Modulation of Inhibitory Transmission by Dopamine in Rat Basal Forebrain Nuclei: Activation of Presynaptic D₁-like Dopaminergic Receptors

Abstract

The effects of dopamine (DA) on inhibitory transmission onto identified magnocellular neurons were examined in rat basal forebrain slices using whole-cell recording. IPSCs evoked by focal stimulation within basal forebrain nuclei were reversibly blocked by 10 M bicuculline and had a decay time constant of 20.1 Ϯ 0.77 msec in the presence of 6-cyano-7-nitroquinoxalline-2,3-dione (5 M). Bath application of DA reduced the amplitude of IPSCs up to 71.1 Ϯ 1.49% in a concentration-dependent manner between 0.003 and 1 mM (the IC 50 value being 6.6 M), without any effect on the holding current at Ϫ70 mV. DA (10 M) reduced the frequency of miniature IPSCs (mIPSCs) recorded in the presence of TTX (0.5 M), without affecting their mean amplitude, rise time, and decay time constant. Furthermore, the DA-induced effect on mIPSCs remained unaffected by 100 M cadmium, suggesting a presynaptic mechanism independent of calcium influx. SKF 81297, a D 1 -like agonist, mimicked DA-induced effect on evoked IPSCs (IC 50 , 10.9 M), whereas R(Ϫ)-TNPA or (Ϫ)-quinpirole, D 2 -like agonists (30 M), had little or no effect on the amplitude of evoked IPSCs. R(ϩ)-SCH 23390, a D 1 -like antagonist, antagonized the DA-induced effect on IPSCs (K B 0.82 M), whereas S(Ϫ)-eticlopride, a D 2 -like antagonist, showed slight antagonism (K B 7.8 M). Forskolin (10 M) reduced the amplitude of evoked IPSCs to ϳ58% of the control and occluded the inhibitory effect of DA. These findings indicate that DA reduces inhibitory transmission onto magnocellular basal forebrain neurons by activating presynaptic D 1 -like receptors. Key words: dopamine; D 1 receptor; inhibitory postsynaptic currents; magnocellular basal forebrain nuclei; presynaptic modulationMagnocellular basal forebrain (MBF) neurons in the vertical and horizontal limbs of diagonal band of Broca (HDBB), substantia innominata (SI), and nucleus basalis (nB) form the principal source of cholinergic innervation to the cerebral and subcortical brain regions (Rye et al., 1984). Pathophysiologically, degeneration of these cholinergic neurons has been observed in patients with Alzheimer's disease (Coyle et al., 1983;Oyanagi et al., 1989), yet the question of how these cortically projecting neurons can be influenced remains to be clarified. Morphological studies using immunohistochemical techniques have demonstrated that the basal forebrain region receives dopaminergic fibers from the ventral tegmental area, substantia nigra pars compacta, and medial zona interna (Martinez-Murillo et al., 1988;Semba et al., 1988;Eaton et al., 1994). Despite these well documented pathways, the basic effects of dopamine (DA) on synaptic transmission within basal forebrain nuclei are still not well understood. Previous electrophysiological studies using anesthetized rats have shown that neuronal activity is variably inhibited or excited by iontophoretic application of DA in other groups of basal forebrain nuclei, namely the globus pallidus (Bergstrom and Walters, 1984) and ventral pallidum (Napier and Maslowski-Cobuzzi, 1994)...

D1/D5Modulation of Synaptic NMDA Receptor Currents

“…In other CNS regions, there is both anatomical (Dumartin et al, 2007;Filloux et al, 1987;Hara and Pickel, 2005) and electrophysiological (Ding et al, 2003;Gao et al, 2001;Hernandez et al, 2007;Momiyama and Sim, 1996;Nicola et al, 1996;Paspalas and Goldman-Rakic, 2005) evidence for D1 mediated presynaptic regulation of neurotransmission. However, examination of paired pulse ratios for either SC (n=4) or TA (n=4) inputs over intervals of 50-300msec, showed no observable effect of SKF-81297, indicative of an absence of D1/5 mediated pre-synaptic modulation of glutamate release onto CA1 pyramidal cells.…”

Toward a Neuro-Cognitive Animal Model of the Cognitive Symptoms of Schizophrenia: Disruption of Cortical Cholinergic Neurotransmission Following Repeated Amphetamine Exposure in Attentional Task-Performing, but Not Non-Performing, Rats

“…In non-performing but extensively habituated animals, repeated AMPH-induced increases in ACh release could reflect a purely pharmacological effect, due primarily to the release of norepinephrine (Rothman et al, 2001;Vanderschuren et al, 2003) and dopamine (Robinson et al, 1988), both of which are capable of stimulating cholinergic neurons in the basal forebrain (Arnold et al, 2001;Berntson et al, 2003a, b;Knox et al, 2004;Momiyama and Sim, 1996;Napier et al, 1991).…”

Presynaptic inhibition by dopamine of a discrete component of GABA release in rat substantia nigra pars reticulata

“…Indeed, apart from the Dµ-like receptors, which are exclusively located on dopaminergic neurones, the only dopamine receptors in the SNr are of the D1 type, and these are generally considered to be located exclusively on the terminals of striato-nigral fibres (Quik et al 1979;Yung et al 1995). This is not a unique mechanism, as there is electrophysiological evidence for presynaptic inhibition by D1-like receptors of GABA release in basal forebrain (Momiyama & Sim, 1996), entorhinal cortex (Pralong & Jones, 1993) and nucleus accumbens (Nicola & Malenka, 1997).…”