Age-related changes in the cholinergic components within the central nervous system of CW1 female mice. I. Structural analysis

Trans-inhibition of axon terminals underlies competition in the habenulo-interpeduncular pathway

Survival of animals is dependent on the correct selection of an appropriate behavioral response to competing external stimuli. Theoretical models have been proposed and underlying mechanisms are emerging to explain how one circuit is selected among competing neural circuits. The evolutionarily conserved forebrain to midbrain habenulo-interpeduncular nucleus (Hb-IPN) pathway consists of cholinergic and non-cholinergic neurons, which mediate different aversive behaviors. Simultaneous calcium imaging of neuronal cell bodies and of the population dynamics of their axon terminals reveals that signals in the cell bodies are not reflective of terminal activity. We find that axon terminals of cholinergic and non-cholinergic habenular neurons exhibit stereotypic patterns of spontaneous activity that are negatively correlated and localize to discrete subregions of the target IPN. Patch-clamp recordings show that calcium bursts in cholinergic terminals at the ventral IPN trigger excitatory currents in IPN neurons, which precede inhibition of non-cholinergic terminals at the adjacent dorsal IPN. Inhibition is mediated through presynaptic GABA_B receptors activated in non-cholinergic habenular neurons upon GABA release from the target IPN. Together, the results reveal a hardwired mode of competition at the terminals of two excitatory neuronal populations, providing a physiological framework to explore the relationship between different aversive responses.

Neuroprotective actions of estradiol and novel estrogen analogs in ischemia: translational implications

This review highlights our investigations into the neuroprotective efficacy of estradiol and other estrogenic agents in a clinically relevant animal model of transient global ischemia, which causes selective, delayed death of hippocampal CA1 neurons and associated cognitive deficits. We find that estradiol rescues a significant number of CA1 pyramidal neurons that would otherwise die in response to global ischemia, and this is true when hormone is provided as a long-term pretreatment at physiological doses or as an acute treatment at the time of reperfusion. In addition to enhancing neuronal survival, both forms of estradiol treatment induce measurable cognitive benefit in young animals. Moreover, estradiol and estrogen analogs that do not bind classical nuclear estrogen receptors retain their neuroprotective efficacy in middle-aged females deprived of ovarian hormones for a prolonged duration (8weeks). Thus, non-feminizing estrogens may represent a new therapeutic approach for treating the neuronal damage associated with global ischemia.

Morphological alterations in the hippocampus following hypobaric hypoxia

1. The morphological consequences of hypobaric hypoxia, exposure to reduced pressure atmospheres, were examined in the hippocampus of male Fischer 344 rats. Severe chronic hypoxia can produce permanent neuronal damage with hippocampal structures being especially vulnerable. 2. Hippocampal morphology was studied using histological observations after a 4 day exposure to sea level, 3500 m, or 6400 m. Two groups tested at 6400 m were sacrificed at different intervals following exposure, 72 and 144 h, to examine the effect of post-exposure time on neuronal damage. 3. Histological damage was observed in rats' brains following exposure to altitude, with cell degeneration and death increasing as altitude increased. In addition, it was found that the longer the time following exposure before sacrifice, the more noticeable the damage, suggesting delayed neurotoxicity. Increases in the number of damaged cells following altitude were significant for the CA3 region of one 6400 m group; however, other differences did not reach statistical significance. Rats exposed to altitude for 4 days ate less and lost significantly more weight than did animals at sea level. 4. It appears that 4 days of exposure to altitudes less than or equal to 6400 m does produce changes in the CA3 subfield, but the damage is different than that seen with other models of non-transient ischemia.

Suppression of age-related changes in mouse hippocampal CA3 nerve cells by a free radical scavenger

This study was designed to evaluate the relationship between oxygen free radicals and age-related morphological changes in hippocampal nerve cells using K-7259 (N,N' bis[4-(3,4,5-trimethoxyphenyl)butyl] homopiperazine dihydrochloride), a known neuro-protective agent. A chemiluminescence assay has shown that this agent is a potent free radical scavenger with an IC50 of 1.6 x 10(-5)M. Mice fed diets containing 10, 20, 40 mg/kg/day of K-7259, for periods ranging from 25 to 40 or 50 weeks of age were used as test groups, and 10-, 20-, 30-, 40-, and 50-week-old mice fed a standard diet were used as controls. We measured the number and area of pyramidal nerve cells within a defined frame in the hippocampal CA3 field using an image analyzer and the density of nerve cells by the disector method. These values decreased gradually in controls as expected, and the number and area yielded a significant difference between control mice at the ages of 10 and 30 weeks. As compared with the corresponding controls, all test groups had greater cell numbers (statistical significance at 40 weeks in the 40 mg/kg/day group) and density, while cell areas were greater in all but a 10 mg/kg/day group (statistical significance at 50 weeks). In summary, the free radical scavenger K-7259 forestalled an age-related decrease in the number and size of hippocampal CA3 nerve cells, thus suggesting that free radicals play an important role in the cellular morphological changes which appear with age.

Aging does not alter the binding characteristics to voltage dependent calcium channels in the brain of CW1 mice

Structural age-related changes in cholinergic regions within the central nervous system of CW1 mice have been described previously. Since elevated calcium concentration has been suggested to play a role in the brain aging processes, the possible involvement of voltage dependent calcium channels in this degeneration was investigated. The binding characteristics of the calcium channel antagonist [3H](+)PN 200-110 to brains of aged CW1 mice were studied. This ligand exhibited high affinity binding (Kd values in the range of 50-70 pM) to a single type of sites with a density (Bmax) of 150-200 fmol/mg protein. No significant differences were observed between the binding parameters measured in young (3 months), mid-aged (9 and 15 months) and old (20 months) mice. Autoradiographic study confirmed these results and extended them to specific brain regions. It is concluded that age-dependent degeneration processes, observed histologically in specific brain regions of these mice, are probably not related to alterations in voltage-dependent calcium channels.