Substantia Nigra: The Involvement of Central and Peripheral Benzodiazepine Receptors in Physical Dependence on Diazepam as Evidenced by Behavioral and EEG Effects

Abstract

Male rats chronically exposed to diazepam (DZ) slowly released from subcutaneously implanted silastic capsules along with empty capsule control rats were focally injected (1 μl) into the substantia nigra (SNR) with the central (CBR) and peripheral (PBR) benzodiazepine receptor antagonists, flumazenil [(FLU) 6.25, 12.5, 25 μg] and PK 11195 [(PK) 3.125, 6.25, 12.5, 25 μg], respectively (weekly intervals; Latin square design). Rats were observed for signs of withdrawal and the EEG was recorded simultaneously from the site of injection (SNR), caudate putamen, thalamus, hippocampus, and frontal cortex. In DZ-dependent rats the Precipitated Abstinence Score (PAS) was significantly related to dose of FLU. The PAS increased with increasing doses of PK (3.125–12.5 μg); however, the highest dose of PK (25 μg) showed less effect. The rapid onset of the PAS was accompanied by a rise in the total power (1–32 Hz) of the EEG (TP EEG) in the SNR and other brain areas. The PAS and TP EEG had similar time courses. Intranigrally injected FLU and PK did not evoke clonic and tonic–clonic convulsions; however, both antagonists induced dose-related twitches and jerks. Additionally, FLU precipitated a dose-related tachypnea and increases in turning and backing. Chronic DZ treatment altered the spectral content of the EEG, as indicated by a decrease and an increase of the slow and fast frequency bands, respectively. FLU and PK rapidly but transiently reversed the EEG. Data suggest that in the SNR the CBR mediate autonomic and motor signs of DZ withdrawal, while both the CBR and PBR are responsible for twitches and jerks and alteration of the EEG. It is possible that PK also acts on the site linked to a GABA A/CBR/ionophore.