Mice were anesthetized using a mixture of ketamine (100 mg/kg IP) and acepromazine (5 mg/kg IP). A rostrocaudal incision was made in the scalp, and a small neodymium magnet (4.57 mm × 4.57 mm × 2.03 mm, 375 mg) was attached to the center of the dorsal surface of the cranium using cyanoacrylate or dental resin; the magnet was mounted with the axis of the N-S poles parallel to the dorsoventral plane of the head. The mice were allowed to recover for 1–2 weeks prior to testing. After magnet implantation, mice were tested multiple times over 4–6 weeks, with a minimum of 1–2 weeks between tests; importantly, it was previously reported that administration of a 5-HT2A agonist at weekly intervals does not alter HTR sensitivity (Gewirtz and Marek, 2000 (link)). To record head movements, the mice were placed in a 12.5 cm diameter glass beaker surrounded by ~150 turns of #30 enameled magnet wire. The output of the coil was recorded using a Powerlab/8SP with LabChart v.7.3.2 (ADInstruments, Colorado Springs, CO, USA). Coil voltage was amplified, low-pass filtered (10 kHz cut-off frequency) to remove radiofrequency interference, and sampled at 40 kHz. Data were imported into the Matlab programming environment (MathWorks, Natick, MA, USA) for Fourier analysis. Voltage and frequency peaks were detected using the LabChart cyclic measurements analysis module. For HTR analysis, the LabChart data were digitally band-pass filtered (40–200 Hz), and responses were identified by manually searching for sinusoidal wavelets with the following characteristics: (1) waveform and spectrum consistent with 40–160 Hz activity; (2) contain more than 2 bipolar peaks; (3) amplitude exceeds the background noise level; and (3) duration <120 ms.
In most experiments, the magnetometer-based assessment of head twitch was combined with simultaneous video recordings. The behavior of the mice within the magnetometer coil was captured at 30-Hz using a CCD video camera located above the glass beaker, digitized, and stored on a PC as an AVI file. Subsequently, head twitches were counted by an observer blind to the treatment and the magnetometer data (Halberstadt et al., 2011 (link)). Potential responses were analyzed frame-by-frame using VirtualDub v.1.9.11 and were counted as head twitches if there was evidence of torsional head movement over consecutive frames. For the experiment with SKF38393, the duration of each grooming bout (including licking the paws, legs, fur, body, tail, or genitals, and washing the head, face, and ears) was assessed by an observer blind to the treatment.
In most experiments, the magnetometer-based assessment of head twitch was combined with simultaneous video recordings. The behavior of the mice within the magnetometer coil was captured at 30-Hz using a CCD video camera located above the glass beaker, digitized, and stored on a PC as an AVI file. Subsequently, head twitches were counted by an observer blind to the treatment and the magnetometer data (Halberstadt et al., 2011 (link)). Potential responses were analyzed frame-by-frame using VirtualDub v.1.9.11 and were counted as head twitches if there was evidence of torsional head movement over consecutive frames. For the experiment with SKF38393, the duration of each grooming bout (including licking the paws, legs, fur, body, tail, or genitals, and washing the head, face, and ears) was assessed by an observer blind to the treatment.
