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Orbital or medial frontal cortical lesions have different effects on tail pressure-elicited oral behaviors in rats
Physiology & Behavior, Vol. 24, pp. 1091-1094.PergamonPress and BrainResearch Publ., 1980. Printedin the U.S.A.
Orbital or Medial Frontal Cortical Lesions Have Different Effects on Tail Pressure-Elicited Oral Behaviors in R a t s
I
J A M E S E. S H I P L E Y , z N E I L R O W L A N D A N D S E Y M O U R M. A N T E L M A N 3
D e p a r t m e n t o f Psychiatry, Western Psychiatric Institute and Clinic and Psychobiology Program, University o f Pittsburgh, P A 15261 R e c e i v e d 12 J a n u a r y 1980 SHIPLEY, J. E., N. ROWLAND AND S. M. ANTELMAN. Orbital or medial frontal cortical lesions have different effects on tail pressure-elicited oral behaviors in rats. PHYSIOL. BEHAV. 24(6) 1091-1094, 1980.--Three groups of rats were tested with daily tail pressure (TP) tests until reliable and stable baseline eating, gnawing or licking was observed. One group then received bilateral aspiration of the medial frontal cortex, a second group received orbital frontal cortical lesions, and a third group received control lesions of the motor cortex. Daily TP tests were continued postoperatively. There was no disruption of TP-elicited oral behaviors after medial frontal or motor cortex lesions. In contrast, orbital frontal lesions abolished TP behaviors on the first day postoperatively, and there was a slow recovery of TP until day 5 when the elicited behaviors were about 80% of preoperative levels. The time course of recovery of TP-elicited oral behavior closely paralleled the recovery of elective eating after orbital frontal lesions, both in the group given TP and in another group given orbital lesions but not TP. These data demonstrate a marked difference between the medial and orbital divisions of the prefrontal cortex in the mediation of stress-induced oral behavior, and we discuss our data in terms of the possible role of dopamine terminals in these regions. Tail pressure Stimulation bound eating Dopamine Stress Prefrontal cortex Orbital frontal cortex Aphagia Recovery of function Brain damage
STRESS, in the form of mild tail pressure (TP), causes ad lib fed rats to exhibit stimulation-bound eating, gnawing and licking of food pellets and other consumables (tail pressure behaviors, TPB) [1,3]. Brain dopamine (DA) seems to be important in the expression of TPB since lesioning the DA systems or the administration of DA receptor blocking agents produce an attenuation of these normally very reliable behaviors [1, 3, 21]. We have suggested that the nigrostriatal DA system might be a crucial neural substrate mediating TPB. Decreased TPB is observed after damage to this system by lateral hypothalamic (LH) lesions [2], or by injections of the neurotoxin 6-hydroxy DA into the substantia nigra or intracerebroventricularly [3,21]. These lesions also produce aphagia and anorexia [8,23] although aphagic rats often may be induced to eat during TP [2,20]. However, in none of these studies have we been able to restrict damage to the nigrostriatal system. Among other partially damaged substrates are the mesolimbic and mesocortical DA projections. In the present study we have investigated the effects on TPB of lesions to the orbital prefrontal cortex (OFC) or to the medial prefrontal cortex (MFC). These areas contain the principal terminal regions of the mesocortical DA system [4,
Medial frontal cortex
9, 19] and, interestingly, OFC lesions are known to be accompanied by aphagia and anorexia [5, 6, 12] similar to the syndromes subsequent to LH or nigrostriatal damage. Our results indicate that the OFC may be important in the organization of both spontaneous and TP-elicited eating, and argue further for a functional subdivision of the frontal cortex in rats. METHOD
Subjects and Housing Male Sprague Dawley rats (Zivic Miller, Pittsburgh) weighing 200 g at the start of the experiment were housed individually in wire cages with Wayne food pellets available at all times on the cage floor. Tap water was also available ad lib. Lights were on from 0800-2000 hr, and all testing was conducted in the afternoon. The animals were divided into four groups, three of which were to receive TP tests. Animals were screened for TPelicited behaviors (all were positive) and were assigned to one of three weight-matched lesion groups: OFC (N=7), MFC (N=6) and control lesions of the motor cortex (MOT: N =5). The fourth group received no TP, but were given OFC
~Supported in part by USPHS grants MH24114 and RSDA 00238, and a grant from the Benevolent Foundation of Scottish Rite Freemasonry, Northern Jurisdiction, USA, to S. M. A. 2Now at Department of Psychiatry, University of Vermont, Burlington, VT 05490. 3Send reprint requests to Seymour M. Antelman, Department of Psychology, University of Pittsburgh, PA 15260.
C o p y r i g h t © 1980 B r a i n R e s e a r c h P u b l i c a t i o n s Inc.--0031-9384/80/061091-04502.00/0
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SHIPLEY, ROWLAND AND ANTELMAN
lesions in order to assess whether TP testing modified the recovery time after OFC lesions. Body weight and food intake (corrected for spillage) were recorded daily for all subjects.
Surgery All lesions were produced bilaterally by aspiration. Using Equithesin anesthetic (2.5 ml/kg), and with the rat held in a stereotaxic frame, the bone overlying the appropriate cortex was carefully removed by a high speed dental drill and rongeurs. The tissue representing the appropriate cortical area as defined by Leonard [18] was removed by gentle sub-pial aspiration with care not to encroach upon the striatum. The defect was then packed with Gelfoam, the wound repaired in anatomical layers, and the skin sutured. Prophylactic penicillin (100,000 Units) was given IM and the animal returned to its home cage.
Tail Pressure Tests On the four days preceding surgery and on postoperative days 1-10 and 15, TP testing was performed according to the procedure of Antelman et al. [3]. Briefly, tests were conducted in 30 cm dia. stainless steel bowls in which food pellets were scattered generously. TP was applied with a padded sponge forceps held 3 cm from the tip of the tail, and the pressure was oscillated until optimal eating was observed without audible vocalization or orientation to the tail. Daily tests consisted of five 60 sec trials with an intertrial interval of 10 min. The mean number of sec of TPB per trial was calculated for each daily block of five trials.
Histology After behavioral testing had been completed, the rats were deeply anesthetized, perfused with 0.9% NaC1 followed by buffered Formalin, and the brain removed for histological examination. Frozen sections (40 /x) were mounted and stained with cresyl violet. The extent of the lesions was estimated by projecting the sections onto plates from the K6nig and Klippel atlas [14]. RESULTS
FIG. 1. Reconstructions of the largest (heavy line) and smallest (shaded area) lesions, projected onto plates from the Krnig and Klippel atlas [14]. (A) Medial frontal cortex; (B) Motor cortex; (C) Orbital frontal cortex.
Histology Reconstructions of the largest (dark line) and smallest (shaded) lesions for each group are shown in Fig. 1. All three types of lesion were of comparable size. Further, there was little variation of lesion size within any group, nor was there any damage to subcortical structures. The OFC lesions removed bilaterally most of the sulcal or orbital frontal cortex, with some tissue spared in the depths in the rhinal sulcus, an area thought to be innervated by the submedial thalamic nucleus [16]. The MFC lesions removed bilaterally all of the prelimbic and supragenual medial frontal cortex [9,18]. The MOT lesions removed the frontal polar cortex, exclusive of the areas removed by either the OFC or M F C lesions. We did not examine thalamic degeneration in these brains, but in similarly lesioned rats we have observed medial thalamic degeneration (c.f. [12]).
Food Intake and Weight Change Postoperatively Animals in the MFC and MOT groups showed one or two days of anorexia after the lesion, with modest weight loss. Thereafter, normal food intake and weight gain were ob-
served. In contrast, both of the OFC groups were severely anorexic and lost considerable weight during the first 2-3 postoperative days when they were almost completely aphagic to pellets (we did not try to promote recovery by offering moist palatable foods). The maximum weight loss was similar in both the OFC groups: the individual minimum weights ranged from 73.6-90.7% (OFC) and 73.%90.1% (OFntp) of the preoperative level. Food intake then recovered slowly (Table 1) and the weight loss was first arrested, then reversed (Fig. 2). However, neither OFC group recovered to the weights of the MOT or MFC groups. Additionally, by day 8-10 postoperatively, when the OFC animals had resumed normal food intakes, we observed excessive food spillage (Table 1) and food pellets gnawed into bizarre shapes, symptoms typical of OFC lesioned rats [5, 6, 12]. There were no differences between the OFC rats given TP and those not receiving TP.
Tail Pressure Tests Before surgery, all animals exhibited short latency, sus-
FRONTAL CORTEX AND EATING TO TAIL PRESSURE
130
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1tI"
120
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o m 100
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tn
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J
~'20 h, o
90
I
I
I
I
I
2
4
6
8
10
DAYS
,,at
15
POSTOPERATIVE
4 3 2 1 ~1 l 1 2 3 4 S 6 7 8 9 10
FIG. 3. Tail pressure-elicited oral behaviors before and after lesions of the medial frontal cortex (MFC), motor cortex (MOT) or orbital frontal cortex (OFC). The values are expressed as the mean duration of five 60 sec trials per rat; representative standard errors are also indicated. The durations of the OFC group are lower than either of the other two groups (p's<0.05, t-tests) on postoperative days 1-6 and 8. for severity of postlesion aphagia and their TPB impairment, there was no significant correlation ( r = - 0 . 1 4 ) .
tained eating and gnawing of pellets on e v e r y trial (Fig. 3). TPB typically lasted for o v e r 50 sec per 60 sec trial. A f t e r the lesion, both M F C and M O T lesioned groups continued to s h o w TPB reliably, at the s a m e high levels as before surgery. In contrast, TPB was c o m p l e t e l y abolished on the first day after O F C lesions. The O F C lesioned rats did not appear lethargic or inattentive at this time. T h e r e were alert and w h e n the pressure was increased they vocalized, occasionally tried to j u m p from the bowls, s h o w e d barrel rotation and ballistic jumping. On s u b s e q u e n t p o s t o p e r a t i v e days, the O F C group showed increasing amounts of food-directed T P B , and by day 5 had r e c o v e r e d to 70% o f the prelesion levels. T h e r e was no further apparent r e c o v e r y (Fig. 3), although the reduction in TP duration was not significant (/9>0.05) on days 7 and 9-15. The time course of r e c o v e r y of TPB in the O F C group (Fig. 3) closely follows their r e c o v e r y of food intake in the h o m e cage (Table 1). W h e n individual animals w e r e ranked
DISCUSSION We h a v e d e m o n s t r a t e d that the O F C of the rat is important for the organization of both spontaneous and TP-elicited food intake. The O F C lesioned animals failed to exhibit TPB on the first p o s t o p e r a t i v e day, although they w e r e clearly aroused by the TP. O v e r the next two w e e k s their T P B , spontaneous food intake, and body weight r e c o v e r e d substantially but not completely. Previous reports h a v e indicated a similar time course of r e c o v e r y for food intake and b o d y weight [5, 6, 12]. B e c a u s e the animals with M F C and M O T lesions did not show a d e c r e m e n t in T P B , we agree with these authors that the O F C seems to subserve a motivational rather than a m o t o r function. Unlike rats with L H lesions which may be induced to lap
TABLE 1 FOOD INTAKE AND FOOD SPILLAGE IN RATS WITH FRONTAL CORTEX LESIONS Group Postop. day
Food measure
1 2 3 4 5 8--10
intake intake intake intake intake intake spillage
MFC 6.1 12.8 17.5 24.1 23.4 24.5 5.8
_+ 2.2 _+ 1.7 _+ 2.8 _+ 0.7 _+ 1.6 ± 1.1 _ 0.6
15 NAYS
LESION
FIG. 2. Weight changes, compared to operative weight 100%, after medial frontal cortex (MFC), motor cortex (MOT) or orbital frontal cortex (OFC) bilateral lesions. The OFntp group received orbital frontal lesions but not tail pressure tests; all the other rats received TP. The weights of the OFC animals are significantly (p<0.01) below both MFC and MOT groups on days 2 through 15; the weights of the OFntp animals are significantly (p<0.01) below both MFC and MOT groups on days 2 through 7. The OFC and OFntp groups differ only on day 10 (p<0.02).
MOT 2.4 16.0 22.3 22.6 29.6 25.0 5.7
-4- 1.0 _+ 1.6 _+ 2.2 _+ 1.8 _+ 2.6 ± 1.4 _+ 0.2
OFC 0.1 2.4 8.2 16.1 24.1 25.0 16.4
_+ 0.1 _+ 1.3t _+ 2.4* _+ 4.2 _+ 2.4 ± 1.7 _+ 4.3t
OFn t p 0.9 2.7 11.4 24.9 23.8 28.9 17.1
_+ 0.5 _+ 1.It __+4.0 _+ 6.0 -+ 3.5 ± 2.1 --+ 1.9t
Values expressed in grams, M _+ SE. Kruskal-Wallis one-way analysis revealed significant group differences on postoperative days 2 and 3, and in the food spillage (p's<0.05). U-tests then gave *p<0.05 and tp<0.005 compared with either MOT or MFC groups.
1094
SHIPLEY, ROWLAND AND A N T E L M A N
sweetened milk by TP [2], we were unable to elicit pellet eating in our OFC rats while they were aphagic. Since palatable diets encourage feeding in OFC lesioned rats [6,12], it is possible that we would have obtained better TP elicited eating in OFC using such a diet. However, we reiterate that unlike LH (or DA depleted) rats, the OFC rats were not inattentive or unresponsive to TP. In view of the role of DA in TPB, we have entertained the possibility that the behavioral changes after OFC lesion may result from the loss of DA terminals in this region. Lesions of the OFC produce changes in affective behavior (e.g. [11]) and frontal cortical DA has already been implicated in stress [17,24] and amphetamine-elicited behaviors [10]. However, either the entire frontal cortex [10], or only the MFC [17,24] were used in these studies. Our data suggest a functional subdivision in these areas of frontal cortex, and such a division is strongly supported by recent neuroanatomical studies of DA projections. Cell bodies in the substantia nigra project not only to the striatum but also to the more lateral areas including central amygdala, entorhinal cortex, and suprarhinal cortex (OFC) [9]. On the other hand, ventral tegmental (AI0) DA cells project to more medial areas including the anterior MFC, lateral septum, and nucleus accumbens. While we cannot be sure that our behavioral effects were due to the DA damage in the lesioned areas, our finding of decreased TPB after OFC lesion is consistent with our ear-
lier suggestions [3] that DA cells in the substantia nigra seem to be important in TPB; however, in a subsequent study we have found decreased TPB in animals with striatal, but not frontal cortical, DA depletion [21]. It is therefore possible that gustatory projections common to amygdala and OFC [16] may be an important factor in TPB and its disruption following OFC lesions (or LH damage). Others have reported functional dissociations between OFC and MF C in rats. Lesions of the MFC, septum, or VTA cause deficits in pup-carrying and food hoarding [22]. In contrast, lesions of the OFC and amygdala produce sensorimotor impairments, affective changes, and decreased food intake [6, 11, 13, 22]. OFC lesions also produce a loss of self stimulation from electrodes in the DA cells of the substantia nigra [7], an effect which might be due to degeneration of an efferent path from OFC to substantia nigra [7,18]. Another interesting dissociation is that self stimulation from the OFC (or substantia nigra) is increased after 72 hr food deprivation, whereas stimulation rates from the MFC were unchanged by deprivation [15]. Clearly, much more work is necessary before we will be able to judge to what extent these dissociations reflect the influence of different DA projections to these areas. However, these data provide good grounds to suggest that future biochemical and behavioral studies should treat the frontal cortex as an inhomogeneous structure.
REFERENCES 1. Antelman, S, M. and A. R. Caggiula. Tails of stress-related behaviors: A neurophan~acological model. In: Animal Models in Psychiatry and Neurology, edited by I. Hanin and E. Usdin. New York: Pergamon Press, 1978, pp. 227-245. 2. Antelman, S. M., N. Rowland and A. E. Fisher. Stress-related recovery from lateral hypothalamic aphagia. Brain Res. 102: 346-350, 1976. 3. Antelman, S. M., H. Szechtman, P. Chin and A. E. Fisher. Tail pinch-induced eating, gnawing and licking behavior in rats: dependence on the nigrostriatal dopamine system. Brain Res. 99: 31%337, 1975. 4. Berger, B., A. M. Thierry, J. P. Tassin and M. A. Moyne. Dopaminergic innervation of the rat prefrontal cortex: a fluorescence histochemical study. Brain Res. 106: 133-145, 1976. 5. Braun, J. J. Neocortex and feeding behavior in the rat. J. comp. physiol. Psychol. 89: 507-522, 1975. 6. Brandes, J. S. and A. K. Johnson. Recovery of feeding in rats following frontal neocortical ablations. Physiol. Behav. 20: 763-770, 1978. 7. Clavier, R. M. and M. E. Corcoran. Attenuation of selfstimulation from substantia nigra but not from dorsal tegmental noradrenergic bundle by lesions of sulcal prefrontal cortex. Brain Res. 113: 5%69, 1976. 8. Epstein, A. N. The lateral hypothalamic syndrome: Its implications for the physiological psychology of hunger and thirst. In: Progress in Physiological Psychology. Vol. 4, edited by E. Stellar and J. M. Sprague. New York: Academic Press, 1971, pp. 263-317. 9. Fallon, J. H. and R. Y. Moore. Catecholamine innervation of the basal forebrain. IV. Topography of the dopamine projection to the basal forebrain and neostriatum. J. comp. Neurol. 180: 545-580, 1978. 10. Kennedy, L. A. and M. J. Zigmond. The behavioral effects of d-amphetamine are correlated with its effects on c-AMP in different brain regions. Brain Res. 168: 408-413, 1979. I 1. Kolb, B. Social behavior of rats with chronic prefrontal lesions. J. comp. physiol. Psychol. 87: 466-474, 1974. 12. Kolb, B. and A. J. Nonneman. Prefrontal cortex and the regulation of food intake in the rat. J. comp. physiol. Psychol. 88: 806-815, 1975.
13. Kolb, B., I. Q. Whishaw and T. Schallert. Aphagia, behavior sequencing and body weight set point following orbital frontal lesions in rats. Physiol. Behav. 19: 93-103, 1977. 14. K6nig, J. F. R. and R. A. Klippel. The Rat Brain. Baltimore: Williams and Wilkins, 1963. 15. Koolhaas, J. M., F. Mora and A. G. Phillips. Effects of food and water deprivation on self-stimulation of medial and sulcal prefrontal cortex and caudate putamen in rat. Physiol. Behav. 18: 32%331, 1977. 16. Krettek, J. E. and J. L. Price. A direct input from the amygdala to the thalamus and cerebral cortex. Brain Res. 67: 16%174, 1974. 17. Lavielle, S., J. P. Tassin, A. M. Thierry, G. Blanc, D. Herve, C. Barthelemy and J. Glowinski. Blockade by benzodiazepines of the selective high increase in dopamine turnover induced by stress in mesocrotical dopaminergic neurons of the rat. Brain Res. 168: 585-594, 1979. 18. Leonard, C. R. The prefrontal cortex of the rat. I. Cortical projection of the mediodorsal nucleus. II. Efferent connections. Brain Res. 12: 321-343, 1969. 19. Lindvall, O., A. Bjorklund and I. Divac. Organization of catecholamine neurons projecting to the frontal cortex in the rat. Brain Res. 142: 1-24, 1978. 20. Marshall, J. F., J. S. Richardson and P. Teitelbaum. Nigrostriatal bundle damage and the lateral hypothalamic syndrome. J. comp. physiol. Psychol. 87: 808-830, 1974. 21. Rowland, N., D. M. Marques and A. E. Fisher. Comparison of the effects of brain dopamine-depleting lesions upon oral behaviors elicited by tail pinch and electrical brain stimulation. Physiol. Behav. 24: 273-281, 1980. 22. Shipley, J. E. and B. Kolb. Neural correlates of species-typical behavior in the Syrian golden hamster..I, comp. physiol. Psychol. 91: 1056-1073, 1977. 23. Stricker, E. M. and M. J. Zigmond. Recovery of function after damage to central catecholamine-containing neurons: A neurochemical model for the lateral hypothalamic syndrome. In: Progress in Psychobiology and Physiological Psychology. Vol. 6, edited by J. M. Sprague and A. N. Epstein. New York: Academic Press, 1976, pp. 121-188. 24. Thierry, A. M., J. P. Tassin, G. Blanc and J. Glowinski. Selective activation of the mesocortical dopaminergic system by stress. Nature 263: 242-244, 1976.
Orbital or Medial Frontal Cortical Lesions Have Different Effects on Tail Pressure-Elicited Oral Behaviors in R a t s
I
J A M E S E. S H I P L E Y , z N E I L R O W L A N D A N D S E Y M O U R M. A N T E L M A N 3
D e p a r t m e n t o f Psychiatry, Western Psychiatric Institute and Clinic and Psychobiology Program, University o f Pittsburgh, P A 15261 R e c e i v e d 12 J a n u a r y 1980 SHIPLEY, J. E., N. ROWLAND AND S. M. ANTELMAN. Orbital or medial frontal cortical lesions have different effects on tail pressure-elicited oral behaviors in rats. PHYSIOL. BEHAV. 24(6) 1091-1094, 1980.--Three groups of rats were tested with daily tail pressure (TP) tests until reliable and stable baseline eating, gnawing or licking was observed. One group then received bilateral aspiration of the medial frontal cortex, a second group received orbital frontal cortical lesions, and a third group received control lesions of the motor cortex. Daily TP tests were continued postoperatively. There was no disruption of TP-elicited oral behaviors after medial frontal or motor cortex lesions. In contrast, orbital frontal lesions abolished TP behaviors on the first day postoperatively, and there was a slow recovery of TP until day 5 when the elicited behaviors were about 80% of preoperative levels. The time course of recovery of TP-elicited oral behavior closely paralleled the recovery of elective eating after orbital frontal lesions, both in the group given TP and in another group given orbital lesions but not TP. These data demonstrate a marked difference between the medial and orbital divisions of the prefrontal cortex in the mediation of stress-induced oral behavior, and we discuss our data in terms of the possible role of dopamine terminals in these regions. Tail pressure Stimulation bound eating Dopamine Stress Prefrontal cortex Orbital frontal cortex Aphagia Recovery of function Brain damage
STRESS, in the form of mild tail pressure (TP), causes ad lib fed rats to exhibit stimulation-bound eating, gnawing and licking of food pellets and other consumables (tail pressure behaviors, TPB) [1,3]. Brain dopamine (DA) seems to be important in the expression of TPB since lesioning the DA systems or the administration of DA receptor blocking agents produce an attenuation of these normally very reliable behaviors [1, 3, 21]. We have suggested that the nigrostriatal DA system might be a crucial neural substrate mediating TPB. Decreased TPB is observed after damage to this system by lateral hypothalamic (LH) lesions [2], or by injections of the neurotoxin 6-hydroxy DA into the substantia nigra or intracerebroventricularly [3,21]. These lesions also produce aphagia and anorexia [8,23] although aphagic rats often may be induced to eat during TP [2,20]. However, in none of these studies have we been able to restrict damage to the nigrostriatal system. Among other partially damaged substrates are the mesolimbic and mesocortical DA projections. In the present study we have investigated the effects on TPB of lesions to the orbital prefrontal cortex (OFC) or to the medial prefrontal cortex (MFC). These areas contain the principal terminal regions of the mesocortical DA system [4,
Medial frontal cortex
9, 19] and, interestingly, OFC lesions are known to be accompanied by aphagia and anorexia [5, 6, 12] similar to the syndromes subsequent to LH or nigrostriatal damage. Our results indicate that the OFC may be important in the organization of both spontaneous and TP-elicited eating, and argue further for a functional subdivision of the frontal cortex in rats. METHOD
Subjects and Housing Male Sprague Dawley rats (Zivic Miller, Pittsburgh) weighing 200 g at the start of the experiment were housed individually in wire cages with Wayne food pellets available at all times on the cage floor. Tap water was also available ad lib. Lights were on from 0800-2000 hr, and all testing was conducted in the afternoon. The animals were divided into four groups, three of which were to receive TP tests. Animals were screened for TPelicited behaviors (all were positive) and were assigned to one of three weight-matched lesion groups: OFC (N=7), MFC (N=6) and control lesions of the motor cortex (MOT: N =5). The fourth group received no TP, but were given OFC
~Supported in part by USPHS grants MH24114 and RSDA 00238, and a grant from the Benevolent Foundation of Scottish Rite Freemasonry, Northern Jurisdiction, USA, to S. M. A. 2Now at Department of Psychiatry, University of Vermont, Burlington, VT 05490. 3Send reprint requests to Seymour M. Antelman, Department of Psychology, University of Pittsburgh, PA 15260.
C o p y r i g h t © 1980 B r a i n R e s e a r c h P u b l i c a t i o n s Inc.--0031-9384/80/061091-04502.00/0
1092
SHIPLEY, ROWLAND AND ANTELMAN
lesions in order to assess whether TP testing modified the recovery time after OFC lesions. Body weight and food intake (corrected for spillage) were recorded daily for all subjects.
Surgery All lesions were produced bilaterally by aspiration. Using Equithesin anesthetic (2.5 ml/kg), and with the rat held in a stereotaxic frame, the bone overlying the appropriate cortex was carefully removed by a high speed dental drill and rongeurs. The tissue representing the appropriate cortical area as defined by Leonard [18] was removed by gentle sub-pial aspiration with care not to encroach upon the striatum. The defect was then packed with Gelfoam, the wound repaired in anatomical layers, and the skin sutured. Prophylactic penicillin (100,000 Units) was given IM and the animal returned to its home cage.
Tail Pressure Tests On the four days preceding surgery and on postoperative days 1-10 and 15, TP testing was performed according to the procedure of Antelman et al. [3]. Briefly, tests were conducted in 30 cm dia. stainless steel bowls in which food pellets were scattered generously. TP was applied with a padded sponge forceps held 3 cm from the tip of the tail, and the pressure was oscillated until optimal eating was observed without audible vocalization or orientation to the tail. Daily tests consisted of five 60 sec trials with an intertrial interval of 10 min. The mean number of sec of TPB per trial was calculated for each daily block of five trials.
Histology After behavioral testing had been completed, the rats were deeply anesthetized, perfused with 0.9% NaC1 followed by buffered Formalin, and the brain removed for histological examination. Frozen sections (40 /x) were mounted and stained with cresyl violet. The extent of the lesions was estimated by projecting the sections onto plates from the K6nig and Klippel atlas [14]. RESULTS
FIG. 1. Reconstructions of the largest (heavy line) and smallest (shaded area) lesions, projected onto plates from the Krnig and Klippel atlas [14]. (A) Medial frontal cortex; (B) Motor cortex; (C) Orbital frontal cortex.
Histology Reconstructions of the largest (dark line) and smallest (shaded) lesions for each group are shown in Fig. 1. All three types of lesion were of comparable size. Further, there was little variation of lesion size within any group, nor was there any damage to subcortical structures. The OFC lesions removed bilaterally most of the sulcal or orbital frontal cortex, with some tissue spared in the depths in the rhinal sulcus, an area thought to be innervated by the submedial thalamic nucleus [16]. The MFC lesions removed bilaterally all of the prelimbic and supragenual medial frontal cortex [9,18]. The MOT lesions removed the frontal polar cortex, exclusive of the areas removed by either the OFC or M F C lesions. We did not examine thalamic degeneration in these brains, but in similarly lesioned rats we have observed medial thalamic degeneration (c.f. [12]).
Food Intake and Weight Change Postoperatively Animals in the MFC and MOT groups showed one or two days of anorexia after the lesion, with modest weight loss. Thereafter, normal food intake and weight gain were ob-
served. In contrast, both of the OFC groups were severely anorexic and lost considerable weight during the first 2-3 postoperative days when they were almost completely aphagic to pellets (we did not try to promote recovery by offering moist palatable foods). The maximum weight loss was similar in both the OFC groups: the individual minimum weights ranged from 73.6-90.7% (OFC) and 73.%90.1% (OFntp) of the preoperative level. Food intake then recovered slowly (Table 1) and the weight loss was first arrested, then reversed (Fig. 2). However, neither OFC group recovered to the weights of the MOT or MFC groups. Additionally, by day 8-10 postoperatively, when the OFC animals had resumed normal food intakes, we observed excessive food spillage (Table 1) and food pellets gnawed into bizarre shapes, symptoms typical of OFC lesioned rats [5, 6, 12]. There were no differences between the OFC rats given TP and those not receiving TP.
Tail Pressure Tests Before surgery, all animals exhibited short latency, sus-
FRONTAL CORTEX AND EATING TO TAIL PRESSURE
130
t0 tt / jl
u
MFC MOT
1tI"
120
1093
OFntl) 111
OFC
y
# 110
II v)
o m 100
an. .a
~
OFC
tn
0 II
J
~'20 h, o
90
I
I
I
I
I
2
4
6
8
10
DAYS
,,at
15
POSTOPERATIVE
4 3 2 1 ~1 l 1 2 3 4 S 6 7 8 9 10
FIG. 3. Tail pressure-elicited oral behaviors before and after lesions of the medial frontal cortex (MFC), motor cortex (MOT) or orbital frontal cortex (OFC). The values are expressed as the mean duration of five 60 sec trials per rat; representative standard errors are also indicated. The durations of the OFC group are lower than either of the other two groups (p's<0.05, t-tests) on postoperative days 1-6 and 8. for severity of postlesion aphagia and their TPB impairment, there was no significant correlation ( r = - 0 . 1 4 ) .
tained eating and gnawing of pellets on e v e r y trial (Fig. 3). TPB typically lasted for o v e r 50 sec per 60 sec trial. A f t e r the lesion, both M F C and M O T lesioned groups continued to s h o w TPB reliably, at the s a m e high levels as before surgery. In contrast, TPB was c o m p l e t e l y abolished on the first day after O F C lesions. The O F C lesioned rats did not appear lethargic or inattentive at this time. T h e r e were alert and w h e n the pressure was increased they vocalized, occasionally tried to j u m p from the bowls, s h o w e d barrel rotation and ballistic jumping. On s u b s e q u e n t p o s t o p e r a t i v e days, the O F C group showed increasing amounts of food-directed T P B , and by day 5 had r e c o v e r e d to 70% o f the prelesion levels. T h e r e was no further apparent r e c o v e r y (Fig. 3), although the reduction in TP duration was not significant (/9>0.05) on days 7 and 9-15. The time course of r e c o v e r y of TPB in the O F C group (Fig. 3) closely follows their r e c o v e r y of food intake in the h o m e cage (Table 1). W h e n individual animals w e r e ranked
DISCUSSION We h a v e d e m o n s t r a t e d that the O F C of the rat is important for the organization of both spontaneous and TP-elicited food intake. The O F C lesioned animals failed to exhibit TPB on the first p o s t o p e r a t i v e day, although they w e r e clearly aroused by the TP. O v e r the next two w e e k s their T P B , spontaneous food intake, and body weight r e c o v e r e d substantially but not completely. Previous reports h a v e indicated a similar time course of r e c o v e r y for food intake and b o d y weight [5, 6, 12]. B e c a u s e the animals with M F C and M O T lesions did not show a d e c r e m e n t in T P B , we agree with these authors that the O F C seems to subserve a motivational rather than a m o t o r function. Unlike rats with L H lesions which may be induced to lap
TABLE 1 FOOD INTAKE AND FOOD SPILLAGE IN RATS WITH FRONTAL CORTEX LESIONS Group Postop. day
Food measure
1 2 3 4 5 8--10
intake intake intake intake intake intake spillage
MFC 6.1 12.8 17.5 24.1 23.4 24.5 5.8
_+ 2.2 _+ 1.7 _+ 2.8 _+ 0.7 _+ 1.6 ± 1.1 _ 0.6
15 NAYS
LESION
FIG. 2. Weight changes, compared to operative weight 100%, after medial frontal cortex (MFC), motor cortex (MOT) or orbital frontal cortex (OFC) bilateral lesions. The OFntp group received orbital frontal lesions but not tail pressure tests; all the other rats received TP. The weights of the OFC animals are significantly (p<0.01) below both MFC and MOT groups on days 2 through 15; the weights of the OFntp animals are significantly (p<0.01) below both MFC and MOT groups on days 2 through 7. The OFC and OFntp groups differ only on day 10 (p<0.02).
MOT 2.4 16.0 22.3 22.6 29.6 25.0 5.7
-4- 1.0 _+ 1.6 _+ 2.2 _+ 1.8 _+ 2.6 ± 1.4 _+ 0.2
OFC 0.1 2.4 8.2 16.1 24.1 25.0 16.4
_+ 0.1 _+ 1.3t _+ 2.4* _+ 4.2 _+ 2.4 ± 1.7 _+ 4.3t
OFn t p 0.9 2.7 11.4 24.9 23.8 28.9 17.1
_+ 0.5 _+ 1.It __+4.0 _+ 6.0 -+ 3.5 ± 2.1 --+ 1.9t
Values expressed in grams, M _+ SE. Kruskal-Wallis one-way analysis revealed significant group differences on postoperative days 2 and 3, and in the food spillage (p's<0.05). U-tests then gave *p<0.05 and tp<0.005 compared with either MOT or MFC groups.
1094
SHIPLEY, ROWLAND AND A N T E L M A N
sweetened milk by TP [2], we were unable to elicit pellet eating in our OFC rats while they were aphagic. Since palatable diets encourage feeding in OFC lesioned rats [6,12], it is possible that we would have obtained better TP elicited eating in OFC using such a diet. However, we reiterate that unlike LH (or DA depleted) rats, the OFC rats were not inattentive or unresponsive to TP. In view of the role of DA in TPB, we have entertained the possibility that the behavioral changes after OFC lesion may result from the loss of DA terminals in this region. Lesions of the OFC produce changes in affective behavior (e.g. [11]) and frontal cortical DA has already been implicated in stress [17,24] and amphetamine-elicited behaviors [10]. However, either the entire frontal cortex [10], or only the MFC [17,24] were used in these studies. Our data suggest a functional subdivision in these areas of frontal cortex, and such a division is strongly supported by recent neuroanatomical studies of DA projections. Cell bodies in the substantia nigra project not only to the striatum but also to the more lateral areas including central amygdala, entorhinal cortex, and suprarhinal cortex (OFC) [9]. On the other hand, ventral tegmental (AI0) DA cells project to more medial areas including the anterior MFC, lateral septum, and nucleus accumbens. While we cannot be sure that our behavioral effects were due to the DA damage in the lesioned areas, our finding of decreased TPB after OFC lesion is consistent with our ear-
lier suggestions [3] that DA cells in the substantia nigra seem to be important in TPB; however, in a subsequent study we have found decreased TPB in animals with striatal, but not frontal cortical, DA depletion [21]. It is therefore possible that gustatory projections common to amygdala and OFC [16] may be an important factor in TPB and its disruption following OFC lesions (or LH damage). Others have reported functional dissociations between OFC and MF C in rats. Lesions of the MFC, septum, or VTA cause deficits in pup-carrying and food hoarding [22]. In contrast, lesions of the OFC and amygdala produce sensorimotor impairments, affective changes, and decreased food intake [6, 11, 13, 22]. OFC lesions also produce a loss of self stimulation from electrodes in the DA cells of the substantia nigra [7], an effect which might be due to degeneration of an efferent path from OFC to substantia nigra [7,18]. Another interesting dissociation is that self stimulation from the OFC (or substantia nigra) is increased after 72 hr food deprivation, whereas stimulation rates from the MFC were unchanged by deprivation [15]. Clearly, much more work is necessary before we will be able to judge to what extent these dissociations reflect the influence of different DA projections to these areas. However, these data provide good grounds to suggest that future biochemical and behavioral studies should treat the frontal cortex as an inhomogeneous structure.
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