Footshock Research Articles

The effects of stress on splenic immune function are mediated by the splenic nerve

Intermittent footshock (FS) suppresses immune function of spleen cells. To determine if the autonomie nervous system mediates this immunosuppression in spleen cells, we tested whether cutting the splenic nerve, which depletes splenic norepinephrine levels by 98–100% and eliminates catecholamine fibers, blocks the effects of stress. Splenic nerve sections, sham operations, or no surgery were performed on male Sprague-Dawley rats. Ten days later, rats were injected with sheep red blood cells (SRBC). Three days later, rats were placed in a chamber equipped with a shock grid. Foot shock (1.6 mA) was administered for 5 s on a VI 3.5 min schedule for 60 min. Each FS was preceded by a 15-s warning tone. Controls were treated identically except for the FS. The next day spleen cells were harvested and the number of IgM plaque-forming cells (PFCs) determined. For the sham and unoperated control animals, the number of PFCs was reduced for the stressed animals relative to the nonstressed controls, and there was no effect of the sham surgeries. In contrast, there was no difference between the stressed and nonstressed groups in which the splenic nerve had been sectioned, and their PFC response was comparable to the controls. Next we examined the effects of FS on the proliferative response to mitogens (PHA and ConA) following splenic nerve sections or sham operations. One week following surgery, animals were given a 60-min session of FS or exposed to the chamber/tone without FS. Rats were then killed, spleens harvested, and the proliferative response to mitogens determined. Foot shock suppressed the response to mitogens in the sham rats, relative to the sham-operated animals not exposed to FS. In contrast, there was no difference between the stressed and nonstressed groups in which the splenic nerve had been cut, and their proliferative responses were comparable to the nonstressed-sham animals. Thus, the effects of stress on the PFC response and the proliferative response of spleen cells is mediated via the splenic nerve. These results indicate that the sympathetic nervous system is a fundamental and significant mediator of brain-immune interactions.

Anti-Stress Effect of Ginseng on the Inhibition of the Development of Morphine Tolerance in Stressed Mice.

We examined how the ginseng extract (GE) acts on the antinociceptive effect induced by footshock (FS)-, psychological (PSY)- and forced swimming (SW)-stress (stress-induced analgesia, SIA), and also on the suppression by FS- and PSY-stress of the development of tolerance to morphine in mice. Neither an acute treatment nor 5 daily pretreatments with GE at 100 mg/kg, p.o. affected each SIA. Pretreatment with GE at 100 mg/kg, p.o. for 5 days followed by the treatment in combination with the exposure to stresses for another 5 days caused no appreciable changes in the development of tolerance to FS- and SW-SIA, but suppressed the development of tolerance to PSY-SIA. When mice were pretreated with GE for 5 days and given GE daily prior to morphine at 10 mg/kg/day, with stress exposure for another 5 days, the inhibitory effect of FS-stress on the development of tolerance to morphine was completely eliminated. The present results suggest that GE, by improving the general metabolism in the body, directs toward normalization of the adaptability which is impaired by stress exposure, while not compromising morphine antinociceptive activity or the SIA, another adaptability produced in confrontation to abnormal environmental stimuli. In addition, the differences in the mechanism underlying the FS- and PSY-stress effect which we have previously demonstrated are also reconfirmed.

Anti-Stress Effect of Ginseng on the Inhibition of the Development of Morphine Tolerance in Stressed Mice

We examined how the ginseng extract (GE) acts on the antinociceptive effect induced by footshock (FS)-, psychological (PSY)- and forced swimming (SW)-stress (stress-induced analgesia, SI A), and also on the suppression by FS- and PSY-stress of the development of tolerance to morphine in mice. Neither an acute treatment nor 5 daily pretreatments with GE at 100 mg/kg, p.o. affected each SIA. Pretreatment with GE at 100 mg/kg, p.o. for 5 days followed by the treatment in combination with the exposure to stresses for another 5 days caused no appreciable changes in the development of tolerance to FS- and SW-SIA, but suppressed the development of tolerance to PSY-SIA. When mice were pretreated with GE for 5 days and given GE daily prior to morphine at 10 mg/kg/day, with stress exposure for another 5 days, the inhibitory effect of FS-stress on the development of tolerance to morphine was completely eliminated. The present results suggest that GE, by improving the general metabolism in the body, directs toward normalization of the adaptability which is impaired by stress exposure, while not compromising morphine antinociceptive activity or the SIA, another adaptability produced in confrontation to abnormal environmental stimuli. In addition, the differences in the mechanism underlying the FS- and PSY-stress effect which we have previously demonstrated are also reconfirmed.

Participation of GABAergic Systems in the Production of Antinociception by Various Stresses in Mice

Based on the data that diazepam, a benzodiazepine (BZP) receptor agonist, antagonized psychological (PSY)-stress induced analgesia (SIA) without prominent action on footshock (FS)- and forced swimming (SW)-SIA and that BZP receptors are coupled with GABA receptors, we examined how the GABAergic system participates in the production of various SIAs. Muscimol, a GABAA receptor agonist, at doses of 0.25 to 1.0 mg/kg, affected each SIA differently, suppressed PSY-SIA at 0.25 mg/kg but tended to potentiate it at 1.0 mg/kg, potentiated SW-SIA dose-dependently and did not affect FS-SIA at the doses employed. Both bicuculline, a GABAa receptor antagonist, 0.5 to 2.0 mg/kg, and picrotoxin, a Cl− channel blocker, 0.25 to 1.0 mg/kg, dose-dependently suppressed PSY- and FS-SIA. Meanwhile, the effects of both drugs on SW-SIA were less than those on PSY- and FS-SIA, namely, bicuculine slightly inhibited it only at 2.0 mg/kg, and picrotoxin did not produce any appreciable effect even at the highest dose. Baclofen, a GABAB receptor agonist, at 5.0 and 10.0 mg/kg had no influence on each SIA. On the contrary, CGP 35348, a GABAB receptor antagonist at 20 to 100 mg/kg caused the dose-dependent blockade of FS-SIA, but affected neither PSY- nor SW-SIA. The production of PSY- and SW-SIA is attributable to the GABAA receptors/Cl− channel mediated mechanism alone, while that of FS-SIA involves both GABAA and GABAB receptor mediated systems. Thus, GABAergic systems play an important role in the production of each SIA; however, the participation of the receptor subtypes in the mechanism was different from each other.

Further Evidence for the Participation of an .ALPHA.2-Adrenoceptor Mediated Mechanism in the Production of Forced Swimming-Stress Induced Analgesia in Mice.

Subanalgesic dose, 0.01 to 0.25 mg/kg, of clonidine (CLO), an alpha 2-adrenoceptor agonist, potentiated forced swimming (SW) stress induced analgesia (SIA) and suppressed psychological (PSY)-SIA in a dose dependent manner but did not affect foot-shock (FS)-SIA. Daily exposure to each stress rapidly developed tolerance, and the development was suppressed by daily concomitant subanalgesic dose of CLO in SW-SIA but not in FS- and PSY-SIA. Meanwhile, SW-stress, applied after injection of CLO, 1 mg/kg, potentiated the analgesic effect of CLO and suppressed the development of tolerance to the effect. On the other hand, FS- and PSY-stress did not affect CLO analgesia and failed to block the tolerance development. These results provide further evidence that alpha 2-adrenergic mechanism is involved in the production of SW-SIA.

Footshock- and Psychological-Stress Prevent the Development of Tolerance to Spinal but Not Supraspinal Morphine

The site of action involved in the suppression by exposure to footshock (FS)- and psychological (PSY)-stress of the development of antinociceptive tolerance to morphine has been investigated. Daily treatment with 10 mg/kg, s.c.; 3 μg, i.t.; and 5 μg, i.c.v. of morphine, regardless of the administration route, resulted in the development of tolerance. Daily exposure to FS- or PSY-stress suppressed the development of tolerance to s.c. and i.t. administered morphine but not that to i.c.v. administered morphine. Pretreatment with 2 mg/kg. i.p. of nor-binaltorphimine (nor-BNI) abolished the suppressive effect of PSY-stress on the development of tolerance to morphine given s.c. The suppression by PSY-stress was also antagonized by 2 μg, i.t. of nor-BNI and not by 2 μg, i.c.v. of nor-BNI. Thus, the development of tolerance in the spinal cord due to interaction of morphine at μ-opioid receptors can be suppressed by exposure to these stresses, probably through the descending signals from the supraspinal area, and activation of x-opioid receptors in the spinal cord could also participate in the suppression by PSY-stress.

Footshock- and psychological-stress prevent the development of tolerance to spinal but not supraspinal morphine.

The site of action involved in the suppression by exposure to footshock (FS)- and psychological (PSY)-stress of the development of antinociceptive tolerance to morphine has been investigated. Daily treatment with 10 mg/kg, s.c.; 3 micrograms, i.t.; and 5 micrograms, i.c.v. of morphine, regardless of the administration route, resulted in the development of tolerance. Daily exposure to FS- or PSY-stress suppressed the development of tolerance to s.c. and i.t. administered morphine but not that to i.c.v. administered morphine. Pretreatment with 2 mg/kg, i.p. of nor-binaltorphimine (nor-BNI) abolished the suppressive effect of PSY-stress on the development of tolerance to morphine given s.c. The suppression by PSY-stress was also antagonized by 2 micrograms, i.t. of nor-BNI and not by 2 micrograms, i.c.v. of nor-BNI. Thus, the development of tolerance in the spinal cord due to interaction of morphine at mu-opioid receptors can be suppressed by exposure to these stresses, probably through the descending signals from the supraspinal area, and activation of kappa-opioid receptors in the spinal cord could also participate in the suppression by PSY-stress.

Picrotoxin enhances latent extinction of conditioned fear.

Male CD1 mice received 20 pairings of tone and footshock (FS) or tone alone in an arm of a Y-maze on Day 1. On Day 2 either extinction (tone alone) or no extinction was followed immediately by saline or picrotoxin (0.5 or 1.0 mg/kg ip). Nonextinguished groups received only saline or picrotoxin (1.0 mg/kg ip) on Day 2. Other groups received saline or picrotoxin (1.0 mg/kg) 2 hr after extinction. On Day 3 all mice were placed in the Y-maze (with doors to all 3 alleys open), and total alley entries during a 2-min test session were recorded. Day 1 FS training resulted in reduced alley entries during the test session. Day 2 extinction session significantly attenuated the effects of the FS training. Day 3 performance of mice given picrotoxin (1.0 but not 0.5 mg/kg) immediately postextinction was comparable to that of mice not given FS on Day 1. The findings suggest that picrotoxin enhanced extinction of conditioned fear.

Further Evidence for the Implication of a κ-Opioid Receptor Mechanism in the Production of Psychological Stress-Induced Analgesia

The analgesic effect induced by exposure to psychological stress, using a communication box (psychological stress-induced analgesia, PSY-SIA), was completely antagonized by 10 min pretreatment with 0.5,1 and 2 mg/kg of nor-binaltorphimine and with 0.5 and 1 mg/kg of Mr2266, selective κ-opioid receptor antagonists, in the tail pinch method. Neither footshock (FS)-nor forced swimming (SW)-SIA was affected by these antagonists. The selective δ-opioid receptor antagonist naltrindole, at doses up to 20 mg/kg, had no appreciable effect on PSY-SIA. Daily morphine treatment, 10 mg/kg, s.c., resulted in tolerance to the analgesic effect, and concurrent exposure to PSY-stress suppressed the development of morphine tolerance. The substitution of treatment with U-50,488H for PSY-stress still resulted in analgesia on the initial day; and likewise, the suppression by U-50,488H of the development of morphine tolerance was replicated by PSY-stress. Pretreatment with nor-binaltorphimine antagonized the suppressive effect of PSY-stress on the development of morphine tolerance without affecting the analgesic effect of morphine per se. These results provide further evidence that PSY-SIA involves the mediation by κ-opioid receptor mechanisms.

Role of Adrenal Glucocorticoids in the Blockade of the Development of Analgesic Tolerance to Morphine by Footshock Stress Exposure in Mice

To elucidate the mechanism for the suppression by concurrent footshock (FS) exposure of the development of morphine tolerance, the effect of adrenalectomy and a possible participation of glucocorticoids in the mechanism were examined. The analgesic effect of morphine was potentiated in adrenalectomized (ADX) mice, and further enhancement of the effect was shown by the simultaneous exposure to FS (2mA,0.2 Hz, 1 sec duration for 15 min) stress, while no such effects were observed in sham-operated (Sham) animals. Daily morphine treatment developed tolerance in Sham and ADX mice. The combined treatment with FS stress suppressed the development of morphine tolerance in Sham mice, whereas such suppression was abolished by adrenalectomy. The suppression of tolerance development was restored in ADX mice by supplement of prednisolone. In contrast to FS stress which produces analgesia through an opioid receptor, forced swimming stress which exerts analgesia through a non-opioid mechanism did not affect the development of morphine tolerance in both Sham and ADX mice. Thus, an opioid mediated stress. FS, could prevent the development of morphine tolerance, and adrenal glucocorticoids play an essential role in the mechanism.

Role of adrenal glucocorticoids in the blockade of the development of analgesic tolerance to morphine by footshock stress exposure in mice.

To elucidate the mechanism for the suppression by concurrent footshock (FS) exposure of the development of morphine tolerance, the effect of adrenalectomy and a possible participation of glucocorticoids in the mechanism were examined. The analgesic effect of morphine was potentiated in adrenalectomized (ADX) mice, and further enhancement of the effect was shown by the simultaneous exposure to FS (2 mA, 0.2 Hz, 1 sec duration for 15 min) stress, while no such effects were observed in sham-operated (Sham) animals. Daily morphine treatment developed tolerance in Sham and ADX mice. The combined treatment with FS stress suppressed the development of morphine tolerance in Sham mice, whereas such suppression was abolished by adrenalectomy. The suppression of tolerance development was restored in ADX mice by supplement of prednisolone. In contrast to FS stress which produces analgesia through an opioid receptor, forced swimming stress which exerts analgesia through a non-opioid mechanism did not affect the development of morphine tolerance in both Sham and ADX mice. Thus, an opioid mediated stress, FS, could prevent the development of morphine tolerance, and adrenal glucocorticoids play an essential role in the mechanism.

Bimodal effects of noxious stimuli on vasopressin secretion in rats

Effects of electric foot shocks (FSs) on plasma immunoreactive vasopressin (ir-VP) were studied in relation to FS frequency in conscious and anesthetized rats under a hypertonic condition. The plasma ir-VP level was significantly lower after low-frequency FSs (0.05–0.2 Hz) but significantly higher after high-frequency FSs (5 Hz) in conscious rats. Plasma ir-VP was significantly higher in anesthetized rats after FSs at frequencies of either 0.2 or 50 Hz compared to unshocked control rats. These data support the hypothesis that FSs activate two distinct neural mechanisms: one potentiates and the other suppresses VP secretion.

Blockade of the Development of Analgesic Tolerance to Morphine by Concurrent Treatment with Opioid- But Not Non-Opioid-Mediated Stress in Mice

Studies have been carried out to determine how the analgesic effect of morphine and the development of tolerance to the effect would be influenced by concurrent exposure to stresses in mice. Application of footshock (FS) stress, which produces analgesia mediated by opioid μ-receptors, or psychological (PSY) stress, which produces analgesia in a manner more closely related to opioid κ-receptors, did not affect the analgesic effect of morphine, but completely blocked the development of tolerance during 5 daily concomitant treatments. On the other hand, forced swimming (SW) stress induced analgesia (SIA), which was not antagonized by naloxone, suppressed morphine analgesia, but failed to block the tolerance development. The blockade of the development of tolerance to morphine analgesia by stresses may not be attributed to the analgesic effect induced by the stresses because a combination of weak FS stress, which induces no analgesia, also effectively suppressed the development of morphine tolerance. In addition to the opioid mechanism, an adrenergic mechanism can not be excluded because of the reserpine antagonism of these SIAs.

Blockade of the development of analgesic tolerance to morphine by concurrent treatment with opioid- but not non-opioid-mediated stress in mice.

Studies have been carried out to determine how the analgesic effect of morphine and the development of tolerance to the effect would be influenced by concurrent exposure to stresses in mice. Application of footshock (FS) stress, which produces analgesia mediated by opioid mu-receptors, or psychological (PSY) stress, which produces analgesia in a manner more closely related to opioid kappa-receptors, did not affect the analgesic effect of morphine, but completely blocked the development of tolerance during 5 daily concomitant treatments. On the other hand, forced swimming (SW) stress induced analgesia (SIA), which was not antagonized by naloxone, suppressed morphine analgesia, but failed to block the tolerance development. The blockade of the development of tolerance to morphine analgesia by stresses may not be attributed to the analgesic effect induced by the stresses because a combination of weak FS stress, which induces no analgesia, also effectively suppressed the development of morphine tolerance. In addition to the opioid mechanism, an adrenergic mechanism can not be excluded because of the reserpine antagonism of these SIAs.

Brain stimulation of the ventral tegmental area attenuates footshock escape: an in vivo autoradiographic analysis of opiate receptors

An in vivo autoradiographic technique was employed to visualize discrete neuroanatomical changes in opiate receptor binding as a result of aversive footshock (FS) and rewarding electrical brain stimulation (ICS). Footshock-induced escape responding was shown to be attenuated by the simultaneous presentation of non-contingent ICS. Rats were divided into 4 groups ( n = 6) receiving ICS, FS, ICS + FS or neither stimulus in an escape paradigm. During the final behavioral test session, rats were injected with 0.002 mg/kg [ 3H]diprenorphine ([ 3H]Dpr) and subsequently prepared for autoradiography. Results indicated two groups of brain areas distinguishable by their treatment-induced changes in [ 3H]Dpr binding. One group of areas included the nucleus accumbens, claustrum, claustrocortex, perirhinal cortex and ventral tegmental area. These structures showed increased binding due to both FS and ICS. The other group consisted of the diagonal band of Broca, bed nucleus of the stria terminalis, lateral hypothalamus-medial forebrain bundle and amygdala. In these regions, an increase in binding ipsilateral to the electrode was observed in animals receiving ICS with no apparent effect of FS. These results demonstrate that non-contingent ICS may not be strictly aversive and suggest an anatomic, opioid-sensitive basis for both a rewarding and aversive component of this stimulus. It appears, further, that ICS can inhibit the release of endogenous opioid peptides in areas along the mesotelencephalic dopamine pathways, possibly to regulate the activity of neurons conveying reward information. Finally, the observed changes in opiate receptor binding may indicate a mechanism for ICS to produce both drive and reward.

Implication of endogenous opioid mechanism in the production of the antinociceptive effect induced by psychological stress in mice.

Psychological (PSY) stress using the communication box produced a short-lasting antinociceptive effect which was less potent than that induced by physical stress such as footshock (FS) and forced swimming (SW) in mice. Naloxone completely antagonized PSY-stress induced analgesia (SIA) when the analgesia was measured by the tail pinch (TP) method; however, the antagonist did not reverse the effect in the tail flick (TF) assay. On the other hand, FS-SIA was antagonized by naloxone in both methods, while naloxone failed to reverse SW-SIA in either TF or TP assessment. Daily exposure to psychological stress developed tolerance to the analgesia. One-way cross-tolerance between PSY-SIA and morphine and the naloxone antagonism of PSY-SIA by the tail pinch method lead to the suggestion that an endogenous opioid system may be involved in the underlying mechanism for its production. On the contrary, from the findings of cross-tolerance between SW- or FS-SIA and the lack of naloxone antagonism in the TF method, the involvement of a more complicated mechanism is suggested in PSY-SIA. In both tests, U-50488H, a selective kappa-agonist, produced profound analgesia; however, no appreciable antagonism of naloxone was found in the TF test, whereas the effect was completely blocked by naloxone in the TP test. From the similarity in naloxone antagonism of PSY-stress and U-50488H induced analgesia, the participation of a common mechanism which may be mediated by kappa-opioid receptors, is suggested in the production of PSY-SIA.

Potentiation of vasopressin secretion by footshocks in rats.

Effects of footshocks (FS) on antidiuretic hormone (vasopressin, VP) in the plasma were studied in rats. Continuously applied FS of 60 s period with 5 ms pulses at 50 Hz frequency significantly increased VP as well as adrenocorticotrophic hormone (ACTH) in the plasma in a time- and shock intensity-dependent manner. Contrarily, the 50 Hz FS of 2 s period as repeated intermittently at every 15 s for over the period of 2, 10, and 30 min were much less effective for increasing plasma VP, whereas these intermittent FS increased plasma ACTH to an extremely high level. During the inter-shock intervals of 13 s between successive two shock periods rats exhibited a "freezing" behavior. Hypertonic saline or urethane injected I.P. immediately after termination of the intermittent FS significantly increased VP as well as ACTH in the plasma. These data clearly indicate that FS potentiate VP secretion and suggest the possibility that emotional stress may suppress the noxious stimuli-induced VP secretion.

Neurophysiological analysis of the development of endocrine and hypertensive reactions in prolonged emotional stress

The model of immobilization stress with aperiodic foot shock (FS) was used to study the effect of a prolonged emotional stress on the functional condition of cortical and subcortica structures (hypothalamic and reticular structures in particular) in EEG activity and to elucidate their role in the development of endocrine and hypertensive reactions. It is shown that the development of hypertensive reactions in animals is stipulated by dynamic changes in the functional condition of the CNS, particularly in the hypothalamic neuroendocrinal control mechanism and reticular formation of the midbrain, which can be conditionally subdivided into 3 stages. The first is characterized by the emergence of short-time cycles of the hypersynchronized activity of slow waves in the cortical and subcortical mechanism, which is accompanied by adaptive hormonal secretion and transient effects of vascular reactions to FS; in the meantime neither neuroendocrinal nor blood pressure (BP) self-regulation mechanisms are impaired. The second stage is characterized (3–4 days after the beginning of the exposure) by the development of ‘persistent’ excitation in the CNS and the stabilization of a high level of hormones in the blood. Vascular reactions to FS are extremely prolonged ones; in intervals between FS applications BP fails to return to initial values. The third stage (1 month after cessation of experiments) is characterized by normal background EEG-activity in cortical-subcortical structures, normal indices of hormonal homeostasis but high level of BP. In response to ‘repeated’ stress, on the first experimental day, prolonged hypersynchronization of slow waves in cortical-subcortical structures occured while BP reactions to FS were also prolonged and high hormonal secretion was observed. The data obtained suggest the high reactivity of reticular-hypothalamic structures which determine primarily the characteristics of both vascular and hormonal reactions that could be understood to be due to the result of previous experience (the first stage of stress).

Comparative Studies on Morphine- and Stress-Induced Analgesia and the Development of Tolerance to the Effects: Implication of Protein Synthesis Mechanism in the Process

Comparative studies were made on morphine- and stress-induced analgesia (SIA) and also on the development of tolerance to the effects. Cycloheximide (CYH), a potent protein synthesis inhibitor, did not affect the analgesic effect of morphine, but effectively suppressed the development of tolerance. CYH, however, potentiated both foot shock (FS) and immobilized-water immersion (IW) SIAs and inhibited the development of tolerance to FS-SIA. Incorporation of 3H-leucine into the TCA-insoluble fraction of mouse brain regions was inhibited by morphine, and the inhibition was reversed by the pretreatment with CYH. The inhibitory effect of morphine was lost in morphine tolerant animals. At the peak of SIA, incorporation of 3H-leucine was not changed in FS-SIA, but significantly inhibited in IW-SIA, and these effects were not modified by the pretreatment with CYH. The reduced incorporation of 3H-leucine in IW-SIA tolerant animals was partially reversed by CYH. Thus, the protein synthesis mechanism is greatly influenced by morphine or stresses, but the direct evidence for the implication of the mechanism in the process of producing analgesia and tolerance formation could not be demonstrated. However, differences in the underlying mechanisms were apparent between morphine and SIAs and also between FS- and IW-SIA.

Diversity of Underlying Mechanisms in the Production of Analgesic and Pentobarbital-Hypnosis Prolonging Effects of Various Analgesic Drugs and Stresses

Stressful stimuli, electric footshock (FS), immobilized-water immersion (IW), and cold-water swimming (CWS), produced analgesia and prolonged the pentobarbital hypnosis as well as morphine and clonidine. Naloxone completely antagonized the analgesic effects of morphine and FS and partially that of IW; however, that of clonidine and CWS were not reversed by naloxone. Naloxone eliminated the hypnosis prolonging effect of morphine and FS, but failed to reverse the effect of clonidine, IW and CWS. Differences in the analgesic and hypnosis prolonging effects and also the respective naloxone sensitivity of each drug and stress suggest the diversity of the underlying mechanisms.