Short-Term Enrichment Makes Male Rats More Attractive, More Defensive and Alters Hypothalamic Neurons

Innate behaviors are shaped by contingencies built during evolutionary history. On the other hand, environmental stimuli play a significant role in shaping behavior. In particular, a short period of environmental enrichment can enhance cognitive behavior, modify effects of stress on learned behaviors and induce brain plasticity. It is unclear if modulation by environment can extend to innate behaviors which are preserved by intense selection pressure. In the present report we investigate this issue by studying effects of relatively short (14-days) environmental enrichment on two prominent innate behaviors in rats, avoidance of predator odors and ability of males to attract mates. We show that enrichment has strong effects on both the innate behaviors: a) enriched males were more avoidant of a predator odor than non-enriched controls, and had a greater rise in corticosterone levels in response to the odor; and b) had higher testosterone levels and were more attractive to females. Additionally, we demonstrate decrease in dendritic length of neurons of ventrolateral nucleus of hypothalamus, important for reproductive mate-choice and increase in the same in dorsomedial nucleus, important for defensive behavior. Thus, behavioral and hormonal observations provide evidence that a short period of environmental manipulation can alter innate behaviors, providing a good example of gene-environment interaction

TRIS-buffer decreases rat's sensitivity to odorants

TRISis commonly used as a buffer in histology but also in medicine to cure metabolic acidosis, as a gastrointestinal and diuretic drug as well as a solvent of drugs delivered in aerosol containers. Mainly because of the application as a solvent in aerosol containers the question arose weather TRISa ffects odor detection ability. Using operant conditioning, male Wistar rats were trained in an air dilution olfactometer to respond to low level concentrations (10-3 % of vapor saturation) of odorants (ethyl acetate or n-octanal) but not to clean air. Rats mastered this task with 90-100 % correct responses. Intranasal perfusion of the olfactory mucosa with Ringer solution did not impair detection performance. However, intranasal perfusion with TRIS-buffer resulted in a reduced detection performance 30 min after treatment of the olfactory mucosa to 61.4 ± 5.6 % (ethyl acetate) and 49.3 ± 5.3 % (n-octanal) correct responses, which represent random choice levels. Increase of odor concentration to 10-2 vol % 50 min after flushing the nasal cavity with TRIS-buffer improved detection performance (95 % correct answers). Four hours after treatment, the detection performance returned to pretreatment levels (90.0 ± 12.2 % ethyl acetate; 91.0 ± 10.2 % n-octanal). We conclude that TRISr educes (but not totally inhibits) olfactory sensitivity unspecifically and reversibly probably by changing either 1) the pH of the mucus or receptor cells and therefore the activity of enzymes in the signaling cascade or 2) by direct interaction with the odorant ligands or the odorant receptors. The underlying mechanisms have to be evaluated

Olfactory deprivation enhances normal spine loss in the olfactory bulb of developing ferrets

Ferrets show a sensitive phase in their postnatal development during which they can become imprinted to food odors. At the same time the number of granule cell spines in the olfactory bulb reaches a maximum, declinging significantly thereafter. In ferrets, exposed continuously to saturated levels of geraniol odor in the cage environment, the normal decline in spine number (occurring between day 60 and 90) is significantly enhanced. No such effects were observed during earlier ontogenetic phases. This late postnatal phase is further associated with a marked and significant decrease in total brain weight. The significance of these events to olfactory imprinting and plasticity in the developing brain is discussed