Preemptive Analgesic Effect of Intrathecal Applications of Neuroactive Steroids in a Rodent Model of Post-Surgical Pain: Evidence for the Role of T-Type Calcium Channels

Abstract

Preemptive management of post-incisional pain remains challenging. Here, we examined the role of preemptive use of neuroactive steroids with activity on low-voltage activated T-type Ca2+ channels (T-channels) and γ-aminobutyric acid A (GABAA) receptors in the development and maintenance of post-incisional pain. We use neuroactive steroids with distinct effects on GABAA receptors and/or T-channels: Alphaxalone (combined GABAergic agent and T-channel inhibitor), ECN (T-channel inhibitor), CDNC24 (GABAergic agent), and compared them with an established analgesic, morphine (an opioid agonist without known effect on either T-channels or GABAA receptors). Adult female rats sustained the skin and muscle incision on the plantar surface of the right paw. We injected the agents of choice intrathecally either before or after the development of post-incisional pain. The pain development was monitored by studying mechanical hypersensitivity. Alphaxalone and ECN, but not morphine, are effective in alleviating mechanical hyperalgesia when administered preemptively whereas morphine provides dose-dependent pain relief only when administered once the pain had developed. CDNC24 on the other hand did not offer any analgesic benefit. Neuroactive steroids that inhibit T-currents—Alphaxalone and ECN—unlike morphine, are effective preemptive analgesics that may offer a promising therapeutic approach to the treatment of post-incisional pain, especially mechanical hypersensitivity.

β-Caryophyllene inhibits monoacylglycerol lipase activity and increases 2-AG levels: a new mechanism of endocannabinoid-mediated analgesia?

“…were compared to the vehicle administration. In animals that underwent skin incision, we focused on mechanical hyper-analgesic effects as an important feature of incisional pain for two main reasons: it is very commonly observed in a clinical setting of incisional pain [16,22,23] and, as published previously, it is sensitive to pharmacological and biochemical modulation [16,17]. The paw withdrawal responses (PWR) were determined in the incised (hyper analgesic effect) right hind paw (Figure 1 left side) and non-operated (left) paws (Figure 1 right panels).…”

“…(2) the majority of current pain studies in animals are performed using males [15]. Thus, we believe that the research focus should also be on female pain perception [13,16]. Incision pain model.…”

“…In order to study the antihyperalgesic effect of BCP after surgery, we used a skin and muscle incision for the induction of post-surgical pain. Our standard model for the induction of postsurgical pain using the skin and muscle incision was described previously [13,[16][17][18] as follows: animals were anesthetized with isoflurane (2.5% for induction and for maintenance) and the plantar surface of the right paw was incised longitudinally with a blade No.11; the underlying plantaris muscle was elevated and also longitudinally incised, whereafter the skin was sutured with 5-0 nylon suture with a FS-2 needle. Animals were allowed to recover in cages, and all experiments were initiated as early as 2 h post-incision.…”

“…Mechanical Sensitivity. Our standard method for assessing mechanical sensitivity was described previously [16,17]. Briefly: we used the electronic Von Frey apparatus (Ugo Basile, Varese, Italy), which utilizes a single rigid filament that exerts pressure to the plantar surface of the paw in a range from 0 to 50 g. Animals were placed in plastic enclosures on a wire mesh stand to habituate for 15 min.…”

The role of voltage-gated calcium channels in the mechanisms of anesthesia and perioperative analgesia

“…Although both alphaxalone and ALLO are well known as positive allosteric modulators of GABA A receptors, we have previously reported that both of these agents are also fairly potent blockers of neuronal Ca V 3.2 isoform of T-channels in sensory neurons [40], and display prominent analgesia in vivo [41]. Over the last decade, our group has extensively studied T-channel blocking properties and analgesic potential of neurosteroids [42,43,44 && ], particularly a novel synthetic 5b-reduced neurosteroid analogue, 3b-OH ((3b,5b,17b)- ] that is at least partly mediated by the inhibition of Ca V 3.1 isoform of T-channels. Specifically, we found that hypnotic effect of 3b-OH was greatly diminished in the global Ca V 3.1 knock-out (KO) mice when compared to their wild-type littermates [46 && ].…”