The HCN Channel Blocker ZD7288 Induces Emesis in the Least Shrew (Cryptotis parva)

Subtypes (1-4) of the hyperpolarization-activated cyclic nucleotide-gated (HCN) channels are widely expressed in the central and peripheral nervous systems, as well as the cells of smooth muscles in many organs. They mainly serve to regulate cellular excitability in these tissues. The HCN channel blocker ZD7288 has been shown to reduce apomorphine-induced conditioned taste aversion on saccharin preference in rats suggesting potential antinausea/antiemetic effects. Currently, in the least shew model of emesis we find that ZD7288 induces vomiting in a dose-dependent manner, with maximal efficacies of 100% at 1 mg/kg (i.p.) and 83.3% at 10 µg (i.c.v.). HCN channel subtype (1-4) expression was assessed using immunohistochemistry in the least shrew brainstem dorsal vagal complex (DVC) containing the emetic nuclei (area postrema (AP), nucleus tractus solitarius and dorsal motor nucleus of the vagus). Highly enriched HCN1 and HCN4 subtypes are present in the AP. A 1 mg/kg (i.p.) dose of ZD7288 strongly evoked c-Fos expression and ERK1/2 phosphorylation in the shrew brainstem DVC, but not in the in the enteric nervous system in the jejunum, suggesting a central contribution to the evoked vomiting. The ZD7288-evoked c-Fos expression exclusively occurred in tryptophan hydroxylase 2-positive serotonin neurons of the dorsal vagal complex, indicating activation of serotonin neurons may contribute to ZD7288-induced vomiting. To reveal its mechanism(s) of emetic action, we evaluated the efficacy of diverse antiemetics against ZD7288-evoked vomiting including the antagonists/inhibitors of: ERK1/2 (U0126), L-type Ca2+ channel (nifedipine); store-operated Ca2+ entry (MRS 1845); T-type Ca2+ channel (Z944), IP3R (2-APB), RyR receptor (dantrolene); the serotoninergic type 3 receptor (palonosetron); neurokinin 1 receptor (netupitant), dopamine type 2 receptor (sulpride), and the transient receptor potential vanilloid 1 receptor agonist, resiniferatoxin. All tested antiemetics except sulpride attenuated ZD7288-evoked vomiting to varying degrees. In sum, ZD7288 has emetic potential mainly via central mechanisms, a process which involves Ca2+ signaling and several emetic receptors. HCN channel blockers have been reported to have emetic potential in the clinic since they are currently used/investigated as therapeutic candidates for cancer therapy related- or unrelated-heart failure, pain, and cognitive impairment.

The pivotal role of glycogen synthase kinase 3 (GSK-3) in vomiting evoked by specific emetogens in the least shrew (Cryptotis parva)

Glycogen synthase kinase 3 (GSK-3) is a constitutively active multifunctional serine-threonine kinase which is involved in diverse physiological processes. GSK-3 has been implicated in a wide range of diseases including neurodegeneration, inflammation, diabetes and cancer. GSK-3 is a downstream target for protein kinase B (Akt) which phosphorylates GSK-3 and suppresses its activity. Based upon our preliminary findings, we postulated Akt's involvement in emesis. The aim of this study was to investigate the participation of GSK-3 and the antiemetic potential of two GSK-3 inhibitors (AR-A014418 and SB216763) in the least shrew model of vomiting against fully-effective emetic doses of diverse emetogens, including the nonselective and/or selective agonists of serotonin type 3 (e.g. 5-HT or 2-Methyl-5-HT)-, neurokinin type 1 receptor (e.g. GR73632), dopamine D₂ (e.g. apomorphine or quinpirole)-, and muscarinic 1 (e.g. pilocarpine or McN-A-343) receptors, as well as the L-type Ca²⁺ channel agonist (FPL64176), the sarco/endoplasmic reticulum Ca²⁺-ATPase inhibitor thapsigargin, and the chemotherapeutic agent, cisplatin. We first determined if these emetogens could regulate the phosphorylation level of GSK-3 in the brainstem emetic loci of least shrews and then investigated whether AR-A014418 and SB216763 could protect against the evoked emesis. Phospho-GSK-3α/β Ser21/9 levels in the brainstem and the enteric nerves of jejunum in the small intestine were upregulated following intraperitoneal (i.p.) administration of all the tested emetogens. Furthermore, administration of AR-A014418 (2.5-20 mg/kg, i.p.) dose-dependently attenuated both the frequency and percentage of shrews vomiting in response to i.p. administration of 5-HT (5 mg/kg), 2-Methyl-5-HT (5 mg/kg), GR73632 (5 mg/kg), apomorphine (2 mg/kg), quinpirole (2 mg/kg), pilocarpine (2 mg/kg), McN-A-343 (2 mg/kg), FPL64176 (10 mg/kg), or thapsigargin (0.5 mg/kg). Relatively lower doses of SB216763 exerted antiemetic efficacy, but both inhibitors barely affected cisplatin (10 mg/kg)-induced vomiting. Collectively, these results support the notion that vomiting is accompanied by a downregulation of GSK-3 activity and pharmacological inhibition of GSK-3 protects against pharmacologically evoked vomiting.

Behaviorally active doses of the CB1 receptor antagonist SR 141716A increase brain serotonin and dopamine levels and turnover

Large doses (10-40 mg/kg) of the selective cannabinoid CB(1) receptor antagonist, SR 141716A, produce the head-twitch response (HTR) and scratching in rodents and vomiting in the least shrew (Cryptotis parva). Agents that increase brain serotonin (5-HT) levels induce the HTR in rodents, whereas enhancements in either brain 5-HT or dopamine concentrations can lead to production of emesis in vomiting species. The present study was undertaken to demonstrate whether large doses of SR 141716A can (1) induce the HTR and scratching in the least shrew and (2) cause concurrent biochemical changes in brain 5-HT and dopamine concentrations. SR 141716A (0, 1, 5, 10, 20 and 40 mg/kg i.p.) administration induced the HTR, scratching and vomiting. The HTR effect was bell shaped with a maximum frequency occurring at the 20 mg/kg SR 141716A dose, whereas the scratching and vomiting behaviors displayed dose-dependent effects. The selective 5-HT(2A/C) receptor antagonist, SR 46349B (0, 0.1, 0.25, 1, 3 and 6 mg/kg i.p.), differentially attenuated all SR 141716A (20 mg/kg)-induced behaviors because the HTR was relatively more potently and completely blocked. In the shrew forebrain, SR 141716A (20 and 40 mg/kg ip) caused dose- and time-dependent increases in the levels of 5-HT and dopamine and the concentrations of their major metabolites [5-hydroxyindole acetic acid (5-HIAA), 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanilic acid (HVA)] and the turnover of both monoamines. Although the effects of SR 141716A on brainstem concentrations of both monoamines and their metabolites were not always consistent, the CB(1) antagonist did increase the turnover of both 5-HT and dopamine. The present findings suggest that the mechanism and the neurochemical substrate for SR 141716A-induced HTR and scratching behaviors is enhancement of 5-HT release, whereas increased release of 5-HT and dopamine probably contributes to the production of emesis.

Anatomic and physiologic reference values in least shrews (Cryptotis parva)

BACKGROUND AND PURPOSE

The least shrew is an established animal model for reproductive and pharmacologic research. Biologic reference data are needed to assess animal health status and provide a rationale for use of novel statistical programs to evaluate the effects of orally administered substances in toxicologic and pharmacologic studies.

METHODS

Organ weights, blood biochemical and hematologic values, and food and water consumption data were collected from 50-day-old shrews after two weeks' consumption of a standard feline diet.

RESULTS

In general, data correlated well with values reported for other mammalian species. Plasma phosphorus concentration was high. There was a significant difference in food and water consumption per gram of body weight between shrews at lower and upper (+/- 1 SD) weight ranges for the study. The 3.2-g animals consumed 27% more food per gram of body weight than did the 5.0-g animals.

CONCLUSIONS

The high phosphorus concentration was attributed to hemolysis resulting from the axillary cut method of blood sample collection. The small size of the shrew allowed demonstration of the Kleiber effect within a +/- 1 SD weight range in a single species. The phenomenon necessitates the use of statistical methods other than the typical tests establishing the significance of the differences between the means of groups for oral toxicologic and pharmacologic studies.

The cannabinoid CB1 receptor antagonist SR 141716A reverses the antiemetic and motor depressant actions of WIN 55, 212-2

The dibenzopyran cannabinoids (delta-9 (Delta9)-tetrahydrocannabinol and nabilone) are clinically used to suppress nausea and vomiting produced by chemotherapeutic agents such as cisplatin. The purpose of this investigation was to investigate the antiemetic potential of the aminoalkylindole cannabinoid receptor agonist WIN 55, 212-2 [R(+)-[2,3-dihydro-5-methyl-3-[(morpholinyl) methyl] pyrolol [1,2,3-de]-1,4-benzoxazin-yl]-(1-naphthalenyl) methanone mesylate] against cisplatin-induced vomiting. Different doses of WIN 55, 212-2 (0, 1, 2.5 and 5 mg/kg, i.p.) reduced both the frequency of cisplatin (20 mg/kg, i.p.)-induced emesis (ID(50)=0.5 mg/kg) as well as the percentage of shrews vomiting (ID50=1.2 mg/kg) in a dose-dependent manner. Significant reductions in emesis frequency occurred from 2.5 mg/kg dose of WIN 55, 212-2, whereas significant total protection from vomiting was afforded at its 5 mg/kg dose. The antiemetic actions of a 5-mg/kg dose of WIN 55, 212-2 against cisplatin (20 mg/kg, i.p.)-induced vomiting were reversed by nonemetic subcutaneous doses (0, 0.25, 0.5 and 1 mg/kg) of the cannabinoid CB1 receptor antagonist/inverse agonist SR 141716A [N-piperidino-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methylpyrazole-3-carboxamide] (ID50=0.27 and 0.47 mg/kg, respectively) but not by a 5-mg/kg dose of the cannabinoid CB2 receptor antagonist SR 144528 [N-[(1S)-endo-1,3,3-trimethylbicyclo [2.2.1] heptan-2-yl]5-(4-chloro-3-methylphenyl)-1-(4-methybenzyl) pyrazole-3-carboxamide]. The effects of the cited doses of WIN 55, 212-2 were also investigated on several motor parameters (spontaneous locomotor activity, duration of movement and rearing frequency). Significant reductions in motor parameters were only observed at its highest tested dose (ID50=1.97, 2.75 and 2.8 mg/kg; respectively). SR 141716A (0, 0.5, 1, 5 and 10 mg/kg) also reversed the motor suppressant effects of a 5-mg/kg dose of WIN 55, 212-2 (ID50=0.39, 0.1 and 0.3 mg/kg, respectively) and significant reversals were seen from its 0.5 and 1 mg/kg doses. These results suggest that WIN 55, 212-2 reduces both emesis and indeces of locomotion via the stimulation of cannabinoid CB1 receptors. However, cannabinoid CB1 receptors in different loci are most likely responsible for the antiemetic and motor suppressive effects of WIN 55, 212-2 since reduction in the frequency of vomiting occurred at lower doses relative to its sedative actions.

Nicotine attenuates DOI-induced head-twitch response in mice: implications for Tourette syndrome

Tourette syndrome (TS), a chronic neuropsychiatric disorder, is characterized by motor and vocal tics. Preliminary clinical studies indicate possible therapeutic benefits of nicotine in the treatment of Tourette's syndrome (TS). It has been proposed that twitches of the head in mice or twitches of head and shoulders in rats following administration of the selective 5HT(2A/C) agonist DOI (1-)2,5-dimethoxy-4-iodophenyl-2-aminopropane, can serve as an animal model of tics in TS. In this study, the effects of acute and chronic administration of nicotine on DOI-induced head twitch response (HTR) in male albino ICR mice were evaluated. Both acute and chronic nicotine (daily injections for 10 days) reduced the DOI-induced HTR. Moreover, chronic administration of DOI (1 mg/kg/day for 10 days) resulted in 65% increase in [125I]alpha-bungarotoxin binding in cerebellum and 41% increase in striatal [3H]cytisine binding. However, the acute inhibitory effects of nicotine were not blocked by pretreatment with the nicotinic antagonist, mecamylamine. Indeed, at higher doses, mecamylamine also reduced the DOI-induced HTR. The data suggest that both nicotine and mecamylamine may be of therapeutic potential in the treatment of some symptoms of TS.

Delta-9-tetrahydrocannabinol differentially suppresses cisplatin-induced emesis and indices of motor function via cannabinoid CB(1) receptors in the least shrew

We have recently shown that the cannabinoid CB(1) receptor antagonist, SR 141716A, produces emesis in the least shrew (Cryptotis parva) in a dose- and route-dependent manner. This effect was blocked by delta-9-tetrahydrocannabinol (Delta(9)-THC). The present study investigates the cannabinoid receptor mechanisms by which Delta(9)-THC produces its antiemetic effects against cisplatin (20 mg/kg, i.p.)-induced emesis as well as its cannabimimetic activity profile (motor reduction) in the least shrew. Intraperitoneal administration of Delta(9)-THC (1, 2.5, 5 and 10 mg/kg) dose-dependently reduced both the percentage of animals vomiting (ID(50)=1.8+/-1.6 mg/kg) and the frequency of vomits (ID(50)=0.36+/-1.18 mg/kg) in a potent manner. The lowest significantly effective antiemetic dose of Delta(9)-THC for the latter emesis parameters was 2.5 mg/kg. Although Delta(9)-THC reduced the frequency of vomits up to 98%, it failed to completely protect all tested shrews from vomiting (80% protection). The cannabinoid CB(1) antagonist (SR 141716A) and not the CB(2) antagonist (SR 144528), reversed the antiemetic effects of Delta(9)-THC in a dose-dependent fashion. Delta(9)-THC (1, 5, 10 and 20 mg/kg, ip) suppressed locomotor parameters (spontaneous locomotor activity, duration of movement and rearing frequency) in a biphasic manner and only the 20-mg/kg dose simultaneously suppressed the triad of locomotor parameters to a significant degree. Subcutaneous (1-10 mg/kg) and intraperitoneal (0.05-40 mg/kg) injection of some doses of SR 141716A caused significant reductions in one or more components of the triad of locomotor parameters but these reductions were not dose dependent. Subcutaneous injection of SR 141716A (0.2, 1, 5 and 10 mg/kg) reversed the motor suppressant effects of a 20-mg/kg dose of Delta(9)-THC (ip) in a dose-dependent manner. Relative to its motor suppressant effects, Delta(9)-THC is a more potent antiemetic agent. Both effects are probably mediated via CB(1) receptors in distinct loci.

Acute and chronic effects of cocaine on isolation-induced aggression in mice

The purpose of the present study was to investigate the effects of acute and chronic cocaine administration on aggressive behaviour in mice. The animals were made more aggressive by individual housing for a period of 6 weeks. Group-housed anosmic conspecifics which were not aggressive were used as intruder controls. In acute studies, cocaine induced no significant change in aggressive behaviour at low doses (0.5-5 mg/kg) but significantly decreased aggressive behaviour after doses of 10 and 20 mg/kg. Cocaine increased the isolation-induced aggressive behaviour in mice when they were injected twice daily for a week with low doses of 0.5 or 1 mg/kg. In particular, the latency to first attack was significantly decreased by the drug and the frequency of attack towards the non-aggressive intruder was dramatically increased. Higher cocaine doses (10 or 20 mg/kg) under the described treatment regimen decreased these agonistic repertories. Tolerance did not develop to the anti-aggressive effects of high doses of cocaine on continued treatment.

Involvement of other neurotransmitters in behaviors induced by the cannabinoid CB1 receptor antagonist SR 141716A in naive mice

The receptor mechanisms by which the selective cannabinoid CB1 receptor antagonist/inverse agonist, SR 141716A [N-piperidino-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-3-pyraz ole-carboxamide] produces scratching and head-twitch response (HTR) in naive mice were examined. Acute intraperitoneal administration of varying doses of SR 141716A produced both scratchings (ED50 = 3.9 mg/kg) and head-twitches (ED50 = 4.6 mg/kg) in a dose-dependent manner. A dose of 10 mg/kg SR 141716A was used to induce the cited behaviors for drug interaction studies. The selective 5-HT2A/C receptor antagonist, SR 46349B [trans-4-[(3Z)3-(2-dimethylaminoethyl) oxyimino-3-(2-fluorophenyl) propen-1-yl] phenol] potently and completely blocked the head-twitches produced by SR 141716A (ID50 = 0.08 mg/kg). The induced scratching behavior was partially (68%) and less potently (ID50 = 0.6 mg/kg) blocked by SR 46349B pretreatment. The AMPA/kainate receptor antagonist, CNQX [6-cyano-7-nitroquinoxaline-2,3-dione], partially attenuated (68-78%) the induced scratching and head-twitching behaviors. On the contrary, the selective NMDA antagonist, AP-3 [(+/-)-2-amino-3-phosphonopropionic acid], had no significant effect on these behaviors. The selective tachykinin NK1 antagonist, CP 94, 994 [(+/-)-(2S, 3S)-3-(2-methoxybenzylamino)-2-phenylpiperidine], also partially attenuated both the scratching (64%) and the head-twitching (76%) symptoms produced by SR 141716A. Since SR 141716A lacks affinity for the discussed receptors, it appears that the induction of the cited behaviors probably involve indirect activation of their respective neurotransmitter systems.

Delta(9)-tetrahydrocannabinol and synthetic cannabinoids prevent emesis produced by the cannabinoid CB(1) receptor antagonist/inverse agonist SR 141716A

There is substantial clinical evidence that Delta(9)-tetrahydrocannabinol (Delta(9)-THC) and its synthetic analogs (nabilone and levonantradol) can prevent emesis in cancer patients receiving chemotherapy. Limited available animal studies also support the antiemetic potential of these cannabinoids. The present study investigates the mechanism of antiemetic action of cannabinoids in an established animal model of emesis, the least shew (Cryptotis parva). Since cannabinoid agonists prevent emesis, it was hypothesized that blockade of either the cannabinoid CB(1) receptor or the cannabinoid CB(2) receptor would induce vomiting. Thus, the emetic potential of SR 141716A (CB(1) receptor antagonist) or SR 144528 (CB(2) receptor antagonist) was investigated. Both intraperitoneal (0, 1, 2.5, 5, 10 and 20 mg/kg, n = 7-15 per group) and subcutaneous (0, 10, 20 and 40 mg/kg, n = 6-9 per group) administration of SR 141716A caused emesis (ED(50) = 5.52 +/- 1.23 and 20.2 +/- 1.02 mg/kg, respectively) in the least shrew in a dose-dependent manner. Indeed, both the frequency of emesis and the percentage of animals vomiting increased with increasing doses of SR 141716A. Significant effects were seen at the 10- and 20-mg/kg doses for the IP route, while only the 40-mg/kg dose produced significant emesis via the SC route. The CB(2) antagonist failed to produce emesis via either route of administration. SR 141716A at an IP dose of 20 mg/kg was used to induce emesis for drug interaction studies. Thus, varying doses of three different classes of cannabinoid agonists [CP 55, 940 (0, 0.1, 0.5 and 1 mg/kg), WIN 55, 212-2 (0, 1, 5 and 10 mg/kg), and Delta(9)-THC (0, 5, 10 and 20 mg/kg)], were administered IP to different groups of shrews 10 min prior to SR 141716A injection. The frequency of emesis was recorded for 30 min following the administration of SR 141716A. The order of potency for redcing both the frequency of emesis and the percentage of shrews vomiting was CP 55, 940 > WIN 55, 212-2 > Delta(9)-THC which is consistent with an action on the CB(1) receptor. These results suggest that the antiemetic activity of Delta(9)-THC and its synthetic analogs reside in their ability to stimulate the cannabinoid CB(1) receptor. Furthermore, the antiemetic potency of CP 55, 940 is 45 times greater than Delta(9)-THC. On the other hand, blockade of CB(1) receptors can induce vomiting, which implicates an important role for endogenous cannabinoids in emetic circuits.

Cannabinoids of diverse structure inhibit two DOI-induced 5-HT(2A) receptor-mediated behaviors in mice

We have recently shown that the selective cannabinoid CB(1) receptor antagonist SR 141716A produces robust frequencies of head-twitch response (HTR) and ear-scratch response (ESR) in drug-naive mice. Both behaviors were potently blocked by the selective 5-HT(2A/C) receptor antagonist SR 46349B. Selective 5-HT(2A/C) agonists such as DOI also produce these behaviors in mice. The purpose of the present study was to: (1) investigate whether Delta(9)-tetrahydrocannabinol (Delta(9)-THC) and its analogs [Delta(8)-tetrahydrocannabinol (Delta(8)-THC), HU-210, CP 55,940, and WIN 55,212-2] can prevent the DOI-induced behaviors and (2) to see whether any correlation exists in the ID(50) potency order of these cannabinoids in inhibiting the DOI-induced HTR and ESR relative to their published ED(50) potency profiles in producing the tetrad of behaviors in mice. Thus, at 0 min, different groups of mice were injected intraperitoneally with either vehicle or varying doses of the following cannabinoids: Delta(9)-THC (0.25-20 mg/kg), Delta(8)-THC (2.5-20 mg/kg), HU-210 (0.02-0.5 mg/kg), CP 55,940 (0.004-0.5 mg/kg), and WIN 55,212-2 (0.5-10 mg/kg). Twenty minutes later, each mouse received an intraperitoneal injection of DOI (1 mg/kg) and the frequencies of DOI-induced behaviors (mean +/- S.E.M.) were recorded for the next 20 min. The tested cannabinoids reduced the frequencies of both DOI-induced HTR and ESR in a dose-dependent fashion. HU-210 was the most potent inhibitor of HTR, whereas CP 55,940 was most effective against ESR. The ID(50) potency order of cannabinoids in blocking the HTR is: HU-210 > CP 55,940 > WIN 55,212-2 > Delta(9)-THC > Delta(8)-THC, which is identical to their published order of potency in producing the tetrad of behaviors in mice. On the other hand, they had the following ID(50) potency order against the ESR: CP 55,940 > HU-210 > WIN 55,212-2 > Delta(9)-THC > Delta(8)-THC. The tested cannabinoids were 3-30 times more potent in preventing the ESR than the HTR. The data show that cannabinoids inhibit 5-HT(2A) receptor-mediated functions in a potent but differential manner.

The role of D2 and D3 dopamine receptors in the mediation of emesis in Cryptotis parva (the least shrew)

This study introduces Cryptotis parva (the least shrew) as a new dopaminergic animal model of emesis. The potential emetogenic effects of a nonselective dopamine agonist [apomorphine], two D1 agonists [SKF-38393 and SKF-82958], a D2 preferring agonist [quinpirole], and two D3-preferring agonists [7-(OH) DPAT and PD 128, 907] were investigated. Intraperitoneal administration of D1 agonists failed to induce emesis. However, other agonists caused a dose-dependent increase in the percentage of animals vomiting as well as potentiating the mean frequency of emesis with the following ED50, potency order: 7-(OH) DPAT < apomorphine < quinpirole < PD 128, 907. For antagonist studies a 2 mg/kg dose of these agonists were used to induce emesis. Thus, the inhibitory dose-response effects of a D2-preferring [sulpride], a D3-preferring [U 99194A] and combination of varying doses of these antagonists [sulpride + U 99194A] were evaluated on the ability of the cited agonists to produce vomiting. Sulpride decreased the number of shrews vomiting and the mean vomiting frequency produced by the cited agonists in a dose-dependent fashion with the following ID50 order [apomorphine < PD 128, 907 < 7-(OH) DPAT < quinpirole]. By itself, U 99194A failed to significantly alter the emesis produced by any of the cited agonists, however, it potentiated (3-8 times) the antiemetic effects of sulpride both in reducing the number of shrews vomiting as well as decreasing the mean vomiting frequency with the following ID50 order: PD 128, 907 < 7-(OH) DPAT < quinpirole. However, U 99194A attenuated the potent antiemetic effect of sulpride on the apomorphine-induced emesis. The results suggest that the tested agonists primarily activate dopamine D2 receptors to induce emesis in the least shrew whereas activation of D3 sites potentiate the vomiting action of D2 dopamine receptors.

Early postnatal cocaine exposure causes sequential, dose-dependent, enduring but reversible supersensitivity in 5-HT2A receptor-mediated function during development in male mice

This report investigated whether postnatal exposure to cocaine affects the index of 5-HT2A receptor function during development by utilizing the ability of the 5-HT2A/C agonist DOI to induce the head-twitch response (HTR) in mice. Thus, several groups of mice litters were treated with varying doses of cocaine (0, 0.5, 1, 5, and 10 mg/kg, IP) twice daily from postnatal days 5 to 14. Then, different groups of cocaine-exposed male mice pups along with their corresponding age-matched vehicle-exposed control groups were HTR tested once during development on the following postnatal test days: 15, 16, 18, 20, 30, 45, and 60. The HTR testing involved administration of DOI (0.5 mg/kg, IP) and counting the frequency of the behavior for the next 20 min. Cocaine exposure caused bell-shaped, dose-dependent, enduring but reversible increase in DOI-induced HTR frequency (mean +/- SEM) during development. The developing pups were most sensitive to low and intermediate doses of cocaine (0.5-5 mg/kg). The greatest degree of increase in HTR frequency in response to DOI challenge occurred in the 1 mg/kg cocaine-exposure group on most test days. The onset of HTR supersensitivity varied from 48 h (5 mg/kg) to 144 h (0.5 mg/kg) following the termination of chronic cocaine exposure. Moreover, maximal supersensitivity for the latter doses of cocaine occurred 96 and 384 h postcocaine treatment, respectively. Other cocaine exposure groups attained their maxima sometime between the latter time periods. The duration of persistence of 5-HT2A receptor supersensitivity varied with different doses of cocaine: the 10-mg/kg group was supersensitive up to 384 h postcocaine treatment, the 1- and 5-mg/kg groups up to 744 h; and the 0.5-mg/kg group up to 1104 h. Although developmentally cocaine-exposed pups exhibit some similarities (i.e., exquisite sensitivity and bell-shaped dose-response) in 5-HT2A receptor adaptation to mature adult mice exposed to cocaine, they also differ from mature adult cocaine-exposed mice in the onset of appearance as well as the enduring persistence of the induced supersensitivity.

Inhibition of B16 melanoma metastasis by overexpression of the cysteine proteinase inhibitor cystatin C

Progression to metastasis has been correlated with increased cysteine proteinase activity for a number of tumour types. One mechanism of cysteine proteinase regulation in normal cells is by natural protease inhibitors, the cystatins. Here we further characterize a transfected cell line showing increased cystatin C transcription driven by cytomegalovirus (CMV) promoter/enhancer sequences. Properties of this cystatin C altered cell line such as growth in vitro, lung colonization after tail vein injection in mice, production of cystatin, and cysteine proteinase inhibitor activities were examined. Although there was no difference between the growth rate of the cystatin transfected cell line and that of the control, there was a substantial difference in metastatic ability. No increase was noted in cystatin C secretion into the media for the cystatin C transfected cell line compared with the control transfected cell line. There was, however, a difference in cysteine protease inhibitor activity in the cell-free extracts. These results show that alteration of cystatin C levels by overexpression in B16 melanoma alters properties associated with metastasis.

Serotonin 5-HT3 receptor antagonists prevent cisplatin-induced emesis in Cryptotis parva: a new experimental model of emesis

The aim of this manuscript is to introduce Cryptotis parva (the least shrew) as a new experimental emesis model. The chemotherapeutic agent, cisplatin, caused a dose-dependent increase in the number of animals exhibiting vomiting and retching behaviours with ED50 values of 6.43+/-1 and 7.9+/-1.2 mg/kg, respectively. The frequencies of these parameters were also dose-dependent. Intraperitoneal administration of 5-HT3 receptor antagonists (tropisetron or MDL 72222) prevented cisplatin-induced emesis and retching behaviours in the least shrew by a dose-dependent mechanism with respective ID50 values of 4.28+/-2.8 and 2.05+/-2 for emesis, and 2.71+/-4.5 and 2.52+/-2.59 for retching. Intraperitoneal injection of selective and nonselective 5-HT3 receptor agonists potently, and in a dose-dependent fashion, induced emesis in the least shrew with the following ED50 potency order: 2-methyl 5-HT approximately 5-HT (p > 0.05) <5-HTQ (p < 0.01) <mCPBG (p < 0.001). As with other established experimental animal emesis models, the present data indicate that cisplatin causes emesis by activating 5-HT3 receptors indirectly via release of 5-HT.

Long-term sequential determination of behavioral ontogeny of 5-HT1A and 5-HT2 receptor functions in the rat

Activation of 5-hydroxytryptamine1A (5-HT1A) receptors in rats produces hypothermia and a number of behaviors [hindleg abduction (HLA), lateral head-weaving (LHW), forepaw treading (FPT), flat body posture (FBP), rollover (RO), tremor (T), and straub tail (ST)] known collectively as the serotonin syndrome (SS). Stimulation of 5-HT2A receptors produces wet-dog shakes (WDS), whereas 5-HT2C sites induce back muscle contraction (BMC). We investigated the functional ontogeny of the cited receptors in rat pups on postnatal days (PD) 7, 14, 18, 22, 28, 35, 60, and 120 by using (1) the 5-HT1A agonist 8-hydroxy-2-dipropylaminotetralin (0, 1.25, and 5 mg/kg) to induce the SS and hypothermia and (2) the 5-HT2A/C agonist (+/-)-1-(2, 5-dimethoxy-4-iodophenyl)-2-aminopropane (0, 0.5, and 4 mg/kg) to produce both WDS and BMC. The age of onset for most symptoms of SS [FBP, HLA, RO, and T] was the first week of life. They attained maximal intensities at ages 7 to 14 days, after which their maxima either reduced or dissipated to zero. Per contra, the onset of LHW and FPT required 14 to 18 days, and their maxima developed later. The onset of (+/-)-1-(2, 5-dimethoxy-4-iodophenyl)-2-aminopropane-induced WDS occurred after PD 14, and by PD 18, it reached its maximal intensity, which persisted up to PD 60, after which it declined. The onset of BMC was evident on PD 28 and attained its maximal frequency at ages 90 to 120 days. The results show that different components of SS appear within 14 days of birth, but they mature differentially, whereas the hypothermic effect of 5-HT1A receptors remains relatively constant during aging. The times of onset and maturation of WDS were intermediate (between the second and third weeks of life), whereas BMC required 1 to 2 months for its appearance and maturation.

The silent and selective 5-HT1A antagonist, WAY 100635, produces via an indirect mechanism, a 5-HT2A receptor-mediated behaviour in mice during the day but not at night. Short communication

The head-twitch response (HTR) in rodents is considered to be a functional index for the activation of 5-HT2A receptors. Intraperitoneal administration of the silent and selective 5-HT1A receptor antagonist, WAY 100635, produced the HTR in mice in a dose-dependent bell-shaped manner. The induced behaviour followed a diurnal pattern in that WAY 100635 only produced a robust HTR frequency during the light period of the 24h daily cycle. Pretreatment with the selective 5-HT2A/C receptor antagonist, SR 46349B, potently, and in a dose-dependent manner attenuated the induced behaviour. It appears that WAY 100635 produces the HTR indirectly via disinhibition of endogenous serotonergic inhibitory tone operating on the somatodenritic pulse-modulating 5-HT1A autoreceptors. The latter antagonism seems to potentiate endogenous 5-HT release in serotonergic terminal field synapses which subsequently stimulates postsynaptic 5-HT2A receptors to produce the head-twitch behaviour.

Production of serotonin syndrome by 8-OH DPAT in Cryptotis parva

We have previously shown that the 5-HT2A/C agonist, DOI, potently and in a dose-dependent manner produces the head-twitch response in the least shrew (Cryptotis parva) via the activation of serotonergic 5-HT2A receptors. The purpose of the present study was to determine whether activation of 5-HT1A receptors by its selective agonist, 8-OH DPAT, can induce the serotonin syndrome (SS) in this species. In the rat, the symptoms of SS include: forepaw splaying, hindleg abduction, forepaw treading, flat body posture, tremor, and straub tail. Intraperitoneal (i.p.) administration of 8-OH DPAT produced four classic symptoms (forepaw splaying, hindleg abduction, forepaw treading, and straub tail) of SS in the least shrew in a dose-dependent manner in the 30-min observation period. The mean total cumulative score for all components of SS also significantly increased in intensity in a dose-dependent fashion. Administration of selective 5-HT1A antagonists [S(-)UH 301 or NAN-190] potently blocked the 8-OH DPAT-induced mean total SS score in a dose-dependent manner. Moreover, these antagonists had similar potencies as indicated by their identical ID50 values (0.5 and 0.52 mg/kg respectively). However, unexpectedly and unlike the published findings in the rat, the nonselective 5-HT1A antagonist with b-blocking activity, propranolol, failed to attenuate the induced response in this species. As was expected, the selective 5-HT2A/C antagonist, SR 46349B, did not affect the intensity 8-OH DPAT-induced symptoms. Overall, these data suggest that the SS produced by 8-OH DPAT in the least shrew is mediated via the activation of serotonergic 5-HT1A receptors. In addition, propranolol is not a useful 5-HT1A antagonist in this species.

Cocaine and selective monoamine uptake blockers (sertraline, nisoxetine, and GBR 12935) prevent the d-fenfluramine-induced head-twitch response in mice

Serotonin release subsequent to 5-HT precursor loading mainly occurs via exocytosis. Acute cocaine or sertraline administration promote the ability of 5-HT precursors (e.g. L-tryptophan) to induce the 5-HT2A receptor-mediated head-twitch response (HTR) in rodents. The 5-HT releaser, d-fenfluramine, at behaviorally active doses, can induce the head-twitch response in rodents by releasing cytoplasmic 5-HT via the serotonin uptake carrier working in reverse. The purpose of the present study was to utilize the d-fenfluramine-induced HTR to determine the serotonergic and nonserotonergic components of cocaine's actions on the d-fenfluramine-sensitive pool of cytoplasmic 5-HT. Because a dramatic differential potentiation in HTR frequency is obtained when cocaine is administered prior relative to after L-tryptophan injection, the effects of varying doses of cocaine and the selective serotonin (sertraline), dopamine (DA) (GBR 12935), and norepinephrine (NE) (nisoxetine) uptake blockers were investigated on the d-fenfluramine-induced behavior in two experimental protocols. Thus, each uptake inhibitor was administered either 10 min following (protocol 1) or 10 min prior to (protocol 2) d-fenfluramine injection. All the tested uptake inhibitors attenuated the d-fenfluramine-induced HTR in a dose-dependent manner in both experimental protocols. However, their order of potency in either protocol 1 (nisoxetine > GBR 12935 > cocaine > sertraline) or protocol 2 (cocaine > GBR 12935 > nisoxetine = sertraline) does not agree with in vitro affinity of these drugs for the 5-HT transporter. In addition, the potency order for cocaine and nisoxetine in protocol 1 was significantly reversed in protocol 2. The inhibitory effects of the cited drugs on the d-fenfluramine-induced HTR are discussed in terms of: 1) high doses of selective monoamine uptake blockers may not exhibit as much selectivity for their target uptake sites as indicated by in vitro tests; and 2) possible pharmacokinetic interactions between d-fenfluramine and the monoamine uptake blockers.

Prolonged deficits in presynaptic serotonin function following withdrawal from chronic cocaine exposure as revealed by 5-HTP-induced head-twitch response in mice

Recent in vivo microdialysis studies have indicated that presynaptic deficits occur in brain 5-HT neurochemistry during cocaine withdrawal. The purpose of the present study was to utilize the head-twitch response (HTR) produced by 5-hydroxytryptophan (5-HTP) to investigate the dose- and time-response effects of this deficit. The HTR is considered to be a sensitive model for activation of central postsynaptic 5-HT2A receptors in rodents. Thus, different groups of mice were injected with cocaine twice daily (0, 0.1, 0.5, 2.5, 5 or 10 mg/kg, i.p.) for 7 or 13 days. During HTR testing, at 24 h following last injection, the treated mice received either 1) no cocaine; 2) their corresponding daily dose as challenge injection; or 3) a 10 mg/kg challenge dose. In a second series of experiments, extended abstinence studies were performed under the conditions of experimental protocols 1 and 2 for both 7- and 13-day cocaine (0, 0.5 and 5 mg/kg, twice daily) exposure regimens at 24, 48, 72 and 96 h following last cocaine injection. In protocol 3, the effects of a 10 mg/kg challenge dose of cocaine were studied following prolonged withdrawal from chronic cocaine exposure (0, 0.5, 5 and 10 mg/kg, twice daily for 7 and 13 days) at 24, 96 and 240 h abstinence. In experimental protocol 1 at 24 h abstinence in the 7 day exposure group, only lower doses of cocaine (0.5-2.5 mg/kg) significantly attenuated the 5-HTP-induced HTR. The deficit in 0.5 mg/kg group persisted up to 72 h abstinence. Although in the 13 day cocaine exposure groups (experimental paradigm 1) mean HTRs were generally reduced, they however failed to attain statistical significance throughout the 96 h abstinence. In protocol 2 very low challenge doses of cocaine (0.1-0.5 mg/kg) in their corresponding pretreatment groups significantly reduced the behavior at diverse abstinence intervals in both 7- and 13-day exposure regimens relative to their chronically vehicle-treated controls which had received a vehicle challenge injection during HTR testing. Unlike small doses of cocaine, larger challenge doses (5-10 mg/kg) of the stimulant potentiated the HTR score at various abstinence periods. However, the degree of the potentiations are considerably less than the ability of acute cocaine administration in enhancing the 5-HTP-induced HTR. The 10 mg/kg challenge injection in experimental protocol 3 at 24 h abstinence in the 7-day exposed mice attenuated the 5-HTP-induced HTR in 0.5, 5 and 10 mg/kg cocaine-treated groups relative to their chronic vehicle-treated controls receiving a 10 mg/kg challenge cocaine injection. The deficit in chronic 10 mg/kg cocaine-exposed mice persisted up to 240 h postcocaine abstinence. On the other hand, in the 13-day regimen, the challenge 10 mg/kg dose exhibited significant potentiations at 24 h and at 96 h for 5 and 0.5 mg/kg chronic cocaine doses respectively, but it also produced significant deficits in 0.5 and 10 mg/kg chronic doses of cocaine at 240 h abstinence. Overall, the present results suggest that enduring deficits occur in presynaptic serotonin neurochemistry and serotonergic adaptive mechanisms are exquisitely sensitive to chronic administration of low- and high-doses of cocaine.

Deficits in D-fenfluramine-sensitive pool of brain 5-HT following withdrawal from chronic cocaine exposure

Recent head-twitch response (HTR) studies in mice have indicated that withdrawal from chronic cocaine exposure produces deficits in CNS conversion of L-tryptophan to 5-HT. In the present study, the ability of 5-HT releaser, d-fenfluramine, was utilized to induce the HTR in mice following abstinence from chronic cocaine exposure. d-Fenfluramine-induced HTR, is a 5-HT2A receptor-mediated phenomenon and its induction frequency can be regarded as an indirect but in vivo measure of basal brain 5-HT concentration. Thus, different groups of mice were injected with cocaine twice daily (0, 0.1, 0.5, 2.5, 5 or 10 mg/kg, i.p.) for either 7 or 13 days. At 24 h after last cocaine injection, the treated mice received d-fenfluramine (5 mg/kg, i.p.) and the induced HTR (mean+/-SEM) was recorded for the next 30 min. Cocaine attenuated the d-fenfluramine-induced HTR frequency by 30-37% in the 13-day regimen and significant effects were observed from 0.5 mg/kg dose. At 24 h withdrawal in the 7-day cocaine exposure group, the mean HTR frequencies were attenuated, however, they did not achieve statistical significance. Extended abstinence studies (i.e. 24, 48, 72 and 96 h postwithdrawal) from chronic cocaine exposure (0, 0.5 and 5 mg/kg/day for either 7 or 13 days) indicated that in the 7-day exposure group, significant reductions (26, 39 and 22%) in HTR frequency occurred at 48, 72 and 96 h following withdrawal from 0.5 mg/kg cocaine, whereas its 5 mg/kg dose failed to induce a significant effect. In the 13-day exposure group significant reductions in HTR frequency were observed at 24 h abstinence (27%) for the 0.5 mg/kg cocaine dose and at 24 and 48 h for the 5 mg/kg. Overall, these results indicate that abstinence from chronic exposure to cocaine produces enduring deficits in basal 5-HT concentration. Lastly, serotonergic function appears to be uniquely sensitive to chronic administration of low doses of cocaine.

Withdrawal from chronic cocaine administration causes prolonged deficits in L-tryptophan-induced head-twitch response in mice

Withdrawal from chronic cocaine exposure potentiates the ability of direct 5-HT2A agonists to induce the head-twitch response (HTR) in rodents. This supersensitivity is assumed to be a consequence of cocaine-induced deficits in presynaptic serotonin neurochemistry. The present study utilized the HTR produced by L-tryptophan (TP) to investigate the dose- and time-response effects of cocaine-induced 5-HT deficit. Thus, different groups of mice were injected with cocaine twice daily (0, 0.1, 0.5, 2.5, 5 or 10 mg/kg, i.p.) for 7 or 13 days. During HTR testing procedure, at 24 h after last chronic injection, treated-mice received either: 1) no cocaine; 2) their corresponding daily dose; or 3) a 10 mg/kg dose. In paradigm 1, the frequency of TP-induced HTR was attenuated in a dose-dependent manner in both chronic cocaine regimens. In paradigm 2, small challenge doses (0.1-2.5 mg/kg) of cocaine in their respective pretreatment groups failed to alter HTR, but larger challenge doses (5 and 10 mg/kg) potentiated the behavior. In paradigm 3, the 10 mg/kg challenge dose potentiated the HTR to a similar degree in both chronically exposed vehicle and various cocaine-treated groups in both treatment regimens. Extended withdrawal studies from cocaine exposure (0, 0.5 and 5 mg/kg twice daily for 7 or 13 days) indicated attenuations in HTR persisted up to 96 h postcocaine abstinence in paradigm 1, whereas paradigm 2 revealed significant attenuations between 48-72 h for 0.5 mg/kg dose; and potentiations for the 5 mg/kg dose persisted throughout the 96 h abstinence. In paradigm 3, no significant effect was observed at 96 h abstinence, but the 10 mg/kg challenge dose significantly potentiated HTR in chronically exposed 10 mg/kg cocaine group 10 days following cocaine abstinence in both exposure regimens. Overall, these results support the notion that chronic cocaine exposure produces prolonged deficits in presynaptic serotonin neurochemistry. Furthermore, serotonergic mechanisms appear to be exquisitely sensitive to chronic administration of both low and high doses of cocaine.

Clobenzorex: evidence for amphetamine-like behavioral actions

Clobenzorex, an optically active N-substituted derivative of (+)amphetamine, has been identified on the illicit market. Because so little is known regarding the pharmacology or abuse potential of this agent, it was examined in tests of stimulus generalization in rats trained to discriminate 1 mg/kg of (+)amphetamine from vehicle to determine if it would produce amphetamine-appropriate responding. Clobenzorex (ED50 = 6.6 mg/kg) substituted for (+)amphetamine (ED50 = 0.3 mg/kg) but was approximately twenty times less potent than the training drug. Clobenzorex was also compared with (+)amphetamine and cocaine for its ability to induce locomotor stimulation and rearing frequency in mice. Clobenzorex was active in both assays but was less potent than either (+)amphetamine or cocaine. It is concluded that, although weaker than (+)amphetamine, clobenzorex constitutes an agent with amphetamine-like central stimulant behavioral properties.

Differential ontogenesis of three DOI-induced behaviors in mice

Our previous studies have shown that intraperitoneal administration of DOI [(+/-)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane] simultaneously produces the head-twitch and ear-scratch responses (HTR and ESR, respectively) in mice via activation of 5-HT2A receptors. In the present study, we have investigated the ontogeny of these DOI-induced behaviors in both male and female mice across a wide age range (i.e., postnatal days 7, 14, 18, 22, 28, 35, 42, 63, 120, and 180). We also measured the effects of DOI on the locomotor activity of these mice. In addition to the vehicle, 2 doses of DOI (1 and 2.5 mg/kg) were used in age-matched different male and female groups. The age of onset for significant production of HTR and ESR by both doses of DOI were between postpartum days 14-18 and 18-22, respectively. Maximal HTR frequency to both doses of DOI (66 and 94 HTRs) occurred on postpartum day 28. Thereafter, the HTR frequency tended to decrease with increasing age, but the attenuation did not attain significance. On the other hand, maximal ESR score (37 and 60 ESRs) generally developed between postpartum days 22-35 for the cited doses of DOI. After 35 days of age, the ESR frequency dramatically decreased and, by postnatal day 180, no significant response was obtained to either dose of DOI. Age-matched vehicle-treated male and female control groups exhibited few (1-8) HTRs and ESRs across the age range tested. DOI dose-dependently enhanced locomotor activity in both male and female mice relative to their age- and sex-matched vehicle-treated controls for the first 28 days of life. Thereafter, no significant effect was observed. None of the cited behaviors exhibited gender differences across the age range tested. The present results suggest that DOI-induced changes in HTR, ESR, and locomotor activity develop and mature differentially, but in a similar manner, in male and female mice. Furthermore, unlike DOI-induced HTR, the ability of DOI to produce ear-scratches and to enhance locomotor activity in mice disappears with old age.

The stimulatory and inhibitory components of cocaine's actions on the 5-HTP-induced 5-HT2A receptor response

Previously we have shown that cocaine attenuates the 5-HT2A receptor-mediated head-twitch response (HTR) in mice produced by the 5-HT2A/C direct agonist (+/-)-1 (2.5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI). This inhibition appears to be due to cocaine-induced indirect stimulation of the inhibitory serotonergic 5-HT1A and noradrenergic alpha 2 receptors via the inhibition of reuptake of synaptic serotonin (5-HT) and norepinephrine (NE), respectively. In the present study, we investigated the effects of cocaine, its phenyltropane analogue WIN 35428, and the selective 5-HT (sertraline). NE (nisoxetine) and dopamine (DA) (GBR 12935) reuptake inhibitors on the 5-hydroxytryptophan (5-HTP)-induced HTR. We utilized two experimental protocols where cocaine or the cited drugs were administered either after (protocol 1) or prior (protocol 2) to 5-HTP injection. Cocaine in both protocols produced a dose-dependent enhancement in the 5-HTP-induced HTR (ED50 4.68 +/- 1.21 and 3.55 +/- 1.31, respectively). Sertraline was more potent (ED50 2.64 +/- 1.1 and 2.1 +/- 1.54, respectively) in enhancing the induced behavior and dose by dose produced greater (3 to 10 times) HTRs than cocaine. On the other hand, nisoxetine dose dependently and completely attenuated the induced behavior (ID50 3.33 +/- 1.32 and 1.72 +/- 1.34, respectively), whereas GBR 12935 only at high doses (ID50 15.34 +/- 1.52 and 11.91 +/- 1.3, respectively) decreased the induced response. The inability of cocaine to induce as many HTRs as sertraline appears to lie in its ability to also indirectly stimulate the inhibitory 5-HT1A and alpha 2 receptors because the stimulant caused greater enhancement in the 5-HTP-induced HTRs in the presence of their corresponding antagonists [S(-)-UH 301 and yohimbine, respectively]. WIN 35428 was more potent (ED50 2.87 +/- 1.3 and 1.79 +/- 1.1 for protocols 1 and 2, respectively) in stimulating the 5-HTP-induced HTR and produced a bell-shaped dose-response curve. The results indicate that cocaine enhances the 5-HTP-induced HTR via the inhibition of synaptic 5-HT reuptake. The stimulant also simultaneously attenuates the induced behavior by indirect simulation of the serotonergic 5-HT1A and noradrenergic alpha 2 receptors via inhibition of reuptake of the corresponding monoamines.

The mechanism by which the selective 5-HT1A receptor antagonist S-(-) UH 301 produces head-twitches in mice

Electrophysiological studies indicate that certain 5-HT1A receptor antagonists increase the basal firing rate of some but not all raphe neurons by antagonizing the inhibitory endogenous serotonin tone operating on the somatodendritic pulse-modulating presynaptic 5-HT1A autoreceptors. This effect should enhance the synaptic concentration of 5-HT (5-hydroxytryptamine) in serotonergic terminal fields, which may then activate postsynaptic 5-HT receptors. However, in vivo microdialysis studies show that generally such 5-HT1A antagonists by themselves do not increase the basal 5-HT release but potentiate the ability of serotonin reuptake blockers to increase the neuronal serotonin terminal output in the rat brain via the above mechanism. The purpose of the present study was to determine whether antagonism of the proposed endogenous serotonin tone on the 5-HT1A autoreceptors can potentiate the activity of other postsynaptic serotonin receptors. To this end, we utilized the head-twitch response (HTR) in mice as an in vivo model of postsynaptic 5-HT2A receptor function. The selective and silent 5-HT1A receptor antagonist, S-(-)UH 301, by itself, in a dose-dependent manner, produced the HTR in normal but not in reserpinized animals. The 5-HT2A antagonist, SR 46349B, completely prevented S-(-)UH 301-induced HTR. Pretreatment with S-(-)UH 301 also potentiated 5-hydroxytryptophan (5-HTP)-induced HTR both in normal and in the reserpinized mice. At low doses (0.06-0.25 mg/kg), the 5-HT2A selective agonist, 8-OH DPAT, significantly but partially inhibited 5-HTP-induced HTR. However, further attenuation was not observed following the administration of larger doses of 8-OH DPAT. Depending upon the dose used, S-(-)UH 301 pretreatment not only antagonized but also broke through the inhibitory effect of 8-OH DPAT on 5-HTP-induced HTR. The selective (sertraline) and nonselective (cocaine) serotonin reuptake blockers potentiated the ability of 5-HTP to induce the head-twitch behavior in mice. Pretreatment with S-(-)UH 301 enhanced the potentiating effect of serotonin reuptake blockers on the 5-HTP induced HTR. These results suggest that an endogenous 5-HT tone via the discussed mechanism controls the terminal field synapticactivity of serotonergic neurons in mice. In addition, disinhibition of pulse-modulating 5-HT1A autoreceptors by S-(-)UH 301 can potentiate the synaptic effects of serotonin reuptake blockers as well as the serotonin precursor 5-HTP. However, a more firm general conclusion regarding antagonism of presynaptic 5-HT1A receptors leading to indirect functional enhancement of other postsynaptic serotonergic receptors can only be made when the above hypothesis is further tested with other selective 5-HT1A receptor antagonists (such as WAY 100 635), which we were unable to obtain. The present study is the first report to show that a selective 5-HT1A antagonist by itself can produce a serotonin-mediated function via indirect stimulation of another serotonin receptor subtype in mice.

Differential potentiation of L-tryptophan-induced head-twitch response in mice by cocaine and sertraline

Using selective monoamine uptake blockers and appropriate selective monoamine receptor antagonists, we have previously shown that cocaine enhances the frequency of 5-HT2A receptor-mediated 5-hydroxytryptophan (5-HTP)-induced head-twitch response (HTR) in mice via inhibition of serotonin uptake. Concomitantly, cocaine prevented the maximal producible HTR frequency via simultaneous indirect stimulation of the inhibitory presynaptic 5-HT1A and postsynaptic alpha 2 receptors. In the present study, we have investigated the effects of cocaine and the selective 5-HT (sertraline), norepinephrine (nisoxetine) and dopamine (GBR 12935) uptake inhibitors on the L-tryptophan-induced HTR in the presence of a nonselective monoamine oxidase inhibitor, tranylcypromine. We utilized two experimental protocols where cocaine or sertraline were administered either after (protocol 1) or prior to (protocol 2) L-tryptophan injection. Cocaine potentiated the ability of L-tryptophan to induce HTR to a greater extent in protocol 1, whereas sertraline induced a greater effect in protocol 2. However, in our earlier study cocaine (and also sertraline) up to 10 mg/kg produced a similar degree of potentiation in both experimental protocols on the 5-HTP-induced HTR. Furthermore, as in the latter study on the 5-HTP-induced HTR, in the present investigation nisoxetine potently attenuated whereas GBR 12935 did not modulate the induced HTR. The results show that the respective serotonergic and noradrenergic effects of cocaine also operate on the L-tryptophan-induced HTR. The differential effects of cocaine and sertraline in experimental protocols 1 and 2 on the L-tryptophan- versus 5-HTP-induced HTRs suggest that cocaine has additional effects on the conversion of L-tryptophan to 5-HT.

Behavioral effects of (+/-)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane, (DOI) in the elevated plus-maze test

The serotonin (5-hydroxytryptamine, 5-HT) system has consistently been implicated in the actions of (+/-)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) and other hallucinogens. Recent evidence suggest that the 5-HT2A/2C receptor subtypes may be major targets for such drugs in the CNS. DOI-treated hooded rats (0.1-5.0 mg/kg) and DOI treated ICR mice (0.1-2.0 mg/kg), displayed aversions at lower doses and anti-aversions at higher doses to the open arms of the plus-maze. Mianserin (0.5 mg/kg) and ketanserin (0.1 mg/kg) blocked the anti-aversive behavior, but only mianserin was effective at reversing the aversions produced by the higher doses of DOI in the ICR mice. DOI produced an intense aversion in the DBA/2 and anti-aversion in the C57/BL6 mice to the open arms of the plus-maze. These opposing actions of DOI in the plus-maze may be exploited in studying the neurobehavioral effects of hallucinogens. Since flumazenil was ineffective at blocking the DOI induced changes, it was concluded that the mechanism of DOI induced anxiolysis or anxiogenesis may not involve an action at the benzodiazepine receptors.

Temporal differential adaptation of head-twitch and ear-scratch responses following administration of challenge doses of DOI

Previously, we reported that administration of the 5-HT2A/C receptor agonist, DOI [(+/-)-1-(2,5-Dimethoxy-4-iodophenyl)-2-aminopropane], can simultaneously produce the head-twitch response (HTR) and the ear-scratch response (ESR) in mice. Our recent studies have indicated that the HTR is a 5-HT2A receptor-mediated phenomenon, whereas the ESR is probably a 5-HT2C receptor-mediated event. The HTR and ESR exhibit subsensitivity to a challenge dose of DOI (2.5 mg/kg) administered 24 h after its acute or termination of its chronic (2.5 mg/kg, once daily for 13 days) administration. When the dose interval for the challenge dose of DOI was increased to 48 h, both the acute- and chronically treated mice exhibited a simultaneous supersensitive HTR response and a subsensitive ESR effect. The purpose of the present study was to investigate the dose-response effects of lower challenge doses of DOI 48 h following their respective first injections as well as determining the effects of repeated DOI injections at 2-h intervals for 8 h. Thus, in the present study, initial administration of DOI produced a dose- and time-dependent increase in the mean frequencies of both HTR and ESR. Significant HTRs were observed after administration of the lowest tested dose of DOI (0.25 mg/kg), whereas a robust frequency of ESR was only evident at 1 mg/kg or greater doses of DOI. A 48-h challenge administration of lower doses of DOI (0.25 and 0.5 mg/kg) did not significantly affect their respective first injection HTR scores.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of acute cocaine administration on the DOI-induced head-twitch response in reserpinized mice

Previously it was shown that acute cocaine administration dose dependently reduces the 5-HT2-receptor-mediated DOI [(+/-)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane]-induced head-twitch response (HTR) in mice via indirect stimulation of the inhibitory adrenergic alpha 2- and serotonergic 5-HT1A receptors. In addition, the inhibitory capacity of cocaine was enhanced fourfold in mice with 5-HT2-receptor supersensitivity induced by a single injection of DOI 48 h prior to experimentation. The aim of the present investigation was to determine the inhibitory capacity of cocaine in reserpinized mice. A single injection of reserpine 48 h prior to DOI administration caused supersensitivity in the DOI-induced HTR. Two reserpine injections did not further enhance this supersensitivity effect. Once reserpinized 5-HT2-receptor supersensitive animals were less responsive to the inhibitory effects of cocaine on the DOI-induced behavior than were the mice, as reported previously, that were made supersensitive by DOI pretreatment. The inhibitory capacity of cocaine was further attenuated when mice were reserpinized twice prior to determination of its effects on the DOI-induced behavior. Taken together with previously published data, the present investigation lends further support for the importance of endogenous levels of 5-HT and norepinephrine on the ability of cocaine to attenuate the DOI-induced HTR.

The head-twitch response in the least shrew (Cryptotis parva) is a 5-HT2- and not a 5-HT1C-mediated phenomenon

Our initial studies suggested that the 5-HT2/1C agonist (+/-)-1-(2,5-dimethoxy-4-iodophenyl-2-aminopropane [(+/-)-DOI] produces both the head-twitch response (HTR) and the ear-scratch response (ESR) in mice via stimulation of 5-HT2 receptors. However, challenge studies revealed that these behaviors are produced via two different receptors (possibly 5-HT2 and 5-HT1C). Due to a lack of selective agents one cannot designate a particular response for the activation of a specific receptor. The purpose of the present study was to investigate such behaviors in the least shrew, which is more sensitive to (+/-)-DOI than rodents. IP injection of (+/-)-DOI in shrews produced a dose-dependent (bell-shaped) and time-dependent increase in the HTR frequency. The (+/-)-DOI-induced HTR was equipotently and completely attenuated by the 5-HT2/1C antagonists ketanserin and spiperone. The 5-HT1C antagonist with 5-HT2 agonist action, lisuride, also produced the HTR in a bell-shaped dose- and time-dependent fashion. Central injections of both (+/-)-DOI (0.2 microgram) and lisuride (0.5 microgram) also induced the behavior. Both peripheral and central administration of lisuride failed to produce the ESR. (+/-)-DOI significantly induced the ESR only at the highest dose tested (2.5 mg/kg, IP). Centrally administered (+/-)-DOI (0.2 microgram) produced more ESRs relative to vehicle controls; however, the difference did not attain significance. At low doses (0.31 and 0.63 mg/kg), (+/-)-DOI had no effect on locomotor activity, but it significantly attenuated the behavior at larger doses. Both low and high doses of lisuride increased the motor activity. Spiperone dose-dependently suppressed locomotion, whereas ketanserin had no effect. The present results suggest that the HTR is a 5-HT2 receptor-mediated event and changes in locomotor activity do not affect the induced HTR.

Role of the inhibitory adrenergic alpha 2 and serotonergic 5-HT1A components of cocaine's actions on the DOI-induced head-twitch response in 5-HT2-receptor supersensitive mice

It was recently reported that acute cocaine pretreatment can reduce the (+/-)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI)-induced 5-hydroxytryptamine2 (5-HT2)-receptor mediated head-twitch response (HTR) in mice via indirect stimulation of adrenergic alpha 2- and serotonergic 5-HT1A-receptors. The aim of the present investigation was to determine whether cocaine can alter the DOI-induced HTR in 5-HT2-receptor supersensitive mice. Supersensitivity was induced by a single injection of DOI 48 h prior to experimentation. These supersensitive mice exhibited a greater frequency of HTR to a challenge dose of DOI 48 h after its initial administration. Cocaine pretreatment dose-dependently reduced the DOI-induced HTR in the supersensitive mice. The stimulant was approximately four times more potent in the 5-HT2-receptor supersensitive mice relative to its reported effects in normal mice. Receptor blockade studies with yohimbine and alprenolol revealed that both of the inhibitory components of cocaine's actions (i.e., adrenergic alpha 2- and serotonergic 5-HT1A-receptor effects, respectively) were more efficient in reducing the DOI-induced HTR in supersensitive mice compared to normosensitive animals. The present results further support the previously suggested hypothesis that acute cocaine administration inhibits the 5-HT2-receptor function by increasing the synaptic concentration of norepinephrine and serotonin via inhibition of their uptake and therefore indirectly stimulating the respective inhibitory adrenergic alpha 2- and serotonergic 5-HT1A-receptors.

Further evidence for enigmas in adaptation mechanisms for the DOI-induced behaviors

The acute and chronic effects of the 5-hydroxytryptamine2/1C (5-HT2/1C) receptor agonist (+/-)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) and the antagonist ketanserin were evaluated on the DOI-induced 5-HT2 receptor-mediated ear-scratch response (ESR) in mice. A challenge dose of DOI (2.5 mg/kg) administered 24 h following its first injection reduced the ESR frequency by 80-97%. The ESR score attained first injection value when the time lag between the first and the second injection was greater than 72 h. On the other hand, a single administration of ketanserin (1.0 mg/kg) caused no significant effect at 24 or 48 h but significantly reduced (51%, p < 0.05) the DOI-induced ESR 120 h following its injection. Chronic once-daily DOI injections reduced the ESR score by 80-97% throughout the treatment regimen. Following cessation from chronic treatment, the DOI-induced ESR frequency returned to control levels in a time-dependent manner. Repeated ketanserin administration significantly reduced the DOI-induced ESR score by 46% when tested 24 or 48 h following cessation of antagonist administration but had no effect at 78 h. Recently, we reported that 48 h following either a single DOI injection or termination from repeated DOI or ketanserin administration the DOI-induced head-twitch response (HTR) in mice exhibited supersensitivity. Thus, it appears that the DOI-induced behaviors exhibit differential adaptation mechanisms following either agonist or antagonist exposure. These studies further support our hypothesis that serotonergic drugs may have the ability to change independently the 5-HT-receptor sensitivity (signal transduction) and receptor density in the same or opposite directions.(ABSTRACT TRUNCATED AT 250 WORDS)

Behavioral evidence for differential adaptation of the serotonergic system after acute and chronic treatment with (+/- )-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) or ketanserin

The 5-hydroxytryptamine (5-HT)2 agonist (+/- )-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) and antagonist ketanserin were evaluated for acute and chronic effects on the 5-HT2 receptor-mediated head-twitch response (HTR) in mice. A single dose of DOI resulted in tolerance to the DOI-induced HTR at 24 hr but supersensitivity at 48 hr. This apparent supersensitivity persisted up to 144 hr after the first DOI injection. Chronic once daily DOI administration significantly reduced the HTR frequency (days 2-6), which then returned slowly to control levels by treatment day 13. A 48-hr withdrawal from this chronic regimen produced a similar supersensitivity to that observed after a single DOI injection upon a 48-hr challenge. This effect also persisted up to 144 hr after cessation of chronic treatment. Acute pretreatment with a single injection of ketanserin significantly reduced the DOI-induced HTR frequency when tested 24 and 48 hr, but not 120 hr, after injection of the antagonist. After withdrawal from chronic ketanserin treatment, the DOI-induced HTR was significantly reduced at 24 hr but significantly increased at 48 hr. This enhanced effect subsided when mice were tested with DOI 72 hr after cessation of chronic antagonist treatment. These data suggest that the serotonergic system adapts to chronic exposure of either agonists or antagonists in a fashion distinctly different from that exhibited by other monoamine neurotransmitter systems.

Chronic prenatal methadone exposure alters central opioid mu-receptor affinity in both fetal and maternal brain

The effects of chronic prenatal methadone exposure (6.3-9.0 mg/kg/day) via osmotic minipumps to pregnant dams on fetal and maternal brain opioid mu-receptors were assessed on gestation day 20 and day 7 postnatally. By using the 3H-DAMGO binding assay, it was shown that chronic methadone treatment (gestation days 7-20) did not affect mu-receptor capacity in both fetal and maternal brains during gestation day 20, nor when tested 7 days after delivery. However, this chronic exposure decreased mu-receptor affinity in both fetal and maternal brain homogenates when determined on day 20 of pregnancy. Scatchard analysis of binding data in both tissues indicated that the methadone-induced increase in KD returned to control values when tested 7 days after delivery. The change in mu-receptor affinity was not due to competition between 3H-DAMGO and residual methadone. Extensive washing of the brain homogenates failed to alter the affinity of the receptor but decreased the concentration of the residual methadone. This decrease in receptor affinity was also observed in extensively washed brain tissue from female adult rats treated acutely with methadone (9.0 mg/kg, IP) or when brain homogenates were exposed to methadone (50 ng/ml) in vitro. Thus, these data suggest that methadone alters mu-receptor affinity by some unknown mechanism.

Repeated administration of low doses of cocaine enhances the sensitivity of 5-HT2 receptor function

The acute and chronic effects of cocaine were evaluated on the 5-hydroxytryptamine (5-HT)-receptor 5-HT2 mediated behavioral function, the head-twitch response (HTR), in mice. In a recent study, we reported that the (+/-)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane HCl (DOI)-induced HTR was dose dependently reduced by cocaine via indirect stimulation of serotonergic 5-HT1A and adrenergic alpha 2 receptors. In the present investigation, the HTR was evoked by the nonselective 5-HT agonist 5-methoxy-N,N-dimethyltryptamine hydrogen oxolate (5-MeO-DMT). Cocaine by itself failed to produce HTR but dose dependently inhibited the 5-MeO-DMT-induced behavior. Cocaine's effects were not due to 5-HT3 antagonism since acute administration of the more potent 5-HT3 antagonist (ICS-205,930) failed to produce or modify the 5-MeO-DMT-induced behavior. During withdrawal from chronic cocaine treatment (5-20 mg/kg), 5-MeO-DMT-induced HTR was enhanced. Depending upon the cocaine dose used, the induced supersensitivity persisted up to 172 h following cessation of cocaine treatment. The mechanisms of cocaine-induced supersensitivity were further investigated using the more selective 5-HT2 agonist DOI. Withdrawal from a low-dose (0.03-1.25 mg/kg) chronic cocaine treatment caused the DOI-induced HTR to increase, whereas withdrawal from a 5- and 10-mg/kg cocaine regimen had no significant effect. The maximal effect persisted up to 36 h following termination of cocaine treatment. Relative to vehicle-exposed controls, withdrawal from cocaine treatment enhanced the inhibitory potency of the 5-HT1A agonist (+-)-8-hydroxy-2-(di-n-propylamino)tetralin HBr (8-OH-DPAT) on DOI-induced HTR.(ABSTRACT TRUNCATED AT 250 WORDS)

Demonstration of physical dependence following chronic continuous methadone delivery via osmotic minipumps in pregnant rats

The effects of a 14-day (gestation days 7-20) chronic methadone (6.3-9.0 mg/kg/day) infusion via osmotic minipumps were studied on the induction of physical dependence in both pregnant and nonpregnant female rats. Following continued methadone exposure, an acute injection of naloxone (2.0 mg/kg, SC) produced the following symptoms of withdrawal in both pregnant and nonpregnant methadone-exposed rats: increased frequency of head shakes, teeth-chattering and face-rubbing episodes, as well as the induction of burrowing, diarrhea, facial tremor, squeaking and vaginal sniffing. Increased fetal movement in the maternal abdomen was also observed in the pregnant rats. In the saline-exposed pregnant controls, naloxone failed to induce a significant effect. In addition, brain and plasma methadone levels during the various stages of pregnancy (gestation days 8-20) were determined. The methadone levels in plasma were initially variable (gestation days 8-12) but became more constant (approximately 50 ng/ml) from gestation day 14 to 20. Methadone brain levels also followed a similar pattern, except that the brain methadone content was at least 20-fold greater than plasma concentrations at any given time. Thus, relative to the high brain levels, the present data suggest that acute changes in methadone plasma concentration may not be a good index of pharmacological effect.

Acute effects of beclamide on brain regional monoamine concentrations, their metabolites and radioligand binding studies

The effects of beclamide on regional brain monoamine levels and radioligand binding have been studied in rats. One hour oral pre-treatment with beclamide (400 mg kg-1) increased rat striatal dopamine turnover by increasing the levels of its major metabolites (DOPAC and HVA) three-fold. Simultaneously the drug reduced the concentration of striatal dopamine by a similar factor, and the concentrations of 5-hydroxytryptamine, (5-HT), 5-hydroxyindoleacetic acid, (5-HIAA) and 3-methoxytyramine in the striatum were reduced below the detection limits of the assay. In the frontal cortex, beclamide depleted the dopamine, 5-HT and 5-HIAA content whilst having no significant effect on the noradrenaline level. The concentrations of bioamines and their metabolites in the hypothalamus were unaffected by such acute beclamide treatment. In radioligand binding studies beclamide lacked affinity and failed to displace radioligands from alpha 2, beta, 5-HT, 5-HT2 and dopamine D2 sites in selective loci of the rat brain.

Inhibition of 5-HT2 receptor-mediated head-twitch response by cocaine via indirect stimulation of adrenergic alpha 2 and serotonergic 5-HT1A receptors

Cocaine inhibits the 5-HT2-mediated (+/-)-DOI-induced head-twitch response (HTR) in mice in a dose-dependent manner. In order to investigate the possible inhibitory mechanism(s) of cocaine on 5-HT2 receptor function, we studied the effects of the selective adrenergic alpha 2 receptor antagonist yohimbine and the beta-adrenergic/5-HT1 receptor antagonist alprenolol, and the 5-HT3 antagonist ICS 205-930 on the inhibitory action of cocaine on the (+/-)-DOI-induced HTR. Neither yohimbine (0.1 and 0.5 mg/kg) nor alprenolol (10 mg/kg) pretreatment had any significant effect on the (+/-)-DOI-induced HTR. However, both antagonists prevented the inhibitory effects of cocaine on the (+/-)-DOI-induced HTR. The 5-HT3 antagonist ICS 205-930 neither produced HTR nor decreased the (+/-)-DOI-induced HTR frequency. The present results suggest that cocaine inhibits 5-HT2 receptor function by increasing the synaptic concentration of norepinephrine and serotonin via inhibition of their uptake and thus indirectly stimulating the respective inhibitory adrenergic alpha 2 and serotonergic 5-HT1A receptors. Furthermore, cocaine's 5-HT3 antagonist properties appear not to play a role in the inhibition of head-twitch behavior.

Multiple populations of serotonin receptors may modulate the behavioral effects of serotonergic agents

In order to establish a functional role for the various populations of serotonin (5-HT) receptors, behavioral studies have been conducted over the past decade with serotonergic agonists and antagonists. And, although there is reason to believe that certain behavioral effects may be mediated via particular populations of 5-HT receptors, evidence now suggests that some serotonin-mediated behaviors may be modulated by the interaction of serotonergic agents at multiple subtypes of 5-HT receptors. The generality of these effects, and the exact mechanism(s) by which they occur, have yet to be elucidated. Nevertheless, over the past year, results from several different laboratories provide a growing recognition of this novel phenomenon.

Does chronic prenatal methadone exposure affect beta-receptor subtypes in placental, fetal and maternal brain homogenates?

Computer competition analysis of 3H-DHA (3H-dihydroalprenolol, a nonselective beta-adrenergic radioligand) binding in the presence of unlabeled metoprolol (a beta 1-selective antagonist) indicates the existence of both beta 1- and beta 2-adrenergic receptor subtypes in the rat placenta and confirms previous reports that both beta-adrenoceptors are present in adult rat cortex. In the fetal brain (20th day of gestation), however, only beta 1-receptors were detected. Pregnant rats were chronically exposed to methadone from day 7 to day 20 of gestation via implanted osmotic minipumps (6.3-9.0 mg/kg/day). This treatment schedule did not induce a change in the affinity and density of either beta-receptor subtype in the placental, fetal and maternal brain homogenates. The results are discussed in terms of the reported monoaminergic and opiate receptor functional interactions.

Withdrawal from chronic treatment with (+/-)-DOI causes super-sensitivity to 5-HT2 receptor-induced head-twitch behaviour in mice

Mice were injected once daily for 13 days with (+/-)-DOI ((+-)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane) and the induced head-twitch response (HTR) was scored. On days 2-5 HTR was reduced to less than 50% of day 1, and then returned to control levels by day 13. Challenge doses of (+/-)-DOI administered on days 15, 17 or 19 elicited significantly exaggerated responses. Thus, chronic treatment with (+/-)-DOI may cause an initial down-regulation followed by an up-regulation of 5-HT2 receptor function after cessation of such treatment.

Pharmacological characterization of ear-scratch response in mice as a behavioral model for selective 5-HT2-receptor agonists and evidence for 5-HT1B- and 5-HT2-receptor interactions

(+/-) 1-(2,5-Dimethoxy-4-iodophenyl)-2-aminopropane [(+/-)-DOI], a phenylisopropylamine hallucinogen, is a 5-HT2-receptor agonist. The drug induced a dose-dependent increase in ear-scratch response (ESR) in mice, and the R(-)-isomer was more than 6 times as potent as its S(+)-enantiomer. The induced behavior was potently inhibited by selective 5-HT2-receptor antagonists such as ketanserin and spiperone. The (+/-)-DOI-induced ESR is also inhibited by stimulation of 5-HT1-receptors and the inhibition seems to be through a 5-HT1B-receptor mechanism. Thus, taken together, the present investigation indicates that ESR is due to selective stimulation of 5-HT2-receptors and that simultaneous costimulation of 5-HT1B-receptors inhibits the induced behavior. The study further suggests that the inability of the indolealkylamine hallucinogens to induce ESR is due to simultaneous excitation of 5-HT1B-receptors which are inhibitory to induction of ESR. Moreover, the data suggest possible inhibitory control mechanisms through 5-HT1-receptor subtypes to provide a damping mechanism to reduce excessive 5-HT2-receptor excitation due to exogenous drug stimulation or pathological conditions.

Do functional relationships exist between 5-HT1A and 5-HT2 receptors?

To investigate the possible functional relationship between 5-HT1 and 5-HT2 receptors, we studied the effects of a nonselective 5-HT agonist (5-MeO DMT), a 5-HT1A-selective (8-OH-DPAT) and a 5-HT1B/5-HT1C-selective (TFMPP) agonist on the head-twitch behavior induced by the putative 5-HT2-selective receptor agonist (+/-)-DOI. In the mouse (+/-)-DOI produced the head-twitch response in a dose-dependent manner and (-)-DOI was twice as potent as the (+) isomer. Selective 5-HT2 antagonists, ketanserin and spiperone, dose-dependently inhibited the (+/-)-DOI-induced head-twitch response. The nonselective and the 5-HT1A-selective agonists also dose-dependently reduced the behavior, whereas 5-HT1B/5-HT1C-selective agonist (TFMPP) failed to affect the (+/-)-DOI-induced response. Taken together with previously published literature data, we propose a 5-HT1A inhibitory action on the 5-HT2 receptor-mediated response when induced by its selective agonist (+/-)-DOI.

Comparison of the inhibitory action of aminobeclamide and beclamide on socially offensive behaviour

The inhibitory effects of aminobeclamide (N-(p-aminobenzyl)-beta-chloropropionamide) on socially offensive behaviour has been studied and compared with those of the parent drug beclamide (N-benzyl-beta-chloropropionamide). Following oral administration in mice which had been individually housed for a 28 day period then paired with normal group-housed opponents, aminobeclamide and beclamide both produced significant and dose-related inhibition of socially offensive behaviour. Aminobeclamide (20-150 mg kg-1 p.o.) and beclamide (50-250 mg kg-1 p.o.) gave increased offense onset latency whilst at the same time they reduced the incidence of offense encounters/animal and decreased the group percentage of animals displaying offense behaviour. It is likely that both drugs have similar monoamine modifying effects though this animal study suggests that aminobeclamide is 1.5 to 2.7 times more potent than beclamide against socially offensive behaviour.

Effects of beclamide on isolation-induced aggression and locomotor activity in mice

The anti-aggressive effects of orally administered beclamide (N-Benzyl-beta-chloropropionamide) have been studied in male albino mice which were individually isolated for a 28-day period. Beclamide (50-250 mg kg-1 p.o.) caused an overall dose-dependent increase in the attack onset latency, a reduction in the percentage of animals attacking and the mean number of attacks/animal for this model of aggression. In addition, the highest dose of beclamide (250 mg kg-1 p.o.) did not significantly modify locomotor activity in mice. It was concluded that beclamide induced anti-aggressive effects at non-sedative doses. This anti-aggressive action was thought be at least partially mediated, through a beclamide-induced release of 5-HT from presynaptic sites.

Dopamine-mediated behaviour following chronic treatment with B-HT 920

Following subchronic (5-day) dosing with B-HT 920 (2-amino-6-allyl-5,6,7,8-tetrahydro-4H-thiazolo(4,5-d)azepine (1 mg kg-1 day-1 i.p.) in rats there was a significant increase in both apomorphine-induced motor activity and stereotypy. On continued B-HT 920 treatment, however, the enhancement of apomorphine motor activity faded into insignificance but the increase in stereotypy persisted beyond 15 days. The results are discussed in terms of dopamine autoreceptor tolerance, postsynaptic D2 supersensitivity and possible differential effects in different brain loci on the above two receptor sub-classes.

Actions and interactions of adenosine, theophylline and enprofylline on the guinea-pig spirally cut trachea

Adenosine, theophylline and enprofylline induced concentration-dependent relaxations of guinea-pig isolated tracheal spirals whether they had intrinsic tone or were precontracted with carbachol or histamine. The potency order was enprofylline greater than theophylline greater than adenosine and the maximum relaxation in absolute terms was generally less for adenosine. The maximum relaxation (measured in absolute terms of change in tension) induced by the three spasmolytics in preparations with intrinsic tone was generally less than in precontracted tissues. This was attributed to the higher resting tone of precontracted tissues than the intrinsic tone. The adenosine transport inhibitor dipyridamole potentiated adenosine but not theophylline or enprofylline so that the potency order became adenosine greater than enprofylline greater than theophylline. Without dipyridamole, theophylline in a concentration producing 10-30% relaxation of the trachea, failed to antagonize adenosine. However, in the presence of dipyridamole, adenosine was antagonized, indicating that the relaxation by adenosine was mediated via an extracellular P1 receptor. Enprofylline, in a concentration producing equivalent direct effects, failed to antagonize adenosine. It is concluded that the tracheal relaxation by xanthines is independent of adenosine antagonism.