long-term effects of lateral hypothalamic lesions on brown adipose tissue in rats

Brain Research Bulletin, Vol. 17, pp. 642-651, 1986. 0 Ankho International Inc. Printed in the U.S.A. 0361-923W86 $3.00 + -00

Long-Term Effects of Lateral Hypothalamic Lesions on

Brown Adipose Tissue in Rats’

IAN R. A. PARK,* JEAN HIMMS-HAGEN** AND DONALD V. COSCINAt

*Department of Biochemistry, University of Ottawa, Ottawa, Ontario, Canada KIH 8M5 tSection of Biopsychology, Clarke Institute of Psychiatry, Departments of Psychiatry and Psychology

University of Toronto, Toronto, Ontario, Canada M5T IR8

PARK, I. R. A., J. HIMMS-HAGEN AND D. V. COSCINA. Long-term effects of lateral hypothalamic lesions on brown a&Dose tissue in rats. BRAIN RES BULL 176) 643-651. 1986.-A classic feature of animals with lateral hvwthalamic (LH) lesions is their reguhuion of body weight at sub-normal levels. The present studies were done to determine whether this is associated with enhanced thermogenic activity of their brown adipose tissue (BAT). Three groups of young chow-fed male Holtzman rats were formed: (1) animals receiving bilateral radiofrequency heat lesions of the dorsal LH and then permitted free access to chow (LH rats); (2) non-lesioned animals that were pair-fed (PF) to the lesioned rats during a 2 week post-operative recovery period (Phase 1); (3) non-lesioned, ad lib fed (NORM) controls. After Phase 1, each group was divided and permitted free access to chow alone or an additional selection of palatable, novel food items (a “cafeteria” diet) for 2-3 weeks (Phase 2) to stimulate diet-induced thermogenesis in BAT. Finally, half of each subgroup was exposed to 4°C for 15 hr to stimulate nonshivering thermogenesis in BAT. During Phase 1 LHs and PFs ate 5% less than NORMS. This resulted in a weight deficit of 11% for LHs and 1% for PFs. After the additional period of feeding palatable foods (Phase 2) LHs collectively weighed 14% less than NORMS whereas previously PFs had a weight deficit of only 4%. They gained less weight than NORMS or PFs despite a similar energy intake. LHs had small deposits of gonadal white adipose tissue [both total amount and expressed per metabolic body mass (kgO.‘s)]. The weight of interscapular BAT was less in the LHs but its concentration of protein (mg/g) was higher. Total protein in BAT was normal but expressed in terms of metabolic body mass (kg”.r3) was significantly greater in the LHs. LHs grew more BAT protein in response to the cafeteria diet than did NORMS or PFs. The thermogenic state of BAT (as indicated by mitochondrial GDP binding) tended to be slightly higher in the LHs. Normal increases in GDP binding in response to the cafeteria diet and to cold-exposure occurred in the LHs. It is concluded that LH-lesioned rats have more BAT relative to their body size than do normal or previously pair-fed rats, are capable of normal cold-induced nonshivering thermogenesis in BAT and exhibit an exaggerated diet- induced growth of BAT. The LH lesion appears to prevent the atrophy of BAT and suppression of thermogenesis in BAT that would be expected to occur as a response to reduced food intake.

Brown adipose tissue Rat Hypothalamus Lateral hypothalamic lesions Cafeteria diet Cold-induced thermogenesis Thermogenesis

Body weight regulation Obesity Diet-induced thermogenesis

LESIONS of the lateral hypothalamus (LH) are known to lower the level at which body weight is regulated [22-24,331. Initially it was believed that damage to neural systems con- trolling feeding behavior and/or motor activity was primarily responsible [29,33,39,441. However, more recent work has implicated enhanced energy expenditure, at least in the ini- tiation of such aberrant body weight regulation [6,7, 10,451. Such enhanced energy expenditure could produce excessive energy wasting which, coupled with anorexia, might con- tribute to sub-normal levels of body weight.

One likely site for such energy wasting is brown adipose

tissue (BAT). BAT is known to be a major site of energy expenditure for cold-induced nonshivering thermogenesis (see [17]) and for diet-induced thermogenesis (see [l&19]), processes which are both controlled by the sympathetic nervous system via its innervation of BAT. The sympathetic nervous system is known to be activated by cold and by diet [53]. Considerable evidence already exists which links the hypothalamus to control of BAT thermogenic function. Elec- trical stimulation of the ventro-lateral medial hypothalamus raises metabolic rate [l] and BAT temperature [32] and the firing rate of the sympathetic nerves to BAT is transiently

‘Part of this work was presented at the Satellite Symposium of the Society for Neuroscience entitled Mechanisms of Appetite and Obesity, held in San Antonio, TX, October, 1985.

‘Requests for reprints should be addressed to Dr. J. Himms-Hagen, Department of Biochemistry, University of Ottawa, Health Sciences Building, 451 Smyth Road, Ottawa, Ont. KlH 8M5 Canada.

643

increased during the first 30 minutes after an electrolytic lesion of the ventromedia~ hypothalamus j 3 I]. Conversely. diet-induced thermogenesis in BAT, hut not cold-induced nonshivering thermogenesis in BAT, is inhibited in rats with lesions of the medial hypothalamus 120.2 I, 34,3X, 40,4l. 47, 48J or with parasagittal knife cuts which separate the medial hypothalamus from the LH [ 11,471. Thus the development of obesity in animals with such hypothalamic damage is asso ciated with suppression of BAT thermogenesis under certain ~onditi~~ns.

It seemed possible, therefore. that the leanness of LH- lesioned rats might be associated with enhanced stimulation of BAT thermogenesis. Compatible with this idea are reports that norepinephrine turnover is increased in BAT of LH- fesioned rats [S?]. In addition, BAT temperature is markedly elevated in association with the increased energy expenditure and hyperthermia that occur as an acute response to LH lesions 16, 7, 251. Against this idea would be reports that metabolic rate [9.50), food intake [9,23], food efficiency 18, 9. 331 and motor activity [9] are all normal for the reduced size of the recovered LH-lesioned rat.

The purpose of this study was to determine whether BAT size and/or thermo~enesis are altered in rats that have recovered from bilateral LH lesions. As in our previous studies of rats made obese by hypothalamic lesions [2().21] or parasagtttat knife cuts [Ill, we studied the thermogenic response of BAT when the rats ate a palatable “cafeteria” diet or were exposed to cold in order to determine whether LH lesions might alter the response of this tissue to either stimulus. Rats that had been pair-fed for two weeks prior to the cafeteria-feeding served as controls for the possible long-term effects of a low body weight during recovery from surgery.

METHOD

Ninety-six male Holtzman rats were used. Animals were purchased from Charles River Breeding Laboratories, MomreaL Quebec, and weighed 140-160 g upaa arrival. Rats were kept in separate wire-mesh cages aa 2@C and with Lights on between 0600 and 1800 hr. Before any manipuIa- tions they were given free access to Purina rodent chow 520 1 and water for 12-14 days (Phase 0).

Surgery. Animals were divided into three graups of 32 based on equivalent growth rates and body weights. Then they were anesthetized with sodium pentobarbitai (Nem- butal, 35 mgikg IP) and received one of the following two treatments: (a) bilateral heat lesions of the LH (50°C for 1 min per hemisphere), made with a Radionics RFG-4 radiofrequency generator and thermistor probe (0.75 mm diameter) at stereotaxic coordinates 6.e6.2 mm anterior to inter- aural tine, 1.8 mm lateral to mid-sag&al sinus, 8.0-8.2 mm below durs with heads f&t (n=32); (5) anesthesia but no surgery fn=64). Anesthesia with or without surgery was done between 0600 and 1000 hr during a 3-day period.

Fwding. Upon return to their cages, all animals were fed Purina chow for the next 2 weeks (Phase I). LH-lesioned rats and half of the anesthetized controls were allowed to eat ad lib. The other half of the anesthetized controls were pair-fed the same amount of chow as eaten by the LH-lesioned rats, pins an additional 10% to correct for spillage. Food intakes of all rats were measured throughout this recovery period. To

ensure adequate hydrati~~n, all LH-lesioneti rat\ rccetced + ml of physiologjcal saline IP each day for Z days aftd~ surgery. Six of these rats required this treatment for J mortb days before their body weights stabilized.

Following the 2 week recovery period (Phase I), each group was divided into two equal sub-groups based on equivalent growth rates and body weights. C)ne sub-gloup continued to receive only chow ad lib including the previ. ously pair-fed rats? while the other had additi~~llal access to ;I variety of palatable “cafeteria” foods which wcrc changed daily ( I I,21 j. This regimen continued for IS-?? days (Phase 2) during which 24-hour food intakes were recorded on four separate occasions.

At the end of Phase 2 each of the six \ub-groups was divided into two sub-groups of equal grawth rate and body weight at 1700 hr on the night before each tissue prepara- tion. One sub-group was kept at 26°C (warm) while the other was exposed to 4°C for IS hr (cold). Food and water were freely available until the animals were killed by decapitation at 0800 hr. Colonic temperatures were recorded within 30 see of decapitation with a BAT-8 digital thermometer and a thermistor probe.

Essl~r~ ~.‘l’c~~ltiiurt~~~rl.s. Interscapular BAT was quickly removed, placed in ice-cold isolation medium. cleaned of adhering muscte and white adipose tissue and weighed. White epididymal adipose tissue was also removed and weighed. The BAT was then homogenized in isolation medium, mito~hondr~a is&ted, and binding of [3~]guanosine di- phosphate to the isolated mitochondria measured as described before ] 131. Total BAT protein was determined by a modified Lowry method as previously described f 131.

Brains from LH-lesioned rats were removed and fixed in IO% formalin before being frozen, coronally sectioned through the lesion sites, and stained with cresyl violet by conventional histological procedures.

.~t~tti.~t~~~~~i mdyseLs. Data were analyzed by one-way, two-way or three-way analysis of variance (ANOVA) with SPSS-X on a DEC 20-20 computer. Corrections for repeated measurements were made as necessary. When significant F- ratios were obtained, post-hoc Duncan Multiple Range tests were performed. Values reported in the text represent group meanscSEMs. Ail p-values are for two-tailed distri- bution\.

RESULTS

Radiofrequency lesions were classified as “small” (O.il- 0.6 mm diameter), “moderate” (one-third of LH tissue medio-laterally) or “large” (two-thirds of LH tissue medio- laterally). Most lesions were small or moderate. The center of these lesions was fairly consistent in being localized to

the dorsa-lateral LH near the basal border of the thrdamus. Bilateral damage to the zona incerta was common. Qcca- sionally. unilateral damage to the fornix was also observed. While injury was always seen in both hemispheres, medio- lateral placements were not always symmetrical. That is, lesions typically deviated to the left or ri& ln a given animal, indicating slight errors in mid&nine determination prior to electrode placement. However, the antero-posterior placement of lesions was quite consistent, being localized between the caudal aspects of the paraventricular nucleus and the middle to caudal aspects of the ventromedial nuclei. No clear relationship was evident between variations in lesion size or location and the variables recorded. A typical LH lesion is shown in Fig. I.

LATERAL HYPOTHALAMIC LESIONS AND BAT

FIG. 1. A typical “moderate” LH lesion. See text for further details.

Body Weights

Body weight gain during the first few days post-lesion (Phase 1) was severely reduced in the LH-lesioned rats, more so than in pair-fed animals (Table 1). Energy intake was reduced by about 50% and metabolic efficiency (weight gain per 100 kcal eaten) was less than in pair-fed rats (Table 1).

At the end of Phase 1 (2 weeks post-lesion) the LH lesioned rats weighed much less than normal and less than the pair-fed rats (Table 2). Their weight gain during Phase 1 was less than that of normal controls but the same as that of pair-fed animals (Table 3). During Phase 2 the LH-lesioned rats gained weight at the same rate as normal rats when eating chow (Table 3); their food intake was also normal (Table 3). Pair-fed rats, in contrast, gained more weight than either normal or LH-lesioned rats during recovery from pair-feeding (Table 3) and had caught up to a normal body weight (Table 2). Energy intake was increased by the cafeteria diet in all groups of rats (Table 3). However, no effect of this overeating on body weight gain was seen in either normal or previously pair-fed animals. Moreover, the cafeteria-fed LH-lesioned rats gained 30% less weight than the chow-fed lesioned rats despite an energy intake that was on average 26% greater (Table 3). These cafeteria-fed LH- lesioned rats gained 40% less than normal rats and 45% less than previously pair-fed rats eating the same diet, despite a very similar energy intake (Table 3). By the end of Phase 2 the cafeteria-fed LH-lesioned rats weighed 2% less than

TABLE 1

INITIAL WEIGHT CHANGES, FOOD INTAKE AND FOOD EFFICIENCY, DAYS l-7 AFTER LESION

Group

Normal LH-lesioned Pair-fed rats rats rats

Weight gain (g) 52.7+ k1.60

Energy intake 607* (kcaN k7.7

Food efficiency 8.8* (g gainkcal 20.25 eaten)

4.2t -2.3$ p<O.OOl 24.9 k3.0

301t 301t p<O.ool f 18.8 218.8 -6.6t 1.4$ p<O.OOl kO.24 +o. 14

The value of p for one-way ANOVA is shown at the end of each line. Within each line, means with different superscripts are significantly different.

normal rats eating the same diet whereas previously pair-fed rats had a deficit of only 7% (Table 2). Chow-fed LH- lesioned rats weighed 14% less than normal rats whereas previously pair-fed rats had a deficit in body weight of only 4% at this time (Table 2).

There was a highly significant effect of lesion to reduce

PARK, HIMMY-HAGEN XNI) (‘OSCINA

TABLE 2 because total protein content actually increased, as &i

BODY WEIGHTS protein concentration (Table 6). Since LH-lesioned rats had a normal or greater than nor-

mal totai content of protein in their BAT yet weighed less than normal it is clear that their proportion of metabolically active BAT in relation to their body weight was elevated. When expressed in terms of metabolic mass (per kg”.‘“), BAT was present in larger amounts than normal in the LH- lesioned rats, pa~icularly when they had eaten the cafeteria diet (Fig. 2). Moreover, the growth of their BAT in response to a cafeteria diet increased its size by 51%. compared with the 1%25% increase seen in the normal or previously pair- fed rats. Thus, the cafeteria-fed LH-lesioned rats had 53-77s more metabolically active BAT, relative to their metabolic mass, than did normal or previously pair-fed rats. Growth of BAT occurred in all animals in response to the relatively brief cold-exposure (Fig. 2) but the change was smaller in the LH-lesioned groups.

Diet Normal

rats

Group

LH-lesioned rats

Pair-fed rats

Chow

Chow

Chow

Chow

Cafe

Initiat (g) 149 147 147 N.S. r1.S 21.1 21.2

At lesioning (g)

253* 2421 246t p<O,OO1 21.7 t1.0 21.3

End Phase 1 (end of pair-feeding) {g)

329* 278t 289$ p<O.OOOl +2,9 t4.5 k8.1

End Phase 2 (end of chow or cafe period) (g)

421* 361t 406” p<o.OoOoI 26.1 27.9 24.6 431” 337s 39% p<O.OOoof 15.6 212.1 F6.8

n=32 for all means except those for the end of Phase 2 where n=16. See leaend to Table 1 for further info~ation. The small but signi~~~t d@erence in body weights at lesion& is due to the stag- gering of the treatments so that LH-lesioned rats and pair-fed rats were started on two consecutive days and normal rats on the third day. Two-way ANOVA for values at end of Phase 2 shows a signif- cant group effect @<0.0001) and no diet effect.

the size of gonadal white adipose tissue, used here as an index of body fat content (Tabie 4). Even in propo~ion to their reduced body size, the LH-lesioned rats had a lower fat content than did normal or previously pair-fed rats which did not differ from each other (Tabie 4). This lower fat content was still found in the cafeteria-fed LH-lesioned rats, when they were compared with rats in the other two groups (Table 4).

Temprrtrtrues

There was a large and highly significant effect of cafeteria feeding to increase body temperature across groups (Table 5). All animals were able to maintain their body temperature in the cold and the effect of the cafeteria diet was still seen in these cold-exposed animals.

The wet weight of BAT was lower in the chow-fed LH- lesioned rats. That this was due to a lesser content of stored fat is indicated by the normal total protein content of the tissue (Table 6). Indeed, the concent~tion of protein in BAT (mg per g of tissue) was elevated in the LH-lesioned rats, i.e., these animals presumably maintained a lower than normal concentration of stored lipid, even when this was elevated as in the cafeteria-fed state (Table 6). The cafeteria diet almost doubled the wet weight of BAT but this was mostly fat storage since the protein content increased by only 25% overalt. Cold-exposure consistently reduced BAT weight in all groups, largely because of mobilization of stored lipid

The thermogenic state of BAT, as indicated by the level of its mitochondrial GDP binding, tended to be higher in the LH-lesioned rats across groups (Fig. 3). It increased in response to cafeteria-feeding in all animals in the warm (Fig. 3). Cold-exposure brought about a much greater increase in all animals. It may be noted that the level of GDP binding in cold-exposed cafeteria-fed LH-lesioned rats was greater than the level in either of the other groups fed this diet (Fig. 3).

The principal finding in this study is that Lo-lesioned rats have more BAT in relation to their body size than do normal rats and adapt to cafeteria-feeding by an exaggerated BAT growth. Their BAT appears to be operating at a normal 01 very slightly enhanced level of thermogenesis. This finding would imply that LH-lesioned rats should have a greater- than-normal capacity for diet-induced thermogenesis, par- ticularly when they eat a palatable diet, and thus a greater capacity to waste ingested energy as heat. Whether or not this capacity is expressed as an increased wasting of energy would depend on whether the expanded mass of BAT was acutely stimulated by norepinephrine. Corbett and Keesey [9] did not find such an increase in diet-induced rher- mogenesis in an energy balance study of four chow-fed LH- lesioned rats. However, diet-induced thermogenesis was a very small proportion (about 11%) of total food energy in their study and the methodology may not have been suffi- ciently sensitive to detect small differences in it. Our finding a similar weight gain and food intake in recovered LH- lesioned rats to those in normal rats would agree with their conclusion about chow-fed rats. In contrast, our finding of a lesser weight gain in cafeteria-fed LH-lesioned rats than in normal rats eating this same diet, despite very similar energy intakes. would suggest an exaggerated thermogenic response of the former to this diet. Indeed, feeding I-H-lesioned rats a palatable (Nutrament) diet does induce a hypermetabolic state even when this is measured after they have been food deprived for some time {10,24); this may well correspond to diet-induced thermogenesis in BAT. An increased utilization of diet-induced thermogenesis in BAT would imply an increased sympathetic nervous system activity in this tissue. Our data would suggest that such an increase would be ex- tremely small in the chow-fed LH-lesioned rat since we found only very small increases in BAT mitochondrial GDP binding in the LH-lesioned animals (Fig. 31. A report that sympathetic nervous system activity in BAT is greatly increased in LH-lesioned rats [YZ] used. as controfs. rats which

LATEBAL ~~~LA~I~ LESIONS AND BAT 647

TABLE 3 BODY WEIGHT GAINS AND FOOD INTAKES

Normal rats

Group

LH-lesioned rats

Pair-fed rats

Phase 0 fnitial to lesioning

Phase 1 Lesioning to end of pair feeding

Phase 2 Diet period

Chow

Cafe

Phase 2

(1) Chow Cafe

(2) Chow Cafe

(3) Chow Cafe

(4) Chow Cafe

Weight gain, g/day

8.03 8.27 *o. 157 *0.14t

6x?* 2.91t kO.279 kO.352

5.03* 4.5g* to.230 TO.353

5.62* 3.31t rtO.258 kO.448

Energy intake, kcakday

94.9 * 2.7* 88.1 r 2.F 122.7 2 4.2* 110.8 z 3.8?

83.6 r 3.0* 74.1 f 2.6? 107.2 -c 2.4 99.6 -’ 4.6

73.3 f 1.9* 85.8 f 3.0t 124.6 4 4.8* 101.0 + 5.7t

80.2 * 1.8 74.6 f 2.5 106.9 z!z 4.3 95.0 + 4.0

7.92 to. 140

3.72t rtO.257

6.44t kO.294

5.97* 1tO.365

104.1 rt 3.3t 119.9 2 1.9?

85.5 rt 2.1* 106.8 2 2.3

100.3 + 2.6$ 123.2 4 3.5*

80.5 2 3.1 104.7 + 4.4

N.S.

p<0.0001

p<0.0002

p<O.oool

p<O.oOl pco.05

p-zo.01 N.S.

p<0.00001 pco.005

N.S. N.S.

n=32 for values in Phase 0 and Phase 1, n= 16 for values in Phase 2. See legend to Table 1 for further information.

Two-way ANOVA for each group in Phase 2 shows a siguificant diet effect on energy intake ~~0.~1) aud a significant variation among days fp<O.ooOL~.

had been pair-fed to the LH-lesioned rats and thus mie,ht be expected to have suppressed sympathetic nervous system activity in their BAT [53]; moreover, all rats had been fasting for 18 hr and the results are probably more relevant to a different response of LH-lesioned rats to fasting than to their sympathetic nervous system activity when they are eating chow ad lib. Studies with agents that block the activity of the sympathetic nervous system, such as guanethidine, have not provided conclusive evidence for any role of altered sympathetic nervous system activity in the recovered chow-fed LH-lesioned rat 143,451.

The LN-lesioned rats maintained a lower body weight than normal animals, as expected from previous studies [22-241, and had a lower proportion of body fat 112,281. Un- like animals which had been food-restricted by prior pair- feeding them to the lesioned rats, they did not catch up to a normal body weight when allowed free access to chow or to chow plus cafeteria food. They did acquire more body fat when they ate the high-fat cafeteria diet, as has been described by others in terms of body weight gain or body fat for different high-fat diets [3, 10, 27, 30, 461, but still had less than normal or previously pair-fed rats.

The finding of a normal thermogenic response of BAT of LH-lesioned rats to cold-exposure shows that this hypothalamic lesion, like the ventromedial lesions [20,21] and parasagittal knife cuts [ 1 l] studied previously, does not inter- fere with the neural mechanisms involved in cold-induced nonshivering thermogenesis. As observed by others [49], the LH-lesioned rats maintained a normal body temperature in the cold. Their long-term failure to maintain an adequate food intake in the cold 1421 was not seen in the very short cold-exposures studied in our experiments. The impaired long-term response reported previously [42] probably has a behavioral basis. The additive effects of adaptation to a cafeteria diet and acclimation to cold on BAT size observed in other experiments f36] was not seen in our animals, probably because of the very short time of exposure to cold.

Starving a normal rat to a lower body weight evokes numerous adaptive changes that increase metabolic efficiency and thus conserves energy [2, 4, 5, 14, 16, 26, 511. These adaptive changes include suppression of BAT size and reduction in its thermogenic activity [15,35,37 such that the capacity for diet-induced thermogenesis is reduced [35]. This reduced capacity for diet-induced thermogenesis prc?SUmablY

64X PARK. HIMMS-HAGEN ‘iSi) ( c )Sl’lh .I

TABLE 4

WEIGHT OF GONADAL WHITE ADIPOSE TISSUE AT END OF PHASE 2

Diet Ambient Normal

Temperature rats

Group

LH-lesioned rats

Pair-fed rats

Chow

Cafe

Warm

Cold

Warm

Cold

Chow

Cafe

Warm

Cold

Warm

Cold

s.2* t0.44

4.7* -+0.25

7.3* 20.52

8.2* to.56

9.9*

to.71 8.Y*

-to.44 13.6*

+0.8Y 15.3*

+-0.92

Total (g)

3st

to.41 3.3’i

r0.27 4.3+

kO.49 4.9t

to.78

7.5t

20.74 7.1t

k0.46 Y.5f

10.84 10.81

_+I.32

4.9* 50.28

4.9* 20.15

6.7* kO.42

7.8* to.49

9.7* 20.52

Y.6* to.31 13.2*

to.79 15.7*

-cl.06

/?<0.0125

p<0.0001

/I<O.OOl

/KO.O05

p<O.OS

p<O.ool

/I <o.oos

p<O.Ol

See legend to Table 1 for further information. Two-way ANOVA across diets shows highly significant @<O.OOOl) effects of

group and of diet with no interaction, both for total weight and for weight per kg.

TABLE 5

RECTAL TEMPERATURES AT END OF PHASE 2

Diet Ambient

Temperature Normal

rats

Group

LH-lesioned rats

Pair-fed rats

Chow Warm 37.2 +0.17

Cold 37.5 to.12

Cafe Warm 38.3 20.17

Cold 38.0 to. 14

37.4 -+o. I9 37.7

50.11 38.7 +0.13 38. I kO.11

37.7 N.S. +0.12 37.7 N.S.

?0.10 38.4 N.S.

to.14 38.3 N.S. +o. 17

n=8 for all means * SE. See legend to Table 1 for further information. Two-way ANOVA shows a diet effect (P<O.OCJOI) and no group effect. There is

an interaction between temperature and diet (p<O.O02).

LATERAL HYPOTHALAMIC LESIONS AND BAT 649

TABLE 6 BROWN ADIPOSE TISSUE

Diet Ambient

Temperature Normal

rats

Group

LH-lesioned rats

Pair-fed rats

Chow

Cafe

Chow

Cafe

Chow

Cafe

Warm

Cold

Warm

Cold

Warm

Cold

Warm

Cold

Warm

Cold

Warm

Cold

Weight, mg

692*t 503** 228.2 274.3 532 392 237.6 256.8 1304 1162 256.1 k76.3 1054 822 262.8 5 108.9

Total protein, mg

21.3 25.5 k2.34 22.75 42.0* 32.3t e2.74 22.17 25.2’ 37.3t

k3.05 k4.18 50.1 44.6 25.70 24.28

Protein concentration, mg/g

30.9 45.4 k3.21 k6.66 80.7 75.0 26.32 k6.16 19.2* 32.4t

Cl.90 14.27 48.4 59.6 k5.27 k-8.27

7243 p<o.o5 k-28.9 493 N.S. k28.3 1138 N.S. 244.8 966 N.S. 283.9

21.9 N.S. 23.04 34.77 p<O.O25 22.22 27.3* pco.05

22.54 37.6 N.S. 23.30

32.0 N.S. k6.72 70.2 N.S. k1.83 24.0* pco.02 22.0 41.2 N.S. 25.09

n=8 for all means ir SE except for cafe-fed LH-lesioned where n=7. See legend to Table 1 for further information. For wet weight, both warm and cold groups, two-way ANOVA shows no effect

of group, a significant effect of diet (p<O.OOOOl) and no interaction. For total protein, there ate significant effects of group (p<O.OS) and of diet @<O.Ol) and no interaction in both warm and cold environments. For protein concentration in warm groups, two-way ANOVA shows a group effect Q~0.02) and a diet effect tp40.01) and no interaction. In the cold groups there is no group effect, a significant (p<O.OOOl) diet effect and no interaction.

contributes to the persistently elevated metabolic efficiency and rapid regain of weight when such starved animals are m-fed [2-4, 14, 261. It is instructive to compare the LH-lesioned rat, with the lower body weight that it has achieved at least in part by reduced food intake, with the fmd-restricted rat. It would appear that the normal adaptive changes that increase metabolic efficiency in the face of the reduced availability of energy are prevented by the LH lesions. Thus, the suppression of sympathetic nervous system activity probably does not occur [52], metabolic efficiency is not increased [9,23], BAT size is not reduced (present experiments) and BAT thermogenic state is not suppressed (present experiments). The LH-lesioned rat is not equivalent to the fed-~st~cted rat, as pointed out previousiy on other grounds [27,431. The

low body weight is not recognized as needing any adjust- ments. As discussed by others [9,24,33], the “set-point” at which adaptive changes are brought into play to raise or lower metabolic efficiency is at a reduced level of body weight and body fat. Our data indicate that the LH-lesioned rat1 is capable of growing more BAT and activating thermogenesis in it when allowed access to a cafeteria diet, indeed to a greater extent than a normal rat that is either at or below its body weight set-point. This capability is associated with a much smaller weight gain than that seen in normal rats eating the same diet and taking in an almost equal amount of food energy. Whether, conversely, the LH-lesioned rat is capable of suppressing thermogenic activity in its BAT when food-restricted remains to be determined. Its normal weight

650 PARK, HIMMS-HAGEN AND C’(‘)SCIN.L\

150

100

50

0

BAT PROTEIN BAT MITOCHONORIAL GDP BINDING mg/kg’.‘= pmol/mg protein:

NORMAL LH-LESION PAIA-FED

CHOW CAFE CHOW CAFE CHOW CAFE

FIG. 2. Protein content of brown adipose tissue (BAT), expressed in FIG. 3. Brown adipose tissue (BAT) mitochondrial GDP binding. terms of body metabolic size. For groups in the warm (W), ANOVA For animals in the warm (W), ANOVA shows no significant differ- shows no differences between chow-fed groups and a significantly ences between chow-fed groups or between cafe-fed groups. Two- greater content in the LH-lesioned cafe group (p<O.Ol) than in cafe- way ANOVA across diet groups shows no group effect and a signifl- fed normal or pair-fed groups. Two-way ANOVA across diet-groups cant diet effect @<O.OOl). For animals in the cold (C), ANOVA shows a significant group effect @<O.OOl) and diet effect (p<O.Ol), shows no significant differences between chow-fed groups and a with no interaction, in the animals in the warm. For groups in the significantly higher value for cafeteria-fed LH-lesioned rats (pcO.01) cold (C), ANOVA shows no significant differences between groups than for normal rats or pair-fed rats. Two-way ANGVA across diet for any given diet. Two-way ANOVA across diet groups shows a groups shows no diet effect but a significant (p<O.O05) group effect significant diet effect (p<O.OOS), no group effect and no interaction. and an interaction (p<O.OOS).

loss during food deprivation followed by a normal and rapid regain of weight to the regulated level [lo,221 suggests that such an energy-conserving mechanism does exist in the LH- lesioned rat but is called into play only below its low but regulated body weight.

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NORMAL LH-LESION PAIR-FED CHOW CAFE CHOW CAFE CHOW CAFE

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WC WC WC WC WC WC

ACKNOWLEDGEMENTS

This research was supported by a grant from the Medical Re- search Council and funds from the Clarke Institute of Psychiatry. We are grateful to Lori Dixon for help with the statistical analyses and to Gisele Larose for help with the animals. I. R. A. Park was supported by a studentship from the Natural Science and Engineer- ing Research Council.

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long-term effects of lateral hypothalamic lesions on brown adipose tissue in rats

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