Detection of the neuroregulatory peptide alarin in cranial autonomic ganglia of the rat

Abstract

Purpose: Alarin is a recently discovered neuroregulatory peptide with vasoconstrictive activity in murine skin. It is expressed in various regions of the brain and was lately also detected in retinal neurons of rat and mouse and in humans in intrinsic choroidal neurons. Autonomic innervation is essential for many aspects of ocular homeostasis, and alarin might be involved in this autonomic control. Here we ask if alarin is present in the various autonomic ganglia supplying the eye and explore its impact in ocular innervation.

Methods: Cranial autonomic ganglia of the rat (i.e. superior cervical, SCG; ciliary, CIL; pterygopalatine, PPG; trigeminal, TRI) were prepared for immunohistochemistry against alarin using affinity purified antibodies and respective established ganglionic markers (SCG: TH; PPG and CIL: ChAT; TRI: SP). For documentation, confocal laser scanning microscopy was used. Presence of alarin was quantified in ten non-consecutive serial sections of each ganglion and quantitative real-time PCR was applied to detect alarin mRNA expression in corresponding ganglia.

Results: Weak alarin-like immunoreactivity was detected in neurons of all cranial autonomic ganglia. Quantitative evaluation revealed that those represent only a minority of the overall cell-population in the ganglia investigated: TRI: 8/772; PPG: 4/940; SCG: 18/903; CIL:11/315. Quantitative real-time PCR was not able to detect a stable alarin mRNA signal in any of the (pooled, n= 4) ganglia.

Conclusions: Alarin has been described in various regions of the CNS and eye. Since it is only present in a minority of neurons of rat cranial autonomic ganglia, and since we were not able to detect alarin mRNA, we consider it of low impact on ocular autonomic innervation, at least under physiological conditions. Further investigations in other species are needed to clarify the role of alarin function in the eye.

Keywords: 419 anatomy • 616 neurotransmitters/neurotransmitter systems • 614 neuropeptides