An Integrated Platform for in vivo Electrophysiology in Spatial Cognition Experiments.

Spatial cognition research requires behavioral paradigms that can distinguish between different navigational elements, such as allocentric (map-like) navigation and egocentric (e.g., body centered) navigation. To fill this need, we developed a flexible experimental platform that can be quickly modified without the need for significant changes to software and hardware. In this paper, we present this inexpensive and flexible behavioral platform paired with software which we are making freely available. Our behavioral platform serves as the foundation for a range of experiments, and though developed for assessing spatial cognition, it also has applications in the non-spatial domain of behavioral testing. There are two components of the software platform, 'Maze' and 'Stim Trigger'. Both programs can work in conjunction with electrophysiology acquisition systems, allowing for precise time stamping of neural events with behavior. The Maze program includes functionality for automatic reward delivery based on user defined zones. 'Stim Trigger' permits control of brain stimulation via any equipment that can be paired with an Arduino board. We seek to share our software and leverage the potential by expanding functionality in the future to meet the needs of a larger community of researchers.

Neonatal corticosterone administration impairs adult eyeblink conditioning and decreases glucocorticoid receptor expression in the cerebellar interpositus nucleus.

Neonatal maternal separation alters adult learning and memory. Previously, we showed that neonatal separation impaired eyeblink conditioning in adult rats and increased glucocorticoid receptor (GR) expression in the cerebellar interpositus nucleus, a critical site of learning-related plasticity. Daily neonatal separation (1 h/day on postnatal days 2-14) increases neonatal plasma corticosterone levels. Therefore, effects of separation on GR expression in the interpositus and consequently adult eyeblink conditioning may be mediated by neonatal increases in corticosterone. As a first step in exploring a potential role for corticosterone in the neonatal separation effects we observed, we assessed whether systemic daily (postnatal days 2-14) corticosterone injections mimic neonatal separation effects on adult eyeblink conditioning and GR expression in the interpositus. Control uninjected animals were compared to animals receiving either daily corticosterone injections or daily injections of an equal volume of vehicle. Plasma corticosterone values were measured in a separate group of control, neonatally separated, vehicle injected, or corticosterone injected pups. In adulthood, rats underwent surgery for implantation of recording and stimulating electrodes. After recovery from surgery, rats underwent 10 daily sessions of eyeblink conditioning. Then, brains were processed for GR immunohistochemistry and GR expression in the interpositus nucleus was assessed. Vehicle and corticosterone injections both produced much larger increases in neonatal plasma corticosterone than did daily maternal separation, with the largest increases occurring in the corticosterone-injected group. Neonatal corticosterone injections impaired adult eyeblink conditioning and decreased GR expression in the interpositus nucleus, while the effects of vehicle injections were intermediate. Thus, while neonatal injections and maternal separation both produce adult impairments in learning and memory, these manipulations produce opposite changes in GR expression. This suggests an inverted U-shaped relationship may exist between both neonatal corticosterone levels and adult GR expression in the interpositus nucleus, and adult GR expression in the interpositus and eyeblink conditioning.

Chronic stress alters neural activity in medial prefrontal cortex during retrieval of extinction.

Chronic restraint stress produces morphological changes in medial prefrontal cortex and disrupts a prefrontally mediated behavior, retrieval of extinction. To assess potential physiological correlates of these alterations, we compared neural activity in infralimbic and prelimbic cortex of unstressed versus stressed rats during fear conditioning and extinction. After implantation of microwire bundles into infralimbic or prelimbic cortex, rats were either unstressed or stressed via placement in a plastic restrainer (3 h/day for 1 week). Rats then underwent fear conditioning and extinction while activity of neurons in infralimbic or prelimbic cortex was recorded. Percent freezing and neural activity were assessed during all phases of training. Chronic stress enhanced freezing during acquisition of conditioned fear, and altered both prelimbic and infralimbic activity during this phase. Stress did not alter initial extinction or conditioned stimulus (CS)-related activity during this phase. However, stress impaired retrieval of extinction assessed 24 h later, and this was accompanied by alterations in neuronal activity in both prelimbic and infralimbic cortex. In prelimbic cortex, unstressed rats showed decreased activity in response to CS presentation, whereas stressed rats showed no change. In infralimbic cortex, neurons in unstressed rats exhibited increased firing in response to the CS, whereas stressed rats showed no increase in infralimbic firing during the tone. Finally, CS-related firing in infralimbic but not prelimbic cortex was correlated with extinction retrieval. Thus, the stress-induced alteration of neuronal activity in infralimbic cortex may be responsible for the stress-induced deficit in retrieval of extinction.

Neonatal maternal separation alters the development of glucocorticoid receptor expression in the interpositus nucleus of the cerebellum.

Adverse early experience impairs adult learning and memory. Previously, we showed that neonatal maternal separation impaired eyeblink conditioning in adult male rats. This impairment was correlated with increases in glucocorticoid receptor expression in the posterior region of the cerebellar interpositus nucleus, a key structure in the neural circuitry controlling eyeblink conditioning. To begin to establish how separation results in altered glucocorticoid receptor expression in adulthood, we assessed the developmental pattern of glucocorticoid receptor expression in the interpositus nucleus in controls versus rats that had undergone maternal separation for 1h per day on postnatal days 2-14. Rat pups were exposed to either standard rearing (control) or maternal separation and glucocorticoid receptor expression was assessed at postnatal day 15, postnatal day 21, and adulthood. In control males, glucocorticoid receptor expression in the interpositus nucleus declined between postnatal days 15 and 21, then increased into adulthood. On postnatal day 15, there was less glucocorticoid receptor expression in the interpositus nucleus in males that were maternally separated than in controls. However, neonatal separation significantly attenuated the normal decline in the third postnatal week, resulting in significantly greater glucocorticoid receptor expression in the interpositus in separated males than in control rats at postnatal day 21. The developmental pattern of glucocorticoid receptor expression was not altered by maternal separation in female rats. Thus, maternal separation may impair learning and memory in adult males by altering normal developmental changes in glucocorticoid receptor expression.

Neonatal maternal separation-induced changes in glucocorticoid receptor expression in posterior interpositus interneurons but not projection neurons predict deficits in adult eyeblink conditioning.

Neonatal maternal separation impairs adult eyeblink conditioning. This impairment is correlated with increases in adult glucocorticoid receptor (GR) expression in the posterior interpositus nucleus [A.A. Wilber, C. Southwood, G. Sokoloff, J.E. Steinmetz, C.L. Wellman, Neonatal maternal separation alters adult eyeblink conditioning and glucocorticoid receptor expression in the interpositus nucleus of the cerebellum, Developmental Neurobiology 67 (2007) 1751-1764], a key structure in the neural circuitry controlling eyeblink conditioning. To further localize this effect, we assessed adult eyeblink conditioning and GR expression in projection versus interneurons in the interpositus of rats that had undergone standard rearing or maternal separation (1h/day) on postnatal days 2-14. At 3 months of age, interpositus neurons were labeled with the retrograde tracer biotinylated dextran amine (BDA). After delay eyeblink conditioning, brains were processed immunohistochemically for GR and BDA labeling of interpositus neurons. GR expression was quantified in BDA-labeled and unlabeled neurons. Neonatal maternal separation impaired adult eyeblink conditioning. Control rats had significantly less GR expression in posterior interpositus BDA-unlabeled versus BDA-labeled neurons, but this difference was absent in maternally separated rats. While neonatal separation significantly increased GR expression in BDA-labeled and unlabeled posterior interpositus neurons, only GR expression in non-BDA-labeled neurons was associated with eyeblink conditioning. Thus, neonatal maternal separation may alter interneuronal modulation of interpositus output neurons, producing deficits in adult eyeblink conditioning.

Reverse microdialysis of a dopamine uptake inhibitor in the nucleus accumbens of alcohol-preferring rats: effects on dialysate dopamine levels and ethanol intake.

BACKGROUND: The mesolimbic dopamine (DA) system has been implicated in mediating the reinforcing actions of ethanol (EtOH). This study examines the effects of local perfusion of the DA uptake inhibitor GBR12909 (GBR) on (1) DA levels in the nucleus accumbens (NAc) and (2) EtOH drinking in alcohol-preferring rats. METHODS: Stable drinking of a 15% (v/v) EtOH solution (minimum of 0.75 g/kg body weight) was established in daily 1 hr limited access sessions. Rats were then implanted with bilateral guide cannulae aimed 4 mm above the NAc. After recovery from surgery, concentric microdialysis probes (2 mm dialysis membrane surface) were inserted into the NAc. Most placements were in the shell or overlapping both shell and core. Two days later, the probes were perfused at 1.0 microl/min with artificial cerebral spinal fluid (aCSF) for at least a 90 min washout period followed by collection of five basal samples over 150 min. Rats were then perfused with either aCSF alone or 10, 25, 100, or 200 microM of GBR for 240 min on the first day of microdialysis. During the last 60 min of the drug treatment phase, rats were given their scheduled access to 15% EtOH. All rats were then perfused with aCSF for the last 90 min of the experiment. The following day, the procedure was repeated, but animals that received aCSF on the first day were given a dose of GBR and rats given GBR on the first day received only aCSF. RESULTS: GBR perfusion increased extracellular NAc DA levels dose dependently to more than 800% of basal levels at 100 to 200 microM but failed to alter EtOH intake (p > 0.05, paired t test) at any concentration tested. Moreover, after 100 microM of GBR perfusion had terminated, the extracellular levels of DA in the NAc remained elevated for approximately 24 hr (790% of day 1 basal; p < 0.05). The increase in dialysate DA levels observed during GBR perfusion with 100 microM was significantly greater for EtOH-experienced rats than for EtOH-naïve rats [F(7,59) = 14.85, p < 0.0001, analysis of variance, Student-Newman-Keuls post hoc test]. CONCLUSIONS: The results suggest (1) that EtOH drinking experience induces neuroadaptations that increase DA release in the NAc, and (2) that additional elevation in synaptic levels of DA in the NAc does not influence the maintenance of ongoing alcohol drinking under scheduled access conditions in alcohol-preferring animals.