Repeated neonatal handling with maternal separation permanently alters hippocampal GABA _A receptors and behavioral stress responses

Abstract

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...

Developmental emergence of fear learning corresponds with changes in amygdala synaptic plasticity

“…For example, early neonatal handling and maternal separation are correlated with changes in limbic system GABA receptor sub-unit expression and receptor function in adults (Hsu et al, 2003), as well as several behavioral effects such as reduced fear responses (Ladd et al, 2000). Similarly, the postnatal sensitive period odor-shock conditioning paradigm used in the present study reduces odor fear conditioning when those animals are later trained as adults (Sevelinges et al, in press).…”

The role of GABAA receptors in the development of alcoholism

“…The mRNAs from the chromosome 4 cluster genes predominate in rat embryo but these genes are generally down regulated in the adult rat except in the hippocampus, the majority of DA neurons in the substantia nigra and the VTA where they are highly expressed (Okada et al, 2004;Steiger and Russek, 2004;. Thus the chromosome 4 cluster of genes are likely to be important in addiction and anxiety and may be vulnerable to epigenetic effects in early development, as indicated above for GABRA2 (Hsu et al, 2003). Moreover, the anxiolytic effects of BZs appear to be mediated in part by GABRA2; mice with a GABRA2 knock-in point mutation are insensitive to BZs' anxiolytic effects (Dias et al, 2005;Low et al, 2000).…”

“…Adult rats that have been subjected to early life stress (maternal separation / handling) have a more active stress response (Hsu et al, 2003). Epigenetic effects on receptors implicated in stress, such as glucocorticoid and GABA A , have been demonstrated in rodents.…”

“…For example, BZ receptor levels in the adult rat central nucleus of the amygdala are highly correlated with the frequency of maternal licking/grooming over the first week of life (Caldji et al, 1998). Early life stress in rats permanently alters GABA A receptor subunit expression in the hippocampus such that α 2 subunits predominate in the stressed animals whereas α 1 predominates in emotionally healthy animals (Hsu et al, 2003). Early life maternal neglect also results in increased levels of α 3 and α 4 in the adult rat amygdala whereas enriched maternal care in the first week of life results in increased α 1 and β 3 mRNA levels almost everywhere, including the hippocampus and amygdala, and increased β 2 and γ 2 in the amygdala.…”

Long-Term Alterations in Neuroimmune Responses after Neonatal Exposure to Lipopolysaccharide

“…For example, physiological and behavioral stress in the neonatal period can profoundly affect the hypothalamic-pituitary-adrenal (HPA) response to noise stress and to LPS in adults (Shanks et al, 1995(Shanks et al, , 2000. This can result in altered expression of experimental arthritis (Shanks et al, 2000), altered reactivity of the hypothalamic-pituitarygonadal axis (Nilsson et al, 2002), and persistent changes in CSF neurotransmitter levels (Coplan et al, 1996;Mathew et al, 2002) and receptor phenotypes (Hsu et al, 2003;Zhang et al, 2004).…”