Developmental exposure to terbutaline and chlorpyrifos: pharmacotherapy of preterm labor and an environmental neurotoxicant converge on serotonergic systems in neonatal rat brain regions

Developmental exposure to unrelated neurotoxicants can nevertheless produce similar neurobehavioral outcomes. We examined the effects of developmental exposure to terbutaline, a tocolytic beta2-adrenoceptor agonist used to arrest preterm labor, and chlorpyrifos (CPF), a widely used organophosphate pesticide, on serotonin (5HT) systems. Treatments were chosen to parallel periods typical of human developmental exposures, terbutaline (10 mg/kg) on postnatal days (PN) 2-5 and CPF (5 mg/kg) on PN11-14, with assessments conducted on PN45, comparing each agent alone as well as sequential administration of both. Although neither treatment affected growth or viability, each elicited similar alterations in factors that are critical to the function of the 5HT synapse: 5HT1A receptors, 5HT2 receptors, and the presynaptic 5HT transporter (5HTT). Either agent elicited global increases in 5HT receptors and the 5HTT in brain regions possessing 5HT cell bodies (midbrain, brainstem) as well as in the hippocampus, which contains 5HT projections. For both terbutaline and CPF, males were affected more than females, although there were some regional disparities in the sex selectivity between the two agents. Both altered 5HT receptor-mediated cell signaling, suppressing stimulatory effects on adenylyl cyclase and enhancing inhibitory effects. When animals were exposed sequentially to both agents, the outcomes were no more than additive and, for many effects, less than additive, suggesting convergence of the two agents on a common set of developmental mechanisms. Our results indicate that 5HT systems represent a target for otherwise unrelated neuroteratogens.     

Developmental exposure to terbutaline alters cell signaling in mature rat brain regions and augments the effects of subsequent neonatal exposure to the organophosphorus insecticide chlorpyrifos

Exposure to apparently unrelated neurotoxicants can nevertheless converge on common neurodevelopmental events. We examined the long-term effects of developmental exposure of rats to terbutaline, a beta-adrenoceptor agonist used to arrest preterm labor, and the organophosphorus insecticide chlorpyrifos (CPF) separately and together. Treatments mimicked the appropriate neurodevelopmental stages for human exposures: terbutaline on postnatal days (PN) 2-5 and CPF on PN11-14, with assessments conducted on PN45. Although neither treatment affected growth or viability, each elicited alterations in CNS cell signaling mediated by adenylyl cyclase (AC), a transduction pathway shared by numerous neuronal and hormonal signals. Terbutaline altered signaling in the brainstem and cerebellum, with gender differences particularly notable in the cerebellum (enhanced AC in males, suppressed in females). By itself, CPF exposure elicited deficits in AC signaling in the midbrain, brainstem, and striatum. However, sequential exposure to terbutaline followed by CPF produced larger alterations and involved a wider spectrum of brain regions than were obtained with either agent alone. In the cerebral cortex, adverse effects of the combined treatment intensified between PN45 and PN60, suggesting that exposures alter the long-term program for development of synaptic communication, leading to alterations in AC signaling that emerge even after adolescence. These findings indicate that terbutaline, like CPF, is a developmental neurotoxicant, and reinforce the idea that its use in preterm labor may create a subpopulation that is sensitized to long-term CNS effects of organophosphorus insecticides.     

No correlation between trapeziometacarpal arthritis and abductor pollicis longus insertion

The primary hypothesis of this study is that supernumerary slips of the abductor pollicis longus (particularly those slips inserting distal to the trapeziometacarpal joint) increase the risk of trapeziometacarpal osteoarthritis on account of increased transarticular forces. Other hypotheses surmised that age and female gender were directly correlated with severity of arthritis. We did cadaveric dissection of the distal first dorsal compartment in 61 specimens, noting the cadaveric age, gender, and number and insertion sites of abductor pollicis longus tendon slips. Each variable was statistically correlated with visual grade of trapeziometacarpal arthritis. The median number of abductor pollicis longus tendon slips in these cadaveric hands was three (range, 1-4). Seventy-nine percent of the hands had a digastric-type insertion into the abductor pollicis brevis. Ninety percent had an insertion into the trapezium. All hands possessed an insertion into the base of the first metacarpal. Age and female gender were directly correlated with severity of arthritis. No other correlations existed. We conclude that trapeziometacarpal joint arthritis progresses with age and occurs independently of any aspect of abductor pollicis longus insertion. Based on our results, we do not recommend surgical release of these supernumerary abductor pollicis longus tendon slips for the treatment of trapeziometacarpal osteoarthritis.     

Relationship of brain and skull in pre- and postoperative sagittal synostosis

Models of vertebrate skull evolution stress the coordinated developmental relationship between the skull and the brain that it houses. This study investigates the relationship between altered skull morphology and brain morphology in premature fusion of the cranial sagittal suture (isolated sagittal synostosis; ISS), a condition associated with dysmorphology of both neurocranium and brain. Although the skull displays a more normal shape following reconstructive cranial vault surgery, effects of this surgery on the brain have not been investigated. Landmark coordinate data were collected from three-dimensional magnetic resonance imaging reconstructions of the brain in a sample of ISS patients and an age-matched unaffected cohort. These data were analysed using Euclidean distance matrix analysis (EDMA). Results show that the brain in ISS is dysmorphic preoperatively, displaying a posteriorly directed neural expansion that does not 'worsen' with growth. Postoperatively, the brain in ISS displays a more globular shape overall as compared with the preoperative morphology, but differs from normal in its subcortical morphology. These results show that the ISS brain is altered following neurocranial surgery, but does not more closely approximate that of unaffected individuals. This suggests that although the brain is affected by manipulation of the skull, it retains a growth pattern that is, at least in part, independent of the skull.     

Dimethylphosphorothioates

Five dimethylphosphorothioates were tested for their toxicity to rats, potentiation of malathion toxicity in rats, inhibition of carboxylesterase in vitro, and reaction with malathion in vitro. The compounds were: potassium salts of (CH₃S)₂P(O)O^–(I), (CH₃O)(CH₃S)P(O)S^–(II), (CH₃O)₂P(O)S^–(III), (CH₃O)₂P(S)S^–(IV), and (CH₃O)(CH₃S)P(O)O^–(V).The dimethylphosphorothioates are not toxic to rats (up to 1 g/kg, orally), they do not potentiate malathion toxicity in rats, and do not inhibit carboxylesterase activity in vitro (up to 1 mM concentrations). However, when the S-acid diesters (II, III, IV) are incubated with malathion for several days at room temperature or for several hours at 50° C they become methylated forming the trimethylphosphorothioates OSS-trimethyl phosphorodithioate, OOS-trimethyl phosphorothioate and OOS-trimethyl phosphorodithioate respectively, which potentiate malathion toxicity. Furthermore, these same acid diesters increase the rate of isomerization of malathion into OS-dimethyl-S-(1,2-dicarbethoxyethyl) phosphorodithioate (isomalathion) particularly, diester IV.The formation of the trimethylphosphorothioates and isomalathion from the interaction of the S-acid diesters with malathion was determined by thin layer chromatography (TLC), gas chromatography and mass spectrometry and could be detected by in vitro inhibition of carboxylesterase. TLC methods can detect 1 mg of the trimethylphosphorothioates and isomalathion per gram malathion.     

The Estimation of Aortic Insufficiency

Thirty patients were investigated to determine the degree of aortic insufficiency present in them, using the test of Braunwald and Morrow in which indicator dye is injected at descending levels in the aorta and regurgitant dye is recorded by oximetry at the right ear. In the presence of aortic insufficiency regurgitant dye was demonstrated from as low as the second lumbar level, while in normal subjects none was demonstrated on injection distal to the fifth thoracic level. In the older patients the level was more proximal than in the younger for similar regurgitant flows. In most patients the test correlated well with the clinical impression of the severity of the lesion. However, tachycardia, bradycardia a reduced forward flow secondary to failure, aortic stenosis, or mitral stenosis or insufficiency will modify the level from which regurgitation occurs. Estimation of forward flow would permit estimation of the percentage regurgitation and allow a more accurate assessment of aortic insufficiency. Preoperative and postoperative estimation permitted objective assessment of successful corrective surgery.     

Clinical experience with zonisamide monotherapy and adjunctive therapy in children with epilepsy at a tertiary care referral center

We evaluated our clinical experience with zonisamide, a broad-spectrum antiepileptic drug, in a group of children with predominantly medically refractory epilepsy. A retrospective chart review was conducted on patients at our tertiary referral center following Institutional Review Board approval. Observers documented reports of seizure frequency, and seizure types were identified either clinically or by prior video-electroencephalography monitoring. We identified 68 patients (age range 1.9-18.1 years [median 6.9 years]; male to female ratio 1.3:1) treated with zonisamide for 0.7 to 28.9 months; at the last visit, 22% and 78% were on monotherapy and adjunctive therapy, respectively. The median duration of treatment and maintenance dose at the end of the follow-up were 11.2 months and 8.0 mg/kg/day, respectively. Seizure types included generalized (primary generalized tonic-clonic, myoclonic, tonic, atonic, absence) and partial (simple, complex, and secondarily generalized tonic-clonic seizures); 10 (15%) patients had both partial and generalized seizures. Sixteen (25.8%) patients were seizure free, although five of them were already in remission prior to starting zonisamide. Thirteen (21.0%) patients had a > 50% seizure reduction, 10 (16.1%) patients had a < 50% seizure reduction, 14 (22.6%) had no improvement in baseline seizures, and 9 (14.5%) reported having increased seizures. The latter were mostly associated with dosage alterations in concomitant antiepileptic drugs. Common side effects were central nervous system related, including behavioral or psychiatric (23.5%), cognitive dysfunction (12.0%), and sedation (10.3%). Eleven (16.2%) patients ultimately discontinued zonisamide, but only five were strictly due to side effects. Zonisamide is clinically effective against multiple seizure types in a significant proportion of children with epilepsy across a broad age range. Drug discontinuation as a result of side effects is uncommon.     

Critical periods for chlorpyrifos-induced developmental neurotoxicity: alterations in adenylyl cyclase signaling in adult rat brain regions after gestational or neonatal exposure

Developmental exposure to chlorpyrifos (CPF) alters the function of a wide variety of neural systems. In the present study we evaluated the effects in adulthood of CPF exposure of rats during different developmental windows, using the adenylyl cyclase (AC) signaling cascade, which mediates the cellular responses to numerous neurotransmitters. Animals were exposed on gestational days (GD) 9-12 or 17-20 or on postnatal days (PN) 1-4 or 11-14 and assessed at PN60. In addition to basal AC activity, we evaluated the responses to direct AC stimulants (forskolin, Mn2+) and to isoproterenol, which activates signaling through ss-adrenoceptors coupled to stimulatory G-proteins. CPF exposure in any of the four periods elicited significant changes in AC signaling in a wide variety of brain regions in adulthood. In general, GD9-12 was the least sensitive stage, requiring doses above the threshold for impaired maternal weight gain, whereas effects were obtained at subtoxic doses for all other regimens. Most of the effects were heterologous, involving signaling elements downstream from the receptors, and thus shared by multiple stimulants; superimposed on this basic pattern, there were also selective alterations in receptor-mediated responses, in G-protein function, and in AC expression and subtypes. Exposures conducted at GD17-20 and later all produced sex-selective alterations. These results suggest that developmental exposure to CPF elicits long-lasting alterations in cell-signaling cascades that are shared by multiple neurotransmitter and hormonal inputs; the resultant abnormalities of synaptic communication are thus likely to occur in widespread neural circuits and their corresponding behaviors.