ERK-FosB signaling in dorsal MPOA neurons plays a major role in the initiation of parental behavior in mice

Increased operant responding for ethanol in male C57BL/6J mice: specific regulation by the ERK1/2, but not JNK, MAP kinase pathway

RATIONALE

Extracellular signal-regulated protein kinase (ERK(1/2)) is a member of the mitogen-activated protein kinase (MAPK) signaling pathway and a key molecular target for ethanol (EtOH) and other drugs of abuse.

OBJECTIVE

The aim of the study was to assess the role of two MAPK pathways, ERK(1/2) and c-Jun N-terminal kinase (JNK), on the modulation of EtOH and sucrose self-administration.

MATERIALS AND METHODS

C57BL/6J mice were trained to lever press on a fixed-ratio 4 schedule with 9% EtOH/2% sucrose, or 2% sucrose, as the reinforcer. In experiments 1 and 2, mice were injected with the MEK(1/2) inhibitor SL 327 (0-100 mg/kg) and the JNK inhibitor AS 6012452 (0-56 mg/kg) prior to self-administration. In experiment 3, SL 327 (0-100 mg/kg) was administered prior to performance on a progressive ratio (PR) schedule of EtOH reinforcement. In experiment 4, SL 327 and AS 601245 were injected 2 h before a locomotor test.

RESULTS

SL 327 (30 mg/kg) significantly increased EtOH self-administration without affecting locomotion. Higher doses of SL 327 and AS 601245 reduced EtOH-reinforced responding and locomotor activity. Reductions of both ligands on sucrose self-administration were due to decreases in motor activity. SL 327 pretreatment had no effect on PR responding.

CONCLUSIONS

ERK(1/2) activity is more directly involved in modulating the reinforcing properties of EtOH than JNK activity due to its selective potentiation of EtOH-reinforced responding. The specificity of this effect to EtOH self-administration, rather than sucrose self-administration, suggests that the mechanism by which ERK(1/2) increases EtOH-reinforced responding does not generalize to all reinforcing solutions and is not due to increased motivation to consume EtOH.

Brain vasopressin is an important regulator of maternal behavior independent of dams' trait anxiety

The neuropeptide arginine vasopressin (AVP) is arguably among the most potent regulators of social behaviors in mammals identified to date. However, only the related neuropeptide oxytocin (OXT) has been shown to promote maternal behavior. Here, we assess the role of AVP in maternal care, in particular in arched back nursing, pup retrieval, and pup contact by using complementary pharmacological and genetic approaches. Also, experiments were performed in rat dams with differences in trait anxiety, i.e., rats bred for either high (HAB) or low (LAB) anxiety-related behavior as well as nonselected (NAB) dams. Viral vector-mediated up-regulation of AVP V1a receptors (AVP-Rs) within the medial preoptic area of lactating NAB rats and chronic central AVP treatment of NAB and LAB dams improved, whereas local blockade of AVP-R expression by means of antisense oligodeoxynucleotides or central AVP-R antagonism impaired, maternal care in NAB dams. Also, in HAB rats with a genetically determined elevated brain AVP activity, intrinsically high levels of maternal care were reversed by blockade of AVP-R actions. Treatment-induced impairment of AVP-mediated maternal behavior increased adult emotionality and impaired social interactions in male offspring of NAB dams. These findings provide direct evidence for an essential and highly potent role of brain AVP in promoting maternal behavior, which seems to be independent of the dam's trait anxiety.