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Effects of formalin pain on hippocampal c-Fos expression in male and female rats
No full textImmediate early genes are crucial intermediates in a cascade linking membrane stimulation to long-term alterations of neuronal activity. In the present experiment, we performed immunohistochemistry for c-Fos to determine the effects of persistent pain on cells of the hippocampus of male and female rats. Animals were subcutaneously injected with formalin (50 mu l, 10%) and perfused: 2 h later, time 2; 24 h later, time 24; 24 h later after 20 min of the open-field test, time 24/OF. Controls were left undisturbed. In control, c-Fos was higher in females than in males in all hippocampal fields. In males at time 2, formalin increased c-Fos in the dentate gyrus (DG) and CA3 fields; at time 24, c-Fos returned to the control level; at time 24/OF, c-Fos was higher than in control in the DG, but not in the other fields. In the formalin-treated females at time 2 and at time 24, c-Fos levels were lower, or tended to be lower, than in control in all hippocampal fields; at time 24/OF, c-Fos levels in the DG were higher than in control and in males. In conclusion, persistent pain had different effects on c-Fos in the hippocampal subfields, depending on the time after treatment and the sex of the subject
Androgens modulate the behavioural and neuronal effects of repeted nociceptive stimulation in male rats
No full textEffects of gonadal hormones and persistent pain on non-spatial working memory in male and female rats.
No full textThere are indications of a modulatory role carried out by gonadal hormones and pain in cognitive functions. We have examined this issue in male and female rats by assessing the impact of gonadectomy and persistent pain on the object recognition test. Intact and gonadectomized male and female rats were exposed to an open field (15 min) in which three objects were placed (Trial 1); the same test was repeated 2 h later (Trial 2), after the replacement of a "familiar" object with a novel one. Three days later (Day 2), the same procedure was repeated (Trial 3 and 4 with 2 h in between) but half of the animals were exposed to formalin-injection immediately before Trial 3. The latency, frequency and duration of approaching the three objects were recorded in each trial and compared by sex, gonadectomy and formalin treatment. The results showed that gonadectomized males and females had lower levels of approach to all objects and less locomotor/exploratory activity than intact animals in all experimental trials; their behaviour was not affected by repetition of the test or by pain. On Day 1, intact males showed a higher level of approach to the novel object than females. In intact males, the 2 h delay between the first and second trial failed to induce any significant modification of exploration of the novel object with respect to the familiar one, while in intact females the novel object was approached much less than the familiar one. Similarly on Day 2, the novel object was approached for a longer time by intact males than by all the other groups. In conclusion, our data show that physiological levels of circulating gonadal hormones significantly affected the performance of male but not female rats when exposed to the object recognition test
Sex differences in the olfactory stimulation-induced effects on the formalin test
No full textAromatic plants and their oils have long been known to exert various psychological and physiological effects on the human mind and body. The ability of olfactory input to stimulate, suppress or modulate various types of behavior in mammalian species has repeatedly been demonstrated. However, no data are available concerning tonic long-lasting pain. The formalin test is a well-characterized method to induce tonic long-lasting pain that shows several features of clinical pain. In the present experiment, male and female rats were subcutaneously injected with 50 μ1 of dilute formalin (5%) and introduced to a hole-board apparatus. Under the bottom of the hole-board, half of the animals received lemon essence in water and half only water. During the test, the formalin-induced responses (licking duration, flexing duration and jerking frequency of the injected limb) and other spontaneous behaviors (rearing, grooming) were recorded. Sixty minutes later, the animals were killed and blood was collected from the abdominal aorta to determine corticosterone plasma levels. The results showed a clear reduction of licking in the lemon essence group during the first 25 min of the test; the effect was greater in female than male rats. There were no differences between the groups in flexing and jerking during the first phase (0-15 min); however, the levels were lower in the lemon-treated group throughout the second phase (16-60 min), the greatest reduction occurring at 16-30 min of the formalin test. Rearing and grooming were increased by the lemon odor only in sham-treated animals, while in formalin-treated ones there were no differences. The present results clearly indicate the ability of lemon odor to modulate persistent pain in male and female rats and support further studies to better define the neuronal circuits involved
Naloxone but not estradiol, affects the gonadectomy-induced increase in hippocampal cholineacetyltransferase activity in male rats.
No full textEffects of the essential oil from citrus lemon in male and female rats exposed to a persistent painful stimulation
No full textThe ability of olfaction to modulate behavior in mammalian species has repeatedly been demonstrated. Here we tested the properties of the volatile components of lemon essential oil. Male and female rats were allowed to inhale the aroma while experiencing a persistent nociceptive input (50 microl formalin, 5%); in the same animals the c-Fos immunohistochemistry was used to test the degree of neuronal activation of areas belonging to the limbic system. In formalin-treated animals, lemon essential oil decreased licking the injected paw, in both sexes; flinching and flexing were decreased in males and increased in females in the interphase (5-20 min) of the formalin test. Essential oil increased the c-Fos expression in the arcuate n. of the hypothalamus. Essential oil and formalin increased c-Fos in the paraventricular n. of the hypothalamus and in the dentate gyrus of the hippocampus. In the paraventricular n. of the thalamus formalin induced higher c-Fos than control in both sexes; when formalin treatment was carried out in presence of essential oil, c-Fos further increased in males, but remained at control levels in females. The present results clearly indicate the ability of lemon essential oil to modulate the behavioral and neuronal responses related to nociception and pain
192 IgG -saporin-induced selective cholinergic denervation modifies formalin pain in male rats.
No full textPrevious studies showed an involvement of ACh in pain processes. The aim of the present experiment was to investigate the role of central cholinergic pathways in formalin pain-induced responses. 192 IgG-saporin, a potent immunotoxin able to induce the loss of cholinergic neurons, was ICV injected into male rats for 3 consecutive days; vehicle was used as control. During the 3 weeks following treatment (saporin or vehicle), the pain threshold (plantar test) and spontaneous behaviors (hole board) were determined, then the animals were subjected to the formalin test (50 l, 5% SC in the dorsal hind paw). The formalin-evoked licking, flexing, and jerking of the injected paw were recorded for 60 min. No differences between groups were found in the plantar test and hole board determinations. None of the formalin-evoked responses showed a saporin-induced modification during the first 15 min (first phase). During the second phase (15–60 min), there was a difference in the first part (ascending) of the curve, with higher levels of licking and jerking in the saporin-treated animals than in controls, and in the second part (descending), with lower levels of licking and jerking in saporin-injected animals. The results show an involvement of the cholinergic system in the second, longer lasting phase of formalin pain. The cholinergic activation, known to be induced by pain mostly during the second phase, appears to delay the behavioral output due to the central processes involved in the maintenance of pain
The behavioral and neuronal effects induced by repetitive nociceptive stimulation are affected by gonadal hormones in male rats
No full textThe role of gonadal hormones in inducing long-term modifications in response to transient nociceptive stimuli was investigated in adult male rats. Three weeks after gonadectomy or sham surgery, animals were randomly divided into groups to be exposed to sham (only a prick in the dorsal hind paw) or formalin treatment (50 microl, 5% s.c. in the dorsal hind paw) once a week for the following 3 weeks. In gonadectomized animals the formalin-induced responses (licking, flexing and jerking of the injected paw) did not differ from those of intact animals after the first formalin injection. However, their levels were higher after the second or third injections. Indeed, in intact animals the formalin-induced responses progressively decreased, being significantly lower after the third injection than after the first; in gonadectomized animals, the formalin-induced responses did not change with repetition of the formalin treatment. In intact rats, c-Fos expression in the paraventricular nucleus of the thalamus and arcuate nucleus of the hypothalamus remained at control levels or decreased in animals injected two or three times with formalin; in gonadectomized rats, c-Fos expression increased with repetition of the noxious stimulation, reaching the highest levels in animals injected three times with formalin. These results show that male gonadal hormones have an inhibitory, adaptive effect on the behavioral and neuronal responses to repeated nociceptive stimulation
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