Effect of treatment with the dihydropyridine-type calcium antagonist darodipine (PY 108-068) on the expression of calbindin D-28K immunoreactivity in the cerebellar cortex of aged rats

Effect of choline-containing phospholipids on brain cholinergic transporters in the rat

The influence of one week treatment with the choline-containing phospholipids cytidine-5'-diphosphocholine (CDP-choline) and choline alphoscerate (L-alpha-glyceryl-phosphorylcholine) at choline-equivalent doses (CDP-choline: 325 mg/kg/day; choline alphoscerate: 150 mg/kg/day) on vesicular acetylcholine transporter (VAChT), on choline transporter (CHT) and on acetylcholine (ACh) concentrations was investigated in rat frontal cortex, striatum and cerebellum. ACh was assayed by HPLC with electrochemical detection, VAChT by Western blot, ELISA and immunohistochemistry, CHT by Western blot and immunohistochemistry. After CDP-treatment, ACh levels were slightly increased in the frontal cortex, not substantially different in the striatum, and reduced significantly in the cerebellum compared to controls. Choline alphoscerate stimulated significantly the neurotransmitter concentration in the frontal cortex, however, the levels were similar to the controls in both the striatum and cerebellum. In comparison to the controls, VAChT expression following either CDP-choline or choline alphoscerate treatment, was enhanced greatly in the striatum and cerebellum. Also, ELISA measurements for VAChT showed significant increases in all choline alphoscerate treated brain areas. In contrast, in the CDP-choline treated rats the vesicular transporter amount was greater than the control only in the striatum. The cholinergic presynaptic transporters VAChT and CHT play a relevant role in sustaining new ACh synthesis and release. To sum up, CDP-choline and choline alphoscerate stimulated to a different extent the expression of VAChT and CHT primarily in a cognitive area such as frontal cortex. In the lack of novel therapeutic strategies, safe compounds developed since a long time such as the choline-containing phospholipids investigated would merit to be further investigated by new and adequate clinical studies. This for assessing their place if any in pharmacotherapy of dementia disorders characterized by diminished cholinergic tone.

Contribution of L‐type channels to Ca 2+ regulation of neuronal properties in early developing Purkinje neurons

Activity driven Ca2+ signaling is an important regulator of neuronal development. Early developing Purkinje neurons (postnatal day 5-7) prior to the stage of dendritic development express a somatic Ca2+ signaling pathway that is electrically driven and communicates information from the cell membrane to the cytosol and nucleus. In the current studies, we examined the properties and potential functional role of this pathway using acutely isolated Purkinje neurons from postnatal day 5-7 rat pups and brief K+ stimulation to activate the pathway. Results show that the amplitude of the nuclear Ca2+ signal increases as a function of the cytosolic Ca2+ signal but is larger than the cytosolic Ca2+ signal at strong K+ stimulations. Both L-type and P-type Ca2+ channels contribute to the Ca2+ signal. We also show using semiquantitative immunohistochemical methods that activation of this Ca2+ signaling pathway results in activation the transcription factor CREB and that L-type Ca2+ channels play a prominent role in this effect. The level of cfos, a transcription factor whose expression is regulated by CREB, was also increased by K+ stimulation. K+ stimulation also altered the level of the Ca2+ binding protein calbindin, an effect that involved L-type Ca2+ channels. The relationship between increases in Ca2+ and calbindin expression was bell-shaped, with high levels of Ca2+ decreasing calbindin expression. The level of the transmitter GABA was also increased by K+ stimulation but this effect was not dependent on L-type Ca2+ channels. Taken together, these results support a role for L-type channels in the phenotypic expression of Purkinje neuron properties during early development and suggest that the different activity patterns of early developing Purkinje neurons could be one mechanism for signaling the induction of specific genes through differences in cytosolic or nuclear Ca2+.

Age-related changes of muscarinic cholinergic receptor subtypes in the striatum of Fisher 344 rats

Striatum expresses a cholinergic system involved in the regulation of its activity and changes in striatal cholinergic receptors may be related to cognitive impairment. This study has investigated muscarinic cholinergic M1-M5 receptor subtype expression in striatum of Fischer 344 rats aged 6 (young), 15 (adult) and 22 months (senescent) to assess the contribution of different muscarinic cholinergic receptor subtypes in age-related changes of striatal cholinergic neurotransmission. Western blot analysis revealed the expression of the M1-M5 muscarinic receptor subtytpes in the striatum of rats of the three age groups investigated. Both radioligand binding assay and light microscope autoradiography showed in young rats a M4>M1>M2>M3>M5 rank order of receptor density. With the exception of M1 receptor, the density of which is similar in the dorsal (motor) and ventral (limbic) striatum, other receptor subtypes were more abundant in ventral than in dorsal striatum. M1 receptor expression was unchanged between young and adult rats and decreased in senescent animals both in dorsal and ventral striatum. In dorsal striatum M2 and M5 receptor expression did not show age-related changes, whereas in ventral striatum it was slightly decreased in adult rats compared to young or senescent cohorts. M3 receptor expression did not show age-related modifications, whereas a progressive age-related decrease of M4 receptor was found, both in dorsal and ventral striatum. These data indicate a heterogeneous response to age of different muscarinic receptor subtypes. Striatal cholinergic markers are thought to correlate with cognitive impairment in aged rats. In view of this, the identification of age-related changes of striatal muscarinic receptor subtypes may contribute to develop cholinergic strategies to counter cholinergic neurotransmission changes occurring with aging.

Effects of chronic nimodipine on working memory of old rats in relation to defects in synaptosomal calcium homeostasis

The present study was designed to investigate whether chronic (from 12 to 23 months of age) dietary treatment with the L-type Ca2+ channel blocker nimodipine (30 mg/kg body weight) enhances the cognitive behavior of aged animals and whether such a treatment would have long-term effects on the mechanisms of Ca2+ regulation in synaptic terminals from the aged rat brain. Cognitive behavior was evaluated in an 8-arm radial maze in 6 test series comprising a total of 105 test sessions, with intervals of no training between series. Nimodipine-treated rats performed better than vehicle-treated, aged-matched controls in all the test series, making more correct choices every time a new series was initiated. However, differences between nimodipine- and vehicle-treated rats were most remarkable in the last three test series, when the rats were 19 to 22 months. In these series 74% of the nimodipine-treated rats were able to perform the task in 4 to 9 test sessions whereas only 12%, 14% or none of the control rats learned the task. To study Ca2+ regulation in synaptosomes derived from cerebral cortex and hippocampus, we analyzed 45Ca2+ accumulation as well as the levels of the Ca2+-binding proteins calbindin-D28K and calreticulin by Western blotting. Nimodipine administration had no effect on hippocampal synaptosomes but increased the levels of calbindin-D28K and calreticulin in cerebral cortex preparations. These results indicate that chronic nimodipine treatment from 12 to 23 months of age prevents age-induced learning deficits without showing any signs of toxicity, and that these effects are associated with a small increase in the levels of synaptosomal Ca2+-binding proteins from cerebral cortex. The up-regulation of these proteins might provide a link between the long-term effects of nimodipine on gene expression and learning ability in old rats.

Calbindin D-28k immunoreactivity in the medial nucleus of the trapezoid body declines with age in C57BL/6, but not CBA/CaJ, mice

This study compared calbindin D-28k immunoreactivity in the medial nucleus of the trapezoid body (MNTB) in young (3-4 month old) and old (24-26 month old) CBA/CaJ mice, and young (3-4 month old), middle-aged (6.5-8.5 month old), and old (24-29 month old) C57BL/6 mice. C57BL/6 mice exhibit progressively more severe peripheral (sensorineural) hearing loss between 4 and 12 months of age, whereas CBA/CaJ mice show little change in peripheral sensitivity until very late in life. We obtained auditory brainstem response audiograms on all subject mice. Old CBA mice were selected for study whose audiograms matched those of young CBA and C57 controls. Middle-aged C57 mice showed elevated thresholds indicative of peripheral degeneration. Brain sections were reacted with anti-calbindin D-28k (CB). Staining patterns in Nissl and anti-CB material were characterized and cells were counted. We found no significant change in the number of CB+ cells or the total number of cells in the MNTB of old CBA mice compared to young controls. However, the mean number of CB+ cells decreased by 11% in middle-aged, and by 14.8% in old C57 mice. Since the decline in C57 mice was significant by 6.5-8.5 months of age, the decrease could be the consequence of a loss of input from the cochlear nucleus where cell numbers are known to decline by this age in this strain. The total number of neurons in MNTB assessed from Nissl material showed a more modest 7.1% decline with age in C57 mice, implying that the greater loss of CB immunoreactive cells with age cannot be completely attributed to a reduction in the total number of cells.

Age-related changes in calbindin D-28k and calretinin immunoreactivity in the inferior colliculus of CBA/CaJ and C57Bl/6 mice

This study examines calbindin D-28k and calretinin immunoreactivity in the inferior colliculus (IC) of young and old mice of two strains. The CBA/CaJ mouse maintains good hearing until very late in life, whereas the C57Bl/6 strain exhibits severe sensorineural hearing loss at an early age. Young and old mice of both strains were selected with matching auditory brainstem response audiograms and gap detection thresholds. Brain sections were reacted with anti-calbindin D-28k (CB) and anti-calretinin (CR). Staining patterns were characterized and cell counts performed. CB immunoreactivity was high only in the nucleus of the commissure (NCO); counts revealed a 22.3% decrease in the number of CB+ cells in old CBA mice and a 25.1% decrease in old C57 mice. Calretinin immunoreactivity was high in the pericentral regions of the IC, but the central nucleus was devoid of CR+ cells. The dorsal cortex, lateral nucleus, and NCO showed increases of 42.3, 49.0, and 61%, respectively, in the number of CR+ cells, but only in the old CBA mice. No significant change was observed in the old C57 mice. Whereas decreases in CB immunoreactivity are common with age, this study is the first to report an age-related increase in CR immunoreactivity in the auditory system. The increase in CR+ cells is a possible compensatory adaptation to the decrease in CB+ cells. That the number of CR+ cells remains constant with age in C57 mice suggests this compensation may depend upon stimulus-driven activity, but this requires further study.