Clozapine attenuates the locomotor sensitisation and the prepulse inhibition deficit induced by a repeated oral administration of Catha edulis extract and cathinone in rats

Locomotor sensitisation and deficits in prepulse inhibition (PPI) induced by psychostimulants are two paradigms that have been widely studied as animal behavioural models of psychosis. Clozapine is one of the atypical antipsychotic agents which has been widely employed to reverse the aforementioned behavioural changes in these usual models. In this particular study, locomotor sensitisation and prepulse inhibition deficit were induced under the same context by intermittent oral administration of S-(-)-cathinone or Catha edulis extract in rats. The rats were then challenged by administration of the atypical antipsychotic drug, clozapine and were finally challenged with psychostimulants after 2-week of withdrawal. Locomotor activity and PPI were assessed and later analyses of the neurotransmitter levels were made. The results of this experiment show that repeated oral administration of cathinone or C. edulis extract enhanced locomotor and exploratory activity and lead to a gradual deficit in prepulse inhibition. This locomotor sensitisation and PPI deficit could be reversed by administration of clozapine. A challenge with psychostimulant on day 40 (i.e., after 2-week of withdrawal) resulted in a response similar to the initial exposure (day 1). Neurotransmitter level analyses showed a significant increase in the level of dopamine in the prefrontal cortex (p < 0.05). There was also a significant decrease in the level of 5-hydroxytryptamine (5-HT) in the nucleus accumbens (p < 0.05) and its metabolite, 5-hydroxyindole acetic acid (5-HIAA) in the prefrontal cortex (p < 0.01). In the remaining regions (anterior and posterior striatum), there were no significant changes. In conclusion, this is the first study to demonstrate that repeated administration of C. edulis extract, or commercial cathinone, induces prepulse inhibition deficit and clozapine reverses both C. edulis or cathinone-induced sensitised locomotion and prepulse inhibition deficit.

Influence of neonatal short-term reduction in brainstem alpha2A-adrenergic receptors on receptor ontogenesis, acoustic startle reflex, and prepulse inhibition in rats

Neonatal treatments can disrupt prepulse inhibition (PPI) of startle response later in life. Alpha2A-adrenergic receptors (alpha2A-ARs) regulate the release of brain neurotransmitters that may influence PPI. The authors examined the effects of short-term reduction in the neonatal brainstem alpha2A-ARs on subsequent development of this receptor system and acoustic startle reflex in rats. Administration of antisense oligodeoxynucleotide complementary to the alpha2A-ARs on Days 2-4 of life reduced receptor expression in the brainstem by Day 5. The treatment increased alpha2-AR numbers in the cortex, hippocampus, and amygdala at 40 days of age, and in cortex and hypothalamus at 90 days of age. Transient increases in hippocampal and amygdalar alpha2-ARs were accompanied by attenuation of acoustic startle response and impairment of PPI.

Reversed Ipsilateral Acoustic Reflex: A Study on Subjects Treated With Muscle Relaxants

OBJECTIVES

To rule out any possible involvement of the middle ear muscles in the genesis of the reversed ipsilateral acoustic reflex (RIAR).

DESIGN

Prospective study to evaluate the effects of muscle relaxants on the RIAR of otosclerotic ears as well as on the acoustic reflex of individuals with normal middle ear function. Admittance recording during ipsilateral acoustic stimulation was performed in patients undergoing pharmacological treatment for surgical procedures. Fentanyl, propofol, and a muscle relaxant were sequentially administered intravenously. Ipsilateral acoustic reflexes were recorded before and after each drug injection. Three patients were affected from otosclerosis, whereas 14 individuals had normal middle ear function. Moreover, the ipsilateral acoustic reflex obtained in normal subjects after their treatment with muscle relaxants was compared with that of 10 otosclerotic patients who were not treated pharmacologically.

RESULTS

The RIAR of three otosclerotic ears was not inhibited by muscle relaxants as well as by fentanyl and propofol. Moreover, muscle relaxants, when administered in normal subjects, always induced the block of the stapedial reflex that was replaced by a reversed reflex strictly similar to the RIAR of the 10 otosclerotic patients not treated pharmacologically. Propofol could also induce, in most of the cases, the reduction and in some occasion even the reversal of the stapedial reflex, whereas fentanyl did not affect it significantly.

CONCLUSION

The RIAR does not appear to be related to the contraction of the middle ear muscles.

Effects of prenatal exposure to chronic mild stress and toluene in rats

The aim of the present study was to elucidate whether prenatal chronic stress, in combination with exposure to a developmental neurotoxicant, would increase effects in the offspring compared with the effects of either exposure alone. Development and neurobehavioral effects were investigated in female offspring of pregnant rats (Mol:WIST) exposed to chronic mild stress (CMS) during gestational days (GD) 9-20, or 1500 ppm toluene, 6 h/day during gestational days 7-20, or a combination of the two. Prenatal CMS was associated with decreased thymic weight and increased auditory startle response. The corticosterone response to restraint seemed modified by prenatal exposure to toluene. Lactational body weight was decreased in offsprings subjected to CMS, primarily due to effects in the combined exposure group. Cognitive function was investigated in the Morris water maze, and some indications of improved function due to CMS were observed. In the present experimental setting, there was no indication of the two exposures potentiating each other with respect to adverse effects on the nervous system. However, the effects of prenatal CMS indicate that stress during fetal life may interfere with the development of the thymus and increase the reactivity (startle reflex) of the offspring.

The medial septum mediates impairment of prepulse inhibition of acoustic startle induced by a hippocampal seizure or phencyclidine

The involvement of the septohippocampal system on the impaired sensorimotor gating induced by phencyclidine (PCP) or by an electrically induced hippocampal seizure was examined in behaving rats. An impaired sensorimotor gating, measured by prepulse inhibition (PPI) of the acoustic startle response, was observed following a hippocampal afterdischarge (AD) or systemic injection of PCP and was accompanied with an increase in hippocampal gamma waves (30-70 Hz). The medial septum infusion with muscimol (0.25 microg), a GABA(A) receptor agonist, 15 min prior to PCP or a hippocampal AD, prevented the impairment of sensorimotor gating and the increase in gamma waves. By itself, muscimol (0.25 microg) injection into the medial septum did not affect PPI, although it significantly suppressed spontaneous gamma waves. In order to identify subpopulations of neurons mediating the sensorimotor gating deficit and the hippocampal gamma wave increase, 0.14-0.21 microg of p75 antibody conjugated to saporin (192 IgG-saporin) was injected into the medial septum to selectively lesion the septohippocampal cholinergic neurons. Neither the PPI deficit nor the gamma wave increase induced by PCP or a hippocampal AD was affected by 192 IgG-saporin lesion of the medial septum. It is concluded that increase in neural activity in the medial septum participates in the impairment of sensorimotor gating and the increase in hippocampal gamma waves induced by PCP or a hippocampal AD. It is suggested that the GABAergic but not the cholinergic septohippocampal neurons mediate the sensorimotor gating deficit.

Acoustic startle response, prepulse inhibition, and spontaneous locomotor activity in MPTP-treated mice

Parkinson's disease (PD) is marked by characterised motor deficits and is accompanied by a severe degeneration of the nigrostriatal dopamine (DA) pathway. It has also been reported that PD patients exhibited additional behavioural deficits, including a deficiency in sensorimotor gating mechanisms. We therefore examined whether the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) model of PD in mice could lead to a sensorimotor gating deficit in the prepulse inhibition (PPI) of the acoustic startle response (ASR) paradigm. Two MPTP treatment schedules were separately examined here in male C57BL/6 mice. Post-mortem HPLC analysis confirmed that they were effective in depleting DA in the dorsal striatum (75-88%). PPI was evaluated on days 2, 9 and 16 after the last MPTP treatment; spontaneous locomotor activity was assessed 24 h before each PPI test. No significant change in the expression of PPI was detected across the three time points. On the other hand, the MPTP treatment reduced activity on post-treatment day 1. This effect subsided on post-treatment day 8, and was reversed on day 15. The possibility remains therefore that the reported sensorimotor gating deficits in PD patients might stem from structural or neurochemical aberrations beyond those induced by MPTP treatment.

Intracochlear perfusion of pneumolysin, a pneumococcal protein, rapidly abolishes auditory potentials in the Guinea pig cochlea

OBJECTIVE

Bacterial meningitis and chronic suppurative otitis media caused by Streptococcus pneumoniae are associated with considerable otological morbidity. Specifically, sensorineural hearing loss is a permanent sequela in a third of those who contract pneumococcal meningitis. Pneumolysin, a pneumococcal protein, has been implicated as one of the main virulence/cytotoxic factors. Its pathogenicity is intimately dependent on an ability to form transmembrane pores on binding with cholesterol in target tissues.

MATERIAL AND METHODS

We perfused wild-type pneumolysin, at a number of different concentrations, into the guinea pig cochlea and used electrocochleography to characterize the effects of this cytolytic exotoxin in the organ of Corti.

RESULTS

Intracochlear perfusion of pneumolysin (10 microg/50 microl) reduced the compound action potential of the auditory nerve within seconds. The cochlear microphonics (f1=8 kHz, f2=9.68 kHz) and their distortion product (2f1-f2) were also reduced, albeit in a slightly less dramatic fashion. At lower concentrations (1 microg/50 microl), a selective and earlier effect on inner hair cells was observed.

CONCLUSIONS

These results clearly show that significant ototoxicity ensues when sensory cells of the organ of Corti are exposed to pneumolysin (and complete cochlear death when the concentration is high enough). Toxicity is dose-dependent and appears to be site-sensitive. This may have implications for any possible future protective strategies against pneumococcal disease in the ear.

Prepulse inhibition of acoustic startle in spontaneously hypertensive rats

Prepulse inhibition is modulated by dopaminergic drugs and is disrupted in attention-deficit hyperactivity disorder, as well as mental illnesses such as schizophrenia. Spontaneously hypertensive rats (SHR) have been proposed as an animal model of attention-deficit hyperactivity disorder and show marked alterations of dopaminergic regulation of behaviour. SHR showed significantly lower startle amplitude than Wistar-Kyoto (WKY) rats and Sprague-Dawley (SD) rats, but no difference in startle habituation. Baseline percentage prepulse inhibition was higher in SHR and WKY rats than in SD rats. Treatment with amphetamine caused significant disruption of prepulse inhibition in SHR and WKY rats, but not SD rats. In contrast, treatment with apomorphine caused prepulse-dependent disruption of prepulse inhibition in SD rats only. Both MK-801 and 8-OH-DPAT treatment caused disruption of prepulse inhibition in all three rat strains. This study shows differential changes in startle level and prepulse inhibition in SHR, however these rats are not uniformly different from either WKY rats or SD rats and WKY rats differ in a number of respects from SD rats. In conclusion, these data further reveal altered dopaminergic regulation of behaviour in SHR, but also shows that caution is needed about the control strain used to compare these animals with.

Developmental treatment with difluoromethylornithine has few effects on behavior or body weight in Sprague-Dawley rats

Developmental difluoromethylornithine (DFMO) treatment reduces cerebellar weight [Neuroscience 17 (1986) 399, Neurotoxicol. Teratol. 22 (2000) 415, Behav. Brain Res. 126 (2001) 135], but the functional alterations resulting from this have been little investigated. Here, Sprague-Dawley rats were subcutaneously injected with 500 mg/kg DFMO on postnatal days (PNDs) 5-12 and a comprehensive set of behavioral assessments measured early developmental behaviors (righting reflex, negative geotaxis), motor coordination, acoustic startle, short- and long-term activity, social behaviors, anxiety, and spatial learning and memory. DFMO treatment appeared to cause a decreased latency to perform the negative geotaxis behavior on PNDs 8-10 and increased latency to hang by the forelimbs on PNDs 12-14. Our previous study did not indicate similar effects, but age at testing differed between the two studies. DFMO treatment caused a decreased latency to maximum acoustic startle response in both the acoustic startle paradigm and in the pulse-alone trials of the prepulse inhibition test. This DFMO treatment paradigm induced a 10% decrease in adult cerebellar weight [Behav. Brain Res. 126 (2001) 135], but the results here imply that such developmental stunting has few functional alterations.

Neonatal impact of leukemia inhibitory factor on neurobehavioral development in rats

Cytokines have been implicated in the etiology or pathology of various psychiatric diseases of developmental origin such as autism and schizophrenia. Leukemia inhibitory factor (LIF) is induced by a variety of brain insults and known to have many influences on mature and immature nervous system. Here, we assessed the neurobehavioral and pathological consequences of peripheral administration of LIF in newborn rats. Subcutaneous LIF injection induced STAT3 phosphorylation in many brain regions and increased glial fibrillary acidic protein (GFAP) immunoreactivity in the neocortex, suggesting that LIF had direct effects in the central nervous system. The LIF-treated rats displayed decreased motor activity during juvenile stages, and developed abnormal prepulse inhibition in the acoustic startle test during and after adolescence. They displayed normal learning ability in active avoidance test, however. Brain neuronal structures and startle responses were grossly normal, except for the cortical astrogliosis during neonatal LIF administration. These results indicate that LIF induction in the periphery of the infant has a significant, but discrete impact on neurobehavioral development.

The selective serotonin-2A receptor antagonist M100907 reverses behavioral deficits in dopamine transporter knockout mice

A hyperdopaminergic state in humans has been hypothesized to contribute to the pathology of a number of psychiatric illnesses, including schizophrenia, bipolar disorder, and attention deficit hyperactivity disorder. Mice that display elevated synaptic levels of dopamine due to a genetically engineered deletion of the dopamine transporter (DAT) model behavioral deficits that simulate the above conditions. As novel treatment strategies for these disorders have focused on the serotonin (5-HT) 2A receptor, we determined the capacity of the highly selective 5-HT(2A) receptor antagonist M100907 to reverse behavioral deficits in DAT knockout (KO) mice. Prior to drug treatment, DAT KO mice exhibited increased levels of locomotor activity and highly linearized movement in a novel environment, as well as reduced prepulse inhibition (PPI) of acoustic startle, compared to wild-type littermates. Treatment with M100907 (0.3-1.0 mg/kg, but not 0.1 mg/kg) reversed locomotor deficits in DAT KO mice. Similarly, treatment with 1.0 mg/kg M100907 reversed the PPI deficits in DAT KO mice. These data indicate that selective 5-HT(2A) receptor antagonists, such as M100907, may represent a class of drugs that can be used to treat conditions in which a chronic, elevated dopaminergic tone is present and contributes to abnormal behavior and sensorimotor gating deficits.

Influence of EEG monitoring on intraoperative stapedius reflex threshold values in cochlear implantation in children

BACKGROUND

Cochlear implantation is a widely used means of treating deafness and severe hearing disorders. The surgical procedure includes inserting the cochlear implant electrode array into the cochlea and embedding the corresponding signal receiver in the mastoid bone behind the ear. Postoperative fitting of the externally worn speech processor is very important for successful use of the cochlear implant. For this purpose, electrically elicited stapedius reflex threshold values can be used. However, stapedius reflex threshold values measured intraoperatively are influenced by anaesthetics. The goal of this retrospective study was to find out whether electroencephalogram (EEG) control of anaesthesia produces more reliable reflex threshold values as a basis for the fitting of the speech processor.

METHODS

Three groups of children, after surgery for cochlear implantation, were analysed with regard to the magnitude of intraoperative electrically elicited stapedius reflex threshold values and their deviations from postoperatively determined maximum comfortable levels (group 1: methohexital/remifentanil with EEG monitoring, n = 10; group 2: isoflurane/fentanyl with EEG monitoring, n = 9; group 3: isoflurane/fentanyl without EEG monitoring, n = 11).

RESULTS

Children with EEG monitoring had significantly lower electrically elicited stapedius reflex threshold values and also significantly lower differences between intraoperative stapedius reflex threshold values and postoperatively determined maximum comfortable levels.

CONCLUSIONS

Electroencephalogram monitoring in cochlear implantation is of considerable value in controlling anaesthesia and improving speech processor fitting based on more reliable intraoperative neurophysiological data.

Chronic pubertal, but not adult chronic cannabinoid treatment impairs sensorimotor gating, recognition memory, and the performance in a progressive ratio task in adult rats

There is evidence from studies in humans and animals that a vulnerable period for chronic cannabinoid administration exists during certain phases of development. The present study tested the hypothesis that long-lasting interference of cannabinoids with the developing endogenous cannabinoid system during puberty causes persistent behavioral alterations in adult rats. Chronic treatment with the synthetic cannabinoid agonist WIN 55,212-2 (WIN) (1.2 mg/kg) or vehicle was extended over 25 days either throughout the rats' puberty or for a similar time period in adult rats. The rats received 20 injections intraperitoneally (i.p.), which were not delivered regularly. Adult rats were tested for object recognition memory, performance in a progressive ratio (PR) operant behavior task, locomotor activity, and prepulse inhibition (PPI) of the acoustic startle response (ASR). PPI was significantly disrupted only by chronic peripubertal cannabinoid treatment. This long-lasting PPI deficit was reversed by the acute administration of the dopamine antagonist haloperidol. Furthermore, we found deficits in recognition memory of pubertal-treated rats and these animals showed lower break points in a PR schedule, whereas food preference and locomotion were not affected. Adult chronic cannabinoid treatment had no effect on the behaviors tested. Therefore, we conclude that puberty in rats is a vulnerable period with respect to the adverse effects of cannabinoid treatment. Since PPI deficits, object recognition memory impairments, and anhedonia/avolition are among the endophenotypes of schizophrenia, we propose chronic cannabinoid administration during pubertal development as an animal model for some aspects of the etiology of schizophrenia.

Reversal of startle gating deficits in transgenic mice overexpressing corticotropin-releasing factor by antipsychotic drugs

Chronically elevated levels of corticotropin-releasing factor (CRF) in transgenic mice overexpressing CRF in the brain (CRF-OE) appear to be associated with alterations commonly associated with major depressive disorder, as well as with sensorimotor gating deficits commonly associated with schizophrenia. In the present study, we tested the hypothesis that antipsychotics may be effective in normalizing prepulse inhibition (PPI) of acoustic startle in CRF-OE mice, which display impaired sensorimotor gating compared to wild-type (WT) mice. The typical antipsychotic haloperidol and atypical antipsychotic risperidone improved PPI in the CRF-OE mice, but were ineffective in WT mice. The atypical antipsychotic clozapine did not influence PPI in CRF-OE mice, but reduced gating in WT mice. This effect of clozapine in the CRF-OE mice may thus be regarded as a relative improvement, consistent with the observed effect of haloperidol and risperidone. As expected, the anxiolytic, nonantipsychotic chlordiazepoxide was devoid of any effect. All four compounds dose-dependently reduced the acoustic startle response irrespective of genotype. These results indicate that antipsychotic drugs are effective in improving startle gating deficits in the CRF-OE mice. Hence, the CRF-OE mouse model may represent an animal model for certain aspects of psychotic depression, and could be a valuable tool for research addressing the impact of chronically elevated levels of CRF on information processing.

Prenatal amphetamine exposure alters behavioral reactivity to amphetamine in rats

In utero exposure to psychostimulants produces neurobehavioral alterations in the offspring of laboratory animals. Most amphetamine-related behavioral changes have been related to changes in the monoamine transmission levels, where monoamines may act as developmental regulatory substances for maturation of neuronal population. This study investigates the effect of prenatal-amphetamine exposure on the offspring's behavioral responses under amphetamine conditioning settings. Pregnant female rats were injected (subcutaneous) with amphetamine or saline during the pregnancy [gestation day (GD) 8 until parturition day]. The prenatal amphetamine exposure resulted in significantly decreased birth weights. The offspring from the saline group displayed a significantly lower number of stereotyped behaviors across the four challenge doses of amphetamine injections. Offspring from the amphetamine-treated prenatal group displayed significantly increased average startle amplitude compared to the controlled offspring. Moreover, offspring from amphetamine-treated prenatal group showed significantly less inhibition for the prepulse startle trials compared to those of the offspring from saline group. These results, taken together, indicate that the prenatally exposed rats displayed a significantly different profile of behavioral reactivity upon amphetamine challenges.

Neuroprotection by aminoguanidine after lateral fluid-percussive brain injury in rats: a combined magnetic resonance imaging, histopathologic and functional study

The present study examined the effects of a selective inducible nitric oxide synthase (iNOS) inhibitor, aminoguanidine (AG), on neuronal cell survival and post-traumatic recovery in rats following a lateral fluid percussive brain injury. Daily treatment of AG at the dosage of 100 mg/kg or normal saline was given intraperitoneally into rats starting 2 h before or 30 min after brain injury. Treatment with AG significantly reduced lesion volumes in the brains of rats after injury, as evaluated by high-resolution magnetic resonance imaging (MRI). Immunohistochemical analysis showed a marked induction of iNOS expression in brain macrophages ipsilateral to the injury. Apoptotic neurons were observed in the ipsilateral cerebral cortex by in situ terminal transferase d-UTP nick-end labelling (TUNEL) and caspase-3 immunohistochemistry. In rats receiving prophylactic or post-injury treatment of AG, the number of degenerating neurons was markedly reduced in the cerebrum compared to those receiving saline injection. The location and extent of these pathologic changes correlated with MRI findings. Neurobehavioral studies showed that rotametric performance, grip-strength score, total and ambulatory locomotor responses and acoustic startle response were reduced in rats subjected to the injury but were significantly improved in AG-treated rats. It is suggested that inhibition of iNOS by AG may represent a potential therapeutic strategy for the treatment of traumatic brain injury.

Heterochronous involvement of neurotrophic factors in the neurochemical organization of learning and memory processes in adult organisms

Studies were performed on the involvement of neurotrophic factors in the neurochemical mechanisms of the integrative functions of the brain. The effects of various intrahippocampal doses of antibodies to neurotrophic factors--protein S100 and lectin CSL--were studied on the formation, retention, and reproduction of a habituated acoustic startle response and conditioned fear in adult rats. S100b contents in the hippocampus, hypothalamus, frontal cortex, and cerebellar hemispheres and vermis, and in the basal nuclei were measured in rat brains 0.5, 1, 2, 4, 6, 8, 24, and 48 h after long-term habituation to the startle response. Antibodies to neurotrophic factors had selective and dose-dependent effects on the different memory and learning processes underlying these types of behavior. Changes in S100b in brain structures were seen, which were specific in terms of quantitative levels and dynamics, after acquisition of the behavioral habit. The results obtained here, along with previously reported data on the effects of antibodies to S100b and CSL given into the cerebellum, are discussed as experimental support for the hypothesis of the heterochronous neurochemical organization of integrative brain activity.

Effects of selective serotonin reuptake inhibitors on auditory processing: case study

Auditory sensitivity and processing ability were evaluated in a patient who suffered from hyperacusis, difficulty understanding speech, withdrawn depression, lethargy, and hypersensitivity to touch, pressure, and light. Treatment with fluvoxamine and fluoxetine (selective serotonin reuptake inhibitors) reversibly alleviated complaints. Testing while medicated and unmedicated (after voluntary withdrawal from medication for several weeks) revealed no difference in pure-tone thresholds, speech thresholds, word recognition scores, tympanograms, or acoustic reflex thresholds. Medicated SCAN-A (a screening test for central auditory processing disorders) results were normal, and unmedicated results were abnormal. Unmedicated transient otoacoustic emissions and auditory brainstem response waves I, III, and V were significantly larger bilaterally. Uncomfortable loudness levels indicated greater tolerance during the medicated condition. Central processing and vigilance were evaluated with analog-synthesized three-formant consonant-vowel syllables. While medicated, responses to stimuli at each ear revealed well-defined, labeling crossovers of about 90 msec. Vowel identification matched normal subject responses; labeling of /gE/jE/ and /bE/wE/ continua was well defined but all crossover points differed from normals (p < .0001). During unmedicated testing, responses to /gE/jE/ began at medicated levels but approached chance levels for the entire continuum within 10 min; labeling of /bE/wE/ was consistent with medicated responses throughout with earlier than normal crossover points.

Effects of alcohol on the acoustic reflex threshold in the chinchilla

The effect of ethanol on the acoustic reflex threshold was examined in a repeated measure design study in six chinchillas. Each subject was weighed and orally administered the control (water) at a dosage of 7.5 ml/kg. Commencing 1 h after alcohol ingestion, the acoustic middle ear reflex measures (AMRs) were taken every other hour, for a total of four recording sessions. Ascending and descending trials were alternated between each recording session. Two weeks later the same chinchillas were administered 35% alcohol by volume. AMRs were recorded under the same conditions and procedures as for the control. Alcohol produced AMRs that were significantly elevated over baseline values 1 h after alcohol ingestion and four of the five had AMRs that remained elevated 3 h after ingestion.

Animal models of deficient sensorimotor gating: what we know, what we think we know, and what we hope to know soon

Sensorimotor gating of the startle reflex can be studied in humans and laboratory animals using measures of prepulse inhibition (PPI) of the startle reflex. PPI is reduced in patients with specific neuropsychiatric disorders and in rats after manipulation of the limbic cortex, striatum, pallidum or pontine tegmentum. Studies are rapidly identifying the neurochemical and neuroanatomical substrates regulating PPI in laboratory animals; this detailed circuit information has been used as a 'blueprint' to identify possible candidate substrates responsible for PPI deficits in psychiatrically disordered humans. In parallel, studies have also begun to assess the homology of pharmacological effects on PPI across species, as an initial step towards translating detailed neural circuit information from rats to humans. Despite this rapid progress, there is an increasing danger of overlooking important methodological and interpretative issues that could impact either positively or negatively on the ultimate utility of models based on measures of PPI. Some of these issues--ranging from the cross-species methods for quantifying specific variables to the relevance of genetic drift to animal and human studies of PPI--and their implications for future studies are the focus of this review.

The diagnostic value of stapedius reflex and stapedius reflex exhaustion in myasthenia gravis

Authors studies impedance, stapedius reflex thresholds and stapedius muscle exhaustion on 31 ears of 16 MG patients. Investigations were carried out using GSI 33 computer-assisted middle ear analyzator. Stapedius reflex threshold values were increased in 93% of patients. Stapedius exhaustion was observed in 71% of patients. After the administration of the reversible cholinesterase inhibitor Mestinon (60 mg pyridostigmin bromide), reflex threshold decreased and exhaustion occurred in only 50% of cases. Authors review the literature in context with the audiometric diagnostics of MG and also recommend the use of these methods in more complicated ocular and bulbar cases of MG.

Quinine reduces the dynamic range of the human auditory system

The aim of the study was to evaluate and quantify quinine-induced changes in the human auditory dynamic range, as a model for cochlear hearing loss. Six otologically normal volunteers (21-40 years old) received quinine hydrochloride (15 mg/kg body weight) in two identical oral doses and one intravenous infusion. Refined hearing tests were performed monaurally at threshold, at moderate hearing levels and at high hearing levels. Quinine induced a maximal pure-tone threshold shift of 23 dB (1000-2000 Hz). The increase in the psychoacoustical click threshold agreed with an increase in the detection threshold of click-evoked otoacoustic emissions. The change in the stimulus-response relationship of the emissions reflected recruitment. The self-attained most comfortable speech level and the acoustic stapedius reflex thresholds were not affected by quinine administration. Quinine is a useful model substance for reversibly inducing complete loudness recruitment in humans as it acts specifically on some parts of the hearing function. Its mechanism of action on the molecular level is likely to reveal further information on the physiology of hearing.

Effect of acute subcutaneous nicotine on prepulse inhibition of the acoustic startle reflex in healthy male non-smokers

In a double-blind placebo-controlled trial, the effects of two doses (6 micrograms/kg, 12 micrograms/kg) of acute SC nicotine were investigated on prepulse inhibition (PPI) of the acoustic startle reflex in healthy non-smoker male volunteers. Each subject received three injections [placebo (saline), 6 micrograms/kg nicotine, 12 micrograms/kg nicotine] on separate occasions, 2 weeks apart. No influence of either 6 micrograms/kg or 12 micrograms/kg nicotine was observed for the amplitude and habituation of the startle response over pulse-alone stimuli, relative to the saline-treated condition. Percent of PPI (expressed as percent reduction of non-prepulse trials) was significantly greater, but PPI as measured by absolute difference scores was not significantly different, when subjects were given the 12 micrograms/kg dose of nicotine than saline. There was an increase in percent of PPI from saline through low to high doses of nicotine, but PPI observed under the low dose did not differ significantly from either the high dose or placebo. These results provide some support for previous findings showing an enhancement in PPI by cigarette smoking in overnight smoking-deprived smokers and by acutely administered nicotine in experimental animals. The findings indicate that previously observed effects of smoking on percent of PPI in smoking-deprived subjects were not attributable to the restoration of a deficit induced by smoking withdrawal, but represent a direct pharmacological action of nicotine.