Actions of amino acids and convulsants on bulbar reticular neurones

Summary A study has been made of the actions of microelectrophoretically administered amino acids and convulsants on spontaneous and glutamate- (or DLH-) induced firing of bulbar reticular neurones in unanaesthetized, decerebrate, cats. DLH was a more potent excitant than glutamate and aspartate on almost all the neurones tested. Although glutamate was usually more effective than aspartate, their relative potencies were often similar. Glycine, -alanine and GABA depressed the majority of neurones tested (93%, 89% and 75%, respectively), and had no action on the remainder. Glycine was invariably more potent than -alanine, which was usually more potent than GABA. Strychnine reversibly blocked the depressant actions of glycine and -alanine but not that of GABA. Electrophoretically administered picrotoxin slightly reduced the depression caused by glycine and GABA on less than half the neurones tested. Intravenously injected picrotoxin (0.3–5 mg/kg) did not block the effects of these amino acids. A comparison of the results with those obtained in the spinal cord provides some evidence that glycine may be an inhibitory transmitter substance released on bulbar reticular neurones.Supported by a grant from the Swiss National Foundation of Scientific Research.     

Pharmacological properties of inhibitions in the cerebellar cortex

Summary Stimulation of the parallel fibres, or the mossy fibres, in the cerebellar cortex depresses the potential generated in the granular layer by anti-dromic invasion of the Purkinje cells (N₁), and that generated by the axon discharge of granule cells (P₂). The reduction of these potentials indicate inhibitions mediated respectively by basket and Golgi cells. The depressions of both N₁ and P₂ potentials are unaffected by strychnine at doses of up to 1 mg/kg. Picrotoxin and bicuculline reduce or suppress both inhibitions at doses of 2 to 5 mg/kg and 0.2 to 0.4 mg/kg respectively. The action of the picrotoxin is long lasting or even possibly irreversible, whereas that of bicuculline lasts only a few minutes. The ratio by weight between the dose of picrotoxin and that of bicuculline necessary to reduce the N₁ and P₂ depression exceeds 10.These results indicate that gamma-aminobutyric acid may be the chemical inhibitory transmitter at basket cell — Purkinje cell and Golgi cell — granule cell synapses.Postgraduate student of the Scuola Normale Superiore of Pisa.From the Clinica delle Malattie Nervose e Mentali della Università di Perugia, Italy.     

Anticonvulsant activity of DNS II fraction in the acute seizure models

Aim of the study

Delphinium nordhagenii belongs to family Ranunculaceae, it is widely found in tropical areas of Pakistan. Other species of Delphinium are reported as anticonvulsant and are traditionally used in the treatment of epilepsy. Delphinium nordhagenii is used by local healer in Pakistan but never used for scientific investigation as anticonvulsant. Thus, Delphinium nordhagenii was subjected to bioassay-guided fractionation and the most active fraction, i.e. DNS II acetone was chosen for further testing in the acute seizure models of epilepsy to study the antiepileptic potential in male mice.

Materials and methods

Different doses (60, 65 and 70 mg/kg, i.p.) of DNS II acetone fraction of Delphinium nordhagenii was administered 30 min prior the chemoconvulsant's injection in the male mice. Convulsive doses of chemoconvulsants (pentylenetetrazole 90 mg/kg, s.c. and picrotoxin 3.15 mg/kg, s.c.) were used. The mice were observed 45–90 min for the presence of seizures. Moreover, four different doses of DNS II (60, 65, 70 and 100 mg/kg, i.p.) were tested in the MES test.

Results

The DNS II acetone fraction of Delphinium nordhagenii has exhibited the anticonvulsant actions by preventing the seizures against PTZ- and picrotoxin-induced seizure as well as 100% seizure protection in MES test. The results are comparable with standard AEDs (diazepam 7.5 mg/kg, i.p. and phenytoin 20 mg/kg, i.p.).

Conclusions

These findings suggest that the Delphinium nordhagenii possesses the anticonvulsant activity. Further analysis is needed to confirm the structure and target the extended activity profile.     

Anxiolytic-like effects of acute and chronic treatment with Achillea millefolium L. extract

Ethnopharmacological relevance

Achillea millefolium L. (Asteraceae), known as yarrow (“mil folhas”), has been used as folk medicine for gastrointestinal disorders, inflammation, anxiety, and insomnia.

Aim

To evaluate the potential anxiolytic-like effect of hydroalcoholic extract of Achillea millefolium L. in animal models.

Methods

The present study evaluated the effects of the hydroalcoholic extract from the aerial parts of Achillea millefolium L. in mice subjected to the elevated plus-maze, marble-burying, and open-field tests. Additionally, the GABA_A/benzodiazepine (BDZ) mediation of the effects of Achillea millefolium was evaluated by pretreatment with the noncompetitive GABA_A receptor antagonist picrotoxin and the BDZ antagonist flumazenil and by [³H]-flunitrazepam binding to the BDZ site on the GABA_A receptor.

Results

Achillea millefolium exerted anxiolytic-like effects in the elevated plus-maze and marble-burying test after acute and chronic (25 days) administration at doses that did not alter locomotor activity. This behavioral profile was similar to diazepam. The effects of Achillea millefolium in the elevated plus-maze were not altered by picrotoxin pretreatment but were partially blocked by flumazenil. Furthermore, Achillea millefolium did not induce any changes in [³H]-flunitrazepam binding.

Conclusion

The results indicate that the orally administered hydroalcoholic extract of Achillea millefolium L. exerted anxiolytic-like effects that likely were not mediated by GABA_A/BDZ neurotransmission and did not present tolerance after short-term, repeated administration.     

Post-training administration of GABAergic antagonists enhances retention of aversively motivated tasks

The effect of sub-convulsive doses of GABAergic antagonists on the retention of two aversively motivated tasks, inhibitory avoidance (IA) and Y-maze discrimination (YMD), was investigated in CFW mice. In the IA task, post-training intraperitoneal injections of picrotoxin and bicuculline induced a dose-dependent enhancement of retention measured 24 h after the training, while retention was not affected by bicuculline methiodide (a GABA receptor antagonist that does not readily cross the blood-brain barrier). In the absence of footshock on the training day, post-training administration of picrotoxin and bicuculline did not affect retention test latencies. In the YMD task, the discrimination was reversed on the retention test and errors made on the reversal trials served as the index of retention of the original training. The reversal error scores of mice given post-training injections of picrotoxin or bicuculline, but not bicuculline methiodide, were significantly higher than those of saline-treated controls. These findings extend previous observations that GABAergic antagonists enhance retention of aversively motivated tasks and suggest the involvement of central GABAergic processes on memory consolidation.     

The possible modulation of morphine analgesia by the supramolecular GABA receptor complex

In the present study, the mechanism of the antagonistic action of 0.5 mg/kg diazepam on the analgesic effect of morphine was investigated. While Ro 15-1788, a benzodiazepine receptor antagonist, was found to partially reverse the inhibitory action of diazepam on morphine analgesia, a chloride channel blocking agent, picrotoxin, produced complete antagonism of the action of diazepam. Furthermore, picrotoxin potentiated the partial antagonistic effect of Ro 15-1788 at a normally ineffective dose to affect the 0.5 mg/kg diazepam-morphine dose-response curve. These overall effects of picrotoxin on the supramolecular GABA receptor complex are discussed.     

SCH 23390 blocks drug-conditioned place-preference and place-aversion: anhedonia (lack of reward) or apathy (lack of motivation) after dopamine-receptor blockade?

The influence of the D₁ antagonist SCH 23390 on the motivational properties of rewarding (morphine, nicotine and diazepam) and aversive (naloxone, phencyclidine and picrotoxin) drugs was studied in the rat in a two-compartment place-conditioning paradigm, which included a pre-conditioning test for spontaneous place-preference. The specific D₁ dopamine-receptor antagonist SCH 23390 (0.05 mg/kg SC), paired with both compartments or, separately, with the preferred or with the non-preferred compartment, failed to affect the spontaneous unconditioned preference of the animal. Pairing of morphine (1.0 mg/kg SC), nicotine (0.6 mg/kg SC) or diazepam (1.0 mg/kg IP) with the less preferred compartment induced significant preference for that compartment. Pairing of SCH 23390 (0.05 mg/kg SC) with both compartments completely blocked the place-preference induced by morphine, nicotine and diazepam. Naloxone (0.8 mg/kg SC), phencyclidine (2.5 mg/kg SC) or picrotoxin (2.0 mg/kg IP) paired with the preferred compartment elicited place-aversion. Pairing of SCH 23390 (0.05 mg/kg SC) with both compartments abolished also the place-aversion induced by naloxone, phencyclidine and picrotoxin. The results indicate that blockade of dopamine transmission blocks the motivational properties of rewarding as well as aversive stimuli. It is suggested that neuroleptics rather than simply blocking the rewarding impact of positive reinforcers (anhedonia, lack of pleasure) exert a more general influence on conditioned behaviour by blocking the affective impact of negative as well as positive reinforcers (apathy, lack of motivation).     

γ-氨基丁酸受体在躯体传入冲动抑制中枢性升压反应中的作用

目的：进一步阐明躯体传入冲动抑制中枢性升压反应的中枢递质机制。方法：用氯醛糖-脲酯混合麻醉、切断迷走神经的健康雄性家兔，侧脑室注射印防己毒（Picrotoxin）或中脑中央灰质（PAG）微量注射印防己毒，观察腓深神经（DPN）抑制电刺激下丘脑背内侧核（DMH）引起的中枢性升压反应的改变。结果：注药后DPN对DMH兴奋引起的升压反应的抑制作用削弱。结论：γ-氨基丁酸（GABA）受体参与了DPN抑制DMH兴奋诱发的升压反应，PAG是GABA受体在刺激DPN抑制DMH兴奋诱发的升压反应作用中的一个重要位点所在区。     

Involvement of the amygdaloid complex in neuromodulatory influences on memory storage

Neuromodulatory systems activated by training experiences appear to play a role in influencing memory storage processes. The research summarized in this paper examined the effects, on memory, of posttraining administration of treatments affecting adrenergic, opioid peptidergic and GABAergic systems. When administered after training, drugs affecting these systems all produce dose- and time-dependent effects on memory storage. The drug effects on memory are blocked by lesions of the amygdaloid complex as well as lesions of the stria terminalis, a major amygdala pathway. The effects of drugs affecting these neuromodulatory systems are also blocked by injections of beta-adrenergic antagonists administered to the amygdaloid complex. Thus, the findings suggest that the neuromodulatory systems affect memory storage through influences involving the activation of beta-adrenergic receptors within the amygdala. These findings are consistent with the view that the amygdala is involved in regulating the storage of memory in other brain regions.     

Studies on picrotoxin binding sites of GABAA receptors in rat cortical synaptoneurosomes

Experiments were performed to characterize [³⁵S]TBPS binding in rat cortical Synaptoneurosomes, which have vesicular structures containing both pre- and postsynaptic elements. Scatchard analysis revealed a single component of [³⁵S]TBPS binding sites with K_D and B_max values of 76.1 nM and 1.97 pmoles/mg protein, respectively, under physiological conditions. GABA and muscimol inhibited [³⁵S]TBPS binding in a concentration-dependent manner. IC₅₀ values of these GABA_A agonists in displacing synaptoneurosomal [³⁵S]TBPS binding are comparable to previously reported EC₅₀ values of the agonist-stimulated ³⁶C1⁻ uptake in Synaptoneurosomes by these agents. Furthermore, the IC₅₀ values of these GABA_A agonists were better correspondence to those determined by [³H]muscimol binding in synaptoneurosomal preparations as reported by Delorey and Brown (3) than those determined in membrane preparations. Although bicuculline increased [³⁵S]TBPS binding in a concentration dependent manner in cortical membranes, it did not affect synaptoneurosomal [³⁵S]TBPS binding. Benzodiazepine agonists and inverse agonists (0.1 to 10 μM) did not show any effects on the binding in the absence of muscimol. However, benzodiazepine agonists potentiated and inverse agonists antagonized muscimol-induced inhibition of synaptoneurosomal [³⁵S]TBPS binding. In addition, an anesthetic steroid, THDOC, and pentobarbital inhibited synaptoneurosomal [³⁵S]TBPS binding in a concentration dependent manner. These results suggest that allosteric modulation of [³⁵S]TBPS binding by various ligands which interact with GABA_A supramolecular complexes remain intact in Synaptoneurosomes. It appears that this preparation is useful for investigating correlation between functional ³⁶Cl⁻ uptake and individual binding studies of each of the GABA_A receptor complex.