Reduction of guinea pig pup isolation calls by anxiolytic and antidepressant drugs

Guinea pigs possess central 5-HT1D receptors similar to humans but different from rats and mice. In order to study the role of this receptor on animal behaviour, it may be of interest to develop a paradigm measuring affective states in the guinea pig. Therefore we assessed the effects of a variety of psychotropic drugs on guinea pig pup isolation calls. Anxiolytic compounds such as the benzodiazepine receptor agonists diazepam and alprazolam, the full 5-HT1A receptor agonists 8-OH-DPAT and flesinoxan, and alcohol reduced isolation calling by the guinea pig pup. Moreover, mixed antidepressant/anxiolytic compounds like the 5-HT uptake inhibitors fluvoxamine and clomipramine or the MAO-inhibitor clorgyline as well as the antidepressant NA uptake inhibitors desipramine and maprotiline suppressed vocalizations. The 5-HT1D/1A receptor agonist 5-CT was also very effective in reducing separation calls. Remarkably, the partial 5-HT1A receptor agonists buspirone and BMY 7378 did not affect calling. The neuroleptic haloperidol, the psychostimulant d-amphetamine, the putative anxiogenics DMCM and m-CPP and the putative anxiolytics ondansetron and CI-988 had no effect on isolation calls of guinea pig pups. We propose this paradigm could be helpful to assess behavioural effects of anxiolytic and antidepressant drugs in a species different from rat or mouse, and in which the effects of 5-HT1D receptor ligands may possibly be established.

The 5-HT1A receptor is not involved in emotional stress-induced rises in stress hormones

To determine whether emotional stress-induced rises in stress hormone levels are mediated by activation of 5-HT1A receptors, we studied the effects of the selective 5-HT1A receptor antagonist, N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridinyl) cyclohexanecarboxamide trihydrochloride (WAY-100635) on plasma ACTH, corticosterone, prolactin, and glucose levels in the conditioned ultrasonic vocalisation (USV) model in adult rats. The effects of WAY-100635 on USVs were also investigated in this paradigm. WAY-100635 (0.3, 1, and 3 mg/kg SC) had no clear effects on basal plasma ACTH, corticosterone, and glucose levels, but the 3 mg/kg dose significantly increased the plasma prolactin levels. The increases in plasma ACTH, corticosterone, and prolactin levels induced by the USV procedure were not affected by WAY-100635. This indicates that the 5-HT1A receptor does not play a major role in the distress-induced activation of the hypothalamic-pituitary-adrenal axis and prolactin secretion. The USVs were significantly enhanced by low doses of WAY-100635 (0.03 and 0.3 mg/kg SC), whereas higher doses (1.0 and 3.0 mg/kg SC) had no effect. These findings suggest that blockade of 5-HT1A receptors during stress may enhance the behavioural stress-response.

Fear-potentiated startle response is remarkably similar in two laboratories

The fear-potentiated startle response paradigm is used to investigate anxiolytic properties of drugs. The first objective of the present study was to further investigate the predictive validity of this paradigm. The anxiolytics chlordiazepoxide (2.5-10 mg/ kg IP) and oxazepam (1-10 mg/kg PO) and the putative anxiolytic flesinoxan (1-10 mg/kg PO) decreased startle potentiation dose-dependently, indicating an anxiolytic effect. The antidepressant fluvoxamine (5-20 mg/kg PO) did not affect startle potentiation. Ideally, anxiolytic drugs attenuate startle potentiation without affecting control startle levels, although some studies report altered control startle amplitudes. The second objective was to investigate whether different effects on control startle amplitudes are related to different startle devices. Therefore, the drugs were tested in two laboratories. Results showed no significant differences between laboratories, indicating that equipment is not a critical factor in the drug-induced alteration of control startle levels. In an additional experiment, it was shown that flesinoxan (10 mg/kg PO) did not affect strychnine-induced startle potentiation, supporting the idea that the attenuating effect of flesinoxan on the fear-potentiated startle response is due to its anxiolytic properties. Thus, the fear-potentiated startle response paradigm appears a valid and reliable model for anxiolytic properties of drugs.

Neuroendocrine effects of diazepam and flesinoxan in the stress-induced hyperthermia test in mice

In the stress-induced hyperthermia (SIH) paradigm in mice, both a benzodiazepine receptor agonist, diazepam, and a 5-HT1A receptor agonist, flesinoxan, reduced the stress-induced increase in rectal temperature. The SIH procedure itself enhanced plasma ACTH and corticosterone levels but not plasma glucose levels. Diazepam (3, 6, and 12 mg/kg p.o.) did neither affect basal plasma ACTH, corticosterone, or glucose levels, nor did it suppress the stress-induced rises in these parameters. Flesinoxan (1, 3, and 10 mg/kg p.o.) enhanced plasma ACTH and corticosterone concentrations under nonstress conditions but did not affect the stress-induced increases in ACTH and corticosterone secretion. No clear effects of flesinoxan on plasma glucose levels were found. Our results indicate that in mice the anxiolytic effects of diazepam and flesinoxan in the SIH paradigm are not paralleled by a blockade of stress-induced increases in plasma ACTH, corticosterone, and glucose levels.

Effects of infusion of cholinergic drugs into the prefrontal cortex area on delayed matching to position performance in the rat

Rats trained on a Delayed Matching To Position (DMTP) task displayed mediating behavior during delays to solve the task. Infusion of the cholinergic antagonist scopolamine into the medial Prefrontal Cortex area (mPFC), dose dependently impaired performance independent of delay. These results indicate that scopolamine does not specifically affect working memory. Infusion of the cholinesterase inhibitor physostigmine, muscarinic subtype receptor antagonists, the dopamine (D1) antagonist SCH23390, and of the GABA-A receptor antagonist bicuculline, did not affect performance in the DMTP task. In a post-hoc analysis scopolamine was found to impair discriminability in a delay-dependent manner only in animals that used mediating behavior in the majority of the trials. Furthermore, a time sampling method indicated that scopolamine infusions into the mPFC disrupted mediating behavior during the task. Results suggest that cholinergic systems in the mPFC play a role in directing attention to task relevant behavior.

Chronic treatment with eltoprazine does not lead to tolerance in its anti-aggressive action, in contrast to haloperidol

The behavioral effects of eltoprazine and haloperidol during a 4 week treatment period were studied in the resident-intruder model of aggression in male rats. Eltoprazine, a serotonergic (5-HT1A/1B) agonist with specific anti-aggressive actions in animals, was compared to haloperidol, a neuroleptic often used to control behavioral disorders. Eltoprazine (1 or 3 mg/kg p.o.) and haloperidol (2 mg/kg p.o.) were given 60 min before a 10 min aggression test. Acutely, eltoprazine reduced aggression, without adversely affecting other behaviors. Eltoprazine (1 or 3 mg/kg p.o.) was subsequently given daily for 4 weeks and aggression tests were performed each week. The anti-aggressive effects of eltoprazine remained stable over the period of 4 weeks whereas exploration was increased. After a wash-out period of 1 week aggression had returned to baseline levels. Acutely given, haloperidol (2 mg/kg p.o.) completely reduced aggression concomitant with massive sedation. Significant tolerance developed to the sedatory actions of haloperidol over the 4 week treatment period. Aggression returned slowly, but remained below baseline values. One week after wash-out a new challenge with haloperidol (2 mg/kg p.o.) revealed significant tolerance. After 2 weeks wash-out aggression had returned to baseline. The data demonstrate persistent and specific anti-aggressive effects after eltoprazine showing no tolerance. In contrast, haloperidol showed tolerance and rebound effects for aggression. The development of tolerance after haloperidol has a different course for sedation than for the anti-aggressive action.

Stress-induced hyperthermia as a putative anxiety model

In group-housed mice (ten per cage), mice removed last from their home cage always have higher rectal temperatures than mice removed first from this cage. Stress-induced hyperthermia is calculated as the difference (delta T) between the basal temperature (mouse number 1) and the end temperature (mouse number 10) when the temperature of the ten mice is sequentially measured using a 1-min interval between rectal measurements. Using this protocol, various drugs, belonging to different pharmacological classes, were tested in order to investigate their putative anxiolytic effect, measured as a decrease in delta T. Benzodiazepines (diazepam, alprazolam), alcohol, and some (flesinoxan, buspirone), but not all (ipsapirone) 5-HT1A receptor agonists had anxiolytic properties with this protocol. Clonidine (alpha 2-adrenoceptor agonist) and prazosine (alpha 1-adrenoceptor antagonist) had, but at high doses, some anxiolytic actions. Antidepressants (desipramine, fluvoxamine, nomifensine, tianeptine, amitriptyline, clomipramine, imipramine), serotonergic ligands (ondansetron, ketanserin, 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI), fenfluramine, metachlorophenylpiperazine (mCPP), eltoprazine) and various other drugs (phenobarbital, pentetrazol, haloperidol, apomorphine, amphetamine, (+)-N-[1-methyl-2-oxo-5-phenyl-2,3-dihydro-1H-1,4-benzodiazepin-3( R)-yl]- N'-(3-methylphenyl)urea (MSD 365260), dizocilpine and acetyl salicylic acid) had no anxiolytic activity. The stress-induced hyperthermia protocol used was unable to detect anxiogenic properties of drugs, probably due to a (physiological) ceiling in the maximal end temperature. The stress-induced hyperthermia protocol with mice can be used to measure anxiolytic properties of drugs and is a fast and robust model which does not need extensive training of animals.

Relation between stimulus discriminability and response bias in a delayed conditional discrimination task in the rat

The present study investigated whether changes in response bias (log b) affect discriminability (log d) in a delayed conditional discrimination (DCD) task. Eight rats were trained on an DCD task and response bias was manipulated by changing the reinforcement ratio (RR) for correct responding on the two response alternatives. Three findings emerged. First, changes in RR produced changes in log b and the magnitude of these changes was related to the value of the RR. Second, log d was affected by changing RRs. Third, the effect of changes in RR on log b was larger after longer delays. These results suggest that log d and log b are not independent and it is concluded that changes in response bias (log b) may affect the discriminability measure log d. This implies that changes in log d may be mediated by changes in response bias and it is therefore recommended that log d and log b values are both reported when investigating effects of, for example, pharmacological manipulations on DCD performance.

Cholinergic drug effects on a delayed conditional discrimination task in the rat

The centrally acting cholinergic antagonist scopolamine (0.025-0.10 mg/kg ip) and the peripherally acting cholinergic antagonist methyl-scopolamine (0.01-0.10 mg/kg) dose dependently impaired discriminability independent of delay in a delayed conditional discrimination task that precludes use of mediating behavior. This indicates that scopolamine does not specifically affect working memory. Drugs that enhance cholinergic transmission neither improved discriminability nor attenuated scopolamine-induced impairments. In a post hoc analysis scopolamine was found to impair discriminability in a delay-dependent manner in rats that performed at a high level in pretest sessions. Methyl-scopolamine impaired performance independently of delay in these rats. The authors suggest that a ceiling effect at short delays produced this Drug x Delay interaction of scopolamine in the best performing rats.

Serotonin receptors and animal models of aggressive behavior

Various models of rodent agonistic behavior are described, which differentiate between offensive and defensive/flight models. Particular attention is given to one male and one female paradigm for offensive aggression, i.e. resident/intruder or territorial aggression (RI) and maternal aggression (MA). After an overview of the serotonin (5-HT) system in the CNS, a description is given of the ligands available. Subsequently, the effects of various drugs affecting serotonergic transmission in the RI- and MA-paradigms are described. The 5-HT1A receptor agonists busipirone, ipsapirone, and 8-OH-DPAT decreased aggression in RI and MA, but simultaneously led to a marked decrease in social interest and activity, indicative of a nonspecific antiaggressive profile. Nonselective 5-HT1 receptor agonists, such as RU24969, eltoprazine, and TFMPP reduced aggression quite specifically, did not decrease social interest or exploration, and sometimes even increased these behaviors. In RI and MA, the behavioral effects of these drugs were roughly similar. In contrast, MA was more sensitive to treatment with the 5-HT reuptake blocker fluvoxamine, which blocked RI aggression nonspecifically at the highest dose only. DOI, a 5-HT2A/2C# receptor agonist, decreased aggressive behavior and increased inactivity, without affecting social interest and exploration in RI as well as MA. This was, however, accompanied by "wet dog shaking" characteristic of 5-HT2 receptor stimulation. The nonspecific 5-HT receptor agonist (and 5-HT2 receptor antagonist) quipazine also induced "wet dog shaking" at doses which suppressed aggression, social interest, and exploration but increased inactive behaviors (sitting and lying). The discussion delineates a specific role for 5-HT1B receptor-subtype involvement in the modulation of aggression, with the restrictions we clearly face with regard to the lack of specific serotonergic agonists and antagonists for certain receptor subtypes. By and large, male and female rats react similarly to treatment with serotonergic drugs, and this fact underlines the consistent role of 5-HT in different forms of aggression.

Discriminative stimulus properties of flesinoxan: effects of enantiomers, (S)-UH301 and WAY-100635

Rats were trained to discriminate the specific 5-HT1A receptor agonist (+)-flesinoxan (R(+)-N(-)[2[4-(2,3-dihydro-2-2-hydroxy-methyl-1,4- benzodioxin-5-yl)-1-piperazinyl]ethyl]-4-fluorobenzoamide) (1.5 mg/kg p.o.) from water in a two-lever operant procedure. Generalization tests were conducted with the enantiomers and racemate of flesinoxan and the 5-HT1A receptor antagonists (S)-UH301 ((S)-5-fluoro-8-hydroxy-2-(dipropylamino)-tetralin) and WAY-100635 ((N(-)[2(-)[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridinyl) cyclohexanecarboxamide trihydrochloride). (S)-UH301, WAY-100635 and fentanyl were investigated for their antagonistic properties. The (+)-flesinoxan stimulus generalized to (-)-flesinoxan and the racemate. The ED50 values for generalization corresponded well with the affinities of the enantiomers and the racemate for the 5-HT1A receptor. The flesinoxan cue could not be mimicked by (S)-UH301 or WAY-100635, but (S)-UH301 reduced response rates. Antagonism tests showed that both (S)-UH301 and WAY-100635 dose dependently antagonized the flesinoxan cue, with ID50 values of 0.52 and 0.03 mg/kg s.c., respectively. Fentanyl had no significant antagonistic properties. It is concluded that rats can learn to discriminate orally administered (+)-flesinoxan from water. The generalization of flesinoxan to the (-)-enantiomer and the antagonism of flesinoxan's cue by specific 5-HT1A receptor antagonists are further evidence for the involvement of flesinoxan's 5-HT1A receptor agonistic properties in its discriminative stimulus effects.

The ambivalent behaviour "stretched approach posture" in the rat as a paradigm to characterize anxiolytic drugs

The effect of various psychotropic drugs on the ambivalent behaviour "stretched approach posture" (SAP) in the rat was assessed. SAP was elicited after a mild startle reaction due to physical contact with an electrified prod at one end of a straight runway. Using ethological observation methods, SAP as well as intention movements, prod contact, crossings, rearing, exploration, grooming and immobility were recorded. The benzodiazepine receptor agonists chlordiazepoxide, diazepam and alprazolam, the 5-HT1A receptor agonists flesinoxan and ipsapirone and the 5-HT uptake inhibitor clomipramine selectively (no effect on crossings) reduced SAP. Except for alprazolam, these drugs also reduced intention movements. In addition, chlordiazepoxide and diazepam enhanced prod contact. Reductions of SAP and intentions with concomitant reductions of crossings (nonspecific antiambivalent effects) were established for the alpha 2-adrenoceptor agonist clonidine and the MAO inhibitor clorgyline. The 5-HT uptake inhibitor fluvoxamine suppressed intention movements, but not SAP. The mixed 5-HT/NA uptake inhibitor imipramine did not significantly affect SAP or intentions, but reduced crossings. The 5-HT2C/1B receptor agonist m-CPP, the inverse BZD receptor agonists FG 7142 and DMCM, and the alpha 2-adrenoceptor antagonist yohimbine, to all of which putative anxiogenic effects have been ascribed, had no effect on SAP directed towards the prod. m-CPP, however, produced an increase in the stretched posture directed away from the prod (SAwayP). FG 7142 reduced intentions while strongly enhancing immobility (freezing). SAwayP and/or freezing may possibly reflect anxiogenic properties of drugs. The putative anxiogenic drug pentylenetetrazol false positively reduced SAP while increasing exploration. The dopamine-D2 receptor antagonist haloperidol and the catecholamine releaser dl-amphetamine had no effect on ambivalent behaviour. The muscarine receptor antagonist scopolamine reduced SAP and intentions while stimulating crossings. Finally, the 5-HT2C receptor antagonist ritanserine, the CCKA receptor antagonist devazepide, the CCKB receptor antagonist L-365.260 and the strychnine-insensitive glycine site antagonist 7-Cl-kynurenic acid were without effect on the behaviours in this paradigm using single doses. In conclusion, SAP and intention movements were reduced selectively by anxiolytic agents from different classes, including benzodiazepine receptor agonists, 5-HT1A receptor agonists and a 5-HT uptake inhibitor, whereas an alpha 2-adrenoceptor agonist and a MAO inhibitor reduced SAP non-selectively. SAP in relation to other behaviours may therefore serve as a valuable paradigm to characterize anxiolytic drugs.

The anxiolytic effects of flesinoxan, a 5-HT1A receptor agonist, are not related to its neuroendocrine effects

The effects of flesinoxan, a selective 5-HT1A receptor agonist, were studied under basal non-stress conditions and in the shock-probe burying paradigm. Flesinoxan (1 and 3 mg/kg s.c.) significantly reduced burying and freezing behaviour, indicating clear anxiolytic properties. Under non-stress conditions, injection of 3 mg/kg flesinoxan significantly enhanced plasma corticosterone and glucose levels, whereas prolactin secretion was significantly enhanced after both 1 mg/kg and 3 mg/kg flesinoxan. Flesinoxan (1 and 3 mg/kg) did not suppress shock-probe stress-induced rises in plasma corticosterone and glucose levels. The enhanced plasma prolactin levels induced by flesinoxan were not further affected by shock-probe exposure. Our data show that the anxiolytic effects of flesinoxan in the shock-probe burying paradigm are not related to increases in plasma corticosterone and glucose levels.

Cholinergic drug effects on a delayed conditional discrimination task in the rat

The centrally acting cholinergic antagonist scopolamine (0.025-0.10 mg/kg ip) and the peripherally acting cholinergic antagonist methyl-scopolamine (0.01-0.10 mg/kg) dose dependently impaired discriminability independent of delay in a delayed conditional discrimination task that precludes use of mediating behavior. This indicates that scopolamine does not specifically affect working memory. Drugs that enhance cholinergic transmission neither improved discriminability nor attenuated scopolamine-induced impairments. In a post hoc analysis scopolamine was found to impair discriminability in a delay-dependent manner in rats that performed at a high level in pretest sessions. Methyl-scopolamine impaired performance independently of delay in these rats. The authors suggest that a ceiling effect at short delays produced this Drug x Delay interaction of scopolamine in the best performing rats.

Local pharmacological manipulations of prefrontal dopamine affect conflict behaviour in rats

Several lines of research have implicated the prefrontal cortex (PFC) and its dopaminergic (DA) innervation in an animal's response to stress and anxiety. To extend these findings we evaluated the effects of bilateral infusions of DA drugs into the medial PFC of rats, in a modified conflict test, consisting of Reward, Conflict and Time-out components. In experiment 1, the effects of infusions of the DA receptor agonist apomorphine (APO) were compared to the effects of systemic injections of the same drug. APO infusions induced a dose-dependent decrease of responding in the Conflict component, indicative of an anxiogenic-like effect. However, response rates in the Reward component were simultaneously decreased, casting some doubt on the specificity of the effect. In comparison, i.p injections of APO in a second group of animals did not affect responding in the Conflict component, but dose-dependently decreased response rates during Time-out and Reward components. In experiment 2, we evaluated the effects of infusions of APO and the DA receptor antagonist cis-flupenthixol (FLU) into the medial PFC in the conflict test, and in one of its variants, the extinction of conflict test. Although both APO and FLU decreased response rates during Reward components, responding in the Conflict components of both tests was differentially affected. APO infusions decreased Conflict responses, the effect being more pronounced in the extinction of conflict test. In contrast, infusions of FLU increased responding in the Conflict components. The respective pro- and anti-conflict effects of APO and FLU infusions are in favour of a direct involvement of prefrontal DA in anxiety-related behavioural responses.

[Outcome of 77 live born children with cardiac or rhythmic anomalies diagnosed in the prenatal period. Apropos of 77 cases]

Seventy-seven live born children (September 1988 to May 1993) had prenatally detected morphological cardiac malformations (61 cases) and/or arrhythmias (17 cases). The outcome of these children was analysed with an average follow-up of 21.4 months (range: 1 day to 11 years). The parameters studied were age and condition of prenatal diagnosis, the term of pregnancy, the extracardiac malformations associated and the outcome of the live born children. Fifty-two children survived with a mean follow-up of 28.2 months (range: 5 months to 11 years) and 25 children died at a mean age of 3.3 months (range: 1 day to 32 months). The cardiac malformations correlated with the postnatal diagnosis in 59 children (60 cardiac malformations). They included left or right outflow tract obstruction in 22%, septal defects or Tetralogy of Fallot with or without pulmonary atresia in 18.4%, arterial malposition in 12.9% and arrhythmias or conduction defects in 20.7% of cases. The main reason for the high mortality was the complexity of the cardiac malformations with, in particular, ventricular hypoplasia with right or left outflow tract obstruction (41% of mortality). The functional consequences of these abnormalities were only partially appreciated at prenatal diagnosis. The extracardiac malformations, more easily diagnosed, contributed less to this mortality rate. The favourable prognosis of the arrhythmias or conduction defects diagnosed prenatally was confirmed but was, however, associated with a mortality rate of 12%.(ABSTRACT TRUNCATED AT 250 WORDS)

Benzodiazepine receptor ligands have no specific action on working memory in a delayed conditional discrimination task in rats

We investigated effects of benzodiazepine (BDZ) receptor ligands on working memory in a delayed conditional discrimination (DCD) task. The BDZ receptor full agonist midazolam (0.1-1.0mg/kg) dose-dependently impaired performance independent of delay, indicating no specific effect on working memory. The non-sedative BDZ receptor partial agonist bretazenil (0.06-0.6mg/kg), the inverse agonist beta-CCM (0.05-0.45mg/kg), the partial inverse agonist FG 7142 (0.5-5.0mg/kg), the antagonist flumazenil (1-10mg/kg), and the antagonist ZK 93 426 (1-10mg/kg) did not significantly affect performance. It is concluded that BDZ ligands do not affect working memory in a positively-motivated DCD task. Midazolam also impaired performance in the no-delay condition, suggesting loss of stimulus control, possibly through an attentional impairment.

The role of the medial prefrontal cortex of rats in short-term memory functioning: further support for involvement of cholinergic, rather than dopaminergic mechanisms

The putative involvement of the dopaminergic innervation of the medial part of the prefrontal cortex (PFC) in short-term memory functioning was investigated by evaluating the effects of local infusions of dopaminergic drugs into the ventral part of the medial PFC of rats in an operant delayed-matching-to-position (DMTP) task. Two separate groups of rats were tested after bilateral microinfusion of several doses of either the dopamine receptor agonist apomorphine (APO) or the dopamine receptor antagonist cis-flupenthixol (FLU) into the ventromedial PFC. In addition, all animals were tested after infusion of several doses of the muscarinic receptor antagonist scopolamine (SCO) and the dopamine DI receptor antagonist SCH-23390 (SCH). The drugs tested affected DMTP performance differentially. APO had no effect on response accuracy, although it dose-dependently affected nose poke activity and response latencies. FLU and SCH both induced a dose-dependent, but delay-independent deterioration of response accuracy that was paralleled by increases in response latencies and decreases in nose poke frequencies, causing some animals to stop responding after infusion of the highest doses of both drugs. In contrast, SCO infusions into the ventromedial PFC induced a dose- and delay-dependent deterioration of response accuracy, that was accompanied by an increase in response latencies only. Taken together, these results provide additional support for the involvement of cholinergic, rather than dopaminergic mechanisms in short-term memory supported by the medial PFC of the rat, and they are not in favor of a functional dissociation between the dorsomedial PFC and the ventromedial PFC in the role.

Predictive validity of the potentiated startle response as a behavioral model for anxiolytic drugs

The fear-potentiated startle (PSR) paradigm is a putative behavioral model for the determination of anxiolytic properties of drugs. The present study further investigated the predictive validity of the model. Predictive validity is high, when only drugs clinically used as anxiolytics attenuate PSR dose dependently. Results showed that startle potentiation decreased dose dependently after the administration of the anxiolytics CDP (2.5-10 mg/kg, IP) and alprazolam (1-3 mg/kg, IP). After administration of the clinically non-anxiolytic drugs amitriptyline (2.5-10 mg/kg, IP), carbamazepine (5-20 mg/kg, IP), fentanyl (0.0025-0.04 mg/kg, SC), naloxone (2.5-10 mg/kg, IP), nicotine (0.4-1.6 mg/kg, IP), alcohol (500-2000 mg/kg, IP), and d-amphetamine (0.6-2.4 mg/kg, IP), a dose-dependent decrease in startle potentiation was not found. The PSR correctly discriminated most of the drugs tested in clinically anxiolytic and clinically non-anxiolytic drugs. However, haloperidol behaved as a false positive, and results of nicotine and alcohol were at variance with results reported by others.

The corticosterone-enhancing effects of the 5-HT1A receptor antagonist, (S)-UH301, are not mediated by the 5-HT1A receptor

We tried to antagonize the endocrine and behavioural changes induced by the selective 5-HT1A receptor agonist, flesinoxan, with the putative 5-HT1A receptor antagonist, (S)-UH301 ((S)-5-fluoro-8-hydroxy-2-(di-n-propylamino)tetralin). The interaction of (S)-UH301 (3 and 10 mg/kg s.c.) with flesinoxan (3 mg/kg s.c.) showed no antagonistic effects of (S)-UH301 on flesinoxan-induced corticosterone secretion. In fact, like flesinoxan (1 and 3 mg/kg s.c.), (S)-UH301 (3 and 10 mg/kg s.c.) itself dose dependently increased plasma corticosterone levels. Unlike flesinoxan, (S)-UH301 did not induce hyperglycemia, lower lip retraction and flat body posture. Moreover, flesinoxan-induced hyperglycemia and behavioural changes were effectively antagonized by (S)-UH301, showing potent 5-HT1A receptor antagonistic effects of (S)-UH301. Therefore we conclude that (S)-UH301 is a potent 5-HT1A receptor antagonist and that the (S)-UH301-induced corticosterone secretion is mediated by a non-5-HT1A receptor mechanism.

Conditioned ultrasonic distress vocalizations in adult male rats as a behavioural paradigm for screening anti-panic drugs

Rats may produce ultrasonic vocalizations (USV) in threatening situations. USV of adult male rats in association with aversive stimulation was evaluated as a screening method for anxiolytic drugs. The triazolobenzodiazepine alprazolam, the 5-HT uptake inhibitors fluvoxamine and clomipramine, the mixed 5-HT/NA uptake inhibitor imipramine, the full 5-HT1A receptor agonists 8-OH-DPAT and flesinoxan, the partial 5-HT1A receptor agonists buspirone, ipsapirone and BMY 7378, the alpha 2-adrenoceptor agonist clonidine and the alpha 2-adrenoceptor antagonist yohimbine reduced conditioned USV. The classical benzodiazepines (BZD) diazepam and chlordiazepoxide were ineffective or had a very low potency to decrease USV. The partial BZD receptor agonists bretazenil, alpidem and zolpidem, the BZD receptor antagonist flumazenil, the NA uptake inhibitors desipramine and maprotiline, and the 5-HT3 receptor antagonist ondansetron had no effect on conditioned USV. The dopamine-D2 receptor antagonist haloperidol reduced USV at a very high dose. In separate experiments the effects of these drugs on locomotor activity were assessed. There was, however, no direct relationship between effects on motor behaviour and USV. In conclusion, the sensitivity of conditioned USV to 5-HT uptake inhibitors and alprazolam versus the insensitivity to classical benzodiazepines and NA uptake inhibitors provides a very interesting profile, which closely resembles the psychopharmacology of panic disorder. Also the face validity of conditioned USV towards situational panic attacks is high. We therefore propose conditioned USV in adult male rats as a novel behavioural paradigm to screen for anti-panic drugs.

Serotonergic drug effects on a delayed conditional discrimination task in the rat; involvement of the 5-HT1A receptor in working memory

We investigated the effects of serotonergic drugs on working memory (WM) in a delayed conditional discrimination task. The 5-HT(1A) receptor full agonist flesinoxan (0.3-3.0 mg/kg) dose- and delay-dependently impaired performance, indicating a specific effect on WM. The 5-HT(1A) receptor partial agonist ipsapirone, the 5-HT( 1B/1D/2C) agonist TFMPP, the 5-HT(1A) antagonist NAN190 and the serotonin re-uptake inhibitor fluvoxamine dose-dependently impaired performance, in a delay-independent manner, indicating no specific effect on WM. The 5-HT( 2) receptor antagonist ketanserin and the 5-HT(3) receptor antagonist ondansetron did not affect performance. It is suggested that the role of central serotonin receptors in WM may be restricted to 5-HT(1A) receptors.

Stress-induced hyperthermia in mice: hormonal correlates

In the stress-induced hyperthermia (SIH) paradigm in group-housed male mice, the rectal temperature of last measured mice is approximately 1.5 degrees C higher than the first measured one when the temperature of each mouse is measured sequentially with an interval of 1 min. In the present study it is demonstrated that SIH is accompanied by increases in plasma ACTH, corticosterone, and glucose levels that return to baseline more or less parallel to the temperature. The simultaneous increases in temperature and plasma stress hormones strongly support the use of the SIH paradigm in mice as an animal model to study putative anti-stress or anxiolytic properties of drugs.