Olfaction, among the First Senses to Develop and Decline

Abstract

Olfaction is one of the most conserved senses across species. It plays a crucial role in animals' and humans' life by influencing food intake, reproduction and social behavior. The olfactory system is composed of a peripheral neuroepithelium and a central olfactory nerve and is one of the few central nervous system (CNS) structures with direct access to the external environment without passage through the Blood Brain Barrier (BBB). This makes this nerve system of importance for understanding how exogenous stimuli may contribute to neuronal damage as well as for diagnostic and therapeutic purposes. Interestingly, olfactory activity physiologically declines with aging, but its alteration can be further impaired by various neurological conditions. For example, in progressive neurodegenerative disorders, such as Alzheimer's disease (AD), olfaction is the first sense to be impaired before the onset of cognitive symptoms, suggesting that olfactory transmission may characterize early neural network imbalances. In this work, we will explore the main olfactory anatomical structures, the cytoarchitecture, the neurogenesis, several pathological conditions characterized by olfactory deficit and the potential use of this sense to diagnose and treat CNS pathologies.

Age-Related Cognitive Decline and the Olfactory Identification Deficit Are Associated to Increased Level of Depression

“…Olfactory and gustatory function allows animals to detect smells and to locate food sources ( Loy et al, 2016 ). In humans, olfactory function regulates food intake, emotional/motivational responses such as pleasantness and reward, anxiety, and social and reproductive behavior ( Hoskison, 2013 ; Brai and Alberi, 2018 ). The olfactory function usually decreases in relation to age ( Doty and Cameron, 2009 ; Doty and Kamath, 2014 ; Masala et al, 2018a ) due to different age-related events such as a reduction in the expression of olfactory receptors, a decrease in neurogenic processes, an increase in the exposure to toxic environmental agents, and an increase in the ossification and/or closure of foramina on the cribriform plate ( Kalmey et al, 1998 ).…”

Una feromona de alarma produce reacción de congelamiento después de una sola exposición

“…42,43 En Revista eNeurobiología 11(26):160220, 2020 este sentido, aunque ambos sistemas sensoriales son importantes para la comunicación, desarrollo y supervivencia de los mamíferos, el sistema olfativo en términos evolutivos es uno de los más antiguos y mejor preservados. 44 Algunos estudios han mostrado que las memorias evocadas por estímulos olfativos son emocionalmente más intensas que las evocadas por estímulos auditivos o visuales. 4 Además, previamente se ha demostrado que la estimulación olfativa con 2-heptanona aumenta la responsividad entre la amígdala medial y el hipocampo 48h después de la exposición.…”

Flurbiprofen sodium microparticles and soft pellets for nose-to-brain delivery: Serum and brain levels in rats after nasal insufflation

“…In fact, olfactory impairment is recognized as an early sign of AD and other neurodegenerative disorders. It is caused by morphological and signaling alterations of the olfactory nerve (Brai and Alberi, 2018) and correlates with cognitive impairment development. According to Bathini et al (2019), this suggests that neuronal network imbalances propagate via olfactory bulb and nerve to higher brain centers of the entorhinal cortex and hippocampus.…”