Final answer:
During the process of habituation in the sea slug Aplysia, there is a decrease in neurotransmitter release at the synapse between the sensory and motor neurons involved in the withdrawal of the siphon tube.
Step-by-step explanation:
Repeated stimulation of the siphon in the sea slug Aplysia results in a process called habituation, not nabitulization as mentioned in the question. During this process, there is a decrease in the neurotransmitter release at the synapse between the sensory and motor neurons involved in the withdrawal of the siphon tube. This decrease in synaptic transmission is due to a reduction in the number of synaptic vesicles released by the presynaptic neuron.