GRP and amyotrophic lateral sclerosis: Interestingly, activation of GRP-expressing neurons (which form glutamatergic synapses on the GRPR cells44) was also found to result in both pain and itch behaviour.56 It is therefore likely that the GRPR cells captured in the GRPRCreERT2 line convey both nociceptive and pruritoceptive information to ALS projection neurons.