Primary Investigators: Gordon M. Burghardt and George Kabalka

To assess, with modern imaging methods, the ontogenetic and environmentally induced changes in the neural structure of squamate reptiles. Garter snakes (Thamnophis) will be reared in stimulus rich and stimulus poor environments, and changes in the amount and extent of brain tissue measured.

It is becoming increasingly apparent that the brain anatomy is altered readily by the type and amount of stimulation animals, especially young mammals, receive. This has many implications for issues from prenatal care to early education in our species. Mammals are often used in this work (Kolb and Whishaw, 1998), but in birds similar effects can be demonstrated (Patel et al., 1997). Reptiles, the ancestral group to both birds and mammals share many similarities with both their descendant taxa, but lack the extensive parental care characteristic of both. If experience dependent brain development also occurs in reptiles, then a model system would be available that would allow ready manipulation of neonates without the complications of maternal care. Furthermore, young reptiles are able to locomote, eat, and carry on other essential activities from birth. Much work is available on the behavior of neonate animals and their rearing in laboratory environments (Burghardt & Layne, 1995).

Environmental conditions are among the most important factors that influence a captive animal’s well being (Burghardt,1996). From the earliest stages of development environmental conditions can affect an organism’s growth. One particular area that is greatly affected is neurological development. During early stages of life, neurological development includes rapid increase in brain tissue mass or neurogenesis (Jacobs, et al. 2000; Kolb and Whishaw 1998). Experimental evidence with rodents has shown that through combinations of complex inanimate and social interactions distinct morphological changes in the hippocampal complex occurs, primarily manifested in increase mass (for summary information see Kempermann et al 1997). The hippocampal complex has historically been associated with an animal’s learning ability, spatial navigation, and increased behavioral activity. Increased spatial learning has also been shown to induce neurogenesis in birds (Patel et al 1996).

Over the past 30 years biologist have began to pay more attention to the effects of housing and rearing conditions on reptile ethology (e.g., Burghardt and Layne, 1995). Although many studies now focus on reptile behavior, many animals are maintained in traditional enclosure designs. This standard design is often a relatively small box-like structure lined with cage paper, furnished with a small hide box, and water bowl. Yet sterile environments have been shown to have detrimental effects on reptile behavior and environmental enrichment is being applied to reptiles (Burghardt, et al. 1996).

We propose to examine the effects of enriched environment on the neurological development of snakes by using a non-invasive high field MRI brain imaging of a garter snake (Thamnophis sirtalis) extending imaging methods developed for this species (Anderson et al 2000). Sample slices from a juvenile (10 g) snakes are depicted in Figure 1.

The potential implications of this study are far reaching. If environmental conditions correlate with distinct morphological brain differences, wide spread revaluation of traditional views of the role of reptiles as research models would be needed (Greenberg, 1989).

Doing this study at the University is particularly relevant since Dr. Burghardt is a long-experienced researcher in reptile behavior and has developed many of the needed housing and testing methods. Dr. Kabalka has pioneered the use of high energy MRI for small specimens. They have already collaborated in the first study on reptile MRI and this project would build on joint efforts already developed between the two research teams.

The initial experiment would involve rearing 40 snakes in four conditions for the first year of life, during which mass should increase six fold. There would be three groups of 10 animals each, balanced by sex and litter. A control group will be maintained in small standard plastic cages with a commercial paperboard substrate, water bowl, and small retreat. The sides of the cages will be blocked so as to limit any potential external visual stimulation. They will be fed a diet of dead earthworms. Handling of these snakes will be kept to a minimum, as will other disturbances. The second group of snakes will be maintained in larger 60 l aquaria with unobstructed views of one another as well as people and events in their surroundings. They will have natural (dirt) substrates, rocks and multiple retreats. They will also be fed dead earthworms. The third group will be treated as the second but live earthworms will be provided in the dirt substrate that the snakes will have to actively forage for and capture. In the fourth group animals will be given live fish in the water bowls as well as worms, so the chemical, as well as physical environment will be enriched. Animals will be weighed and measured at the beginning of the study and at two month intervals. At birth, 2 months, six months, and 12 months of age standard tests of chemoreceptive and foraging behavior will be carried out in which the plasticity of the responses will be evaluated using protocols we have already used for many years (e.g., Burghardt, 1993; Burghardt and Krause, 1999). Brain imaging will be done at birth and at 6 and 12 months of age following the methods in Anderson, et al. (2000). From multiple scans in the three dimensions relative volumes of the brain and various components will be calculated and compared among the four groups.