cyprinid NR project to the NI. The NR in both lineages is located in a similar area and projects to the optic tectum [Grover and Sharma, 1981;Luiten, 1981;Striedter and Northcutt, 1989;Shimizu et al, 1999;Sawai et al, 2000; present study]. All of these common features indicate that the cyprinid NR is not homologous to the percomorph NP but to the NR.…”

“…Our isthmic injections labeled somata of NR neurons in carp and tilapia, and axons of NR neurons that terminate in the SGC of the optic tectum were labeled only in the carp, but not in the tilapia. Tectal projections from the NR have been reported in percomorphs [Shimizu et al, 1999;Sawai et al, 2000]. Our isthmic injections in tilapia might have failed to label axon collaterals of NR neurons, or there might be two neuronal populations of percomorph NR, one of which projects to the NI and the other to the optic tectum.…”

Topographical Organization of an Indirect Telencephalo-Cerebellar Pathway through the Nucleus paracommissuralis in a Teleost, <i>Oreochromis niloticus</i>

“…The NPC of tilapia is quite well-developed, and the fish is thus a suitable animal for tracer injections to this nucleus. Also, connectional data of various brain regions have been accumulated in this species [Yoshimoto et al, 1998;Yamamoto et al, 1998;Sawai et al, 2000;Yamamoto and Ito, 2000;Xue et al, 2001], which would facilitate interpretations of results obtained in the present study. The fishes were obtained from commercial sources and maintained in aquaria at 26°C.…”

Can fish suffer?: perspectives on sentience, pain, fear and stress

“…The mammillary bodies and habenulae of tetrapods function in olfaction. Mammillary bodies may be represented in the fish brain, although their structural and functional limits are not clear (Sawai et al, 2000). The habenulae are better studied in fish (Bradford and Northcutt, 1983;Corrêa et al, 1998), and may contribute to several forebrain pathways, including those involved in olfaction (Yañez and Anadón, 1996).…”