Insulin and Memory in Invertebrates

Abstract

Insulin and insulin-like peptides (ILP) help to maintain glucose homeostasis, whereas insulin-like growth factor (IGF) promotes the growth and differentiation of cells in both vertebrates and invertebrates. It is sometimes difficult to distinguish between ILP and IGF in invertebrates, however, because in some cases ILP has the same function as IGF. In the present review, therefore, we refer to these peptides as ILP/IGF signaling (IIS) in invertebrates, and discuss the role of IIS in memory formation after classical conditioning in invertebrates. In the arthropod Drosophila melanogaster, IIS is involved in aversive olfactory memory, and in the nematode Caenorhabditis elegans, IIS controls appetitive/aversive response to NaCl depending on the duration of starvation. In the mollusk Lymnaea stagnalis, IIS has a critical role in conditioned taste aversion. Insulin in mammals is also known to play an important role in cognitive function, and many studies in humans have focused on insulin as a potential treatment for Alzheimer’s disease. Although analyses of tissue and cellular levels have progressed in mammals, the molecular mechanisms, such as transcriptional and translational levels, of IIS function in cognition have been far advanced in studies using invertebrates. We anticipate that the present review will help to pave the way for studying the effects of insulin, ILPs, and IGFs in cognitive function across phyla.

Expression Level Changes in Serotonin Transporter are Associated with Food Deprivation in the Pond Snail Lymnaea stagnalis

“…Furthermore, it is important to note that that we confirmed the co-expression of LymSERT mRNA and 5-HT, especially in the CGCs. CGCs innervate multiple interneurons and motor neurons involved in feeding behavior and CTA (Yeoman et al, 1996; Kojima et al, 1997; Sunada et al, 2017; Hatakeyama et al, 2022b; Nakai et al, 2022). The report by Dyakonova et al (2015a) also showed that 5-HTergic neuron activity increases during fasting.…”

Octopamine integrates the status of internal energy supply into the formation of food-related memories

“…Such longrange signals from the muscles exist. Skeletal muscles are secretory organs (Pedersen and Febbraio, 2012). For example, the muscle-secreted Amyrel amylase reduces the age-related accumulation of polyubiquitinated proteins in the brain (Rai et al, 2021).…”

Identification of Putative Molecules for Adiponectin and Adiponectin Receptor and Their Roles in Learning and Memory in Lymnaea stagnalis

“…Insulin-like peptides in the brain are strongly involved in the learning and memory mechanisms of Lymnaea [ 7 , 8 , 9 , 10 ]. For example, in long-term memory formation following a conditioned taste aversion (CTA) protocol [ 9 ], molluscan insulin-related peptides (MIPs) are up-regulated at the mRNA level in the Lymnaea central nervous system (CNS) [ 11 ], and MIPs enhance the neural transmission efficacy at a synapse in the CTA neural circuit [ 12 ]. A common role of insulin and insulin-like peptides is to lower blood glucose levels, and MIPs lower hemolymph glucose levels in Lymnaea [ 13 ].…”