Self-stimulation, salicylate and ambient temperature

Physiology & Behavior, Vol. 26, pp. 1069-1072. Pergamon Press and Brain Research Publ., 1981. Printed in the U.S.A.

Self-Stimulation, Salicylate and Ambient Temperature EDUARDO BRIESE 1AND EURO MURZI

Laboratorio de Fisiolog(a de la Conducta, Universidad de Los Andes, M~rida, Venezuela Received 2 J a n u a r y

1980

BRIESE, E. AND E. MURZI. Self-stimulation, salicylate and ambient temperature. PHYSIOL. BEHAV. 26(6) 10691072, 1981.--Effects of sodium salicylate and of cold or warm environment on intracranial self-stimulation and on colonic temperature ot rats were assessed. Colonic temperature at the end of intracranial self-stimulation sessions was significantly lower after salicylate than after saline in 33 out of 36 animals. Self-stimulation rate was either decreased or increased by one or several of the three independent variables (salicylate, warm environment, cold environment), at only some scattered sites. These effects were frequently independent of one another. These results suggest that only some rewarding sites are related to temperature regulation and, that each rewarding site operates as a discrete elementary reinforcing unit with its particular pattern of susceptibilities to distinct drives or substances. Self-stimulation Salicylate Temperature regulation

Cold and warm environment

A RELATIONSHIP between electrical intracranial selfstimulation (ICSS) and temperature regulation has already been reported, but results are contradictory and difficult to interpret. In initial studies, it was found that ICSS produced hyperthermia in rats [1] and dogs [5], and that cold environment enhanced and warm environment depressed ICSS [2]. It was later reported [18], however, that ICSS at medial preoptic nucleus produced hypothermia, and that cold environment depressed lateral hypothalamic self-stimulation. In another study [4] it was found that cold (-5°C) depressed either posterior or rostral hypothalamic self-stimulation in shaved rats and that ICSS induced hyperthermia at anterior placements but not at placements in the supramammilary region. However, other results were in agreement with the initial findings [8, 11, 14]. Our aim in the present study was to clarify these contradictions. The reasoning was that if there is any link between temperature regulation and ICSS, salicylate, a drug reputed to influence the mechanisms of temperature regulation [7, 12, 13, 15], should also affect ICSS behavior. In addition, we expected that ICSS placements affected by salicylate would also be affected by the cold and/or warm environment. However, the results obtained fall short of these expectations. METHOD

We assessed the effect of sodium salicylate and those of a cold or warm environment on the ICSS rates and on colonic temperature. We used 36 self-stimulating Sprague-Dawley male adult rats. Each animal had been implanted with one bipolar electrode made of nichrome 0.25 or 0.12 mm diameter twisted wires, insulated except for the cross-sectional area of the tip. Histological sections of the brains showing the lowest visible part of the electrode track were photographed. In 16 "hypothalamic" rats the electrode was in the lateral and

Colonic temperature

Drives

posterior hypothalamus. In the other 20 animals "septal rats" the electrode was in the ventral septal region (diagonal band of Broca, nucleus accumbens, tractus striohypothalamicus, fasciculus medialis prosencephali, tuberculum olfactorium). The rats were allowed to self-stimulate 30 rain each day at the same hour in the same Skinner box. A press on the lever produced a 0.3 sec train of 60 Hz sine-wave electrical stimulation. For each rat, stimulus intensity was constant throughout the experiments. At the end of each ICSS session we measured each rat's colonic temperature with ordinary medical thermometers inserted for at least 2 min at 7 cm beyond the anus [9]. On alternate days sodium salicylate (Fisher Scientific Co.) 200 mg/kg or saline was injected IP one hour before the ICSS session. Hypothalamic rats were allowed to self-stimulate 4 times after receiving salicylate and 4 times after saline injections. Septal rats self-stimulated 5 times after salicylate and 5 times after saline; in a replicate experiment, (Salicylate 2 in Table 2) 62 days later, septal rats self-stimulated 6 times after salicylate and 6 after control injections. To assess the effect of ambient temperature (Ta) on ICSS rates and on colonic temperature, the animals were allowed to self-stimulate at three Ta: "normal" 23-25°C, "cold" 5-6°C and "warm" 32-33°C. The salicylate experiments were carried out at "normal" 23-25°C. Statistical analysis was done by a t test for the salicylate experiments, and by ANOVA followed by the Newman-Keuls test [19] for the T~ experiments. RESULTS

Salicylate Effects On colonic temperature. At the end of ICSS sessions under salicylate, the colonic temperature was invariably lower than after saline injections. As Table 1 (column 5) and Table 2 (columns 6 and 7) show, this was statistically signifi-

1Send reprint requests to Dr. Eduardo Briese, Apartado Postal 109, M6rida 5101A, Venezuela.

Copyright © 1981 Brain Research Publications Inc.--0031-9384/81/061069-04502.00/0

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TABLE 1 RATS WITH ELECTRODEIN THE HYPOTHALAMUS:CHANGESIN SELF-STIMULATIONRATESAND COLONICTEMPERATUREINDUCEDBY SALICYLATE,COLD AND WARMENVIRONMENT* Self-Stimulation (A %)

Colonic Temperature (A °C)

Rat (1)

Salicylatet (2)

Cold (3)

Warm (4)

Salicylate (5)

Cold (6)

Warm (7)

37 52 61 16 14 2 25 56 32 34 39 27

-62 -54 -53 -42 -22 -14 -11 -10 - 8 - 4 NS NS NS NS NS + 9

1,31 § +20 +56 NS NS -42 NS NS 1' 4 § $10 NS NS § +62

$46 § $3 $34 -20 NS -34 NS -25 -14 § -47 NS NS § 1' 5

-0.47 -1.00 -2.18 -0.96 -0.68 -0.49 -0.43 -0.51 -0.45 -0.52 -0.99 -0.37 -0.66 -0.62 -0.74 NS

-0.73 § $0.25 $0.10 $0.19 -0.60 1,0.22 0.0 $0.03 $0.16 § 1,0.15 $0.08 NS § $0.23

+0.85 § +0.40 +0.33 +0.85 +0.85 +1.04 +0.62 +0.58 +0.73 § +0.84 +0.38 NS § +0.83

1

40 5 45

*Overall level of statistical significancep<0.05, assessed by t test (df=8) when effects of salicylate were compared with those of saline and by oneway ANOVA (df=2/6) followed by Newman-Keuls test when effects of cold (5--6°C), normal (23-25°C) and warm (32-33°C) environment were compared. t200 mg/kg IP one hr before self-stimulation compared with normal saline injections. NS=not significant; §=experiment was not carried on, not measured; A %=percent of deviation from mean control rate at 23-25°C; A °C=mean differences in °C with colonic temperature at the end of 30 rain selfstimulation sessions after saline or self-stimulation at 23--25°C. 1,$Deviationfrom normal in the direction indicated not significant according to Newman-Keuls test, if compared with normal, but significantly different from data at opposite temperature.

cant for all 36 animals except 3, one hypothalamic and 2 septal. On self-stimulation rates. The effect of salicylate on self-stimulation was restricted to some specific placements, and was heterogeneous: either inhibition or facilitation occurred. As Table 1 and Table 2 show, salicylate decreased ICSS rates in about 2/3 of the hypothalamic rats and in about 2/5 of the septal rats. ICSS rates were enhanced by salicylate in 1/10 of the septal and 1/16 of the hypothalamic rats. These frequency distribution differences between hypothalamic and septal rats were not significant, X2=2.46, df=2, p=0.29.

Cold and Warm Environment Effects On colonic temperature after self-stimulation. At the end of ICSS sessions in the warm environment colonic temperature was significantly higher than after ICSS at normal Ta in 12 out of 13 hypothalamic rats (Table 1, column 7) and 8 out of 20 septal rats (Table 2, column 9). In the cold environment (Table 1, column 6; Table 2, column 8) ICSS yielded a significantly lower colonic temperature in 2 hypothalamic and 2 septal rats and a higher colonic temperature in 2 septal rats. On self-stimulation. Table 1 (columns 3 and 4) shows that out of 13 tested hypothalamic rats cold significantly in-

TABLE 2 RATS WITH ELECTRODESIN THE SEPTALAREA: CHANGESIN SELF-STIMULATIONRATESAND COLONICTEMPERATURE INDUCED BY SALICYLATE,COLD AND WARMENVIRONMENT* Self-Stimulation (A %) Rat Salicylatet 1 2 (1) (2) (3)

Cold Warm (4) (5)

163 149 152 155 128 130 148 129 157 153 125 131 137 162 97 84 107 126 161 164

$17 NS NS NS +66 NS NS NS NS NS 1' 4 NS -64 $17 1,35 +84 NS NS -31 $16

-52 NS -45 NS NS -37 -30 NS -26 -30 -26 NS -17 NS -14 NS NS NS NS NS NS NS NS NS NS NS NS NS NS § NS § NS § NS NS +25 +47 NS +36

'~12 NS NS NS $6 NS NS NS NS NS $12 NS 1'15 +33 $28 NS NS NS 1' 7 1' 5

Colonic Temperature (A °C) Salicylate 1 2 (6) (7) -0.84 -1.20 NS -0.84 -0.92 -0.76 -0.78 -0.68 -1.50 -1.20 -1.05 -0.57 -0.44 -0.44 - 1.32 -0.70 -1.06 -1.40 -0.60 -0.58

-0.57 -0.84 -0.40 NS -0.73 -0.86 -0.72 -0.67 -0.66 -0.60 -1.29 -0.34 -0.40 -0.42 § § § -0.74 -0.95 -0.77

Cold Warm (8) (9) NS NS NS NS $0.22 +0.35 NS NS +0.31 1`0.06 NS NS NS NS +0.29 +0.34 $0.30 1,0.21 $0.23 1'0.10 NS NS 1'0.06 +0.33 NS +0.54 NS +0.26 -1.52 +0.54 1,0.05 +0.46 NS NS NS NS -0.24 NS 1'0.04 +0.20

*Statistical treatment, symbols and abbreviations same as in Table 1. tEffect of salicylate on septal rats was assessed in two experiments separated by 62 days.

creased ICSS in 3 and decreased it in 1 while the warm environment significantly decreased it in 5. Effects of salicylate cannot be correlated with the effects of Ta. The reciprocal effect of cold and warm environment on ICSS rates was present in 4 hypothalamic rats (37, 61, 16 and 34) out of seven which were affected both by the cold and warm environment. In the other 3 (rats 25, 27 and 45) cold and warm environment affected ICSS rates in the same direction (both decreased ICSS in rats 25 and 27 and both increased it in rat 45). A smaller proportion of the septal rats was affected in their ICSS rates by the Ta (see Table 2). In fact, the cold environment increased ICSS in rats 128 and 84 and decreased it in rats 137 and 161. This cannot be correlated with the effect of salicylate on the same reward sites since salicylate decreased ICSS in rat 128 and increased it in rat 161, but had no significant effect in the other two (137 and 84). In the warm environment ICSS rates of septal rats were not significantly different from those at normal temperature except in rat 162. Facilitation of ICSS by the warm environment, as in rat 162, is a rare occurrence. Table 2 shows (columns 4 and 5) that in septal rats when a site was affected by the cold or by the warm environment the reciprocal action was present, except in rat 84 in which ICSS rate was increased by the cold but not affected by the warm.

REWARD AND TEMPERATURE REGULATION

FIG. 1. Brain sections showing the lowest visible part of the electrode tracks. Effect of salicylate on self-stimulation rates is indicated by arrows (down=inhibition; up=facilitation) and mean percent of deviation from control rates. NS: not significant. Identification numbers of the rats are at left inferior corner of each photograph.

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Histology

Figure 1 shows that cold and warm environments or salicylate may increase or decrease ICSS both in septal and hypothalamic placements. There is no evidence of any topographical pattern. Self-stimulation in close locations was distinctly affected by the three independent variables, as for instance in rats 128, 161 and 162, or in rats 27 and 45. DISCUSSION Specific Thermal Modulation

A common drawback of ICSS studies is that effects of the independent variablies may be attributed to a general impairment or activation of the organism rather than to a specific action on specific ICSS placements. Since salicylate affected ICSS only at certain placements and because salicylate at some placements decreased and at other placements increased ICSS, it may be concluded that the effect of salicylate on ICSS is not due to general impairment or activation of the animals. For a given locus the effect was stable and reproductible and thus it may be considered as a locusspecific effect. In other words, the brain-stimulation reward loci are not equal in their susceptibility to salicylate. Since salicylate is a drug well known for its action on thermoregulatory central mechanisms, it may be supposed that salicylate-affected ICSS sites are linked to thermal stimuli or responses. Cold and/or warm environment also significantly affected ICSS only at some sites. At a given locus cold and/or warm environment either decreased or increased ICSS rates. This indicates also that selective loci can be specifically modulated by thermal stimuli (or drives).

The results reported here show that this concept may be erroneous. Since salicylatae and Ta either facilitated or inhibited ICSS only at some scattered placements and often independently of one another we are tempted to postulate that self-stimulation sites (at least those linked to thermoregulation) operate as discrete reinforcing units independently modulated by different drives or substances. Discrete entities as neuroanatomical substrates of ICSS have already been suggested [17]. The hypothesis of discrete reinforcing units distinctly related to the thermoregulatory system is in accord with the idea that the central nervous system achieves temperature regulation through several independent circuits [3,16]. Analogous observations were reported: estrus cycle or estradiol in female rats modulated ICSS rates only at some given placements: ICSS rates at those placements were increased either at oestrus or at dioestrus; at the same sites food deprivation effects did or did not overlap [6]. Olds [10] noticed that close to placements sensitive to hunger drive there were equally rewarding sites which were unaffected (or sometimes inversely affected) by hunger drive. Conclusion

From the experiments reported here, two conclusions may be drawn. First, a portion of ICSS sites in the hypothalamus and septum is likely to be related to the thermoregulatory system since these sites are specifically modulated by salicylate and by the cold or warm environment. Second, cold, warm, and salicylate affect individual ICSS sites independently of one another, as if each ICSS locus was a separate, elementary reinforcing unit with its own pattern of susceptibilities.

Discrete Elementary Reinforcing Units

In the literature self-stimulation at one point of the brain is often taken as equivalent to that of a nearby point. Implicit ACKNOWLEDGEMENT in this concept is the expectation that, at least for a given anatomical structure, self-stimulation points should be We are grateful to Michel Cabanac for critical reading of the homogeneously affected by a given independent variable. manuscript and valuable suggestions. REFERENCES 1. Briese, E. Hyperthermia in self-stimulating rats. Acta physiol. 11. Olds, M. E. and M. Gardner. Effects of diazepam and phenolatinoam. 15: 357-361, 1965. barbital on self-stimulation in posterior hypothalamic and preoptic regions and on the thermoregulatory responses in re2. Briese, E., Y. Echeverria and M. G. de Quijada. Ambient temwarding brain stimulation. Neuropharmacology 15: 103-115, perature and self-stimulation. Acta physiol, latinoam. 16: 2091976. 215, 1966. 12. Polk, D. L. and J. M. Lipton. Effects of sodium salicylate, 3. Cabanac, M. Interaction of cold and warm temperature signals aminopyrine and chlorpromazine on behavioral temperature in the brain stem. In: Physiological and Behavioral Temperaregulation. Pharmac. Biochem. Behav. 3: 167-172, 1975. ture Regulation, edited by J. D. Hardy, A. P. Gagge and J. A. J. 13. Pittman, Q. J., W. L. Veale and K. E. Cooper. Observations on Stolwijk. Springfield, IL: C. C. Thomas, 1970, pp. 549-561. the effect of salicylate in fever and the regulation of body tem4. Carlisle, H. J. and E. Snyder. The interaction of hypothalamic perature against cold. Can. J. Physiol. Pharmac. 54: 101-106, self-stimulation and temperature regulation. Experientia 26: 1976. 1092-1093, 1970. 14. Sadowski, B., Z. Brezezinska and H. Kaciuba-Uscilko. On the 5, Dembinska, M. Hyperthermia in self-stimulating dogs. J. mechanism of hyperthermia during self-stimulation: a possible Physiol., Paris 66: 163-170, 1973. role of nervous and humoral factors. In: Brain-Stimulation Re6, Drewett, R. F. and L. J. Herberg. Hypothalamic self-stimulaward, edited by A. Wauquier and E. T. Rolls. Amsterdam: tion in the female rat: effects of oestrus and food deprivation. North-Holland Publ., 1976, pp. 467-471. Physiol. Behav. 14: 285-289, 1975. 15. Satinoff, E. Salicylate: action on normal body temperature in 7. Green, M. D. and P. Lomax. The effect of sodium salicylate on rats. Science 176: 532-533, 1972. body temperature in the normothermic rat. Proc. west. Phar16. Satinoff, E. Neural organization and evolution of thermal regumac. Soc. 16: 257-261, 1973. lation in mammals. Science 201: 16-22, 1978. 8. Latash, L. P. and V. M. Kovalzon. LHA self-stimulation effects 17. Steiner, S. S., R. J. Bodnar, W. T. Nelson, R. F. Ackermann on EEG and brain temperature in white rats. Physiol. Behav. 10: and S. J. EUman. Intracranial self-stimulation site specificity: 651-655, 1973. The myth of current spread. Brain Res. Bull. 3: 349-356, 1978. 9. Lomax, P. Measurement of "core" temperature in the rat. Na18. Wagener, J. W. Self-stimulation of preoptic and lateral hypoture 210: 854-855, 1966. thalamus during behavioral thermoregulation in the albino rat. 10. Olds, J. Differential effects of drives and drugs on selfJ. comp. physiol. Psychol. 84: 652-660, 1973. stimulation at different brain sites. In: Electrical Stimulation oJ 19. Zivin, J. A. and J. J. Bartko. Statistics for disinterested scienthe Brain, edited by D. E. Sheer. Austin: University of Texas tists. Life Sci. 18: 15-26, 1976. Press, 1961, pp, 350-366.