Cleatus J Wallis

Effects of NMDA Antagonists on Ethanol-Withdrawal Induced “Anxiety” in the Elevated Plus Maze

The anxiolytic effects of NMDA antagonists during ethanol withdrawal were assessed in Long-Evans rats. Anxiety was measured by the elevated plus maze. Male rats were exposed to ethanol (6.5%) in a liquid diet for 10 days. Behavioral testing took place 12 h after withdrawal of ethanol. The competitive NMDA antagonists, AP-7 (0.02-0.32 mg/kg) and CGP-37849 (0.64-10 mg/kg), at least partially reversed the anxiety-like effects induced by withdrawal from ethanol. Both drugs produced a small increase in total arm entries, and a much larger increase in the percentage of open arm entries. AP-7, but not CGP-37849, also increased the percentage of open arm time. In contrast, the NMDA channel blocker, dizocilpine (MK-801; 0.08-0.32 mg/kg), produced only a small increase in the percentage of open arm entries and of open arm time. HA-966, a glycine-site antagonist, also failed to produce changes in ethanol withdrawal induced changes in anxiety at the doses tested. These results suggest that competitive NMDA antagonists may be useful for reduction of signs of anxiety during ethanol withdrawal.

Abecarnil and alprazolam reverse anxiety-like behaviors induced by ethanol withdrawal

This study investigated the effects of a benzodiazepine partial agonist, abecarnil, and a full agonist, alprazolam, on ethanol withdrawal-induced anxiety-like behaviors in rats. Anxiety was assessed in two models: elevated plus maze and pentylenetetrazol (GABA(A) antagonist) discrimination assay. Male rats received an ethanol-containing (4.5%) liquid diet for 7 to 10 days and were tested for withdrawal symptoms 12 h after termination of the diet. In the elevated plus maze, ethanol-withdrawn rats displayed less open arm activity and total arm entries than pair-fed rats. Abecarnil (0.08-0.32 mg/kg, IP) and alprazolam (0.08-1.25 mg/kg, IP) each produced a dose-dependent, full reversal of ethanol withdrawal-induced reduction of open arm activity, but only alprazolam increased the total arm entries. In the pentylenetetrazol assay, ethanol-withdrawn rats selected the pentylenetetrazol lever (100%) over the salin-lever. Abecarnil (0.04-0.32 mg/kg, IP) and alprazolam (0.08-0.32 mg/kg, IP) dose dependently reduced pentylenetetrazol-lever responding to control levels (10-20%). Alprazolam was more potent than abecarnil in reversing ethanol withdrawal-induced decrease in open arm activities, but showed comparable potency and efficacy to abecarnil in blocking the pentylenetetrazol-like ethanol withdrawal stimulus. These results suggest that abecarnil and alprazolam may have therapeutic potential for treatment of ethanol withdrawal-induced anxiety-like symptoms.

Effects of ritanserin on ethanol withdrawal–induced anxiety in rats

This study investigated the ability of ritanserin, a 5-HT2 antagonist, to modify ethanol withdrawal (EW) symptoms in two animal models of anxiety: the elevated plus-maze (EPM) and the pentylenetetrazol (PTZ) discrimination assay. Long-Evans hooded rats were given a nutritionally balanced liquid diet containing 4.5% ethanol for 10 days. Twelve hours after removal of the ethanol diet, rats were tested in the EPM. A significant reduction in the open-arm activity and the number of total arm entries was observed, which is indicative of EW. Acute ritanserin (0.16-0.64 mg/kg, i.p., 60 min) had no effect on EW-induced anxiety-like behavior on the EPM. Ritanserin (0.08-0.64 mg/kg, i.p., b.i.d. 12 h) administered concurrently with the last 5 days of ethanol diet produced an increase in the time spent on the open arms of the EPM and reversed the EW-induced reduction in total arm entries. Rats trained to discriminate between saline and PTZ (an anxiogenic drug), selected the PTZ lever during EW. Chronic ritanserin (0.32 mg/kg, i.p., b.i.d. ) did not block PTZ lever responding during EW. On the rotorod, ritanserin (0.32 mg/kg, i.p.) increased the motor incoordination induced by ethanol. In conclusion, coadministration of ritanserin with ethanol prevented the development of EW-induced anxiety as measured by the EPM, but not in the PTZ drug discrimination.

The Effects of Adenosine Ligands R-PIA and CPT on Ethanol Withdrawal

The potential anxiogenic or anxiolytic effects of R(-)-N6-(2-phenylisopropyl)adenosine (R-PIA), an adenosine agonist, and 8-cyclopentyl-1,3,dimethylxanthine (CPT), an adenosine antagonist, were tested during chronic exposure to ethanol and to ethanol-induced withdrawal in rats. Effects on anxiety were measured by the elevated plus maze and dark-light box. Ethanol consumption and preference was tested in an additional experiment. In testing of elevated plus maze performance during withdrawal from ethanol, R-PIA produced no change in the anxiety-related behaviors of total arm entries and percent open arm entries, but produced a significant decrease in percent open arm time. CPT produced at least partial recovery from the anxiogenic effects of ethanol withdrawal on all three measures of elevated plus maze performance, although peak effects were seen at the intermediate dose of CPT (0.08 mg/kg) for total arm entries and percent open arm time. CPT also showed anxiolytic effects at low to intermediate doses (0.04, 0.08 mg/kg) in the dark-light box. CPT did not reduce the preference for ethanol over water or the total consumption of ethanol over a range of ethanol doses. In summary, the adenosine agonist, R-PIA, exacerbated the effects of ethanol withdrawal, whereas the adenosine antagonist, CPT, at least partially blocked the anxiogenic effects produced by ethanol withdrawal. These results suggest that adenosine antagonists, at least at some doses, may be useful for ameliorating the anxiogenic effects produced by ethanol withdrawal, although it does not appear useful for reducing consumption.

Sex differences in nicotine substitution to a pentylenetetrazol discriminative stimulus during ethanol withdrawal in rats.

Abstract Rationale: Nicotine and ethanol are frequently co-abused in men and women, but few studies compare common stimulus effects produced by these substances between males and females. Objectives: This study compared the anxiety-like behavior induced by nicotine prior to and during ethanol withdrawal in intact male, sham-operated female, and ovariectomized (OVX) rats. Methods: Using an animal model of anxiety, the pentylenetetrazol (PTZ) drug-discrimination assay, rats were trained to discriminate PTZ (16 mg/kg, i.p.) from saline and were subjected to the following tests: (1) PTZ-lever selection at 12 h after termination of ethanol diet (4.5% for 10 days); (2) dose–response tests for nicotine (0.08– 1.3 mg/kg) prior to ethanol and 1.5, 6, and 7 days after ethanol withdrawal. Results: (1) During acute ethanol withdrawal (12 h), more male rats (43.4%) responded on the PTZ lever than OVX (29%) or sham female (15.3%) rats. (2) For nicotine dose–response tests, more male rats (70%) selected the PTZ lever than OVX (37.5%) or sham female (50%) rats prior to ethanol. At 1.5 days, nicotine fully generalized to the PTZ stimulus in male (100%) and OVX (90%), but only partially in sham female (50%) rats. At 6 days and 7 days after ethanol withdrawal, the PTZ-lever selection decreased, but more male rats (78%) tended to respond on a PTZ lever than OVX (63.6%) or sham female rats (62.5%). Conclusions: Acute nicotine produces anxiety-like behavior similar to that of PTZ in male and female rats, and this effect of nicotine is intensified during ethanol withdrawal in male and OVX rats, but not in sham female rats.

Sex differences in the discriminative stimulus effects of m-chlorophenylpiperazine and ethanol withdrawal.

Abstract Rationale: The serotonergic system plays a role in regulation of anxiety and ethanol withdrawal (EW). Nevertheless, few studies have assessed sex differences in serotonergic effects on EW. Objectives: This study examined sex differences in the anxiogenic stimu-li induced by a serotonin (5-HT)1b/2 agonist, meta- chlorophenylpiperazine (mCPP), prior to ethanol and during EW. Methods: Gonadectomized or sham-operated adult male and female rats and 17β-estradiol (2.5 mg, 21-day release, s.c.) -replaced ovariectomized (OVX) rats were trained to discriminate mCPP (1.2 mg/kg, i.p.) from saline in a two-lever choice task for food. Latency to the first lever press and mCPP lever selection were measured following mCPP (0–1.2 mg/kg). Rats then received chronic ethanol-containing liquid diet (6.5%) for 10 days and were tested for mCPP lever selection 12 h and 36 h after removal of ethanol. Results: Fewer sham female and β-estradiol-replaced OVX rats selected the mCPP lever than male or OVX rats, and showed an increased initiation latency after mCPP injection. During EW (12 h and 36 h), fewer sham female and β-estradiol-replaced OVX rats responded on the mCPP-lever after saline injection as well as after mCPP challenge than male or OVX rats. Castration did not alter any response of male rats to mCPP. Conclusions: (1) mCPP discrimination is a useful measure of EW in male and female rats; and (2) sham female and β-estradiol-replaced OVX rats are less sensitive to the discriminative stimulus prior to and during EW, but more sensitive to impaired behavioral initiation induced by mCPP than male or OVX rats.

Lack of tolerance to ethanol-induced motor impairment on accelerod performance in rats.

The effect of ethanol on rats was investigated at increasing rates of acceleration for bar rotation speed. Ethanol was given to rats by a liquid diet starting with 2.4% ethanol (v/v) for 3 days. Then the ethanol concentration was increased to 4.8% (v/v) for 3 days and finally to 7.2% (v/v) for 15 days. Accelerod performance was recorded before and throughout 20 days of ethanol intake. Mean blood ethanol levels were 266.34+/-13.11 and 285.20+/-9.77 mg/dl on the 7th and 15th days of ethanol (7.2% v/v) consumption, respectively, as measured in a parallel group of animals. Ethanol produced significant concentration-dependent impairments in the accelerod performance of rats. The motor impairment effect of ethanol was most prominent in the test using the greatest rate of acceleration (from 0 to 79 rpm within 2 min). The impairment effect of ethanol on accelerod performance occurred throughout the period of ethanol exposure. Our results indicate that motor impairment on the accelerod performance test produced by an ethanol liquid diet depends on the concentration of ethanol and the rate of acceleration. In addition, under free-access conditions accelerod performance may not be a suitable behavioral test for detecting tolerance development to ethanol in rats.

Nitric oxide synthase inhibition attenuates saccharin or ethanol reinforced responding in long-evans rats

Abstract 1. 1. Effect of 7-nitro indazole (7-NI), brain specific inhibitor of nitric oxide synthase (NOS), on saccharin or ethanol reinforcement was investigated in male Long-Evans rats. 2. 2. Twenty-four rats were trained to lever press both for a 1-% (w/v) saccharin solution and 10% (v/v) ethanol solution using a lever-pressing schedule of progressive ratio. 3. 3. Well-trained rats were tested with 7-NI (10, 20 and 40 mg/kg) or a vehicle (methylcellulose, 2%) injected ip. 60 min before each test. In some tests, L-arginine (1000 mg/kg, ip), a NO precursor, was injected 30 min before a 7-NI (40 mg/kg) injection. 4. 4. Treatment with 7-NI reduced the lever pressing for either saccharin or ethanol reinforcement in a dose dependent manner. The inhibitory effects of 7-NI on the lever pressing for saccharin or ethanol were blocked by L-arginine pre-administration. 5. 5. Our results suggest that reduction in ethanol reinforcement by NOS inhibition may be related to central mechanisms modulating feeding behavior in rats.

Effects of calcium channel blockers on pentylenetetrazol drug discrimination in rats

The effects of the dihydropyridine L-type calcium channel blockers nitrendipine and nimodipine on the pentylenetetrazol (PTZ) drug discrimination, an operant model of anxiety, were investigated. Male Long-Evans rats were trained to discriminate PTZ (16 mg/kg, i.p.) from saline. Both nitrendipine (5.0-25 mg/kg, i.p.) and nimodipine (5.0-25 mg/kg, i.p.) partially substituted for the PTZ discriminative stimulus. However, pretreatment with nitrendipine (25 mg/kg, i.p.) or nimodipine (25 mg/kg, i.p.) produced no change in the PTZ dose-effect function. Rats were given a nutritionally balanced liquid diet containing 6.5% ethanol for 10 days. Rats selected the PTZ drug lever during withdrawal. Subchronic coadministration of nitrendipine (1.25-5.0 mg/kg, i.p., b.i.d.) with ethanol failed to dose-dependently reduce PTZ-lever responding, but it did reverse withdrawal signs. Acute administration of nitrendipine (5, 10, and 20 mg/kg, i.p.) produced marked suppression of lever responding, but it failed to significantly reduce levels of PTZ-lever responding. Although calcium channel blockers reduce signs of ethanol withdrawal, they also markedly reduce rates of behavior and produce no clear effects on anxiety-like behaviors induced by ethanol withdrawal.

Effects of GABAA compounds on mCPP drug discrimination in rats

Male Long-Evans rats were trained to discriminate mCPP (1.4 mg/kg, i.p.) from saline, using a two-lever, food-reinforced operant task. The GABA(A) antagonist, bicuculline (0.16-0.64 mg/kg), partially substituted for mCPP, whereas the benzodiazepine antagonist, flumazenil (1-10 mg/kg), and the benzodiazepine inverse agonist, Ro 15-4513 (0.25-2.5 mg/kg), failed to substitute for mCPP. Bicuculline produced no change in response rate, whereas Ro 15-4513 dose-dependently decreased responding. Flumazenil produced a small increase in response rates. Flumazenil (10 mg/kg), Ro 15-4513 (1.25 mg/kg), and the benzodiazepine agonists alprazolam (0.64 mg/kg) and diazepam (5 mg/kg) full agonist all failed to block the mCPP discriminative stimulus. When given in combination with mCPP, Ro15-4513 and alprazolam both produced lower response rates than did mCPP alone, whereas flumazenil and diazepam did not significantly alter response rates. These findings provide evidence that GABA(A) antagonists modulate the discriminative stimulus effects of mCPP, but that these effects are not mediated by activity at the benzodiazepine site.