Effects of acute and subacute treatment with ergot drugs on the GABA system in specific brain regions

Species dependent dual modulation of the benzodiazepine/GABA receptor chloride channel by dihydroergosine

Dihydroergosine (50 and 100 mg/kg) enhanced the incidence of bicuculline (3 mg/kg)-induced convulsions in female rats, while 100 mg/kg of dihydroergosine given to female mice made 45% convulsive dose of bicuculline (2.5 mg/kg) to be subconvulsive. The same dose of dihydroergosine enhanced in mice the latency of bicuculline (4 mg/kg)-induced convulsions. Although, in in vitro experiments dihydroergosine showed very weak ability to prevent the binding of 3H-muscimol, the drug was able to diminish and to augment the IC50 of bicuculline and GABA when added to crude synaptosomal pellet of the rat and mouse brain respectively. Lower concentrations of dihydroergosine stimulated and higher inhibited 3H-TBOB binding to the crude synaptosomal pellet of the rat brain. In the preparation of mouse brain dihydroergosine produced only inhibition of 3H-TBOB binding. Only slight quantitative differences were observed in bicuculline-induced stimulation and in GABA- and diazepam-induced inhibition of 3H-TBOB binding between the two species. The results suggest that the opposite species-dependent effects of dihydroergosine on bicuculline-induced convulsions are due to the ability of this drug to modulate species-dependently the benzodiazepine/GABA receptor chloride channel complex.

Effect of dihydroergosine (DHESN) on the serotoninergic system and behaviour: is DHESN a new antidepressive agent?

Acute (50.0 mg/kg) and repeated (0.1-10.0 mg/kg) administration of dihydroergosine (DHESN) to rats over 5 days lowered the concentration of 5-HIAA in the brain. DHESN given acutely increased the brain 5-HT in p-CPA-treated animals and diminished the probenecid-induced increase in brain 5-HIAA. In pargyline-treated rats DHESN enhanced the 5-HT/5-HIAA ratio. DHESN administered to rats repeatedly over 5 days decreased the level of 5-HT in blood platelets, and in vitro at concentrations of 10(-4) M and 10(-3) M inhibited the uptake of [14C]-5-HT in platelets. DHESN (10.0-100.0 mg/kg) potentiated the 5-HT syndrome produced in rats by pargyline and 5-HTP. This potentiation was blocked with cyproheptadine but not with haloperidol. DHESN (1.0 and 10.0 mg/kg) lowered the locomotor activity of rats and 10.0 mg/kg DHESN also reduced the duration of immobility in rats forced to swim in a restricted space. The results indicate that DHESN, like antidepressants, decreases the turnover of serotonin in the brain and potentiates the 5-HT-mediated behaviour. This might suggest that the drug should be further investigated for its potential antidepressive properties.

Effect of dihydroergotoxine on the susceptibility of rats to convulsions produced by different convulsant agents

The study was undertaken to test further whether diminished GABAergic transmission might be responsible for the increased susceptibility of rats to picrotoxin-induced convulsions. In rats kept individually in cages in a noise-free room, the time between the intraperitoneal injection of the convulsant agent and the onset of convulsions was measured. Acute and subacute treatment with low doses of dihydroergotoxine (0.01-1.0 mg/kg) increased the occurrence and decreased the latency of picrotoxin-induced convulsions. Acute administration of dihydroergotoxine, 1.0 mg/kg, caused convulsions in animals injected with the subconvulsive dose (3 mg/kg) of bicuculline and of 10.0 mg/kg dihydroergotoxine in animals injected with the subconvulsive dose (1.5 mg/kg) of strychnine. Some of the animals injected with the 100% convulsive dose of strychnine were protected by dihydroergotoxine pretreatment (1.0 mg/kg) as evidenced by the lower occurrence of convulsions and fewer animals dying, as well as by a delay in the appearance of convulsions at 10.0 mg/kg. These results together with the previous findings on the GABA system suggest that dihydroergotoxine potentiates the appearance of picrotoxin and bicuculline-induced convulsions by a diminution of GABAergic transmission.