I want to induce mechanical allodynia in a reversible way. Capsaicin is one way, but I’ve also looked at bicuculline/strychnine, which are GABA and glycine antagonists, respectively.
In this paper by Cheng et al. they used 20 ng Bicuc and 50 ng strychnine intrathecally.
I tried this dose today, but mechanical hypersensitivity wasn’t apparent at 1 hour. I think maybe I waited too long to test. The time course might be very short.
As suggested by this paper, peak effects were in
G Hathway, E Harrop, M Baccei, S Walker, A Moss and M Fitzgerald,
The European journal of neuroscience, Jan 2006
GABAergic signalling exerts powerful inhibitory control over spinal tactile and nociceptive processing, but during development GABA can be depolarizing and the functional consequences of this upon neonatal pain processing is unknown. Here we show a postnatal switch in tonic GABA(A) receptor (GABA(A)R) modulation of cutaneous tactile and nociceptive reflexes from excitation to inhibition, but only in the intact spinal cord. Neonatal and 21-day-old (P21) rats were intrathecally treated with one of the GABA(A)R antagonists bicuculline and gabazine, with both compounds dose-dependently decreasing hindpaw mechanical and thermal withdrawal thresholds in P21 rats but increasing them in P3 neonates. Intrathecal gabazine also produced an increase in the cutaneous evoked electromyography (EMG) response of the biceps femoris in P21 rates but lowering the response in neonates. Injections of 3H-gabazine in the L4-L5 region at P3 confirmed that gabazine binding was restricted to the lumbar spinal cord. Spinalization of P3 neonates at the upper thoracic level prior to drug application reversed the behavioural and EMG responses to GABA antagonists so that they resembled those of P21 rats. The effects of spinalization were consistent with gabazine facilitation of ventral root potentials observed in isolated neonatal spinal cord. These data show a marked postnatal developmental switch in GABAergic control of neonatal nociception that is mediated by supraspinal structures and illustrate the importance of studying developmental circuits in the intact nervous system.
That doesn’t give you much wiggle room to do your testing and inject a whole cohort of mice.
I saw in Francois 2017, they used 1 ng bicuculline, which is much less than Cheng 2017. The time frame is not indicated (AFAIK)
A François, SA Low, EI Sypek, AJ Christensen, C Sotoudeh, KT Beier, C Ramakrishnan, KD Ritola, R Sharif-Naeini, K Deisseroth, SL Delp, RC Malenka, L Luo, AW Hantman and G Scherrer,
Neuron, Feb 22 2017
Pain thresholds are, in part, set as a function of emotional and internal states by descending modulation of nociceptive transmission in the spinal cord. Neurons of the rostral ventromedial medulla (RVM) are thought to critically contribute to this process; however, the neural circuits and synaptic mechanisms by which distinct populations of RVM neurons facilitate or diminish pain remain elusive. Here we used in vivo opto/chemogenetic manipulations and trans-synaptic tracing of genetically identified dorsal horn and RVM neurons to uncover an RVM-spinal cord-primary afferent circuit controlling pain thresholds. Unexpectedly, we found that RVM GABAergic neurons facilitate mechanical pain by inhibiting dorsal horn enkephalinergic/GABAergic interneurons. We further demonstrate that these interneurons gate sensory inputs and control pain through temporally coordinated enkephalin- and GABA-mediated presynaptic inhibition of somatosensory neurons. Our results uncover a descending disynaptic inhibitory circuit that facilitates mechanical pain, is engaged during stress, and could be targeted to establish higher pain thresholds. VIDEO ABSTRACT.
So does anyone have experience using these agents in mice?
@liz @lfqueme @tberta @SamineniV @Boninrp