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Rhythm generation by the pre-Bötzinger complex in medullary slice and island preparations: effects of adenosine A(1) receptor activation.

Vandam RJ, Shields EJ, Kelty JD - BMC Neurosci (2008)

Bottom Line: The A(1)R agonist N6-Cyclopentyladenosine (NCPA) reduced population burst frequency in slices by ca. 33% and in islands by ca. 30%.Converting slices to island preparations decreased synaptic input to inspiratory neurons.NCPA further decreased the frequency of synaptic inputs to neurons in island preparations and lowered the input resistance of inspiratory neurons, even when chemical communication between neurons and other cells was impeded.

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Affiliation: Department of Biology, Central Michigan University, Mount Pleasant, MI 48858, USA.

ABSTRACT

Background: The pre-Bötzinger complex (preBötC) is a central pattern generator within the ventrolateral medulla oblongata's ventral respiratory group that is important for the generation of respiratory rhythm. Activation of adenosine A(1) receptors (A(1)R) depresses preBötC rhythmogenesis. Although it remains unclear whether A(1)R activation is important for organisms in a normal metabolic state, A(1)R activation is important to the response of the preBötC to metabolic stress, such as hypoxia. This study examined mechanisms linking A(1)R activation to depression of preBötC rhythmogenesis in medullary slice and island preparations from neonatal mice.

Results: Converting medullary slices to islands by cutting away much of the medullary tissue adjacent to the preBötC decreased the amplitude of action potential bursts generated by a population of neurons within the preBötC (recorded with an extracellular electrode, and integrated using a hardware integrator), without noticeably affecting burst frequency. The A(1)R agonist N6-Cyclopentyladenosine (NCPA) reduced population burst frequency in slices by ca. 33% and in islands by ca. 30%. As in normal (drug-free) artificial cerebrospinal fluid (aCSF), NCPA decreased burst frequency in slices when GABA(A)ergic or GABA(A)ergic and glycinergic transmission were blocked, and in islands when GABA(A)ergic transmission was antagonized. Converting slices to island preparations decreased synaptic input to inspiratory neurons. NCPA further decreased the frequency of synaptic inputs to neurons in island preparations and lowered the input resistance of inspiratory neurons, even when chemical communication between neurons and other cells was impeded.

Conclusion: Together these data support the suggestion that depression of preBötC activity by A(1)R activation involves both decreased neuronal excitability and diminished inter-neuronal communication.

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Manipulation of A1R affects synaptic input to preBötC neurons. A. Representative current traces from slice (left) and island preparations (right). Vertical scale: 50 pA. B. Converting slices to island preparations reduced the frequency of total sPSCs and sEPSCs evoked in preBötC neurons (*P < 0.05, Two-sample t-test). This trend appeared to hold true for sIPSCs but did not attain statistical significance. C. NCPA (1 μM) decreased the frequency of sEPSCs and sIPSCs received by preBötC neurons within slice (i, ii) and island preparations (iii, iv) in the presence of strychnine (1 μM). The insets in (ii) and (iv) are magnified views of sIPSC frequencies in the presence of strychnine. Letters above columns show difference from mean frequency under baseline (a, P < 0.05) conditions and in the presence of strychnine (b, P < 0.05).
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Figure 6: Manipulation of A1R affects synaptic input to preBötC neurons. A. Representative current traces from slice (left) and island preparations (right). Vertical scale: 50 pA. B. Converting slices to island preparations reduced the frequency of total sPSCs and sEPSCs evoked in preBötC neurons (*P < 0.05, Two-sample t-test). This trend appeared to hold true for sIPSCs but did not attain statistical significance. C. NCPA (1 μM) decreased the frequency of sEPSCs and sIPSCs received by preBötC neurons within slice (i, ii) and island preparations (iii, iv) in the presence of strychnine (1 μM). The insets in (ii) and (iv) are magnified views of sIPSC frequencies in the presence of strychnine. Letters above columns show difference from mean frequency under baseline (a, P < 0.05) conditions and in the presence of strychnine (b, P < 0.05).

Mentions: During baseline recording, inspiration-related neurons (those receiving increased excitatory input during the population burst) within slice preparations received sEPSCs at 15.6 ± 3.6 Hz, and sIPSCs at 17.5 ± 5.3 Hz (Fig. 6B. Strychnine eliminated almost all sIPSCs, reducing their frequency to 0.6 ± 0.1 Hz (n = 8; P = 0.001), without noticeably affecting sEPSC frequency (Fig. 6A, C). NCPA further decreased the frequency of sIPSCs to 0.3 ± 0.1 Hz (n = 8; P = 0.001). In each of the 8 neurons treated sequentially with strychnine and then NCPA, subsequent treatment with bicuculline eliminated all remaining sIPSCs. As with sIPSCs, NCPA decreased the frequency of sEPSCs received by inspiratory neurons, in this case from 15.6 ± 3.6 to 4.0 ± 1.4 Hz (n = 8, P = 0.004; Fig. 6C).


Rhythm generation by the pre-Bötzinger complex in medullary slice and island preparations: effects of adenosine A(1) receptor activation.

Vandam RJ, Shields EJ, Kelty JD - BMC Neurosci (2008)

Manipulation of A1R affects synaptic input to preBötC neurons. A. Representative current traces from slice (left) and island preparations (right). Vertical scale: 50 pA. B. Converting slices to island preparations reduced the frequency of total sPSCs and sEPSCs evoked in preBötC neurons (*P < 0.05, Two-sample t-test). This trend appeared to hold true for sIPSCs but did not attain statistical significance. C. NCPA (1 μM) decreased the frequency of sEPSCs and sIPSCs received by preBötC neurons within slice (i, ii) and island preparations (iii, iv) in the presence of strychnine (1 μM). The insets in (ii) and (iv) are magnified views of sIPSC frequencies in the presence of strychnine. Letters above columns show difference from mean frequency under baseline (a, P < 0.05) conditions and in the presence of strychnine (b, P < 0.05).
© Copyright Policy - open-access
Related In: Results  -  Collection

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Show All Figures
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Figure 6: Manipulation of A1R affects synaptic input to preBötC neurons. A. Representative current traces from slice (left) and island preparations (right). Vertical scale: 50 pA. B. Converting slices to island preparations reduced the frequency of total sPSCs and sEPSCs evoked in preBötC neurons (*P < 0.05, Two-sample t-test). This trend appeared to hold true for sIPSCs but did not attain statistical significance. C. NCPA (1 μM) decreased the frequency of sEPSCs and sIPSCs received by preBötC neurons within slice (i, ii) and island preparations (iii, iv) in the presence of strychnine (1 μM). The insets in (ii) and (iv) are magnified views of sIPSC frequencies in the presence of strychnine. Letters above columns show difference from mean frequency under baseline (a, P < 0.05) conditions and in the presence of strychnine (b, P < 0.05).
Mentions: During baseline recording, inspiration-related neurons (those receiving increased excitatory input during the population burst) within slice preparations received sEPSCs at 15.6 ± 3.6 Hz, and sIPSCs at 17.5 ± 5.3 Hz (Fig. 6B. Strychnine eliminated almost all sIPSCs, reducing their frequency to 0.6 ± 0.1 Hz (n = 8; P = 0.001), without noticeably affecting sEPSC frequency (Fig. 6A, C). NCPA further decreased the frequency of sIPSCs to 0.3 ± 0.1 Hz (n = 8; P = 0.001). In each of the 8 neurons treated sequentially with strychnine and then NCPA, subsequent treatment with bicuculline eliminated all remaining sIPSCs. As with sIPSCs, NCPA decreased the frequency of sEPSCs received by inspiratory neurons, in this case from 15.6 ± 3.6 to 4.0 ± 1.4 Hz (n = 8, P = 0.004; Fig. 6C).

Bottom Line: The A(1)R agonist N6-Cyclopentyladenosine (NCPA) reduced population burst frequency in slices by ca. 33% and in islands by ca. 30%.Converting slices to island preparations decreased synaptic input to inspiratory neurons.NCPA further decreased the frequency of synaptic inputs to neurons in island preparations and lowered the input resistance of inspiratory neurons, even when chemical communication between neurons and other cells was impeded.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Biology, Central Michigan University, Mount Pleasant, MI 48858, USA.

ABSTRACT

Background: The pre-Bötzinger complex (preBötC) is a central pattern generator within the ventrolateral medulla oblongata's ventral respiratory group that is important for the generation of respiratory rhythm. Activation of adenosine A(1) receptors (A(1)R) depresses preBötC rhythmogenesis. Although it remains unclear whether A(1)R activation is important for organisms in a normal metabolic state, A(1)R activation is important to the response of the preBötC to metabolic stress, such as hypoxia. This study examined mechanisms linking A(1)R activation to depression of preBötC rhythmogenesis in medullary slice and island preparations from neonatal mice.

Results: Converting medullary slices to islands by cutting away much of the medullary tissue adjacent to the preBötC decreased the amplitude of action potential bursts generated by a population of neurons within the preBötC (recorded with an extracellular electrode, and integrated using a hardware integrator), without noticeably affecting burst frequency. The A(1)R agonist N6-Cyclopentyladenosine (NCPA) reduced population burst frequency in slices by ca. 33% and in islands by ca. 30%. As in normal (drug-free) artificial cerebrospinal fluid (aCSF), NCPA decreased burst frequency in slices when GABA(A)ergic or GABA(A)ergic and glycinergic transmission were blocked, and in islands when GABA(A)ergic transmission was antagonized. Converting slices to island preparations decreased synaptic input to inspiratory neurons. NCPA further decreased the frequency of synaptic inputs to neurons in island preparations and lowered the input resistance of inspiratory neurons, even when chemical communication between neurons and other cells was impeded.

Conclusion: Together these data support the suggestion that depression of preBötC activity by A(1)R activation involves both decreased neuronal excitability and diminished inter-neuronal communication.

Show MeSH
Related in: MedlinePlus