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The Morris water maze is widely used to study spatial memory and learning. Animals are placed in a pool of water that is colored opaque with powdered non-fat milk or non-toxic tempera paint, where they must swim to a hidden escape platform. Because they are in opaque water, the animals cannot see the platform, and cannot rely on scent to find the escape route. Instead, they must rely on external/extra-maze cues. As the animals become more familiar with the task, they are able to find the platform more quickly. Developed by Richard G. Morris in 1984, this paradigm has become one of the "gold standards" of behavioral neuroscience. The main component of the water maze set up should be a round pool, about 6 feet in diameter and about 3 feet deep. If you are recording the task with a video camera, make sure all sides of the maze are within the camera's field of view. 2. Fill up the water maze with tap water, which should be close to 26°C. This may take several hours, so should be done well in advance.Periodically check the water temperature so that it is within one degree of 26°C. 3. Place the escape platform in the center of the pool. During training, it must be exposed, one inch above the water. This teaches the rat that there is a platform, and that it is the way to get out of the water. Later, after the animal is trained and ready for testing, the escape platform will be just below the surface of the water, and will not be visible because the water will be made opaque with milk or non-toxic paint. Now, the water maze is ready for training the animals.1. For the water maze training, the platform should be in the center of the pool and exposed one inch above the surface, so the animal knows that it's there. The water should be within one degree of 26°C. 2. Each animal will undergo three consecutive trials. First, place the animal on the platform for twenty seconds. 3. The water maze has 4 starting positions: north, south, east, or west. Take the animal to one of these positions. Lower the animal into the water by supporting it with your hand and bringing it down gently into the water tail-end first. Do not stress the animal out by dunking it in head first. 4. Let the animal swim/search for the platform for a maximum of 60 seconds. At first, the animal may swim around the edge of the pool looking for a way out. Eventually, the animal will learn to search for the platform and climb up. 5. Once the rodent reaches the platform, stop the timer, and record the time. If it doesn't find the platform in 60 seconds, then record the time for this trial as one minute. Do not pick up the animal if it fails to reach the platform. Teach the animal that it must swim to the platform. Therefore, gently guide the animal to the platform with your hand. Let the animal sit on the platform for 15 seconds. If it falls or jumps off, gently guide it back. This will train the animal that it must stay on the platform to be rescued from the pool. 6. Repeat the same procedure for two more trials, starting at a different direction for ea...

Gamma-aminobutyric acid (GABA) is as an excitatory neurotransmitter during brain development. Activation of GABA(A) receptors in neonatal rat hippocampus results in chloride efflux and membrane depolarization sufficient to open voltage sensitive calcium channels. As development progresses, there is a decline in the magnitude of calcium influx subsequent to GABA(A) receptor activation and the number of cells that respond to GABA with excitation. By the second postnatal week in the rat, GABA action in the hippocampus is predominantly inhibitory. The functional consequences and endogenous regulation of developmental GABA-mediated excitation remains under-explored. Hippocampal neurons in the newborn male and female rat respond to GABA(A) receptor activation with increased intracellular calcium and are susceptible to GABA-mediated damage -- both being indicative of the excitatory nature of GABA. In the present study we observed that by postnatal day 7, only males are susceptible to GABA(A) agonist-induced damage and respond to GABA(A) agonist administration with elevated levels of intracellular calcium in cultured hippocampal neurons. By postnatal day 14, GABA(A) agonist administration was without effect on intracellular calcium in both males and females. The age-related sex difference in the impact of GABA(A) receptor activation correlates with a sex difference in chloride co-transporter expression. Males have elevated protein levels of pNKCC1 on PN0 and PN7, with no sex difference by PN14. In contrast, females displayed elevated levels of KCC2 on PN7. This converging evidence infers that sex affects the duration of GABA(A) receptor-mediated excitation during normal hippocampal development, and provides a mechanism by which the effect is mediated.

Previous work from our lab has documented a sex difference in neuron number in the binocular region of the adult rat primary visual cortex (Oc1B), with males having 19% more neurons than females. In the present study, the role of developmental steroid hormones in the formation of this difference was explored. Male and female rats underwent neonatal hormone manipulation (female + testosterone or dihydrotestosterone; male + flutamide) followed by gonadectomy on postnatal day 20. Animals that did not undergo hormone manipulation were either gonadectomized or sham operated at day 20. Neuron number was quantified in the monocular (Oc1M) and binocular (Oc1B) subfields of the adult rat primary visual cortex using the optical disector technique. As adults, day 20 gonadectomized females, as well as females + testosterone and females + dihydrotestosterone, had significantly more neurons than intact females. There was no difference in neuron number between postnatal day 20 gonadectomized males, males + flutamide, and intact males. Also, intact males had significantly more neurons than intact females in both in Oc1M and Oc1B. It appears that ovarian steroids after day 20 are the primary cause of the lower number of neurons in the primary visual cortex of the female rat.

Hypoxic/ischemic (HI) brain injury in newborn full-term and premature infants is a common and pervasive source of life time disabilities in cognitive and locomotor function. In the adult, HI induces glutamate release and excitotoxic cell death dependent on NMDA receptor activation. In animal models of the premature human infant, glutamate is also released following HI, but neurons are largely insensitive to NMDA or AMPA/kainic acid (KA) receptor-mediated damage. Using primary cultured hippocampal neurons we have determined that glutamate increases intracellular calcium much more than kainic acid. Moreover, glutamate induces cell death by activating Type I metabotropic glutamate receptors (mGluRs). Pretreatment of neurons with the gonadal steroid estradiol reduces the level of the Type I metabotropic glutamate receptors and completely prevents cell death, suggesting a novel therapeutic approach to excitotoxic brain damage in the neonate.