- Email: [email protected]
Effect of low dose ethanol on the EEG of alcohol-preferring and -nonpreferring rats
Brain Research Bulletin, Vol. 21, pp. 101-104.0 Pergamon Press plc, 1988.Printed in the U.S.A.
0361-9230/88 $3.00+ .OO
Effect of Low Dose Ethanol on the EEG of Alcohol-Preferring and -Nonpreferring Rats S. MORZORATI,’ B. LAMISHAW,* L. LUMENG, T.-K. LI, K. BEMIS*AND J. CLEMENS* Department and The Regenstriej’Institute,
of Psychiatry, Institute of Psychiatric Research Indiana University School of Medicine, V.A. Medical and *Eli Lilly and Co., Indianapolis, IN
Received
18 January
Center
1988
MORZORATI, S., B. LAMISHAW,
L. LUMENG, T.-K. LI, K. BEMIS AND J. CLEMENS. Effect oflow dose ethanol rats. BRAIN RES BULL 21( 1) 101-104, 1988.-Low dose ethanol has been shown to differentially affect the behavior of alcohol-preferring (P) and -nonpreferring (NP) rats. The present study was undertaken to determine if this differential effect is reflected in the EEG of these two rat lines. Frontocortical and hippocampal EEG were recorded from P and NP rats after intragastric infusions of ethanol (0.5 g/kg) and vehicle. Spectra were created from sequential g-second epochs and power was calculated for frequency bands O-4,4-8,8-16 and 16-50 Hz.
on rhe EEG ofalLohol-preferring
and -nonpreferring
Band power data was then grouped according to the rat’s behavior and compared for P and NP rats. During nonREM sleep, ethanol produced a persistent increase in power in the NP rats, while power in the P rats was initially decreased, then returned to baseline. This differential effect was seen at both recording sites. The results suggest the P rats were midly aroused by low dose ethanol, while the NP rats were mildly sedated. EEG
Alcohol
Alcohol-preferring and -nonpreferring rats
IN our laboratories two lines of rats have been genetically selected for their alcohol-preferring (P) and alcoholnonpreferring (NP) drinking behavior [3]. Recently, it was reported that the P and NP rats differ in their response to a low dose of ethanol [8]. Whereas the spontaneous motor activity (SMA) of P rats increased after an intraperitoneal injection of ethanol (0.12-0.25 g/kg), that in NP rats remained unchanged. Overt behavior, such as SMA, is a manifestation of the activity of the central nervous system. The electroencephalogram (EEG) provides a continuous record of the electrical activity of selected brain areas, thus making it possible to examine the electrophysiological correlates of the effects of ethanol on behavior. Since the P and NP rats differ in their behavioral response to low dose ethanol, it was hypothesized that the EEG of these rats would reflect this interline difference. The present study was undertaken to test this hypothesis.
METHOD
Animals The selectively bred alcohol-preferring (P) and nonpreferring (NP) lines of rats originated from a randomly bred Wistar colony at the Walter Reed Army Institute of Research [3]. The present study used adult male P (n=4) and NP (n=4) rats, 400-550 g, from the S 26 generation. All rats were tested for ethanol preference at puberty [2]. The oral intakes of ethanol by the P and NP rats were 6.OkO.4 and 0.098?0.08 g/kg body weight/day. All rats were abstinent from alcohol for at least one month prior to surgery. Surgery The rats were anesthetized with methoxyflurane (Metofane) and a transesophageal cannula was inserted for intragastric delivery of fluids [7]. The exposed end of the
‘Requests for reprints should be addressed to Dr. S. Morzorati, Department University School of Medicine, 791 Union Dr., Indianapolis, IN 46223.
101
of Psychiatry,
Institute of Psychiatric
Research,
Indiana
MORZORATI
ET A L .
rats
q
i
I
o-to
IO-20
I 20-30
I
30-40
t
i
o-10
ro-20
I
20-30
NP rats
L
30-40
MINUTES FIG. I. The differential effect of ethanol (0.5 g/kg, IG) on the frontocortical (right) and hippocampal (left) EEG power spectra of P and NP rats during nonREM sleep. (A) O-4 Hz. (B) 4-8 Hz. (C) %I6 Hz. Bars represent group means23.E.M. Mean band power after ethanol was normalized with respect to baseline mean band power and is plotted as a function of time after infusion. N=4 in each group. *p
cannula was threaded through a harness to keep it in place. The rats were then positioned in a stereotaxic frame with the skull level 151. Stainless steel screw electrodes were implanted over the frontal cortex (from bregma, A: 2.0 and 4.0 mm; L: 2.0 mm) and a concentric bipolar electrode (Rhodes Medical Instruments, Inc.) was implanted in the dorsal hippocampus (from bregma, P: 3.8 mm; L: 2.0 mm; from dura, V: 2.7 mm). A ground screw was placed rostra1 to the other electrodes. The electrode leads were inserted into an Amphenol plug and the entire assembly was fixed to the skull with dental cement. Following surgery, the rats were allowed to recover for at least seven days, during which time they were housed individually and provided food and water ad lib. A 14/10-hour light/dark cycle was maintained, with lights on at 0400 hours. Recording
During an experiment, the rat was housed in a glass cylinder in a sound-attenuated environmental chamber equipped with a ventilation fan and internal lighting. The Amphenol plug was connected with Microdot cable to a slip ring contact assembly (Airflyte Electronics Co.). The transesophageal
cannula was connected through the fluid channel of the assembly to an infusion pump outside the chamber. A fine insulated wire loosely attached to the cable indicated the rat’s movement. The rat was adapted to this environment for at least 24 hours before the data were acquired. Signals from the EEG electrodes and movement detector were recorded on a Grass Model 78 polygraph and on magnetic tape for off-line anaiysis. Exparitnentul Protocol
The experiments were conducted between 0900 and 1200. The rats were fasted for 16 hours prior to experimentation. Baseline EEG was recorded for 20 minutes following an infusion of water. Ethanol (0.5 g/kg, lo%, v/v) or water (vehicle control) was then infused and the EEG recorded for 40 minutes. All infusions were of equal volume, delivered at a rate of 1 mi/min and begun while the rat was asleep. Throughout the experiment, the rat’s behavior was recorded regularly on the polygraph paper.
The EEG was later subjected to power spectral analYSiS
EFFECT
OF ETHANOL
103
ON EEG
using a Hewlett-Packard 3561A Dynamic Signal Analyzer controlled by a Hewlett-Packard 87 desktop computer. The analysis process digitized the EEG and performed a Fast Fourier Transform on sequential 8-second epochs. For each epoch, a power spectrum from 0 to 50 hertz (Hz) was created and the power in four frequency bands (O-4, 4-8, 8-16, and 1650 Hz) was measured. The corresponding epochs were marked on the polygraph record and scored by the experimenter as representing one of four behaviors: nonREM sleep, REM sleep, moving (locomotion), or awake/immobile. Behaviors such as stereotypy were excluded from the analysis. The band power data were then grouped according to behavior for the baseline period and for four lO-minute intervals after the ethanol or vehicle infusions. For each block of behaviorally-sorted data, mean power was computed for each frequency band. The resultant mean band power after ethanol and vehicle were normalized using the baseline data. A two-sample t-test was used to compare the group mean band power for the P and NP rats after the ethanol and vehicle infusions for each behavior at each lo-minute interval. In order to determine if ethanol produced behavioral stimulation in either the P or NP rats, time spent in sleep (nonREM plus REM sleep) was expressed as a percent of total recording time. Group mean percent sleep times after the ethanol infusions were compared to that after the vehicle infusions for each rat line at each IO-minute interval using a paired t-test. Blood Alcohol Determination In a separate set of experiments, the same animals were again infused with ethanol. Blood was withdrawn from the retro-orbital sinus [6] at 5, 1.5,25 and 35 minutes for determination of blood alcohol concentrations which were measured in a gas chromatograph [4]. Since previous reports have shown that the blood alcohol elimination rates of P and NP rats do not differ [l], the values obtained in the present experiment for the two lines were combined and a single blood alcohol concentration curve was plotted. Placements of the hipp~ampal electrodes were verified histologically. RESULTS
Neither the P nor the NP rats exhibited statistically significant behavioral changes following the intragastric infusion of ethanol. In fact, the amount of time spent in sleep after the ethanol and vehicle infusions did not differ for either the P or the NP rats for any of the lO-minute intervals postinfusion. Data collected during the behavioral states of moving and awake/immobile were minimal and were therefore excluded from analysis. Ethanol (0.5 g/kg, IG) produced a differential effect in the frontocortical and hippocamp~ EEG power spectra of P and NP rats during nonREM sleep (Fig. 1). Specifically, the NP rats showed an increase in power frequency bands O-4, 4-8 and 8-16 Hz which persisted for 40 minutes, while power in the P rats was initially decreased, then returned to baseline levels. The differential effect between the two rat lines was statistically significant at O-10 minutes and, less frequently, at 30-40 minutes after the ethanol infusion. Frequency band 16-50 Hz was not significantly affected by ethanol. At 5, 15, 25 and 35 minutes after the ethanol infusion, the combined blood alcohol concentrations for the P and NP rats averaged 32?4, 2957, 2724 and 18*4 mg%, respectively (mean2S.D.).
Ethanol did not produce a differential effect in the P and NP rats during REM sleep in either the frontal cortex or hippocampus. The infusion of water had no effect on the EEG of either the P or NP rats. DISCUSSION
Low dose ethanol (0.5 g/kg, IG) produced a differential effect in the EEG power spectra of P and NP rats during nonREM sleep. This differential effect was characterized by a persistent increase in power in the lower frequencies in the NP rats, while the power in the P rats was initially decreased. As rats cycle through a behavioral continuum from wakefulness to drowsiness to deep nonREM sleep, the amplitude and power in the EEG increases, especially in the lower frequency components. A decrease in power is thus indicative of a more aroused state. In the present experiments, the behavioral category of nonREM sleep encompassed both drowsiness and deep sleep. Therefore, a druginduced change in the spectral characteristics of the EEG during epochs scored as nonREM sleep may reflect a change in EEG amplitude during sleep and/or a change in the relative amounts of time spent in drowsiness compared to deeper sleep. Previous work [SJ showed that a low dose of ethanol produced behavioral stimulation in P rats, but not in NP rats. It is likely, then, that the decrease in power observed in the EEG of the P rats is due to an increase in the time spent in drowsiness at the expense of deep sleep. Conversely, the increase in power in the NP rats may be due to more time spent in deep sleep at the expense of drowsiness. The results, therefore, suggest that the P rats were midly aroused, whereas the NP rats were mildly sedated. Although, in the present experiments, behavioral stimulation was not statistically significant in the P rats as a group, it is noteworthy that two of the four P rats studied spent considerable time in the awake state O-10 minutes after the ethanol infusion. The lack of a consistent behavioral response to ethanol in our findings compared with those of an earlier report [8] in the same rat line may be attributed to the state of the rat at the time of ethanol administ~tion, that is, asleep and undisturbed versus awakened and handled. The ethanol-induced arousal seen in the P rats appears to be restricted to lower doses. In the report by Wailer et al. [8], behavioral stimulation was not observed at higher doses of ethanol (0.5-1.5 g/kg, IP). In accordance with these findings, we obtained preliminary evidence which showed that, in P rats, a slightly higher dose of ethanol (0.75 g/kg, IG) did not produce the decrease in power during nonREM sleep, indicative of arousal, that was seen at the lower dose. In summary, our results demonstrate that a low dose of ethanol differentiates the electroencephalographic response of rats genetically selected for differences in alcohol preference. Furthermore, the data indicate a relationship between ethanol preference and ethanol-induced stimulation (arousal) and suggest that stimulation is an expression of the positive reinforcing effects of ethanol for the alcohol-preferring rats.
ACKNOWLEDGEMENTS
The authors would like to thank Gregory Gatto and Joyce Harts for their skillful technical assistance. This project was supported in part by grant ROI AA03243-10 from the PHS.
MORZORATI
104
ET AL.
REFERENCES
Li, T.-K.: Lumeng. L. Alcohol metabolism of inbred strains of rats with alcohol preference and nonpreference. In: Thurman, R. G.; Williamson. J. R.: Drott. H.: Chance, B., eds. Alcohol and aldehyde metabolizing systems. vol. 3. New York: Academic Press; 1917~625-633. Li, T.-K.; Lumeng, L.: McBride, W. J.; Waller, M. B.; Hawkins. T. D. Progress toward a voluntary oral consumption model of alcoholism. Drug Alcohol Depend. 4:45-60; 1979. Lumeng. L.; Hawkins, T. D.: Li, T.-K. New strains of rats with alcohol preference and nonpreference. In: Thurman, R. G.; Williamson, J. R.: Drott, H.; Chance, B., eds. Alcohol and aldehyde metabolizing systems. vol. 3. New York: Academic Press; 1977:537-544.
4. Lumeng, L.; Waller. M. B.: McBride, W. J.: Li. T.-K. Different sensitivities to ethanol in alcohol-preferring and -nonpreferring rats. Pharmacol. Biochem. Behav. 16: 145-149: 1982. 5. Paxinos, G.: Watson, C. The rat brain in stereotaxic coordinates. Sydney: Academic Press; 1982. Riley, V. Adaptation of orbital bleeding technique to rapid serial blood studies. Proc. Sot. Exp. Biol. Med. 1041751-754: 1960. Smith, S. G.; Werner. T. E.: Davis. W. M. Technioue for intragastric delivery of solutions; application for selfadministration of morphine and alcohol by rats. Physiol. Psychol. 3~220-224: 1975. Waller, M. B.; Murphy. J. M.; McBride, W. J.: Lumeng. L.; Li, T.-K. Effect of low dose ethanol on spontaneous motor activitv in alcohol-preferring and -nonpreferring lines of rats. Pharmacoi. Biochem. Behav. 24:617-623: 1986.
0361-9230/88 $3.00+ .OO
Effect of Low Dose Ethanol on the EEG of Alcohol-Preferring and -Nonpreferring Rats S. MORZORATI,’ B. LAMISHAW,* L. LUMENG, T.-K. LI, K. BEMIS*AND J. CLEMENS* Department and The Regenstriej’Institute,
of Psychiatry, Institute of Psychiatric Research Indiana University School of Medicine, V.A. Medical and *Eli Lilly and Co., Indianapolis, IN
Received
18 January
Center
1988
MORZORATI, S., B. LAMISHAW,
L. LUMENG, T.-K. LI, K. BEMIS AND J. CLEMENS. Effect oflow dose ethanol rats. BRAIN RES BULL 21( 1) 101-104, 1988.-Low dose ethanol has been shown to differentially affect the behavior of alcohol-preferring (P) and -nonpreferring (NP) rats. The present study was undertaken to determine if this differential effect is reflected in the EEG of these two rat lines. Frontocortical and hippocampal EEG were recorded from P and NP rats after intragastric infusions of ethanol (0.5 g/kg) and vehicle. Spectra were created from sequential g-second epochs and power was calculated for frequency bands O-4,4-8,8-16 and 16-50 Hz.
on rhe EEG ofalLohol-preferring
and -nonpreferring
Band power data was then grouped according to the rat’s behavior and compared for P and NP rats. During nonREM sleep, ethanol produced a persistent increase in power in the NP rats, while power in the P rats was initially decreased, then returned to baseline. This differential effect was seen at both recording sites. The results suggest the P rats were midly aroused by low dose ethanol, while the NP rats were mildly sedated. EEG
Alcohol
Alcohol-preferring and -nonpreferring rats
IN our laboratories two lines of rats have been genetically selected for their alcohol-preferring (P) and alcoholnonpreferring (NP) drinking behavior [3]. Recently, it was reported that the P and NP rats differ in their response to a low dose of ethanol [8]. Whereas the spontaneous motor activity (SMA) of P rats increased after an intraperitoneal injection of ethanol (0.12-0.25 g/kg), that in NP rats remained unchanged. Overt behavior, such as SMA, is a manifestation of the activity of the central nervous system. The electroencephalogram (EEG) provides a continuous record of the electrical activity of selected brain areas, thus making it possible to examine the electrophysiological correlates of the effects of ethanol on behavior. Since the P and NP rats differ in their behavioral response to low dose ethanol, it was hypothesized that the EEG of these rats would reflect this interline difference. The present study was undertaken to test this hypothesis.
METHOD
Animals The selectively bred alcohol-preferring (P) and nonpreferring (NP) lines of rats originated from a randomly bred Wistar colony at the Walter Reed Army Institute of Research [3]. The present study used adult male P (n=4) and NP (n=4) rats, 400-550 g, from the S 26 generation. All rats were tested for ethanol preference at puberty [2]. The oral intakes of ethanol by the P and NP rats were 6.OkO.4 and 0.098?0.08 g/kg body weight/day. All rats were abstinent from alcohol for at least one month prior to surgery. Surgery The rats were anesthetized with methoxyflurane (Metofane) and a transesophageal cannula was inserted for intragastric delivery of fluids [7]. The exposed end of the
‘Requests for reprints should be addressed to Dr. S. Morzorati, Department University School of Medicine, 791 Union Dr., Indianapolis, IN 46223.
101
of Psychiatry,
Institute of Psychiatric
Research,
Indiana
MORZORATI
ET A L .
rats
q
i
I
o-to
IO-20
I 20-30
I
30-40
t
i
o-10
ro-20
I
20-30
NP rats
L
30-40
MINUTES FIG. I. The differential effect of ethanol (0.5 g/kg, IG) on the frontocortical (right) and hippocampal (left) EEG power spectra of P and NP rats during nonREM sleep. (A) O-4 Hz. (B) 4-8 Hz. (C) %I6 Hz. Bars represent group means23.E.M. Mean band power after ethanol was normalized with respect to baseline mean band power and is plotted as a function of time after infusion. N=4 in each group. *p
cannula was threaded through a harness to keep it in place. The rats were then positioned in a stereotaxic frame with the skull level 151. Stainless steel screw electrodes were implanted over the frontal cortex (from bregma, A: 2.0 and 4.0 mm; L: 2.0 mm) and a concentric bipolar electrode (Rhodes Medical Instruments, Inc.) was implanted in the dorsal hippocampus (from bregma, P: 3.8 mm; L: 2.0 mm; from dura, V: 2.7 mm). A ground screw was placed rostra1 to the other electrodes. The electrode leads were inserted into an Amphenol plug and the entire assembly was fixed to the skull with dental cement. Following surgery, the rats were allowed to recover for at least seven days, during which time they were housed individually and provided food and water ad lib. A 14/10-hour light/dark cycle was maintained, with lights on at 0400 hours. Recording
During an experiment, the rat was housed in a glass cylinder in a sound-attenuated environmental chamber equipped with a ventilation fan and internal lighting. The Amphenol plug was connected with Microdot cable to a slip ring contact assembly (Airflyte Electronics Co.). The transesophageal
cannula was connected through the fluid channel of the assembly to an infusion pump outside the chamber. A fine insulated wire loosely attached to the cable indicated the rat’s movement. The rat was adapted to this environment for at least 24 hours before the data were acquired. Signals from the EEG electrodes and movement detector were recorded on a Grass Model 78 polygraph and on magnetic tape for off-line anaiysis. Exparitnentul Protocol
The experiments were conducted between 0900 and 1200. The rats were fasted for 16 hours prior to experimentation. Baseline EEG was recorded for 20 minutes following an infusion of water. Ethanol (0.5 g/kg, lo%, v/v) or water (vehicle control) was then infused and the EEG recorded for 40 minutes. All infusions were of equal volume, delivered at a rate of 1 mi/min and begun while the rat was asleep. Throughout the experiment, the rat’s behavior was recorded regularly on the polygraph paper.
The EEG was later subjected to power spectral analYSiS
EFFECT
OF ETHANOL
103
ON EEG
using a Hewlett-Packard 3561A Dynamic Signal Analyzer controlled by a Hewlett-Packard 87 desktop computer. The analysis process digitized the EEG and performed a Fast Fourier Transform on sequential 8-second epochs. For each epoch, a power spectrum from 0 to 50 hertz (Hz) was created and the power in four frequency bands (O-4, 4-8, 8-16, and 1650 Hz) was measured. The corresponding epochs were marked on the polygraph record and scored by the experimenter as representing one of four behaviors: nonREM sleep, REM sleep, moving (locomotion), or awake/immobile. Behaviors such as stereotypy were excluded from the analysis. The band power data were then grouped according to behavior for the baseline period and for four lO-minute intervals after the ethanol or vehicle infusions. For each block of behaviorally-sorted data, mean power was computed for each frequency band. The resultant mean band power after ethanol and vehicle were normalized using the baseline data. A two-sample t-test was used to compare the group mean band power for the P and NP rats after the ethanol and vehicle infusions for each behavior at each lo-minute interval. In order to determine if ethanol produced behavioral stimulation in either the P or NP rats, time spent in sleep (nonREM plus REM sleep) was expressed as a percent of total recording time. Group mean percent sleep times after the ethanol infusions were compared to that after the vehicle infusions for each rat line at each IO-minute interval using a paired t-test. Blood Alcohol Determination In a separate set of experiments, the same animals were again infused with ethanol. Blood was withdrawn from the retro-orbital sinus [6] at 5, 1.5,25 and 35 minutes for determination of blood alcohol concentrations which were measured in a gas chromatograph [4]. Since previous reports have shown that the blood alcohol elimination rates of P and NP rats do not differ [l], the values obtained in the present experiment for the two lines were combined and a single blood alcohol concentration curve was plotted. Placements of the hipp~ampal electrodes were verified histologically. RESULTS
Neither the P nor the NP rats exhibited statistically significant behavioral changes following the intragastric infusion of ethanol. In fact, the amount of time spent in sleep after the ethanol and vehicle infusions did not differ for either the P or the NP rats for any of the lO-minute intervals postinfusion. Data collected during the behavioral states of moving and awake/immobile were minimal and were therefore excluded from analysis. Ethanol (0.5 g/kg, IG) produced a differential effect in the frontocortical and hippocamp~ EEG power spectra of P and NP rats during nonREM sleep (Fig. 1). Specifically, the NP rats showed an increase in power frequency bands O-4, 4-8 and 8-16 Hz which persisted for 40 minutes, while power in the P rats was initially decreased, then returned to baseline levels. The differential effect between the two rat lines was statistically significant at O-10 minutes and, less frequently, at 30-40 minutes after the ethanol infusion. Frequency band 16-50 Hz was not significantly affected by ethanol. At 5, 15, 25 and 35 minutes after the ethanol infusion, the combined blood alcohol concentrations for the P and NP rats averaged 32?4, 2957, 2724 and 18*4 mg%, respectively (mean2S.D.).
Ethanol did not produce a differential effect in the P and NP rats during REM sleep in either the frontal cortex or hippocampus. The infusion of water had no effect on the EEG of either the P or NP rats. DISCUSSION
Low dose ethanol (0.5 g/kg, IG) produced a differential effect in the EEG power spectra of P and NP rats during nonREM sleep. This differential effect was characterized by a persistent increase in power in the lower frequencies in the NP rats, while the power in the P rats was initially decreased. As rats cycle through a behavioral continuum from wakefulness to drowsiness to deep nonREM sleep, the amplitude and power in the EEG increases, especially in the lower frequency components. A decrease in power is thus indicative of a more aroused state. In the present experiments, the behavioral category of nonREM sleep encompassed both drowsiness and deep sleep. Therefore, a druginduced change in the spectral characteristics of the EEG during epochs scored as nonREM sleep may reflect a change in EEG amplitude during sleep and/or a change in the relative amounts of time spent in drowsiness compared to deeper sleep. Previous work [SJ showed that a low dose of ethanol produced behavioral stimulation in P rats, but not in NP rats. It is likely, then, that the decrease in power observed in the EEG of the P rats is due to an increase in the time spent in drowsiness at the expense of deep sleep. Conversely, the increase in power in the NP rats may be due to more time spent in deep sleep at the expense of drowsiness. The results, therefore, suggest that the P rats were midly aroused, whereas the NP rats were mildly sedated. Although, in the present experiments, behavioral stimulation was not statistically significant in the P rats as a group, it is noteworthy that two of the four P rats studied spent considerable time in the awake state O-10 minutes after the ethanol infusion. The lack of a consistent behavioral response to ethanol in our findings compared with those of an earlier report [8] in the same rat line may be attributed to the state of the rat at the time of ethanol administ~tion, that is, asleep and undisturbed versus awakened and handled. The ethanol-induced arousal seen in the P rats appears to be restricted to lower doses. In the report by Wailer et al. [8], behavioral stimulation was not observed at higher doses of ethanol (0.5-1.5 g/kg, IP). In accordance with these findings, we obtained preliminary evidence which showed that, in P rats, a slightly higher dose of ethanol (0.75 g/kg, IG) did not produce the decrease in power during nonREM sleep, indicative of arousal, that was seen at the lower dose. In summary, our results demonstrate that a low dose of ethanol differentiates the electroencephalographic response of rats genetically selected for differences in alcohol preference. Furthermore, the data indicate a relationship between ethanol preference and ethanol-induced stimulation (arousal) and suggest that stimulation is an expression of the positive reinforcing effects of ethanol for the alcohol-preferring rats.
ACKNOWLEDGEMENTS
The authors would like to thank Gregory Gatto and Joyce Harts for their skillful technical assistance. This project was supported in part by grant ROI AA03243-10 from the PHS.
MORZORATI
104
ET AL.
REFERENCES
Li, T.-K.: Lumeng. L. Alcohol metabolism of inbred strains of rats with alcohol preference and nonpreference. In: Thurman, R. G.; Williamson. J. R.: Drott. H.: Chance, B., eds. Alcohol and aldehyde metabolizing systems. vol. 3. New York: Academic Press; 1917~625-633. Li, T.-K.; Lumeng, L.: McBride, W. J.; Waller, M. B.; Hawkins. T. D. Progress toward a voluntary oral consumption model of alcoholism. Drug Alcohol Depend. 4:45-60; 1979. Lumeng. L.; Hawkins, T. D.: Li, T.-K. New strains of rats with alcohol preference and nonpreference. In: Thurman, R. G.; Williamson, J. R.: Drott, H.; Chance, B., eds. Alcohol and aldehyde metabolizing systems. vol. 3. New York: Academic Press; 1977:537-544.
4. Lumeng, L.; Waller. M. B.: McBride, W. J.: Li. T.-K. Different sensitivities to ethanol in alcohol-preferring and -nonpreferring rats. Pharmacol. Biochem. Behav. 16: 145-149: 1982. 5. Paxinos, G.: Watson, C. The rat brain in stereotaxic coordinates. Sydney: Academic Press; 1982. Riley, V. Adaptation of orbital bleeding technique to rapid serial blood studies. Proc. Sot. Exp. Biol. Med. 1041751-754: 1960. Smith, S. G.; Werner. T. E.: Davis. W. M. Technioue for intragastric delivery of solutions; application for selfadministration of morphine and alcohol by rats. Physiol. Psychol. 3~220-224: 1975. Waller, M. B.; Murphy. J. M.; McBride, W. J.: Lumeng. L.; Li, T.-K. Effect of low dose ethanol on spontaneous motor activitv in alcohol-preferring and -nonpreferring lines of rats. Pharmacoi. Biochem. Behav. 24:617-623: 1986.