Pinprick hyperalgesia with mice - Thoughts and Experiences?

Many studies of mechanical pain rely entirely on von Frey fibers. However, it’s unclear what a withdrawal to a VF hair really is. Are the VF stimuli noxious? It’s tough to tell. A paw withdrawal to a VF fiber might just be the mouse being tickled, annoyed, touch, or whatever.

Pinprick, with a needle or something, is undeniably noxious (can cause tissue damage). A naive mouse responds with a very rapid and almost invariable quick lift of the paw to a needle stick on the ventral surface. After inflammation or injury, the same stimulus would still cause pain (presumably) and if the pain is more than normal, it’d be hyperalgesia. Because the mouse can’t tell us what it feels, we have to infer hyperalgesia from the character of the response to the pinprick.

In the literature, I’ve seen people quantify the duration of withdrawal response (time until the mouse puts the paw back down) and also quality scores (biting, prolonged lifting, flinching, shaking, etc.).

To be honest though, I’ve never had much success with any other these. Right now I’m trying with zymosan-injected mice, and since the mice already are holding their paws off the ground at baseline (since they’re inflammed in presumably in pain), it’s tough to score duration of lifting reliably. The character of the response is also tough to reliably score.

What do you do? Any protocols or tips? I’m using a 29 g insulin needle with moderate speed of application.