ABSTRACT
The rostral ventromedial medulla [RVM] acts a key role in the descending inhibitory pain modulation. Neuropeptide orexin-A [ORXA] is confined to thousands of neurons in the lateral hypothalamus [LH]. While RVM gets the orexinergic projections, the orexin receptors are also expressed in this structure. The aim of this study was to specify the cellular effects of ORXA on RVM neurons in vitro by using the whole cell patch-clamp recording. RVM neurons were classified into three types based on their electrophysiological characteristics. Type 1 neurons exhibited an irregular spontaneous activity which was interrupted by periods of pause in 25% of recorded neurons. Type 2 neurons did not show any spontaneous baseline activity [53.8% of recorded neurons]. Type 3 neurons fired repetitively without interruption [51.2% of recorded neurons]. ORXA had either inhibitory or excitatory effects on 53.8% [7/13] of type 1 neurons. ORXA excited 46.4% [13/28] of type 2 neurons and 27.3% [3/11] of type 3 neurons. The excitatory effect of ORXA observed in type 2 neurons was suppressed by an orexin 1 receptor [OXR1] antagonist, SB-334867. Briefly, we hypothesized that the ORXA mediated excitation and/or inhibition in RVM neurons might work as a mechanism to modulate pain processing by orexinergic neurons
ABSTRACT
Background: Several systems of pain modulation in the central nervous system modulated the responses to painful stimuli in stressful and excitement situations. Stimulation of the hypothalamus induces analgesia through information relay to the brain stem including Rostral- Ventromedial medulla. The Rostral-Ventromedial medulla as output gate of the brain stem medulated pain through neurons in the dorsal horn. This pain modulation in central nerous system in various psychological conditions was based on existing of different neural groups and the special connections between them. These neurons cause pain modulation. The functional relationship between activation of one group of them and increasing pain and activation of another group and reduction of pain has been observed. In this review, it is discussed about the role of different neural groups of rostral-ventromedial medulla in pain modulation.
Conclusion: The Rostral-Ventromedial medulla has a major role in modulating pain and higher centers of the brain by altering the activity of the special groups of neurons cause to induce inhibition or facilitate pain in different stress and emotional conditions.
ABSTRACT
The present study examined the possible role of endogenous opioidergic system in effect of food deprivation on formalin-induced nociceptive behaviors in male and female rats. Also, we investigated the effect of food deprivation on the plasma level of beta-endorphin and sex hormones. Food was withdrawn 48 h prior to performing the formalin test, but water continued to be available ad libitum. The formalin was injected into hind plantar paw. There is significant difference between male and female control rats during phase 2B. Following 48-h food deprivation, both male and female rats exhibited enhanced nociceptive behavior in response to formalin. Food deprivation for 12 and 24 h increased and for 48 h decreased beta-endorphin level in male and female rats. Food deprivation for 24 h decreased testosterone level in male, while it had no significant effect on female rats and food deprivation for 48 h decreased testosterone level in both sexes. Food deprivation for 24 h increased estradiol level in female and that for 48 h had no significant effect on male and female rats. The present study demonstrates the existence of food deprivation for 48 h causes enhancement of nociception in the formalin test in male and female rats that has correlation with decrease in plasma beta-endorphin and testosterone levels
ABSTRACT
Introduction: It is well recognized that gender and race differences play a role in pain sensitivity, pain perception, response to analgesic drug and prevalence of certain chronic pain disorders. In this study investigated gender and strainrelated differences in the effect of food deprivation on formalin induced nociceptive behaviors in rats
Methods: This study was done in Qazvin University of Medical Sciences 8 groups of rats [220-300gr]. Groups 1 and 2: Effect formalin-induced nociceptive behaviours in male and female Sprague-Dawley rats. Groups 3 and 4: Effect formalin-induced nociceptive behaviours in male and female Wistar rats. Groups 5 and 6: Effect of food deprivation on formalin-induced nociceptive behaviours in male and female Sprague-Dawley rats. Groups 7 and 8: Effect of food deprivation on formalin-induced nociceptive behaviours in male and female Wistar rats. Food was withdrawn 48 h [short-term food deprivation] prior to performing the formalin test, but water continued to be available ad libitum. The formalin [50 microL, 2%] was injected into hind plantar paw. Immediately after the formalin injection, pain behaviors recorded for 90 minutes
Results: There is significant difference between male and female control Sprague-Dawley rats during phase 2B. Although interphase in male rats is more than female ones, but the phase 2B in female rats is more than male ones and phase 2 finished with delay in Sprague-Dawley race. There are no significant differences between male and female control Wistar rats during formalin test. Following 48-h food deprivation, male and femalerats exhibited enhanced nociceptive behaviors in response to formalin injection during phase 1, the interphase, phase 2. In contrast, 48 h food deprivation had significant effect on formalinevoked nociceptive behaviors in phase 2B for male Wistar and in interphase and phase 2B for female rats
Conclusion: The present study demonstrates the existence of gender and strain-related differences in rats in the development and maintenance of inflammatory hyperalgesia. Also, these differences observed following food deprivation