Prostaglandin D2-induced potentiation of hexobarbitone hypnosis in rats: role of 5-hydroxytryptamine

Prostaglandins and central serotonergic activity in the rat

Pharmacological and biochemical studies indicate that prostaglandins (PGs) exert a modulatory influence on rat brain serotonergic activity. With several experimental approaches, it has been shown that PGEs and PGD2 facilitate central serotonergic activity in rats. On the contrary, PGF2α not only inhibits rat brain serotonergic activity but also antagonizes the facilitatory effect of the other PGs. The studies support the proposed neuromodulatory role for PGs in central synaptic transmission.

Prostaglandin D2 inhibits pentylenetetrazole-induced convulsions in rats by a serotonin-mediated mechanism

Prostaglandins (PGs) of the E series are known to exert anticonvulsant action in experimental animals. Earlier studies from this laboratory have indicated that PGE1 inhibits pentylenetetrazole (PTZ)-induced convulsions in rats through a serotonin-mediated mechanism. PGD2, the major PG in the rodent brain, shares a number of central pharmacological actions of the PGEs, and like the latter it potentiates the anticonvulsant action of phenobarbitone and phenytoin in rats. The present study was undertaken to investigate the putative anticonvulsant action of PGD2 against PTZ-induced convulsions in rats and to evaluate the role of serotonin in the anticonvulsant action of PGD2. PGD2 (5, 10, and 20 micrograms, icv) produced a dose-related inhibition of PTZ-induced clonic convulsions in rats. The anticonvulsant action of PGD2 (20 micrograms, icv) was significantly attenuated following pretreatment of the rats with pharmacologic agents known to reduce central serotonergic activity, including 5,6-dihydroxytryptamine, a selective neurotoxin for serotonergic neurons, p-chlorophenylalanine, a specific inhibitor of serotonin biosynthesis, metergoline, a serotonin postsynaptic receptor antagonist, and quipazine, which is known to inhibit neuronal release of serotonin. These findings, in conjunction with an earlier study from this laboratory indicating that PGD2 augments rat brain serotonergic activity, suggest that the anticonvulsant activity of PGD2 against PTZ-induced convulsions in rats is mediated through a serotonergic mechanism.

Prostaglandin D2-induced catalepsy in rats: role of 5-hydroxytryptamine

Prostaglandin D2 (PGD2), the major PG in the rat brain, induced a dose-related catalepsy in rats on intracerebroventricular (i.c.v.) administration. This cataleptic response was significantly attenuated following the i.c.v. administration of pharmacological agents that decrease rat brain 5-hydroxytryptamine (5-HT) activity. PGE1 synergized but PGF2 alpha antagonized the catalepsy induced by PGD2. PGD2 and PGE1 have previously been shown to augment rat brain 5-HT activity, whereas PGF alpha inhibited it. It is therefore likely that the observed effects of these PGs on catalepsy involve a central 5-HT mechanism.

The effect of neurotransmitters on cataleptic behavior induced by PG D2 in rats

The effects of several neurotransmitters on prostaglandin (PG) D2-induced cataleptic behavior in rats were investigated by the high bar test. Intracerebroventricular administration of PG D2 elicited cataleptic behavior in a dose-dependent manner without producing a marked change in spontaneous motor activity. The incidences of cataleptic behavior were 20% and 100% at doses of 2 nmol and 50 nmol of PG D2, respectively. Intraperitoneal pretreatment with L-DOPA (100 mg/kg), apomorphine (1 mg/kg), amantadine (0.2 mg/kg), atropine (0.5 mg/kg) or p-chlorophenylalanine (300 mg/kg) significantly decreased the cataleptic behavior induced by 50 nmol of PG D2. Conversely, simultaneous treatment with 5-hydroxy-L-tryptophan (30 mg/kg), 5-methoxy-N,N-dimethyltryptamine (5 mg/kg), imipramine (20 mg/kg) or clomipramine (10 mg/kg) markedly increased the cataleptic behavior induced by 2 nmol of PG D2. Propranolol (10 mg/kg) and phenoxybenzamine (10 mg/kg) did not affect the induction of cataleptic behavior by either 2 nmol or 50 nmol of PG D2. These results suggest that PG D2 might be involved in inducing cataleptic behavior by modulating serotonergic, cholinergic and dopaminergic systems.