Enhancement of benzodiazepine receptor binding by L-lysine is chloride-dependent and due to increase in binding affinity

The Role of Amino Acids in Neurotransmission and Fluorescent Tools for Their Detection

Neurotransmission between neurons, which can occur over the span of a few milliseconds, relies on the controlled release of small molecule neurotransmitters, many of which are amino acids. Fluorescence imaging provides the necessary speed to follow these events and has emerged as a powerful technique for investigating neurotransmission. In this review, we highlight some of the roles of the 20 canonical amino acids, GABA and β-alanine in neurotransmission. We also discuss available fluorescence-based probes for amino acids that have been shown to be compatible for live cell imaging, namely those based on synthetic dyes, nanostructures (quantum dots and nanotubes), and genetically encoded components. We aim to provide tool developers with information that may guide future engineering efforts and tool users with information regarding existing indicators to facilitate studies of amino acid dynamics.

Anticonvulsant and depressant effects of aqueous extracts of Carum copticum seeds in male rats

In this study, the effects of aqueous extracts of Carum copticum seeds (CCS) were evaluated in kindling models of epilepsy. Additionally, the sedative and anxiolytic effects of the extract were assessed. For pentylenetetrazole (PTZ) kindling, rats received a subconvulsant dose of PTZ (40 mg/kg, ip) every second day and seizure stages were recorded. CCS aqueous extract (200, 400, or 600 mg/kg, ip) was injected 30 minutes prior to each PTZ injection. In electrical kindling, bipolar stimulating and monopolar recording electrodes were implanted stereotaxically in the right basolateral amygdala of male Sprague-Dawley rats. After kindling, the effect of aqueous extracts of CCS (200, 400, or 600 mg/kg, ip) on afterdischarge duration, duration of rearing, forelimb clonus, and loss of equilibrium (stage 5 seizure), and latency to the onset of bilateral forelimb clonus were measured. The sedative and the anxiolytic effects of CCS extracts were evaluated in an open-field apparatus and elevated plus maze, respectively. The results indicate that aqueous extracts of CCS have a significant anticonvulsant effect. Different doses of extract significantly delayed the incidence of every seizure stage in the PTZ model of kindling. Moreover, CCS extract (400 and 600 mg/kg, ip) suppressed afterdischarge duration, latency to the onset of bilateral forelimb clonus, and stage 5 seizure in the electrical kindling model. These results suggest that CCS extract has remarkable antiepileptic and central depressant effects.

L-lysine is a barbiturate-like anticonvulsant and modulator of the benzodiazepine receptor

Our earlier observations showed that L-lysine enhanced the activity of diazepam against seizures induced by pentylenetetrazol (PTZ), and increased the affinity of benzodiazepine receptor binding in a manner additive to that caused by gamma-aminobutyric acid (GABA). The present paper provides additional evidence to show that L-lysine has central nervous system depressant-like characteristics. L-lysine enhanced [3H]flunitrazepam (FTZ) binding in brain membranes was dose-dependent and stimulated by chloride, bromide and iodide, but not fluoride. Enhancement of [3H]FTZ binding by L-lysine at a fixed concentration was increased by GABA but inhibited by pentobarbital between 10(-7) to 10(-3)M. While GABA enhancement of [3H]FTZ binding was inhibited by the GABA mimetics imidazole acetic acid and tetrahydroisoxazol pyridinol, the enhancement by pentobarbital and L-lysine of [3H]FTZ binding was dose-dependently increased by these two GABA mimetics. The above results suggest that L-lysine and pentobarbital acted at the same site of the GABA/benzodiazepine receptor complex which was different from the GABA binding site. The benzodiazepine receptor antagonist imidazodiazepine Ro15-1788 blocked the antiseizure activity of diazepam against PTZ. Similar to pentobarbital, the anti-PTZ effect of L-lysine was not blocked by Ro15-1788. Picrotoxinin and the GABA, receptor antagonist bicuculline partially inhibited L-lysine's enhancement of [3H]FTZ binding with the IC50s of 2 microM and 0.1 microM, respectively. The convulsant benzodiazepine Ro5-3663 dose-dependently inhibited the enhancement of [3H]FTZ binding by L-lysine. This article shows the basic amino acid L-lysine to have a central nervous system depressant characteristics with an anti-PTZ seizure activity and an enhancement of [3H]FTZ binding similar to that of barbiturates but different from GABA.

Chronic L-lysine develops anti-pentylenetetrazol tolerance and reduces synaptic GABAergic sensitivity

L-Lysine 10 mmol/kg given to mice for 1 to 10 days significantly increased clonic and tonic seizure latencies caused by 60 mg/kg pentylenetetrazol (PTZ). On day 1 the clonic and tonic seizure latencies were increased from 160.4 +/- 26.3 and 828.6 +/- 230.8 s to 286.1 +/- 103.3 and 982.3 +/- 98.6 s, respectively. Both clonic and tonic seizure latencies increased steadily with additional L-lysine treatment without significant change in survival rate. On day 10, the anticonvulsant effect reached its highest level with a block of tonic seizures and a survival rate of 100% without tolerance developing. Acute L-lysine treatment significantly increased the mean clonic latency from 85.8 +/- 5.24 to 128.2 +/- 9.0 s and the mean tonic seizure latency from 287.2 +/- 58.7 to 313.5 +/- 42.2 s with 80 mg/kg PTZ. On the day 10 of treatment, the anticonvulsant effect of L-lysine was highest, with a significant increase of 155 and 184% in clonic and tonic latencies over the control, respectively. After 15- and 20-day treatment, clonic and tonic seizures latencies and survival rate decreased, suggesting development of tolerance. Brain membranes from tolerant mice showed decreased enhancement by gamma-aminobutyric acid of specific [3H]flunitrazepam binding from 210 +/- 8 to 169 +/- 5% with EC50 values of 4.1 +/- 1.4 and 7.8 +/- 1.5 microM, respectively. Scatchard analysis of [3H] flunitrazepam binding showed no significant change of apparent binding affinity (KD) or binding density (Bmax) after chronic L-lysine exposure. L-Lysine enhanced the specific [35S]tert-butyl bicyclophosphorothionate (TBPS) binding in brain membranes dose dependently.(ABSTRACT TRUNCATED AT 250 WORDS)

Brain levels of amines and amino acids in taste aversion-prone and -resistant rats

Possible biological contributions to taste aversion (TA) conditionability were explored by comparing whole-brain levels of five neurotransmitter amines and 14 common amino acids within TA-prone (TAP) and TA-resistant (TAR) rats. The selectively bred strains had been developed via 22 generations of bidirectional nonsibling matings based on susceptibility to cyclophosphamide-induced conditioned TAs. The target substances were separated by HPLC and were measured by electrochemical or fluorometric procedures. The TAP brains had higher levels of serotonin (5-HT) and lower levels of norepinephrine (NE) than TAR brains. No strain differences were found with respect to dihydroxyphenylalanine (DOPAC), dopamine (DA), or 5-hydroxyindoleacetic acid (5-HIAA). Among amino acids, TAP rats had lower levels of lysine than TARs: no other differences were detected. Therefore, higher levels of 5-HT and lower levels of NE and lysine were associated with enhanced TA conditionability. The 5-HT and NE results extend prior indications of their central neurotransmitter TA involvements. The functional role of lysine in TA or other brain functions remains obscure.

Correlation between enhancement of [3H]flunitrazepam binding and suppression of pentylenetetrazol-induced seizures by L-lysine

L-Lysine enhanced the specific [3H]flunitrazepam (FTZ) binding of bovine brain membranes in vitro. Inhibition of specific [3H]FTZ binding to brain membranes in vitro by pentylenetetrazol (PTZ) at concentrations 0.46 mM and below was reversed by increasing L-lysine concentrations in the incubation mixture; further increase of L-lysine concentration enhanced this binding. However, inhibition of [3H]FTZ binding by PTZ higher than 2.3 mM was reversed only partially by L-lysine. L-Lysine enhanced specific [35S]t-butylbicyclophosphorothionate (TBPS) binding on mouse brain membranes in a dose-dependent manner (EC approximately 5 microM). This enhancement was inhibited by PTZ dose dependently. Inhibition of [35S]TBPS binding by PTZ was attenuated slightly by L-lysine. L-Lysine enhanced [3H]FTZ binding in intact mice in a dose- or concentration-dependent manner with an ED50 of 6 mmol/kg body weight or EC50 of 3 mumol/g brain tissue, respectively. Similar effect was observed for L-lysine in ex vivo [3H]FTZ binding study when [3H]FTZ was incubated in vitro with an ED50 of 1 mmol/kg mouse or EC50 of 0.7 mumol/g brain. PTZ not only induced seizures, but also inhibited specific [3H]FTZ binding to brain membranes in a dose-dependent manner. L-Lysine, in a dose-dependent manner, suppressed seizures caused by PTZ at 50 or 60 mg/kg, or prolonged the time of seizure onset (seizure latency) caused by higher doses of PTZ (90 or 100 mg/kg). Pretreatment with L-lysine at 1, 5, 10 or 20 mmol/kg not only reversed the inhibition of the specific [3H]FTZ binding caused by PTZ at 50, 90 or 100 mg/kg, but also enhanced this binding above control level.(ABSTRACT TRUNCATED AT 250 WORDS)