Effect of low frequency modulated microwave exposure on human EEG: individual sensitivity

The aim of this study was to evaluate the effect of modulated microwave exposure on human EEG of individual subjects. The experiments were carried out on four different groups of healthy volunteers. The 450 MHz microwave radiation modulated at 7 Hz (first group, 19 subjects), 14 and 21 Hz (second group, 13 subjects), 40 and 70 Hz (third group, 15 subjects), 217 and 1000 Hz (fourth group, 19 subjects) frequencies was applied. The field power density at the scalp was 0.16 mW/cm(2). The calculated spatial peak SAR averaged over 1 g was 0.303 W/kg. Ten cycles of the exposure (1 min off and 1 min on) at fixed modulation frequencies were applied. All subjects completed the experimental protocols with exposure and sham. The exposed and sham-exposed subjects were randomly assigned. A computer also randomly assigned the succession of modulation frequencies. Our results showed that microwave exposure increased the EEG energy. Relative changes in the EEG beta1 power in P3-P4 channels were selected for evaluation of individual sensitivity. The rate of subjects significantly affected is similar in all groups except for the 1000 Hz group: in first group 3 subjects (16%) at 7 Hz modulation; in second group 4 subjects (31%) at 14 Hz modulation and 3 subjects (23%) at 21 Hz modulation; in third group 3 subjects (20%) at 40 Hz and 2 subjects (13%) at 70 Hz modulation; in fourth group 3 subjects (16%) at 217 Hz and 0 subjects at 1000 Hz modulation frequency.     

Alterations in protein kinase activity following exposure of cultured human lymphocytes to modulated microwave fields

Cultures of human tonsil lymphocytes were exposed in a Crawford cell to a 450-MHz field (peak envelope intensity 1.0 mW/cm2), sinusoidally amplitude modulated (depth 80%) at frequencies between 3 and 100 Hz for periods up to 60 min. The Crawford cell was housed in a temperature-controlled chamber (35 degrees C) and control cultures were placed in the same chamber. Activity of cAMP-dependent protein kinase relative to controls remained unaltered by fields modulated at 16 or 60 Hz with exposures of 15, 30, and 60 min. By contrast, total non-cAMP-dependent kinase activity fell to less than 50% of unexposed control levels after 15 and 30 min exposures, but, despite continuing field exposure, returned to control or preexposure levels by 45 and 60 min. A smaller reduction (20-25%) also occurred with 60-Hz modulation and was also restricted to exposure durations of 15 and 30 min. CW 450-MHz fields were without effect. Reduced enzyme activity occurred with 16-, 40-, and 60-Hz modulation frequencies, but not with 3-, 6-, 80-, or 100-Hz modulation. The specific identity of this kinase is unknown. This rapid but transient reduction in lymphocyte protein kinase activity restricted to modulation frequencies between 16 and 60 Hz and to less than 30 min exposure is consistent with "windowing" with respect to modulation frequency and exposure duration.     

Development of GPCR modulation of GABAergic transmission in chicken nucleus laminaris neurons

Neurons in the nucleus laminaris (NL) of birds act as coincidence detectors and encode interaural time difference to localize the sound source in the azimuth plane. GABAergic transmission in a number of CNS nuclei including the NL is subject to a dual modulation by presynaptic GABA(B) receptors (GABA(B)Rs) and metabotropic glutamate receptors (mGluRs). Here, using in vitro whole-cell patch clamp recordings from acute brain slices of the chick, we characterized the following important but unknown properties pertaining to such a dual modulation: (1) emergence of functional GABA synapses in NL neurons; (2) the temporal onset of neuromodulation mediated by GABA(B)Rs and mGluRs; and (3) the physiological conditions under which GABA(B)Rs and mGluRs are activated by endogenous transmitters. We found that (1) GABA(A)R-mediated synaptic responses were observed in about half of the neurons at embryonic day 11 (E11); (2) GABA(B)R-mediated modulation of the GABAergic transmission was detectable at E11, whereas the modulation by mGluRs did not emerge until E15; and (3) endogenous activity of GABA(B)Rs was induced by both low- (5 or 10 Hz) and high-frequency (200 Hz) stimulation of the GABAergic pathway, whereas endogenous activity of mGluRs was induced by high- (200 Hz) but not low-frequency (5 or 10 Hz) stimulation of the glutamatergic pathway. Furthermore, the endogenous activity of mGluRs was mediated by group II but not group III members. Therefore, autoreceptor-mediated modulation of GABAergic transmission emerges at the same time when the GABA synapses become functional. Heteroreceptor-mediated modulation appears at a later time and is receptor type dependent in vitro.     

Changes in expression of the delta subunit of the GABA (A) receptor and in receptor function induced by progesterone exposure and withdrawal

Type A receptors for GABA (GABA(A) receptors) that contain the delta subunit are located predominantly at extrasynaptic sites and are implicated in modulation of neuronal excitability through tonic inhibition. We have examined the effects of chronic exposure to and subsequent withdrawal of progesterone or the progesterone metabolite 3alpha-hydroxy-5alpha-pregnan-20-one (3alpha,5alpha-THPROG) on expression of the delta subunit of GABA(A) receptors and on receptor function in cultured rat hippocampal neurons. Progesterone treatment for 1 day increased the amounts of both delta subunit mRNA and protein, whereas such treatment for 6 days induced marked decreases in the abundance of both the mRNA and protein. Subsequent progesterone withdrawal up-regulated expression of the delta subunit, which was significantly increased at 9-12 h after withdrawal. These effects of progesterone were mimicked by 3alpha,5alpha-THPROG and blocked by the 5alpha-reductase inhibitor finasteride. They were also accompanied by parallel changes in the function of GABA(A) receptors in hippocampal neurons. These results show that chronic exposure to and withdrawal of progesterone induce differential effects on both expression of the delta subunit of GABA(A) receptors and receptor function that are mediated by 3alpha,5alpha-THPROG. They are consistent with the notion that this progesterone metabolite plays a key physiological role in modulation of GABAergic synapses.     

Modulation of cardiopulmonary depressor reflex in nucleus ambiguus by electroacupuncture: roles of opioids and γ-aminobutyric acid

Stimulation of cardiopulmonary receptors with phenylbiguanide (PBG) elicits depressor cardiovascular reflex responses, including decreases in blood pressure and heart rate mediated in part by the brain stem parasympathetic cardiac neurons in the nucleus ambiguus (NAmb). The present study examined NAmb neurotransmitter mechanisms underlying the influence of electroacupuncture (EA) on the PBG-induced hypotension and bradycardia. We hypothesized that somatic stimulation during EA modulates PBG responses through opioid and γ-aminobutyric acid (GABA) modulation in the NAmb. Anesthetized and ventilated cats were studied during repeated stimulation with PBG or cardiac vagal afferents while low-frequency EA (2 Hz) was applied at P5-6 acupoints overlying the median nerve for 30 min and NAmb neuronal activity, heart rate, and blood pressure were recorded. Microinjection of kainic acid into the NAmb attenuated the PBG-induced bradycardia from -60 ± 11 to -36 ± 11 beats/min. Likewise, EA reduced the PBG-induced depressor and bradycardia reflex by 52 and 61%, respectively. Cardiac vagal afferent evoked preganglionic cellular activity in the NAmb was reduced by EA for about 60 min. Blockade of opioid or GABA(A) receptors using naloxone and gabazine reversed the EA-related modulation of the evoked cardiac vagal activity by 73 and 53%, respectively. Similarly, naloxone and gabazine reversed EA modulation of the negative chronotropic responses from -11 ± 5 to -23 ± 6 and -13 ± 4 to -24 ± 3 beats/min, respectively. Thus EA at P5-6 decreases PBG evoked hypotension and bradycardia as well as the NAmb PBG-sensitive preganglionic cardiac vagal outflow through opioid and GABA neurotransmitter systems.     

Physiological and pharmacological studies on annelid and nematode body wall muscle

1. This review covers the pharmacology and physiology of the body wall muscle systems of nematodes and annelids.2. Both acetylcholine and gamma-aminobutyric acid (GABA) play important roles in the control of body wall muscle in both phyla. In annelids and nematodes, acetylcholine is the excitatory neuromuscular transmitter while GABA is the inhibitory neuromuscular transmitter. In addition, 5-hydroxytryptamine (5-HT) has a modulatory role at annelid body wall muscle but little if any effect on nematode body wall muscle.3. The acetylcholine receptor of the body wall muscle can be classified as nicotinic-like in both phyla though the annelid receptor has not been analysed in detail. In nematodes, vertebrate ganglionic nicotinic agonists were the most effective of those so far examined while mecamylamine and benzoquinonium were the most effective antagonists. Both neuronal bungarotoxin and neosurugatoxin were potent antagonists of acetylcholine excitation at the nematode receptor.4. The GABA receptor of the body wall muscle exhibits similarities with the vertebrate GABA-A receptor in both phyla. Picrotoxin is a very weak or inactive antagonist at leech and nematode GABA receptors, while bicuculline methiodide blocks leech GABA receptors but is inactive on nematode GABA receptors. Picrotoxin does block GABA responses of earthworm body wall muscle. All these GABA responses are chloride mediated.5. Neuroactive peptides of the RFamide family occur m both phyla and FMRFamide has been identified in leeches. RFamides probably have an important role in heart regulation in leeches and in modulation of their body wall muscles. RFamides also modulate nematode body wall muscle activity with KNEFIRFamide raising muscle tone while SDPNFLRFamide relaxes the muscle. It is likely that this family and other neuroactivc peptides play an important role in the physiology of body wall muscle throughout both phyla.     

Modulation by GABA(B) and delta opioid receptors of neurally induced responses in isolated guinea-pig taenia coli and human colonic circular muscle.

The GABA-ergic and opioid modulation of neurally induced muscle responses was studied in isolated guinea-pig taenia coli and human colonic circular muscle, using identical field stimulation parameters (rectangular pulses of 0.5 ms duration, 9 V x cm(-1) intensity, trains of 3 pulses at 0.5 Hz, repeated every 1/3/5 min). The stimulation-induced contractions were inhibited in both preparations by GABA and baclofen; the IC50 values in human colonic circular muscle were approximately 100 and 31.0 microM, respectively. In guinea-pig taenia coli, the inhibition by 10(-4) M GABA was dose-dependently reversed by 10(-4)-10(-3) M of GABA(B) receptor antagonist CGP 35348; antagonism by phaclofen was less effective in the same concentration range. In human colonic circular muscle, inhibition by 3 x 10(-5) M baclofen was fully reversed by 10(-3) M CGP 35348. With the exception of caecum, the delta 2 opioid receptor agonist deltorphin II was a potent inhibitor in human colonic circular muscle. 10(-8) M Deltorphin caused a 74.4 +/- 9.6% (n = 4) inhibition which was reversed by 10(-6) M of delta receptor selective peptide antagonist BOC-Tyr-Pro-Gly-Phe-Leu-Thr(OtBu). Deltorphin II was ineffective in guinea-pig taenia coli even at 10(-6) M; the same concentration caused an 84.3 +/- 7.9 (n = 4) inhibition in human preparations. It is concluded that: 1) GABA-ergic modulatory mechanisms are present both in human colonic circular muscle and guinea-pig taenia coli; 2) the GABA receptors involved are of type B; and 3) delta opioid receptor-mediated modulation functions only in human colonic circular muscle in regions other than the caecum.     

Involvement of NMDA receptor in low-frequency magnetic field-induced anxiety in mice

It had been reported that exposure to extremely low-frequency magnetic field (ELFMF) induces anxiety in human and rodents. Anxiety mediates via the activation of N-methyl-d-aspartate (NMDA) receptor, whereas activation of γ-aminobutyric acid (GABA) receptor attenuates the same. Hence, the present study was carried out to understand the contribution of NMDA and/or GABA receptors modulation in ELFMF-induced anxiety for which Swiss albino mice were exposed to ELFMF (50?Hz, 10?G) by subjecting them to Helmholtz coils. The exposure was for 8?h/day for 7, 30, 60, 90 and 120 days. Anxiety level was assessed in elevated plus maze, open field test and social interaction test, on 7th, 30th, 60th, 90th and 120th exposure day, respectively. Moreover, the role of GABA and glutamate in ELFMF-induced anxiety was assessed by treating mice with muscimol [0.25?mg/kg intraperitoneally (i.p.)], bicuculline (1.0?mg/kg i.p.), NMDA (15?mg/kg i.p.) and MK-801 (0.03?mg/kg i.p.), as a GABA_A and NMDA receptor agonist and antagonist, respectively. Glutamate receptor agonist exacerbated while inhibitor attenuated the ELFMF-induced anxiety. In addition, levels of GABA and glutamate were determined in regions of the brain viz, cortex, striatum, hippocampus and hypothalamus. Experiments demonstrated significant elevation of GABA and glutamate levels in the hippocampus and hypothalamus. However, GABA receptor modulators did not produce significant effect on ELFMF-induced anxiety and elevated levels of GABA at tested dose. Together, these findings suggest that ELFMF significantly induced anxiety behavior, and indicated the involvement of NMDA receptor in its effect.     

Response of cyclic AMP by DMSO differentiated HL-60 cells exposed to electric interferential current after prestimulation

The action of interferential current (IFC) upon intracellular content of cyclic adenosine monophosphate (cAMP) after prestimulation with the chemotactic peptide N-formyl-methionyl-leucyl-phenylalanine (fMLP) has been investigated. Human promyelocytes (HL-60) differentiated to granulocytes by dimethylsulphoxide (DMSO) have been treated with different concentrations of fMLP. This enhances their cAMP content. The half maximal effective concentration (EC50) was about 4 nM. Exposure to IFC with modulation frequencies of 35 and 125 Hz (5 min, 250 microA/cm2) after prestimulation with various concentrations of fMLP had no enhancing effect at low or high concentrations of fMLP. In contrast, at medium concentrations in the range of about 100 pM fMLP, a significant enhancement of cAMP could be observed. This synergistic effect of fMLP and IFC has been examined in detail by varying the modulation frequency, current density, and exposure time. Enhancement of cAMP content could be observed at certain modulation frequencies and exposure times suggesting a window effect, whereas for the current density in the range measured (8.5 microA/cm2-2.5 mA/cm2) a constant enhancement could be observed. The synergistic effect of fMLP and IFC could only be observed in the treatment sequence of fMLP followed by IFC; an inverse sequence had no effect on the cAMP content. .     

Exposure to extremely low-frequency magnetic field restores spinal cord injury-induced tonic pain and its related neurotransmitter concentration in the brain

Spinal cord injury (SCI) is unequivocally reported to produce hyperalgesia to phasic stimuli, while both hyper- and hypoalgesia to tonic stimuli. The former is spinally mediated and the latter centrally. Besides, its management is unsatisfactory. We report the effect of magnetic field (MF; 17.96 μT, 50 Hz) on tonic pain behavior and related neurotransmitters in the brain of complete thoracic (T13) SCI rats at week 8. Adult male Wistar rats were divided into Sham, SCI and SCI+MF groups. Formalin-pain behavior was compared utilizing 5 min block pain rating (PR), 60 min session-PR, time spent in various categories of increasing pain (T0–T3) and flinch incidences. Serotonin (5-HT), dopamine (DA), norepinepherine (NE), gamma-aminobutyric acid (GABA), glutamate and glycine were estimated in brain tissue by liquid chromatography–mass spectrometry. Session-PR, block-PR and number of flinches were significantly lower, while time spent in categories 0–1 was higher in the SCI versus Sham group. These parameters were comparable in the SCI+MF versus Sham group. 5-HT concentration in cortex, remaining forebrain areas and brain stem (BS), was lower while GABA and NE were higher in BS of SCI, which were comparable with Sham in the SCI+MF group. The concentration of DA, glutamate and glycine was comparable amongst the groups. The data indicate significant hypoalgesia in formalin pain while increased in GABA, NE and decreased in 5-HT post-SCI, which were restored in the SCI+MF group. We suggest beneficial effect of chronic (2 h/day × 8 weeks) exposure to MF (50 Hz, 17.96 μT) on tonic pain that is mediated by 5-HT, GABA and NE in complete SCI rats.     

Multi-endpoint biological monitoring of phosphine workers

5-Aminosalicylic acid (5ASA), a prescribed drug for ulcerative colitis, is a potent scavenger of oxygen-derived free radicals. The present study was undertaken to ascertain its ability to protect against radiation-induced damage. The drug dose-dependent effect, optimum time of drug administration and radiation dose-dependent effect (0-4 Gy) on in vivo radiation protection against micronuclei induction in polychromatic erythrocytes (PCE) and normochromatic erythrocytes (NCE) were studied in the bone marrow of mice. Intraperitoneal injection of 10-125 mg/kg of the drug 30 min before whole body irradiation with 3 Gy produced a significant reduction in the frequency of micronucleated erythrocytes at 24 h after exposure. The optimum dose for protection without drug toxicity was 25 mg/kg body weight. Injection of 25 mg/kg of the drug 60 or 30 min before or within 15 min after 3 Gy whole body gamma-irradiation resulted in a significant decrease in the radiation-induced PCE and NCE with micronuclei (MPCE and MNCE) and an increase in the ratio of PCE to NCE (P/N), at 24 h post-irradiation. Maximum effect was seen when the drug was administered 30 min before irradiation. Therefore, to study the radiation dose-response, mice were pre-treated with 25 mg/kg of 5ASA 30 min before 1-4 Gy of gamma-irradiation. Radiation increased the MN frequency linearly (r(2)=0.99) with dose. Pre-treatment with 5ASA significantly reduced the MN counts to 40-50% of the radiation (RT) alone values, giving a dose modification factor (DMF) of 2.02 (MPCE) and 2.53 (MNCE). Irradiation resulted in a dose-dependent decline in the P/N ratio at all the doses of radiation studied. 5ASA produced a significant increase in the P/N ratio from that of irradiated controls, at all doses of radiations tested. These results show that 5ASA protect mice against radiation-induced MN formation and mitotic arrest.     

Modulation of noradrenaline release in the median preoptic area by GABAergic inputs from the organum vasculosum of the lamina terminalis in the rat

Previous observations have shown that gamma-aminobutyric acid (GABA) receptor mechanisms modulate the release of noradrenaline (NA) in the median peptic nucleus (MnPO). The present study was carried out to investigate whether neural inputs from the organum vasculosum of the lamina terminalis (OVLT) to the MnPO are involved in the GABAergic modulation of NA release in the MnPO area using in vivo microdialysis techniques. In urethane-anesthetized rats, electrical stimulation (5 and 10 microA, 10Hz) of the OVLT region, but not its surrounding region, significantly enhanced dialysate NA concentration in the MnPO area. The enhancement in the NA level caused by the OVLT region stimulation was significantly increased by perfusion with either bicuculline (10 microM), a GABA(A) receptor antagonist, or phaclofen (10 microM), a GABA(B) receptor antagonist, through a microdialysis probe. The amount of the antagonist-induced increase was much greater in the phaclofen-treated group than in the bicuculline-treated group. These results show that the OVLT region may exert both excitatory and inhibitory influences on the release of NA in the MnPO area, and imply that the inhibitory influence may be mediated through GABA(B) receptors rather than GABA(A) receptors.     

Effects of varying frequency of sympathetic stimulation on chloride and amylase levels of saliva elicited from rat parotid gland with electrical stimulation of both autonomic nerves.

Simultaneous stimulation of the parasympathetic and sympathetic nerves to the parotid gland of rats elicited saliva at a rate dependent on the frequency of sympathetic stimulation when parasympathetic frequency was maintained at 16 Hz. The flow rate was lowest at 2 Hz (sympathetic), moderate at 5 Hz, and highest at 16 Hz. Cl concentration of the saliva evoked with stimulation of both nerves was highest at the highest frequency and flow rate (maintained at the level of 102 mEq/liter, for 35 min) and lowest at 2 Hz (declining from 40 mEq/liter initially to 28 mEq/liter). With sympathetic nerve stimulation alone, Cl concentration ranged from 27 to 58 mEq/liter when frequency was varied from 2 to 16 Hz, and with parasympathetic stimulation alone (16 Hz), it ranged from 132 to 124 mEq/liter. Amylase concentration of sympathetically elicited saliva was, in contrast, highest at 2 Hz (1.5 times the level at 5 Hz, and twice the level at 16 Hz), and nearly 18-38 times that seen with parasympathetic stimulation alone. The same pattern was found when both nerves were stimulated, and at 2 Hz (sympathetic), amylase concentration was 1.6 times the level at 5 Hz and 2.6 times the level at 16 Hz. When the two nerves were simultaneously stimulated, the total amount of amylase secreted over 35 min was twice as high as that observed with sympathetic nerve stimulation alone, at any frequency. The relation of frequency to norepinephrine concentration was examined. There was no consistent difference in norepinephrine concentration related to variation in frequency of sympathetic stimulation. Only when both nerves were stimulated at 16 Hz was there a statistically significant reduction in norepinephrine concentration of 46%. A relation between frequency of sympathetic stimulation, flow rate, amylase concentration, and Cl concentration was established, but these changes could not be directly correlated with quantitative differences in norepinephrine concentration.     

Effect of low-intensity pulse-modulated microwave on human blood aspartate aminotransferase activity

Pulse-modulated microwaves (frequency 2375 MHz, intensity: 2 microW/cm2 and 8 microW/cm2, pulse modulation from 50 to 390 Hz with step of 20 Hz; exposure time 5 min) changed the activity of aspartataminotranspherase of the donor blood. Aspartataminotranspherase activity was strongly dependent both on modulation frequency and microwave intensity. Maximum activity was found at 390 Hz and 8 microW/cm2. Maximum observed activity was about six times greater than control level of activity.     

Phosphorylation and chronic agonist treatment atypically modulate GABAB receptor cell surface stability

GABA(B) receptors are heterodimeric G protein-coupled receptors that mediate slow synaptic inhibition in the central nervous system. The dynamic control of the cell surface stability of GABA(B) receptors is likely to be of fundamental importance in the modulation of receptor signaling. Presently, however, this process is poorly understood. Here we demonstrate that GABA(B) receptors are remarkably stable at the plasma membrane showing little basal endocytosis in cultured cortical and hippocampal neurons. In addition, we show that exposure to baclofen, a well characterized GABA(B) receptor agonist, fails to enhance GABA(B) receptor endocytosis. Lack of receptor internalization in neurons correlates with an absence of agonist-induced phosphorylation and lack of arrestin recruitment in heterologous systems. We also demonstrate that chronic exposure to baclofen selectively promotes endocytosis-independent GABA(B) receptor degradation. The effect of baclofen can be attenuated by activation of cAMP-dependent protein kinase or co-stimulation of beta-adrenergic receptors. Furthermore, we show that increased degradation rates are correlated with reduced receptor phosphorylation at serine 892 in GABA(B)R2. Our results support a model in which GABA(B)R2 phosphorylation specifically stabilizes surface GABA(B) receptors in neurons. We propose that signaling pathways that regulate cAMP levels in neurons may have profound effects on the tonic synaptic inhibition by modulating the availability of GABA(B) receptors.     

INTERFERENTIAL ELECTRIC FIELDS REVEAL NONUNIFORM EFFECTS ON PROLIFERATION AND hCG SECRETION IN JAr CELLS

The effect of low frequency electromagnetic fields on changes in intracellular cAMP concentrations was investigated in the frequency range 10–100 Hz using a choriocarcinoma cell line. JAr cells significantly reduce proliferation and increase β-hCG secretion upon dibutyryl cAMP and forskolin treatment after 10 days of culturing. Choriocarcinoma cells exposed to a modulation frequency of 10 Hz for 5 min change their intracellular cAMP level significantly to higher as well as to lower concentrations in half of the experimental series, respectively. At frequencies of 70 and 100 Hz levels, half of the experimental series revealed a significant decrease in cAMP levels. Long term exposure at 100 Hz for 10 days leads to a significant reduction in proliferation but not in β-hCG secretion. These results point to a modulatory effect of low frequency electromagnetic fields on intracellular cAMP levels which are dependent on the frequency window. The reduced proliferation after long term exposure at the frequency of 100 Hz, which lowers cAMP levels, is discussed.     

Invivo inactivation of γ-aminobutyric acid-α-ketoglutarate transaminase by 4-amino-5-fluoropentanoic acid

Intraperitoneal injection into mice of varying concentrations of (S)-4-amino-5-fluoropentanoic acid ((S)-AFPA) produces a dose-dependent irreversible decrease in brain γ-aminobutyric acid-α-ketoglutaric acid aminotransferase (E.C. 2.6.1.19) activity. Concomitant with this inactivation is an increase in whole brain γ-aminobutyric acid (GABA) levels. Four hours after a dose of 100 mg/kg body weight of (S)-AFPA to mice, endogenous brain GABA concentrations increase to 16 times that of the untreated animals and the enzyme activity decreases to 20% that of the controls. The binding of (S)-AFPA to GABA receptors was more than three orders of magnitude poorer than for GABA itself.     

Pharmacological evidence for a role of gamma-aminobutyric acid A receptor mechanism in modulating nitric oxide synthase activity in rat brain

The role of gamma-aminobutyric acid (GABA) mechanism on the synthesis of nitric oxide (NO) has been investigated by measuring the activity of nitric oxide synthase (NOS) and the concentration of NO in rat brain 15 min after administration of anticonvulsant doses of diazepam (0.25 and 0.5 mg/kg) which is known to activate GABA A receptor for its anticonvulsant action. Diazepam enhanced both NOS activity and the concentration of NO in a dose-dependent manner. A reversal has been observed in animals treated with a convulsant dose of picrotoxin (5 mg/kg) which is known to produce convulsions by blocking GABA A receptor mechanism. These results suggest that a functional interaction occurs between GABA A receptor activity and NO synthesis in the brain.     

Diazotization and Thiocyanate Differentiate Agonists from Antagonists for the High- and Low-Affinity Receptors of γ-Aminobutyric Acid

The differentiation of high- and low-affinity postsynaptic gamma-aminobutyric acid (GABA) receptors was examined in a washed cortical membrane preparation of the rat. The selective elimination of the high- and low-affinity GABA sites by the chaotropic anion thiocyanate and diazotization by p-diazobenzenesulfonic acid (DSA), respectively, offered two model systems for the separate sites. The [3H]GABA displacing potencies of some GABA agonists [GABA, 4,5,6,7-tetrahydro- isoxazole [4,5c]pyridine-3-ol (THIP), and muscimol] and antagonists [bicuculline methiodide (BCM), 3-alpha-hydroxy-16-imino-5 beta-17-aza-androstan-11-one (R-5135), and d-tubocurarine] and their slope factors were examined in these model systems and in control membranes. The displacing potency of the agonists was increased in the DSA-pretreated membranes and decreased in the presence of thiocyanate. The displacing potency of the antagonists was shifted in an opposite manner. The chaotropic effect of thiocyanate was reversible and not additive with the inhibitory effect of diazotization on the specific binding of GABA. Inhibition of specific GABA binding by pyridoxal-5-phosphate (PLP) could not be protected by GABA antagonists (BCM and R-5135) but only by agonists. The results can be interpreted in the framework of a dual (agonist-antagonist) receptor model, postulating a hydrophobic accessory site at the low-affinity GABA receptor. The effect of thiocyanate on the GABA receptor may result in the exposure of the hydrophobic accessory sites.