Elsevier

Neuroscience

Volume 124, Issue 4, 2004, Pages 973-984
Neuroscience

Functional organization of preoptic vasotocin and isotocin neurons in the brain of rainbow trout: central and neurohypophysial projections of single neurons

https://doi.org/10.1016/j.neuroscience.2003.12.038Get rights and content

Abstract

Preoptic magnocellular neurosecretory cells (NSCs) in the brain of rainbow trout show synchronization of periodic Ca2+ pulses, patterns of which differ between vasotocin (VT) and isotocin (IT) neurons. To provide neuroanatomical bases of the synchronized periodic Ca2+ pulses and their biological implications, we examined the organization of preoptic VT and IT neurons in the brain of rainbow trout. The cytoarchitecture of the preoptic neurosecretory system was characterized by a confocal double-color immunofluorescence. Two to five VT neurons, and also IT neurons, aggregate to form cell-type specific clusters. VT clusters tend to localize medially, while IT clusters laterally. VT neurons are closely apposed at the proximal neuronal processes. A Golgi-like immunohistochemistry demonstrated that VT and IT fibers distribute widely in the brain, such as ventral telencephalon, diencephalon, and various mesencephalic structures, in addition to the neurohypophysial projections. Projections from single VT and IT neurons were examined by an intracellular staining with biocytin injection in a sagittally hemisected brain preparation, which contains the entire forebrain region. Single VT and IT neurons project toward the pituitary and the extrahypothalamic regions. Some IT neurons, but not VT neurons, were dye-coupled. These results support the idea that the same types of NSCs are connected to form cell-type-specific networks responsible for the synchronization of periodic Ca2+ pulses. The organization of the preoptic neurosecretory system shown in the present study is suitable for the simultaneous control of neurohypophysial and extrahypothalamic outputs through the synchronization of electrical activity.

Section snippets

Animals

Immature rainbow trout (Oncorhynchus mykiss; fork length 17–19 cm, body weight 50–70 g) were obtained from a commercial source (Sapporo Nijimasu Co. Ltd., Sapporo, Japan), and were maintained in a 0.5 ton circular tank (100 cm in diameter and 80 cm in depth) at 15 °C under 12-h light/dark photoperiod for more than a week. Animals were obtained in July, October, and December. Four fish were used for the double color immunofluorescence and two fish for the Golgi-like immunohistochemistry. All

Organization of the preoptic vt and it neurons

A confocal image of the hemisected brain viewed from the ventricular side illustrates an overall sagittal aspect of preoptic NSCs that expand two-dimensionally beneath the ependymal layer (Fig. 1A). NSCs form a paired nucleus located very close to the third ventricle. NSCs that occupy the dorsocaudal portion of the preoptic area comprise the magnocellular preoptic nucleus (PM). The ventrolateral portion of the mass of NSCs comprises the anterior parvocellular part of the preoptic region (PPa).

Discussion

In the present study, we clarified the neuroanatomical organization of the preoptic neurosecretory system in a teleost model using a combination of immunohistochemical and intracellular staining methods. Confocal double immunofluorescence characterized the cytoarchitecture of the PM, that is, (1) clustering of the same types of NSCs, (2) medial localization of VT clusters and lateral localization of IT clusters, and (3) contact among VT neurons at the proximal processes. Golgi-like

Acknowledgements

We thank E. Ito and H. Ando for helpful advice. This work was supported by grants-in-aid for Scientific Research and for JSPS Fellows of the Ministry of Education, Culture, Sports, Science, and Technology of Japan.

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