Predicting Time to Delivery in Hypertensive Disorders: Assessing PlGF and sFlt-1 with the Novel Parameter 'Mtp-Multiples of a Normal Term Placenta'

Background: Imbalanced angiogenesis is characteristic of normal placental maturation but it also signals placental dysfunction, underlying hypertensive disorders during pregnancy. This study aimed to investigate the relationship between angiogenic placental aging, measured by markers placental growth factor (PlGF) and soluble fms-like tyrosine kinase-1 (sFlt-1) using the new index "Multiples of a normal term placenta" (Mtp) and the duration of pregnancy. Methods: A retrospective observational study was conducted, including singleton pregnancies diagnosed or suspected of hypertensive disorders after the 20th gestational week. Mtp measures how far a single dosage of angiogenic marker deviates from the expected value in an uncomplicated full-term pregnancy (Mpt = sFlt-1/sFlt-1 reference value or PIGF/PIGF reference value). We considered the 90th, 95th, and 97.5th centiles for sFlt-1 and the 2.5th, 5th, and 10th centiles for PlGF as references. Results: The categories with longer time to delivery, regardless of gestational age, were: Mtp PlGF 10th c ≥ 2, ≥3 and Mtp sFlt-1 90th c ≤ 0.5 (median days of 9, 11, 15 days, respectively). These two categories Mtp sFlt-1 90th c ≥ 3 and Mtp sFlt-1 97.5th c ≥ 2 allow the identification of women at risk for imminent delivery within 1 day. Women who were deemed at low/medium risk based on the sFlt-1/PIGF ratio appeared to be at high risk when considering the individual values of sFlt-1 and/or PIGF. Conclusions: This new Mtp index for sFlt-1 and PlGF could be employed to assess the degree of placental aging in women with hypertensive disorders. It represents a valid tool for evaluating the risk of imminent birth, irrespective of gestational age, surpassing the current stratification based on the sFlt-1/PIGF ratio.

sFlt-1 Levels as a Predicting Tool in Placental Dysfunction Complications in Multiple Pregnancies

BACKGROUND

several studies have demonstrated that angiogenic markers can improve the clinical management of hypertensive disorders (HDs) and fetal growth restriction (FGR) in singleton pregnancies, but few studies have evaluated the performance of these tests in multiple pregnancies. Our aim was to investigate the role of soluble fms-like tyrosine kinase 1 (sFlt-1) in predicting adverse obstetric outcomes in hospitalized multiple pregnancies with HD (preeclampsia/gestational hypertension/uncontrolled chronic hypertension) and/or FGR in one or more fetuses.

METHODS

A retrospective analysis of multiple pregnancies with HD/FGR occurring after the 20th gestational week. Pregnant women were divided into two groups: women with high levels of sFlt-1 and those with low levels of sFlt-1. A value of sFlt-1 greater than or equal to 15,802 pg/mL was considered arbitrarily high, as it is equivalent to two times the 90th percentile expected in an uncomplicated full-term singleton pregnancy based on data from a prospective multicenter study (7901 pg/mL).

RESULTS

The cohort included 39 multiple pregnancies. There were no cases of birth <34 weeks, HELLP syndrome, ICU admission, and urgent cesarean sections for HD/FGR complications reported among women with low levels of sFlt-1.

CONCLUSIONS

A cut-off value of sFlt-1 ≥ 15,802 pg/mL could represent a valuable tool for predicting adverse obstetric outcomes in multiple pregnancies hospitalized for HD/FGR disorders, regardless of gestational age and chorionicity.

Splenic artery aneurysm in obstetric patients: a series of four cases with different clinical presentation and outcome

OBJECTIVE

To describe four consecutive cases of splenic artery aneurysm with different clinical patterns of presentation among obstetric patients.

METHOD

A series of four cases of splenic artery aneurysm diagnosed in pregnant or post-partum women at our University center between January 1998 and December 2020. Clinical and radiological data were retrospectively obtained by reviewing paper and electronic medical records after acquiring patient's consent.

RESULTS

One case was completely asymptomatic and incidentally identified at the beginning of pregnancy, thus allowing for multidisciplinary treatment. The other three cases were unknown: two manifested with maternal collapse due to aneurysm rupture in the third trimester of gestation, whereas one presented with acute abdominal pain during the post-partum period and was successfully managed before rupture occurred.

CONCLUSION

Although being extremely rare, SAA rupture in obstetric patients can be associated with dramatic consequences. Since early suspicion and prompt intervention are essential to avoid fatal outcomes, promotion of knowledge of all the potential clinical patterns of presentation of SAA rupture among obstetric patients is mandatory.

sFlt-1/PlGF ratio in hypertensive disorders of pregnancy in patients affected by COVID-19

Objectives

To analyze soluble Fms-like tyrosine Kinase 1 (sFlt-1) and Placental Growth Factor (PlGF) ratio concentrations in COVID-19 pregnant patients with and without Hypertensive Disorders of Pregnancy (HDP), compared with non COVID-19 pregnant patients with HDP and a control group.

Study design

We recruited and obtained a complete follow-up of 19 COVID-19 pregnant patients with HDP and of 24 COVID-19 normotensive pregnant patients. Demographic, clinical and sFlt-1/PlGF ratio findings were compared with a group of 185 non COVID-19 pregnant patients with HDP and 41 non COVID normotensive patients. Findings were based on univariate analysis and on a multivariate adjusted model, and a case by case analysis of COVID-19 pregnant patients with an abnormal sFlt-1/PlGF ratio > 38 at recruitment.

Main outcome measures

sFlt-1/PlGF ratio.

Results

We confirmed a significant higher prevalence of HDP in women affected by COVID-19 compared to control population. sFlt-1/PlGF ratio was found high in HDP patients, with and without of Sars-Cov2 infection. COVID-19 patients with worse evolution of the disease showed greater rates of obesity and other comorbidities. sFlt/PlGF ratio proved not to be helpful in the differential diagnosis of the severity of this infection.

Conclusions

COVID-19 pregnant patients showed a higher prevalence of HDP compared to non COVID-19 controls, as well as higher comorbidity rates. In spite of the possible common endothelial target and damage, between Sars-Cov-2 infection and HDP, the sFlt1/PlGF ratio did not correlate with the severity of this syndrome.

Placental growth factor as a predictive marker of preeclampsia - PREBIO study - PREeclampsia BIOchemical study

INTRODUCTION

To evaluate the clinical utility of placental growth factor (PlGF) for the prediction of preeclampsia (PE).

MATERIALS AND METHODS

This prospective cohort study included women divided into three groups: (1) pregnancies without preconceptional risk of developing PE; (2) pregnancies with a preconceptional and/or current risk of developing PE; (3) PE-complicated pregnancies (control group). Blood samples were collected every 4-5 weeks or during hospitalization from early second trimester until delivery in the group 1 and 2, at the diagnosis of PE in the group 3. Plasma levels of PlGF were measured using The Triage PlGF test (Alere) and considered pathological under the 5th centile for gestational age. Sensitivity (Sn), specificity (Sp), positive and negative predictive value (PPV, NPV) were calculated.

RESULTS

In group 1, 30% of women (3/10) had pathological test but none of them developed PE (Sp 70%, NPV 100%). In group 2 (n = 75), none of the patients with normal test developed PE (0/24), while 39% of women with PlGF < 5th centile (20/51) developed PE (Sn 100%, Sp 44%, PPV 39%, NPV 100%). In group 3 (n = 11) all women except one had a pathological PlGF test (Sn 90%, PPV 100%).

CONCLUSIONS

Our data support recent studies which identify PlGF as a biochemical marker not only of PE, but also of placental dysfunction. In fact, it is useful for ruling out PE in women at risk because of the high Sn and high NPV: a normal PlGF is related with a positive pregnancy outcome. Therefore, the measurement of this biomarker would simplify PE clinical management and would reduce costs.

Management of pregnancy blood pressure increase in the emergency room: role of PlGF-based biochemical markers and relative economic impact

INTRODUCTION

To evaluate the clinical and economic impact of healthcare management of pregnant women with blood pressure increase (BPI) accessing emergency room (ER) and the utility of the introduction of a PlGF-based test in clinical practice.

MATERIALS AND METHODS

This retrospective cohort study included women with single pregnancies who performed at least 1 ER access for BPI after the 20th gestational week in 2016. BPI was subsequently classified as significant if associated with preeclampsia (PE) or Fetal Growth Restriction (FGR) and not significant otherwise. Two experts evaluated potential changes in patients' management with the introduction of a PlGF-based test. The direct healthcare cost was estimated.

RESULTS

We enrolled 107 patients, of which 30% showed significant BPI (17 PE cases, 13 FGR, and 2 both pathologies). Anamnestic, clinical, and laboratory evaluations were not effective in differentiating between significant and not significant BPI (p-values: .8320, .2856, and .2297, respectively). The introduction of a PlGF-based test would have reduced overtreatment and undertreatment. The test would have avoided 18% of all hospitalizations, 35% of hospitalizations for BPI, 43% of outpatient referrals, and 13% of ER accesses. The number of avoidable accesses was higher in women with not significant BPI. Overall, the mean total cost (from first ER access until delivery) was €2634 per woman and €401 would have been avoidable.

CONCLUSION

The clinical integration of PlGF-based tests is advantageous in diagnostic, prognostic and economic terms, as an objective marker of placental dysfunction.

Parental counseling in trisomy 18: Novel insights in prenatal features and postnatal survival

Data on the outcome of trisomy T18 (T18) when diagnosed during pregnancy are lacking. We performed a retrospective study of pregnancies complicated by T18 diagnosed at our center and a literature search for publications on the topic, with pooled estimates of survival rates at different gestational and post-natal ages. In our series, all the 60 patients included in the analysis had prenatally detected ultrasound anomalies, which were evidenced in the first trimester or at the second trimester scan in 73% of cases. In the continued pregnancies, ultrasound findings did not correlate with prenatal or post-natal outcome. A meta-analysis of available literature and our data showed that 48% [37-60%] of fetuses were live born, and among these 39% [11-72%] survived beyond 48 hr and 11% [3-21%] beyond 1 month. Our results confirm that prenatal ultrasound has high sensitivity in detection of T18 but is not predictive of the outcome of the continued pregnancies. The data on survival support that T18, even when antenatally diagnosed, cannot be considered as a uniformly lethal syndrome.

Influencing factors for late-onset preeclampsia

OBJECTIVE

Different etiologies for early- (<34.0 weeks) and late (≥34.0 weeks)-onset preeclampsia (EO-LO PE) are reported. The aim of our study is to identify influencing factors for the LO form.

METHODS

Retrospective study of 284 consecutive women diagnosed as preeclamptic at 22.4-41.5 weeks, from 3/2005 to 10/2011, evaluated in relation to EO versus LO PE.

RESULTS

LO PE was identified in 151 cases. Gestational Diabetes Mellitus (11% versus 4%, p = 0.04), body mass index (BMI) ≥35 kg/m(2) (9% versus 2%, p = 0.03), pathological weight gain for BMI class (30% versus 13%, p = 0.001), ≥5 (58% versus 23%, p < 0.001) and ≥7 kg/m(2) BMI increase (19% versus 9%, p = 0.04) were more common in LO than in EO PE. At Estimation Regression analysis weighted for Gestational Age (GA) at delivery BMI ≥35 and ≥5 kg/m(2) BMI increase resulted related to LO PE (OR = 3.76, CI(95%) = 1.97-17.04; OR = 4.28, CI(95%) = 2.44-7.54).

CONCLUSIONS

BMI ≥35 and ≥5 kg/m(2) increase appeared as influencing factors for LO PE, thus supporting the role of systemic inflammation in its pathogenesis.

Immunohistochemical expression of Annexin A5 in preeclamptic placentas

OBJECTIVE

To study the expression of Annexin A5 (A5) in relation to preeclampsia using immunohistochemical Tissue Microarray (TMA) technique.

STUDY DESIGN

Case-control study of 66 singleton preeclamptic (PE) patients matched for gestational age (GA) at delivery with 63 normotensive controls with normally grown fetuses. Immunohistochemical expression of A5 and other population characteristics were compared between the two groups using Chi-square, One-way ANOVA, Spearman's Correlation, and Linear Regression.

RESULTS

The two groups were similar for maternal age and rate of corticosteroid administration, but differed for nulliparity, Body Mass Index (BMI), blood pressure, presence of placental histological lesions, and placental weight. Expression of A5 was similar in PE and controls (p = 0.10); however it was found to be lower in PE cases complicated by fetal growth restriction (FGR, n = 34) compared with matched controls (n = 55) (p = 0.04). An inverse correlation was found between A5 and GA in cases but not in controls (p = 0.04 vs p = 0.71). The association was even more significant in the subgroup of PE complicated by FGR (p = 0.02). A5 expression was not influenced by blood pressure, proteinuria, or placental weight.

CONCLUSIONS

Annexin A5 expression seems to be related only to FGR and not to PE or its clinical severity.

Role of radiography and ultrasonography in the diagnosis of the pediatric gastro-esophageal reflux disease

Twenty-four hour esophageal pH-monitoring is gold standard for evaluate pathological GERD. Role of radiography and ultrasonography in the diagnosis of gastro-esophageal reflux disease (GERD) has been studied. Our results have been shown that radiography and ultrasonography have a limited role in the diagnosis of pathological GERD. However, such investigations an useful the follow-up of patients affected by pathological GERD.

Effects of dopamine depletion from the caudate-putamen and nucleus accumbens septi on the acquisition and performance of a conditional discrimination task

Three experiments compared the effects of dopamine depletion from the caudate-putamen (CAUD; dorsal striatum) or nucleus accumbens septi (NAS; ventral striatum), or a systemically administered dopamine receptor antagonist (alpha-flupenthixol) on the acquisition and performance of a conditional discrimination task involving temporal frequency. In Expt. 1, rats receiving 6-hydroxydopamine (6-OHDA) lesions of the CAUD were impaired in the acquisition of a visual version of the task, and rats with 6-OHDA lesions of the NAS were not reliably impaired. Even when the rats with CAUD lesions had acquired the discrimination, they were still significantly slower to collect earned food pellets. Both CAUD and NAS lesions reduced a bias to respond to the faster of the two discriminative stimuli. In Expt. 2, rats with 6-OHDA lesions of CAUD were markedly impaired in their accuracy and speed of responding when they had been trained to criterion preoperatively. These effects could not be mimicked in controls by prefeeding (which had only minor effects on performance). Rats with 6-OHDA-induced lesions of the NAS were unimpaired in either visual or auditory discrimination performance, but were slower to extinguish responding than controls. In Expt. 3, alpha-flupenthixol (0.1-0.56 mg/kg, i.p.) produced dose-dependent impairments in both latency to respond and choice accuracy in visual and auditory versions of the task. In conjunction with other results, these data suggest that (1) dopamine receptor blockade and central dopamine depletion can impair discrimination performance under certain conditions (2) dopamine depletion from the ventral and dorsal striatum, respectively, have dissociable effects on behaviour controlled by conditioned reinforcers and discriminative stimuli and (3) the disruption of discrimination performance by dorsal striatal dopamine depletion is probably attributable to several factors.

Effects of excitotoxic lesions of the substantia innominata, ventral and dorsal globus pallidus on visual discrimination acquisition, performance and reversal in the rat

Rats received infusions of ibotenic acid into the substantia innominata, in the region of the nucleus basalis of Meynert (nbM), before and after training on simple (simultaneous) and conditional visual discriminations. The ibotenate infusions reduced cortical choline acetyltransferase (ChAT) levels by about 20%, destroyed many ChAT-immunoreactive neurons in the nbM, but also caused the loss of many neurons in the substantia innominata and adjacent areas. These lesions did not impair the acquisition and performance of a simple visual discrimination, but did impair reversal of the discrimination and the performance of a conditional visual discrimination. However, the degree of impairment was unrelated to the degree of cortical ChAT loss. Ibotenic acid lesions to the dorsal globus pallidus also impaired reversal of discrimination but left acquisition and performance unaffected. Striatal dopamine depletion produced by 6-hydroxydopamine (6-OHDA) infusions into the mid-ventral caudate nucleus impaired performance of the simultaneous visual discrimination. Cortical noradrenaline depletion produced by 6-OHDA lesions of the dorsal noradrenergic bundle either alone or in combination with ibotenic acid lesions of the substantia innominata had no effect on acquisition of the discrimination. It is concluded that ibotenic acid lesions of the substantia innominata or to the dorsal globus pallidus affect learning and performance of conditional visual discrimination performance and impair reversal learning without affecting the capacity to discriminate visual events. These results are compared to those following cortical noradrenaline depletion or striatal dopamine loss.

Behaviorally augmented versus other components in organophosphate tolerance: the role of reinforcement and response factors

Male Wistar-derived rats were used to assess the behaviorally augmented component of tolerance to paraoxon depression of a feeding response. Separate groups of animals were treated daily by 0.125 mg/kg of the compound given sc either 1 hr before the start or 45 min after the end of a 90-min feeding session. However, the dose was reduced to 0.0625 mg/kg from Day 9 to Day 12 of the treatment series if animals showed too severe a reduction in food consumption. After development of tolerance by the presession treatment group, the animals treated after feeding were shifted to treatment before feeding. This shift produced a marked depression in food consumption. This confirms similar data previously obtained by a different test (two-way avoidance), and indicates that behaviorally augmented tolerance to paraoxon related to practice factors may be a fairly general phenomenon. Other experiments were to assess the effects of paraoxon in the conditioned taste aversion (CTA) paradigm. These showed the development of an aversion only at high dosage levels (two pairings between the flavor cue and 0.25 mg/kg sc, or four pairings with a 0.17-mg/kg dose). However, the failure of lower doses to produce CTA may have depended on the relatively slow onset of the intoxication, producing an extended interval between the end of cue exposure and the development of malaise or illness. Two pretreatments given 6 and 3 days before the first conditioning session in an experiment using the 2 X 0.25-mg/kg schedule did not affect the development of CTA as measured by a conventional double-bottle test. However, a typical interference effect produced by prior exposure was shown by a substantial acceleration of subsequent CTA extinction in pretreated animals.

Conditioned taste aversion to chlorpromazine, but not to haloperidol

Using in rats a Conditioned Taste Aversion (CTA) procedure, chlorpromazine was shown to possess significant US properties at the highest dose tested (8 mg/kg IP repeated four times). In contrast, haloperidol failed to exert a similar effect at a dosage (1.6 mg/kg IP X 4) at least twice as high, in terms of pharmacological activity, as the effective chlorpromazine dosage. These data suggest that the induction of neuroleptic extrapyramidal side effects and the antidopaminergic properties shared by the two drugs may not be responsible for the aversive effect of chlorpromazine. However, it cannot be excluded than haloperidol produces an aversion which is antagonized by some action of the drug not shared by chlorpromazine.

Influence of housing conditions and state of partner on conditioning and extinction of taste aversion to lithium and chlorpromazine

Rats were used in two experiments to investigate the influence of social variables on the acquisition of Conditioned Taste Aversion (CTA) to either lithium chloride (10 ml/kg IP of a 0.3-M solution given twice) or chlorpromazine (8 mg/kg IP given four times) and on subsequent extinction. CTA acquisition was not affected by original housing assignment (isolation or paired housing for 15-23 days prior to conditioning), by the shifted social assignment during conditioning, or by the drugged state of the paired animals' partners on drug-scheduled days. However, for both drugs, permanently isolated animals extinguished CTA more slowly than rats housed permanently in pairs. Shifts from isolation to pairing or vice versa failed to alter CTA extinction in the case of lithium, but affected it significantly in chlorpromazine-treated rats. Shifts from isolation to paired housing with an undrugged partner produced faster extinction for lithium than the corresponding group with a drugged partner. For chlorpromazine, the effect of the same shift was exactly the opposite. Overall, the results show that changes in CTA extinction can be a function of social variables.

Nicotine cue in rats analysed with drugs acting on cholinergic and 5-hydroxytryptamine mechanisms

The nicotine discriminative stimulus (cue) has been used to characterize further the underlying receptor mechanisms. Rats were trained to discriminate the effects of nicotine in a standard, two-bar operant conditioning procedure with food reinforcement. Mecamylamine blocked both the discriminative effect of nicotine and the reducing effect on the response-rate. The block of the discriminative effect could not be overcome by increasing the dose of nicotine, whereas the block of the reducing effect on the response-rate could be reversed. Mecamylamine was effective when administered by either the subcutaneous or the intraventricular route, but hexamethonium was inactive by both routes. Mecamylamine, but not hexamethonium, blocked the discriminative effect of the nicotinic cholinergic agonist, cytisine. Methergoline did not block the discriminative effects of nicotine, even in doses considerably larger than those which blocked the discriminative effects of the 5-HT agonist, quipazine. Mecamylamine did not block the effects of quipazine. The results are consistent with the view that the nicotinic cue is mediated primarily through cholinergic receptors, and that 5-HT mechanisms are not involved. The block of the quipazine cue supports the view that the discriminative effects of this drug are mediated through 5-HT receptors.

Scopolamine and acquisition of go-no go avoidance: a further analysis of the perseverative antimuscarinic deficit

Rats treated with scopolamine (0.5 mg/kg SC daily) during the acquisition of a discrimination task with symmetrical negative reinforcement (light-go, noise/light-no go) showed a learning impairment, with both active and passive avoidance deficits. In the initial stage of such training, however, fewer passive avoidance errors and more active avoidance errors were made by treated animals if active avoidance pretraining had occurred in the no-drug state. A similar experiment using the same stimulus arrangement with asymmetrical reinforcement (no punishment of intertrial, and no go signal, responses) showed a scopolamine effect consisting mainly of increased responding to extinction signals and during intertrial intervals, with little or no active avoidance deficit. Furthermore, interactions due to changes in treatment conditions in successive stages of training were minimized in the latter task, suggesting that the effects of the shift-no shift factor on distribution of errors in the early stages of active-passive avoidance learning were unlikely to have been due to a genuine drug dissociation. Overall, these results and others obtained previously in the same and related tasks tend to rule out some unidimensional explanations of antimuscarinic effects, e.g., response disinhibition (an exclusively motor deficit) or impairment of stimulus sensitivity (an exclusively sensory deficit). The data rather confirm the notion of a sensorimotor drug bias leading to a shift in response prepotencies depending jointly on stimuli, responses, and response consequences. Prior learning history and behavioural compensation for adverse treatment consequences at the reinforcement level may interact with the sensorimotor bias so as to produce "set perseveration" (perseveration of response tendencies).

Discriminative stimulus properties of nicotine: further evidence for mediation at a cholinergic receptor

Rats were trained to discriminate nicotine (0.4 mg/kg SC) from saline in a standard two-bar operant conditioning procedure with food reinforcement. The response to nicotine was dose-related and at the ED50 of 0.14 mg/kg, plasma nicotine concentrations were similar to those reported previously for cigarette smokers who inhale. The nicotine analogues anabasine and cytisine increased nicotine-appropriate responding in a dose-related manner. Animals predominantly responded on the saline-associated lever when administered drugs from a range of pharmacological classes, even at doses that were sufficiently large to reduce the overall numbers of responses. The results confirm that the nicotine discriminative stimulus is highly specific. Previous work has shown anabasine and cytisine to be active at nicotinic-cholinergic binding sites in rat brain. The finding that there is some correlation between the behavioural effects of these compounds and their actions at the nicotine binding site may indicate that the nicotine cue is mediated through a cholinergic receptor.

Behaviorally augmented tolerance during chronic cholinesterase reduction by paraoxon

Repeated injection of paraoxon to pretrained rats 2 hr before avoidance sessions, at a dose causing considerable intoxication symptoms and reduction of brain acetylcholinesterase (0.125 mg/kg SC daily), induced marked performance depression followed by progressive development of tolerance. Additional groups treated either after each session (i.e., 23.5 hr before each subsequent session), or treated and not tested, showed a substantial depression when shifted to treatment 2 hr before sessions after achievement of tolerance by the animals tested from the beginning of the experiment at the time of maximal paraoxon effect. This indicates that chronic paraoxon tolerance cannot be ascribed entirely to metabolic and/or physiological changes occurring as a consequence of repeated treatment per se, but must be explained at least in part by postulating a behaviorally augmented (or "learned") component. In an additional experiment chronic paraoxon animals (0.1 mg/kg SC daily) were indistinguishable from control rats with respect to acquisition of light/go, noise-light/no go discrimination, i.e., of an active-passive avoidance task known to be highly sensitive to the disrupting (response-disinhibiting) effect of antimuscarinics. Therefore, the enhanced sensitivity to antimuscarinics in organophosphate tolerant rats, which is usually ascribed to cholinergic receptor changes, does not appear to be associated with a spontaneous "antimuscarinic-like" syndrome.

Test factors affecting the time course of avoidance depression after DFP and paraoxon

The time course of avoidance depression induced by DFP and Paraoxon in rats was measured in four experiments using sublethal doses which induced approximately equivalent changes at the time for maximal behavioral depression (3 hr after 1.1 mg/kg DPF or 0.25 mg/kg Paraoxon SC). The trends obtained with pretrained animals intoxicated for the first time, and not tested during the period between treatment and testing at any given interval (3, 8, 13, 18, and 24 hr after injection), served as baselines to assess (1) proactive consequences of one or more avoidance sessions on subsequent measurements, and (2) sensitivity changes upon repetition of treatment with the same or the other agent after a 5-week resting period. The changes in the time course of avoidance depression due to these factors were generally unimpressive. Some of the interactions observe, however, provided direct or indirect evidence (1) for an enhanced residual depression at long post-treatment intervals upon repetition of organophosphate intoxication; (2) for a proactive impairing effect sometimes appearing after behavioral testing at the time of maximal depression (3 hr), when total or near-total avoidance failure causes extensive exposure to shock; and (3) for a proactive facilitating effect sometimes appearing after testing at a time of moderate avoidance impairment (8 hr), which may be ascribed to behaviorally augmented tolerance ("learned" tolerance).

Reactivity of the cerebral resistance and capacitance vessels and blood-brain water exchange in the experimental brain injury

In conclusion, an estimate of the intracranial volumetric effects produced in anesthetized dogs by histamine, acetylcholine and CO2 shows that, on a basis of equiactivity on CBF, the effects of histamine on the intracranial content are twice greater than those produced by acetylcholine and CO2. This difference may be explained by a greater activity of histamine on the intracranial capacitance vessels and/or by an increase in the fluid escape from blood to the brain produced by histamine. Data obtained after the production of an acute, cold induced brain lesion support the second possibility.