Role of the Bed Nucleus of Stria Terminalis (BNST) in addiction and depression: a microdialysis study

Introduction: The bed nucleus of stria terminalis (BNST) is a limbic brain area included in the extended amygdala. The BNST is innervated by norepinephrine, dopamine and serotonin projections, it sends and receives a robust corticotropin-realising factor innervation to/from the paraventricular nuclei of hypothalamus. These connections allow the BNST to play a crucial role not only in the control of the stress response, but also in a control of stressful state associated with drug-seeking that occurs after abstinence from chronic drug exposure. Earlier we observed that stimulant and non stimulant drugs of abuse, dose-dependently, increased DA extracellular concentration (output) in the BNST, as well as traditional antidepressants, confirming a role of this nucleus in drug addiction and depression. The non selective N-methyl-D-aspartate (NMDA) receptor antagonist ketamine has been suggested as a promising medication in a treatment of therapy-resistant patients, evoking long-lasting effect already after infusion of a single dose. Aim: We investigated here by means of microdialysis the acute effect of stimulant and non stimulant drugs of abuse on norepinephrine transmission in the BNST, to better understand its role in drug abuse, addiction and relapse, as well as the effect of ketamine on NE and DA transmission in the BNST. Methods: Each implanted rat received a single acute i.p. injection of each dose of tested drugs: nicotine (0.2-0.4 mg/kg s.c), morphine (1.0-3.0 mg/kg s.c.), cocaine (2.5-5.0 mg/Kg mg/kg i.p.), amphetamine (0.25-0.5 mg/kg s.c.) and ethanol (0.5-1.0 g/kg, i.p.); ketamine (10, 20 and 40 mg/kg i.p.). Norepinephrine was assessed in dialysate samples by HPLC and coulometric detection (ESA). Samples were collected (and immediately analysed) every 20 min (flow: 1 mL/min) from freely moving rats implanted in the BNST (coordinates: ant. - 0.40; lat. 0.8; vert. 8). Statistical analysis was carried out by STATISTICA (Statsotf, Tulsa, OK, USA). Two-way analysis of variance (ANOVA) for repeated measures was applied to the data expressed as a percentage of basal NE concentration. Results showing significant overall changes were subjected to post hoc Tukey´s tests with significance for p < 0.05. Results: Two-way ANOVA showed that all above listed drugs significantly, dose and time-dependently increased norepinephrine output in the BNST (nicotine: F2,11= 23.6, p <0.001, F7,77= 18.05, p <0.001; cocaine: F2,9 = 37.7, p <0.001, F7,63 = 25.9, p <0.001; morphine: F2,13 = 10.37, p <0.001 F7,91 = 7.21, p <0.001; ethanol: F2,13 = 4.85, p <0.05, F7,91 = 8.0, p <0.001 and amphetamine: F2,9= 41.7, p <0.001, F7,63 = 16.85, p <0.001); Post-hoc analysis showed that the increase of NE output obtained in doses of 0.4 mg/Kg for nicotine, 5 mg/kg for cocaine, 3 mg/kg for morphine, 1 g/kg for ethanol and 0.5 mg/kg for amphetamine, was significantly higher than the output produced by lower doses of the same drug or saline. When it comes to ketamine, it increased NE (127, 155, and 186 %) and DA output (114, 156, and 176 %) when administered in doses of 10, 20, and 40 mg/Kg, respectively. Two-way ANOVA of the results showed for doses of 20 and 40 mg/Kg a significant treatment effect (F3,19 = 3.76, p < 0.02 and F3,19 = 4.63, p < 0.01), time effect (F9,171 = 31.41, p < 0.001 and F9,171 = 12.72, p < 0.001), and time × dose interaction (F27,171 = 6.29, p < 0.001 and F27,171 = 3.04, p < 0.001) for NE and DA, respectively. These results show that NE transmission in the BNST is involved in the acute effects of drugs of abuse. These alterations of neurotransmission in the BNST may be crucial for a stress-induced drug relapse and for the anxiety/stress modulation of drug-seeking. Results showed that ketamine produces a less increase in NE and DA levels compared with other antidepressants, pointing that the BNST may only be partly involved in its immediate antidepressant effect but still important for this process.