Increased bursting glutamatergic neurotransmission in an auditory forebrain area of the zebra finch (Taenopygia guttata) induced by auditory stimulation

Abstract

The caudomedial nidopallium (NCM) is a telencephalic area involved in auditory processing and memorization in songbirds, but the synaptic mechanisms associated with auditory processing in NCM are largely unknown. To identify potential changes in synaptic transmission induced by auditory stimulation in NCM, we used a slice preparation for path-clamp recordings of synaptic currents in the NCM of adult zebra finches (Taenopygia guttata) sacrificed after sound isolation followed by exposure to conspecific song or silence. Although post-synaptic GABAergic and glutamatergic currents in the NCM of control and song-exposed birds did not present any differences regarding their frequency, amplitude and duration after song exposure, we observed a higher probability of generation of bursting glutamatergic currents after blockade of GABAergic transmission in song-exposed birds as compared to controls. Both song-exposed males and females presented an increase in the probability of the expression of bursting glutamatergic currents, however bursting was more commonly seen in males where they appeared even without blocking GABAergic transmission. Our data show that song exposure changes the excitability of the glutamatergic neuronal network, increasing the probability of the generation of bursts of glutamatergic currents, but does not affect basic parameters of glutamatergic and GABAergic synaptic currents.

Fig. 1

Protocol used for song exposure and song-induced ZENK protein expression in NCM. a Top sonograms of the adult male zebra finch songs used in the song-exposure protocol. Bottom scheme of the song-exposure protocol. The numbers in the boxes correspond to the song presented (top), see “Methods” for details. b Song-induced ZENK expression in NCM slices prepared as for electrophysiology from a song-exposed (left) and a control (right) adult male zebra finch

Fig. 2

Spontaneous GABAergic post-synaptic currents in the NCM are not affected by song exposure. a Representative sIPSCs recorded at −70 mV using a high-chloride internal solution in the presence of DNQX. b i sIPSC frequency in the NCM of control and song-exposed birds (control: 3.2 ± 0.4 Hz, n = 23; song-exposed: 3.4 ± 0.4 Hz, n = 20), b ii sIPSC frequency in the NCM of control and song-exposed birds segregated by gender (control females: 3.4 ± 0.5 Hz, n = 11; song-exposed females: 2.8 ± 0.7 Hz, n = 8; control males: 3.1 ± 0.6 Hz, n = 12; song-exposed males: 3.9 ± 0.6 Hz, n = 12). c i sIPSC amplitude in the NCM of control and song-exposed birds (control: 41.1 ± 3.6 pA, n = 23; song-exposed: 37.5 ± 2.6 pA, n = 20). c ii sIPSC amplitude in the NCM of control and song-exposed birds segregated by gender (control females: 40.6 ± 5 pA, n = 11; song-exposed females: 37.9 ± 4 pA, n = 8; control males: 41.7 ± 5 pA, n = 12; song-exposed males: 37.2 ± 3 pA, n = 12). d Representative sIPSCs recorded at −20 mV using a low-chloride internal solution. Outward currents are indicated by asterisks and inward currents by arrowheads. e sIPSC frequency measured at −20 mV with a low-chloride internal solution (control: 2.3 ± 0.5 Hz, n = 9, 6 males and 3 females; song-exposed: 2.0 ± 0.4 Hz, n = 12, 6 males and 6 females). f sIPSC amplitude measured at −20 mV in a low-Cl internal solution (control: 25.3 ± 3 pA, n = 9, 6 males and 3 females; song-exposed: 20.9 ± 3 pA, n = 12, 6 males and 6 females). Values above correspond to the mean ± SEM; on the graphs, each symbol corresponds to a value of a single neuron and the horizontal line represents the mean

Fig. 3

Miniature GABAergic synaptic currents in the NCM are not affected by song exposure. a Representative recording of mIPSCs in the presence of TTX. b i mIPSC frequency in the NCM of control and song-exposed birds (control: 0.34 ± 0.07 Hz, n = 10; song-exposed: 0.37 ± 0.08 Hz, n = 9). b ii sIPSC frequency in the NCM of control and song-exposed birds segregated by gender (control females: 0.33 ± 0.2 Hz, n = 4; song-exposed females: 0.24 ± 0.06 Hz, n = 5; control males: 0.3 ± 0.2 Hz, n = 6; song-exposed males: 0.5 ± 0.1 Hz, n = 4). c i mIPSC amplitude in the NCM of control and song-exposed birds (control: 26.2 ± 2.1 pA, n = 10; song-exposed: 25.7 ± 2.7 pA, n = 9). c ii sIPSC amplitude in the NCM of control and song-exposed birds segregated by gender (control females: 27 ± 4 pA, n = 4; song-exposed females: 21.2 ± 2 pA, n = 5; control males: 25.7 ± 2 pA, n = 6; song-exposed males: 31.3 ± 4 pA, n = 4). d i mIPSC half width in the NCM of control and song-exposed birds (control: 4.7 ± 0.8 ms, n = 10; song-exposed: 3.6 ± 0.6 ms, n = 9). d ii mIPSC half width in the NCM of control and song-exposed birds segregated by gender (control females: 4.6 ± 1 ms, n = 4; song-exposed females: 2.5 ± 0.6 ms, n = 5; control males: 4.8 ± 1 ms, n = 6; song-exposed males: 4.8 ± 0.6 pA, n = 4). Values above correspond to the mean ± SEM; on the graphs, each symbol corresponds to a value of a single neuron and the horizontal line represents the mean

Fig. 4

Spontaneous glutamatergic synaptic currents in the NCM are not affected by song exposure. a Representative sEPSCs recorded at −70 mV using a high-chloride internal solution in the presence of bicuculline. b i sEPSC frequency in the NCM of control and song-exposed birds (control: 0.46 ± 0.12 Hz, n = 11; song-exposed: 0.48 ± 0.15 Hz, n = 10). b ii sEPSC frequency in the NCM of control and song-exposed birds segregated by gender (control females: 0.5 ± 0.2 Hz, n = 7; song-exposed females: 0.6 ± 0.2 Hz, n = 6; control males: 0.4 ± 0.2 Hz, n = 4; song-exposed males: 0.3 ± 0.1 Hz, n = 4). c i sEPSC amplitude in the NCM of control and song-exposed birds (control: 21.4 ± 2.1 pA, n = 11; song-exposed: 19.4 ± 1.5 pA, n = 10). c ii sEPSC amplitude in the NCM of control and song-exposed birds segregated by gender (control females: 18.4 ± 1.8 pA, n = 7; song-exposed females: 18.01 ± 1.7 pA, n = 6; control males: 26.7 ± 3.9 pA, n = 4; song-exposed males: 21.5 ± 3 pA, n = 4; *p < 0.05). d i sEPSC half width in the NCM of control and song-exposed birds (control: 3.7 ± 0.5 ms, n = 9; song-exposed: 2.9 ± 0.4 ms, n = 9). d ii sEPSC half width in the NCM of control and song-exposed birds segregated by gender (control females: 3.7 ± 0.5 ms, n = 5; song-exposed females: 3.3 ± 0.7 ms, n = 5; control males: 3.8 ± 1 ms, n = 4; song-exposed males: 2.4 ± 0.5 ms, n = 4). e Representative recording of sEPSCs recorded at −50 mV using a low-chloride internal solution. f sEPSC frequency measured at −50 mV in a low-chloride internal solution (control: 0.5 ± 0.1 Hz, n = 7; song-exposed: 0.6 ± 0.1 Hz, n = 5). g sEPSC amplitude measured at −50 mV in a low-chloride internal solution (control: 23.1 ± 3 pA, n = 7; song-exposed: 24.08 ± 5 pA, n = 5;). Data in e–g were from male birds. Values above correspond to the mean ± SEM; on the graphs, each symbol corresponds to a value of a single neuron and the horizontal line represents the mean

Fig. 5

Bursting EPSCs are increased by song exposure. a Generation of bursting behavior of glutamatergic neurotransmission after bicuculline application to NCM slices. Left trace no drug, right trace after bicuculline application. b Percentage of neurons that presented bursting neurotransmission after bicuculline (Ccontrol, S song-exposed, *p < 0.05); values in parentheses indicate absolute numbers of recorded cells with bursting behavior and total number of recorded cells per group. c Example of an individual spontaneous bursting EPSC observed in an NCM neuron from a song-exposed male without blocking GABAergic transmission. The currents were measured at −20 mV using a low-chloride internal solution. Under these conditions, glutamatergic currents are downward and GABAergic currents upward