Figure 6.

Microinjection of low nanomolar concentrations of nicotine (Nic) into the preBötC increased the frequency of respiratory-related XIIn rhythmic activity, and into hypoglossal nucleus (XII nu) induced tonic/seizure-like activity in L9′A mice. DHβE greatly reduced these effects. A, Microinjection locations, the responses to Nic injections recorded from XIIn in the absence (middle) and presence (right) of bath-applied DHβE (0.1–0.5 μm). Trace 1, Injection of 50 nm Nic (10–15 nl) into contralateral preBötC corresponding to the injection pipette #1. Trace 2, Injection of Nic (15–20 nl) into contralateral XII nu corresponding to the injection pipette #2. Trace 3, Injection of Nic (15–20 nl) into ipsilateral XII nu corresponding to the injection pipette #3. ∫XIIn, Integrated XIIn activity. Inset, Raw (nonintegrated) XII activity on an expanded time scale from the indicated section of trace 3 showing seizure-like activity. Injection pipettes were inserted into the target areas 100–200 μm below the surface of the slice. Arrow indicates the time of Nic injection. B, Summary data (mean ± SE) of frequency (Freq) and amplitude (Amp) of integrated XIIn rhythmic activity in response to Nic injection into the preBötC in the absence and presence of bath applied DHβE. Amplitude was determined with averaged envelopes of five to six consecutive inspiratory bursts for each condition. C, Summary data of the effects of Nic injection into ipsilateral XII nu in the absence and presence of bath-applied DHβE on frequency and amplitude of integrated XIIn rhythmic activity (C1), Nic-induced tonic/seizure-like activity amplitude (Seizure Amp; C2), and duration (Seizure Dur; C3) measured at 20% of peak amplitude of integrated XIIn activity. *Statistically significant difference between Nic injection versus pre-Nic conditions (paired t test). ^▵Statistically significant difference of Nic effects between the absence and presence of bath applied DHβE.