This simple cartoon shows how CS, HC₃N and CH₃CCH could be distributed in the giant molecular clouds within the central hundred parsecs of the four galaxies from the LVG model results. The size scales range from  ∼ 145 to  ∼ 560 pc depending on the galaxy distance and beam size. We have found a region I with densities of about  ∼ 10⁴ cm^-3, an intermediate region II with densities of  ∼ 10⁵ cm^-3, and a region III with high densities of around  ∼ 10⁶ cm^-3. Maffei 2 shows two density components, but no core (region III) is detected. In NGC 253 and IC 342, up to three gas components of different densities are distinguished ( ∼ 10⁴,  ∼ 10⁵ and  ∼ 10⁶ cm^-3). M 82 shows a region of intermediate densities and a core. The region I is not detected by the molecules used here, although it should be surrounding the region II.