Effect of cerebral ventricles perfusion with naloxone on trigemino-hypoglossal reflex in rats

Opioid and Endocannabinoid System in Orofacial Pain

Orofacial pain disorders are frequent in the general population and their pharmacological treatment is difficult and controversial. Therefore, the search for novel, safe and efficient analgesics is an important but still elusive goal for contemporary medicine. In the recent years, the antinociceptive potential of endocannabinoids and opioids has been emphasized. However, concerns for the safety of their use limit their clinical applications. the possibility of modulating the activity of endocannabinoids by regulation of their synthesis and/or degradation offers an innovative approach to the treatment of pain. A rat model of trigeminal pain, utilizing tongue jerks evoked by electrical tooth pulp stimulation during perfusion of the cerebral ventricles with various neurotransmitter solutions can be used in the pharmacological studies of nociception in the orofacial area. The aim of this review is to present the effects of pharmacological activity of opioids and endocannabinoids affecting the transmission of the sensory information from the orofacial area on the example of trigemino-hypoglossal reflex in rats.

Effects of intra-hippocampal microinjection of vitamin B12 on the orofacial pain and memory impairments induced by scopolamine and orofacial pain in rats

In the present study, we investigated the effects of microinjection of vitamin B₁₂ into the hippocampus on the orofacial pain and memory impairments induced by scopolamine and orofacial pain. In ketamine-xylazine anesthetized rats, the right and left sides of the dorsal hippocampus (CA1) were implanted with two guide cannulas. Orofacial pain was induced by subcutaneous injection of formalin (1.5%, 50μl) into the right vibrissa pad, and the durations of face rubbing were recorded at 3-min blocks for 45min. Morris water maze (MWM) was used for evaluation of learning and memory. Finally, locomotor activity was assessed using an open-field test. Vitamin B₁₂ attenuated both phases of formalin-induced orofacial pain. Prior administration of naloxone and naloxonazine, but not naltrindole and nor-binaltorphimine, prevented this effect. Vitamin B₁₂ and physostigmine decreased latency time as well as traveled distance in Morris water maze. In addition, these chemicals improved scopolamine-induced memory impairment. The memory impairment induced by orofacial pain was improved by vitamin B₁₂ and physostigmine used alone. Naloxone prevented, whereas physostigmine enhanced the memory improving effect of vitamin B₁₂ in the pain-induced memory impairment. All the above-mentioned chemicals did not alter locomotor activity. The results of the present study showed that at the level of the dorsal hippocampus, vitamin B₁₂ modulated orofacial pain through a mu-opioid receptor mechanism. In addition, vitamin B₁₂ contributed to hippocampal cholinergic system in processing of memory. Moreover, cholinergic and opioid systems may be involved in improving effect of vitamin B₁₂ on pain-induced memory impairment.

Effects of centrally administered vasopressin on orofacial pain perception in rats

Vasopressin (AVP) appears in the cerebrospinal fluid and plays an important role in nociceptive modulation in the central nervous system. The effect of increased concentration of AVP in the cerebrospinal fluid on the excitability of the hypoglossal nerve nucleus was investigated. The experiments were carried out on rats under chloralose anesthesia. Amplitudes of the retractory evoked tongue jerks (ETJ) of the outstretched tongue during the perfusion of cerebral ventricles with solutions containing AVP or its antagonists and also opioid and serotonin antagonists were recorded. Perfusion of the ventricles with AVP in 100 microM concentration suppressed the ETJ amplitude to 66 +/- 3.83%, and in 200 microM concentration, to 53 +/- 3.18% of the control. V1 vasopressin receptor antagonist, d(CH2)5,Tyr(Me)AVP, blocked the suppressive effect caused by cerebral ventricle perfusion with AVP from 64 +/- 4.11% to 83 +/- 1.58%, whereas V2 vasopressin receptor antagonist, d(CH2)5[Ile2, Ile4]AVP, did not block the antinociceptive effect of AVP. Analgesic effect of AVP was also inhibited by opioid and serotonin receptor antagonists, naloxone and methysergide, respectively. Naloxone blocked the suppressive effect of 100 microM AVP from 64 +/- 5.63% to 92 +/- 3.70% and methysergide from 65 +/- 3.62% to 80 +/- 2.72% of the control. The results indicate that exogenous AVP plays an antinociceptive role in the brain of rats penetrating the lining of the cerebral ventricles into the cerebrospinal fluid and exerting a modulating effect on the tongue motor center situated near III and IV cerebral ventricle. V1 vasopressin receptor, but not V2 vasopressin receptor, is involved in this activity in the CNS. The antinociception of AVP seems to be mediated by opioid and serotonergic pathways.

Endogenous opiates and behavior: 2001

This paper is the twenty-fourth installment of the annual review of research concerning the opiate system. It summarizes papers published during 2001 that studied the behavioral effects of the opiate peptides and antagonists. The particular topics covered this year include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology(Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); and immunological responses (Section 17).

Substance P content in the cerebrospinal fluid and fluid perfusing cerebral ventricles during elicitation and inhibition of trigemino-hypoglossal reflex in rats

The aim of this study was to establish whether tooth pulp and periaqueductal central gray (PAG) stimulation affects the release of substance P (SP) into the fluid perfusing the cerebral ventricles in rats. The content of substance P in the cerebrospinal fluid and fluid perfusing cerebral ventricles was determined during incisor pulp stimulation with electrical impulses inducing nociceptive trigemino-hypoglossal reflex and then during inhibition of the reflex by stimulation of PAG. Perfusion of the cerebral ventricles was carried out using artificial cerebrospinal fluid (aCSF). SP-like immunoreactivity (SP-LI) was determined in the samples by radioimmunoassay. Samples were collected in four groups: first group-cerebrospinal fluid (CSF); second group-aCSF perfusates without stimulation; third group-aCSF perfusates during incisor pulp stimulation; fourth group-aCSF perfusates during incisor pulp stimulation and simultaneous inhibition of trigemino-hypoglossal reflex by PAG stimulation. It was shown that incisor pulp stimulation led to the increased release of SP-LI into the fluid perfusing cerebral ventricles. Stimulation of PAG reduced the release of SP-LI into the cerebro-ventricular system to the values obtained before the tooth pulp stimulation. The results indicate that PAG significantly inhibits the release of SP-LI into the rat cerebral ventricular system and may be involved in the inhibition of trigemino-hypoglossal reflex.