NGF (Nerve growth factor) is a neurotrophic protein with important functions in maintaining the integrity and proper function of target neurons in the developing and adult brain. It controls the plasticity, differentiation and proliferation of cholinergic neurons in the nervous system, which are important for cognition. NGF metabolism is altered in Alzheimer’s disease, which leads to neuronal atrophy and a loss of cortical synapses. Several decades of study indicates that NGF has neuro-protective and regenerative characteristics in neurodegenerative diseases such as Alzheimer’s and in aging. Delivery of NGF to cholinergic cell bodies in the cortex and hippocampus has been attempted as a means of rehabilitating cholinergic signaling and suppressing cognitive decline. Separately, high NGF levels in the plasma are correlated with recent feelings of romantic love, in part due to its stimulation of adrenocorticotrophic hormone and cortisol release. In immunohistochemistry, NGF has variable levels of secretory, extracellular and cytoplasmic positivity in most tissues throughout the body. References: Front Neurosci. 2019 Feb 5;13:38, PMID: 30804738; Rev Neurosci. 1994 Jul-Sep;5(3):179-211, PMID: 7889213; Progress in Brain Research. 2004. 146: 111–26,PMID: 14699960; Brain Research. 217 (1): 207–211, PMID: 6114784;