FIGURE 1.

Refined catheter-based intranasal technique. (A) The sketch displays the conventional pipette-based technique to administer drops onto, or into, the nostril. This method is unable to discriminate the nasal regions and additionally holds a high risk for swallowing and ingestion of the drug solution. (B) Anatomy of a sagittal section though a murine head showing the nasal cavity with the respiratory and the olfactory regions. The ethmoid bone separates the nasal cavity from the brain (for a better visibility the structure was encircled with a dotted line). Located caudally from the ethmoid bone are the olfactory bulbs (OB) that receive neuronal connections from the olfactory mucosa through the ethmoid bone. (C) The recently developed refined technique uses a catheter for neonates to enter the nasal cavity via the nostrils. The correct angle for insertion through the nostrils is important to reach to dorsal meatus and, hence, to reach the olfactory region with the ethmoid turbinates (arrowhead). (D) A too low angle during insertion results in targeting the middle meatus (arrowhead). It is impossible to reach the olfactory region from here. Therefore, a sufficient training of the technique is required to target the olfactory region in alive animals. For a better visibility the catheter tip was encircled with a dotted line and the olfactory and respiratory regions were colored in (C) and (D). Sketch (A) was created under license with Biorender.