Marlene A. Wilson

The effects of chronic treadmill and wheel running on behavior in rats

In order to better understand the behavioral adaptations induced by physical activity, this set of experiments assessed the effects of two modes of running exercise on a battery of behavioral tests. The effects of 8 weeks of forced treadmill running and voluntary wheel running on behavior measures in the elevated plus maze, open field, social interaction and conditioned freezing paradigms were investigated. Eight weeks of treadmill running did not alter behavior in any test paradigm. Rats given unrestricted access to running wheels (WR) had a lower percent open arm time (6.0+/-2.3%) compared to locked wheel controls (LC) (20.7+/-5.7%) in the elevated plus maze. WR also showed decreased entries into center (0.2+/-0.2) and crossed fewer lines (61.0+/-14.9) in the open field compared to control groups. Both WR and LC groups showed increased social interaction; however, these differences are attributed to housing conditions. The effects of 4 weeks of wheel running on elevated plus maze and open field behavior were also investigated to address the possibility of a temporal effect of exercise on behavior. Four weeks of wheel running produced behavioral changes in the open field similar to those found at 8 weeks, but not in the elevated plus maze suggesting a temporal effect of wheel running on plus maze behavior. The behavioral adaptations found after 4 and 8 weeks of wheel running were not due solely to enriched environment and appear to be indicative of enhanced defensive behavior.

Influences of gender, gonadectomy 5 and estrous cycle on GABA/BZ receptors and benzodiazepine responses in rats

Benzodiazepines (BZ) and steroid hormone derivatives can potentiate the inhibitory actions of GABA through interactions with the GABAA/BZ/chloride ionophore complex. The present study examines whether the in vivo hormone milieu of rats modulates GABA/BZ receptors and/or benzodiazepine responses. The influences of gender, estrous cycle, and the diminution of steroid levels on GABA/BZ receptors and BZ anticonvulsant responses were tested by comparing these parameters in groups of intact male, intact female, orchidectomized, and ovariectomized rats. The hormonal milieu appears to modulate the GABA recognition site and possibly GABA-related responses in rats. This is evidenced by the decrease in cortical GABAA receptor affinity seen in females compared with other hormone groups and the gender-related difference observed in susceptibility to seizures induced by the GABA antagonist bicuculline. In cycling females, high circulating levels of progesterone were correlated with heightened seizure thresholds, suggesting that progestins serve a protective role in the control of seizure activity. Although a gender-related difference in cortical BZ binding affinity was observed, BZ receptor parameters in several other brain areas and BZ anticonvulsant responses were unaffected by physiological fluctuations in gonadal hormones.

Anxiolytic effects of diazepam and ethanol in two behavioral models: comparison of males and females.

The present study compared the anxiolytic effects of the benzodiazepine agonist diazepam and ethanol in adult male and female rats. Varying doses of diazepam (1-3 mg/kg) or ethanol (0.5-2.0 g/kg) were tested using both the elevated plus maze and defensive prod-burying models. Two time points following ethanol administration (10 and 30 min) were tested in the plus maze. Sex differences were seen in some anxiety-related behaviors, with females showing greater open arm time and reduced burying behavior than males. Although this suggests females displayed less anxiety-like behavior than males, the differences in the plus maze were not observed in all testing situations. Both diazepam and ethanol dose-dependently increased open arm times in the plus maze and reduced burying behavior in the defensive prod-burying task. The parallel nature of the dose-response curves suggests that both diazepam and ethanol have similar anxiolytic effects in males and females. No sex differences were seen in the brain levels of diazepam-like activity or blood alcohol levels with these treatments. A greater corticosterone response was observed in females than males with these two behavioral tests, but neither diazepam nor ethanol decreased this response. These results suggest a dissociation between the anxiety-reducing influences of these compounds and the changes in stress-related endocrine responses.

Integrin-mediated collagen gel contraction by cardiac fibroblasts. Effects of angiotensin II.

Angiotensin II (Ang II), a vasoactive octapeptide, has been implicated in cardiac growth and the development of hypertrophy and fibrosis secondary in hypertensive disease. These consequences of Ang II imply an effect on the function and morphology of cardiac interstitial cells (fibroblasts). The present investigation was designed to (1) determine whether neonatal heart fibroblasts (NHFs) possess functional Ang II receptors on their plasma membrane and (2) examine the effects of Ang II on NHFs in vitro using three- and two-dimensional (3D and 2D, respectively) cultures. Several analytic techniques were used to test the specific questions of the present study. Since cardiac fibroblast phenotype can be influenced by culture conditions, both 2D and 3D cultures were used in the present investigations. Reverse-transcriptase polymerase chain reaction and radioligand binding analysis were used to test for the presence of Ang II receptors on NHFs. Both revealed that NHFs in 2D culture possess Ang II receptor mRNA and Ang II receptors. When isolated NHFs were cultured in 3D collagen gels and treated with Ang II, gel contraction was stimulated by NHFs. This effect was attenuated by the specific Ang II receptor antagonist [Sar1,Ala8]Ang II. Ang II-stimulated gel contraction was completely inhibited by extracellular matrix receptor (beta 1-integrin) antibodies (P < .05), supporting previous studies indicating that collagen gel contraction is mediated via the integrins. Immunofluorescent staining was used to test the localization of cell-surface integrins. A more intense staining pattern for beta 1-integrin in Ang II-treated versus control cells was observed.(ABSTRACT TRUNCATED AT 250 WORDS)

SEX DIFFERENCES IN HIPPOCAMPAL SLICE EXCITABILITY: ROLE OF TESTOSTERONE

In vivo fluctuations in gonadal hormones alter hippocampal excitability and modulate both physiological and pathological hippocampal processes. To assess hormonal effects on excitability within a functional hippocampal circuit, extracellular CA1 field responses were compared in slices from intact male, intact female, orchidectomized male, and ovariectomized female rats. Secondly, the effects of in vitro applications of 17-beta estradiol, progesterone, or testosterone on baseline excitability of slices from gonadectomized rats were assessed versus pre-hormone baseline measures. Finally, using the in vitro kindling model of slice epileptogenesis, steroid hormone effects on interictal-like activity were also examined. Significant sex differences in excitatory postsynaptic potential amplitude were observed, with slices from males having larger excitatory postsynaptic potential amplitudes than those from females. Gonadectomy significantly decreased excitatory postsynaptic potential amplitude in slices from male rats. Slices from gonadectomized male and female rats also showed a decreased dendritic excitatory postsynaptic potential slope relative to slices from intact male and females rats. In vitro application of testosterone significantly increased excitatory postsynaptic potential amplitudes in slices from both orchidectomized males and ovariectomized females and the population spike amplitude of slices from ovariectomized females. Following in vitro kindling, slices from intact males showed greater spontaneous burst rates than slices from intact females, further suggesting an excitatory effect of testosterone. These results suggest: (1) a sex difference in the level of baseline excitability between slices from intact males and females as measured by excitatory postsynaptic potential amplitudes, (2) testosterone has excitatory effects on baseline physiology and kindled hippocampal responses, and (3) slices from males show a greater level of excitability than those from females in the in vitro kindling model.

Sex differences in GABA/benzodiazepine receptor changes and corticosterone release after acute stress in rats

Since many hormonal indices of stress responsiveness are sexually dimorphic in rats, we examined sex differences and the effects of gonadectomy on the stress-related changes in GABAA/benzodiazepine receptors in rats. Intact or ovariectomized female rats displayed a markedly greater corticosterone response and a more pronounced increase in benzodiazepine receptors than males (intact or orchidectomized) after acute handling or swim stress. Swim stress increased benzodiazepine receptor density without modifying affinity in cortex, hippocampus, and hypothalamus. Corticosterone treatment induced benzodiazepine receptor levels comparable to those seen after swim stress in all hormone groups. Handling stress also enhanced cortical low-affinity GABAA receptor levels in males and ovariectomized females. Both GABA and benzodiazepine receptor levels were positively correlated with circulating corticosterone levels in female, but not male, groups. GABA/benzodiazepine coupling was unaffected by stress or hormonal status. These sexual dimorphisms in hormonal responses to stress may help elucidate the causes and consequences of stress-induced changes in the GABAA/benzodiazepine receptor complex.

Effects of altered amygdalar neuropeptide Y expression on anxiety-related behaviors

Neuropeptide Y (NPY) decreases anxiety-related behaviors in various animal models of anxiety. The purpose of the present study was to examine the role of the amygdalar NPY system in anxiety-related responses in the elevated plus maze. The first experiment determined if herpes virus-mediated alterations in amygdalar NPY levels would alter anxiety-related behaviors in the elevated plus maze. Viral vectors encoding NPY, NPY antisense, or LacZ (control virus) were bilaterally injected into the amygdala, and 4 days postinjection, rats were tested in the elevated plus maze test. NPY-like immunoreactivity (NPY-ir) was measured in the amygdala of these rats. In rats injected with the viral vector encoding NPY, reduced anxiety-related behaviors in the elevated plus maze accompanied by moderate increases in NPY-ir were detected compared to NPY-antisense viral vector-treated subjects. Elevated plus maze behavior did not differ compared to LacZ-treated controls. NPY overexpression at this time point was also suggested by enhanced NPY mRNA expression seen in the amygdala 4 days postinjection using real-time polymerase chain reaction analysis. Experiment 2 was conducted to provide further evidence for a role of amygdalar NPY in regulating anxiety-related behaviors in the elevated plus maze test. The nonpeptide NPY Y1 receptor antagonist, BIBP 3226 (1.5 μg/μl), was bilaterally injected into the amygdala and rats were tested in the elevated plus maze test. Rats receiving BIBP 3226 exhibited increased anxiety-related behaviors in this test. The results of these experiments provide further support for the role of amygdalar NPY in anxiety-related behaviors.

Increased open field locomotion and decreased striatal GABAA binding after activity wheel running.

Open-field behavior has been used to model reductions in anxiety-related behaviors in the rat after chronic physical activity. Plausible mechanisms for the increased open field locomotion observed after physical activity have not been studied. Open field locomotion is decreased by gamma-aminobutyric acid (GABA) and its agonists, and increased by GABA antagonists, in the ventral striatum. Hence, we tested the hypothesis that increased open field locomotion following chronic physical activity would be accompanied by a decrease in the number of GABAA receptors in the corpus striatum. Young (approximately 55 days) male Sprague-Dawley rats (N = 24) were randomly assigned to three conditions: 24-h access to an activity wheel (AW), running for 1 h without shock 6 days/week on a motorized treadmill (TM), or sedentary control (C). Open field locomotion (total and center squares traversed), defecation, and urination were assessed on each of 3 consecutive days prior to and again after 8 weeks of physical activity. Open field locomotion (total and center squares) increased after activity wheel running, decreased after treadmill training, and did not change for control animals. GABAA receptor density indicated by [3H] bicuculline binding (fmol/mg) was lower for activity wheel animals compared with treadmill animals and controls. GABA concentration (mumol/g) was not different between activity wheel and treadmill groups but was higher for both groups contrasted with controls. Our findings of decreased GABAA density in the corpus striatum concomitant with an increase in open field locomotion are consistent with an anxiolytic effect of chronic activity wheel running.

Influence of gender and brain region on neurosteroid modulation of GABA responses in rats

Neuroactive steroid derivatives of progesterone, testosterone and glucocorticoids can alter physiological responses to gamma-aminobutyric acid (GABA), apparently through direct, non-steroid receptor mechanisms. The present study examined gender-related differences and regional variations in the ability of tetrahydrodeoxycorticosterone (THDOC), 3alpha-hydroxy-5alpha-pregnan-20-one (3alpha-5alpha-THP, tetrahydroprogesterone), androsterone, and dihydroandrosterone (DHA) to alter physiological GABA responses. Steroid modulation of GABA-activated 36chloride influx into microsac preparations from cortex, hippocampus, amygdala, cerebellum and hypothalamus-preoptic area in adrenalectomized-gonadectomized rats of both sexes were tested. The effects of THDOC and 3alpha-5alpha-THP were also examined in groups of intact male and female rats. All four steroids increased GABA-activated chloride influx, although the maximal enhancement in GABA responses differed significantly among brain regions. The rank order of maximal THDOC and 3alpha-5alpha-THP effects was hippocampus > cortex approximately amygdala > hypothalamus-preoptic area approximately cerebellum. Regional differences in potentiation of GABA responses were seen with androsterone, but not dihydroandrosterone. The rank order of androgenic potentiation of GABA responses was amygdala approximately hippocampus > cortex approximately HPA > cerebellum. Slight gender-related differences in responses to steroids were seen with THDOC, with males showing greater maximal enhancement of GABA responses with THDOC than females in the amygdala and hypothalamus-preoptic area. Since sex differences were observed with the glucocorticoid derivative THDOC, but not the progesterone derivative 3alpha-5alpha-THP or androgenic steroids, it appears neuroactive steroid modulation of GABA responses can be differentially affected by the hormonal milieu in a regionally-specific manner.

Hippocampal Insulin Resistance Impairs Spatial Learning and Synaptic Plasticity

Insulin receptors (IRs) are expressed in discrete neuronal populations in the central nervous system, including the hippocampus. To elucidate the functional role of hippocampal IRs independent of metabolic function, we generated a model of hippocampal-specific insulin resistance using a lentiviral vector expressing an IR antisense sequence (LV-IRAS). LV-IRAS effectively downregulates IR expression in the rat hippocampus without affecting body weight, adiposity, or peripheral glucose homeostasis. Nevertheless, hippocampal neuroplasticity was impaired in LV-IRAS–treated rats. High-frequency stimulation, which evoked robust long-term potentiation (LTP) in brain slices from LV control rats, failed to evoke LTP in LV-IRAS–treated rats. GluN2B subunit levels, as well as the basal level of phosphorylation of GluA1, were reduced in the hippocampus of LV-IRAS rats. Moreover, these deficits in synaptic transmission were associated with impairments in spatial learning. We suggest that alterations in the expression and phosphorylation of glutamate receptor subunits underlie the alterations in LTP and that these changes are responsible for the impairment in hippocampal-dependent learning. Importantly, these learning deficits are strikingly similar to the impairments in complex task performance observed in patients with diabetes, which strengthens the hypothesis that hippocampal insulin resistance is a key mediator of cognitive deficits independent of glycemic control.