Expression of the lacZ reporter gene in the rat basal forebrain, hippocampus, and nigrostriatal pathway using a nonreplicating herpes simplex vector.

We recently demonstrated the efficacy of a nonreplicating herpes simplex type 1 virus construct, employing the Moloney murine leukemia virus long terminal repeat promoter, in providing long-term expression of the lacZ gene in rat hippocampal neurons. We now report the utility of this construct in expressing the reporter gene in neurons of the basal forebrain and substantia nigra and examine the spread of the virus to other brain regions. Dorsal and ventrolateral hippocampal formation injection of the virus resulted in numerous beta-gal-expressing cells in the stratum pyramidale, stratum oriens, stratum lacunosum-moleculare, and stratum granulosum. Scattered cells of the medial septum/diagonal band were positively stained following direct injection into this region. More intense staining of the basal forebrain was observed following hippocampal injection as a result of retrograde transport of the virus as shown by PCR analysis of viral DNA. Hippocampal injection also resulted in positive cell staining in several other afferent projection nuclei, namely, the supramammillary bodies, dorsal and caudal linear raphe, and perirhinal/entorhinal cortex. Very few cells were labeled around injection sites in the striatum or substantia nigra. However, substantia nigra zona compacta cells were blue following striatal injection, as were pallidal neurons following nigral injection. These data demonstrate the feasibility of using this virus construct to express foreign genes such as neurotrophic factors in basal forebrain and substantia nigra neurons, taking advantage of retrograde transport of the virus to preserve local anatomy.