Nitric oxide synthase in the hypothalamic paraventricular nucleus of the female rat; organization of spinal projections and coexistence with oxytocin or vasopressin

doi:10.1016/S0006-8993(01)02539-2

Brain Research

Volume 908, Issue 1, 10 July 2001, Pages 10-24

https://doi.org/10.1016/S0006-8993(01)02539-2 Get rights and content

Abstract

We investigated the distributions and interrelations of neuronal nitric oxide (NO) synthase- (nNOS), oxytocin- (OT), and 8-arginine vasopressin- (AVP) immunoreactive (IR) neurons in the paraventricular nucleus (PVN), and the occurrence and distribution of nNOS spinally projecting neurons in the PVN of the female rat. Using double labelling immunohistochemistry, we mapped the distribution of nNOS-, OT- and AVP-immunoreactive (IR) neuronal cell bodies in the different parts of the PVN. About 80% of nNOS-IR cell bodies were magnocellular. About 30% of the nNOS-IR cell bodies were OT-IR, colocalization being most frequent in the rostral parts. In comparison, only ∼3% of all nNOS-IR cell bodies were AVP-IR, evenly distributed throughout the PVN. True Blue (TB), administered unilaterally into the spinal cord, disclosed that most spinally projecting cell bodies in the PVN were localized in caudal parts. Combined TB tracing and nNOS immunohistochemistry showed that ∼30% of spinally projecting neurons in the PVN were nNOS-IR, and that ∼40% of these were magnocellular. Ipsilateral nNOS spinal projections were about eight times more frequent than the contralateral nNOS projections. The study describes the detailed neuroanatomical organization of nNOS neurons coexpressing OT or AVP, and of nNOS spinally projecting neurons within defined parts of the PVN. In contrast to the paraventriculo-spinal system in general, we show that the nNOS paraventriculo-spinal pathway to a large extent originates in magnocellular cell bodies. The results suggest that NO is an important messenger in the paraventriculo-spinal pathway that may in part act in concert with OT.

Introduction

Neuronal nitric oxide (NO) synthase (nNOS) is present in several different cellular locations in the rat hypothalamus including the paraventricular nucleus (PVN) [6]. A considerable number of nNOS-, 8-arginine vasopressin- (AVP) and oxytocin- (OT) containing neurons are present in the PVN [6], [16], [43]. The PVN is involved in different autonomic functions, such as cardiovascular regulation [17] and sexual behaviour [26], [27]. These functions have been proposed to involve actions by NO as well as by OT and/or AVP [24], [27]. There is a neuronal coexistence of nNOS with OT or AVP in the PVN [37], [48], [53], suggesting functional intracellular interactions of NO with these peptides [12], [27].

Based on cytoarchitectural characteristics, the PVN can be subdivided into different magno- or parvocellular parts [45], which also differ with respect to chemical neuroanatomy and projectional targets [46]. Neurons containing OT and/or AVP project from the PVN to the neurohypophysis, the brainstem and the spinal cord [4], [41]. From the PVN, nNOS containing neurons are suggested to project to the same target regions [16], [23], [51].

The organization within the PVN of nNOS neurons projecting to the spinal cord has not been established, and neither is the detailed distribution of magno- and parvocellular nNOS- and OT- or AVP-containing cell bodies within the different parts of the PVN clear. Since many of the autonomic functions involving the PVN are NO-dependent, it is of interest to elucidate the morphological background for the above indicated interactions between NO and OT or AVP in the paraventriculo-spinal pathway.

We used combined immunohistochemistry and retrograde neuronal tract tracing from the spinal cord in the female rat to obtain such information.

Section snippets

Tissue handling

Female virgin rats (Sprague–Dawley, B&K Universal, Sollentuna, Sweden, 200–300 g body weight) were used. The experimental protocols were approved by the Animal Ethics Committee, University of Lund.

The rats had free access to water and standard pellets and were housed under controlled conditions with 12 h of light and 12 h of darkness. During the light period, the animals were anaesthetized with ketamine (50 mg/kg; Ketalar^®, Parke-Davis, Barcelona, Spain) and xylazine (10 mg/kg; Rompun vet^®,

Distribution of nNOS-IR neuronal cell bodies

Both magno- and parvocellular nNOS-IR cell bodies were distributed throughout the PVN (Fig. 1, Fig. 2; levels 1–10). About 80% of nNOS-IR neurons were magnocellular, and ∼20% were of the parvocellular type (Table 1).

Within the PVN, the majority of nNOS-IR neuronal cell bodies were of magnocellular type, located in am (levels 1–3) and in pm (levels 6–9). A significant number of nNOS-IR cell bodies were localized in mp (levels 6–10) and rostral pv (levels 2–4), whereas relatively few cells were

Discussion

The present study describes the detailed neuroanatomical and morphological organization of nNOS-IR cell bodies, their coexpression with OT- and AVP-immunoreactivity, and spinally projecting nNOS-IR neurons in the PVN of the female rat. The results concerning the general organization confirm observations from other studies using different techniques, whereas the detailed distributional results together with spinal tracings add new data concerning the cell type of the nNOS-, OT- and

Acknowledgements

We thank Lillemor Thuresson, Gun Hansson, Elsie Renfjärd, Agneta Kristensen and Brita Sundén-Andersson for excellent technical assistance. This work was supported by the Swedish Medical Research Council (grants no. 6837 and 11205), the Medical Faculty, Lund University, the foundations of Magnus Bergwall, Crafoord, Anna Lisa and Sven-Eric Lundgren for medical research, Åke Wiberg and Thelma Zoëga, and the Royal Physiographic Society, Lund, Sweden.

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Research reportNitric oxide synthase in the hypothalamic paraventricular nucleus of the female rat; organization of spinal projections and coexistence with oxytocin or vasopressin

Abstract

Introduction

Section snippets

Tissue handling

Distribution of nNOS-IR neuronal cell bodies

Discussion

Acknowledgements

Brain Res. Bull.

Neuroscience

Brain Res.

Brain Res. Bull.

Neuroscience

Brain Res.

Neurosci. Lett.

J. Chem. Neuroanat.

J. Immunol. Methods

Brain Res.

Pharmacol. Biochem. Behav.

Neurosci. Lett.

Ann. Anat.

Peptides

Neuroscience

Neuroscience

J. Chem. Neuroanat.

Brain Res.

Brain Res.

Brain Res.

Brain Res.

Mol. Cell. Neurosci.

Brain Res.

J. Chem. Neuroanat.

Neuroscience

Brain Res.

Neuroscience

Brain Res.

Research report
Nitric oxide synthase in the hypothalamic paraventricular nucleus of the female rat; organization of spinal projections and coexistence with oxytocin or vasopressin