The hippocampus of birds and mammals has been shown to play a crucial role in spatial memory and navigation. The hippocampus exhibits plasticity in adulthood in response to diverse environmental factors associated with spatial demands placed on an animal. The cortical telencephalon of squamate reptiles has been implicated as a functional homologue to the hippocampus. This study sought to experimentally manipulate the navigational demands placed on free-ranging northern Pacific rattlesnakes (Crotalus o. oreganus) to provide direct evidence of the relationship between spatial demands and neuroplasticity in the cortical telencephalon of the squamate brain. Adult male rattlesnakes were radio-tracked for two months, during which one of three treatments was imposed weekly: 225 meter translocation in a random direction, 225 meter walk and release at that day’s capture site (handling control), and undisturbed control. Snakes were then sacrificed and brains were removed and processed for histological analysis of cortical features. The volume of the medial cortex was significantly larger in the translocated group compared to undisturbed controls. No differences in dorsal or lateral cortical volume were detected among the groups. Numbers of 5-Bromo-2’-deoxyuridine (BrdU) -labeled cells in the medial and dorsal cortices three weeks after BrdU injection were not affected by treatment. The activity range was larger in the translocated group compared to handled and undisturbed controls. A causal relationship between increased navigation in a free-ranging reptile and changes in brain morphology was established. The use of translocation as a conservation strategy for reptiles is a controversial topic revisited many times. Previous studies have demonstrated the aberrant movement patterns and mortality caused by translocation and have established that short-distance translocation within an animal’s home range is best for the animal. In conjunction with the neuroplasticity study, we examined the physiological impacts that repeated short-distance translocation and handling have on reptiles. This is essential knowledge if the efficacy of the technique is to be properly evaluated. Baseline and stressed concentrations of corticosterone and testosterone were assayed in blood taken immediately upon capture and following one hour of confinement in a bucket. Neither baseline nor stressed concentrations of either hormone were impacted by translocation or handling. Body condition and change in mass were not affected. Translocated animals had larger MCP activity ranges than handled and undisturbed animals at the 95%, but not 100% levels, while an interaction between time and treatment impacted other movement parameters.Treatment had no effect on a number of behaviors observed during visits to each animal. We suggest that rattlesnakes are quite resistant to potential impacts on their physiology and behavior enacted by frequent short-distance translocation or handling. Additionally, studies that require frequent handling of reptilian subjects are not likely to severely alter stress physiology.

The hippocampus is a brain region that can undergo tremendous plasticity in adulthood. The hippocampus is related to the formation of spatial memories in birds and mammals. In birds, plasticity in the hippocampus occurs when formation of such memories is directly relevant to survival or reproduction, such as for breeding or food caching. In reptiles, the homologues to the hippocampus are the dorsal and medial cortices (DC and MC). In several lizard, snake and turtle species, these structures have been related to spatial memory. Experimental investigations indicate that differences in DC volume are related to space use associated with differing foraging ecologies. Differences in MC volume have been associated with territory size-based mate acquisition strategies. Furthermore, territory size has previously been correlated with plasma testosterone (T) levels. Therefore, I hypothesized that neuroplasticity within the MC/DC is controlled by demands on spatial navigation and seasonal differences and that these changes may involve the action of T. During two experimental trials, male Western Fence Lizards (Sceloporus occidentalis) were placed into either large or small semi-natural enclosures and allowed to interact with a female and intruder males over the span of seven weeks. One trial was performed during the spring breeding season and the other during the summer non breeding season, to examine seasonal differences in plasticity. Blood samples were collected at initial time of capture and before sacrifice to measure plasma T. Immunostaining for doublecortin was used to determine the density of immature neurons in each region, and cresyl violet staining allowed for volume measurements of specific regions. MC cell layer neurogenesis was higher in lizards placed in large enclosures than those in small enclosures and higher in the summer than in the spring. DC volume was smaller in lizards held in large enclosures than those in small enclosures. The decreased DC volume seen lizards held in large enclosures may indicate a cost to the increased neurogenesis in the MC of lizards in the same enclosures. These results indicate a possible trade-off between DC volume and MC neurogenesis that allows for switching between the ability to solve novel spatial tasks using the DC while storing a cognitive map in the MC. During the spring, T had no relationship with MC volume, while during the summer this was negative, so effects of T on the MC may be seasonal.

Due to its significance in many cellular functions, fatty acid binding protein 7 (FABP7) has become a rising topic of interest for many scientists. Immunocytochemistry was used to map the distribution of FABP7 and test whether the amount of FABP7 immunoreactivity (FABP7-IR) differed in animals that were defeated in a fight, as compared to control animals that did not engage in any social interaction. The male green anole was used as the subject because its natural tendency to establish social classes within its species provides an ideal model to observe for variation in FABP7-IR. The results showed FABP7-IR in cells and fibers of the cortex, hypothalamus, thalamus, medial preoptic area, dorsoventricular ridge, amygdala, suprachiasmatic nucleus, nucleus accumbens, nucleus rotundus, habenular area, tectum, dorsal noradrenergic and lateral forebrain bundles, and lining the third and lateral ventricles. Qualitative observation suggested higher FABP7 levels in socially defeated males than controls in all areas.