Roger P. Maickel

Stress-induced consumption of ethanol by rats.

Rats were maintained in a continuous choice situation for consumption of either 0.1% aqueous saccharin or 10% ethanol- 0.1% saccharin with daily tube position reversal and 24 hour fluid consumption measurement. After a stabilized baseline was achieved, groups were exposed to either no stress, or to an unpredictable schedule of isolation or immobilization stress for 14 days. During baseline and stress-exposure periods, the rats consumed predominantly the saccharin solution. Upon cessation of the stress exposures the isolation and immobilization groups markedly increased their consumption of the ethanol solution, reaching intakes as high as 9.1 g/kg/24 hours in 2-3 weeks. In addition, after 3 weeks of ethanol consumption, placement of saccharin in both tubes resulted in the stressed animals preferentially consuming from the tube that should have contained ethanol. The results suggest that unpredictable exposure to stressful stimuli can, upon cessation of exposure, induce an alcohol consummatory behavior in rats.

The role of the hypothalamic-pituitary-adrenocortical axis in post-stress induced ethanol consumption by rats

1. Previous studies conducted in our laboratory demonstrated that rats given a choice between a 0.1% saccharin solution or 10% ethanol/0.1% saccharin solution and repeatedly exposed on an unpredictable basis to stressful stimuli, consumed increasing quantities of the ethanol solution following cessation of stressor presentation as compared to nonstressed control rats. 2. Stressful stimuli potently activate the hypothalamic-pituitary-adrenocortical (HPA) axis, thus a systematic investigation of the HPA axis and its involvement in post-stress induced ethanol consummatory behavior was undertaken. 3. Exposure to repetitive unpredictable stressful stimuli did not induce the free-choice consumption of ethanol in either hypophysectomized rats or chronic dexamethasone treated rats. 4. Adrenalectomized rats exposed to chronic unpredictable stressful stimuli consumed increased quantities of ethanol following cessation of stressful stimuli in both a quantitative and qualitative manner which mirrored that of intact animals. 5. Repeated intravenous administration of exogenous adrenocorticotropin (ACTH1-39) on an unpredictable basis also induced ethanol consuming behavior, following the discontinuation of its administration. 6. These results suggest that elimination of the pituitary or pharmacological antagonism of stress-induced HPA activation will prevent post-stress induced ethanol consummatory behavior. 7. Conversely, activation of a functional hypothalamic-pituitary system or repeated administration of exogenous ACTH1-39 will initiate ethanol consumption in rats. 8. Thus, hormones secreted from the pituitary, namely ACTH, appear to play a crucial role in the post-stress induced initiation of ethanol consuming behavior in rats.

Comparative biochemical responses of rats to different stressful stimuli

Adult male rats were exposed to single applications of one of three stressful stimuli (low environmental temperature, immobilization, random footshock) for periods up to 4 hours and plasma levels of corticosterone (PCS), fatty acids (PFA), and glucose (PGL) were determined at various points during the stress exposure and 1 and 2 hours post-exposure. The levels of PCS were increased by all 3 stressful stimuli in a similar temporal pattern, with the greatest magnitude of effect seen for immobilization and the least for cold exposure. The time courses of increased PFA levels were similar for immobilization and cold exposure; the response to foot shock was delayed in onset by 2 hours. The PGL response was minimal for cold exposure and foot shock, but showed a marked elevation during the first 2 hours of immobilization. The results suggest that the response pattern obtained is characteristic of the stressful stimulus employed, with PCS showing the least degree of specificity.

Free-choice ethanol consumption by rats: effects of ACTH4–10

The individual and interactive effects of immobilization stress, ACTH11-24 and ACTH4-10 on the free-choice consumption of ethanol in rats were studied. Stress and ethanol both result in activation of the HPA axis and release of ACTH1-39. The animals were offered a two-bottle choice consumption of 0.2% saccharin and 10% ethanol. They were exposed to immobilization stress or IP injections of ACTH4-10 or ACTH11-24 on an irregular, unpredictable schedule. Stress resulted in a decrease in ethanol consumption during the stress period while ACTH11-24 was devoid of any effect. The ACTH4-10 fragment produced an almost complete block of ethanol consumption during the injection period. Saccharin consumption was not affected by any of the above treatments. These results suggest an important role for ACTH4-10 (produced from ACTH1-39) in ethanol consummatory behavior in rats.

Alterations of biochemical parameters by acute and repetitive stress situations in mice

Abstract (1) Mice were subjected to acute or repetitive exposure to cold, immobilization, or amphetamine stress and changes in plasma levels of corticosterone, fatty acids, and glucose were measured. (2) The results obtained indicate that plasma corticosterone is the only valid stress marker of the three tested. (3) When mice were subjected to repetitive stress for 14 days, acute challenges showed dramatic effects only in plasma corticosterone.

Calcium Channel Blockade by Certain Opioids

The calcium entry blocker, verapamil, enhanced morphine analgesia, but neither methadone nor propoxyphene analgesia was affected by verapamil in the mouse hot-plate test. To explain this, it was hypothesized that methadione and propoxyphene differ from morphine because they, like verapamil, block calcium channels and subsequent studies were done to confirm this. Verapamil, methadone and propoxyphene all depressed barium-induced bovine adrenal catecholamine release and KCl-induced contractions of guinea pig ileum, which are known to be calcium-dependent events. Calcium reversed opioid-induced inhibition in both tissues. Morphine did not affect either catecholamine release or ileal contractions. Procaine also did not influence catecholamine release or ileal contraction. Therefore, local anesthesia was eliminated as a mechanism for the inhibitory action of methadone and propoxyphene in these tissues. Opioids which block calcium channels should, like verapamil, produce bradycardia and hypotension. In the spinal vagotomized rat, methadone, propoxyphene, and verapamil produced bradycardia and hypotension, whereas, morphine produced tachycardia and (at low doses) hypertension. The results of this work suggest that methadone and propoxyphene, in contrast to morphine, block calcium channels in a manner similar to verapamil, and that some pharmacological and especially toxicological differences between these drugs are due to different degrees of verapamil-like calcium channel blockade.

Subcellular distribution of tissue radiocopper following intravenous administration of 67Cu-labeled Cu-PTSM

The subcellular distribution of radiocopper in the brain and liver of rats has been determined following i.v. administration of Cu-PTSM, pyruvaldehyde bis(N4-methylthiosemicarbazonato)copper(II), labeled with copper-67. Homogenized tissue samples were separated by differential centrifugation into four subcellular fractions: (I) cell membrane + nuclei; (II) mitochondria; (III) microsomes; and (IV) cell cytosol. Upon sacrifice at 10 min post-Cu-PTSM injection, brain fractions, I, II, III and IV contain 35 +/- 12, 11 +/- 3, 2.8 +/- 1.3 and 51 +/- 7% of brain activity, respectively (n = 4). In animals sacrificed 24 h post-injection the subcellular fractions of brain tissue show little change from the radiocopper distribution seen at 10 min post-injection, although the mitochondrial fraction may contain slightly more tracer and the cytosolic fraction slightly less (I, 40 +/- 10%; II, 18 +/- 5%; III, 3.4 +/- 1.5%; and IV, 38 +/- 5%; n = 5). Subcellular fractions I, II, III and IV of liver contain 25 +/- 5, 12 +/- 3, 17 +/- 4 and 46 +/- 6% of 67Cu tracer in animals sacrificed 10 min post-Cu-PTSM injection. An identical subcellular distribution of 67Cu, was found in the liver following i.v. administration of ionic radiocopper (as Cu-citrate). The liver and brain cytosolic fractions at 10 min post-injection were further separated by Sephadex column chromatography. In liver cytosol, three different radiocopper components with molecular weights of about 140,000, 41,000-46,000 and 10,000-16,000 Da were found. In the brain supernatant fraction, most of the radiocopper was bound to a single low molecular weight cytosolic component (14,000-16,000 Da).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of stress and ebiratide (Hoe-427) on free-choice ethanol consumption: Comparison of lewis and Sprague-Dawley rats

The effects of immobilization stress, isolation stress and administration of Hoe-427 on free-choice consumption of ethanol by Lewis and Sprague-Dawley rats were studied. The animals were offered two-bottle choice consumption of 0.2% saccharin and 10% ethanol/0.2% saccharin, then exposed to 4 days of immobilization stress or isolation stress on an irregular, unpredictable schedule or 4 days of i.p. doses of Hoe-427 at 1800 hours. Both stresses resulted in significant decreases in ethanol consumption during the stress period. Hoe-427 produced a significant decrease in ethanol consumption, in a dose-dependent manner. Saccharin consumption was not significantly affected by any of the treatments. The ability to correlate the Lewis and Sprague-Dawley rat response further aids in supporting the role of the adrenocorticotropic peptide in the development of ethanol consumption.

Drug interactions with brain biogenic amines and the effects of amphetamine isomers on locomotor activity

Administration of single IP doses of 1.0 or 4.0 mg/kg of d-amphetamine evoked an increase in mouse spontaneous motor activity (SMA); in contrast, 1.0 mg/kg of l-amphetamine had no significant effect, while 4.0 mg/kg caused a decreased SMA. Pretreatment with aMT or pargyline had little effect on the actions of the l-isomer, but reduced the magnitude and duration of the stimulatory effect of d-amphetamine. Pretreatment with p-chlorophenylalanine had little effect on the actions of d-amphetamine but completely abolished the depressant actions of the l-isomer. Reserpine pretreatment markedly reduced basal SMA levels; such pretreatment caused both d- and l-amphetamine to act as stimulants of SMA.

The effect of Hoe-427 (an ACTH4–9 analog) on free-choice ethanol consumption in male and female rats

Ethanol consummatory patterns of individual male and female rats and the effects of Hoe-427 (Ebiratide), an ACTH4-9 analog, thereon, were studied in a test system using 24 hour, two-bottle free choice consumption between 0.2% saccharin and 10% ethanol in 0.2% saccharin. Single, daily i.p. doses (0.03mg/rat) of either ACTH4-10 or its analog resulted in a significant reduction of daily ethanol consumption with no effects on saccharin consumption. After 4 days of treatment, male rats consistently exhibited a rebound increase in ethanol consumption; this effect was not seen in females. The daily ethanol consummatory patterns of the female animals seemed to exhibit a 4-6 day cyclic rhythymicity, suggesting an interaction with estrous cycles. These results support a role for ACTH4-10 in the initiation of ethanol consummatory behavior in rats and suggests the existence of sex differences in this phenomenon.