Elsevier

Brain Research

Volume 947, Issue 2, 30 August 2002, Pages 299-306
Brain Research

Interactive report
Comparative distribution of NK1, NK2, and NK3 receptors in the rat brainstem auditory nuclei

https://doi.org/10.1016/S0006-8993(02)03139-6Get rights and content

Abstract

While the distribution of substance P in the auditory system is well illustrated, the localization of its receptors has not yet been documented. The goal of our study was to characterize the distribution of the tachykinin receptors NK1-R, NK2-R and NK3-R in the brainstem auditory nuclei of the adult rat using immunohistochemical techniques. The immunoreactivity of the neurokinin receptors was found to be widely distributed in most neurons of the cochlear nucleus (CN), the lateral superior olive (LSO), the medial nucleus of the trapezoid body (MNTB) and in the inferior colliculus (IC). Immunoreactivity was generally confined to post-synaptic targets (neuronal cell body and proximal or primary dendrites) in all auditory nuclei. However, unlike brainstem nuclei, the IC showed, in addition to neuronal cell body staining, a positive axonal immunolabeling (axons and pre-synaptic terminals) with the anti-NK1-R antibody. This axonal staining, revealing a pre-synaptic expression of NK1-R, is in good agreement with the known presence of substance P in the IC neurons. The absence of axonal staining in the superior olivary complex nuclei which projects afferent to the IC indicated that the NK1-R labeled axons are rather intrinsic IC fibers or descending thalamic projections to the IC. Overall, the wide distribution of the three types of tachykinin receptors observed in the present study argues for an important role of tachykinin neuropeptides in the central auditory system.

Introduction

Tachykinins are a family of neuropeptides that include substance P (SP), neurokinin A (NKA) and neurokinin B (NKB). These structurally related neuropeptides share a common carboxyl-terminal pentapeptide sequence [3]. Tachykinins have been shown to have a wide distribution in both the central and the peripheral nervous systems (see Ref. [15] for review). To exert their effect, SP, NKA and NKB interact with three different G-protein coupled receptors (neurokinin receptors) NK1-R, NK2-R and NK3-R. These neurokinin receptors bind tachykinin neuropeptides with different affinities (NK1-R: SP>NKA>NKB; NK2-R: NKA>NKB>SP; NK3-R: NKB>NKA>SP) [4], [13], [17].

The distribution of SP has been widely studied in the central auditory system of different species [1], [6], [8], [10], [11], [12], [16], [19], [20], [21], [26], [27]. These studies showed a strong expression of SP in fibers innervating most auditory nuclei. However, the origin of these SP fibers remains unknown, although some SP positive cell bodies have been observed in the ventral cochlear nucleus, the lateral lemniscus nucleus and in the inferior colliculus using immunohistochemical techniques and in situ hybridization [26], [27]. In addition, recent electrophysiological studies on brain slices in vitro have shown that SP depolarizes and increases the firing rates of neurons of the superior olive complex nuclei, suggesting the presence of functional NK1-R receptors and that these auditory structures receive excitatory input from a substance P-utilizing neural pathway [22], [23], [24].

Although an immunohistochemical mapping of the neurokinin receptor subunits has been reported in the central nervous system using autoradiography and immunohistochemistry [7], [9], [28], there is no information regarding their distribution in the central auditory system. The aim of the present study was to characterize the expression of neurokinin receptors in the central auditory system using immunohistochemical techniques. For this purpose, three polyclonal antibodies each recognizing specifically one member of the tachykinin receptors NK1-R, NK2-R and NK3-R were used [2].

Section snippets

Materials and methods

Two to 3-month-old (n=10) Sprague–Dawley rats were used in this study. Rats were deeply anaesthetized (sodium pentobarbital; 80 mg/kg), and perfused intra-cardially with a fresh solution of 4% paraformaldehyde and 0.2% glutaraldehyde in 0.1 M phosphate buffer solution (PBS). Brains were removed and post-fixed overnight at 4 °C in the same solution. Vibratome sections (30–70 μm) were obtained and incubated in 1% sodium borohydrate to remove excess fixative. Sections were incubated in 1% H2O2 to

NK1-R immunolabelling

NK1-R immunoreactivity was observed in the majority of neurons of both ventral (VCN) and dorsal (DCN) cochlear nucleus (CN) subdivisions (Fig. 1A and C). At high magnification NK1-R labeling was observed in neuronal cell bodies and proximal dendrites (Fig. 1B and D). Some of the NK1-R staining was observed as dots on the surface of the neuronal cell membranes. In the DCN, some neurons revealed the NK1-R staining in their principal dendrites. No immunoreactivity was observed in fibers all over

Discussion

The present study describes for the first time the cellular localization of the three tachykinin receptors NK1-R, NK2-R and NK3-R in the rat central auditory system. The immunoreactivity reveals a wide and similar distribution of the three receptors in the central auditory nuclei. The immunoreactivity was restricted to neurons and more specifically to the somatic compartment suggesting the presence of tachykinin terminals around the neuronal perikarya. Although the immunoreactivity was

Acknowledgements

We thank Dr N.W. Bunnett (Department of Surgery, School of Medicine, University of California, San Francisco, CA, USA) for providing us with the antibodies against the NK receptors. We would also like to thank the Conseil Régional d’Aquitaine and the Fondation pour la Recherche Médicale for grant support.

References (28)

  • X. Wang et al.

    Substance P-sensitive neurones in the rat auditory brainstem: possible relationship to medial olivocochlear neurones

    Hear. Res.

    (1998)
  • X. Wang et al.

    Effects of bioamines and peptides on neurones in the ventral nucleus of trapezoid body and rostral periolivary regions of the rat superior olivary complex: an in vitro investigation

    Hear. Res.

    (1997)
  • B. Wynne et al.

    Neurotransmitter and neuromodulator systems of the rat inferior colliculus and auditory brainstem studied by in situ hybridization

    J. Chem. Neuroanat.

    (1995)
  • E.F. Grady et al.

    Characterization of antisera specific to NK1, NK2, and NK3 neurokinin receptors and their utilization to localize receptors in the rat gastrointestinal tract

    J. Neurosci.

    (1996)
  • Cited by (6)

    • Interaction of neurotransmitters and neurochemicals with lymphocytes

      2019, Journal of Neuroimmunology
      Citation Excerpt :

      Trauma and infections of the CNS are associated with elevated pro-inflammatory cytokines (Ziebell and Morganti-Kossmann, 2010), and immunomodulatory neuropeptides including substance P (Ho et al., 1997). The non-peptide tachykinin antagonist, CP-96,345, has been shown to downregulate TH1-type cytokines and improve the outcome of multiple sclerosis (Hafidi et al., 2002; Harrison et al., 2004; Monastyrskaya et al., 2005). Substance P increases pain under pathological conditions by recruiting glial cells to the site of injury (Grace et al., 2014).

    • Exposure of Wistar rats to 24-h psycho-social stress alters gene expression in the inferior colliculus

      2012, Neuroscience Letters
      Citation Excerpt :

      In addition, Sp was found in several locations of the auditory pathway including the inner and outer hair cells and SG neurons [10] as well as the auditory brainstem [8]. The Sp receptor, NK1R, was identified as being expressed in most of the cells in the IC [16]. Precise function of Sp in the auditory brainstem remains to be clarified.

    • Involvement of midbrain tectum neurokinin-mediated mechanisms in fear and anxiety

      2012, Brazilian Journal of Medical and Biological Research
    View full text