Early sensory and hormonal experience modulate age-related changes in NR2B mRNA within a forebrain region controlling avian vocal learning

Abstract

Male zebra finches are most apt to mimic songs heard between posthatch days (PHD) 35 and 65, and this vocal learning depends, in part, on the activation of N-methyl-D-aspartate receptors (NMDAR) within a discrete forebrain circuit that includes the lateral magnocellular nucleus of the anterior neostriatum (lMAN) and area X. Using in situ hybridization, we show that transcripts for both the constitutive NMDAR subunit NR1 and the modulatory subunit NR2B decrease abruptly in the lMAN between PHD20 and 40. This downregulation corresponds to the onset of song learning and a transition from slow to faster NMDAR currents in lMAN neurons. In area X, NR1 mRNA increases as NR2B mRNA decreases during song development. To understand how these changes in NMDAR mRNA might regulate song learning, we next investigated how manipulations that influence song development affect NMDAR mRNA expression. Early isolation from conspecific song (which delays closure of the sensitive period for song learning) selectively increases NR2B, but not NR1 mRNA, within lMAN at PHD60. In contrast, exposure to testosterone beginning at PHD20 (which impairs song development and hastens the developmental transition to faster NMDAR current kinetics within lMAN) accelerates the decline in NR2B mRNA in lMAN, again without affecting NR1 transcript levels. Neither manipulation significantly effects NR1 or NR2B mRNA levels in area X. Our data suggest that developmental changes in the expression of specific NMDAR subunits may regulate periods of neural and behavioral plasticity and that flexibility in the timing of these sensitive periods may be achieved through experience and/or hormone-dependent modulation of NMDAR gene expression.

Developmental patterns of NMDAR expression within the song system do not recur during adult vocal plasticity in zebra finches

“…Manipulations that alter the course of song learning did not significantly affect the developmental regulation of NR2A or NR2B mRNA expression in either RA or HVC at the ages evaluated (Table 1). These data are in sharp contrast to previous investigations within the AFP, where both early isolation and T treatment modified NMDAR physiology and transcript expression of NMDAR modulatory subunits (White et al, 1999;Livingston et al, 2000;Singh et al, 2000;Heinrich et al, 2002). T treatment beginning at 20 d, which disrupts song learning in zebra finches (Korsia and Bottjer, 1991) and can accelerate song crystallization in at least some species (Whaling et al, 1995), did not significantly alter NR2A or NR2B subunit expression in RA or HVC at 35 d. Also, while early isolation extends the ability to learn song beyond 60 d (Eales, 1985;, this manipulation did not alter the levels of NR2A or NR2B mRNA in RA or HVC at 60 d. NR1 mRNA expression in RA also was not affected by T treatment or isolation.…”

“…We show here that vocal learning in zebra finches is accompanied by marked changes in NMDAR gene expression within the vocal motor pathway. Specifically, within both HVC and RA, NR2A mRNA increases and NR2B mRNA decreases during song acquisition and sensorimotor learning, changes similar to those that occur within the developing AFP (Basham et al, 1999;Singh et al, 2000;Heinrich et al, 2002). NR1 mRNA expression does not change significantly within the HVC, and exhibits only a transient elevation within RA, patterns that support earlier observations that MK801 binding in these regions is similar in 30 d as compared to adult zebra finches (Aamodt et al, 1992).…”

“…Indeed, in RA, a steep decrease in NMDAR EPSC decay times (Stark and Perkel, 1999;Livingston et al, 2000) occurs in tandem with the steep increase in NR2A gene expression between 20 and 40 d posthatch, while the decrease in NR2B expression is more protracted. A similar relationship between maturation of NMDAR gene expression and physiology is evident in the lMAN (White et al, 1999;Livingston et al, 2000;Singh et al, 2000;Heinrich et al, 2002). Although NMDAR-mediated currents in HVC have not been studied, the changes in NR2A:NR2B gene expression reported here predict that currents also would shorten in this region during the course of song learning.…”

Developmental patterns of NMDAR expression within the song system do not recur during adult vocal plasticity in zebra finches

“…Manipulations that alter the course of song learning did not significantly affect the developmental regulation of NR2A or NR2B mRNA expression in either RA or HVC at the ages evaluated (Table 1). These data are in sharp contrast to previous investigations within the AFP, where both early isolation and T treatment modified NMDAR physiology and transcript expression of NMDAR modulatory subunits (White et al, 1999;Livingston et al, 2000;Singh et al, 2000;Heinrich et al, 2002). T treatment beginning at 20 d, which disrupts song learning in zebra finches (Korsia and Bottjer, 1991) and can accelerate song crystallization in at least some species (Whaling et al, 1995), did not significantly alter NR2A or NR2B subunit expression in RA or HVC at 35 d. Also, while early isolation extends the ability to learn song beyond 60 d (Eales, 1985;, this manipulation did not alter the levels of NR2A or NR2B mRNA in RA or HVC at 60 d. NR1 mRNA expression in RA also was not affected by T treatment or isolation.…”

“…We show here that vocal learning in zebra finches is accompanied by marked changes in NMDAR gene expression within the vocal motor pathway. Specifically, within both HVC and RA, NR2A mRNA increases and NR2B mRNA decreases during song acquisition and sensorimotor learning, changes similar to those that occur within the developing AFP (Basham et al, 1999;Singh et al, 2000;Heinrich et al, 2002). NR1 mRNA expression does not change significantly within the HVC, and exhibits only a transient elevation within RA, patterns that support earlier observations that MK801 binding in these regions is similar in 30 d as compared to adult zebra finches (Aamodt et al, 1992).…”

“…Indeed, in RA, a steep decrease in NMDAR EPSC decay times (Stark and Perkel, 1999;Livingston et al, 2000) occurs in tandem with the steep increase in NR2A gene expression between 20 and 40 d posthatch, while the decrease in NR2B expression is more protracted. A similar relationship between maturation of NMDAR gene expression and physiology is evident in the lMAN (White et al, 1999;Livingston et al, 2000;Singh et al, 2000;Heinrich et al, 2002). Although NMDAR-mediated currents in HVC have not been studied, the changes in NR2A:NR2B gene expression reported here predict that currents also would shorten in this region during the course of song learning.…”

Overexpression of human NR2B receptor subunit in LMAN causes stuttering and song sequence changes in adult zebra finches

“…Also in both juveniles and adults, expression in LMAN was lower than the adjacent nidopallium, but the developmental decrease in LMAN was larger (Fig. 2m,o), consistent with what is seen anatomically at the mRNA level using in situ hybridizations 34, 35 . Importantly, injections of the eGFPhNR2B lentivirus in LMAN in adults brought back NR2B protein levels to the same as those seen in juveniles (Fig.…”

Early auditory experience‐induced composition/ratio changes of N‐methyl‐D‐aspartate receptor subunit expression and effects of D‐2‐amino‐5‐phosphonovaleric acid chronic blockade in rat auditory cortex

“…5D). Consistently with previous work, it has been proposed that NR2B have a greater involvement in auditory developmental plasticity compared with NR2A (Riva et al,1997; Tang et al,1999; Singh et al,2000; Chen and Bear,2007).…”

Developmental patterns of NMDAR expression within the song system do not recur during adult vocal plasticity in zebra finches

“…Manipulations that alter the course of song learning did not significantly affect the developmental regulation of NR2A or NR2B mRNA expression in either RA or HVC at the ages evaluated (Table 1). These data are in sharp contrast to previous investigations within the AFP, where both early isolation and T treatment modified NMDAR physiology and transcript expression of NMDAR modulatory subunits (White et al, 1999;Livingston et al, 2000;Singh et al, 2000;Heinrich et al, 2002). T treatment beginning at 20 d, which disrupts song learning in zebra finches (Korsia and Bottjer, 1991) and can accelerate song crystallization in at least some species (Whaling et al, 1995), did not significantly alter NR2A or NR2B subunit expression in RA or HVC at 35 d. Also, while early isolation extends the ability to learn song beyond 60 d (Eales, 1985;, this manipulation did not alter the levels of NR2A or NR2B mRNA in RA or HVC at 60 d. NR1 mRNA expression in RA also was not affected by T treatment or isolation.…”

“…We show here that vocal learning in zebra finches is accompanied by marked changes in NMDAR gene expression within the vocal motor pathway. Specifically, within both HVC and RA, NR2A mRNA increases and NR2B mRNA decreases during song acquisition and sensorimotor learning, changes similar to those that occur within the developing AFP (Basham et al, 1999;Singh et al, 2000;Heinrich et al, 2002). NR1 mRNA expression does not change significantly within the HVC, and exhibits only a transient elevation within RA, patterns that support earlier observations that MK801 binding in these regions is similar in 30 d as compared to adult zebra finches (Aamodt et al, 1992).…”

“…Indeed, in RA, a steep decrease in NMDAR EPSC decay times (Stark and Perkel, 1999;Livingston et al, 2000) occurs in tandem with the steep increase in NR2A gene expression between 20 and 40 d posthatch, while the decrease in NR2B expression is more protracted. A similar relationship between maturation of NMDAR gene expression and physiology is evident in the lMAN (White et al, 1999;Livingston et al, 2000;Singh et al, 2000;Heinrich et al, 2002). Although NMDAR-mediated currents in HVC have not been studied, the changes in NR2A:NR2B gene expression reported here predict that currents also would shorten in this region during the course of song learning.…”

Overexpression of human NR2B receptor subunit in LMAN causes stuttering and song sequence changes in adult zebra finches

“…Also in both juveniles and adults, expression in LMAN was lower than the adjacent nidopallium, but the developmental decrease in LMAN was larger (Fig. 2m,o), consistent with what is seen anatomically at the mRNA level using in situ hybridizations 34, 35 . Importantly, injections of the eGFPhNR2B lentivirus in LMAN in adults brought back NR2B protein levels to the same as those seen in juveniles (Fig.…”

Early auditory experience‐induced composition/ratio changes of N‐methyl‐D‐aspartate receptor subunit expression and effects of D‐2‐amino‐5‐phosphonovaleric acid chronic blockade in rat auditory cortex

“…5D). Consistently with previous work, it has been proposed that NR2B have a greater involvement in auditory developmental plasticity compared with NR2A (Riva et al,1997; Tang et al,1999; Singh et al,2000; Chen and Bear,2007).…”

Developmental patterns of NMDAR expression within the song system do not recur during adult vocal plasticity in zebra finches

“…Manipulations that alter the course of song learning did not significantly affect the developmental regulation of NR2A or NR2B mRNA expression in either RA or HVC at the ages evaluated (Table 1). These data are in sharp contrast to previous investigations within the AFP, where both early isolation and T treatment modified NMDAR physiology and transcript expression of NMDAR modulatory subunits (White et al, 1999;Livingston et al, 2000;Singh et al, 2000;Heinrich et al, 2002). T treatment beginning at 20 d, which disrupts song learning in zebra finches (Korsia and Bottjer, 1991) and can accelerate song crystallization in at least some species (Whaling et al, 1995), did not significantly alter NR2A or NR2B subunit expression in RA or HVC at 35 d. Also, while early isolation extends the ability to learn song beyond 60 d (Eales, 1985;, this manipulation did not alter the levels of NR2A or NR2B mRNA in RA or HVC at 60 d. NR1 mRNA expression in RA also was not affected by T treatment or isolation.…”

“…We show here that vocal learning in zebra finches is accompanied by marked changes in NMDAR gene expression within the vocal motor pathway. Specifically, within both HVC and RA, NR2A mRNA increases and NR2B mRNA decreases during song acquisition and sensorimotor learning, changes similar to those that occur within the developing AFP (Basham et al, 1999;Singh et al, 2000;Heinrich et al, 2002). NR1 mRNA expression does not change significantly within the HVC, and exhibits only a transient elevation within RA, patterns that support earlier observations that MK801 binding in these regions is similar in 30 d as compared to adult zebra finches (Aamodt et al, 1992).…”

“…Indeed, in RA, a steep decrease in NMDAR EPSC decay times (Stark and Perkel, 1999;Livingston et al, 2000) occurs in tandem with the steep increase in NR2A gene expression between 20 and 40 d posthatch, while the decrease in NR2B expression is more protracted. A similar relationship between maturation of NMDAR gene expression and physiology is evident in the lMAN (White et al, 1999;Livingston et al, 2000;Singh et al, 2000;Heinrich et al, 2002). Although NMDAR-mediated currents in HVC have not been studied, the changes in NR2A:NR2B gene expression reported here predict that currents also would shorten in this region during the course of song learning.…”

Overexpression of human NR2B receptor subunit in LMAN causes stuttering and song sequence changes in adult zebra finches

“…Also in both juveniles and adults, expression in LMAN was lower than the adjacent nidopallium, but the developmental decrease in LMAN was larger (Fig. 2m,o), consistent with what is seen anatomically at the mRNA level using in situ hybridizations 34, 35 . Importantly, injections of the eGFPhNR2B lentivirus in LMAN in adults brought back NR2B protein levels to the same as those seen in juveniles (Fig.…”

Early auditory experience‐induced composition/ratio changes of N‐methyl‐D‐aspartate receptor subunit expression and effects of D‐2‐amino‐5‐phosphonovaleric acid chronic blockade in rat auditory cortex

“…5D). Consistently with previous work, it has been proposed that NR2B have a greater involvement in auditory developmental plasticity compared with NR2A (Riva et al,1997; Tang et al,1999; Singh et al,2000; Chen and Bear,2007).…”