Postnatal exposure to MK801 induces selective changes in GAD67 or parvalbumin.

Brain injury during the last trimester to the first 1-4 years in humans is now thought to trigger an array of intellectual and emotional problems later in life, including disorders such as schizophrenia. In adult schizophrenic brains, there is a specific loss of neurons that co-express glutamic acid decarboxylase-parvalbumin (GAD67-PV). Loss of this phenotype is thought to occur in mature animals previously exposed to N-methyl-D: -aspartate receptor (NMDAR) antagonists during late gestation or at postnatal day 7 (P7).

Postnatal expression of GAD67.

N-methyl-D-aspartate receptor blockade promotes apoptosis at postnatal day 7 (P7) and is linked to loss of glutamic acid decarboxylase 67 (GAD67) expression in older animals. To more fully appreciate this relationship we must first understand how GAD67 is regulated postnatally. Thus, the brains of P7, P14 and P21 rats were examined for expression of GAD67 protein and we found that levels of this GABAergic marker increased steadily with age, such that by P21 there was as much as a 6-fold increase compared to P7 animals and a 1.

MK801-induced activated caspase-3 exhibits selective co-localization with GAD67.

Blockade of the N-methyl-d-aspartate receptor (NMDAR) in postnatal day 7 (P7) rats can promote rapid and robust induction of the pro-apoptotic marker activated caspase-3 (AC3) and loss of the GABAergic marker GAD67 at P56. Thus, we hypothesized that NMDAR blockade-induced AC3 occurs in GAD67 positive cells at P7. To test this idea, we injected P7 rat pups with vehicle or MK801 and after 8h (peak of AC3 induction) we examined brain sections for both AC3 and GAD67.

Neonatal exposure to MK801 promotes prepulse-induced delay in startle response time in adult rats.

The acoustic startle reflex in rats can be inhibited if a prepulse stimulus is presented just before the startle stimulus (prepulse inhibition; PPI). When postnatal day 7 (P7) rats are exposed to agents that block the NMDA receptor (NMDAR), robust apoptosis is observed within hours and is thought to be followed at later ages by a significant loss of PPI. To understand these observations further, we exposed rat pups to vehicle or the NMDAR antagonist MK801 (1 mg/kg) at P6, P8, and P10.

NMDAR blockade-induced neonatal brain injury: Reversal by the calcium channel agonist BayK 8644.

We have previously shown that P7 rat pups injected with the N-methyl-d-aspartate receptor (NMDAR) blocker MK801 displayed robust apoptotic injury within hours after injection. Further studies from our lab suggest that loss of calcium cannot be compensated for when vulnerable neurons lack calcium buffering capabilities. Thus, to elevate calcium in these neurons prior to MK801 exposure, we injected P7 rats with the calcium channel agonist BayK 8644.

Decline in age-dependent, MK801-induced injury coincides with developmental switch in parvalbumin expression: somatosensory and motor cortex.

MK801-induced activation of caspase-3 is developmentally regulated, peaking at postnatal day (P) 7 and decreasing with increasing postnatal age thereafter. Further, at P7, cells displaying activation of caspase-3 lack expression of calcium binding proteins (CaBPs). To further explore this relationship, we investigated postnatal expression of calbindin (CB), calretinin (CR) and parvalbumin (PV) in two brain regions susceptible to MK801-induced injury, the somatosensory cortex (S1) and layer II/III of motor cortex (M1/M2).

Intraneuronal vesicular organelle transport changes with cell population density in vitro.

Primary neuron cultures are widely used in research due to the ease and usefulness of observing individual cells. Therefore, it is vital to understand how variations in culture conditions may affect neuron physiology. One potential variation for cultured neurons is a change in intracellular transport.

Effects of disrupting calcium homeostasis on neuronal maturation: early inhibition and later recovery.

It has become increasingly clear that agents that disrupt calcium homeostasis may also be toxic to developing neurons. Using isolated primary neurons, we sought to understand the neurotoxicity of agents such as MK801 (which blocks ligand-gated calcium entry), BAPTA (which chelates intracellular calcium), and thapsigargin (TG; which inhibits the endoplasmic reticulum Ca(2+)-ATPase pump). Thus, E18 rat cortical neurons were grown for 1 day in vitro (DIV) and then exposed to vehicle (0.

Decline in age-dependent, MK801-induced injury coincides with developmental switch in parvalbumin expression: cingulate and retrosplenial cortex.

Age-dependent, MK801-induced, activated caspase-3 expression in the postnatal brain is generally not observed in neurons expressing calcium-binding proteins (CaBPs), suggesting that apoptosis and calcium buffering are inversely related. In regions such as the cingulate and retrosplenial cortex, injury peaks at postnatal Day 7 (P7) and rapidly diminishes thereafter, whereas expression of calbindin (CB) and calretinin (CR) was relatively low from P0 to P7 and steadily increased from P7 to P14. At ages thereafter, CB and CR expression either remained stable then declined or rapidly declined.

Neonatal exposure to MK801 induces structural reorganization of the central nervous system.

Schizophrenia, a progressive disorder displaying widespread pathological changes, is associated with the loss of glutamatergic function and selective loss of cytoskeletal proteins, such as MAP2, in regions severely affected by this disease. As schizophrenia is associated with perinatal brain trauma, we monitored changes in several functionally different proteins following injury-promoting MK801 blockade of N-methyl-D-aspartate receptors in neonatal rats. Within the somatosensory cortex, MK801 triggered robust, caspase-3-dependent apoptotic injury, reduced expression of cytoskeletal proteins MAP2 and tau, and increased synapse associated protein SNAP25.

A1 adenosine receptors mediate hypoxia-induced ventriculomegaly.

Periventricular leukomalacia is characterized by a reduction in brain matter and secondary ventriculomegaly and is a major cause of developmental delay and cerebral palsy in prematurely born infants. Currently, our understanding of the pathogenesis of this condition is limited. In animal models, features of periventricular leukomalacia can be induced by hypoxia and activation of A1 adenosine receptors (A1ARs).

Cytoskeletal protein 4.1G binds to the third intracellular loop of the A1 adenosine receptor and inhibits receptor action.

To identify binding partners of the A1AR (A1 adenosine receptor), yeast two-hybrid screening of a rat embryonic cDNA library was performed. This procedure led to the identification of erythrocyte membrane cytoskeletal protein (represented as 4.1G) as an A1AR-binding partner.

Reduction in intracellular calcium levels induces injury in developing neurons.

The neurotransmitter glutamate influences intracellular Ca(2+) levels and plays an essential role in maintaining neuronal viability during early development. Blockade of NMDA receptors induces cell death in the neonatal forebrain via mechanisms that are not understood. Other neuromodulators that can influence intracellular Ca(2+) levels include the nucleoside adenosine, which acts via A(1) adenosine receptors subtypes (A(1)ARs).

A1 adenosine receptor activation induces ventriculomegaly and white matter loss.

A1 adenosine receptors (A1ARs) are widely expressed in the brain during development. To examine whether A1AR activation can alter postnatal brain formation, neonatal rats from postnatal days 3 to 14 were treated with the A1AR agonist N6-cyclopentyladenosine (CPA) in the presence or absence of the peripheral A1AR antagonist 8-(p-sulfophenyl)-theophylline (8SPT). CPA or CPA + 8SPT treatment resulted in reductions in white matter volume, ventriculomegaly, and neuronal loss.