Accelerated benzodiazepine receptor recovery ... - The FASEB Journal

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allows estimation of receptor recovery in vivo. To assess benzodiazepine receptor recov- ery after benzodiazepine discontinuation, we treated mice with ...
Accelerated

benzodiazepine

receptor

recovery

after

lorazepam

discontinuation LAWRENCE Division New

G. MILLER,

of Clinical

England

Medical

to a behavioral

syndrome

LUMPKIN,

DAVID

discontinuation in animals

and

can lead

humans.

In

a

mouse model, this syndrome is associated with benzodiazepine receptor up-regulation. The protein-modifying reagent, (EEDQ),

N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline has been used to irreversibly inactivate

ber of neurotransmitter

receptors thus allows

including estimation

a num-

benzodiazeof receptor

pine receptors, and recovery in vivo. To assess benzodiazepine receptor recovery after benzodiazepine discontinuation, we treated mice with lorazepam (LRZ), 2 mg. kg-1 day-1 for 1 wk. After 24 h, EEDQ (12.5 mg/kg) was administered, and benzodiazepine binding in the cortex and cerebellum was determined after 4-144 h. EEDQ treatment decreased receptor density in the cortex in both LRZ- and vehicletreated groups by approximately 50%, with no change in apparent affinity as previously reported. Binding in both groups returned to control values after 96 h. Kinetic analysis indicated a more rapid increase in binding in LRZcompared with vehicle-treated animals, with t1,2 for LRZ 19.1 h, and for vehicle, 30.8 h (P < 0.05). Receptor density was decreased in the cerebellum after EEDQ by approximately 40% in both treatment groups, with no change in apparent affinity. Receptor density returned to control values at 96 h, with no difference in kinetics in LRZ- compared with vehicle-treated mice. The decrease in receptor ti,2 associated with lorazepam discontinuation is consistent with the observed increase in benzodiazepine receptors in this setting. Miller, L. G.; Lumpkin, M.; Greenblatt, D. J.; Shader, R. I. Accelerated benzodiazepine receptor recovery after lorazepam discontinuation. FASEB J. 5: 93-97; 1991. Key

Words:

lorazepam

. discontinuation

benzodiaze-

BENZODIAZEPINE ADMINISTRATION is associated with the development of behavioral tolerance (1). Most neurochemical evidence indicates that chronic treatment is also associated with alterations in binding or function at the GABAA receptor (2). In particular, studies have indicated decreased benzodiazepine binding or decreased GABAdependent chloride uptake during administration of several benzodiazepines (3-6). Benzodiazepine discontinuation in humans and animals can produce a characteristic behavioral syndrome (7). Previous studies from our laboratory indicate that this syndrome is associated with increased binding and function at the GABAA receptor (8, 9). These data suggest a pattern of receptor down-regulation during treatment, followed by up-regulation after discontinuation. Such a pattern might be expected to result in altered rates of benzodiazepine synthesis. CHRONIC

1/0005-0093/$01

GREENBLATT,

AND

.50. © FASEB

RICHARD

I. SHADER

School of Medicine

and

The protein-modifying reagent, N-ethoxycarbonyl-2-ethoxy1,2-dihydroquinoline (EEDQ),’ has been used to irreversibly inactivatea number of neurotransmitter receptors,including cholinergic,dopaminergic, adrenergic, and serotonergic receptors (10-13). We have previously demonstrated that EEDQ inactivates approximately 50% of benzodiazepine receptors in cortical and cerebellar membranes both in vitro and in vivo (14). Use of this agent in vivo allows determination of receptor recovery and approximation of benzodiazepine receptor half-life. To assess the effects of chronic benzodiazepine administration on benzodiazepine receptor synthetic rate, we administered lorazepam (LRZ), 2 mg kg . day, to mice for 1 wk, followed by EEDQ (12.5 mg/kg). We evaluated benzodiazepine receptor binding in cortex and cerebellum at intervals from 4 to 144 h after EEDQ administration.

METHODS Materials Male CD1 mice, 6-8 wk of age, were purchased from Charles River (Wilmington, Mass.), maintained on a 12-h light/dark cycle, and given food and water ad libitum. [3H]Flunitrazepam (FNTZ, sp act 70 Ci/mmol) was purchased from New England Nuclear (Boston, Mass.). EEDQ was obtained from Aldrich (Milwaukee, Wis.). Flurazepam was a giftfrom Hoffmann-La Roche (Nutley, N.J.). Osmotic pumps were obtained from Alza (Palo Alto, Calif.). All other reagents were obtained from standard commercial sources.

Drug EEDQ

pine#{149} GABA

0892-6638/9

J.

Pharmacology and Departments of Pharmacology and Psychiatry, Tufts University Center, Boston, Massachusetts 02111, USA

Benzodiazepine

ABSTRACT

MONICA

administration

Lorazepam (2 mg. kg’ . day) was dissolved in PEG 400 and administered for 1 wk by subcutaneously implanted osmotic pumps as previously described (4). After 7 days, pumps were removed. After an additional 24 h to allow elimination of lorazepam, EEDQ (12.5 mg/kg) was administered i.p. This interval is required to prevent antagonism of EEDQ effects by residual lorazepam (14). Previous studies indicate that concentrations of lorazepam at 24 h after discontinuation using this protocol are negligible or undetectable (8). The dose ofEEDQwas chosen on the basis of previous studies indicating benzodiazepine receptor inactivation without mortality (14). EEDQ was dissolved in 50% ethanol and diluted in water to an ethanol concentration of 2.5%. Vehicle contained a similar ethanol concentration. At 4, 24, 48, 96, or 144 h after injection, the animals were killed and brains were rapidly

‘Abbreviations: quinoline; FNTZ,

EEDQ N-ethoxycarbonyl-2-ethoxy-1,2-dihydro[3H]flunitrazepam; LRZ, lorazepam.

93

removed (P2) were described

and dissected prepared from (4).

Benzodiazepine

on ice. Synaptosomal cortex and cerebellum

membranes as previously

binding

1.25

Benzodiazepine binding was performed as described previously (4). [3H]FNTZ, 0.1-20 nM in 50 mM Tris-HC1 (pH 7.4), was added to duplicate or triplicate samples. To an identical set of samples was added flurazepam, i0 M, to determine nonspecific binding. After incubation at 4#{176}C for 45 mm, samples were filtered using a Brandel M48R (Gaithersburg, Md.) onto Whatman GF/B filters. Filters were washed twice with cold buffer and counted by scintillation spectrometry. Data

1.50

0 0. C’

E 0

1.00

E 0.

-0--

S

E 0.75

analysis I

the EBDA programs. Data were analyzed by the Mann-Whitney test for two groups, analysis of variance for more than two groups, and linear regression for determination of rate constants. Receptor

analyses

were

performed

0

using

24

t’Eil!CLE

#{149}#{149}.-LORAZEPAM

-

48

A

72

TIME

96

120

144

(hours)

RESULTS Four hours after administration of EEDQ(12.5 mg/kg), benzodiazepine receptor binding was significantly decreased in the cortex of lorazepam- and vehicle-treated mice (Fig. 1). This decrement was caused in both groups by a decrease of approximately 50% in receptor density (Bm,,,;Fig. IA), as there was no change in apparent affinity at the receptor (Fig. 1B). Receptor density returned gradually to control values with both treatments by 96 h. Again, no changes were observed in apparent affinity during this period. However, density appeared to increase more rapidly in mice treated with lorazepam compared with vehicle-treated mice (Fig. 1A). To assess the kinetics of receptor turnover from these experiments, the procedure of Battaglia et al. (13) was used. Repopulation kinetics can be described briefly as:

1.50

1.00

t’EH!CLE

-0--

----#{149}-LOAZEPAM -I

ItII

0.50

[Rt]

=

r/k

x (l-e”)

where [Rt] = receptor concentration production rate constant, and K dation. Log transformation yields: In [Rss]/([Rss}

-

=

ERt])

at time t, r rate constant

=

kt

Vol. 5

January

1991

B

= receptor

48

72

TIME

96

120

144

(hours)

for degra-

Eq. 2

where (Rss] = receptor concentration at steady state. It should be added that this procedure assumes that receptor appearance occurs at a constant rate, and that the rate of receptor degradation is proportional to receptor concentration. These assumptions have been verified for several systems (13), and our previous studies of benzodiazepine receptors indicate that the assumptions appear valid for this system (14). A semi-logarithmic plot of the time course of benzodiazepine receptor recovery in cortex is presented in Fig. 2. Although [Rss] values are similar in lorazepamand vehicletreated mice ([Rss] = Bmax at day 6 minus Bmax at 4 h; lorazepam = 0.56 ± 0.08 pmol/mg prot; vehicle = 0.48 ± 0.09 pmol/mg protein), lorazepam-treated mice had rate constants approximately 40% greater than those in vehicletreated mice. Using the general relationship 11,2 = ln 2/k, this yields receptor half-lives (11/2) of 19.1 and 30.8 h for lorazepam and vehicle treatment, respectively (P < 0.05).

94

24

Eq. 1

Figure 1. Benzodiazepine receptor recovery in cortex after treatment with EEDQ Mice were treated with lorazepam, 2 mg kg’ . day’, for I wk. At 24 h after discontinuation, animals were treated with EEDQ (12.5 mg/kg) and binding was determined at 4-144 h. Results are mean ± SEM, n = 3-5 at each point. A) Receptor density (Bm,,j. Box represents mean ± SEM for control Bm,, values. B) Apparent affinity (Kd).

In cerebellum, receptor density was reduced by approximately 40% at 4 h after EEDQ administration in both lorazepamand vehicle-treated groups (Fig. 3A). No change was observed in apparent affinity in cerebellum (Fig. 3B). Density returned to control values by 96 h in both treatment groups, with similar time courses. Apparent affinity was unchanged during this period. Analysis of rate constants (analysis described above, Fig. 4) yielded similar values for lorazepamand vehicle-treated mice: receptor half-life for lorazepam-treated mice was 35.0 h, and for vehicle-treated mice it was 42.3 h.

The FASEB Journal

MILLER ET AL.

CORTEX 5

VEHICLE

0

#{149} = LORAZEPAM

-

4

3

--

S

2

-

The current results with lorazepam suggest that alterations in benzodiazepine receptor half-life might contribute to the increase in benzodiazepine receptor binding afterbrazepam discontinuation. Receptor half-life was decreased by ap#{149}proximately 40% during the period beginning 24 h after lorazepam discontinuation. This time point was chosen for the administration of EEDQ as residual lorazepam before this point might interfere with EEDQ effects (14). Although EEDQ administration might affectthe time course for recepo (or alterations, the relatively rapid increase in binding at 24-48 h after EEDQ (48-72 h after drug discontinuation) corresponds in general to the period of benzodiazepine receptor overshoot noted previously (48-96 h). These results suggest that the decrease in half-life and the previously observed increase in binding may be related.

0

1.0

0.8

0 0

24

48

72

96

0 0.

0.6 Ci

TIME (hours) 2. Kinetics of benzodiazepine receptor recovery in cortex. Results are based on data shown in Fig. IA with analysis described in the text. The slopes of the regression lines are significantly different (P < 0.05). Half-life (t,,2) is calculated from Eq. 2 in the text as t,,2 = ln 2/k, where k is the slope of the regression line. Figure

E 0

E 0.

0.4

‘C

S

#{163}

-0-

VEH4E

---.--

WRAZEPAM

0.2

DISCUSSION 0

Our results are consistent with previous data indicating that EEDQ appears to inactivate approximately 50% of benzodiazepine receptors in the cortex, and a slightly smaller percentage in the cerebellum (14). The percentage of receptors inactivated was unchanged by administration of lorazepam or vehicle. In addition, duration of receptor recovery was also similar to that reported previously, approximately 96 h. Kinetic analysis indicates similar receptor 1/2 in cortex for vehicle-treated mice in the present study and untreated mice in our previous studies (30.8 and 25.3 h, respectively) (14). Half-life is also similar to calculated mean half-lifein cultured neurons (15). Thus, our results confirm the usefulness of EEDQ in estimating benzodiazepine receptor half-life in vivo. Several recent studies indicate that chronic benzodiazepine administration is associated with decreases in benzodiazepine receptor density in several brain regions (3, 4). However, other studies indicate little or no change in binding (16). Variations in results may be due to differences in drug, mode of administration, and receptor binding assays (2). Fewer reports have addressed effects of benzodiazepine discontinuation. In our previous studies, benzodiazepine receptor binding increased rapidly after termination of lorazepam administration and had returned to control values by 24 h after drug discontinuation (8). However, receptor binding increased further and was greater than control levels by 4 days after drug discontinuation, returning to control values after 7 days. Similar receptor alterations, with slight differences in time course, were observed for alprazolam (9) and clonazepam (W. R. Galpern, M. Lumpkin, D. J. Greenblatt, R. I. Shader, L. G. Miller, unpublished results).

ACCELERATED

BENZODIAZEPI

NE RECEPTOR RECOVERY

24

72

48

A

TIME

96

120

144

120

144

(hours)

3.00

2.00 C

1.00

-0-

VENE

----#{149}-LOFAZEPAM

0

B

24

48

72

TIME

96

(hours)

Figure 3. Benzodiazepine receptor recovery in cerebellum after treatment with EEDQ. Mice were treated with lorazepam, 2 mg kg’ . day’, for I wk. At 24 h after discontinuation, animals were treated with EEDQ (12.5 mg/kg) and binding was determined at 4-144 h. Results are mean ± SEM, n = 3-5 at each point. A) Receptor density (Bm,,). Box represents mean ± SEM for control Bm1,, values. B) Apparent affinity (Ku).

95

recent study indicates that chronic borazepam administration might have different regional effects based on subtype distribution (19). Studies of GABAA receptor subunit mRNA may elucidate this issue. In conclusion, our results indicate the usefulness of the protein-modifying reagent EEDQ in assessing receptor kinetics in vivo. These data indicate that benzodiazepine receptor half-life is decreased after lorazepam discontinuation, consistentwith the increase in receptor binding that occurs in this situation.

CEREBELLUM 4

o

= VEHICLE = LORAZEPAM

--

3

The

authors

Shim

2

for

thank

Wendy

assistance.

and AG-01006

MH-34223,

L. G. M. is the recipient cal Pharmacology ation

Galpern,

Supported

Shelley

in

part

Development

the Pharmaceutical

and

grants

from the U.S. Public

of a Faculty

from

Chesley,

by

Young

DA-05258,

Health

Service.

Award

in Clini-

Manufacturers

Associ-

Foundation.

REFERENCES

0

0

48

24

TIME

96

72

(hours)

Figure 4. Kinetics of benzodiazepine receptor recovery in lum. Results are based on data shown in Fig. IA, with described in the text. The slopes of the regression lines significantly different. Half-life (t112) is calculated from Eq. text as 11,2 = In 2/k, where k is the slope of the regression

These receptor ate tor

results do not necessarily synthesis. Analysis using

alterations degradation,

in synthesis increased

cerebel-

analysis are not 2 in the line.

indicate an alteration in EEDQ cannot differenti-

from potential turnover of

changes receptors,

in recepor even

cellular pool (13, 17). Finally, it is possible that chronic drug treatment alters receptors response to EEDQ itself. Thus, although it is tempting to speculate that our results represent increases in receptor synthesis, the data cannot directly confirm this hypothesis. In addition, EEDQ affects other neurotransmitter receptors as noted above; in several systems studies, EEDQ reduces receptor density by 70% or more (10-13). It is possible that effects at these sites might contribute indirectly to the observed alterations at the benzodiazepine site. The differential effects observed in this study of cortex compared with cerebellum are consistent with previous studies involving EEDQ. This compound affects slightly fewer benzodiazepine receptors in cerebellum than in cortex (14), perhaps because of differential abundance of receptor subtypes in the two regions (18). However, rate of receptor recovery appears to be similar in the two regions, as previously reported (14). With regard to effects of lorazepam discontinuation, in a previous study we found a small but significant increase in benzodiazepine binding in cerebellum (8). This increment was substantially less than that which occurred in the cortex. The lack of change in receptor 1112 in cerebellum despite the increase in binding may result from insufficient sensitivity of the EEDQ/receptor binding methodology, especially in light of the lower level of binding in the cerebellum compared with that in the cortex. Alternatively, receptor recovery might be less affected in cerebellum than in cortex, perhaps because of receptor subtype differences. A mobilization

96

Vol. 5

of receptors

January

1991

from

another

1. Greenblatt, D. J., and Shader, R. I. (1978) Dependence, tolerance and addiction to benzodiazepines: clinical and pharmacokinetic considerations. Drug Metab. Rev. 8, 13-28 2. Miller, L. G., Greenblatt, D. J., Lopez, F., Schatzki, A., Heller, j,, Lumpkin, M., and Shader, R. I. (1990) Chronic benzodiazepine administration: effects in vivo and in vitro. In GABAA Receptor Subtypes (Biggio, G., and Costa, E., eds) Raven, New York pp. 167-176 3. Tietz, E. I., Rosenberg, H. C., and Chiu, T. H. (1986) Autoradiographic localization of benzodiazepine receptor lation. j Pharmacol. Exp. T/zer 236, 284-291

downregu-

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Chronic benzodiazepine administration. of tolerance and receptor downregulawith alprazolam administration. Biochem. Phar-

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dence. 8. Miller,

D. W. (1989) Chronic

diazepam

produces regionally specific changes in GABAchloride influx. Eur. J. Phar,nacol. 159, 217-223 H., and Lader, M. H. (1981) Benzodiazepine depenBr. j Addict. 76, 133-145

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W.

R.,

and

administration: with upregulation and function.

D. J., Chesley, administration

9. Lopez, F., Miller, L. G., Greenblatt, A., and Shader, R. I. (1990) Chronic

Shader,

II. j

Disof y-

Phar-

S., Schatzki,

of benzodi-

azepine: V. Rapid onset of behavioral and neurochemical alterations after discontinuation of alprazolam. Neuropharmacology

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T.

J.,

and

Sanberg,

P. R. (1989)

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cortical

es-adrenoceptors

using N-ethoxycarbonyl-2-ethoxy-1,2Brain Res. 493, 8-13 13. Battaglia, G., Norman, A. B., and Creese, I. (1987) Differential serotonin2 receptor recovery in mature and senescent rat brain after irreversible receptor modification: effect of chronic reserdihydroquinoline

pine

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(EEDQ).

j

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Exp.

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Lumpkin, M., Galpern, W. R., Greenblatt, D. J., R. I. (1990) Modification of GABAA receptor function by N-ethoxycarbonyl-2-ethoxy-1,2-dihyin vitro and in vivo: effects of aging. J. Neurochem.

L. A., Czajkowski, C., Chan, C. Y., and Farb, D. H. (1984) Benzodiazepine receptor synthesis and degradation by neurons in culture. Science 226, 857-860 16. Gallager, D. D., Lakoski, J. M., Gonsales, S. F, and Fauch, S. L. (1984) Chronic benzodiazepine treatmentdecreasespostsynaptic GABA sensitivity. Nature (London) 308, 74-77 17. Hess, E. J., Norman, A. B., and Creese, I. (1988) Chronic treat15. Borden,

ACCELERATED

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NE RECEPTOR RECOVERY

ment with dopamine receptor antagonist: behavioral and pharmacological effects on D1 and D2 dopamine receptors. j Neurosci. 8, 2361-2370 18. Sieghart, W. (1989) Multiplicityof GABAA-benzodiazepine receptors. TIPS 10, 407-411 19. Galpern, W. R., Miller, L. G., Greenblatt, D. J., and Shader, R. I. (1990) Differential effectsof chronic borazepam and alprazolam on benzodiazepine binding and GABAA receptor function. Br. j P/zarrnacoL In press Received for publication July Accepted for publication September

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97