Dopaminergic Substantia Nigra Neurons Express Functional NMDA Receptors in Postnatal Rats

Abstract

Activation of N-methyl-D-aspartate (NMDA) receptors in the Substantia Nigra zona compacta (SNc) may determine the degree of physiological apoptosis during the early postnatal period. However, the expression of these receptors during this stage of development is uncertain, as a recent study failed to detect responses to NMDA in unidentified SNc neurons isolated from 2-wk-old rats. Using conventional or perforated-patch whole cell recordings, we examined the presence of NMDA-evoked responses in SNc neurons acutely dissociated from P4 to P16 rats, applying strict criteria for identification of these neurons as nigrostriatal and dopaminergic. The SNc neurons were identified by retrograde labeling after striatal injection of Fluoro-Gold; the presence of I(h) current; and the inhibition of firing by dopamine (50 microM). NMDA (100 microM, V(hold) = -60 mV) evoked inward, APV-sensitive currents (56.4 +/- 8.6 pA) in all tested neurons (n = 29). Strong depolarizing responses were observed under current-clamp. These results indicate that NMDA receptors play a functional role in SNc neurons during the first two postnatal weeks.

Functional heterogeneity of NMDA receptors in rat substantia nigra pars compacta and reticulata neurones

“…SNc neurones were identified on the basis of the presence of a clear, time‐dependent, hyperpolarization‐activated inward current ( I h ) in whole‐cell mode (Fig. 1A) in response to a voltage step from −60 to −120 mV, as described previously (Johnson & North, 1992; Lin & Lipski, 2001; Jones & Gibb, 2005). P28 SNc cells had an average I h relaxation amplitude of 325 ± 25 pA and activation time constant ( τ ) of 742 ± 42 ms (at P7, amplitude = 224 ± 36 pA, and τ = 867 ± 78 ms).…”

Functional NR2B‐ and NR2D‐containing NMDA receptor channels in rat substantia nigra dopaminergic neurones

“…Functional NMDA receptors have previously been described in midbrain dopaminergic neurones (Mereu et al 1991;Wu & Johnson, 1996;Lin & Lipski, 2001) although their subunit composition was not investigated. Here we show NMDA receptor channels of four different conductances are consistently observed in SNc dopaminergic neurones, although the proportion of 30 pS openings varied between patches suggesting the receptor population is not homogeneous.…”

“…Patch pipettes were made from thick-walled borosilicate glass (GC150F, Harvard Apparatus, Kent, UK), fire polished to a final resistance of 10-15 M and filled with solution containing (mm): CsCl 140; Hepes 10; EGTA 10; pH 7.2. Recordings were made from visually identified neurones in the SNc of the midbrain that had a clear time-dependent, hyperpolarization-activated inward current in whole-cell mode in response to a voltage step from −60 to −120 mV, typical of dopaminergic neurones Lin & Lipski, 2001). Outside-out patches were made from dopaminergic neurones and voltage-clamped at −80 to −40 mV (routinely −60 mV).…”

“…Although SNc dopaminergic neurones express functional NMDA receptors (Mereu et al 1991;Wu & Johnson, 1996;Lin & Lipski, 2001), their subunit composition is not known. NR2D subunit mRNA (Monyer et al 1994) and protein (Dunah et al 1996) is expressed in the developing and adult rat brain, particularly in brainstem and diencephalon, and NR2D protein is present in SNc (Dunah et al 1996).…”

Glutamatergic synaptic currents of nigral dopaminergic neurons follow a postnatal developmental sequence

“…In juvenile rats, both AMPA (α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid) and NMDA receptors are critical for transient burst-like, high-frequency firing ( Blythe et al, 2007 ). Juvenile (P7–P28) rodent SNc neurons express AMPA-evoked currents mediated by GluA2-containing AMPA receptors, kainate (KA)-evoked currents mediated by GluK3 and GluK5-containing KA receptors and NMDA-evoked currents mediated by GluN2B- and GluN2D-containing (but not GluN2A-containing) NMDA receptors ( Mereu et al, 1991 ; Bischoff et al, 1997 ; Gotz et al, 1997 ; Wullner et al, 1997 ; Counihan et al, 1998 ; Chatha et al, 2000 ; Lin and Lipski, 2001 ; Vivo et al, 2002 ; Jones and Gibb, 2005 ; Brothwell et al, 2008 ; Suarez et al, 2010 ). AMPA and NMDA receptors are selectively localized to a subpopulation of asymmetric synapses in the adult SNc and the two receptor types, at least partially, co-localize at individual synapses ( Chatha et al, 2000 ).…”