Pharmacological activation of 5-HT 7 receptors reduces nerve injury- induced mechanical and thermal hypersensitivity

PAIN is UNIVERSAL

YET, DIFFERENT for EVERYONE

ANIMAL MODELS for PAIN

5-HT 7 GPCR – Stimulates cAMP – Found in hypothalamus, thalamus, hippocampus, cortex, blood vessels, intestines – Found in inverts and verts

Receptor signaling – Activates ERK through Ras monomemric GTPase- dependent mechanism – But independent from PKA through cAMP- activated guanine nucleotide exchange factor E.g. stimulates ERK in hippocampal neurons  affect hippocampal function and mood regulation 5-HT 7

Functional roles – Thermoregulation – Learning and memory – Circadian rhythm – Endocrine regulation 5-HT 7

METHODS and DESIGN Male, 6-8 week old CD1 mice Housed in groups of 5 with water and food Maintained in 21 degrees C with 12 hr light/dark cycles

METHODS and DESIGN

Neuropathic pain model: partial sciatic nerve ligation – Partial injury to the SN at mid-thigh level – Common SN exposed Tied tight ligatures around approx 33-50% of diameter of SN Ligature enclosed outer 1/3-1/2 SN, while rest of SN (inner 2/3- 1/2) was left alone Muscle stitched up – Controls had same procedure w/o ligation

Mechanical hypersensitivity – Quantified by pressure TH eliciting withdrawal of ipsilateral hindpaw through von Frey Thermal hyperalgesia – Quantified by hindpaw withdrawal latency in response to radiant heat (a mobile infared photobeam) in plantar test Motor coordination – Assess by an automated rotarod METHODS and DESIGN

Experimental approach (acute admin) – 2 day habituation period, then pre-surgery pretest – Surgery (sham or nerve ligation) – Post-surgery responses of vehicle mice tested at day 10 – Days 11-13, mice were treated with three different doses (.1, 1, 10mg/kg) of agonist AS-19 or antagonist SB Day 11 – antagonist Day 12 – agonist Day 13 – combo – Day 14, mice given vehicle and post- treatment responses were assessed METHODS and DESIGN

Experimental approach (repeated admin) – Effect of agonist E on development of neuropathic pain behaviors – 2 day habituation period, then pre- surgery pretest of von Frey and plantar tests for 15 min intervals between each test – Surgery (sham or nerve ligation) – E or vehicle started the day of surgery to day 11 – Tested on days 3, 6, and 10 – All mice received vehicle on days 12, 15, and 20 and were tested METHODS and DESIGN

RESULTS AS19 = 5-HT 7 agonist Mechanical Hypersensitivity

RESULTS AS19 = 5-HT 7 agonist Thermal Hyperalgesia

RESULTS SB = 5-HT 7 antagonist Mechanical Hypersensitivity

RESULTS Thermal Hyperalgesia SB = 5-HT 7 antagonist

RESULTS Mechanical Hypersensitivity

RESULTS Thermal Hyperalgesia

RESULTS

DISCUSSION Activation of 5-HT 7 receptors (agonist AS- 19)  dose-dependent inhibition of mechanical hypersensitivity and thermal hyperalgesia Co-admin with antagonist, SB , blocked effects Overall effect was anti-nociceptive and maintained throughout treatment period

SO CUTE!

Marcel the Shell with Shoes On!