Seasonal plasticity in the adult somatosensory cortex

Abstract

Seasonal cycles govern life on earth, from setting the time for the mating season to influencing migrations and governing physiological conditions like hibernation. The effect of such changing conditions on behavior is well-appreciated, but their impact on the brain remains virtually unknown. We investigate long-term seasonal changes in the mammalian brain, known as Dehnel’s effect, where animals exhibit plasticity in body and brain sizes to counter metabolic demands in winter. We find large seasonal variation in cellular architecture and neuronal activity in the smallest terrestrial mammal, the Etruscan shrew, Suncus etruscus. Their brain, and specifically their neocortex, shrinks in winter. Shrews are tactile hunters, and information from whiskers first reaches the somatosensory cortex layer 4, which exhibits a reduced width (−28%) in winter. Layer 4 width (+29%) and neuron number (+42%) increase the following summer. Activity patterns in the somatosensory cortex show a prominent reduction of touch-suppressed neurons in layer 4 (−55%), the most metabolically active layer. Loss of inhibitory gating occurs with a reduction in parvalbumin-positive interneurons, one of the most active neuronal subtypes and the main regulators of inhibition in layer 4. Thus, a reduction in neurons in layer 4 and particularly parvalbumin-positive interneurons may incur direct metabolic benefits. However, changes in cortical balance can also affect the threshold for detecting sensory stimuli and impact prey choice, as observed in wild shrews. Thus, seasonal neural adaptation can offer synergistic metabolic and behavioral benefits to the organism and offer insights on how neural systems show adaptive plasticity in response to ecological demands.

Geographic patterns in seasonal changes of body mass, skull, and brain size of common shrews

“…A recent study on the Etruscan shrew Suncus etruscus revealed a 3.8% decrease in cortical volume from summer to winter, and a slight regrowth in the next spring (Ray et al., 2020). The changes are most pronounced in the thickness of somatosensory cortex (28/29%).…”

Prognostic value of splenic volume in hepatocellular carcinoma patients receiving transarterial chemoembolization

“…Plain scanning and dynamic contrast-enhanced computed tomography (CT) examinations were carried out on a CT scanner (Aquilion 64, Toshiba Medical System, Tokyo, Japan) using the scanning protocol as follows: tube voltage, 120 kV; tube current, 250 mAs; rotation time, 0.358 s; field of view, 400 mm; reconstruction interval, 1.0 mm; and slice thickness, 0.8 mm. Image analyses were processed using AnalyzePro 1.0 software (AnalyzeDirect, Overland Park, KS, USA) (17). To determine the SV, radiologist blind to clinical data delineated the spleen manually slide by slide on cross section portal venous phase (PVP) images, and large vessels in spleen were excluded (Figure 2).…”

Cytoskeletal Arrest: An Anoxia Tolerance Mechanism

“…While there has been little investigation of the cytoskeleton in anoxia-tolerant animals, research of the neuronal cytoskeleton in cold-tolerant mammals has been relatively abundant, and cytoskeleton-mediated shrinkage of the brain appears to be a widespread adaptation [ 79 , 80 , 81 , 82 , 83 , 84 , 85 , 86 ] that we will explore to inform hypotheses of metabolic arrest in anoxic animals. Mammals that utilize torpor or hibernation depress metabolism while overwintering at low temperatures in burrows that may become hypoxic [ 87 ].…”

“…Mammals that utilize torpor or hibernation depress metabolism while overwintering at low temperatures in burrows that may become hypoxic [ 87 ]. Popov et al [ 83 ] first described degradation of dendrites and dendritic spines in torpid Siberian ground squirrels ( Citellus undulatus ) in 1992, but torpid brain shrinkage has since been demonstrated in shrews [ 80 , 85 ] and hamsters [ 81 ], and is suspected in black bears [ 86 ] as well. During ground squirrel torpor, neuronal protrusions are degraded [ 83 , 84 ].…”