Brain benzodiazepine binding in aged rats

Diazepam as an oral hypnotic increases nocturnal blood pressure in the elderly

BACKGROUND

No study has evaluated the cardiovascular effects of diazepam in elderly subjects that assume diazepam to induce sleep.

PURPOSE

The present study was carried out in order to evaluate the effects of chronic administration of diazepam as hypnotic drug on blood pressure (BP) and heart rate (HR) in healthy elderly subjects.

PATIENTS AND METHODS

Healthy, elderly subjects, aged 65-74 years, were treated with diazepam 5 mg or placebo-both administered once a day in the evening-for 4 weeks in two cross-over periods, each separated by a 2-week placebo period, according to a randomized, double-blind, cross-over design. At the end of each study period, clinical as well as 24-h ambulatory BP and HR were evaluated.

RESULTS

A total of 25 subjects were included in the analysis. At the end of a 4-week diazepam treatment, clinical as well 24-h BP and HR mean values were not significantly affected. Analysis of sub-periods showed that during night-time, systolic BP (SBP) values under diazepam were 7.6% higher than under placebo, with a mean difference of 7.9 mmHg (p < 0.01), diastolic BP (DBP) values were 5.8% higher, with a mean difference of 3.7 mmHg (p < 0.05 vs placebo) and HR values were 6.6% higher with a mean difference of 4.2 b/min (p < 0.05). The HR increase observed with diazepam persisted during the morning hours, whereas during the afternoon and evening hours SBP, DBP and HR values were similar in the two treatment groups.

CONCLUSIONS

In elderly subjects chronic assumption of diazepam as hypnotic agent produced an increase in BP, in particular SBP, during night-time and of HR during night-time and morning hours. These effects, which probably depend on a diazepam-mediated increase in sympathetic drive and decrease in vagal tone, might be of clinical relevance due to the role of increased BP and HR as independent predictors of cardiovascular morbidity and mortality.

In vivo molecular imaging of the GABA/benzodiazepine receptor complex in the aged rat brain

The GABA-ergic system, known to regulate neural tissue genesis during cortical development, has been postulated to play a role in cerebral aging processes. Using in vivo molecular imaging and voxel-wise quantification, we aimed to assess the effects of aging on the benzodiazepine (BDZ) recognition site of the GABA(A) receptor. To visualize BDZ site availability, [(11)C]-flumazenil microPET acquisitions were conducted in young and old rats. The data were analyzed and region of interest analyses were applied to validate the voxel-wise approach. We observed decreased [(11)C]-flumazenil binding in the aged rat brains in comparison with the young control group. More specifically, clusters of reduced radioligand uptake were detected in the bilateral hippocampus, cerebellum, midbrain, and bilateral frontal and parieto-occipital cortex. Our results support the pertinence of voxel-wise quantification in the analysis of microPET data. Moreover, these findings indicate that the aging process involves declines in neural BDZ recognition site availability, proposed to reflect alterations in GABA(A) receptor subunit polypeptide expression.

Acute and rebound effects of lorazepam on orolingual motor function in young versus aged Fischer 344/Brown Norway rats

The purpose of this study was to measure the acute effects of lorazepam [a short-acting benzodiazepine (BZ) with no active metabolites] on orolingual motor function in young (6 months) versus aged (24 months) Fischer 344/Brown Norway hybrid (F344/BN) rats. Rats licked water from an isometric force-sensing operandum so that the number of licks per session, licking rhythm (licks/second), and lick force could be measured during daily sessions. Acute doses (1.0 and 2.0 mg/kg) of lorazepam were administered 30 min before the testing sessions, 4 days apart. Whereas aged rats produced more licks per session, lorazepam increased this measure primarily in the young group. On the days after each lorazepam dose, rats licked less than they did before receiving the drug. This effect was shown by both groups. Aged rats showed significantly slower licking rhythm than young rats. Lorazepam slowed this measure in both groups. Peak tongue forces were significantly increased by lorazepam. These findings suggest that BZs such as lorazepam can affect tongue force output and exacerbate age-related tongue motility deficits. They also suggest that although BZs can directly influence motivation to engage in water-reinforced tasks, opposite 'rebound' effects may occur, even after acute dosing.

The effect of chronic lorazepam administration in aging mice

To assess benzodiazepine tolerance in aged animals, lorazepam or vehicle was administered chronically to male Crl: CD-1(ICR)BR mice. Pharmacodynamic and neurochemical endpoints were examined on days 1 and 14 of drug administration. There was no age-related significant difference in plasma lorazepam levels. Young and middle-aged animals demonstrated behavioral tolerance to lorazepam, while the aged animals showed a similar trend which failed to reach significance. In addition, aged animals also showed a trend toward tolerance to the anticonvulsant effects of lorazepam. There were no changes in alpha1 mRNA levels in cortex or hippocampus following administration of lorazepam when compared to vehicle-treated animals in any age group. Aged animals, however, had an initial increase in alpha1 mRNA expression in cortex and hippocampus on day 1 of vehicle treatment followed by decreased expression on day 14. These age-related changes were abolished by lorazepam administration. In summary, age-related sensitivity to the effects of lorazepam was not demonstrated in the present study. However, comparison of these data to other studies indicates that the effect of chronic benzodiazepine treatment may be specific to the benzodiazepine administered, the technique used to quantify mRNA expression changes, the subunits of the GABA(A) receptor investigated and the brain region analyzed. The phenomenon of benzodiazepine sensitivity in the elderly is an area of research which remains controversial and may well be compound specific. Determining benzodiazepines that do not produce pharmacodynamic sensitivity, such as lorazepam, may allow more careful prescribing and dosing of these drugs, and perhaps even the development of specific agents which could avoid this sensitivity.

Effects of D-galactose on the expression of hippocampal peripheral-type benzodiazepine receptor and spatial memory performances in rats

The changes in spatial memory performances and the binding of hippocampal peripheral-type benzodiazepine receptor (PBR) induced by D-galactose (D-gal) were investigated in rats. The animals were randomly divided into two groups: saline-treated group and D-gal-induced aging group. All rats received 56 days of injection followed by 5 days of behavioral tests. The D-gal-induced aging rats presented significant impairment in water maze performance, compared with that in the saline-treated rats. A significant decrease in [3H]PK11195 binding in the synaptosomes from hippocampus in the D-gal-induced aging rats was observed, compared to that in the saline-treated rats. Meanwhile, the Scatchard analysis revealed that there was a decrease in Bmax, with no significant change in KD. Further analysis demonstrated that water maze performance was closely related to the PK11195 binding in all rats. These results suggest that D-gal decreased the density of PBR in hippocampal synaptosomes, which may be attributable to the progressive pathogenesis of aging in rats.

Mid-aged and aged wild-type and progestin receptor knockout (PRKO) mice demonstrate rapid progesterone and 3alpha,5alpha-THP-facilitated lordosis

RATIONALE

Progesterone (P) and its 5alpha-reduced metabolite, 3alpha-hydroxy-5alpha-pregnan-20-one (3alpha,5alpha-THP), facilitate sexual behavior of rodents via agonist-like actions at intracellular progestin receptors (PRs) and membrane GABA(A)/benzodiazepine receptor complexes (GBRs), respectively.

OBJECTIVE

Given that ovarian secretion of progestins declines with aging, whether or not senescent mice are responsive to progestins was of interest.

METHODS

Homozygous PR knockout (PRKO) or wild-type mice that were between 10-12 (mid-aged) or 20-24 (aged) months of age were administered P or 3alpha,5alpha-THP, and the effect on lordosis were examined. Effects of a progestin-priming regimen that enhances PR-mediated (experiment 1) or more rapid, PR-independent effects of progestins (experiments 2 and 3) on sexual behavior were examined. Levels of P, 3alpha,5alpha-THP, and muscimol binding were examined in tissues from aged mice (experiment 4).

RESULTS

Wild-type, but not PRKO, mice were responsive when primed with 17beta-estradiol (E(2); 0.5 microg) and administered P (500 microg, subcutaneously). Mid-aged wild-type mice demonstrated greater increases in lordosis 6 h later compared to their pre-P, baseline test than did aged wild-type mice (experiment 1). Lordosis of younger and older wild-type, but not PRKO, mice was significantly increased within 5 min of intravenous (IV) administration of P (100 ng), compared with E(2)-priming alone (experiment 2). However, wild-type and PRKO mice demonstrated significant increases in lordosis 5 min after IV administration of 3alpha,5alpha-THP, an effect which was more pronounced in mid-aged than in aged animals (100 ng-experiment 3). In tissues from aged wild-type and PRKO mice, levels of P, 3alpha,5alpha-THP, and muscimol binding were increased by P administration (experiment 4). PR binding was lower in the cortex of PRKO than that of wild-type mice.

CONCLUSIONS

Mid-aged and aged PRKO and wild-type mice demonstrated rapid P or 3alpha,5alpha-THP-facilitated lordosis that may be, in part, independent of activity at PRs.

Acute zolpidem administration produces pharmacodynamic and receptor occupancy changes at similar doses

Zolpidem is chemically unrelated to classical benzodiazepines but has demonstrated relatively high affinity binding to the alpha(1) GABA(A) receptor. To assess pharmacodynamic and neurochemical effects of zolpidem, open-field behavior, pentylenetetrazole-induced seizure threshold and benzodiazepine receptor binding in vitro were evaluated in the same animal following a single dose of zolpidem. Zolpidem (2, 5 and 10 mg/kg), lorazepam (2 mg/kg) or vehicle was administered intraperitoneally in male CD-1 mice. Behavioral activity, assessed by three open-field parameters, was decreased following the two highest doses of zolpidem (5 and 10 mg/kg), and reached significance at the 10 mg/kg dose. Locomotor activity was also decreased significantly by lorazepam as expected. Pentylenetetrazole-induced seizure threshold was increased with the administration of 2 and 10 mg/kg zolpidem as well as with lorazepam. Apparent affinity (K(D)) of [3H]flunitrazepam, a non-selective ligand, for the benzodiazepine receptor in cortical membrane preparations was not significantly changed, while receptor number (Bmax) was decreased at all doses of zolpidem, reaching significance at the 10 mg/kg dose. These results confirm that the behavioral effects of zolpidem are similar to those of classical benzodiazepines. In addition, zolpidem had no significant effect on the affinity of the benzodiazepine receptor for [3H]flunitrazepam, but did decrease the density of receptor binding sites.

Topical clonazepam in stomatodynia: a randomised placebo-controlled study

Stomatodynia is characterised by a spontaneous burning pain in the oral mucosa without known cause or recognised treatment. The purpose of this double-blind, randomised, multicentre parallel group study was to evaluate the efficacy of the topical use of clonazepam. Forty-eight patients (4 men and 44 women, aged 65+/-2.1 years) were included, of whom 41 completed the study. The patients were instructed to suck a tablet of 1 mg of either clonazepam or placebo and hold their saliva near the pain sites in the mouth without swallowing for 3 min and then to spit. This protocol was repeated three times a day for 14 days. The intensity was evaluated by a 11-point numerical scale before the first administration and then after 14 days. Two weeks after the beginning of treatment, the decrease in pain scores was 2.4+/-0.6 and 0.6+/-0.4 in the clonazepam and placebo group, respectively (P = 0.014). Similar effects were obtained in an intent-to-treat analysis (P = 0.027). The blood concentration of clonazepam was similar whether it was measured 14 days after sucking a tablet three times a day or during the 5 h that followed sucking a single tablet (n = 5). It is hypothesised that clonazepam acts locally to disrupt the mechanism(s) underlying stomatodynia.

Pharmacodynamics in the elderly

An overview is given of the influence of age on the pharmacodynamics of drugs used during general and locoregional anaesthesia. For some groups of agents a distinct separation into age-related changes in the pharmacokinetics and pharmacodynamics is possible, whereas for others the literature indicates only that responses in the elderly are enhanced. I start with an overview of the influence of age on cardiovascular and neuroendocrine function and include a short account of the state-of-the-art in pharmacodynamic modelling. The physiological changes that occur with age are associated with an increased sensitivity to the effects of anaesthetic agents. For most intravenous hypnotic agents, and inhalational anaesthetic agents, the increased sensitivity with age is, at least in part, explained by altered pharmacodynamics. For opioids and local anaesthetics applied for blockade of the central nervous system, the pharmacodynamic involvement is not always clear. For neuromuscular blocking agents, pharmacodynamic involvement appears to be nearly absent in the reduced dose requirements seen with age--so that the latter appear to be caused by altered pharmacokinetics. Future studies, using pharmacokinetic-pharmacodynamic (PK-PD) mixed-effects modelling, should further explore this area to obtain clinically applicable data for improving our insight into the delivery of anaesthetics to the elderly and improving the quality of anaesthesia in this fast-growing population.

Are lorazepam-induced deficits in attention similar to those resulting from aging?

The purpose of this experiment was to compare, in three tasks of attention, the impairment caused by lorazepam (1 and 2.5 mg) administered to young volunteers with the impairment that results from aging. Performance on digit cancellation (DC), digit-symbol substitution (DSS), and Paced Auditory Serial Addition Task (PASAT) was significantly impaired by lorazepam (2.5 mg) and was significantly worse in the middle-aged group (mean +/- SEM, aged 58.9+/-0.8 years) compared with the younger, IQ-matched group (20.7+/-0.2 years). However, there were interesting differences in the extent of impairments among the three tests. In the DC test, lorazepam (2.5 mg) produced a significantly greater impairment than was seen in either the middle-aged men or middle-aged women. However, in the DSS test, the middle-aged women were significantly more impaired than either the middle-aged men or the young volunteers tested after lorazepam (2.5 mg). In the PASAT, both the lorazepam (2.5 mg) group and the middle-aged women were more impaired than the middle-aged men. These results raise the important possibility of gender differences in age-related decline of attentional processes.

Effects of chronic salicylate on GABAergic activity in rat inferior colliculus

It is well accepted that salicylate ototoxicity results in reversible tinnitus in humans. Salicylate-induced tinnitus may be an example of plasticity of the central auditory system and could potentially serve as a model to further understand mechanisms of tinnitus generation. This study examined levels of glutamic acid decarboxylase (GAD) and the binding characteristics of the GABA(A) receptor in auditory brainstem structures of Long-Evans rats chronically treated with salicylate. Western blotting revealed a significant 63% (P<0.008) elevation of GAD levels in the inferior colliculus (IC) of salicylate-treated subjects. This occurred in subjects demonstrating behavioral evidence of tinnitus. Muscimol saturation analysis was indicative of a salicylate-related increase in receptor affinity. Linear regression of [(3)H]muscimol saturation analysis data revealed a significant (P<0.05) reduction in K(d) values in whole IC (-48%), as well as in the central nucleus of IC (CIC, -58%) and combined external and dorsal cortex of IC (E/DCIC, -46%). The number of GABA(A) binding sites (B(max)) were also significantly (P<0.05) decreased. These changes were observed only in central auditory structures. This suggests that GAD expression and GABA(A) receptor binding characteristics may be altered with chronic exposure to sodium salicylate and these changes may represent aberrant plasticity clinically experienced as tinnitus.

Age-dependent changes in adenosine A1 receptor and uptake site binding in the mouse brain: an autoradiographic study

Ageing is a multifactorial, inevitable event of life span, which affects neurotransmission in the CNS. Since adenosine is a major neuromodulator of the synaptic activity, it was of interest to investigate the possible modification of the adenosinergic system in the brain during ageing. Using "in vitro" quantitative autoradiography and the radioactive ligands [(3)H]Cyclohexyladenosine and [(3)H]Nitrobenzylthioinosine, we have studied the distribution of A1 adenosine receptors and adenosine uptake sites in the aged mice (26 months) compared to the young ones (3 months). Our results showed a widespread reduction in A1 receptor binding in the aged animals, which was brain area-specific, occurring in areas where adenosine plays a significant neuromodulatory role such as the hippocampus, cortex, basal ganglia, and thalamus. Interestingly, the significant reduction in NBI-sensitive adenosine uptake sites was restricted to few areas of the aged brain, mainly in thalamic nuclei. Since the alterations in the density of A1 receptors and adenosine uptake sites showed no regional correlation and since no significant changes in either neuronal or glial cell number are observed, at least in hippocampus and cortex in this mouse strain during ageing, our findings could be explained by a selective age-dependent reduction of these adenosinergic components rather than by a general neuronal cell degeneration. As adenosine depresses electrical activity in hippocampus, a downregulation of adenosinergic function could probably be related to enhanced excitability seen in hippocampal neurons of the CA1 subregion and dentate gyrus of aged animals.

Aging in peripheral nerves: regulation of myelin protein genes by steroid hormones

The process of aging deeply influences morphological and functional parameters of the peripheral nerves. Interestingly, recent observations performed in our laboratory on the rat sciatic nerves have indicated that the deterioration of myelin occurring in the peripheral nerves during aging may be explained by the fall of the messenger levels of the major peripheral myelin proteins (glycoprotein Po, myelin basic protein and peripheral myelin protein 22). At least in the case of the Po, the low levels of its messengers and of the protein itself found in aged animals are increased by the treatment with a physiological progesterone derivative like dihydroprogesterone. It has also been found that in normal adult male rats the levels of the messengers for Po in the sciatic nerve are increased by progesterone, dihydroprogesterone and tetrahydroprogesterone; surprisingly, the gene expression of peripheral myelin protein 22 is stimulated only by tetrahydroprogesterone. These observations have been confirmed in parallel studies performed on Schwann cell cultures. Since tetrahydroprogesterone does not bind to the progesterone receptor but is a ligand for the GABAA receptor, the hypothesis has been put forward that part of the steroidal effects reported might occur not through the classical progesterone receptor, but rather via an interaction with the GABAA receptor. In other experiments it has been found that the gene expression of Po may be decreased by orchidectomy and restored by treatment with the androgen dihydrotestosterone. Altogether, these observations suggest the future use of physiological and/ or synthetic steroid hormones as a possible therapeutic approach for some pathological situations occurring in peripheral nerves during aging and demyelinating diseases.

Effect of surgical stress on benzodiazepine receptors as a consequence of placebo pellet implantation in rat: an autoradiographic study

This paper reports modifications in benzodiazepine (BZ) receptors induced by minimally invasive surgery, such as pellet implantation, a widely used surgical process for chronic drug administration. The intrinsic stress induced by this manipulation on BZ receptors was analysed in an autoradiographic saturation study determining the affinity (K(D)) and total number (Bmax) of binding sites of a number of brain areas from the mesencephalon, cerebral cortex, hippocampus, and cerebellum. The radioligand used for the study was [3H]flunitrazepam, which permitted overall characterization of BZ binding sites. Use of the specific BZ1 agonist zolpidem as an inhibitor of this radioligand permitted the direct characterization of subtype 2 (BZ2) and the indirect characterization of subtype 1 receptor (BZ1). Significant increases in Bmax and K(D) values were observed in pellet-implanted animals with respect to those not implanted. The results support the notion of an up-regulation of these receptors, mainly in BZ1 receptors, following sustained desensitization as a result of the surgical stress induced by pellet implantation.

Progesterone derivatives are able to influence peripheral myelin protein 22 and P0 gene expression: possible mechanisms of action

The present study has analyzed the effect of progesterone and its derivatives (dihydroprogesterone and tetrahydroprogesterone) on the gene expression of the peripheral myelin protein 22 utilizing in vivo and in vitro models. The data obtained indicate that tetrahydroprogesterone is able to stimulate the gene expression of peripheral myelin protein 22 both in vivo (in adult but not in old animals) and in Schwann cell cultures. An effect of this steroid, which is known to interact with the GABA(A) receptor, would not be surprising, since in the present study we show the presence in Schwann cells and in the sciatic nerve of the messengers for several subunits (alpha2, alpha3, beta1, beta2, and beta3) of the GABA(A) receptor. An effect of tetrahydroprogesterone is also evident on the gene expression of another myelin protein, the peripheral myelin protein zero. However, in this case also dihydroprogesterone, which is able to bind the progesterone receptor, is involved, both in old and adult animals, in the stimulation of messengers levels of this myelin protein. In conclusion, the present data show that the gene expression of two important peripheral myelin proteins can be influenced by progesterone derivatives. The hypothesis has been put forward that part of their effects might occur not through the classical progesterone receptor, but rather via an interaction with the GABA(A) receptor.