Seasonal changes in neuron numbers in the hippocampal formation of a food-hoarding bird: The black-capped chickadee

Abstract

The volume of the hippocampal formation (HF) in black-capped chickadees (Poecile atricapillus) varies across the seasons, in parallel with the seasonal cycle in food hoarding. In this study, we estimate cell density and total cell number in the HF across seasons in both juveniles and adults. We find that the seasonal variation in volume is due to an increase in the number of small and large cells (principally neurons) in the fall. Adults also have lower neuron densities than juveniles. Both juveniles and adults show an increase in cell density in the rostral part of the HF in August and a subsequent decrease toward October. This suggests that the net cell addition to the HF may already start in August. We discuss the implications of this early start with respect to the possibility that the seasonal change in HF volume is driven by the experience of food hoarding. We also speculate on the functional significance of the addition of neurons to the HF in the fall.

Memory in Food Caching Animals

“…This seemed to complement the results of Barnea and Nottebohm (1994). Smulders et al (2000), however, concluded that this change in volume was related to an increase in the total number of neurons in the hippocampus. Barnea and Nottebohm did not find seasonal changes in total neuron number, only in the number of new neurons.…”

“…Lavenex et al (2000a,b) found no seasonal variations in hippocampal volume, total neuron number, or cell proliferation rates in the adult scatter-hoarding eastern gray squirrel (Sciurus carolinensis), an interesting contrast with the results from birds (Smulders et al 1995(Smulders et al , 2000 in terms of seasonal changes in volume and neuron number. Barker et al (2005) compared the yellow pine chipmunk, both a lar-der-and scatter-hoarder, to the scatter-hoarding eastern gray squirrel during the fall when both species were actively collecting and storing food for winter.…”

“…This differs from Barnea and Nottebohm's hypothesis of neuron replacement with no net gain in number of neurons. Hoshooley and Sherry (2004) attempted to distinguish between the hypotheses of Barnea and Nottebohm (1994) and Smulders et al (2000) by determining if the seasonal changes in chickadee hippocampus were a result of more 'new' neurons or an increase in the actual 'production' of neurons. They found no seasonal change in hippocampal volume, total neuron number, or neuron production, which suggests enhanced survival of new neurons in the fall, not an increase in neuron production.…”

Sex differences in the effects of captivity on hippocampus size in brown-headed cowbirds (Molothrus ater obscurus).

“…We do know that species-specific reactions to spatial experience (food storing or other spatial learning tasks) during development contribute to differences between some species of food-storing versus non-food-storing birds. In adults, food-storing experience alone does not appear to alter the volume of the Hp in some species (Cristol, 1996); although combined with other seasonal effects, it may increase Hp volume, cell number, or new cell recruitment in other species such as the black-capped chickadee (Barnea & Nottebohm, 1994;Smulders et al, 1995;Smulders, Shiflett, Sperling, & DeVoogd, 2000). Changes in Hp neuroanatomy across seasons that are correlated with seasonal demand for spatial memory appear to be triggered directly by changes in photoperiod in some mammals (Prendergast, Nelson, & Zucker, 2002).…”

Songbirds: A novel perspective on estrogens and the aging brain

“…As mentioned previously, some songbirds store food reserves during the autumn and winter. In one such species, the black-capped chickadee, mitotic neurons migrate into the adult hippocampus (Barnea and Nottebohm 1996), thereby increasing hippocampal volume via changes in neuron number (Smulders et al 1995(Smulders et al , 2000; but see Hoshooley and Sherry 2004). Importantly, peaks in hippocampal recruitment occur in good temporal agreement with increases in foodstoring and retrieval.…”