Differential effects of prenatal cocaine exposure on selected subunit mRNAs of the GABA(A) receptor in rabbit anterior cingulate cortex

GABA system as the cause and effect in early development

GABA is the primary inhibitory neurotransmitter in the adult brain and through its actions on GABAARs, it protects against excitotoxicity and seizure activity, ensures temporal fidelity of neurotransmission, and regulates concerted rhythmic activity of neuronal populations. In the developing brain, the development of GABAergic neurons precedes that of glutamatergic neurons and the GABA system serves as a guide and framework for the development of other brain systems. Despite this early start, the maturation of the GABA system also continues well into the early postnatal period. In this review, we organize evidence around two scenarios based on the essential and protracted nature of GABA system development: 1) disruptions in the development of the GABA system can lead to large scale disruptions in other developmental processes (i.e., GABA as the cause), 2) protracted maturation of this system makes it vulnerable to the effects of developmental insults (i.e., GABA as the effect). While ample evidence supports the importance of GABA/GABAAR system in both scenarios, large gaps in existing knowledge prevent strong mechanistic conclusions.

Digital holographic microscopy discriminates sex differences in medial prefrontal cortex GABA neurons following amphetamine sensitization

Sex differences have been noted in patterns of drug use and relapse, and in particular with amphetamine abuse, implicating estradiol in mediating female neurobehavioral responses. To investigate the interaction of estradiol with amphetamine-induced hyperactivity, we compared male, intact female (INTACT), ovariectomized (OVX) and ovariectomized estradiol-treated (OVX+EB) female rats receiving repeated amphetamine (AMPH) treatment. All rats received intermittent AMPH injections for three days, and baseline and post-injection locomotor activity as well as fine-motor movements were recorded. Upon completion of behavioral experiments, immunohistochemistry was performed to assess parvalbumin-immunoreactive (PV-IR) GABAergic neurons in the medial prefrontal cortex (mPFC). Results indicate that AMPH induced greater behavioral response during habituation among the INTACT animals, and post-injection hyperactivity was apparent on days 2 and 3, among INTACT and OVX+EB females. For INTACT animals, the hyperactivity was most pronounced when estrogen levels were high. Immunohistochemical analysis using digital holographic microscopy revealed INTACT and OVX+EB females had less expression and smaller somatic area of PV-IR neurons in the mPFC. These data provide evidence for rapid development of sex differences in response to AMPH that correlates with sexually dimorphic alterations in a subset of mPFC GABAergic neurons implicated in modulating forebrain dopamine projections.

Chronic nicotine exposure during adolescence differentially influences calcium-binding proteins in rat anterior cingulate cortex

We have recently shown that chronic amphetamine exposure selectively up-regulates parvalbumin (PV) calcium-binding proteins in the anterior cingulate cortex (ACC). In this study, we evaluated the effects of chronic nicotine (NIC) exposure on PV, calbindin D28k (CB) and calretinin (CR) calcium-binding protein immunostaining in ACC GABAergic interneurons. Chronic NIC exposure for 3 weeks in adolescent rats, either via drinking water (the oral group) or by twice daily subcutaneous injections (the injection group), resulted in the expression of high levels of CR proteins in the ACC but not in the parietal cortex. Larger increases in the density of CR-immunoreactive (ir) neurons were noted in the NIC-injected rats at 0-day withdrawal (45% increase) compared with the oral group (26% increase). The larger increases in CR-ir neuron density in the NIC-injected rats were also reflected by prominent CR-ir processes across cortical layers. The density of PV-ir neurons was also increased (37%) at 0-day withdrawal but only in the oral NIC group and no changes in CB-ir neuron density were observed in either NIC group. Combined dual-immunofluorescence and confocal microscopy revealed that somatodendritic alpha4 nicotinic acetylcholine receptors colocalized with cortical neurons stained positively for CR, PV or CB. These results suggest that CR- and/or PV-ir-containing GABA interneurons may be involved in channeling the effects of NIC in the ACC, which is closely associated with the ventral basal ganglia circuit that is linked to brain reward function.