Progesterone prevents developmentof neuropathic pain in a rat model: Timing

and duration of treatment are critical

Presented by:Nikita Dambale

Guided by:Dr. M. A. Upadhya

Introduction• Neuropathic pain is a chronic, debilitating condition that results from various

injuries and diseases of the central and peripheral nervous system( Kehlet et al).

• Progesterone has been reported to reduces neuronal damage and improves functional outcome in animal models of traumatic brain injury ( Roof et al).

• Therefore, the rationale for the present study is that because progesterone plays a protective role following nerve injury, it may be effective in alleviating the resulting

pain scores in a rat model of peripheral neuropathy.

Materials and methodsAnimals :Male Sprague-Dawley rats were housed and maintained on a 12-hour light cycle, with

food and water available ad libitum.

Model induction: The method of sciatic nerve cuffing as described by Mosconi and Kruger.

Rats were anesthetized with a combination of ketamine ( 5 mg/100 g) + xylazine ( 0.5 mg/100 g) + acepromazine (0.1 mg/100 g) given i.p.

The left sciatic nerve was exposed after blunt dissection of the overlying muscle and freed from the surrounding tissue. 2 mm-long polyethylene cuff was inserted around one sciatic nerve of the rat.

Antibiotic ointment ( nitrofurazone 0.2%) was applied over the wound, and 0.03 mL of antibiotic (trimethoprim-sulfadiazine) was injected subcutaneously.

PAW WITHDRAWAL THRESHOLD

• 30 × 30 × 30 cm Plexiglas box with a clear Plexiglas floor, containing 0.5 cm diameter holes that were spaced 1.5 cm apart ( Pitcher et al).

• von Frey filaments were applied to the soft tissue of the plantar surface of the hind paw to determine the withdrawal threshold.

• 1st filament was applied with a force of 2 g. Each filament was applied 3 times, at intervals of 3 sec.

• Rat shows either

• A 50% response threshold was calculated according to the response pattern observed (Chaplan et al). The maximum score possible was 15 g, and the minimum was 0.25 g.

Negative response

Positive response

Drug• Test group - Progesterone was given at a dose of 4 mg/kg, dissolved in peanut oil

and administered i.p. at a volume of 0.1 mL/100 g body weight.• Control group - peanut oil ( 0.1 mL/100 g) i.p.

Repeated treatment Baseline paw withdrawal thresholds were measured.1) Early treatment – Daily progesterone administration starting one hour after surgery.a) From days 0 to 4b) From days 0 to 10

2) Late treatment - Daily progesterone administration starting 20 days after surgery.a) From days 20 to 23b) From days 20 to 30

Vehicle groups were given peanut oil injections according to the same schedule.

Single-dose treatment Baseline paw withdrawal thresholds were measured. Withdrawal thresholds were

measured again at 30, 60, and 90 minutes after injection.

1) Early treatment - vehicle was given on day 3 and progesterone on day 4 after cuff implantation.

2) Late treatment - vehicle was given on day 87 (to rats previously given progesterone on days 20–30) and progesterone was given on day 88 (to another group of rats previously given vehicle on days 20–30).

STATISTICAL ANALYSES

Repeated treatment = 2-way ANOVASingle-dose treatment = 1 - way ANOVA

Figure 1: Early treatment on days 0 to 4.

Figure 2: Early treatment on days 0 to 10.

Figure 3 : Late treatment (days 20 to 23).

Figure 4 : Late treatment (days 20 to 30).

Figures 5. Single-dose treatment did not have an effect on paw withdrawal thresholds, as measured at 30, 60, and 90 minutes after injection.

Figure 6. Single-dose treatment did not have an effect on paw withdrawal thresholds, as measured at 30, 60, and 90 minutes after injection.

Discussion• Aim of the present study was to determine if progesterone administration in a rat

model of peripheral neuropathic pain would delay or limit the development of tactile hypersensitivity in a rat model of neuropathic pain.

• Repeated progesterone treatment for 4 days/23 days/ 30 days, did not have a significant effect on the development of tactile hypersensitivity over observation period.

• However, in progesterone treatment continued for 10 days, a recovery of tactile hypersensitivity in the later part of the study was observed.

• In summary, progesterone promoted the recovery of this model of peripheral neuropathic pain, when given as repeated injections during the early phase of model development and for a sufficient period of time.

References1.Kehlet H, Jensen TS, Woolf CJ. Persistent postsurgical pain: Risk factors and prevention.

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3. Mosconi T, Kruger L. Fixed-diameter polyethylene cuffs applied to the rat sciatic nerve induce a painful neuropathy: Ultrastructural morphometric analysis of axonal alterations. Pain. 1996;64(1):37–57.

4. Pitcher GM, Ritchie J, Henry JL. Paw withdrawal threshold in the von Frey hair test is influenced by the surface on which the rat stands. J Neurosci Methods. 1999; 87(2):185–193.

5. Chaplan SR, Bach FW, Pogrel JW, Chung JM, Yaksh TL. Quantitative assessment of tactile allodynia in the rat paw. J Neurosci Methods. 1994;53(1):55–63.

6. Berger A. Clinical characteristics and economic costs of patients with painful neuropathic disorders. J Pain. 2004;5(3):143–149.

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