Benzodiazepine Recognition Sites Research Articles

Age-related decrease in the density of benzodiazepine recognition sites in the brain of the fresh water eel ( Anguilla anguilla)

The binding parameters of benzodiazepine receptors labeled with [ 3H]flunitrazepam were investigated in the brain of male adult eels at the trophic phase (4 years old) and of male silver eels (6 year old ocean migrants). The density of [ 3H]flunitrazepam binding sites was significantly decreased (−26%) in the brain of silver eels compared with younger counterparts. In contrast, the apparent dissociation constant ( K d) was not significantly different in the two experimental groups. These results are discussed in terms of the possible involvement of stress, behavioral and environmental factors and age-related degenerative processes.

Benzodiazepine receptors: new vistas

The therapeutic effects of benzodiazepines are triggered by their interaction with allosteric sites (benzodiazepine recognition sites) on GABA A receptors in the CNS in a way that facilitates GABA-mediated inhibitory neurotransmission. The discovery of a spectrum of ligands interacting with differing efficacies at benzodiazepine receptors, as well as the growing evidence for a diversity of GABA A receptors, has created new opportunities for producing benzodiazepine receptor ligands with potentially unique and even unexpected therapeutic profiles.

Experience influences environmental modulation of function at the benzodiazepine (BZD)/GABA receptor chloride channel complex

Function of the benzodiazepine (BZD)/GABA receptor chloride channel complex was selectively altered by specific aspects of an environmental challenge, i.e. encountering a stranger in a familiar versus an unfamiliar environment. Chloride (Cl-) enhancement of [3H]flunitrazepam [( 3H]flu) binding was facilitated in rats tested in an unfamiliar environment relative to that in rats tested in a familiar environment. Basal [3H]flu binding (binding in the absence of NaCl) also was greater in rats tested in the unfamiliar environment than in rats tested in the familiar environment, and Scatchard analysis of [3H]flu binding indicated that increased [3H]flu binding in the unfamiliar environment reflected an increase in both binding affinity and maximal binding capacity. In addition, both the sensitivity of [3H]flu binding to Cl- and the affinity of BZD recognition sites were decreased in handled control rats relative to non-handled control rats as well as to environmentally-challenged (prehandled) rats, suggesting that the experience of daily handling as well as familiarization with the environment modulates function at the BZD/GABA receptor complex. GABA-mediated 36Cl- uptake was facilitated by testing in either the familiar or unfamiliar environment relative to that measured in non-handled control rats. Thus, changes in GABA-gated chloride channel function may reflect a more fundamental response of this complex to challenging situations. These findings suggest that components of the BZD/GABA receptor complex are differentially influenced by specific aspects of an environmental challenge. Furthermore, function at the BZD recognition site/chloride channel component of this receptor complex is influenced by both repeated and single exposure to specific environments.

Tricyclic Heteroaromatic Systems: [1]Benzopyrano-pyrazol-4-ones as Benzodiazepine Receptor Ligands

The synthesis of a series of 8-substituted 1,4-dihydro-1 -aryl- 3-methyl-[1]benzopyrano[3,4-d]pyrazol-4-ones (series 7) and 2,4- dihydro-2-aryl-3-methyl[1]benzopyranol[4,3-c]pyrazol-4-ones (series 8) is reported. Compounds of series 7 and 8 were tested for their ability to displace [3H]flunitrazepam from bovine brain membranes and for their in vitro biological activity. The results allowed some conclusions to be drawn about the structural requirements of the benzodiazepine recognition site within this class of unusual ligands.

Neurochemical action of the general anaesthetic propofol on the chloride ion channel coupled with GABA A receptors

The effect of propofol, a novel short acting anaesthetic, on the function of the GABA A/ionophore receptor complex was studied in vitro in cortical membrane preparations from rat cerebral cortex and was compared with the action of pentobarbital and alphaxalone, two general anaesthetics known to enhance GABAergic transmission. Propofol, mimicking the action of pentobarbital and alphaxalone, increased [ 3H]GABA binding, reduced [ 35S]TBPS binding and enhanced muscimol-stimulated 36CI − uptake in a concentration-dependent manner. While the efficacy of the drugs in affecting these biochemical parameters was similar, they differed markedly in potency being alphaxalone > propofol > pentobarbital. However, separate sites of action or different mechanisms for these drugs can be suggested by the result that the concomitant addition of propofol either with alphaxalone or pentobarbital or diazepam produced a simple additive inhibition of [ 35S]TBPS binding as well as an addictive enhancement of [ 3H]GABA binding and muscimol-stimulated 36CI − uptake. The effect of propofol at the level of the GABA/ionophore receptor complex seems to be strictly dependent on the interaction of GABA with its recognition site. In fact, the specific GABA A receptor antagonist bicuculline antagonized the decrease of [ 35S]TBPS binding as well as the enhancement of [ 3H]GABA binding and muscimol-stimulated 36CI − uptake induced by propofol. On the other hand, propofol was able to enhance [ 3]GABA binding in membranes previously incubated with the specific chloride channel blocker picrotoxin.Finally, the finding that propofol fails to affect [ 3H]flunitrazepam binding together with the failure of Ro 15–1788 and PK 11195 to antagonize its effect on [ 35S]TBPS binding excludes a direct interaction at the level of benzodiazepine recognition sites. Taken together these results strongly suggest that an enhancement in the function of the GABA A/ionophore receptor complex may have a relevant role in mediating the anaesthetic effect of propofol as well as those of other general anaesthetics.

Chronic exposure to anxiolytic drugs, working by different mechanisms causes up-regulation of dihydropyridine binding sites on cultured bovine adrenal chromaffin cells

Exposure of bovine adrenal chromaffin cells to ethanol [50 mM], alprazolam [10 −7 M] and buspirone [10 −7 M] inhibited basal and carbachol-induced release of catecholamines from these cells. The inhibition produced by alprazolam was prevented, and that produced by ethanol inhibited, by the presence of the benzodiazepine receptor antagonist, flumazenil [10 −8 M]. The inhibition produced by buspirone was unaffected by flumazenil, but was mimicked by the selective 5-HT 1A receptor agonist, 8-OH DPAT and prevented by the 5-HT receptor antagonist spiperone [10 −6 M]. These results suggest that bovine adrenal chromaffin cells express GABA A receptors, containing a benzodiazepine recognition site and also 5-HT 1A receptors. Ethanol and alprazolam appear to inhibit the excitability of bovine adrenal chromaffin cells by an action related to the former, while buspirone probably inhibits the cells through the latter. Maintaining bovine adrenal chromaffin cells for several days in culture medium, containing inhibitory concentrations of ethanol alprazolam or buspirone, produced a marked increase in binding sites for a [ 3H]dihydropyridine [DHP] calcium channel antagonist, on cell membranes. The increase in binding sites produced by alprazolam was greater than that produced by the other two agents and was almost completely prevented by the concomitant presence of flumazenil. The effects of ethanol and buspirone on the binding of DHP were not prevented by flumazenil. The results suggest that drugs which decrease excitability of bovine adrenal chromaffin cells by different mechanisms, may evoke a similar adaptive response involving an increase in DHP-sensitive calcium channels.

GABAA-benzodiazepine receptors: demonstration of pharmacological subtypes in the brain.

The GABAA receptor is a ligand-gated chloride ion channel that mediates the majority of rapid-acting inhibitory synapses in the central nervous system (Olsen and Venter, 1986). The GABAA receptors are also the target of numerous clinically important depressant and excitatory drugs (Olsen, 1981; Tallman and Gallager, 1985; Biggio and Costa, 1988). The convulsant drug bicuculline acts as a competitive antagonist at the GABA recognition site, beta-carbolines block GABA function as ’ inverse agonists’ at the benzodiazepine recognition site, and picrotoxin and cage convulsants inhibit the chloride channel function at a site on the receptor complex distinct from the GABA and benzodiazepine receptor sites. Clinically important depressant benzodiazepines enhance GABA-mediated inhibition via their own binding sites on the receptor complex. Still additional sites on the receptor-ion channel complex mediate the action of barbiturates, steroid anesthetics, and possibly ethanol to enhance GABAA receptor function at the membrane level (Olsen and Venter, 1986; Biggio and Costa, 1988).

Alterations of GABA-A and dopamine D-2 brain receptors in dogs with portal-systemic encephalopathy

The binding characteristics of gamma-aminobutyric acid-A (GABA-A) receptors and the kinetic characteristics of the target enzyme of GABA synthesis in nerve terminals, glutamic acid decarboxylase (GAD), were studied in a dog model of portal-systemic encephalopathy obtained by porta-caval shunt performed in dimethylnitrosamine pretreated animals. Furthermore the properties of dopamine receptors and the levels of catecholamines of encephalopathic dogs were investigated. The mild stage of encephalopathy was characterized by an up-regulation of the inhibitory GABA-A receptors probably related to a decrease of GABA in nerve terminals since GAD was decreased and by a slight decrease of catecholamines and by an increased synthesis of octopamine associated with a decreased affinity of dopamine receptors. In the severe stage there was a selection of high affinity GABA-A receptors with an increased number of benzodiazepine recognition sites which were supersensitive to GABA stimulation, a decreased number of Dopamine D-2 receptors and a marked reduction of catecholamines. These data seem to suggest that the neurological disturbances of experimental portal-systemic encephalopathy might be the result of an imbalance between inhibitory and excitatory systems leading to a prevalence of the first one.

The pharmacological properties of the imidazobenzodiazepine, FG 8205, a novel partial agonist at the benzodiazepine receptor

1. The pharmacological properties of the benzodiazepine receptor ligand, FG 8205 (7-chloro-5,6-dihydro-5-methyl-6-oxo-3-(5-isopropyl-1,2,4-oxadiazol++ +-3-yl)-4H- imidazol[1,5a][1,4]benzodiazepine) have been examined. 2. FG 8205 potently displaced [3H]-flumazenil binding in rat cortical membranes with a Ki of 3.3 nM, but was inactive at 13 neurotransmitter recognition sites. 3. Consistent with a partial agonist profile, the affinity of FG 8205 for the benzodiazepine recognition site was increased in the presence of gamma-aminobutyric acid (GABA, 300 microM) by a degree (-log [IC50 in the presence of GABA/IC50 alone] = 0.34) significantly less than found for diazepam (0.46). FG 8205 also potentiated the inhibitory potency of the GABAA-receptor agonist, isoguvacine, on the hippocampal CA1 population spike and, again, the maximum shift (-log dose-ratio = 0.2) was significantly less than that seen with diazepam (0.4). 4. In anticonvulsant studies, the ED50 doses of FG 8205 and diazepam needed to antagonize seizures induced by pentylenetetrazol (PTZ) or by sound in audiogenic seizure prone mice were similar with values of 0.2-0.3 mg kg-1, i.p. However, even high doses of FG 8205 (50 mg kg-1) did not protect against seizures induced by electroshock. 5. FG 8205 released responding suppressed by footshock in a rat operant conditioned emotional response task over the dose range 0.5-50 mg kg-1 (i.p.). Similar doses of FG 8205 had a marked taming effect in cynomolgus monkeys. However, measures of sedation and ataxia (as measured by rotarod in the mouse, climbing behaviour in the rat, and by scoring arousal and co-ordination in primates) were slight and only transiently affected by FG 8205, and FG 8205 significantly antagonized the rotarod performance deficit induced by diazepam in the mouse. 6. While the potentiation by FG 8205 of the response to isoguvacine in the rat hippocampal slice and the anxiolytic-like effects of the compound in both rats and primates were reversed by the benzodiazepine receptor antagonist, flumazenil, high doses of the antagonist were able only marginally to block the protective effects of FG 8205 against seizures induced by PTZ in the mouse. 7. Thus, FG 8205 does not show the marked motor impairment characteristic of full agonists at the benzodiazepine receptor, consistent with its partial agonist profile in in vitro assay systems. Nevertheless, the compound has sufficient intrinsic activity to maintain high efficacy in anticonvulsant and anxiolytic tests.

Differences in pharmacological profiles of a new generation of benzodiazepine and non-benzodiazepine hypnotics

The hypnotics, quazepam (a benzodiazepine), brotizolam (a thienotriazolodiazepine), zopiclone (a cyclopyrrolone) and zolpidem (an imidazopyridine) have a common ability to bind to the benzodiazepine recognition site (ω receptor) within the GABA A receptor. For this reason we compared their pharmacological profiles in mice. All compounds shared anticonvulsant and central depressant effects. However, the sedative activity of zolpidem appeared at much lower doses than did the anticonvulsant and myorelaxant effects but the opposite was observed with the other hypnotics. In contrast to brotizolam, quazepam and zopiclone, zolpidem did not increase food intake in mice placed in a novel environment, indicating that this drug lacks disinhibitory activity. Moreover the efficacy of zolpidem at the GABA A receptor, as indicated by its activity against convulsions induced by the GABA synthesis inhibitor, isoniazid, was much greater than that of other hypnotics. These results suggest that the hypnoselective properties observed with zolpidem might be related to a high selectivity for the ω 1 recognition site of the GABA A receptor coupled with a very high intrinsic activity.

Cofractionation of the 17-kD PK 14105 binding site protein with solubilized peripheral-type benzodiazepine binding sites

To examine the relationship between PKBS, a 17-kD protein covalently photolabeled by [ 3H]PK 14105, and its association with peripheral-type benzodiazepine binding sites, rat adrenal mitochondrial fractions were photolabeled with [ 3H]PK 14105, solubilized in digitonin, and subjected to anion-exchange chromatography over Q-Sepharose. The Chromatographic behavior of PKBS was evident as principally two major fractions, signified as Q-I and Q-II. Specific binding sites for [ 3H]Ro5-4864 and [ 3H]PK 11195 were also assayed and found to cofractionate with each other and in a manner which coincided with the photolabeled PKBS profile. The Q-I and Q-II fractions were further distinguished based on their different molecular sizes observed by gel filtration, yet both fractions were characterized as containing peripheral-type benzodiazepine recognition sites according to the following criteria. Scatchard analysis of both subpopulations revealed a single class of binding sites for [ 3H]Ro5-4864 with an apparent K D of 14 nM for Q-I and 22 nM for Q-II; these affinities were slightly lower than those found in mitochondrial membrane preparations used as the starting material for solubilization. The rank order of potency to inhibit [ 3H]Ro5-4864 binding in both subpopulations was PK 11195 > Ro5-4864 > diazepam > clonazepam, in connection with the pharmacological specificity of membrane-associated peripheral-type benzodiazepine binding sites. These studies provide direct biochemical evidence that the recognition sites for benzodiazepines and isoquinoline carboxamides cofractionate in unison with the 17-kD PKBS protein, demonstrating an intimate relationship between this protein and the binding domains for peripheral-type benzodiazepine ligands.

Tricyclic heteroaromatic systems. [1]benzopyranopyrrol-4-ones and [1]benzopyrano-1,2,3-triazol-4-ones as benzodiazepine receptor ligands. Synthesis and structure-activity relationships

The synthesis, ability to displace [3H]flunitrazepam binding from bovine brain membranes, and GABA ratio of some [1]benzopyranopyrroles 1a-i and [1]benzopyrano-1,2,3-triazoles 2a,b are reported. The GABA ratios of some previously synthesized pyrazoloquinolines A and [1]benzopyranopyrazoles C are also presented in order to draw some structure-activity relationships among our benzodiazepine receptor ligands. 1,3-Diarylpyrrole derivatives 1a-h show similar affinity and efficacy to that of diazepam, while the 1-aryltriazoles 2a,b have no receptor affinity. Comparison of the latter results with those on previously reported compounds suggests that there are several hydrophobic regions on the benzodiazepine recognition site whose occupation gives rise to different affinity and efficacy.

Cerebellar GABAA receptor selective for a behavioural alcohol antagonist

Benzodiazepines are widely prescribed anxiolytics and anticonvulsants which bind with high affinity to sites on the GABAA receptor/Cl- channel complex and potentiate the effect of the neurotransmitter GABA (gamma-aminobutyric acid). The heterogeneity of benzodiazepine recognition sites in the central nervous system was revealed by studies showing different classes of GABAA receptor subunits (classes alpha, beta and gamma) and variant subunits in these classes, particularly in the alpha-class. Expression of recombinant subunits produces functional receptors; when certain alpha-variants are coexpressed with beta- and gamma-subunits the resulting receptors have pharmacological properties characteristic of GABAA-benzodiazepine type I or type II receptors. The alpha-variants are differentially expressed in the central nervous system and can be photoaffinity-labelled with benzodiazepines. Here we report a novel alpha-subunit (alpha 6) of cerebellar granule cells. We show that recombinant receptors composed of alpha 6, beta 2 and gamma 2 subunits bind with high affinity to the GABA agonist [3H]muscimol and the benzodiazepine [3H]Ro15-4513 but not the other benzodiazepines or beta-carboniles. The same distinctive pharmacology is observed with GABAA receptors from rat cerebellum immunoprecipitated by an antiserum specific for the alpha 6 subunit. We conclude that this alpha-subunit is part of a cerebellar receptor subtype, selective for Ro15-4513, an antagonist of alcohol-induced motor incoordination and ataxia.

Increased endogenous neuropeptide ligand for benzodiazepine receptors in hepatic encephalopathy

The neuropeptide diazepam binding inhibitor (DBI) is an endogeneous allosteric modulator of gammaaminobutyric acid (GABA) receptors at the benzodiazepine recognition site. Recent theories on the neurochemical cause for hepatic encephalopathy have implicated activation of inhibitory neurotransmitter GABA systems. In 20 patients with hepatic disease, blood and cerebrospinal fluid (CSF) levels of ammonia and amino acids were measured. As in previous studies there was a selective elevation of CSF amino acids as well as a correlation between CSF glutamine levels and encephalopathy. CSF DBI levels were maximally elevated 5-fold in patients with hepatic encephalopathy, but they were normal in those patients with liver disease not associated with changes in mental status and in patients with nonhepatic encephalopathy. Levels of DBI correlated with the clinical staging of hepatic encephalopathy. These data suggest that DBI may participate in the modulation of cerebral function in hepatic encephalopathy.

Reduction of reticulata neuronal activity by zolpidem and alpidem, two imidazopyridines with high affinity for type I benzodiazepine receptors

Zolpidem and alpidem, two imidazopyridines with high affinity for the type I benzodiazepine recognition site, have recently been proposed as preferential hypnotic (zolpidem) and anxiolytic (alpidem) drugs notable for the minor incidence of side-effects. To further characterize the molecular mechanism involved in the action of these drugs, we studied their effects in comparison with those of diazepam on the spontaneous electrical activity of substantia nigra pars reticulata (SNR) neurons. These cells have been shown to be extremely sensitive to various positive and negative modulators of GABAergic transmission. All three drugs consistently produced a dose-dependent (0.03–8.0 mg/kg i.v.) inhibition of the firing of SNR cells when administered as a single bolus. However, zolpidem was more potent and efficacious than diazepam or alpidem. The ID 50s were 0.076, 0.492 and 0.821 mg/kg, respectively. When the drugs were injected in exponentially (ratio 2) increasing doses up to 8.0 mg/kg, the rank order for tachyphylaxis was zolpidem ⪢ diazepam > alpidem. Since the effects of the drugs were abolished and prevented by a small dose (0.5 mg/kg i.v.) of flumazenil (Ro 15-1788), it is likely that the effects were mediated through activation of benzodiazepine receptors. The results indicate that the hypnotic, zolpidem, has a more potent inhibitory action on SNR cell activity than the anxiolytics, alpidem and diazepam.

Characterization of peripheral benzodiazepine receptors in human blood mononuclear cells

In the present study, peripheral-type benzodiazepine receptors in human circulating mononuclear cells were characterized, using [ 3H]PK 11195 as specific ligand. The specific binding was saturable, with a B max of 14 pmol/mg protein and a K d of 7 nM. The pharmacological characterization, using different displacing drugs, indicated a mitochondrial type of peripheral benzodiazepine receptor since it was not coupled to the GABA receptor and was displaced by protoporphyrin IX. These data indicate that human circulating mononuclear cells possess benzodiazepine recognition sites, similar to non-neuronal receptors. The role of these receptors and possible modifications in different diseases need to be investigated.

The peripheral-type benzodiazepine receptor is functionally linked to Leydig cell steroidogenesis.

Testicular mitochondria were previously shown to contain an abundance of peripheral-type benzodiazepine recognition site(s)/receptor(s) (PBR). We have previously purified, cloned, and expressed an Mr 18,000 PBR protein (Antkiewicz-Michaluk, Mukhin, A. G., Guidotti, A., and Krueger, K. E. (1988) J. Biol. Chem. 263, 17317-17321; (Sprengel, R., Werner, P., Seeburg, P. H., Mukhin, A. G., Santi, M. R., Grayson, D. R., Guidotti, A., and Krueger, K. E. (1989) J. Biol. Chem. 264, 20415-20421); and in this report, we present evidence that PBR are functionally linked to Leydig cell steroid biosynthesis. A spectrum of nine different ligands covering a range of over 4 orders of magnitude in their affinities for PBR were tested for their potencies to modulate steroidogenesis in the MA-10 mouse Leydig tumor cell line. The Ki for inhibition of [3H]1-(2-chlorophenyl)-N-methyl-N-(1-methylpropyl)-3-isoquinoline carboxamide binding and the EC50 for steroid biosynthesis for this series of compounds showed a correlation coefficient of r = 0.95. The most potent ligands stimulated steroid production by approximately 4-fold in these cells. This stimulation was not inhibited by cycloheximide, unlike human chorionic gonadotropin- or cyclic AMP-activated steroidogenesis. The action of PBR ligands was not additive to stimulation by human chorionic gonadotropin or cyclic AMP, but was additive to that of epidermal growth factor, another regulator of MA-10 Leydig cell steroidogenesis. Moreover, PBR ligands stimulated, in a dose-dependent manner, pregnenolone biosynthesis by isolated mitochondria when supplied with exogenous cholesterol. This effect was not observed with mitoplasts (mitochondria devoid of the outer membrane). Cytochrome P-450 side chain cleavage activity, as measured by metabolism of (22R)-hydroxycholesterol, was not affected by PBR ligands in intact cells. Similar results were also obtained with purified rat Leydig cells. In conclusion, PBR are implicated in the acute stimulation of Leydig cell steroidogenesis possibly by mediating the entry, distribution, and/or availability of cholesterol within mitochondria.

From binding studies to the molecular biology of GABA receptors

The GABAA-complex remains enigmatic despite the substantial amount of information that has been gathered. The work of Barnard's group on the structure of the complex and the relationship of the recognition sites for GABA and benzodiazepines to its protein subunits has raised as many questions as have been answered. The existence of multiple forms of the α subunit and the ability of various combinations of the subunits to mediate GABA-gated choloride conductance suggest that there may be many forms of the GABAA-complex. Thus, the identification of previously unsuspected drug interactions, and evidence for the existence of additional endogenous ligands beside GABA (e.g. benzodiazepine-binding inhibitor (68) and certain steroids (69), all suggest that the characterization of the GABAA-complex has only begun.

Receptive-field Size of S1 Cortical Neurones is Altered by Methaqualone via a GABA Mechanism

Methaqualone (Mtq; quaaludes or 'ludes) is a controlled substance, having a molecular structure related to the imidiazobenzodiazepine series of drugs, that has gained some notoriety recently due to its history of widespread abuse on the street. Users report experiencing peripheral paresthesia and transient numbness on body parts receiving dense cutaneous innervation (lips, fingertips, etc.). Since the receptive-field (RF)-sizes of many primary somatosensory (S1) cortical neurones are controlled by local, gamma-aminobutyric acid (GABA)-mediated inhibitory processes, we tested Mtq to see whether its clinical symptoms might have a basis in an action through central GABA-mediated synaptic processes. This report supports this contention and describes a likely pharmacological mechanism involved as one being related to the Ro 15-1788-sensitive benzodiazepine (Bzd) recognition site(s) of the GABA receptor complex.

Molecular biology of Diazepam Binding Inhibitor peptide

Complementary DNA (cDNA) clones containing the entire coding sequence for Diazepam Binding Inhibitor (DBI) peptide, a 10-kDa precursor of putative natural ligands of benzodiazepine recognition sites, were isolated from rat, human and cow libraries. The sequence of all these clones is highly conserved; however, the N-terminal sequence predicted by the human DBI clone differed from that of the other two clones. DBI cDNA, utilized as hybridization probe in Southern blot analysis, revealed that DBI of both human and rat might be encoded by a multiple family of 4-6 genes. Furthermore, we have used in situ chromosomes hybridization to map human DBI genes. The results indicate that a human DBI gene is localized on chromosome 2 and that three of the four hybridization signals detected by the human DBI probe are located on three other chromosomes. These findings raise a question as whether multiple DBI genes encode for different molecular forms of DBI. In the attempt to test this hypothesis, cow cDNA and human genomic libraries were screened with DBI cDNA. In this paper I report the isolation of clones from these libraries which, although hybridizing well to DBI cDNA, possess a low percentage of homology (46.7%), randomly distributed within the coding region of DBI cDNA. Whether or not these clones encode for peptides sharing the same physiological role as DBI is under investigation.