Relaxin-3 innervation of the intergeniculate leaflet of the rat thalamus - neuronal tract-tracing and in vitro electrophysiological studies

Eur J Neurosci. 2013 Apr;37(8):1284-94. doi: 10.1111/ejn.12155. Epub 2013 Feb 25.


Behavioural state is controlled by a range of neural systems that are sensitive to internal and external stimuli. The relaxin-3 and relaxin family peptide receptor 3 (RXFP3) system has emerged as a putative ascending arousal network with putative involvement in regulation of stress responses, neuroendocrine control, feeding and metabolism, circadian activity and cognition. Relaxin-3/γ-aminobutyric acid neuron populations have been identified in the nucleus incertus, pontine raphe nucleus, periaqueductal grey (PAG) and an area dorsal to the substantia nigra. Relaxin-3-positive fibres/terminals densely innervate arousal-related structures in the brainstem, hypothalamus and limbic forebrain, but the functional significance of the heterogeneous relaxin-3 neuron distribution and its inputs to specific brain areas are unclear. Therefore, in this study, we used neuronal tract-tracing and immunofluorescence staining to explore the source of the dense relaxin-3 innervation of the intergeniculate leaflet (IGL) of the thalamus, a component of the neural circadian timing system. Confocal microscopy analysis revealed that relaxin-3-positive neurons retrogradely labelled from the IGL were predominantly present in the PAG and these neurons expressed corticotropin-releasing factor receptor-like immunoreactivity. Subsequently, whole-cell patch-clamp recordings revealed heterogeneous effects of RXFP3 activation in the IGL by the RXFP3 agonist, relaxin-3 B-chain/insulin-like peptide-5 A-chain (R3/I5). Identified, neuropeptide Y-positive IGL neurons, known to influence suprachiasmatic nucleus activity, were excited by R3/I5, whereas neurons of unidentified neurotransmitter content were either depolarized or displayed a decrease in action potential firing and/or membrane potential hyperpolarization. Our data identify a PAG to IGL relaxin-3/RXFP3 pathway that might convey stress-related information to key elements of the circadian system and influence behavioural state rhythmicity.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Chromatography, High Pressure Liquid
  • Electrophysiology
  • Immunohistochemistry
  • Male
  • Microscopy, Confocal
  • Nerve Tissue Proteins / metabolism*
  • Neural Pathways / cytology*
  • Neural Pathways / metabolism
  • Neurons / cytology
  • Neurons / metabolism
  • Patch-Clamp Techniques
  • Rats
  • Rats, Wistar
  • Relaxin / metabolism*
  • Stress, Physiological
  • Thalamus / cytology*
  • Thalamus / metabolism


  • Nerve Tissue Proteins
  • RLN3 protein, rat
  • Relaxin