## 3 Discussion
### Reduced Chemical and Thermal Perception Reduces Net-Energy  
The main reason for ingestion is to maximize the net-energy-uptake, the difference between energy gained from food and energy upset to receive it. [43]. The chemo-sensorial system of _C. elegans_ is quite firmly set and is used for detection and evaluation of food sources [44, 45]. Reduced chemical perception thereby may negatively affect the energy balance (Figure 5) and may also decrease the ability to avoid infective bacteria and fungi [46].  
The high concentrated TBBP-A and the mixture of the 50 \(\upmu\)M organobromines decreased the chemical perception. This may cause a decreased detection and evaluation of food, resulting in a lower amount of energy by the consumed food. The energy upset to receive the food would rise at the same time, because fast and targeted searching is affected. As explained in Section 3.1, this loss of energy can cause decreased body length, reproduction, and perhaps faster senescence. _In natura_ with limited food available, the toxic effect of the substances could be enhanced by this feature. Under the artificial circumstances in the laboratory and feeding _ad libitum_, however, reduced chemo-perception most likely does not display a negative effect and can probably be ruled out as reason for the observed reduction of lifespan and offspring [7].  
Figure 7: Regulation of the expulsion step of the defecation cycle, created on information from [41] and [42]; **IM**: intestinal muscle, **AS**: anal sphinter, **AD**: anal depressor, **DVB (green)** and **AVL (red)**: polymodale interneurons/motor neurons; It is unclear, whether AVL acts directly on the muscles or via DVB, therefore dotted lines are used to show the connections.  
Thermal perception allows _C. elegans_ to seek out the temperature where enzymes have optimal functionality. Disturbance of the thermo-sensory system can lead to developmental delays and sterility [47] and therefore may also affect lifespan [48]. All substances had only a poor impairment on isothermal behavior. As a consequence, no indication on disrupted thermotaxis as a reason for shortened lifespan could be found.  
Perception of sodium and chloride and thermal perception is mediated by the glutamatergic neurons ASE, ASH, and AWC [49, 50] (Figure 8). Transcription of _hen-1_, which is needed for different types of learning, including salt- and thermotaxis [51], was decreased by the combination of the high concentrated substances and may be the reason for the reduced chemotaxis. Neither _eat-4_[52] and _casy-1_[53], nor _che-12_[54] or _srab-6_[55] seem to influence chemical and thermal perception. For detailed information about the gene function please refer to Table 2.  
Figure 8: Regulation of chemical and thermal sensory, created on information from [PERSON] _et al._[56], [PERSON] _et al._[57] and [49]. **ASE**, **AFD** and **AWC**: sensorial neurons, **AIY**, **RIA** and **AIZ**: interneurons, **red**: chemical sensory, **green**: thermal sensory, **Glu**: glutamate, **ACh**: acetylcholine, **?**: unknown mechanism, **--**: excitatory, **--**: inhibitory, **\(\Delta\mathbf{T_{\mathrm{c}}}\)**: deviation from cultivating temperature \(T_{\mathrm{c}}\).