Effect of antipsychotic drugs on the firing of dorsal raphe cells. II. Reversal by picrotoxin

Benzodiazepines: potentiation of a GABA inhibitory response in the dorsal raphe nucleus

Based on evidence that the dorsal raphe nucleus (DR) has specific and independent receptors for 5HT, GABA and glycine (Gallager and Aghajanian, 1976; Wang and Aghajanian, 1977), alterations in the firing rate of DR neurons following the administration of benzodiazepines (BZ) were evaluated to determine whether they were the result of a direct interaction with 5HT receptors or due to interactions of these drugs with GABA and/or glycine. The effects of BZs after both direct and systemic application were tested in rats using microiotophoretic and single-cell recording techniques. Although the BZs did not alter the spontaneous firing rate of the DR, both the systemic and iontophoretic administration of these drugs were found to potentiate the inhibitory response produced by GABA. The data suggest that this potentiation is mediated postsynaptically. Since the effects of BZs on the spontaneous activity of the DR are only apparent following pretreatments with AOAA, it is speculated that these drugs may only have pronounced effects when GABAergic input is prominent.

Comparative simultaneous measurement of cerebrospinal fluid 5-hydroxyindoleacetic acid and blood serotonin levels in delirium tremens and clozapine-induced delirious reaction

Cerebrospinal fluid 5-hydroxyindoleacetic acid and total blood serotonin levels were measured simultaneously in 11 female patients with delirium tremens and nine schizophrenic women with clozapine-induced acute delirium. Both groups had significantly raised levels of 5HIAA in CSF and significantly reduced blood 5HT levels as compared with normal control subjects, symptom-free alcoholics, or clozapine-treated schizophrenics. The two delirious groups were not distinguishable from each other in respect of their CSF 5HIAA or blood 5HT values. After clinical recovery both values returned to normal levels.

Alterations of cerebrospinal fluid 5-hydroxyindoleacetic acid, and total blood serotonin content during clozapine treatment

Cerebrospinal fluid 5-hydroxyindoleacetic acid level, and total blood serotonin content was measured in groups of manic and schizophrenic patients before and after 2, 4, 6, 10, 20, and 30 days of clozapine treatment. CSF 5-HIAA values were elevated after 2 and 4 days and returned to baseline levels after 6 days or more. Blood serotonin content, in contrast, increased gradually and remained high even after 30 days. Neither CSF 5-HIAA nor blood 5-HT correlated with age, drug dose, or clinical effectiveness, but some relationship between these and the sedative component of the clozapine action was observed.

Physiological evidence for habenula as major link between forebrain and midbrain raphe

The lateral habenula is one of the few forebrain areas that project to the midbrain raphe nuclei. Electrical stimulation of the habenula markedly suppressed serotonergic neurons in the midbrain raphe. The suppression was blocked by systemic or microiontophoretic administration of picrotoxin, which suggests that gamma-aminobutyric acid is the inhibitory transmitter in the habenula-raphe pathway. These results support the concept that the habenula may serve a pivotal role in funneling information from the forebrain to the midbrain raphe.