B-vitamins enhance afferent inhibitory controls of nociceptive neurons in the rat spinal cord

Synergistic interaction between B vitamins and statins to counter nociception in rats

Evidence suggests that the antinociceptive activity of various drugs can be increased when administered in combination with B vitamins (BVs). The aim of this study was to examine the potential interaction between statins and BVs to counter nociception, the latter measured by the formalin test. Rats were orally administered atorvastatin (1, 3, 10 and 30 mg/kg), pravastatin (1, 3, 10 and 30 mg/kg), rosuvastatin (1, 3, 10 and 30 mg/kg), BVs (31, 56, 100 and 180 mg/kg) or calculated combinations of BVs with each drug. The effective dose 30 (ED₃₀ ) was calculated for each statin and BVs and subjected to isobolographic analysis, thus finding the ED₃₀ of the combinations. The antinociceptive experimental ED₃₀ values for BVs administered with atorvastatin, pravastatin or rosuvastatin were 1.53 ± 0.38, 6.74 ± 0.04 and 4.26 ± 0.39, respectively, being lower (p < .05) than the corresponding theoretical ED₃₀ : 28.02 ± 2.20, 28.17 ± 2.20 and 29.86 ± 2.21. Since BVs likely boost the antinociceptive effect of statins, these combinations could possibly be advantageous in pain management.

Thiamine, cobalamin, locally injected alone or combination for herpetic itching: a single-center randomized controlled trial

OBJECTIVES

The present study was designed to explore the efficacy of locally injected thiamine or cobalamin in relieving itch or pain and improving the daily living activities among patients with herpetic itching.

METHODS

Eighty eligible patients with herpetic itching with a worst itching score of ≥ 4 were randomized to receive locally injected thiamine (B1 group), cobalamin (B12 group), lidocaine (LD group), or combination of thiamine and cobalamin (COB group) for 4 weeks. The treatment efficacy was assessed based on the patients' pruritus and pain severity, global impression of change, and activities of daily living and quality of life.

RESULTS

After 7 days, thiamine yielded a significant itch relief, cobalamin yielded a significant pain relief, and their combination significantly relieved both pain and itch; which all continued till the endpoint (all Ps<0.001). However, lidocaine did not provide significant itch or pain relief than the other groups. Sixteen patients in the thiamine group achieved ≥ 30% itch reduction; 18 patients in the cobalamin group obtained ≥ 30% pain reduction; and 18 patients achieved ≥ 30% itch reduction and 19 patients obtained ≥ 30% pain reduction in the combination group. The activities of daily living and quality of life data at the endpoint were consistent with a significant benefit in the thiamine (P<0.05), cobalamin, and combination groups (both Ps<0.001).

DISCUSSION

Locally injected thiamine had a significant antipruritic effect, cobalamin had an analgesic effect, and their combination had the dual effect with no obvious synergies. This intervention was efficacious, tolerable, and safe for herpetic itching.

Noxious peripheral stimulation produces antinociception mediated via substance P and opioid mechanisms in the rat tail-flick test

Physiological experiments were run to examine the effects of noxious thermal stimulation of one hindpaw on the tail-flick reflex in the lightly anesthetized rat. Male Sprague-Dawley rats were anesthetized with an i.p. injection of a mixture of Na-pentobarbital (20 mg/kg) and chloral hydrate (120 mg/kg). After baseline readings were taken in the tail-flick test, either a non-noxious or a noxious stimulus was applied which consisted of immersion of one hindpaw in water at 40, 45, 50 or 55 degrees C for 1.5 min. After immersion, tail-flick readings were taken at 3-min intervals for at least 16 min. Paw immersion in water at 55 degrees C induced an antinociceptive response, consisting of an increase in the reaction time, at 0.5 min after immersion. Recovery to baseline levels occurred over the next 3-6 min. Immersion at lower temperatures provoked smaller antinociceptive responses, except at 40 degrees C, where readings remained around the baseline values. The increase in reaction time in response to immersion at 55 degrees C was attenuated or blocked by the novel, nonpeptide substance P (NK-1) receptor antagonist, CP-96,345, administered s.c. 30 or 60 min, respectively, prior to paw immersion. Similar injection of CP-96,344, the inactive stereoisomer, had no effect on the response, while another NK-1 receptor antagonist, CP-99,994, also attenuated the antinociceptive effect of the immersion. The increase in reaction time induced by immersion at 55 degrees C was absent in animals treated neonatally with capsaicin.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibitory effects of phrenic afferent fibers on primate lumbosacral spinothalamic tract neurons

Studies were conducted to determine if electrical or mechanical stimulation of phrenic afferent fibers (PHR) would inhibit the activity of lumbosacral spinothalamic tract (STT) neurons. Twelve monkeys were anesthetized, paralyzed, and artificially ventilated. Extracellular action potentials were recorded from 78 STT neurons located in L2-S3 spinal segments. Electrical stimulation of PHR reduced the activity of 65%, did not affect 33%, and excited 1% of STT neurons. Mechanical stimulation of the diaphragm reduced the activity of 63%, did not effect 34%, and excited 1% of lumbosacral STT neurons. Distention of the urinary bladder (UBD) inhibited 52%, did not affect 23%, excited 23%, and elicited a biphasic response in 1% of STT neurons. However, there was no correlation between the effect of PHR and UBD or somatic classification of the neurons. We conclude that electrical or mechanical stimulation of PHR can produce a generalized inhibition of lumbosacral STT neurons. This inhibitory effect of PHR is similar to inhibitory effects reported for a variety of other afferent systems.