The effect of chronic ethanol consumption on [14C]deoxyglucose uptake in rat brain in vivo

The effect of chronic ethanol consumption on [14C]deoxyglucose uptake in rat brain in vivo

Neuroscience Letters, 100 (1989) 181 187 181 Elsevier Scientific Publishers Ireland Ltd. NSL 05962 The effect of chronic ethanol consumption on [14...

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Neuroscience Letters, 100 (1989) 181 187

181

Elsevier Scientific Publishers Ireland Ltd. NSL 05962

The effect of chronic ethanol consumption on [14C]deoxyglucose uptake in rat brain in vivo Eva R. Pietrzak, Peter A. Wilce and Brian C. Shanley Department of Biochemistry, University of Queensland, St. Lucia, Qld. (Australia)

(Received 16 October 1988; Revised version received29 November 1988; Accepted 30 November 1988) Key wordy: Ethanol;Deoxyglucoseuptake; Autoradiography

The uptake of lt4C]deoxyglucoseby brains of rats that were givenalcohol in drinking water for 7 months was investigated. There was a general, approximately 50%, increase in deoxyglucoseuptake in brains of ethanol-treated rats with areas of the limbic system being particularly affected.

The metabolic consequences of ethanol exposure in the brain have been extensively studied. Acute ethanol treatment in the form of an injection is followed by an increase in the levels of glucose [13, 18]. In vitro experiments indicate that this may result from depressed glucose oxidation [9]. Chronic ethanol treatment has yielded inconsistent results, probably reflecting the variety of experimental conditions. Decreased levels of glucose indicative of increased glucose utilisation have been reported by Veech et al. [17], while Rawat et al. [12] found decreased 14CO2 production from [14C]glucose. In intoxicated animals uptake of [14C]deoxyglucose was unaffected [3] but was markedly elevated in rats undergoing withdrawal [3, 4]. We have previously reported that prolonged ethanol treatment increased 14CO2 production from [14C]glucose in rat cerebral cortex prisms in vitro, while a single injection of a low dose ethanol had no effect [14]. We have now extended these studies to include measurement of [14C]deoxyglucose uptake in vivo. The uptake of [14C]deoxyglucose has had extensive application as an indicator of the level of neuronal activity and energy metabolism in vivo [15]. In the present study we used the technique coupled to quantitative autoradiography to monitor the effects of prolonged ethanol treatment on individual brain areas. Male Wistar rats (260 __+ 13 g b.wt.: mean + S.D. at the start of the experiment) received 15% (v/v) ethanol in water at their only source of fluid for 7 months as previously described [14]. The daily dose of ethanol was 4.3 _ 0.8 g/kg of body weight, which constituted approximately 28% of total metabolic energy. Control animals Correspondence: E.R. Pietrzak, Department of Biochemistry, University of Queensland, St. Lucia, Qld.

4067, Australia. 0304-3940/89/$ 03.50 © 1989 ElsevierScientific Publishers Ireland Ltd.

182 received sugar cubes in amounts isocaioric to the ethanol consumed. There were no significant differences in final body weight between control and ethanol-treated animals (mean + S.D. was 418 + 48 g and 403 + 52 g, respectively). Blood alcohol measured at the end of the dark period (12/12 h light-
183 TABLE I T H E E F F E C T O F C H R O N I C E T H A N O L T R E A T M E N T O N T O T A L [t4C]DEOXYGLUCOSE U P T A K E IN R A T B R A I N SECTIONS Coronal sections were cut and their radioactivity content determined. A: pair-fed controls for chronically treated animals. B: age-matched controls for naive animals injected with ethanol. N u m b e r o f animals is indicated in brackets. Each value given is a mean + S.D. Values given are expressed in dpm/section. G r o u p of animals

dpm/section

Control A Ethanol, chronic

1752 + 128 (5) 2780 __+ 152" (5)

Control B Ethanol, injected

1982 + 183 (3) 2020 + 45 (3)

*P < 0.05, significantly different from its respective control. T A B L E II A U T O R A D I O G R A P H I C A N A L Y S I S OF T H E E F F E C T O F C H R O N I C E T H A N O L T R E A T M E N T O N [14C]DEOXYGLUCOSE U P T A K E IN R A T B R A I N Values given are expressed in nCi/g of tissue. Each value is a m e a n _ S.D. of triplicate sections from 3-5 animals.

Brain region

Control

Ethanol

% of increase, P

Cortex, cingulate Cortex, frontal Cortex, frontoparietal, motor area Cortex, frontoparietal, somatosensory area Cortex, auditory area Caudate p u t a m e n Accumbens Globus pallidus Septum Amygdala Thalamus, anterior Thalamus, ventrolateral Thalamus, dorsal Subthalamus Mammillary bodies Geniculate nucleus Hippocampus, regions CA l, CA2, CA3 Hippocampus, dentate Substantia nigra Inferior colliculus Superior olive Deep mesenceph, nu. Vestibular nucleus Corpus callosum

103+22 152_+_10

196_+20 183.-_31

90 20

P
131 _+21

184.-, 15

40

P
111 .--24 135+13 123 ___32 119--,30 75 _+ 15 71 +- 14 93--- 1 117+13 127 + 14 135-+16 120+9 108 _+ 11 107 _ 4 88+12

191 + 4 2 198--,24 187 __+30 174.-,17 119 +- 14 125 _+ 17 158-+65 197_+33 166_+ 25 167-+21 170_+ 15 184--, 14 206 + 63 115.-,9

72 40 52 46 59 76 70 69 31 24 42 70 93 31

P < 0.05 P<0.02 P < 0.02 P<0.05 P < 0.01 P<0.01 P<0.05 P<0.02 P < 0.05 P<0.05 P < 0.01 P < 0.01 P < 0.05 P<0.01

97.-- 14 90-t- 21 136 +- 18 101 + 2 110_+ 21 143 _+47 63 -+ 10

126+8 105 + 16 177 _+24 112--,25 118 + 10 176 _+20 8 7 + 19

29 N.S. N.S. N.S. N.S. N.S. 38

P < 0.02

P < 0.05

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185 both groups of animals. Ethanol treatment, however, resulted in a significant increase in uptake into this area. White matter showed a slight, but uniform increase in [14C]deoxyglucose uptake after ethanol treatment. A representative example of the colour enhanced image analysis of autoradiograms is presented in Fig. 1. The results showed that chronic ethanol treatment resulted in an overall increase in [14C]deoxyglucose uptake with the increase in some brain areas being more evident. None of the brain regions analysed showed any inhibition of uptake. Previous studies on the effect of ethanol on brain [14C]deoxyglucose uptake have shown a selective decrease in uptake following an acute dose [5], no change immediately following four days of intensive ethanol treatment and markedly increased overall uptake during withdrawal [3, 4]. When specific brain areas were considered, in overtly withdrawn rats the most affected areas were connected with m o t o r functions but in postwithdrawn rats these areas were unchanged [4]. In the present study of chronically-treated rats we have shown an average increase in these regions of 40-50%. On the other hand the limbic system structures, some of which showed only modest elevation in the withdrawn rats, were the most affected in our chronicallytreated rats (70-90%). Furthermore, areas having auditory function, which showed depressed [14C]deoxyglucose uptake following an acute dose of ethanol [5], were slightly elevated or unaffected by chronic treatment in the present study. Our results indicate that in comparison to short-term treatment, prolonged treatment has different effects on brain. The inconsistency with the results of Campbell et al. [3] who found no increase in [14C]deoxyglucose uptake in intoxicated animals may reflect the different ethanol administration regime used. The regime employed by Campbell et al. [3] was designed to produce signs of withdrawal after short but intense ethanol administration, with doses of 8-11 g of ethanol/kg of body weight given over a 4 day period. In the present study an extended ethanol-treatment protocol was used (about 4 g of ethanol/kg b.wt. daily for 7 months). The elevated uptake of [14C]deoxyglucose in brains of chronically treated rats does not seem to be a result of changed energy metabolism of the brain. Ethanol is only minimally metabolised in the brain [l 1] and even in optimal conditions could supply less than 1/1000 of the energy requirements in the brain [8, 17]. Acute, hypnotic doses of ethanol are able to depress energy expenditure of the brain without alteration of the redox-state or impairment of energy production [18]. Low, acute doses did not change glucose utilisation by cortical prisms in vitro [14] and failed to elicit any general change in [14C]deoxyglucose uptake (Table I). Hence, we can assume that the

Fig. 1. Pseudo-color photographs of autoradiograms from rat brain after injection of [~4C]deoxyglucose. Coronal and sagittal sections were cut from rats treated with ethanol for 7 months and age-matchedcontrois. A: coronal sections 9.7 9.2 mm from the interaural marker. Major areas: caudate putamen, septal nuclei and vertical limb of diagonal band. B: coronal sections, 6.9-7.2 mm from the interaural marker. Major areas: amygdaloid nuclei, anterior thalamic nuclei and hippocampus (region CA3). C: sagittal sections, 1.9 2.2 mm lateral. Major areas: caudate putamen and accumbens nuclei, hippocampus, inferior colicullus and ventral thalamic nuclei. D: sagittal sections, 0.44).9 mm lateral. Major areas: septal nuclei, accumbens nuclei, hypothalamic nuclei and medial thalamic nuclei. Colour scale is calibrated in nCi/g.

186 marked overall increase in [t4C]deoxyglucose u p t a k e seen in the chronically treated a n i m a l s is a reflection o f adaptive changes d u r i n g t r e a t m e n t rather than a short-term e t h a n o l - i n d u c e d p e r t u r b a t i o n o f c a r b o h y d r a t e metabolism. There are a n u m b e r of e x p l a n a t i o n s for the general increase in [14C]deoxyglucose uptake following e t h a n o l treatment. E t h a n o l has been shown to p e r t u r b m e m b r a n e function a n d it is conceivable that the general effect may indicate a n e t h a n o l - d e p e n dent increase in glucose t r a n s p o r t into the cells or release into the intercellular spaces. Alternatively, e t h a n o l t r e a t m e n t may p r o m o t e delivery of [14C]deoxyglucose to the brain. This could be a result of increased b l o o d flow, or a n altered b l o o d distribution. However, G o l d m a n et al. [6] fail to d e m o n s t r a t e a n effect o f m o d e r a t e c o n c e n t r a t i o n s of ethanol on cerebral blood flow in the rat. A more likely e x p l a n a t i o n , consistent with our previous finding of an increased rate of glucose oxidation in vitro, is an e t h a n o l - i n d u c e d increase in neural activity. In s u m m a r y , the results presented here have shown that [lac]deoxyglucose m e t a b o l i s m in vivo is m a r k e d l y affected by longterm ethanol treatment. This work was supported by a g r a n t from the A u s t r a l i a n N a t i o n a l Health a n d Medical Research Council. The a u t h o r s t h a n k Steven M a s o n for his skilled technical assistance.

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