Molly M. Huntsman

BDNF mRNA expression is increased in adult rat forebrain after limbic seizures: temporal patterns of induction distinct from NGF.

We have localized brain-derived neurotrophic factor (BDNF) mRNA in rat brain and examined its regulation by seizure activity. In situ hybridization of BDNF 35S-cRNA most prominently labeled neurons in hippocampal stratum pyramidale and stratum granulosum, superficial olfactory cortex, pyramidal cell layers of neocortex, amygdala, claustrum, endopiriform nucleus, anterior olfactory nucleus, and ventromedial hypothalamus. Hybridization to BDNF mRNA was markedly increased in all of these regions after lesion-induced recurrent limbic seizures and within dentate gyrus granule cells following one electrically stimulated epileptiform afterdischarge. In contrast to seizure-elicited changes in nerve growth factor (NGF) mRNA expression, increases in BDNF mRNA occur in a greater number of different neuronal populations and develop several hours more rapidly in extrahippocampal loci. These results indicate that regulation by physiological activity may be an intrinsic property of this class of neurotrophic factor but that, in the recurrent seizure paradigm, different mechanisms mediate increased expression of mRNAs for BDNF and NGF outside hippocampus.

COMPARISON OF MAMMALIAN, CHICKEN AND XENOPUS BRAIN-DERIVED NEUROTROPHIC FACTOR CODING SEQUENCES

We have used the polymerase chain reaction (PCR) to amplify and clone coding sequences of the mature region of brain‐derived neurotrophic factor (BDNF) from monkey, rat, chicken and Xenopus genomic DNA. Consistent with previous reports, the predicted amino acid sequences obtained in this manner from monkey and rat were identical to other mammalian BDNF sequences. The chicken and Xenopus BDNF sequences are also highly conserved, but contain 7 and 8 amino, acid substitutions, respectively, compared to mammalian BDNF. Comparison of these sequences with the homologous NGF and NT3 coding regions provides further insight into amino acid residues that may be responsible for the different receptor specificities of these factors.

GABAB RECEPTOR GENE EXPRESSION IN MONKEY THALAMUS

Expression of γ‐amino butyric acid type B (GABAB) receptor gene transcripts was examined in the macaque monkey thalamus by in situ hybridization, using monkey‐specific cRNA probes. GABAB transcript expression was widespread and of much higher density in the dorsal thalamus than in the reticular nucleus and other parts of the ventral thalamus and was highest in the epithalamus. In the dorsal thalamus, highest mRNA levels were found in the anteroventral nucleus and in the parafascicular nucleus. Sensory relay nuclei showed moderate GABAB mRNA levels. Neurons of all sizes were labeled, suggesting expression in relay cells and interneurons, and there was no labeling of neuroglial cells. Following 10‐day periods of monocular deprivation, levels of GABAB mRNA were decreased in the deprived magno‐ and parvo‐cellular laminae of the dorsal lateral geniculate nuclei, indicating activity‐dependent regulation. High levels of GABAB receptors in the dorsal thalamus are likely to reflect the high density of synaptic inputs from the reticular nucleus while low expression in the reticular nucleus implies weak, GABAB‐mediated intrareticular inhibition. J. Comp. Neurol. 394:118–126, 1998.

Cell‐specific expression of type II calcium/calmodulin‐dependent protein kinase isoforms and glutamate receptors in normal and visually deprived lateral geniculate nucleus of monkeys

In situ hybridization histochemistry and immunocytochemistry were used to map distributions of cells expressing mRNAs encoding α, β, γ, and δ isoforms of type II calcium/calmodulin‐dependent protein kinase (CaMKII), α‐amino‐3‐hydroxy‐5‐methyl‐4‐isoxazoleproprionate (AMPA)/kainate receptor subunits, (GluR1–7), and N‐methyl‐D‐aspartate (NMDA) receptor subunits, NR1 and NR2A‐D, or stained by subunit‐specific immunocytochemistry in the dorsal lateral geniculate nuclei of macaque monkeys. Relationships of specific isoforms with particular glutamate receptor types may be important elements in neural plasticity. CaMKII‐α is expressed only by neurons in the S laminae and interlaminar plexuses of the dorsal lateral geniculate nucleus, but may form part of a more widely distributed matrix of similar cells extending from the geniculate into adjacent nuclei. CaMKII‐β, ‐γ, and ‐δ isoforms are expressed by all neurons in principal and S laminae and interlaminar plexuses. In principal laminae, they are down‐regulated by monocular deprivation lasting 8–21 days. All glutamate receptor subunits are expressed by neurons in principal and S laminae and interlaminar plexuses. The AMPA/kainate subunits, GluR1, 2, 5, and 7, are expressed at low levels, although GluR1 immunostaining appears selectively to stain interneurons. GluR3 is expressed at weak, GluR 6 at moderate and GluR 4 at high levels. NMDA subunits, NR1 and NR2A, B, and D, are expressed at moderate to low levels. GluR4, GluR6 and NMDA subunits are down‐regulated by visual deprivation. CaMKII‐α expression is unique in comparison with other CaMKII isoforms which may, therefore, have more generalized roles in cell function. The results demonstrate that all of the isoforms are associated with NMDA receptors and with AMPA receptors enriched with GluR4 subunits, which implies high calcium permeability and rapid gating. J. Comp. Neurol. 390:278–296, 1998.