Changes in hypothalamic calmodulin concentration induced by perinatal hormone manipulation in the rat

Role of the neurogranin concentrated in spines in the induction of long-term potentiation

Synaptic plasticity in CA1 hippocampal neurons depends on Ca2+ elevation and the resulting activation of calmodulin-dependent enzymes. Induction of long-term depression (LTD) depends on calcineurin, whereas long-term potentiation (LTP) depends on Ca2+/calmodulin-dependent protein kinase II (CaMKII). The concentration of calmodulin in neurons is considerably less than the total concentration of the apocalmodulin-binding proteins neurogranin and GAP-43, resulting in a low level of free calmodulin in the resting state. Neurogranin is highly concentrated in dendritic spines. To elucidate the role of neurogranin in synaptic plasticity, we constructed a computational model with emphasis on the interaction of calmodulin with neurogranin, calcineurin, and CaMKII. The model shows how the Ca2+ transients that occur during LTD or LTP induction affect calmodulin and how the resulting activation of calcineurin and CaMKII affects AMPA receptor-mediated transmission. In the model, knockout of neurogranin strongly diminishes the LTP induced by a single 100 Hz, 1 s tetanus and slightly enhances LTD, in accord with experimental data. Our simulations show that exchange of calmodulin between a spine and its parent dendrite is limited. Therefore, inducing LTP with a short tetanus requires calmodulin stored in spines in the form of rapidly dissociating calmodulin-neurogranin complexes.

Microarray profiling of gene expression patterns in adult male rat brain following acute progesterone treatment

Progesterone can influence various behaviors in adult male rats, however, little is known about which particular genes are regulated by progesterone in the male rat brain. Using focused microarray technology, we where able to define a subset of genes that are responsive to progesterone. Nylon membrane-based cDNA microarrays were used to profile gene expression patterns in the preoptic area/mediobasal hypothalamus (POA/MBH) of male rat brain 7 h following a single injection of progesterone. RNA was isolated from the brains of 6 male rats injected with progesterone and 6 male rats injected with sesame oil. Next, we hybridized the RNA from each animal to individual cDNA microarrays that contained more than 100 target genes, all of which are involved in cAMP and or calcium signaling pathways. Direct side-by-side comparison of all 12 arrays revealed differences in the expression patterns of 12 different genes. We confirmed the data gathered from the arrays on 4 different genes using Real-Time PCR. These data begin to outline the important role played by progesterone in mediating changes in gene expression within the male brain.

Asymmetric calmodulin distribution in the hypothalamus: role of sexual differentiation in the rat

The Ca2+/calmodulin (CaM) system plays important roles both in hypothalamic sexual differentiation and in the progesterone-induced facilitation of lordosis behavior in the adult rat. We recently showed sex-dependent differences in rat hypothalamic CaM levels, both in newborn and in adult animals. Here, we evaluated the presence of left-right hypothalamic asymmetries in CaM concentration in male and female rats, as well as the changes induced on these parameters by neonatal (1 h after birth) subcutaneous administration of tamoxifen (200 microg/rat) or testosterone (30 microg/rat). CaM was measured by RIA in each half of the hypothalamus (at 2, 6, 12, and 24 h and at 90 days after birth) in both control and treated animals. In untreated young rats (2-24 h after birth), CaM concentration was significantly higher in the right half of the hypothalamus of males, whereas in females, it was higher in the hypothalamic left half. Treatment of females with testosterone or tamoxifen to males, consistently reversed these results. In the hypothalamus of treated animals, we found higher CaM levels in the left half of males, as well as in the right half of females. In control adult females, CaM concentration was also higher in the left half of the hypothalamus, as it was in the right half of adult males. However, this asymmetry was lost after neonatal hormone manipulation. These results reinforce the role of CaM in the development of sex-related hypothalamic functions.