Reversal of inhibition of putative dopaminergic neurons of the ventral tegmental area: Interaction of GABAB and D2 receptors

Abstract

Neurons of the ventral tegmental area (VTA) are critical in the rewarding and reinforcing properties of drugs of abuse. Desensitization of VTA neurons to moderate extracellular concentrations of dopamine (DA) is dependent on protein kinase C (PKC) and intracellular calcium levels. This desensitization is called DA inhibition reversal (DIR), as it requires concurrent activation of D2 and D1-like receptors; activation of D2 receptors alone does not result in desensitization. Activation of other G-protein linked receptors can substitute for D1 activation. Like D2 receptors, GABAB receptors in the VTA are coupled to G-protein-linked potassium channels. In the present study, we examined interactions between a GABAB agonist, baclofen, and dopamine agonists, dopamine and quinpirole, to determine whether there was some interaction in the processes of desensitization of GABAB and D2 responses. Long-duration administration of baclofen alone produced reversal of the baclofen-induced inhibition indicative of desensitization, and this desensitization persisted for at least 60 min after baclofen washout. Desensitization to baclofen was dependent on protein kinase C. Dopamine inhibition was reduced for 30 min after baclofen-induced desensitization and conversely, the magnitude of baclofen inhibition was reduced for 30 min by long-duration application of dopamine, but not quinpirole. These results indicate that D2 and GABAB receptors share some protein kinase C-dependent mechanisms of receptor desensitization.

Reversal of dopamine‐mediated firing inhibition through activation of the dopamine transporter in substantia nigra pars compacta neurons

“…Interestingly, extracellular dopamine also dampens GABA B receptor-mediated inhibition. A similar interplay has previously been reported in VTA dopaminergic neurons, occurring through a cross-desensitization process (Nimitvilai et al, 2012b), while our results point to a DAT-dependent mechanism, as it is prevented by cocaine. In any case, these results confirm a much more complex and heterogeneous action exerted by extracellular dopamine in the ventral midbrain, than a simple self-inhibitory role through D 2 receptor stimulation.…”

Suppression of Gq Function Using Intra-Pipette Delivery of shRNA during Extracellular Recording in the Ventral Tegmental Area

“…After 2 h of recording with a micropipette containing Gq shRNA packaged in lentivirus (1 × 10 5  IFU per 500 μl), we applied dopamine for 40 min; the inhibition produced by dopamine did not subside over time. In contrast, if lentivirus that did not contain shRNA was included in the micropipette (1 × 10 5  IFU per 500 μl), we saw a clear reversal of the dopamine-induced inhibition over the 40-min time period of administration (Figure 2B) similar to the phenomenon of DIR that we have described previously (Nimitvilai and Brodie, 2010; Nimitvilai et al, 2012a,b,c, 2013). Likewise, if lentivirus containing shRNA directed against a different G-protein, Golf, was included in the pipette (1 × 10 5  IFU per 500 μl), dopamine inhibition subsided over time (Figure 2C), again illustrating DIR that is observed under control conditions, and which we have described extensively previously.…”

VTA CRF neurons mediate the aversive effects of nicotine withdrawal and promote intake escalation

“…Dopamine neurons were identified at the time of recording by previously published functional criteria 23,24 (Fig. S6), and a subset of neurons was collected after recording for TH expression using single-cell RT-PCR.…”

“…Slices that contained the VTA were prepared as described previously 24 from 20 adult male C57BL/6 mice subjected to brief anesthesia (3–5% isoflurane) followed by rapid decapitation and removal of the brain to an ice-cold high-sucrose solution (pH 7.3–7.4) that contained 206.0in mM sucrose, 2.5 mM KCl, 0.5 mM CaCl 2 , 7.0 mM MgCl 2 , 1.2 mM NaH 2 PO 4 , 26 mM NaHCO 3 , 5.0 mM glucose, and 5 mM HEPES. The brains were cut into transverse sections (300 μm) on a vibrating microtome (Leica VT1000S, Leica Microsystems, Buffalo Grove, IL, USA) and placed in an oxygenated (95% O 2 /5% CO 2 ) artificial cerebrospinal fluid (aCSF) solution composed of the following: 120 mM NaCl, 2.5 mM KCl, 5 mM EGTA, 2.0 mM CaCl 2 , 1.0 mM MgCl 2 , 1.2 mM NaH 2 PO 4 , 26 mM NaHCO 3 , 1.75 mM glucose, and 5 mM HEPES.…”