Although fluorescence microscopy has proven to be one of the most powerful tools in biology, its application to the intact animal has been limited to imaging several hundred micrometers below the surface. The rest of the animal has eluded investigation at the microscopic level without excising tissue or performing extensive surgery. However, the ability to image with subcellular resolution in the intact animal enables a contextual setting that may be critical for understanding proper function. Clinical applications such as disease diagnosis and optical biopsy may benefit from minimally invasive in vivo approaches. Gradient index (GRIN) lenses with needle-like dimensions can transfer high-quality images many centimeters from the object plane. Here, we show that multiphoton microscopy through GRIN lenses enables minimally invasive, subcellular resolution several millimeters in the anesthetized, intact animal, and we present in vivo images of cortical layer V and hippocampus in the anesthetized Thy1-YFP line H mouse. Microangiographies from deep capillaries and blood vessels containing fluorescein-dextran and quantum dot-labeled serum in wild-type mouse brain are also demonstrated.

Two methods are described for using the jellyfish green fluorescent protein (GFP) as a reporter gene for ion channel expression. GFP fluorescence can be used to identify the transfected cells, and to estimate the relative levels of ion channel expression, in cotransfection experiments. A GFP-NMDAR1 chimera can be constructed that produces a functional, fluorescent receptor subunit. These methods should facilitate studies of ion channel expression, localization, and processing.

Recent postmortem studies have suggested that reduced gamma-aminobutyric acid (GABA)ergic activity in limbic cortex may be one component to the pathophysiology of schizophrenia. This hypothesis has underscored the importance of knowing whether midbrain dopamine afferents interact extensively enough with inhibitory interneurons to suggest a direct functional relationship. Toward this end, a double immunofluorescence approach combined with confocal laser scanning microscopy has been used to localize dopamine and GABA simultaneously in rat medial prefrontal cortex. The results confirm studies from other laboratories showing a rich network of dopamine-immunoreactive fibers forming a gradient across the cortical laminae, with deeper layers having the highest density. When viewed with oil immersion optics, dopamine-immunoreactive fibers were frequently found to be in close apposition with GABA-immunoreactive cell bodies. The percentage of GABA-containing neurons showing such contacts was highest in layer VI (65%) and progressively decreased toward layer I (9%). Varicose regions of the dopamine fibers were typically present at the point of contact with a GABA-immunoreactive cell body. Using an immunoperoxidase technique to localize dopamine fibers and cresyl violet staining to visualize neurons simultaneously, two separate statistical analyses were performed to assess whether the frequency of contacts between dopamine fibers and cell bodies in general may be due to random effects. In layer VI, a high percentage of both pyramidal and nonpyramidal neurons were found to be in contact with dopamine varicosities (71% and 76%, respectively), but these were not significantly different from that observed for GABA-containing cells (65%) in double-immunofluorescence specimens. A Chi-square statistical test was used to compare the observed and predicted number of varicosities forming cell body contacts. This analysis indicated that the percentage of dopamine varicosities (30%) that form appositions with cell bodies is much greater than would be expected if these appositions were due to random effects (15%). Moreover, using an estimate of intensity for a stationary Poisson process, it was again found that random effects can not account for these interactions (P = 0.01). Taken together with earlier electron microscopic studies from other laboratories, the present findings support the idea that GABAergic interneurons have extensive interactions with dopamine varicosities. While these interactions are not unique to GABAergic cell bodies, they suggest that inhibitory interneurons can play a direct role in mediating the effects of midbrain dopamine afferents in rat medial prefrontal cortex.

A double immunofluorescence technique has been used to assess postnatal maturational changes in the extent to which dopamine-immunoreactive (DA-IR) varicose fibers form contacts with gamma-aminobutyric acid (GABA)-immunoreactive (IR) neuronal cell bodies in rat medial prefrontal cortex (mPFCx). Two separate measures of interaction, the percentage of GABA-IR cell bodies having DA-IR varicosities in apposition and the number of such profiles in contact with any given GABA-IR cell, were assessed. Between birth and adulthood, there was a progressive linear increase (r = 0.75, P < or = 0.0005) in the percentage of GABA-IR cell bodies having at least one DA-IR varicosity in apposition. While the number of varicosities in contact with any given GABA cell body showed very little change during the preweanling period, later during the postweanling interval, this parameter increased in a curvilinear fashion toward adult levels (r = 0.81, P < or = 0.0005). Taking together these latter two measures, an index of interaction was found to be 1.8 times higher when adult animals were compared to postweanling rats, and 2.5 times higher when compared to preweanling rats. Overall, these results are consistent with the view that there are late postnatal changes in the extent to which midbrain DA afferents interact specifically with GABAergic interneurons in rat mPFCx.

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