ABSTRACT
The purpose of this study was to examine the effects of inactivation of ventral tegmental area (VTA) projection neurons, while sparing fibers of passage, on maternal behavior in rats. Because VTA neurons contain GABA-A and GABA-B receptors, the effects of muscimol or baclofen were studied. Although bilateral injections of either drug into the VTA disrupted maternal behavior, it is likely that they did so through different underlying mechanisms. Muscimol disrupted both retrieval of pups and nursing behavior, while causing stereotyped motor activity. Baclofen disrupted retrieval behavior without affecting nursing behavior, and control injections of baclofen into the region dorsal to VTA were ineffective. The effects of VTA baclofen on maternal behavior are similar to the effects of interference with mesolimbic dopamine (DA) function. The case is made that muscimol probably caused a hyperexcitation of VTA DA neurons through a process of disinhibition. In contrast, baclofen may have depressed the activity of all VTA projection neurons, including VTA DA neurons. Baclofen is a promising tool to explore whether medial preoptic area neurons interact with VTA neurons to control active maternal responses.
Subject(s)
Baclofen/pharmacology , GABA Agonists/pharmacology , Maternal Behavior/drug effects , Muscimol/pharmacology , Ventral Tegmental Area/drug effects , Analysis of Variance , Animals , Baclofen/administration & dosage , Catheterization , Dose-Response Relationship, Drug , Female , GABA Agonists/administration & dosage , Grooming/drug effects , Maternal Behavior/physiology , Motor Activity/drug effects , Muscimol/administration & dosage , Neurons/drug effects , Neurons/physiology , Rats , Time Factors , Ventral Tegmental Area/physiologyABSTRACT
There is good evidence that interference with the mesolimbic dopamine (DA) system results in impaired maternal responding in postpartum female rats. However, whether activation of the mesolimbic DA system is capable of promoting maternal behavior has not been investigated. This study examined whether increasing DA activity in various brain regions of pregnancy-terminated, naive female rats would stimulate the onset of maternal behavior. Experiments 1 and 2 examined the effects of microinjection of various doses (0, 0.2, or 0.5 microg/0.5 microl/side) of a D1 DA receptor agonist, SKF 38393, or a D2 DA receptor agonist, quinpirole, into the nucleus accumbens (NA) on latency to show full maternal behavior, and Experiment 3 determined the effects of SKF 38393 injection into a control site. Finally, because the medial preoptic area (MPOA) is also important for maternal behavior, receives DA input, and expresses DA receptors, the authors examined whether microinjection of SKF 38393 into MPOA was capable of stimulating the onset of maternal behavior. Results indicated that microinjection of SKF 38393 into either the NA or the MPOA facilitates maternal responding in pregnancy-terminated rats.
Subject(s)
Maternal Behavior/drug effects , Nucleus Accumbens/physiology , Pregnancy, Animal/physiology , Pregnancy, Animal/psychology , Preoptic Area/physiology , Receptors, Dopamine D1/agonists , 2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-benzazepine/administration & dosage , 2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-benzazepine/pharmacology , Abortion, Induced/psychology , Animals , Dopamine Agonists/administration & dosage , Dopamine Agonists/pharmacology , Female , Hormones/physiology , Hysterectomy , Image Processing, Computer-Assisted , Male , Microinjections , Nucleus Accumbens/drug effects , Ovariectomy , Pregnancy , Preoptic Area/drug effects , Quinpirole/administration & dosage , Quinpirole/pharmacology , Rats , Receptors, Dopamine D2/agonistsABSTRACT
Several experiments explored the roles of nucleus accumbens (NA), ventral pallidum (VP) and medial preoptic area (MPOA) in the regulation of maternal behavior in rats. A preliminary experiment found that bilateral radiofrequency lesions of medial NA did not disrupt maternal behavior. Experiment 1 found that bilateral infusions of muscimol into VP, but not into medial NA, reversibly disrupted maternal behavior. Experiment 2 found that unilateral muscimol injections into VP disrupted maternal behavior to a greater extent when paired with a contralateral N-methyl-d-aspartic acid (NMDA) MPOA lesion than when paired with a sham MPOA lesion. Experiment 3 showed that a unilateral NMDA MPOA lesion paired with a contralateral NMDA VP lesion (Contra group) disrupted maternal behavior to a much greater extent than did sham NMLA lesions or NMDA lesions of MPOA and VP ipsilateral to one another. Experiment 3 focused on the specificity of the maternal behavior disruptions and found that the primary maternal deficit in the Contra females was a severe deficit in retrieval behavior. Importantly, these females showed normal hoarding behavior, home cage activity, and elevated plus maze activity. Experiment 3 used Neu N immunohistochemistry to define the extent of MPOA and VP excitotoxic lesions. It is hypothesized that MPOA acts to facilitate the active components of maternal behavior by inhibiting NA, which then releases VP from GABAergic inhibition, and such disinhibition of VP allows pup stimuli to trigger appropriate maternal responses.
Subject(s)
Globus Pallidus/physiology , Maternal Behavior/physiology , Nerve Net/physiology , Nucleus Accumbens/physiology , Preoptic Area/physiology , Analysis of Variance , Animals , Dose-Response Relationship, Drug , Excitatory Amino Acid Agonists/pharmacology , Female , Functional Laterality , GABA Agonists/pharmacology , Globus Pallidus/drug effects , Immunohistochemistry/methods , Maternal Behavior/drug effects , Motor Activity/drug effects , Muscimol/pharmacology , N-Methylaspartate/pharmacology , Neural Networks, Computer , Phosphopyruvate Hydratase/metabolism , Postpartum Period/drug effects , Postpartum Period/physiology , Preoptic Area/drug effects , Preoptic Area/injuries , Rats , Reaction Time/drug effects , Staining and Labeling/methods , Time FactorsABSTRACT
The medial preoptic area (MPOA), ventral pallidum (VP), and nucleus accumbens (NA) receive dopaminergic afferents and are involved in maternal behavior. Experiments investigated whether dopamine (DA) receptor antagonism in NA disrupts maternal behavior, determined the type of DA receptor involved, and investigated the involvement of drug spread to VP or MPOA. Injection of SCH 23390 (D1 DA receptor antagonist) into NA of postpartum rats disrupted retrieving at dosage levels that were ineffective when injected into MPOA or VP. Motor impairment was not the cause of the deficit. Injection of eticlopride (D2 DA receptor antagonist) into NA or VP was without effect. Results emphasize the importance of DA action on D1 receptors in NA for retrieval behavior.
Subject(s)
Dopamine Antagonists/pharmacology , Dopamine D2 Receptor Antagonists , Globus Pallidus/drug effects , Maternal Behavior/physiology , Nucleus Accumbens/drug effects , Preoptic Area/drug effects , Receptors, Dopamine D1/antagonists & inhibitors , Animals , Behavior, Animal/drug effects , Circadian Rhythm/physiology , Dose-Response Relationship, Drug , Female , Models, Biological , Motor Activity/drug effects , Postpartum Period/drug effects , Rats , Reaction Time/drug effects , Time FactorsABSTRACT
The medial preoptic area (MPOA) is essential for normal maternal behavior in the rat. Hormone stimulation of the MPOA facilitates the behavior and lesions of the MPOA and the adjoining ventral part of the bed nucleus of the stria terminalis (vBST) disrupt the behavior. The MPOA/vBST also show increases in Fos protein expression during maternal behavior. The present study examines the larger neural circuitry within which the MPOA/vBST might operate to influence maternal behavior. Combining Fos immunocytochemistry with unilateral excitotoxic amino acid lesions or lateral knife cuts of the MPOA/vBST, we sought to identify brain regions which might be under the influence of Fos expressing neurons in the MPOA/vBST. Two brain regions, the shell of the nucleus accumbens (NAs), and the intermediate part of the lateral septum (LSi) were identified. Both the NAs and LSi exhibited elevated Fos expression during maternal behavior, while unilateral MPOA/vBST damage resulted in an ipsilateral reduction of maternal behavior-induced Fos expression in each area, suggesting that MPOA/vBST neurons modulate Fos expression and associated neural activity in both of these structures during maternal behavior. Importantly, these unilateral preoptic lesions also depressed maternal behavior-induced Fos expression in the ipsilateral MPOA and vBST. The effects of these lesions on Fos expression in the periaqueductal gray (PAG) and other brain regions are also presented.
