P-glycoprotein (P-gp/ABCB1), multidrug resistance associated protein 1 (MRP1/ABCC1), and breast cancer resistance protein (BCRP/ABCG2) are plasma membrane efflux pumps that limit the intracellular uptake and retention of numerous lipophilic, amphipathic xeno- and endobiotics. Little is known about the neonatal and developmental expression of P-gp/ABCB1, MRP1/ABCC1, and BCRP/ABCG2 in the human central nervous system (CNS), therefore post-mortem CNS tissue from infants born at 22 (0/7)-42 (0/7) weeks of gestation and adults was immunostained to determine their ontogeny and cellular localization. P-gp/ABCB1 immunostaining was observed in microvessel endothelial cells as early as 22 (0/7) weeks, increasing in prevalence and intensity with maturation, and later in gestation in large pyramidal neurons. MRP1/ABCC1 immunostaining was prominent early in the choroid plexus and ventricular ependyma, and noted later in large pyramidal neurons. BCRP/ABCG2 expression was limited to microvessel endothelial cells. P-gp/ABCB1, MRP1/ABCC1 and BCRP/ABCG2 in adult brain matched term newborn CNS but with more intense immunostaining. We conclude that P-gp/ABCB1, MRP1/ABCC1, and BCRP/ABCG2 are expressed in a developmental, cell specific, fashion in the human CNS. The complementary pattern of P-gp/ABCB1 and BCRP/ABCG2 at the blood-brain with MRP1/ABCC1 at the blood-CSF barriers may limit CNS uptake and retention of drugs and toxins in neonates.

ABC transporter (P-gp/ABCB1, MRP1/ABCC1, BCRP/ABCG2) expression in the developing human CNS.

Acid-sensing ion channels (ASICs), activated by a decrease of extracellular pH, are found in neurons throughout the nervous system. They have an amino acid sequence similar to that of ion channels activated by membrane stretch, and have been implicated in touch sensation. Here we characterize the pH-dependent activation of ASICs in cerebellar Purkinje cells and investigate how they are modulated by factors released in ischaemia. Lowering the external pH from 7.4 activated an inward current at −66 mV, carried largely by Na+ ions, which was half-maximal for a step to pH 6.4 and was blocked by amiloride and gadolinium. The H+-gated current desensitized within a few seconds, but approximately 30% of cells showed a sustained inward current (11% of the peak current) in response to the maintained presence of pH 6 solution. The peak H+-evoked current was potentiated by membrane stretch (which occurs in ischaemia when [K+]o rises) and by arachidonic acid (which is released when [Ca2+]i rises in ischaemia). Arachidonic acid increased to 77% the fraction of cells showing a sustained current evoked by acid pH. The ASIC currents were also potentiated by lactate (which is released when metabolism becomes anaerobic in ischaemia) and by FMRFamide (which may mimic the action of related mammalian RFamide transmitters). These data reinforce suggestions of a mechanosensory aspect to ASIC channel function, and show that the activation of ASICs reflects the integration of multiple signals which are present during ischaemia.

Modulation of ASIC channels in rat cerebellar Purkinje neurons by ischaemia-related signals.

Time of origin of unipolar brush cells in the rat cerebellum as observed by prenatal bromodeoxyuridine labeling

Ca 2+ signaling is important in many fundamental neuronal processes including neurotransmission, synaptic plasticity, neuronal development, and gene expression. In cerebellar Purkinje neurons, Ca 2+ signaling has been studied primarily in the dendritic region where increases in local Ca 2+ have been shown to occur with both synaptic events and spontaneous electrical activity involving P-type voltage-gated Ca 2+ channels (VGCCs), the predominant VGCC expressed by Purkinje neurons. Here we show that Ca 2+ signaling is also a prominent feature of immature Purkinje neurons at developmental stages that precede expression of dendritic structure and involves L-type rather than P-type VGCCs. Immature Purkinje neurons acutely dissociated from postnatal day 4–7 rat pups exhibit spontaneous cytoplasmic Ca 2+ oscillations. The Ca 2+ oscillations require entry of extracellular Ca 2+ , are blocked by tetrodotoxin, are communicated to the nucleus, and correlate closely with patterns of endogenously generated spontaneous and evoked electrical activity recorded in the neurons. Immunocytochemistry showed that L-, N-, and P/Q-types of VGCCs are present on the somata of the Purkinje neurons at this age. However, only the L-type VGCC antagonist nimodipine effectively antagonized the Ca 2+ oscillations; inhibitors of P/Q and N-type VGCCs were relatively ineffective. Release of Ca 2+ from intracellular Ca 2+ stores significantly amplified the Ca 2+ signals of external origin. These results show that a somatic signaling pathway that generates intracellular Ca 2+ oscillations and involves L-type VGCCs and intracellular Ca 2+ stores plays a prominent role in the Ca 2+ dynamics of early developing Purkinje neurons and may play an important role in communicating developmental cues to the nucleus.

https://www.jneurosci.org/content/jneuro/20/19/7394.full.pdf

L-Type Calcium Channels Mediate Calcium Oscillations in Early Postnatal Purkinje Neurons

Whole-cell patch recording tech- neous or quiescent cells. Spontaneous activity did cor-niques were used to analyze spontaneous electrical relate with a lower activation threshold of the Na cur-activity in cerebellar Purkinje cells acutely isolated rent, resulting in substantial overlap of the activationfrom postnatal rats. Spontaneous activity was present and inactivation curves. TTX reduced the holding cur-in 65% of the cells examined, and it included simple rent of spontaneous cells clamped between 050 andand complex ﬁring patterns which persisted under 030 mV, consistent with the presence of a Na ‘‘win-conditions that eliminated residual or reformed syn- dow’’ current. We were unable, however, to measureaptic contacts. Under voltage clamp, both spontaneous a persistent component of the Na current using voltageand quiescent cells displayed similar voltage-depen- steps, a result which may reﬂect the complex gatingdent conductances. Inward current was carried by properties of Na channels. An Na window currentNa

Sangy C. Nam

Papers

Identification of Acutely Isolated Cells from Developing Rat Cerebellum