Figure 8.

Modeling the effects of respiratory rhythm entrainment by somatic afferent activation. A, Schematic of the model of the pontomedullary respiratory network (modified from Rybak et al., 2004a,b). The circles represent populations of different respiratory neurons. Excitatory and inhibitory synaptic connections are shown by arrows and small filled circles, respectively. For details, see the description in Materials and Methods. Input from somatic afferents provided excitation to the pontine population S, which in turn transmitted this excitation to the medullary population of E2 neurons. B, Entrainment (1:1) of the respiratory rhythm in the model produced by a series of somatic stimuli (bottom trace). C, Model performance. Activity of some neural populations (ramp-I, early-I, pre-I, post-I, and E2) and PND is represented by the average histogram of firing frequency (number of spikes per second per neuron; bin of 30 ms) in the population. Each modeled population consisted of 50 neurons. The bottom trace shows a series of somatic stimuli. Note that each stimulus produces the following: (1) a strong activation of E2 population, (2) consequent premature inhibition of the post-I population, and (3) early onset of inspiratory burst with respect to the applied stimulus (latency). D, A fragment of same simulation, but each neuron trace shows the membrane potential trajectory of a randomly selected single neuron from each population (ramp-I, early-I, pre-I, post-I, and E2). It is seen that each stimulus produces the following: (1) an increase of firing frequency of the E2 neuron, (2) consequent premature inhibition of the post-I neuron, and (3) early onset of inspiratory burst with latency of ∼300 ms. Note also that each stimulus produces a short hyperpolarization of the ramp-I neuron. E, The results of modeling investigation for the latency of evoked PND as a function of phase of stimulus application. The black dots connected with the black curve represent the results obtained from the model simulation. The small gray circles represent the results of experimental studies from Figure 4C, which have been included for comparison. The vertical dash-dot lines separate inspiratory (Insp), postinspiratory (Post-Inspir.), and E2 phases, as defined in our experimental studies (from Fig. 4C). Note that the latency measured in modeling studies decreases with an increase of stimulus phase during the post-I phase and increases slightly during the E2 phase.