Benzodiazepines (BZs) suppress ventilation possibly by augmenting the GABA(A) receptor activity in the respiratory control system, but precise sites of action are not well understood. The goals of this study were: (1) to identify GABA(A) receptor subunits in the carotid body (CB) and petrosal ganglion (PG); (2) to test if BZs exert their effects through the GABA(A) receptor in the CB chemosensory unit. Tissues were taken from euthanized adult cats. RNA was extracted from the brain, and cDNA sequences of several GABA(A) receptor subunits were determined. Subsequent RT-PCR analysis demonstrated the gene expression of alpha2, alpha3, beta3, and gamma2 subunits in the CB and the PG. Immunoreactivity for GABA and for GABA(A) receptor beta3 and gamma2 subunits was detected in chemosensory glomus cells (GCs) in the CB and neurons in the PG. The functional aspects of the GABA-GABA(A) receptor system in the CB was studied by measuring CB neural output using in vitro perfusion setup. Two BZs, midazolam and diazepam, decreased the CB neural response to hypoxia. With continuous application of bicuculline, a GABA(A) receptor antagonist, the effects of BZs were abolished. In conclusion, the GABA-GABA(A) receptor system is functioning in the CB chemosensory system. BZs inhibit CB neural response to hypoxia by enhancing GABA(A) receptor activity.

2419 Poster Board II-396 Syncope is generally defined as a state of temporary, partial or complete, loss of consciousness (fainting) with spontaneous recovery. The basis for the phenomenon is complex and includes a variety of orthostatic intolerance conditions including neurocardiogenic syncope (NCS), postural orthostatic tachycardia syndrome (POTS), and other disorders affecting the autonomic nervous system. NCS patients and POTS patients can be differentiated with an upright tilt test because either bradycardia or tachycardia will occur with hypotension, respectively. Both are induced by the inability to maintain adequate systemic blood pressure. Though the two primary types of syncope are different in origin, both conditions are treated similarly. Recent reports suggest that syncope is a low serotonin (5HT) disorder and selective serotonin reuptake inhibitors (SSRIs) are a commonly prescribed treatment for both NCS and POTS patients. The major storage pool of serotonin, independent of the central nervous system, is contained in platelet dense granules (DG). Peripheral serotonin aids in vasoconstriction and blood clotting. Individuals prone to syncope may be deficient in serotonin. Insufficient peripheral serotonin may create conditions that lead to hypotension and excessive bleeding in an individual. We previously reported that patients having episodes of syncope (Blood, 112(11):451, 2008) had statistically significant decreases of DG/PL, consistent with DG storage pool deficiency (δSPD), and PL 5HT concentrations when compared to control subjects. Our test subjects were screened by questionnaire to determine syncope and distinction between NCS and POTS was not considered. These patients had an average of 3.08 ± 0.52 DG/PL and a mean 5HT concentration of 248.40 ± 37.94 ng/109 PL (PL 5HT normal range = 215-850 ng/109 PL). Control subjects (n=24) had an average of 4.22 ± 0.12 DG/PL and a 5HT concentration of 666.54 ± 56.25; both values having a significant difference (p=.003 and p<.001) by a Mann-Whitney Rank Order test respectively. We now report the DG/PL and 5-HT values obtained exclusively from patients diagnosed with POTS by tilt-table assessment and compared with control subjects. Patients for this study were obtained from our cardiology clinic and all were positive for POTS; they were not currently taking or were recently prescribed a SSRI for therapeutic management of their condition. Control subjects did not have syncope or history of bleeding. Peripheral blood was collected and PLs obtained via centrifugation to determine the mean DG/PL by electron microscopy and the mean 5HT concentration extracted from PLs using an ELISA technique. POTS patients (n=14) had a mean serotonin level of 326.6 ± 76.7 ng/109 PL compared to 589.6 ± 56.3 ng/109PL (p<0.004) for control subjects (n=21). POTS patients exhibited a mean of 2.6 ± 0.31 DG/PL compared to the control subject value of 4.16 ± 0.09 DG/PL (p<0.001). To date there is no significant difference in the number of PL DG or 5HT levels POTS patients compared to our previous evaluation of undefined syncope patients. These results support the hypothesis that syncope (NCS and POTS) may be the result of low peripheral serotonin levels. Our preliminary data demonstrates that POTS patients have low serotonin levels and δSPD when compared to control subjects. This study is ongoing to increase the total number of POTS patients enrolled as well as to recruit subjects diagnosed with NCS to determine whether a difference in DG and/or 5HT exists to explain either bradycardia or tachycardia as an early symptom in the development of hypotension. Disclosures: No relevant conflicts of interest to declare.

No abstract

4456 The etiology of autism is thought to be neurobiological, but the mechanisms involved are not known. One possible clue into this disorder can be found in multiple clinical studies which have established that at least 30-40% of individuals diagnosed with autism have significantly elevated levels of serotonin (5HT) in their blood. Serotonin transport by platelets and 5HT plasma levels have been found to be altered in patients with multiple neurobiological disorders, including bipolar disorder, schizophrenia, depression, aggression, autism, and migraine headache. Serotonin has numerous functions, including regulation of vasoconstriction, vasodilatation, and coagulation. A review of the literature reveals few studies of coagulopathy related to autism other than attempts to associate vaccination or infections with the etiology of autism. One recent study, of a limited number of individuals with autism spectrum disorders (ASD) and their families, reported a significant incidence of thrombophilia. All children evaluated (10/10) and 15 of 16 family members in the study were found to be at risk for thrombophilia disorders. We have been evaluating patients for PL dysfunction for many years and recently, have included ELISA tests to determine the 5HT concentration in PLs of patients suffering from migraine headache or syncope. All of our investigations to date have evaluated patients for a deficiency of the PL storage pool (DG SPD) including a decrease of PL DGs and their stored biochemical constituents; we have never conducted a study related to potentially increased numbers of DGs or the concentration of biochemicals contained in these granules. As at least one report exists in the literature suggesting the potential for thrombophilia in patients diagnosed with an autism spectrum disorder and their families, we decided to assess the platelet storage pool in autistic patients and their families as a potential model of platelet dysfunction due to elevated DGs and/or 5HT levels and/or as a potential biomarker for autism. As the major storage pool of 5HT in the circulation is known to exist in platelet PL DGs, it is possible that a PL DG storage pool could be an important mediator of ASD. Our hypothesis is that autistic children may have elevated numbers of DGs and increased levels of PL 5HT. Peripheral blood samples were obtained from children diagnosed with autism as well as their parents and siblings. Platelets were obtained via centrifugation and DG content determined by electron microscopy and an ELISA assay was utilized to determine PL 5HT concentration for all subjects. A questionnaire was also used to evaluate family bleeding history and drug therapy for the autistic children. At present, 4 families have been recruited for the study. Autistic children (n = 5) have an average of 5.42 ± 0.69 DG/PL and a mean 5HT concentration of 447.6.4 ± 85.6 ng/109 PL (PL 5HT normal range = 215-850 ng/109 PL). Their parents have an average of 5.00 ± 0.54 DG/PL and a mean 5HT concentration of 427.6.4 ± 82.66 ng/109 PL and one five year old sibling was found to have 8.17 DG/PL and 2233 ng/109 PL. Control subjects (n=21) have an average of 4.16 ± 0.09 DG/PL and a 5HT concentration of 589.6 ± 56.25 ng/109. There is no statistically significant difference between controls, parents or autistic subjects by ANOVA. Our preliminary data does not support our hypothesis. However, with serotonin being the immediate precursor of melatonin, we do not discount the fact that all of our subjects were receiving drug therapies including melatonin supplementation (n=2) or selective serotonin reuptake inhibitors (n=3) which diminish the PL 5HT concentration. Thus, the therapeutic regimens for these subjects could account for their normal 5HT levels. This project had been initiated just prior to the time of abstract submission; we are currently recruiting study participants and will present additional data at the meeting. Disclosures: No relevant conflicts of interest to declare.