This study describes a method for amplifying heterogeneous populations of RNA from limited quantities of cDNA, which is useful for cloning and analyzing low-abundance messenger RNAs in the brain. The method involves using a synthetic oligonucleotide containing the T7 RNA polymerase promoter sequence to prime cDNA synthesis, followed by T7 RNA polymerase-mediated transcription to generate amplified antisense RNA (aRNA). This technique allows for up to 80-fold molar amplification from nanogram quantities of cDNA, producing aRNA with a size distribution similar to the parent cDNA and showing sequence heterogeneity. Specific messages for moderate-abundance mRNAs for actin and guanine nucleotide-binding protein (G-protein) α subunits have been detected in the amplified material. Additionally, sequences for cyclophilin have been detected in aRNA derived from single cerebellar tissue sections, and cDNA derived from a single cerebellar Purkinje cell has been amplified and yields material that hybridizes to cognate whole RNA and mRNA but not to Escherichia coli RNA. The diversity of neuronal phenotypes presents a challenge for studying gene regulation in the brain. While in situ hybridization and in situ transcription can assess mRNA levels in selected brain regions, identifying and cloning novel regulated messages from discrete neuronal populations remains difficult. PCR is a powerful method for amplifying rare DNA species but requires sequence information for primer synthesis, limiting its general applicability. Modified PCR strategies have been implemented to improve the range of cDNAs that can be cloned with PCR, but issues such as low fidelity of Taq polymerase and difficulty transcribing sequences longer than 3 kb limit its usefulness. The described technique allows for the amplification of broad classes of cDNAs by incorporating a T7 RNA polymerase promoter into each cDNA molecule through priming with a synthetic oligonucleotide. After synthesis of double-stranded cDNA, T7 RNA polymerase is used to transcribe antisense RNA from the cDNA template, resulting in amplified antisense RNA (aRNA) that can serve as starting material for cloning procedures using random primers. The study characterizes aRNA generated from whole cerebellum, cerebellar tissue sections, and individual Purkinje cells and discusses possible applications of this technique. The results show that aRNA produced from total cerebellar RNA has a size distribution similar to the parent cDNA and shows sequence heterogeneity. The aRNA also shows a higher affinity for cognate species RNA and is representative of the parent cDNA in terms of abundance. The technique is useful for studying neural gene expression, particularly for identifying mRNAs that vary with arousal state, behavior, drug treatment, and development. The method allows for the amplification of low-abundance mRNAs from small brain nuclei and may facilitate the cloning of important low-abundance messages. The study also discusses potential applications of this technology, including the use of aRNA as anThis study describes a method for amplifying heterogeneous populations of RNA from limited quantities of cDNA, which is useful for cloning and analyzing low-abundance messenger RNAs in the brain. The method involves using a synthetic oligonucleotide containing the T7 RNA polymerase promoter sequence to prime cDNA synthesis, followed by T7 RNA polymerase-mediated transcription to generate amplified antisense RNA (aRNA). This technique allows for up to 80-fold molar amplification from nanogram quantities of cDNA, producing aRNA with a size distribution similar to the parent cDNA and showing sequence heterogeneity. Specific messages for moderate-abundance mRNAs for actin and guanine nucleotide-binding protein (G-protein) α subunits have been detected in the amplified material. Additionally, sequences for cyclophilin have been detected in aRNA derived from single cerebellar tissue sections, and cDNA derived from a single cerebellar Purkinje cell has been amplified and yields material that hybridizes to cognate whole RNA and mRNA but not to Escherichia coli RNA. The diversity of neuronal phenotypes presents a challenge for studying gene regulation in the brain. While in situ hybridization and in situ transcription can assess mRNA levels in selected brain regions, identifying and cloning novel regulated messages from discrete neuronal populations remains difficult. PCR is a powerful method for amplifying rare DNA species but requires sequence information for primer synthesis, limiting its general applicability. Modified PCR strategies have been implemented to improve the range of cDNAs that can be cloned with PCR, but issues such as low fidelity of Taq polymerase and difficulty transcribing sequences longer than 3 kb limit its usefulness. The described technique allows for the amplification of broad classes of cDNAs by incorporating a T7 RNA polymerase promoter into each cDNA molecule through priming with a synthetic oligonucleotide. After synthesis of double-stranded cDNA, T7 RNA polymerase is used to transcribe antisense RNA from the cDNA template, resulting in amplified antisense RNA (aRNA) that can serve as starting material for cloning procedures using random primers. The study characterizes aRNA generated from whole cerebellum, cerebellar tissue sections, and individual Purkinje cells and discusses possible applications of this technique. The results show that aRNA produced from total cerebellar RNA has a size distribution similar to the parent cDNA and shows sequence heterogeneity. The aRNA also shows a higher affinity for cognate species RNA and is representative of the parent cDNA in terms of abundance. The technique is useful for studying neural gene expression, particularly for identifying mRNAs that vary with arousal state, behavior, drug treatment, and development. The method allows for the amplification of low-abundance mRNAs from small brain nuclei and may facilitate the cloning of important low-abundance messages. The study also discusses potential applications of this technology, including the use of aRNA as an