The selective 5-HT6 receptor antagonist SLV has putative cognitive- and social interaction enhancing properties in rodent models of cognitive impairment.

In the present study, our aim was to investigate whether the novel highly selective 5-hydroxytryptamine6 (5-HT6) receptor antagonist SLV can ameliorate impairments in cognition and social interaction with potential relevance for both schizophrenia and Alzheimer's disease (AD). SLV sub-chronically - treated Wistar rats reared in isolation showed significantly enhanced prepulse inhibition (PPI) and object recognition performance when compared to vehicle - treated rats. In the isolated rats, also a significant reduction in expression of hippocampal neural cell adhesion molecule polysialylation (NCAM-PSA) was found which was ameliorated following treatment with SLV (30mg/kg). The social engagement deficit in rats exposed in utero (on gestational day 12.5) to valproic acid (VPA) was reversed by treatment with SLV (30mg/kg). SLV (20 and 30mg/kg, p.o.) fully reversed MK-801 - induced deficits in the ORT and also scopolamine - induced deficits in both the Object Recognition Task (ORT) and Object Location Task (OLT) in Wistar rats. In addition, a combination of sub-optimal doses of SLV and donepezil attenuated scopolamine-induced ORT deficits. Furthermore, SLV (10mg/kg, p.o.) reversed spontaneous alternation deficits in the T-maze induced by MK-801 administration in Swiss mice and in aged C57Bl/6J mice. SLV additionally improved T-Maze spatial learning and passive avoidance learning in Sprague-Dawley rats with amyoid-beta (Aß) injections into the hippocampus. In contrast, no benefits were found with SLV or the tested reference compounds (donepezil and RVT-101) on cognitive performance of 12months old Tg2576 mice. Also, in the social recognition task, an absence of cognitive enhancing properties was observed with SLV on "normal forgetting" in Wistar rats. Finally, analysis of spontaneous inhibitory postsynaptic currents (sIPSCs) frequency recorded from pyramidal cells revealed a reduction in the presence of 1µM of SLV. In conclusion, SLV was investigated in several rodent animal models and found to be effective at a least effective dose (LED) of 20mg/kg and 10mg/kg (p.o.) in the rat and the mouse, respectively.

Nano-LC-MS/MS for the quantitation of prostanoids in immune cells.

Prostanoids, derivatives of arachidonic acid, are involved in inflammation and immune reactions. To understand the role of prostanoids produced by diverse immune cells, a highly sensitive quantitation method for prostaglandin E2 (PGE2), prostaglandin D2 (PGD2), 6-keto prostaglandin F1α (6-keto PGF1α), prostaglandin F2α (PGF2α), and thromboxane B2 (TXB2) by means of nano-liquid chromatography-tandem mass spectrometry has been developed. It was validated according to the guidelines of the Food and Drug Administration (FDA) in terms of linearity, precision, accuracy, recovery, stability, and lower limit of quantitation (LLOQ). The LLOQ were 25 pg/mL in the injected solution (75 fg on column (o.c.)) for PGE2 and PGD2 and 37.5 pg/mL (112.5 fg on column) for 6-keto PGF1α, PGF2α, and TXB2, respectively. It was successfully applied to murine mast cells isolated from paws after zymosan injection and to CD4(+) and CD8(+) T lymphocytes from blood of sensitized versus non-sensitized mice in context of a delayed type hypersensitivity model. About 5,000 (T cells) to 40,000 (mast cells) cells were sufficient for quantitation. In the mast cells, the production of PGE2 increased at a significantly higher extent than the synthesis of the other prostanoids. The T lymphocytes did not show any difference in prostanoid production, no matter whether they were obtained from sensitized mice or non-sensitized mice.

Two novel 5-HT6 receptor antagonists ameliorate scopolamine-induced memory deficits in the object recognition and object location tasks in Wistar rats.

The 5-hydroxytryptamine(6) (5-HT(6)) receptor has been suggested to play an important role in the regulation of memory and cognition. In the present study, our aim was to investigate whether the novel, selective 5-HT(6) antagonists compound (CMP) X and CMP Y and the reference 5-HT(6) antagonist GSK-742457 could ameliorate impairments in episodic memory in 3-months-old male Wistar rats. The acetylcholinesterase inhibitor (AChEI) donepezil (Aricept®, approved for symptomatic treatment of Alzheimer's disease, AD) was used as a positive reference compound. First, effects of the 5-HT(6) antagonists CMP X, CMP Y and GSK-742457 were investigated on object recognition task (ORT) performance in rats treated with the muscarinic antagonist scopolamine (0.1mg/kg, administered intraperitoneally, i.p., 30 min before trial 1). Second, effects of the combination of suboptimal doses of 5-HT(6) antagonists CMP X and CMP Y with the AChEI donepezil were studied, to determine whether the 5-HT(6) antagonists show additive synergism with donepezil in the ORT. Finally, effects of CMP Y, GSK-742457 and donepezil were investigated on object location task (OLT) performance in rats treated with scopolamine. Donepezil (1mg/kg, oral administration, p.o.), GSK-742457 (3mg/kg, i.p.), CMP X (3mg/kg, i.p.) and CMP Y (30 mg/kg, p.o.), all ameliorated the scopolamine-induced deficits in object recognition. In the ORT, we have found that combined administration of subthreshold doses of CMP X (1mg/kg, i.p.) and CMP Y (10mg/kg, p.o.) with the AChEI donepezil (0.1mg/kg, p.o.), enhanced memory performance in Wistar rats with deficits induced by scopolamine. Donepezil (0.1mg/kg, p.o.) alone had no discernable effects on performance. This suggests additive synergistic effects of the 5-HT(6) antagonists (CMP X and CMP Y) with donepezil on cognitive impairment. Finally, donepezil (1mg/kg, p.o.), GSK-742457 (10mg/kg, p.o.) and CMP Y (30 mg/kg, p.o.) also reduced scopolamine-induced deficits in the OLT. In conclusion, the 5-HT(6) antagonists were found to clearly improve episodic memory deficits induced by scopolamine. In addition, co-administration of the 5-HT(6) receptor antagonists CMP X and CMP Y with the AChEI donepezil to cognitively impaired rats also resulted in potentially additive enhancing effects on cognition. This suggests that these compounds could have potential as monotherapy, but also as adjunctive therapy in patients with AD treated with common treatments such as donepezil.

SLV330, a cannabinoid CB1 receptor antagonist, ameliorates deficits in the T-maze, object recognition and Social Recognition Tasks in rodents.

Cannabinoid CB(1) receptor (CB(1)R) signaling has been suggested to play an important role in the regulation of memory and cognition. In the present study, our aim was to investigate whether the CB(1)R antagonist SLV330 (doses ranging from 0.3 to 10mg/kg, given orally, p.o.) could ameliorate impairments in distinct aspects of cognition using different disruption models in both mice and rats. Effects of SLV330 were tested on working memory deficits in the T-maze Continuous Alternation Task (T-CAT) in mice; episodic memory deficits in the Object Recognition Task (ORT) and Social Recognition Task (SRT) in rats. The acetylcholinesterase inhibitor (AChEI) donepezil (Aricept, approved for symptomatic treatment of Alzheimer's disease) and nicotine were used as reference compounds. SLV330 markedly improved aging and scopolamine-induced memory deficits in the T-CAT in mice with a lowest effective dose (LED) of 1mg/kg p.o., while reversing the cognitive dysfunction induced by the N-methyl-D-aspartate (NMDA) antagonist dizocilpine (MK-801) only at the middle dose of 3mg/kg. In the ORT, we have found that combined administration of subthreshold doses of SLV330 (1mg/kg, p.o.) and the AChEI donepezil (0.1mg/kg, p.o.), that had no discernable effects on performance when given alone, enhanced memory performance in Wistar rats with deficits induced by the muscarinic antagonist scopolamine, suggestive of additive synergistic effects of SLV330 and donepezil on cognitive impairment. Finally, SLV330 was found to have cognition enhancing properties in a time delay paradigm in the SRT at a LED dose of 3mg/kg (p.o.). In conclusion, the CB(1)R antagonist SLV330 was found to clearly improve memory in several preclinical models for cognitive impairment.

Dysregulation of lysophosphatidic acids in multiple sclerosis and autoimmune encephalomyelitis.

Bioactive lipids contribute to the pathophysiology of multiple sclerosis. Here, we show that lysophosphatidic acids (LPAs) are dysregulated in multiple sclerosis (MS) and are functionally relevant in this disease. LPAs and autotaxin, the major enzyme producing extracellular LPAs, were analyzed in serum and cerebrospinal fluid in a cross-sectional population of MS patients and were compared with respective data from mice in the experimental autoimmune encephalomyelitis (EAE) model, spontaneous EAE in TCR1640 mice, and EAE in Lpar2 -/- mice. Serum LPAs were reduced in MS and EAE whereas spinal cord LPAs in TCR1640 mice increased during the 'symptom-free' intervals, i.e. on resolution of inflammation during recovery hence possibly pointing to positive effects of brain LPAs during remyelination as suggested in previous studies. Peripheral LPAs mildly re-raised during relapses but further dropped in refractory relapses. The peripheral loss led to a redistribution of immune cells from the spleen to the spinal cord, suggesting defects of lymphocyte homing. In support, LPAR2 positive T-cells were reduced in EAE and the disease was intensified in Lpar2 deficient mice. Further, treatment with an LPAR2 agonist reduced clinical signs of relapsing-remitting EAE suggesting that the LPAR2 agonist partially compensated the endogenous loss of LPAs and implicating LPA signaling as a novel treatment approach. Graphical summary of lysophosphatidic signaling in multiple sclerosis.

Attentional performance of (C57BL/6Jx129Sv)F2 mice in the five-choice serial reaction time task.

Impaired attention is evident in several neurological and psychiatric disorders. In the present study, attentional capabilities were measured in the operant five-choice serial reaction time task (5-CSRTT) in male (C57BL/6Jx129Sv)F2 hybrid (B6129F2) mice. Main aims were to validate and standardize the test in these mice: to setup procedures, measure potential beneficial effects of sub-chronic nicotine in degraded versions of the 5-CSRTT (by decreasing stimulus duration, inducing white noise and making the stimuli unpredictable) and study disruptive effects of additional administration of the muscarinic antagonist scopolamine. During the baseline pre-nicotine sessions, the B6129F2 mice attained a very good performance in the test (95% accuracy). As stimulus duration was reduced from 2 s to 1 s, response accuracy of the mice decreased. Mice treated with nicotine (0.16 mg/kg) attained significantly higher response accuracy and had a lower percentage of incorrect responses in comparison with the solvent-treated animals. No further beneficial effects of nicotine were found. Reduced response accuracy was also obtained when stimulus duration was reduced from 1 s to 0.5 s and when a variable intertrial interval was introduced. Noise interpolation between trials did not impair performance. Finally, scopolamine (0.16 mg/kg) disrupted attentional functioning. Although most studies have been performed in rats, these results add to the existing evidence that the 5-CSRTT can also be used to assess attentional performance in mice. This offers the opportunity to test transgenic and knockout mice with similar background as the B6129F2 as animal models of psychiatric and neurological diseases.

Multiple rodent models and behavioral measures reveal unexpected responses to FTY720 and DMF in experimental autoimmune encephalomyelitis.

Experimental autoimmune encephalomyelitis (EAE) is a widely-used rodent model for multiple sclerosis (MS), but a single model can hardly capture all features of MS. We investigated whether behavioral parameters in addition to clinical motor function scores could be used to assess treatment efficacy during score-free intervals in the relapsing-remitting EAE model in SJL/J mice. We studied the effects of the clinical reference compounds FTY720 (fingolimod, 0.5mg/kg/day) and dimethyl fumarate (DMF, 20-30 mg/kg/day) on clinical scores in several rodent EAE models in order to generate efficacy profiles. SJL/J mice with relapsing-remitting EAE were studied using behavioral tests, including rotarod, gait analysis, locomotor activity and grip strength. SJL/J mice were also examined according to Crawley's sociability and preference for social novelty test. Prophylactic treatment with FTY720 prevented clinical scores in three of the four EAE rodent models: Dark Agouti (DA) and Lewis rats and C57BL/6J mice. Neither prophylactic nor late-therapeutic treatment with FTY720 reduced clinical scores or reversed deficits in the rotarod test in SJL/J mice, but we observed effects on motor functions and sociability in the absence of clinical scores. Prophylactic treatment with FTY720 improved the gait of SJL/J mice whereas late-therapeutic treatment improved manifestations of reduced social (re)cognition or preference for social novelty. DMF was tested in three EAE models and did not improve clinical scores at the dose used. These data indicate that improvements in behavioral deficits can occur in absence of clinical scores, which indicate subtle drug effects and may have translational value for human MS.

Body fat and fat-free mass in infants: new and classic anthropometric indexes and prediction equations compared with total-body electrical conductivity.

Anthropometry is frequently used for nutritional assessment. Little is known in infants about the validity of anthropometric measurements in relation to whole-body fat (TBF) and fat-free mass (FFM) composition. We compared TBF and FFM estimations by total-body electrical conductivity (TOBEC) with anthropometry in 435 healthy infants ages 21-365 d. TBF was best correlated with weight-for-length and calf circumference (r2 = 0.84, r2 = 0.83). FFM was best correlated with body weight (r2 = 0.93). Upper-arm anthropometry, skinfold thickness, and Quetelet's and Ponderal indexes were poorly correlated with TBF and FFM (r2 < 0.65). New anthropometry-based prediction equations were calculated (r2 = 0.90 for TBF and r2 = 0.95 for FFM). New simple indexes (analogous to Quetelet's index) were calculated for TBF (weight x calf circumference/length; r2 = 0.87) and for FFM (square root of weight x length; r2 = 0.95). Prediction equations and indexes were cross-validated in a second population by a second observer. Interobserver variation was largest for equations with skinfold thicknesses included. We conclude that anthropometry can be used for rough estimations of infant body composition, although indexes different than those used in children and adults are preferred.

Quantitative assessment of infant body fat by anthropometry and total-body electrical conductivity.

Measurement of total-body electrical conductivity (TOBEC) has emerged as a rapid, safe, and reproducible method for estimation of infant total body fat (TBF). Agreement of two anthropometric methods [by Dauncey et al (1977) and Weststrate et al (1989)] with TOBEC-TBF was assessed in 435 healthy infants aged 21-365 d. Dauncey-TBF correlated with TOBEC-TBF by r2 = 0.61 and exceeded TOBEC-TBF by 0.14 +/- 0.25 kg in infants < 4 mo of age. Thereafter, TOBEC-TBF exceeded Dauncey-TBF by 0.20 +/- 0.47 kg. We modified Dauncey's method, which significantly improved the correlation to r2 = 0.75. Weststrate-TBF correlated with TOBEC-TBF by r2 = 0.87, but exceeded TOBEC-TBF by 0.5 kg. Both methods showed poor agreement with TOBEC-TBF. We conclude that both methods, although suitable for comparison of TBF between groups, cannot be used to accurately assess TBF in an individual infant.

Energy utilization and growth in breast-fed and formula-fed infants measured prospectively during the first year of life.

This study is the first to report approximations of energy requirements for male and female breast-fed and formula-fed infants based on individual estimates of total daily energy expenditure (TDEE) and energy deposition derived from total body fat (TBF) and fat-free mass (FFM) gain as determined by total-body electrical conductivity. In 46 healthy, full-term infants the effect of > or = 4 mo of exclusive breast-feeding compared with formula feeding on macronutrient and energy intake, TDEE, energy deposition, and growth were investigated prospectively. Metabolizable energy intake (MEI) was assessed from macronutrient intake by test weighing (MEI-TW) and from the sum of TDEE and energy deposition (MEI-Pred). At 1-2, 2-4, 4-8, and 8-12 mo of age MEI-Pred averaged 431 +/- 38, 393 +/- 33, 372 +/- 33, and 355 +/- 21 kJ x kg(-1) x d(-1) for boys, and 401 +/- 59, 376 +/- 25, 334 +/- 33, and 326 +/- 17 kJ x kg(-1) x d(-1) for girls. No significant difference between breast-fed and formula-fed infants was found with respect to weight, length, head circumference, TBF, FFM, and TDEE at all ages, or for gain in length, weight, TBF, and FFM. MEI-TW was significantly different between feeding groups at 1-4 mo of age (formula-fed being greater than breast-fed, P < 0.005). This feeding effect, however, was not significant for MEI-Pred (MJ/d). MEI-TW differed from MEI-Pred only in breast-fed infants at 1-4 mo (P < 0.05 at 2-4 mo). The data from this study indicate that energy requirements in infants are lower than the recommendations in guidelines currently in use.

Hippocampal and cortical sensory gating in rats: effects of quinpirole microinjections in nucleus accumbens core and shell.

Sensory processing disturbances, as measured in the P50/sensory gating paradigm, have been linked to aberrant auditory information processing and sensory overload in schizophrenic patients. In this paradigm, the response to the second of paired-click stimuli is attenuated by an inhibitory effect of the first stimulus. Sensory gating has been observed in most healthy human subjects and normal laboratory rats. Because mesolimbic dopamine has been implicated in other filtering disturbances such as prepulse inhibition of the acoustic startle response and given the fact that amphetamine and apomorphine have been shown to disrupt gating, this study was performed to investigate the role of mesolimbic dopamine in sensory gating. The dopamine D2 receptor agonist quinpirole (10 microg/0.5 microl) was injected bilaterally in nucleus accumbens core and shell and effects on cortical and hippocampal sensory gating were investigated. Also, effects of the dopamine D2 receptor antagonist haloperidol (0.1 mg/kg, subcutaneously) as pretreatment were studied. First, quinpirole significantly reduced both the amplitude to the first click and gating as measured in the cortex and in the hippocampus. There was a tendency for the quinpirole effects on hippocampal gating to be more pronounced in rats injected in the shell. Secondly, haloperidol did not antagonize effects of quinpirole on hippocampal parameters, whereas haloperidol pretreatment fully antagonized quinpirole effects on cortical parameters. In conclusion, gating can be significantly reduced when a dopamine agonist is specifically targeted at mesolimbic dopamine D2 receptors. However, an important consideration is that the dopaminergic effects in the present study on gating are predominantly mediated by the effects on the amplitude to the first click. This has also been suggested for systemic amphetamine injections in rats and schizophrenic patients. This casts doubt on whether dopamine receptor activation affects the putative inhibitory process between the first and the second stimulus.

Auditory information processing in rat genotypes with different dopaminergic properties.

RATIONALE: Auditory filtering disturbances, as measured in the sensory gating and prepulse inhibition (PPI) paradigms, have been linked to aberrant auditory information processing and sensory overload in schizophrenic patients. In both paradigms, the response to the second stimulus (S2) is attenuated by an inhibitory effect of the first stimulus (S1). Dopamine (DA) agonists have been found to reduce gating of auditory evoked potentials (AEPs) and PPI in healthy human subjects and in rats. These effects have been linked to DA hyperactivity in the mesolimbic system. A non-invasive approach in studying the role of the DA system in PPI and AEP gating is to compare rat genotypes that are marked by distinct DA systems. OBJECTIVES: Several questions were asked in the present study. Are PPI and AEP gating disturbed in (a) rats that are marked by a relatively high DA reactivity of the mesolimbic system, namely apomorphine-susceptible (APO-SUS) and WAG/Rij rats or in (b) rats that are marked by a relatively high DA activity of the nigrostriatal system, namely apomorphine-unsusceptible (APO-UNSUS) and ACI rats? Moreover, is the particular DA balance (c) between the nigrostriatal and mesolimbic system related to deficits in PPI and AEP gating? METHODS: For this purpose, the above-mentioned four rat genotypes (APO-SUS, APO-UNSUS, ACI and WAG/Rij) that vary in DA balance between both systems, were compared in the AEP gating paradigm. PPI was only measured in the ACI and WAG/Rij rats, since it has already been shown in a previous study that APO-SUS rats show diminished PPI as compared to rats of the APO-UNSUS genotype. RESULTS: AEP gating of the vertex N50 was significantly reduced in WAG/Rij rats as compared to the remaining three rat genotypes (APO-SUS, APO-UNSUS and ACI). No PPI deficits were found in the ACI and WAG/Rij rats, although ACI rats had a significantly higher basal startle amplitude. CONCLUSIONS: The PPI deficit in APO-SUS and not in the other genotypes, suggests that especially a relatively high DA reactivity of the mesolimbic system, together with a relatively low activity of the nigrostriatal system, contributes to this deficit. In contrast, the N50 gating deficit in WAG/Rij rats and not in the other genotypes suggests that a relatively high DA activity of the nigrostriatal system together with a relatively high DA reactivity of the mesolimbic system is necessary for the presence of a N50 gating deficit. On the basis of these results we have concluded that both auditory filtering processes are differently regulated by DA in the nigrostriatal and mesolimbic systems.

Differential effects of ketamine on gating of auditory evoked potentials and prepulse inhibition in rats.

Schizophrenic patients suffer from deficits in information processing. Patients show both a decrease in P50 gating [assessed in the conditioning-testing (C-T) paradigm] and prepulse inhibition (PPI), two paradigms that assess gating. These two paradigms might have a related underlying neural substrate. Gating, as measured in both the C-T paradigm (the gating of a component of the auditory evoked potential (AEP)], and PPI can easily be measured in animals as well as in humans. This offers the opportunity to model these information processing paradigms in animals in order to investigate the effects of neurotransmitter manipulations in the brain. In order to validate the animal model for disturbances in AEP gating, d-amphetamine (0.5 and 1 mg/kg, i.p.) was administered. Gating of an AEP component was changed due to injection of d-amphetamine (1 mg/kg) in the same way as seen in schizophrenic patients: both the amplitude to the conditioning click and the gating were significantly reduced. Next, the effect of the N-methyl-D-aspartate (NMDA) antagonist ketamine (2.5 and 10 mg/kg, i.p.) was investigated to assess its effects in the two gating paradigms. It was found that ketamine (10 mg/kg) did not affect gating as measured with components of the AEP. However, ketamine (10 mg/kg) disrupted PPI of the startle response to the extent that prepulse facilitation occurred. Firstly, it is concluded that AEP gating was disrupted by d-amphetamine and not by ketamine. Secondly, PPI and the C-T paradigm reflect distinct inhibitory sensory processes, since both paradigms are differentially influenced by ketamine.

Dopamine characteristics in different rat genotypes: the relation to absence epilepsy.

Dopaminergic neurotransmission has been shown to participate in the control of absence epilepsy. This type of epilepsy, a generalized non-convulsive form, is associated with bursts of bilateral synchronous spike wave discharges (SWDs) recorded in the EEG. In a previous study, it was suggested that two features of the apomorphine-susceptible (APO-SUS) rat genotype, a relatively low dopaminergic reactivity of the nigrostriatal system and relatively high dopaminergic reactivity of the mesolimbic system, contribute to the high incidence of SWDs. Indeed, apomorphine-unsusceptible (APO-UNSUS) rats, characterized by opposite dopaminergic features, show considerably less SWDs than APO-SUS rats. The first goal of the present study was to assess the baseline SWD incidence in four rat genotypes (WAG/Rij, ACI, APO-SUS and APO-UNSUS) in order to replicate previous findings. It was expected that both the APO-SUS and WAG/Rij rats would show a considerably higher SWD incidence in comparison to the APO-UNSUS and ACI rats. For this purpose, rats were registered for a 19 hour period. Assuming that haloperidol decreases dopaminergic transmission in the nigrostriatal system via inhibition of the dopamine receptors and enhances dopaminergic transmission in the mesolimbic system via inhibition of the noradrenergic receptors, it was postulated that haloperidol would enhance the difference in dopaminergic reactivity between both systems in favor of the accumbens. Therefore, the second purpose in the present study was to investigate whether haloperidol (2 mg/kg, IP) could further potentiate SWD incidence when injected in the APO-SUS rats, already characterized by a relatively low dopaminergic reactivity of the nigrostriatal system and relatively high dopaminergic reactivity of the mesolimbic system, in comparison to the APO-UNSUS rat genotype. Finally, the third aim was to study if another epileptic rat genotype, the WAG/Rij, would show similar increases in SWD incidence following an injection with haloperidol as expected for the APO-SUS. First, previous findings were replicated: the value of the hourly number of SWDs decreased in the following order: APO-SUS > WAG/Rij > APO-UNSUS and ACI. Secondly, earlier data were extended by the fact that the APO-SUS responded to a systemic injection of haloperidol with an increase in SWD number and duration, in contrast to the APO-UNSUS rats. The hypothesis that the SWD incidence would be mostly affected by haloperidol in the APO-SUS rats, was confirmed by these findings. It is suggested that haloperidol increases the SWD incidence in APO-SUS rats by enhancing the difference between the dopaminergic reactivity in the nigrostriatal and mesolimbic system. Finally, further research is required to provide evidence in favor of the hypothesis that the relative dominance of the dopaminergic mesolimbic system is smaller in WAG/Rij than in APO-SUS.

Neural correlates of sensory gating in the rat: decreased Fos induction in the lateral septum.

In the P(50) gating or conditioning-testing paradigm in the rat, two identical click stimuli are presented with an inter-click interval of 500 ms. The reaction towards the second click, as measured with evoked potentials, is reduced in respect to that towards the first click; this phenomenon is called sensory gating. In the present experiments, the inter-click interval was varied systematically and auditory evoked potentials were measured. Sensory gating was found to occur only at intervals between 500 and 1000 ms, but not at longer intervals. Fos immunohistochemistry was then performed using two groups of rats exposed to double clicks: the inter-click interval was 500 ms in the experimental group and 2500 ms in the control group. Fos induction was analyzed in selected brain structures. In the auditory pathways, Fos-immunoreactive neurons were found in both groups of rats in the inferior colliculus and medial geniculate body. Fos-immunoreactive cells were also examined in the septum and hippocampus. In the ventral part of the lateral septal nucleus, the labeled neurons were significantly fewer in the experimental animals compared to the control group. Smaller and non-significant quantitative differences of Fos-positive neurons were documented in the medial septum and hippocampal CA1 region. These data point out a selective decrease in the lateral septum of Fos induced by auditory sensory gating, and suggest an involvement of this structure, and possibly of other parts of the septo-hippocampal system, in sensory gating mechanisms. The results might be relevant for theories on sensory gating deficits in schizophrenia.

Anatomical and functional aspects of mu opioid receptors in epileptic WAG/Rij rats.

Involvement of opioid systems in the pathogenesis of absence epilepsy has been postulated. However, the role of the mu opioid receptor has not been fully elucidated as yet. In the present study the role of this receptor in absence epilepsy was investigated autoradiographically and pharmacologically. The density of mu opioid receptors in discrete brain areas was quantified in WAG/Rij rats, which are regarded as a genetic model of primarily generalized absence epilepsy and in three control groups of non-epileptic rats. The autoradiographic study showed an abundance of mu opioid receptors (labelled with [3H]DAMGO) in the structures involved in generation and propagation of spike-wave discharges, such as the thalamus, cortex and striatum. A significant decrease in the mu receptor density was found only in the frontal cortex of epileptic WAG/Rij rats. In the pharmacological study, the effect of mu opioid receptor activation in different brain structures of WAG/Rij rats on the number of complexes of spike-wave discharges was investigated. DAMGO (0.02 and 0.07 microg/0.5 microl) was bilaterally injected into the thalamus, striatum and frontal cortex. DAMGO resulted in a dose-related increase in the number of spike-wave discharges after intracortical and intrastriatal administration by approximately 200-300% and after intrathalamic administration by approximately 500%. The injection of DAMGO into those structures had no significant effect of any kind on the behavior measured, except for passive behavior which was reduced after intrastriatal injection. The high density of mu opioid receptors in the areas involved in the genesis of spike-wave discharges, as well as the highest responsiveness of thalamic mu opioid receptors to the epileptogenic effects of DAMGO, suggest involvement of mu receptors in the genesis of spike-wave discharges.

Sensory gating of auditory evoked potentials in rats: effects of repetitive stimulation and the interstimulus interval.

In the P50 gating or conditioning-testing (C-T) paradigm, the P50 response, a small positive midlatency ( approximately 50 ms after stimulus onset) component of the human auditory evoked potential (AEP), is reduced towards the second click (S2) as compared to the response to the first click (S1). This phenomenon is called sensory gating. The putative function of sensory gating is thought to protect subjects from being flooded by irrelevant stimuli. Comparative studies have been done in rats in order to elucidate the underlying neural substrate of sensory gating. However, for a direct comparison of rat and human AEP components, it is imperative for both components to show similar characteristics. The amount of sensory gating in humans is dependent on repetitive stimulation and the interstimulus interval (ISI). In the present study effects of repetitive stimulation (Experiment 1) and various ISIs (Experiment 2) were determined on rat AEP components. The results demonstrate that gating is not limited to a restricted cortical area or a single midlatency component and that repetitive stimulation and ISI affect gating of several rat AEP components. Components such as the vertex P17 and N22 show a decrease in gating within several S1-S2 presentations, mainly due to a decrease in amplitude to S1 (Experiment 1). Gating for vertex components (such as the P17, N22 and N50) is ISI dependent (Experiment 2), but there is no interval in the 200-600 ms range at which optimal gating occurs. The ISI effects on gating are due to an increase of the amplitude to S2. The results have implications for the discussion about the rat homologue of the human P50.

The effect of alterations in physical and chemical characteristics on TOBEC-derived body composition estimates: validation with non-human models.

The measurement of total-body electrical conductivity (TOBEC) has become one of the standard methods for the estimation of body composition in infants. We investigated, using non-human models, the effect on the accuracy of TOBEC-derived body composition estimates of alterations in physical and chemical characteristics of the fat-free mass (FFM). The effect of electrolyte type, concentration and volume on TOBEC was determined using 2, 3 and 51 solutions of six different chlorides and sodium bicarbonate. Equimolar concentrations yielded TOBEC values in accordance with known ion conductivities: H+ >> Ca2+ > Mg2+ > K+ > Na+ > Li+ and Cl- > HCO3-. The behaviour of these solutions was described very accurately over a wide range of concentrations (1-200 mM) by a simple exponential law. Dissolved egg-white protein, glycine and L-glutamine elicited no TOBEC signal. In vitro, using polyethylene bottles filled with physiologic saline, in the interval of 2-45 degrees C a linear relation was observed between temperature and TOBEC. Below the freezing point no TOBEC signal was elicited. The effect of tissue autolysis and body temperature on TOBEC was examined by repeated measurements of TOBEC and temperature in seven fresh infant minipig cadavers. Five minipigs were allowed to cool. Shortly after death TOBEC decreased by 2.5% per degrees C. Two animals were kept at constant temperature. The TOBEC signal showed a gradual increase of 9% after 7 h due to autolysis. We conclude that in vivo TOBEC measurements are affected by ion concentration (e.g. non-isotonic hydration changes), geometry (e.g. deviations in body shape), temperature (e.g. fever, skin cooling) and tissue autolysis (measurements after death). Proteins, molecules with strong dipole moments and ions trapped in crystalline structures do not significantly affect the TOBEC reading.

Growth and body composition in preterm infants with bronchopulmonary dysplasia.

OBJECTIVE: To compare growth and body composition in preterm infants with bronchopulmonary dysplasia (BPD) with normal healthy term infants during the first year of life. DESIGN: Twenty nine preterm infants with BPD (mean (SD) gestational age 27.1 (1.6) weeks; birth weight 852 (173) g) were followed prospectively. Anthropometry and body composition determined by total body electrical conductivity were measured and compared with those of healthy term infants at the same post-term age. RESULTS: In infants with BPD, the mean weight standard deviation scores (SD scores) 6 weeks after term were significantly lower (-1.44 and -2.68, boys and girls respectively) than in healthy term infants of the same age and did not improve during the first year. The mean length SD score was significantly lower in infants with BPD 6 weeks after term than in healthy term infants of the same age, and, although it improved significantly during the first year, the mean length SD score in girls with BPD was significantly below 0 12 months after term. In infants with BPD, the mean free fat mass (FFM) SD score and the mean total body fat (TBF) SD score at 6 weeks post-term age were significantly below 0. The mean FFM SD scores (-1.01 and -2.56, boys and girls respectively) and the mean TBF SD scores (-1.14 and -2.40, boys and girls respectively) 12 months after term were significantly lower than in healthy term infants of the same age. CONCLUSIONS: Preterm infants with BPD have impaired growth, with a deficit in TBF and FFM already 6 weeks after term; FFM and TBF remain low compared with healthy term infants during the first year of life. Nutritional intervention studies in infants with BPD are needed to evaluate if nutrition is the major determinant of growth and body composition or if this pattern of growth in preterm infants with BPD is the result of disturbed endocrine control.

Effects of risperidone, clozapine and the 5-HT6 antagonist GSK-742457 on PCP-induced deficits in reversal learning in the two-lever operant task in male Sprague Dawley rats.

Reasoning and problem solving deficits have been reported in schizophrenic patients. In the present study, we have tested rats in a two-lever reversal learning task in a Skinner box to model these deficits. In other studies using the Skinner box, atypical antipsychotics fully reversed phencyclidine (PCP)-induced impairments in reversal learning which is in contrast to clinical observations where antipsychotics lack the ability to fully reverse cognitive deficits in schizophrenia. Therefore, it can be argued that the outcome of these tests may lack predictive value. In the present study, after training on a spatial discrimination between two levers, rats were exposed to a reversal of the previously learned stimulus-response contingency during 5 days. We first investigated the effects of sub-chronic treatment with the non-competitive N-methyl-d-aspartate (NMDA) antagonists dizocilpine (MK-801) and PCP on reversal learning and extinction in male Sprague Dawley rats. Subsequently, we studied the effects of different PCP treatment regimes. Then, we investigated whether the atypical antipsychotics risperidone and clozapine and the 5-hydroxytryptamine6 (5-HT6) antagonist GSK-742457 could reverse the PCP-induced deficits. All drugs were administered subcutaneously (s.c.). MK-801 did not impair reversal learning, while PCP (1.0 and 2.0 mg/kg) induced a clear deficit in reversal learning. Both compounds, however, disrupted extinction at all tested doses. Risperidone and clozapine were both ineffective in significantly ameliorating the PCP-induced deficit in reversal learning which fits well with the clinical observations. The lowest dose of clozapine (1.25 mg/kg) had an intermediate effect in ameliorating the deficit in reversal learning induced by PCP (not different from control or PCP-treated rats). The lowest dose of GSK-742457 (0.63 mg/kg) fully reversed the PCP-induced deficits while the higher dose (5.0 mg/kg) had an intermediate effect.