Role of Pituitary Adenylate-Cyclase Activating Polypeptide and Tac1 gene-derived tachykinins in sensory, motoric and
vascular functions under normal and neuropathic conditions
Bálint Botz1,3* (botzb@dravanet.hu), András Imreh1, Katalin Sándor1, Krisztián Elekes1, János Szolcsányi1, Dóra Reglődi2, John P. Quinn4, James Stewart5, Andreas Zimmer6, Zsuzsanna Helyes1,3
Departments of 1Pharmacology and Pharmacotherapy, and 2Anatomy, Faculty of Medicine, University of Pécs, 3János Szentágothai Research Center, University of Pécs, Hungary 4School of Biomedical Sciences, Liverpool University, Liverpool, UK 5School of Infection and Host Defense, University of Liverpool, UK 6Laboratory of
Molecular Neurobiology, Department of Psychiatry, University of Bonn, Bonn, Germany
1. Background and Aims
Pituitary Adenylate-Cyclase Activating Polypeptide (PACAP) and Tac1 gene-encoded tachykinins (substance P: SP, neurokinin A: NKA) are expressed in capsaicin-sensitive peptidergic nerves, but data regarding their role in nociception, inflammation and vascular responses are contradictory. Therefore, we aimed to investigate the function of these sensory neuropeptides, and the NK1 tachykinin receptor (derived from the Tacr1 gene) in the partial sciatic nerve ligation-induced traumatic mononeuropathy model using gene deficient (PACAP-/-, Tac1-/-, and Tacr1-/-) mice compared to their respective wildtype (WT) counterparts.
2. Methods
Experimental traumatic mononeuropathy was induced by tight ligation of 1/3 of the left sciatic nerve (Seltzer et al.
1991; Fig. 1.). The mechanonociceptive threshold of the plantar surface of the paw was determined by dynamic plantar aesthesiometry (Fig. 2.). . Motor-coordination was measured with a Rota-Rod device (Fig 2.) before and after the nerve ligation Plantar microcirculation was measured with Laser Doppler imaging (Perimed, Fig 4.) 21 days after the operation. Neurogenic vasodilation was induced by topical application of 5% mustard oil, which selectively stimulates the Transient Potential Ankyrin Repeat 1 (TRPA1) receptors/ion channel on capsaicin-sensitive peptidergic sensory nerve endings and induces neuropeptide release.
3.Results
4. Conclusions
1. Partial sciatic nerve ligation does not induce motor and vasoregulatory impairment, only sensory neuropathy.
2. Both PACAP and SP/NKA participate in normal motor coordination, while the NK1 receptor does not.
3. PACAP is a crucial mediator of neuropathic mechanical hyperalgesia and neurogenic vasodilation, while SP/NKA and the NK1 receptor are involved in the regulation of the basal skin blood flow.
4. According to our current results PACAP-mediated pathways on the periphery provide a challenging new direction for preclinical
drug development in neuropathic conditions. Acknowledgements SROP-4.2.2.A-11/1/KONV-2012-0024, SROP-4.2.1.B-10/2/KONV-2010-0002, SROP-4.2.2.B-10/1/2010-0029
Fig 6./A,B,C In both WT groups (PACAP+/+, C57Bl/6) a 30-40% mechanical hyperalgesia developed one week after nerve ligation, which persisted during the study. This hyperalgesia was not altered in Tac1-/- and Tacr1-/- mice, while it was absent in the PACAP-/- group. n=12 **p<0.01, ***p<0.001 vs. respective WT control (repeated measures ANOVA + Bonferroni’s modified t-test).
Fig 7./A,B,C Motor coordination of the PACAP-/- and Tac1-/- groups was significantly worse both before and after nerve ligation compared to their wild types, but it was not altered in Tacr1-/- mice. n=6-12 *p<0.05, **p<0.01,***p<0.001;
#p<0.05 vs. respective preoperative value (repeated measures ANOVA + Bonferroni’s modified t-test).
1/3 ligation of the sciatic nerve
PACAP KO + WT
Tac1 KO + WT mice
Tacr1 KO + WT
Traumatic
mononeuropathy
7 to 21 days postoperatively
Mechanical hyperalgesia
Motor coordination
Laser Doppler imaging
PACAP:
Tac1 (SP, NKA):
Tacr1 (NK1):
Results
Neurogenic vasodilation Vascular tone
Vascular tone
The overview of the experiment
(Fig 10.)Fig 1. Fig 2.
Fig 3. Fig 4.
Fig8./A,B,C Cutaneous perfusion of the PACAP-/- mice did not differ from the wild types during the postoperative control measurements, but it was significantly lower in the Tac1-/- and Tacr1-/- groups. Mustard oil-induced neurogenic vasodilation was significantly smaller in PACAP-/- mice, but remained unchanged in Tacr1-/- and Tac1-
/- animals. (Fig 9.) n=5-6 (two-way ANOVA)
.
Fig 9.
