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This study investigated the effects of prenatal stress and complete maternal deprivation, using the artificial rearing (AR) paradigm, on the expression of neural plasticity markers and hypothalamic-pituitary-adrenal (HPA) axis responsivity to stress. Rats were exposed to stress during gestation (day 10-21) and postnatally were either artificially reared (AR) or mother reared (MR). AR involves complete separation of the pup from both the dam and the litter throughout the pre-weaning period. In adulthood, we measured levels of corticosterone (CORT) in response to restraint stress. Also, we examined the expression of synaptophysin (SYN) and brain-derived neurotrophic factor (BDNF) in the medial prefrontal cortex (MPFC) and the nucleus accumbens (Nacc), areas of the brain that mediate behavioral activation and attention, among other behaviors. Earlier work on the same rats indicated that these behavioral endpoints, such as locomotor activity and sensorimotor gating, are affected by our prenatal and postnatal manipulations. Prenatal stress decreased CORT at 20 and 90 min post-stressor in MR, but not in AR, animals. Also, in comparison to MR groups, AR decreased SYN and BDNF expression in the MPFC and Nacc. Additional somatosensory 'licking-like' stroking stimulation partially reversed the effects of AR. Prenatal stress did not have a robust main effect but affected the impact of the postnatal rearing condition on SYN expression and stress-induced CORT. These results suggest that both prenatal and postnatal adversities have an influence on HPA axis responsivity and alter the expression of plasticity related neuronal proteins.

The present study investigated the release of dopamine from the nucleus accumbens (shell) in response to pup-stimuli in the absence of lactation and maternal behaviors at time of sample collection. Subjects were female rats given maternal experiences through prior parturitions, recent pup-induced sensitization, or a combination of both. Nulliparous (N) or multiparous (M, had 2 prior litters but cycling) female rats either received pup-sensitization (S+) until they responded maternally in their homecage or no pup-sensitization (S-), thus, there were four groups: NS- (n=5), NS+ (n=6), MS- (n=5), and MS+ (n=8). Four hours after removal of pups (from homecage for S+ groups), all females were placed into the microdialysis chamber for sample collection. After baseline collection, four foster pups were given to the females. In this paradigm females show little to no maternal behavior in the test chamber. Samples (collected every 8 min) were analyzed for dopamine (DA) and 3,4-dihydroxyphenylacetic acid (DOPAC) with electrochemical detection using HPLC. Relative to the inexperienced NS- females, the experienced NS+, MS- and MS+ females displayed significantly increased DA levels only during the first 8 min of pup-exposure. The more experience a female had with pups, the greater was the DA response (p.05). The results suggest that enhanced responding to pups following previous maternal experiences may be mediated through accumbal DA.

Rat pups reared apart from their siblings, mother, and nest environment in the 'pup-in-a-cup' regime show many alterations in behavior reminiscent of the Institutional Inattention/Overactivity Syndrome that characterizes children whose first few months are spent in institutions. In this report, we compare mother-reared (MR) and artificially reared (AR) male rats in concentrations and distributions of brain proteins that are involved in normal brain development. When assessed during the juvenile period and in adulthood, AR animals showed elevations in Neu-N (a neuronal marker) and in S-100 (an astrocyte marker) but reductions in synaptophysin (synapse protein), N-CAM (cell-adhesion molecule), GAP-43 (axon elongation protein), and BDNF (brain derived neurotrophic factor) in comparison to MR controls in many brain sites involved in attention, impulsivity, activity, and social behavior. Daily 'licking-like' stimulation provided to AR animals (AR-MAX) throughout early development that reverses many of the behavioral deficits, also reverses many of the isolation effects on brain proteins. Study 2 showed that elevations in the number of neurons in combination with decreases in functionality are associated with a reduction in neuronal pruning and apoptosis during the very early post-partum period in AR animals and their reversal through daily 'licking-like' stimulation.

Neuro-2a neuroblastoma cells, when differentiated via a cAMP-dependent pathway by treatment with anti-GM 3 monoclonal antibody, accumulated a high level of pp60 c-src protein and pp60 c-src kinase activity just before the onset of neurite formation. The specific kinase activity of the accumulated c-src protein was found to be comparable to that of normal cerebellar neurons, but was about 6- to 8-fold higher than that of normal astrocytes. These results, and migrations of peptide fragments in the SDS-polyacrylamide gels after V8 proteolysis, strongly indicate the accumulation of the neuron-specific isoform of the c-src protein (pp60 c-srcN ) in the GM 3 antibody-treated Neuro-2a cells. Similar high levels of pp60 c-src protein and pp60 c-src kinase activity were observed in the Neuro-2a cells differentiated via a cAMP-dependent pathway by treatment with dibutyryl cAMP, but not in the same cell line when differentiated via a cAMP-independent pathway with 5-bromo-2′-deoxyuridine. These results demonstrate that the accumulation of high levels of the neuron-specific isoform of the pp60 c-src protein (pp60 c-srcN ) in the Neuro-2a neuroblastoma cells depends on the specific signal transduction pathway involved during the differentiation of these cells.

A monoclonal antibody against GM3 ganglioside (GM3 Ab) was found to trigger differentiation of Neuro-2a cells in culture. The differentiation of Neuro-2a cells by GM3Ab was accompanied by increased levels of intracellular serotonin and amino acid neurotransmitters viz. aspartate, glutamate, glutamine, glycine and taurine. Further study indicated that the increase in the serotonin level was not due to a higher rate of serotonin synthesis but rather to a higher rate of active transport of serotonin from the medium. Studies on the cell surface gangliosides revealed that unlike the proliferating cells, the GM3Ab-mediated differentiated cells contained higher gangliosides in addition to GM3 and GM2 gangliosides. Analysis of total cellular proteins indicated the appearance of a 25 kDa protein, pI 5.4, in the GM3Ab-treated cells—a small amount of this protein was observed in dibutyryl cAMP (Bt2cAMP)-treated cells, however, the protein was totally absent in the 5-bromo-2′-de-oxyuridine (BrdU)-treated cells. Investigation of the mode of action of GM3Ab indicated that the cellular differentiation was due to increased cAMP accumulation resulting from an increase in the adenylate cyclase activity. Further studies with different agents affecting protein kinase C (PKC) activity and direct assay of PKC ruled out the possibility that GM3Ab mediated its effect via PKC. This GM3Ab-induced differentiation could be inhibited by protein kinase A (PKA) inhibitor, H8, but could not be inhibited by sphingosine, an inhibitor of PKC. Pertussis toxin could mimic the effect of GM3Ab, suggesting that GM3Ab caused the elevation in the adenylate cyclase activity by reducing the Gi-protein inhibition of the adenylate cyclase. The data suggests that GM3Ab, after interaction with cell surface GM3, elevated intracellular cAMP level by withdrawing the inhibitory effect of some undefined factor(s) present in culture medium which normally keeps adenylate cyclase activity low through activation of Gi-protein.