How about non-target cells? I found several examples of that usage including:
A book section titled: 9.3 How are steroid hormone target cells differentiated from non-target cells?1
Containing the following line:
Thus, estrogen will stimulate mRNA and protein synthesis in a target cell, but not in a non-target cell.
A book chapter titled: Target or non-...
No, p53 and other tumor suppressor proteins do not belong to Cyclin dependent kinase(CDK)family. p53 blocks the cell cycle by promoting the synthesis of Cyclin dependent kinase inhibitors (CKI proteins). These CKI proteins bind with the Cyclin and CDK complex and inhibit the cell cycle at G1 checkpoint.
(Image Source: https://www.khanacademy.org/science/...
Integrating the information from @WYSIWYG's excellent answer, it appears the dopaminerig neuron count lies at:
4k for mice - Triarhou, 1988
10k for rats - German and Manaye, 1993
250k-440k for humans - Rice et al, 2016