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Stimulation of the lateral septum attenuates immobilization-induced stress ulcers
Physiology & Behavior, Vol. 59, Nos. 4 / 5 , pp. 883-886, 1996 Copyright © 1996 Elsevier Science lnc. Printed in the USA. All rights reserved 0031-9384/96 $15.00 + .00
ELSEVIER
SSDI 0031-9384(95)02184-1
Stimulation of the Lateral Septum Attenuates Immobilization-Induced Stress Ulcers ELNA Y A D I N 1 AND EARL THOMAS
Department of Psychology, Bryn Mawr College, Bryn Mawr, PA 19010 USA Received 31 July 1995 YADIN, E. AND E. THOMAS. Stimulation of the lateral septum attenuates immobilization-induced stress ulcers. PHYSIOL BEHAV 59(4/5) 883-886, 1996.--Rats with electrodes implanted in their dorsolateral septal area underwent a cold-immobilization restraint procedure during which the experimental group received electrical stimulation while the control group did not. Electrical stimulation of the dorsolateral septal region clearly reduced the number of gastric ulcers formed during the cold-immobilization stress procedure. The pattern of results with septal stimulation contrasts with that seen by other investigators after stimulation of the central amygdaloid nucleus. The mitigation of stress-induced ulceration after lateral septal stimulation is consistent with the proposed function for the lateral septal area in relief from aversive emotional states. Cold-immobilization stress
Lateral septum
Stimulation
Gastric ulcers
lati~n ,,-nay protect an organism from some of the effects of known stressors. One example of a stressor used in animals to approximate situations of psychological stress in humans is immobilization stress (l l). This behavioral paradigm typically entails restraining and immobilizing the animal for a given period of time and examining the development of stress-induced gastric ulcers (1). Henke and colleagues have amassed a body of evidence linking the central nucleus of the amygdala and related structures to the development and severity patterns of stress-induced ulceration (6). Electrical and chemical stimulation of the central nucleus of the amygdala have been shown to increase severity of such ulcers, while chemical inhibition, such as with local administration of dopamine, has resulted in decreased severity and size of the ulcers (13). Based on experimental evidence gathered from numerous behavioral and physiological approaches, it has been suggested that the central amygdaloid nucleus may be part of a system in the brain whose function is the mediation of fear and anxiety [e.g., (2)]. Because the lateral septal nucleus appears to be the opposite from the central amygdala in its effects on and responses to fear stimuli, the prediction was that lateral septal stimulation would retard the development of stress-induced gastric ulcers during immobilization stress. The purpose of the present study was to test that prediction, using the same immobilization procedure used by Henke et al., namely, cold-immobilization stress (CIS).
THE lateral septum has been implicated in~,,.~,. . . ..,,.u,,~lv. . . . . . . . . . . .v, . . .,,.l,,., ... from aversive states (15). Based on evidence from an array of experimental approaches, activation of the anterior dorsolateral septal region of the forebrain resulted in the mitigation of fear-induced physiological and behavioral responses (18). Single-unit activity recorded during classically conditioned excitation and inhibition of fear was shown to closely reflect the animals' emotional state. Thus, the activity of cells in the lateral septum was inhibited during presentations of an established conditioned excitor of fear and was enhanced during presentations of an established conditioned inhibitor of fear (17). It has also been shown that the pattern of electrophysiological responses was altered in the presence of anxiolytic agents in a way that is consistent with a fear-relief role for the lateral septum. For example, administration of the benzodiazepine chlordiazepoxide raised the spontaneous activity of the cells in this brain region and resulted in a significant diminution of the inhibitory effect of the conditioned excitor of fear (14). Electrical stimulation of the dorsolateral septum during performance of a lick suppression conflict task produced a significant increase in the number of licks during a signaled punished period (18). The increased punished licking could be due neither to the rewarding quality of the stimulation nor to its general activating properties, because electrical stimulation of the highly rewarding and activating site, the medial forebrain bundle, produced no changes in the same situation (18). Similarly, the resulting pattern of licking behavior could not be attributed to changes in thirst, because the effect was specific to the punished period, leaving the unpunished period unaltered. It was reasoned that if stimulation of the anterior dorsolateral septal area possessed stress-relieving properties, then such stimu-
METHOD
Subjects The subjects were 12 albino male Sprague-Dawley rats, approximately 80 days old at the start of the experiment. They
1 TO whom requests for reprints should be addressed. 883
884
YADIN AND THOMAS
30 09 r~ W
o, h 0 n," W rn
Z
20
10
STRESS
STRESS+SEPTAL STIMULATION
FIG. 1. The mean number of stomach ulcers ( + SEM) present in two groups of rats undergoing cold-immobilization stress. Asterisk (*) marks a significant difference between the two groups.
were housed individually in a climate-controlled colony, with a 12 D: 12 L cycle (lights on at 0800 and off at 2000 h). They were maintained on ad lib food and water.
Apparatus Plexiglas rat restrainers were used to immobilize the rats. The restrainers were custom made, allowing adjustments for individual rat size to assure total immobilization. It was seen in pilot testing that the ability of a rat to move within the restraining apparatus resulted in a diminished number of ulcers produced during the same procedure. Brain stimulation was provided by a stimulator (Grass model $88), in series with an isolation unit (Grass model SIU5) and a constant current unit (Grass model CCU1A).
Procedure Rats were first implanted unilaterally with standard bipolar stimulating electrodes (Plastics One, VA), under pentobarbital anesthesia (40 m g / k g ) . The coordinates for the anterior dosrolat-
eral septum were: 0.5 m m anterior to bregma, 0.75 mm lateral to the midline, 5.0 mm from the surface of the skull. After at least a l-week recovery period food was removed. Twenty-four hours later the immobilization session was administered. The animals were run in pairs. Each rat was placed in its own restrainer, a connector attached to the stimulating electrode, and then both animals were placed in a ventilated cold room at 4°C, for a duration of 3 h. During the entire restraint session the experimental animals received trains of septal brain stimulation every 90 s. Stimulation consisted of 0.5 s trains of biphasic square-wave pulses, 0.1 ms duration, delivered at a rate of 100 pulses per second. The current was 50 /,amp throughout the 3-b period. These stimulation parameters are the same parameters that were used in previous experiments testing the effects of septal stimulation on conflict behavior (l 8). The current chosen for use in these experiments was 2 / 3 of the current that typically sustains selfstimulation in these rats. The control animals were placed in the same conditions but received no stimulation. After the cold immobilization session was complete animals were anesthetized and their stomachs and brains removed. The stomachs were cut along the greater curvature, rinsed lightly in distilled water, and stretched and pinned onto Styrofoam boards. The number of hemorrhages overlying the ulcers in the acid secreting portion of the stomach were recorded. For verification of the electrode locations brains were first placed in 10% formaldehyde, and then frozen sections were taken and photographed, using the fresh sections as negatives. RESULTS
Stimulation of the anterior dorsolateral septum during a 3-h session of cold immobilization restraint dramatically reduced the number of stress-induced stomach ulcers (Fig. 1). A significant decrease in number of ulcers was found in the stimulated group compared with their unstimulated matched controls, t(10) = 2.28, p < 0.05. An example of stomachs from a pair of rats that simultaneously underwent the experimental manipulation is presented in Fig. 2. The stomach in panel A is from a control rat that was immobilized but received no stimulation. As can be seen, a
D
i
i
FIG. 2. Photographs of representative stomachs from two rats that had undergone the cold-immobilization stress procedure. (A) Stress with no lateral septal stimulation. (B) Stress with lateral septal stimulation.
LATERAL SEPTUM STIMULATION MITIGATION ULCERS
TABLE 1 NUMBER OF STRESS-INDUCED GASTRIC ULCERS FOR INDIVIDUAL SUBJECTS Subject Pair
C I S + No Stimulation
1
35
CIS + Stimulation
0
2 3 4 5 6
5 13 19 45 12
0 0 3 20 6
typical control stomach specimen is riddled with ulcers. The stomach in panel B is from an experimental rat that was immobilized and, concurrently, received lateral septal brain stimulation. It can be clearly seen that this stomach is devoid of ulcers entirely. In some of the animal pairs the effect of septal stimulation was not complete elimination of ulcers but rather a drastic reduction in their number. Table 1 shows the number of ulcers found in individual rat pairs. As can be seen in Table 1, while there is some variability in the number of ulcers found in different rat pairs, dorsolateral septal stimulation yielded a consistent reduction of the incidence of stress-induced ulceration, regardless of the severity of the ulcers (initial number). A representative example of a brain section with the stimulating electrode tip located in the anterior dorsolateral portion of the septal area is shown in Fig. 3. Electrode tip locations were consistently within this brain site. DISCUSSION Electrical stimulation of the dorsolateral septal region clearly reduced the number of gastric ulcers formed during a cold-immobilization stress procedure. This decrease is consistent with the proposed function for the lateral septal area in relief from aversive emotional states (15,18). The pattern of results with septal stimulation contrasts with that seen after stimulation of the central amygdaloid nucleus. Whereas amygdala stimulation ag-
885
gravated stress-induced gastric ulcers (8), septal stimulation alleviated them. The parameters used by Henke (7) to stimulate the central amygdala nucleus were comparable to the ones used in this study to stimulate the lateral septum. The mean number of ulcers resulting from the restraint paradigm reported in this experiment is somewhat higher than the mean number of ulcers reported by other investigators, using a cold-immobilization procedure (8,9,13). Pilot testing showed a relationship between the degree of immobilization and the number of ulcers found after 3 h of restraint in the cold. It is possible that the use of a custom-made restrainer that could be individually adjusted to snugly fit each animal, produced overall a higher number of ulcers. We are currently exploring a stress response curve, varying the stress parameters, to address this possibility. The first three pairs of rats run in this experiment were also compared at the time of restraint to three handled, but unstressed control rats. Because gross physiological measures such as body weight and ulceration were not different in these animals, these control animals were omitted from the experimental design. It has been demonstrated in several other behavioral paradigms that the lateral septal nucleus and the central nucleus of the amygdala exert effects that appear to be opposite to each other (10). For instance, electrophysiological studies that measured changes in neuronal activity during conditioning paradigms showed increased activity to the conditioned excitor of fear in the amygdala (12) and suppression of activity to that stimulus in the lateral septal nucleus (16). LeDoux has recently made the recommendation that circuits of emotion are best worked out empirically (9). Thus, it has become generally accepted that the amygdala, and in particular its central nucleus, plays a crucial role in acquisition and expression of fear based behaviors. One example of such a behavior is the fear-potentiated startle response, which is an enhanced expression of startle to a stimulus that had been previously paired with an aversive stimulus. Chemical or electrolytic lesions of the lateral, basolateral, or central amygdaloid nuclei block the expression of fear-potentiated startle (4). It is thought that the lateral and basolateral nuclei process sensory information per-
FIG. 3. A photograph, using a fresh tissue slice as a negative, of a representative brain section with electrode tip in the dorsolateral septal area.
886
YADIN AND THOMAS
ceived by various modalities. They project to the central nucleus, which projects in turn, to other sites downstream (hypothalamus, central gray), thus producing the specific signs of fear or anxiety (3,9). The cold-immobilization stress procedure has been used extensively to explore the role of the amygdala and related structures and transmitter systems in stress-induced phenomena (6). Structures whose activation resulted in a reduction in immobilization-induced stress ulcers include the medial prefrontal cortex, the posterior cingulate cortex, the ventral entorhinal cortex, the dentate gyrus and the ventral hippocampus, and the posterolateral amygdala. These anatomical structures have been referred to by Henke as inhibitory during stressful experiences (6). Based on the results of the present experiment, one must add the lateral septal nucleus to that category of emotion modulating structures. In Henke's category of facilitatory structures during stressful situa-
tions, on the other hand, one finds the centromedial amygdala and the anterior cingulate cortex (6). The mechanism by which these structures influence each other is a matter of speculation. In the startle paradigm it was shown that with combined lesions of the septum and amygdala, the amygdala effects predominate (10). The same pattern was found to be true in the water-lick conflict test (5). These combined-lesion data indicate that septal inhibition of stress and other aversive emotional states may operate via inhibitory control of the amygdala. ACKNOWLEDGEMENTS We acknowledge the hospitality of members of the Pharmacology Department at the Israel Institute for Biological Research where the preliminary work for this research was carried out, and we thank Dr. Gad Simon for photographing the stomachs.
REFERENCES 1. Bonfils, S.; Lamling, A. Psychological factors and psychopharmacological actions in the restraint induced gastric ulcer. In: Skornya, S. C., ed. Pathophysiology of peptic ulcer. Montreal: McGill University Press; 1963:153-171. 2. Davis, M. The role of the amygdala in fear and anxiety. Annu. Rev. Neurosci. 15:353-375; 1992. 3. Davis, M.; Falls, W. A.; Campeau, S.; Kim, M. Fear-potentiated startle: A neural and pharmacological analysis. Behav. Brain Res. 58:175-198; 1993. 4. Davis, M. J.; Hitchcock, J. M.; Rosen, J. B. Anxiety and the amygdala: Pharmacological and anatomical analysis of the fearpotentiated startle paradigm. In: Bower, G. H., ed. The psychology of learning and motivation. 21. New York: Academic Press; 1987:263305. 5. Grishkat, H. L. Modulation of anxiety: A role for the septum and amygdala in the effects of benzodiazepine anxiolytics. Unpublished Master's Thesis, Bryn Mawr College; 1991. 6. Henke, P. G. The telencephalic limbic system and experimental gastric pathology: A review. Neurosci. Biobehav. Rev. 6:381-390; 1982. 7. Henke, P. G. The amygdala and forced immobilization of rats. Behav. Brain Res. 6:19-24; 1985. 8. Henke, P. G.; Sullivan, R. M. Kindling in the amygdala and susceptibility to stress ulcers. Brain Res. Bull. 14:5-8; 1985. 9. LeDoux, J. E. Emotional memory systems in the brain. Behav. Brain Res. 58:69-79; 1993.
10. Melia, K. R.; Sananes, C. B.; Davis, M. Lesions of the central nucleus of the amygdala block the excitatory effects of septal ablation on the acoustic startle reflex. Physiol. Behav. 51:175-180; 1992. 11. Pare, W. P.; Glavin, G. B. Restraint stress in biomedical research: A review. Neurosci. Biobehav. Rev. 10:339-370; 1986. 12. Pascoe, J. P.; Kapp, B. S. Electrophysiological characteristics of amygdaloid central nucleus neurons during Pavlovian fear conditioning in the rabbit. Behav. Brain Res. 16:117-133; 1985. 13. Ray, A.; Henke, P. G.; Sullivan, R. M. Effects of intra-amygdalar dopamine agonists and antagonists on gastric stress lesions in rats. Neurosci. Lett. 84:302-306; 1988. 14. Strickland, C. E.; Thomas, E.; Yadin, E. Effects of chlordiazepoxide on septal single unit activity following pavlovian conditioning: A regional comparison. Soc. Neurosci. Abstr. 18:360; 1992. 15. Thomas, E. Forebrain mechanisms in the relief of fear: The role of the lateral septum. Psychobiology 16:36-44; 1988. 16. Thomas, E.; Yadin, E.; Strickland, C. E. Septal unit activity during classical conditioning: A regional comparison. Brain Res. 547:303308; 1991. 17. Yadin, E.; Thomas, E. Septal correlates of conditioned inhibition and excitation. J. Comp. Physiol. Psychol. 95:331-340; 1981. 18. Yadin, E.; Thomas, E.; Grishkat, H. L.; Strickland, C. E. The role of the lateral septum in anxiolysis. Physiol. Behav. 53:1077-1083; 1993.
ELSEVIER
SSDI 0031-9384(95)02184-1
Stimulation of the Lateral Septum Attenuates Immobilization-Induced Stress Ulcers ELNA Y A D I N 1 AND EARL THOMAS
Department of Psychology, Bryn Mawr College, Bryn Mawr, PA 19010 USA Received 31 July 1995 YADIN, E. AND E. THOMAS. Stimulation of the lateral septum attenuates immobilization-induced stress ulcers. PHYSIOL BEHAV 59(4/5) 883-886, 1996.--Rats with electrodes implanted in their dorsolateral septal area underwent a cold-immobilization restraint procedure during which the experimental group received electrical stimulation while the control group did not. Electrical stimulation of the dorsolateral septal region clearly reduced the number of gastric ulcers formed during the cold-immobilization stress procedure. The pattern of results with septal stimulation contrasts with that seen by other investigators after stimulation of the central amygdaloid nucleus. The mitigation of stress-induced ulceration after lateral septal stimulation is consistent with the proposed function for the lateral septal area in relief from aversive emotional states. Cold-immobilization stress
Lateral septum
Stimulation
Gastric ulcers
lati~n ,,-nay protect an organism from some of the effects of known stressors. One example of a stressor used in animals to approximate situations of psychological stress in humans is immobilization stress (l l). This behavioral paradigm typically entails restraining and immobilizing the animal for a given period of time and examining the development of stress-induced gastric ulcers (1). Henke and colleagues have amassed a body of evidence linking the central nucleus of the amygdala and related structures to the development and severity patterns of stress-induced ulceration (6). Electrical and chemical stimulation of the central nucleus of the amygdala have been shown to increase severity of such ulcers, while chemical inhibition, such as with local administration of dopamine, has resulted in decreased severity and size of the ulcers (13). Based on experimental evidence gathered from numerous behavioral and physiological approaches, it has been suggested that the central amygdaloid nucleus may be part of a system in the brain whose function is the mediation of fear and anxiety [e.g., (2)]. Because the lateral septal nucleus appears to be the opposite from the central amygdala in its effects on and responses to fear stimuli, the prediction was that lateral septal stimulation would retard the development of stress-induced gastric ulcers during immobilization stress. The purpose of the present study was to test that prediction, using the same immobilization procedure used by Henke et al., namely, cold-immobilization stress (CIS).
THE lateral septum has been implicated in~,,.~,. . . ..,,.u,,~lv. . . . . . . . . . . .v, . . .,,.l,,., ... from aversive states (15). Based on evidence from an array of experimental approaches, activation of the anterior dorsolateral septal region of the forebrain resulted in the mitigation of fear-induced physiological and behavioral responses (18). Single-unit activity recorded during classically conditioned excitation and inhibition of fear was shown to closely reflect the animals' emotional state. Thus, the activity of cells in the lateral septum was inhibited during presentations of an established conditioned excitor of fear and was enhanced during presentations of an established conditioned inhibitor of fear (17). It has also been shown that the pattern of electrophysiological responses was altered in the presence of anxiolytic agents in a way that is consistent with a fear-relief role for the lateral septum. For example, administration of the benzodiazepine chlordiazepoxide raised the spontaneous activity of the cells in this brain region and resulted in a significant diminution of the inhibitory effect of the conditioned excitor of fear (14). Electrical stimulation of the dorsolateral septum during performance of a lick suppression conflict task produced a significant increase in the number of licks during a signaled punished period (18). The increased punished licking could be due neither to the rewarding quality of the stimulation nor to its general activating properties, because electrical stimulation of the highly rewarding and activating site, the medial forebrain bundle, produced no changes in the same situation (18). Similarly, the resulting pattern of licking behavior could not be attributed to changes in thirst, because the effect was specific to the punished period, leaving the unpunished period unaltered. It was reasoned that if stimulation of the anterior dorsolateral septal area possessed stress-relieving properties, then such stimu-
METHOD
Subjects The subjects were 12 albino male Sprague-Dawley rats, approximately 80 days old at the start of the experiment. They
1 TO whom requests for reprints should be addressed. 883
884
YADIN AND THOMAS
30 09 r~ W
o, h 0 n," W rn
Z
20
10
STRESS
STRESS+SEPTAL STIMULATION
FIG. 1. The mean number of stomach ulcers ( + SEM) present in two groups of rats undergoing cold-immobilization stress. Asterisk (*) marks a significant difference between the two groups.
were housed individually in a climate-controlled colony, with a 12 D: 12 L cycle (lights on at 0800 and off at 2000 h). They were maintained on ad lib food and water.
Apparatus Plexiglas rat restrainers were used to immobilize the rats. The restrainers were custom made, allowing adjustments for individual rat size to assure total immobilization. It was seen in pilot testing that the ability of a rat to move within the restraining apparatus resulted in a diminished number of ulcers produced during the same procedure. Brain stimulation was provided by a stimulator (Grass model $88), in series with an isolation unit (Grass model SIU5) and a constant current unit (Grass model CCU1A).
Procedure Rats were first implanted unilaterally with standard bipolar stimulating electrodes (Plastics One, VA), under pentobarbital anesthesia (40 m g / k g ) . The coordinates for the anterior dosrolat-
eral septum were: 0.5 m m anterior to bregma, 0.75 mm lateral to the midline, 5.0 mm from the surface of the skull. After at least a l-week recovery period food was removed. Twenty-four hours later the immobilization session was administered. The animals were run in pairs. Each rat was placed in its own restrainer, a connector attached to the stimulating electrode, and then both animals were placed in a ventilated cold room at 4°C, for a duration of 3 h. During the entire restraint session the experimental animals received trains of septal brain stimulation every 90 s. Stimulation consisted of 0.5 s trains of biphasic square-wave pulses, 0.1 ms duration, delivered at a rate of 100 pulses per second. The current was 50 /,amp throughout the 3-b period. These stimulation parameters are the same parameters that were used in previous experiments testing the effects of septal stimulation on conflict behavior (l 8). The current chosen for use in these experiments was 2 / 3 of the current that typically sustains selfstimulation in these rats. The control animals were placed in the same conditions but received no stimulation. After the cold immobilization session was complete animals were anesthetized and their stomachs and brains removed. The stomachs were cut along the greater curvature, rinsed lightly in distilled water, and stretched and pinned onto Styrofoam boards. The number of hemorrhages overlying the ulcers in the acid secreting portion of the stomach were recorded. For verification of the electrode locations brains were first placed in 10% formaldehyde, and then frozen sections were taken and photographed, using the fresh sections as negatives. RESULTS
Stimulation of the anterior dorsolateral septum during a 3-h session of cold immobilization restraint dramatically reduced the number of stress-induced stomach ulcers (Fig. 1). A significant decrease in number of ulcers was found in the stimulated group compared with their unstimulated matched controls, t(10) = 2.28, p < 0.05. An example of stomachs from a pair of rats that simultaneously underwent the experimental manipulation is presented in Fig. 2. The stomach in panel A is from a control rat that was immobilized but received no stimulation. As can be seen, a
D
i
i
FIG. 2. Photographs of representative stomachs from two rats that had undergone the cold-immobilization stress procedure. (A) Stress with no lateral septal stimulation. (B) Stress with lateral septal stimulation.
LATERAL SEPTUM STIMULATION MITIGATION ULCERS
TABLE 1 NUMBER OF STRESS-INDUCED GASTRIC ULCERS FOR INDIVIDUAL SUBJECTS Subject Pair
C I S + No Stimulation
1
35
CIS + Stimulation
0
2 3 4 5 6
5 13 19 45 12
0 0 3 20 6
typical control stomach specimen is riddled with ulcers. The stomach in panel B is from an experimental rat that was immobilized and, concurrently, received lateral septal brain stimulation. It can be clearly seen that this stomach is devoid of ulcers entirely. In some of the animal pairs the effect of septal stimulation was not complete elimination of ulcers but rather a drastic reduction in their number. Table 1 shows the number of ulcers found in individual rat pairs. As can be seen in Table 1, while there is some variability in the number of ulcers found in different rat pairs, dorsolateral septal stimulation yielded a consistent reduction of the incidence of stress-induced ulceration, regardless of the severity of the ulcers (initial number). A representative example of a brain section with the stimulating electrode tip located in the anterior dorsolateral portion of the septal area is shown in Fig. 3. Electrode tip locations were consistently within this brain site. DISCUSSION Electrical stimulation of the dorsolateral septal region clearly reduced the number of gastric ulcers formed during a cold-immobilization stress procedure. This decrease is consistent with the proposed function for the lateral septal area in relief from aversive emotional states (15,18). The pattern of results with septal stimulation contrasts with that seen after stimulation of the central amygdaloid nucleus. Whereas amygdala stimulation ag-
885
gravated stress-induced gastric ulcers (8), septal stimulation alleviated them. The parameters used by Henke (7) to stimulate the central amygdala nucleus were comparable to the ones used in this study to stimulate the lateral septum. The mean number of ulcers resulting from the restraint paradigm reported in this experiment is somewhat higher than the mean number of ulcers reported by other investigators, using a cold-immobilization procedure (8,9,13). Pilot testing showed a relationship between the degree of immobilization and the number of ulcers found after 3 h of restraint in the cold. It is possible that the use of a custom-made restrainer that could be individually adjusted to snugly fit each animal, produced overall a higher number of ulcers. We are currently exploring a stress response curve, varying the stress parameters, to address this possibility. The first three pairs of rats run in this experiment were also compared at the time of restraint to three handled, but unstressed control rats. Because gross physiological measures such as body weight and ulceration were not different in these animals, these control animals were omitted from the experimental design. It has been demonstrated in several other behavioral paradigms that the lateral septal nucleus and the central nucleus of the amygdala exert effects that appear to be opposite to each other (10). For instance, electrophysiological studies that measured changes in neuronal activity during conditioning paradigms showed increased activity to the conditioned excitor of fear in the amygdala (12) and suppression of activity to that stimulus in the lateral septal nucleus (16). LeDoux has recently made the recommendation that circuits of emotion are best worked out empirically (9). Thus, it has become generally accepted that the amygdala, and in particular its central nucleus, plays a crucial role in acquisition and expression of fear based behaviors. One example of such a behavior is the fear-potentiated startle response, which is an enhanced expression of startle to a stimulus that had been previously paired with an aversive stimulus. Chemical or electrolytic lesions of the lateral, basolateral, or central amygdaloid nuclei block the expression of fear-potentiated startle (4). It is thought that the lateral and basolateral nuclei process sensory information per-
FIG. 3. A photograph, using a fresh tissue slice as a negative, of a representative brain section with electrode tip in the dorsolateral septal area.
886
YADIN AND THOMAS
ceived by various modalities. They project to the central nucleus, which projects in turn, to other sites downstream (hypothalamus, central gray), thus producing the specific signs of fear or anxiety (3,9). The cold-immobilization stress procedure has been used extensively to explore the role of the amygdala and related structures and transmitter systems in stress-induced phenomena (6). Structures whose activation resulted in a reduction in immobilization-induced stress ulcers include the medial prefrontal cortex, the posterior cingulate cortex, the ventral entorhinal cortex, the dentate gyrus and the ventral hippocampus, and the posterolateral amygdala. These anatomical structures have been referred to by Henke as inhibitory during stressful experiences (6). Based on the results of the present experiment, one must add the lateral septal nucleus to that category of emotion modulating structures. In Henke's category of facilitatory structures during stressful situa-
tions, on the other hand, one finds the centromedial amygdala and the anterior cingulate cortex (6). The mechanism by which these structures influence each other is a matter of speculation. In the startle paradigm it was shown that with combined lesions of the septum and amygdala, the amygdala effects predominate (10). The same pattern was found to be true in the water-lick conflict test (5). These combined-lesion data indicate that septal inhibition of stress and other aversive emotional states may operate via inhibitory control of the amygdala. ACKNOWLEDGEMENTS We acknowledge the hospitality of members of the Pharmacology Department at the Israel Institute for Biological Research where the preliminary work for this research was carried out, and we thank Dr. Gad Simon for photographing the stomachs.
REFERENCES 1. Bonfils, S.; Lamling, A. Psychological factors and psychopharmacological actions in the restraint induced gastric ulcer. In: Skornya, S. C., ed. Pathophysiology of peptic ulcer. Montreal: McGill University Press; 1963:153-171. 2. Davis, M. The role of the amygdala in fear and anxiety. Annu. Rev. Neurosci. 15:353-375; 1992. 3. Davis, M.; Falls, W. A.; Campeau, S.; Kim, M. Fear-potentiated startle: A neural and pharmacological analysis. Behav. Brain Res. 58:175-198; 1993. 4. Davis, M. J.; Hitchcock, J. M.; Rosen, J. B. Anxiety and the amygdala: Pharmacological and anatomical analysis of the fearpotentiated startle paradigm. In: Bower, G. H., ed. The psychology of learning and motivation. 21. New York: Academic Press; 1987:263305. 5. Grishkat, H. L. Modulation of anxiety: A role for the septum and amygdala in the effects of benzodiazepine anxiolytics. Unpublished Master's Thesis, Bryn Mawr College; 1991. 6. Henke, P. G. The telencephalic limbic system and experimental gastric pathology: A review. Neurosci. Biobehav. Rev. 6:381-390; 1982. 7. Henke, P. G. The amygdala and forced immobilization of rats. Behav. Brain Res. 6:19-24; 1985. 8. Henke, P. G.; Sullivan, R. M. Kindling in the amygdala and susceptibility to stress ulcers. Brain Res. Bull. 14:5-8; 1985. 9. LeDoux, J. E. Emotional memory systems in the brain. Behav. Brain Res. 58:69-79; 1993.
10. Melia, K. R.; Sananes, C. B.; Davis, M. Lesions of the central nucleus of the amygdala block the excitatory effects of septal ablation on the acoustic startle reflex. Physiol. Behav. 51:175-180; 1992. 11. Pare, W. P.; Glavin, G. B. Restraint stress in biomedical research: A review. Neurosci. Biobehav. Rev. 10:339-370; 1986. 12. Pascoe, J. P.; Kapp, B. S. Electrophysiological characteristics of amygdaloid central nucleus neurons during Pavlovian fear conditioning in the rabbit. Behav. Brain Res. 16:117-133; 1985. 13. Ray, A.; Henke, P. G.; Sullivan, R. M. Effects of intra-amygdalar dopamine agonists and antagonists on gastric stress lesions in rats. Neurosci. Lett. 84:302-306; 1988. 14. Strickland, C. E.; Thomas, E.; Yadin, E. Effects of chlordiazepoxide on septal single unit activity following pavlovian conditioning: A regional comparison. Soc. Neurosci. Abstr. 18:360; 1992. 15. Thomas, E. Forebrain mechanisms in the relief of fear: The role of the lateral septum. Psychobiology 16:36-44; 1988. 16. Thomas, E.; Yadin, E.; Strickland, C. E. Septal unit activity during classical conditioning: A regional comparison. Brain Res. 547:303308; 1991. 17. Yadin, E.; Thomas, E. Septal correlates of conditioned inhibition and excitation. J. Comp. Physiol. Psychol. 95:331-340; 1981. 18. Yadin, E.; Thomas, E.; Grishkat, H. L.; Strickland, C. E. The role of the lateral septum in anxiolysis. Physiol. Behav. 53:1077-1083; 1993.