1. Contribution of Vanilloid Receptor-Expressing
Methods
Results
Figure 1. Experimental setup for behavioral experiments. Adult rats were presented with various olfactory/trigeminal stimuli, utilizing applicator sticks placed in the vicinity of the cage. Each rat’s response within the first few seconds of encountering the stimuli was scored using a scale ranging from -2 to +2 as described above. Stimuli were presented randomly, with three repetitions per stimulant.
Figure 2. Electrophysiological setup. Stimuli were presented via a computer-controlled air-dilution olfactometer. Data were recorded using an automated acquisition system controlled by the olfactometer. Respiration was monitored via a thermocouple inserted into the rat’s breathing tube.
Neural response, integrated response, and respiration were recorded for a period of at least 40 seconds per 5 second stimulus presentation.
Figure 3. Behavioral Response
Figure 1. Experimental Setup for Behavioral Experiments
Literature List
Introduction
Conclusions
Neonatal capsaicin desensitization produces significantly decreased aversion reactions to amyl acetate, ethanol, cyclohexanone and nicotine in adult rats.
In contrast, capsaicin-desensitized adult rats continue to show strong aversive reactions to acetic acid.
In accord with results from behavioral experiments, capsaicin desensitized adults display no significant trigeminal nerve responses to amyl acetate, ethanol, cyclohexanone or nicotine, while displaying robust nerve responses to tactile stimulation of the nose, and chemical stimulation by acetic acid and carbon dioxide (we have previously shown that nasal trigeminal chemosensitivity to carbon dioxide is mediated via a transient intraepithelial acidification mechanism).
Since neonatal capsaicin treatment results in a reduction or elimination of VR1-expressive trigeminal fibers, the present results suggest that a significant degree of trigeminal nerve acid sensitivity, as demonstrated with carbon dioxide and acetic acid, is mediated via non-VR1-expressive fibers.
In addition, these results suggest that nasal trigeminal sensitivity to amyl acetate, ethanol, cyclohexanone and nicotine is mediated by VR1-expressive fibers.
Contribution of Vanilloid Receptor-Expressing
Fibers to Overall Trigeminal Nerve Chemosensitivity
Hessamedin Alimohammadi and Wayne L. Silver
Department of Biology, Wake Forest University, Winston-Salem, NC
Acetic Acid
Amyl Acetate
Cyclohexanone
Ethanol
Nicotine
Carbon Dioxide
Figure 2. Experimental Setup for Electrophysiology
Figure 4. Ethmoid Nerve Response
Figure 5. Sample Recordings
Figure 3. Behavioral response. Mean behavioral score values for a series of 8 olfactory/trigeminal stimuli, plus control (water). Error bars indicate one standard error unit.
Figure 4. Mean ethmoid nerve response. Neural response was calculated as the % change in standard deviation in neural activity, during and before stimulus presentation. Error bars indicate one standard error unit.
Figure 5. Sample recordings. Representative respiration records and neural responses to 6 different stimuli from a capsaicin-desensitized rat. Inserted stimulus marker bar represents 5 seconds.
Ethmoid Nerve
Ethmoid Prep
Behavioral Response Scale
-2 Trigeminal Reflex: Reflexive Withdrawal Movement
-1 Aversive Response: Head Turn or Rejection Movement
0 Neutral Response: No Response or Lack of Interest
+1 Favorable Response: Inspiratory Sniffing & Investigation
+2 Highly Favorable Response: Attempted Feeding Behavior
Stimulus Presentation
Applicator Stick
Cage Opening
Stimulus