Increasing evidence suggests that postnatal events, such as handling or maternal separation, can produce long-term changes in brain function. These are often expressed as changes in the profile of endocrine or behavioral responses to stress. Changes in ␥-aminobutyric acid type A receptors (GABARs), which mediate the majority of fast synaptic inhibition in adult brain, have been proposed as one potential mediator of these behavioral effects. In the current article, we use a combination of single-cell electrophysiology and antisense mRNA amplification to demonstrate permanent molecular and functional differences in GABARs within hippocampal dentate granule neurons after as few as two episodes of neonatal handling with brief maternal separation. Adult animals that as pups experienced handling with maternal separation maintained a more immature GABAR phenotype and exhibited increased activity in response to swim stress. These findings demonstrate the exquisite sensitivity of the developing GABAergic system to even subtle environmental manipulations and provide an unique molecular mechanism by which postnatal handling with maternal separation may alter stress-related behavior.development ͉ glucocorticoid ͉ dentate granule neurons ͉ patch clamping ͉ single-cell antisense mRNA amplification T he developing nervous system can be exquisitely sensitive to even minor perturbations in the environment. It has been recognized for decades that handling of neonatal rats could produce profound effects on later neuroendocrine and behavioral responses to stress (1, 2). Repetitive brief handling in neonatal rats has been shown to result in permanent alterations in hippocampal glucocorticoid (GC) receptors, decreased GC responses to stress in adulthood, and a relative protection against age-related hippocampal neuronal death and cognitive impairments (3). Adult animals handled as pups also demonstrate decreased expression of fear-related behaviors under stressful conditions (4-6). The molecular mechanisms underlying handling-induced behavioral and cognitive changes are not fully understood. ␥-Aminobutyric acid (GABA) is the major inhibitory neurotransmitter in mammalian brain and regulates both endocrine and behavioral responses to stress (7-9). Benzodiazepines (BZs) and other drugs that potentiate GABA currents can be potent anxiolytics. Rats exposed to early-life handling have been found to have altered BZ receptor levels in several brain regions including brainstem nuclei, amygdala, and frontal cortex (5, 6), but handling effects on GABA type A receptor (GABAR) subunit expression and function in hippocampal neurons have not, to our knowledge, previously been reported.GABARs are chloride ion channel-associated ligand-gated heteromeric receptors composed of five subunits, which are modulated by BZs, barbiturates, zinc, and neurosteroids. Many genetically distinct subunit subtypes, including ␣1-6, ␤1-4, ␥1-3, ␦, , , , and 1-3, have been identified (10, 11). GABARs can be assembled in different subunit combinations, resulting in a st...

Prolonged early-life seizures are considered potential risk factors for later epilepsy development, but mediators of this process remain largely unknown. Seizure-induced structural damage in hippocampus, including cell loss and mossy fiber sprouting, is thought to contribute to the hyperexcitability characterizing epilepsy, but a causative role has not been established. To determine whether early-life insults that lead to epilepsy result in similar structural changes, we subjected rat pups to lithium-pilocarpine-induced status epilepticus during postnatal development (day 20) and examined them as adults for the occurrence of spontaneous seizures and alterations in hippocampal morphology. Sixty-seven percent of rats developed spontaneous seizures after status epilepticus, yet only one third of these epileptic animals exhibited visible hippocampal cell loss or mossy fiber sprouting in dentate gyrus. Most epileptic rats had no apparent structural alterations in the hippocampus detectable using standard light microscopy methods (profile counts and Timm's staining). These results suggest that hippocampal cell loss and mossy fiber sprouting can occur after early-life status epilepticus but may not be necessary prerequisites for epileptogenesis in the developing brain.

Prolonged seizures in early childhood are associated with an increased risk of development of epilepsy in later life. The mechanism(s) behind this susceptibility to later development of epilepsy is unclear. Increased synaptic activity during development has been shown to permanently alter excitatory neurotransmission and could be one of the mechanisms involved in this increased susceptibility to the development of epilepsy. In the present study we determine the effect of status-epilepticus induced by lithium/pilocarpine at postnatal day 10 (P10 SE) on the expression of glutamate receptor and transporter mRNAs in hippocampal dentate granule cells and protein levels in dentate gyrus of these animals in adulthood. The results revealed a decrease in glutamate receptor 2 (GluR2) mRNA expression and protein levels as well as an increase in protein levels for the excitatory amino acid carrier 1 (EAAC1) in P10 SE rats compared to controls. Expression of glutamate receptor 1 (GluR1) mRNA was decreased in both P10 SE rats and identically handled, lithium-injected littermate controls compared to naive animals, and GluR1 protein levels were significantly lower in lithium-controls than in naive rats, suggesting an effect of either the handling or the lithium on GluR1 expression. These changes in EAA receptors and transporters were accompanied by an increased susceptibility to kainic acid induced seizures in P10 SE rats compared to controls. The current data suggest that early-life status-epilepticus can result in permanent alterations in glutamate receptor and transporter gene expression, which may contribute to a lower seizure threshold.