Central Nervous System Active Drugs Research Articles

Commentary on: Borrows DL, Hagardorn AN, Harlan GC, Wallen EDB, Ferslew KE. A fatal drug interaction between oxycodone and clonazepam. J Forensic Sci 2003;48(3):683-86.

Abstract Sir: This letter is in response to information published within a case report written by David L. Burrows et al. in the May 2003 issue of J Forensic Sci (1). We credit the authors for bringing to light the potentially fatal consequence of the concomitant abuse of two central nervous system (CNS) depressant drugs, such as oxycodone and clonazepam, as there may be an under-appreciation of such a risk. The risk of fatal overdose is indeed substantially increased when opioids are abused in combination with other CNS active drugs (2). However, in the article, titled “A fatal drug interaction between oxycodone and clonazepam,” the authors provide a table with OxyContin® (oxycodone HCl controlled-release) pharmacokinetic and dosage information (Table 1) that is inaccurate and potentially misleading.

Immunolocalization of TASK-3 (KCNK9) to a subset of cortical neurons in the rat CNS

Tandem pore domain (2P) K channels constitute the most diverse family of K channels and are responsible for background (leak or baseline) K currents. Of the 15 human 2P K channels, TASK-1, TASK-2, and TASK-3 are uniquely sensitive to physiologic pH changes as well as being inhibited by local anesthetics and activated by volatile anesthetics. In this study polyclonal antibodies selective for TASK-3 have been used to localize its expression in the rat central nervous system (CNS). TASK-3 immunostaining was found in rat cortex, hypothalamus, and hippocampus. Double immunofluorescent studies identified a discrete population of TASK-3 expressing neurons scattered throughout cortex. Using immunogold electron microscopy TASK-3 was identified at the cell surface associated with synapses and within the intracellular synthetic compartments. These results provide a more finely detailed picture of TASK-3 expression and indicate a role for TASK-3 in modulating cerebral synaptic transmission and responses to CNS active drugs.

Development of an in vitro blood–brain barrier model based on immortalized porcine brain microvascular endothelial cells

Immortalized porcine brain microvessel endothelial cells (PBMEC/C1-2) were used to develop a model for measurement of blood–brain barrier permeation of central nervous system active drugs. Previous studies showed that a system using C6 astrocyte glioma conditioned medium leads to cell layers with transendothelial electrical resistance values up to 300 Ω cm 2 and a permeability coefficient P e of 3.24 ± 0.14 × 10 –4 cm/min for U-[ 14C]sucrose, which is in good agreement to published values and thus indicates the formation of tight junctions in vitro. However, commercially available inserts for the Transwell ® system were not permeable for highly lipophilic compounds, such as diazepam. Systematic studies with different insert showed, that inserts with a pore width of 1 μm proved to be optimal for permeation studies of lipophilic compounds. Permeability studies with a set of three benzodiazepines further supported this finding.

Cytochrome P450 2D catalyze steroid 21-hydroxylation in the brain.

mRNA of cytochrome P450 21-hydroxylase (P450c21) is expressed in the brain, but little is known about the enzymatic properties of P450c21 in the brain. In the present study, we showed, by using various recombinant cytochrome P450 (CYP)2D enzymes and anti-CYP2D4- or P450c21-specific antibodies, that rat brain microsomal steroid 21-hydroxylation is catalyzed not by P450c21, but by CYP2D isoforms. Rat CYP2D4 and human CYP2D6, which are the predominant CYP2D isoforms in the brain, possess 21-hydroxylation activity for both progesterone and 17alpha-hydroxyprogesterone. In rat brain microsomes, these activities were not inhibited by anti-P450c21 antibodies, but they were effectively inhibited by the CYP2D-specific chemical inhibitor quinidine and by anti-CYP2D4 antibodies. mRNA and protein of CYP2D4 were expressed throughout the brain, especially in cerebellum, striatum, pons, and medulla oblongata, whereas the mRNA and protein levels of P450c21 were extremely low or undetectable. These results support the idea that CYP2D4, not P450c21, works as steroid 21-hydroxylase in the brain. Allopregnanolone, a representative gamma-aminobutyric acid receptor modulator, was also hydroxylated at the C-21 position by recombinant CYP2D4 and CYP2D6. Rat brain microsomal allopregnanolone 21-hydroxylation was inhibited by fluoxetine with an IC(50) value of 2 microm, suggesting the possibility that the brain CYP2D isoforms regulate levels of neurosteroids such as allopregnanolone, and that this regulation is modified by central nervous system-active drugs such as fluoxetine.

Zonula Occludens Toxin Increases the Permeability of Molecular Weight Markers and Chemotherapeutic Agents Across the Bovine Brain Microvessel Endothelial Cells

The purpose of this study was to examine the ability of Zonula occludens toxin (Zot) to reversibly open tight junctions in bovine brain microvessel endothelial cells (BBMECs) to enhance drug delivery via the paracellular pathway. Transport across BBMEC monolayers was examined for molecular weight markers and chemotherapeutic agents ([(14)C]sucrose, [(14)C]inulin, [(3)H]propranolol, [(3)H]doxorubicin, and [(14)C]paclitaxel) with Zot (0.0-4.0 microg/mL). TEER of monolayers was measured to assess effect and reversibility of Zot. Cell viability of BBMEC in the presence of Zot was assessed by trypan blue exclusion staining. Apparent permeability (P(app)), enhancement ratio (R), and percent increase in transport determined were statistically compared by ANOVA. A significant increase (p < 0.05) in P(app) was observed for the transport of [(14)C]sucrose, [(14)C]inulin, [(3)H]doxorubicin, and [(14)C]paclitaxel at a 4.0 microg/mL concentration of Zot. A significant concentration-dependent decrease in TEER was observed on treatment with Zot with rapid reversal to baseline after removal. Zot (4 micro/ml) was found to be nontoxic to the BBMECs after 2 hours incubation. In conclusion, Zot increased paracellular transport across the BBMEC in a reversible, concentration-dependent manner. Modulation of paracellular transport with Zot may be used to increase the brain permeability of potent central nervous system-active drugs, including anticancer agents.

Pharmacokinetic-pharmacodynamic relationships of (2S,3S)-valnoctamide and its stereoisomer (2R,3S)-valnoctamide in rodent models of epilepsy.

Racemic valnoctamide (VCD) is a central nervous system-active drug commercially available in Europe. VCD possesses two chiral centers and, therefore, it exists as a mixture of four stereoisomers. The purpose of this study was to evaluate the anticonvulsant activity of two VCD stereoisomers in comparison with VCD (racemate), valpromide (VPD), and valproic acid (VPA) and to study their pharmacokinetic-pharmacodynamic relationships. The ability of racemic VCD, (2S,3S)-VCD, (2R,3S)-VCD and VPD to block partial seizures was studied in the 6Hz psychomotor seizure model in mice and in the hippocampal kindled rat. The ability of (2S,3S)-VCD and (2R,3S)-VCD to prevent generalized seizures was evaluated in the maximum electroshock (MES) and subcutaneous metrazole (sc Met) seizure tests. The PK of (2S,3S)-VCD, (2R,3S)-VCD, and VPD was studied in the mice utilized in the 6Hz model. All of the tested compounds were effective in the models tested. No significant difference in ED50 values was observed but the plasma and brain EC50 values of (2R,3S)-VCD in the 6Hz model at 32 mA stimulation were 2-fold higher than the EC50 values of (2S,3S)-VCD. An excellent pharmacokinetic-pharmacodynamic correlation was found between the plasma and brain concentrations of the VCD stereoisomers and their anticonvulsant effect in mice. Stereoselectivity was observed in clearance, volume of distribution, and in brain-to-plasma AUC ratio at a dose of 25 mg/kg, but the difference disappeared at higher doses as the clearance of the stereoisomers decreased and their half-life increased. For (2R,3S)-VCD the brain-to-plasma AUC ratio doubled at the tested dose range, while it remained constant for (2S,3S)-VCD. Racemic VCD, VPD, (2R,3S)-VCD, and (2S,3S)-VCD are effective anticonvulsants in animal models of partial seizures and are more potent than VPA. The more favorable brain penetration of (2S,3S)-VCD and its lower EC50 value in the 6Hz test provides one advantage over (2R,3S)-VCD as a new antiepileptic drug.

An in vitro Model for Blood Brain Barrier Permeation

The ability to permeate accross the blood brain barrier (BBB) is essential for drugs acting on the central nervous system (CNS). Thus, systems that allow rapid and inexpensive screening of the BBB-permeability properties of novel lead compounds are of great importance for speeding up the drug discovery process in the CNS-area. We used immortalized porcine brain microvessel endothelial cells (PBMECICl-2) to develop a model for measurement of blood-brain barrier permeation of CNS active drugs. Investigation of different cell culture conditions showed, that a system using C6 astrocyte glioma conditioned medium and addition of a cyclic AMP analog in combination with a type IV phosphodiesterase inhibitor (R020-1724) leads to cell layers with transendothelial electrical resistance values up to 300 Ω.cm2. Permeability studies with U-[14C]sucroseg ave a permeability coefficient Pe of 3.24 + 0.14 × 10−4 cm/min, which is in good agreement to published values and thus indicates the formation of tight junctions in vitro.

Micellar nanoparticles: a new topical emulsion for systemic delivery of estradiol and testosterone

Objective: To design a topical oil-and-water—based drug delivery system containing low concentrations of ethanol (<10%) that safely and effectively delivers ethanol-soluble drugs systemically. Design: A retrospective overview of formulation development and preclinical testing in rabbits and rhesus monkeys. Materials/Methods: A nanoemulsion was produced by injecting water into a mixture of oil, surfactant, and either estradiol or testosterone (solubilized in ethanol). The preferred ratio of the pre-mixed materials to water is 7:3 on a volume/volume basis. The delivery system is described in US Patent #5,629,021 (assignee: Novavax, Inc., Columbia, Md). Results: The final products have the consistency and properties of a cosmetic—like lotion. Each gram of the Estrasorb™ product contains 2.5 mg of estradiol and each gram of the Androsorb® product contains 31.25 mg of testosterone. The resulting emulsions have mean particle sizes <1 micron. The products are stable at 30°C for 24 months. Preclinical topical testing of Estrasorb and Androsorb in single-dose rhesus monkey and/or rabbit models resulted in significant systemic delivery of estradiol and testosterone, respectively, with acceptable preclinical safety profiles. Conclusions: A novel topical emulsion drug delivery system has been developed for ethanol-soluble drugs like estradiol and testosterone. These products are safe and deliver drugs systemically after a single topical application in our animal models. Both products are candidates for human clinical trials. This delivery system may also be suitable for other ethanol-soluble drugs, such as other steroids, anti-inflammatory agents, and central nervous system-active drugs. Supported by: Novavax, Inc.

The correlation of the bispectral index monitor with clinical sedation scores during mechanical ventilation in the pediatric intensive care unit.

In patients who are mechanically ventilated in the pediatric intensive care unit (PICU), sedative and/or analgesic medications are routinely provided and titrated to effect based on clinical assessment of the patient. The bispectral index (BIS) monitor uses a modified electroencephalogram to quantify the effects of central nervous system-acting drugs on the level of consciousness. To evaluate the usefulness of the BIS monitor to predict clinical sedation levels in the PICU, we compared BIS values with simultaneously obtained clinical sedation scores in 24 mechanically ventilated pediatric patients aged 5.7 plus minus 6.1 yr. For each sedation scale used, the BIS value correlated with increasing depth of sedation (P < 0.0001) and was independent of the drug(s) used for sedation. To differentiate adequate from inadequate sedation, a BIS value <70 had a sensitivity of 0.87--0.89 and a positive predictive value of 0.68--0.84. To differentiate adequate from excessive sedation, a BIS value <50 had a sensitivity of 0.67--0.75 and a positive predictive value of 0.07--0.52. We conclude that the BIS monitor may be a useful adjunct for the assessment of sedation in PICU patients. We demonstrate the usefulness of the bispectral index monitor for assessing sedation in pediatric intensive care unit patients. The bispectral index monitor correlated with clinically assessed sedation levels and was useful for differentiating adequate from inadequate sedation, which would be of value when the clinical examination is unavailable.

Is caffeine a flavoring agent in cola soft drinks?

Concern has been expressed about the nutrition and health impact of high rates of soft drink consumption. Caffeine is an added ingredient in approximately 70% of soft drinks consumed in the United States. The soft drink manufacturers' justification to regulatory agencies and the public for adding caffeine to soft drinks is that caffeine is a flavoring agent. To examine the claim that caffeine plays an integral role in the flavor profile of soft drinks, by examining the effect of caffeine on the threshold for detection of flavor differences in cola beverages. Double-blind crossover study starting November 1998 and ending July 1999. An academic research center. Twenty-five adult regular consumers of cola soft drinks. Based on a screening session, all were able to detect a flavor difference between cola containing sugar and diet cola. A sensitive version of a forced-choice flavor-detection procedure was used to evaluate the effects of a wide range of caffeine concentrations (range, 0.05-1.6 mg/mL) on the ability to detect flavor differences between caffeinated and caffeine-free cola beverages. Repeated tests permitted determination of significant detection at each concentration in individual subjects. Percentage of subjects significantly detecting a flavor difference and mean percentage of trials correct at each caffeine concentration. Detection of flavor differences increased as a function of caffeine concentration. At the 0.1-mg/mL concentration, which is the approximate concentration in the majority of cola soft drink products, 2 subjects (8%) significantly detected a flavor difference and the mean percentage correct (53%) was at chance levels. The finding that only 8% of a group of regular cola soft drink consumers could detect the effect of the caffeine concentration found in most cola soft drinks is at variance with the claim made by soft drink manufacturers that caffeine is added to soft drinks because it plays an integral role in the flavor profile. It is valuable for the general public, the medical community, and regulatory agencies to recognize that the high rates of consumption of caffeinated soft drinks more likely reflect the mood-altering and physical dependence-producing effects of caffeine as a central nervous system-active drug than its subtle effects as a flavoring agent. Arch Fam Med. 2000;9:727-734

Complications of cirrhosis III. Hepatic encephalopathy

Hepatic encephalopathy (HE) is a major neuropsychiatric complication of cirrhosis. HE develops slowly in cirrhotic patients, starting with altered sleep patterns and eventually progressing through asterixis to stupor and coma. Precipitating factors are common and include an oral protein load, gastrointestinal bleeding and the use of sedatives. HE is common following transjugular intrahepatic portosystemic stent shunts (TIPS). Neuropathologically, HE in cirrhotic patients is characterized by astrocytic (rather than neuronal) changes known as Alzheimer type II astrocytosis and in altered expression of key astrocytic proteins. Magnetic resonance imaging in cirrhotic patients reveals bilateral signal hyperintensities particularly in globus pallidus on T 1-weighted imaging, a phenomenon which may result from manganese deposition. Proton ( 1H) magnetic resonance spectroscopy shows increases in the glutamine resonance in brain, a finding which confirms previous biochemical studies and results no doubt from increased brain ammonia removal (glutamine synthesis). Additional evidence for increased brain ammonia uptake and removal in cirrhotic patients is provided by studies using positron emission tomography and 13NH 3. Recent molecular biological studies demonstrate increased expression of genes coding for neurotransmitter-related proteins in chronic liver failure. Such genes include monoamine oxidase (MAO-A isoform), the peripheral-type benzodiazepine receptor and nitric oxide synthase (nNOS isoform). Activation of these systems has the potential to lead to alterations of monoamine and amino acid neurotransmitter function as well as modified cerebral perfusion in chronic liver failure. Prevention and treatment of HE in cirrhotic patients continues to rely on ammonia-lowering strategies which include assessment of dietary protein intake and the use of lactulose, neomycin, sodium benzoate and L-ornithineaspartate. The benzodiazepine receptor antagonist flumazenil may be effective in certain cases. A more widespread use of central nervous system-acting drugs awaits a more complete understanding of the precise neurotransmitter systems involved in the pathogenesis of HE in chronic liver failure.

Memantine led to functional improvement and reduced care dependence in severe dementia

Winblad B, Poritis N . Memantine in severe dementia: results of the 9 m-best study (benefit and efficacy in severely demented patients during treatment with memantine). Int J Geriat Psychiatry1999...

A knowledge-based approach in designing combinatorial or medicinal chemistry libraries for drug discovery. 1. A qualitative and quantitative characterization of known drug databases.

The discovery of various protein/receptor targets from genomic research is expanding rapidly. Along with the automation of organic synthesis and biochemical screening, this is bringing a major change in the whole field of drug discovery research. In the traditional drug discovery process, the industry tests compounds in the thousands. With automated synthesis, the number of compounds to be tested could be in the millions. This two-dimensional expansion will lead to a major demand for resources, unless the chemical libraries are made wisely. The objective of this work is to provide both quantitative and qualitative characterization of known drugs which will help to generate "drug-like" libraries. In this work we analyzed the Comprehensive Medicinal Chemistry (CMC) database and seven different subsets belonging to different classes of drug molecules. These include some central nervous system active drugs and cardiovascular, cancer, inflammation, and infection disease states. A quantitative characterization based on computed physicochemical property profiles such as log P, molar refractivity, molecular weight, and number of atoms as well as a qualitative characterization based on the occurrence of functional groups and important substructures are developed here. For the CMC database, the qualifying range (covering more than 80% of the compounds) of the calculated log P is between -0.4 and 5.6, with an average value of 2.52. For molecular weight, the qualifying range is between 160 and 480, with an average value of 357. For molar refractivity, the qualifying range is between 40 and 130, with an average value of 97. For the total number of atoms, the qualifying range is between 20 and 70, with an average value of 48. Benzene is by far the most abundant substructure in this drug database, slightly more abundant than all the heterocyclic rings combined. Nonaromatic heterocyclic rings are twice as abundant as the aromatic heterocycles. Tertiary aliphatic amines, alcoholic OH and carboxamides are the most abundant functional groups in the drug database. The effective range of physicochemical properties presented here can be used in the design of drug-like combinatorial libraries as well as in developing a more efficient corporate medicinal chemistry library.

In vitro Effect of Central Nervous System Active Drugs on the ATPase-ADPase Activity and Acetylcholinesterase Activity from Cerebral Cortex of Adult Rats

1. The effect of several central nervous system active drugs was studied in vitro on ATPase-ADPase activity and acetylcholinesterase (AChE) activity from the cerebral cortex of adult rats. 2. Lithium (1.0–10.0 mM) had no effect on either ATPase-ADPase or acetylcholinesterase activity. 3. Imipramine (0.5–5.0 mM), desipramine (0.5–5.0 mM), amitriptyline (0.1–1.0 mM) and diazepam (0.5–2.0 mM) inhibited ATP and ADP hydrolysis at all concentrations tested. 4. AChE activity was altered by imipramine (1.0–2.0 mM) and by diazepam (0.5–2.0 mM). 5. The possible participation of ATP diphosphohydrolase and AChE in the action of these drugs cannot be ruled out. The probable reduction of ATP, ADP and acetylcholine hydrolysis by the inhibitory effect of these drugs is discussed.

Mechanistic data and risk assessment of selected toxic end points of the thyroid gland.

Many goitrogenic xenobiotics that increase the incidence of thyroid tumors in rodents exert a direct effect on the thyroid gland to disrupt one of several possible steps in the biosynthesis, secretion, and metabolism of thyroid hormones. This includes (a) inhibition of the iodine trapping mechanism, (b) blockage of organic binding of iodine and coupling of iodothyronines to form thyroxine (T4) and triiodothyronine (T3), and (c) inhibition of thyroid hormone secretion by an effect on proteolysis of active hormone from the colloid. Another large group of goitrogenic chemicals disrupts thyroid hormone economy by increasing the peripheral metabolism of thyroid hormones through an induction of hepatic microsomal enzymes. This group includes central nervous system-acting drugs, calcium channel blockers, steroids, retinoids, chlorinated hydrocarbons, polyhalogenated biphenyls, and enzyme inducers. Thyroid hormone economy also can be disrupted by xenobiotics that inhibit the 5'-monodeiodinase that converts T4 in peripheral sites to biologically active T3. Inhibition of this enzyme by FD&C Red No. 3 lowers circulating T3 levels, which results in a compensatory increased secretion of thyroid-stimulating hormone (TSH), follicular cell hypertrophy and hyperplasia, and an increased incidence of follicular cell tumors in 2-yr or lifetime studies in rats. Physiologic perturbations alone, such as the feeding of an iodine-deficient diet, partial thyroidectomy, natural goitrogens in certain foods, and transplantation of TSH-secreting pituitary tumors in rodents also can disrupt thyroid hormone economy and, if sustained, increase the development of thyroid tumors in rats. A consistent finding with all of these goitrogens, be they either physiologic perturbations or xenobiotics, is the chronic hypersecretion of TSH, which places the rodent thyroid gland at greater risk to develop tumors through a secondary (indirect) mechanism of thyroid oncogenesis associated with hormonal imbalances.

Characteristics of individuals with Huntington disease in long-term care.

This is a retrospective review of 97 Huntington disease (HD) patients living in long-term care facilities in the Twin Cities. The purpose of the study was to describe the demographic features, patterns of behavior, weight change, nursing issues, medication use, and hospitalization in this population. On admission to the nursing home, the "average" HD patient was of either sex, 45 years old, previously employed, a high school graduate, and not married. One third had severe behavior problems. Half gained and half lost weight; weight loss was not a predictor of death. Almost all used central nervous system-active drugs, most commonly neuroleptics. Eighty-four percent were ambulatory on admission, but 88% of those who died were nonambulatory at the time of death. We concluded that (a) HD patients are demographically different from other residents of long-term care facilities, (b) weight gain can occur in some late-stage patients, (c) negative behavior is a significant problem but is restricted to a subset of patients, and (d) adapting creatively to increasing multifaceted disability is the greatest challenge to the staff in facilities caring for HD patients.

Age-related alterations of skeletal muscle metabolism by intermittent hypoxia and trhanalogue treatment

The characteristics of the energy metabolism were evaluated in the gastrocnemius muscle from 3- and 24-month-old rats in normoxia or subjected to either mild or severe chronic (4 weeks) intermittent normobaric hypoxia. Furthermore, 4-week treatment with saline or the TRH-analogue posatireline was performed. The muscular concentration of the following metabolites related to the energy metabolism was evaluated: glycogen, glucose, glucose 6-phosphate, pyruvate, lactate, lactate-to-pyruvate ratio; citrate, a-ketoglutarate, succinate, malate; aspartate, glutamate, alanine; ammonia; ATP, ADP, AMP, creative phosphate; energy charge potential. Furthermore the maximum rate of the following muscular enzymes was evaluated: hexokinase, phosphofructokinase, pyruvate kinase, lactate dehydrogenase; citrate synthase, malate dehydrogenase; total NADH cytochrome c reductase; cytochrome oxidase. The age-related decrease in muscular glucose 6-phosphate, pyruvate and alanine concentrations and increase in citrate concentration were consistent with the age-related decreased hexokinase and increased citrate synthase activities. Ageing was characterized by a decrease in muscular creative phosphate concentration, while the energy mediators and the energy charge potential were unchanged. The chronic (4 weeks) intermittent normobaric mild and severe hypoxia-induced alterations of the components in the anaerobic glycolytic pathway, tricarboxylic acid cycle and energy storage, that were magnified in the skeletal muscle from the oldest animals. The effect of the chronic treatment with the TRH-analogue posatireline suggests that the action of central nervous system-acting drugs could also be related to their direct influence on the muscular biochemical mechanisms related to the energy transduction.

Fetal Drug Exposure and Its Possible Implications for Learning in the Preschool and School-Age Population

For the past 5 years there has been an exponential increase in the use of cocaine, phenylcyclidine hydrochloride (PCP), and other central nervous system (CNS) active drugs. A significant amount of this accelerated usage is in sexually active females, resulting in some urban hospitals reporting positive drug screens in over 16% of the infants born on their busy obstetrical service. There is a growing body of data showing that fetal exposure to cocaine, phenylcyclidine hydrochloride (PCP), and other CNS-active drugs results in infants and children with abnormal brain wave patterns, short-term neurologic signs, depression of interactive behavior, and poor organizational responses to environmental stimuli. Whether such neurologic findings will translate into a significant number of children with learning and behavioral problems needs to be the focus of long-term longitudinal studies of children with fetal drug exposure to cocaine, PCP, and other CNS-active drugs.

Research Challenges, New Drug Development, Preclinical and Clinical Trials in the Ageing Population

The aged are now viewed as a special population for the purposes of drug development. This has produced challenges for the investigator, in that separation of age- and disease-related changes in drug effect is only beginning to be defined. In addition, development of measurement tools for use in the elderly, particularly for central nervous system-active drugs, is an important ongoing process. As investigations proceed, we can look forward to an improved understanding of the physiology of normal ageing and the impact of disease processes and drugs on this physiological functioning. For the regulatory agency, evaluation of both efficacy and toxicity data in elderly patients for a drug-in-development is required; however, at present these data will be obtained in a 'young' elderly group, whereas much of the clinical use of the drug will be in the 'old' elderly. Extrapolation from one group to the other is required, although the relevance of this extrapolation is unknown. It is reassuring that, so far, few if any drug effects or toxicities have been identified which are truly unique to the elderly, though the magnitude of pharmacological or toxicological effects may differ.

Characterization of Peptide YY Receptors in the Brain

We studied the pharmacological and structural characteristics of peptide YY (PYY) receptors in porcine brain. PYY and neuropeptide Y (NPY) bound with high affinity to crude membrane preparations from the hippocampus, but their C-terminal fragments bound with 30- to 450-fold lower affinity Guanine nucleotides, especially the nonhydrolyzable GTP analog GTP gammas inhibited the binding of [125I]PYY, but other transmitters, hormones, and central nervous system-acting drugs did not, except for gangliosides at high concentrations. These results suggest that PYY receptor binding resides in the N-terminal part of the PYY molecule and is coupled to a guanine nucleotide regulatory protein. To elucidate PYY receptor structure, we used the cross-linking reagent disuccinimidyl suberate to covalently attach [125I]PYY to its receptors in the hippocampus membrane. Gel electrophoresis followed by autoradiography revealed a band centered at the mol wt of 50,000. Competitive inhibition of binding by unlabeled PYY resulted in a parallel inhibition of labeling of the 50,000 mol wt protein. The reducing agent 2-mercaptoethanol did not affect the appearance of this band, suggesting that the PYY receptor does not have subunits connected by sulfhydryl bonds. Furthermore, cross-linking [125I]NPY to its receptors in the porcine hippocampus produced the same 50,000 mol wt band regardless of 2-mercaptoethanol. The identity in the size of NPY and PYY receptors together with their similarities in binding properties including regional distribution and peptide specificity, indicate that NPY and PYY regulate brain function through interaction at a common receptor site.