FG7142 causes opposite changes in [3H]GABA release from nigrocollicular regions

Voluntary exercise offers anxiolytic potential and amplifies galanin gene expression in the locus coeruleus of the rat

Although exercise improves anxiety in humans, it is controversial whether exercise is anxiolytic in rodents. We tested the hypothesis that stress influences the effect of exercise on anxiety-like and defensive behaviors. To explore the neurobiological mechanisms of exercise, we also examined whether exercise alters gene expression for the stress-related peptide galanin. Rats were housed in the presence or absence of a running wheel for 21 d. A subset of these rats were (1) not injected or received a single high, dose of the β-carboline FG7142 (inverse agonist at the benzodiazepine receptor site) immediately prior to testing or (2) were injected repeatedly with vehicle or FG7142 during the last 10d of exercise. On day 22, anxiety-like and defensive behaviors were measured in the elevated plus maze, shock probe defensive burying, and defensive withdrawal tests. Locus coeruleus prepro-galanin mRNA was measured by in situ hybridization. Exercise and sedentary rats that were not injected exhibited similar behavior in all tests, whereas FG7142 injected immediately prior to the test battery produced intense avoidance and immobility consistent with an anxiety-like response. However, exercise produced anxiolytic-like and active defensive behaviors in the test battery relative to the sedentary condition in rats injected repeatedly with vehicle or FG7142. Exercise also increased prepro-galanin mRNA in the locus coeruleus relative to sedentary controls. These data suggest that the emergence of enhanced adaptive behavior after chronic voluntary exercise is influenced by stress. Our data support a role for galanin in the beneficial consequences of wheel running.

Endogenous GABA release is reduced in the striatum of cocaine-sensitized rats

The magnitude of behavioral sensitization to cocaine is correlated with decreased striatal GABA(A) receptor function. We examined whether GABA release from striatal slices is also altered in cocaine-treated rats. Behavioral sensitization was measured in rats receiving either saline or cocaine (15 mg kg(-1)) daily for 14 days. Cocaine-treated rats showed a significant increase in locomotion and stereotypy over days. Potassium-stimulated endogenous GABA release was measured from superfused striatal slices of these rats. GABA release was significantly decreased in cocaine-treated rats. However, striatal slices preloaded with [(3)H]GABA exhibited a slight but significant increase in release after cocaine sensitization. Similar treatment with a nonsensitizing dose of cocaine (7.5 mg kg(-1)) did not change endogenous GABA release. Saline- and cocaine-treated rats showed no differences in striatal glutamic acid decarboxylase activity at either a saturating or K(m) concentration of glutamate. Therefore, the decrease in endogenous GABA release is not due to a decrease in GABA synthesis, but may reflect changes in GABA storage pools. These data are consistent with an overall decrease in GABA transmission, both pre- and postsynaptically, in the striatum of sensitized rats, which could contribute to enhanced striatal output and behavioral sensitization.

Cytoarchitecture of the substantia nigra pars lateralis in the opossum (Didelphis virginiana): a correlated light and electron microscopic study

BACKGROUND

The substantia nigra has been divided into three subdivisions. However, the cytoarchitecture of one of these subdivisions, the pars lateralis (SNl), has not been previously examined in detail at the light and electron microscopic levels in any species. In the adult opossum, the three nigral subdivisions can be easily distinguished as distinct, rostrocaudally oriented cell groups separated by neuron-free zones. Thus it was possible to determine the boundaries of the SNl unambiguously. This report covers the results of an examination of the morphology and organization of the SNl in the opossum.

METHODS

Material from 13 opossums was used for this study. Eight of the animals had been previously stained for Nissl substance (n = 4) or impregnated by the Golgi technique (n = 4). The remaining five animals were prepared for electron microscopic studies using standard procedures.

RESULTS

Two cell types were identified on the basis of morphological differences, small and medium-large neurons. Small neurons (10-18 microns long axis) have large nuclei with moderate amounts of heterochromatin and a thin rim of cytoplasm. They have long (up to 500 microns), spine-free dendrites. Medium-large neurons (18-54 microns long axis) have rounded nuclei with electron-lucent nucleoplasm. Few indentations of the nuclear envelope were observed. The surrounding cytoplasm has dense arrays of organelles. Nissl bodies are particularly prominent in the form of pyramids with their bases at juxtanuclear positions and their apices directed toward emerging dendrites. Dendrites of medium-large neurons are long (some > 1 mm in length), are primarily oriented in the frontal plane, and extend along the dorsal surface of or into the cerebral peduncle. Some cells have dendrites that are moderately spinous, whereas other neurons possess sparsely spinous dendrites. Relatively few synaptic profiles are observed to contact somata and proximal dendrites.

CONCLUSION

This report provides added morphological support for the idea that the SNl is a distinct subdivision of the substantia nigra, a distinction previously made on the basis of the physiologically characterized relationship between the lateral substantia nigra and orienting behaviors and seizure-related function.