@article{c46ea332d34b422899002eec538520f0,
title = "Suckling behavior of the infant rat: Modulaton by a developing neurotransmitter system",
abstract = "Drugs which alter serotonin receptor activity modified the suckling behavior of 20-day-old rat pups. Suckling could be reinstated in nondeprived pups, which normally do not suckle, by blockade of serotonin receptors with methysergide. Stimulation of serotonin receptors with quipazine inhibited suckling in deprived pups, and this effect was prevented by methysergide pretreatment. This evidence suggests that suckling in weaning age pups is controlled by a serotonergic inhibitory mechanism.",
keywords = "Development, Methysergide, Quipazine, Serotonin, Suckling behavior",
author = "B. Nock and Williams, {C. L.} and Hall, {W. G.}",
note = "Funding Information: The results of these experiments indicate that 5-HT receptor blockade with methysergide stimulates suckling in nondeprived pups, and that 5-HT receptor stimulation with quipazine has the opposite behavioral effect, inhibiting the suckling of deprived pups. Although the specificity of both quipazine and methysergide has been questioned \[9, 10, 11, 18\], a common serotonergic receptor site for the behavioral effects of these drugs is supported by the data which shows that methysergide pretreatment antagonizes the behavioral effects of quipazine. In addition, we have recently found that the 5-HT receptor blocker metergoline \[30\] also stimulates suckling in older rat pups, whereas drugs that affect catecholaminergic receptor activity (pimozide, phenoxybenzamine, and apomorphine) have little or no effect on suckling behavior. Together, these results suggests a serotonergic inhibitory mechanism controlling the suckling of weaning age rat pups. It is also known that 5-HT mechanisms are involved in temperature regulation \[23\], and we have found that methysergide at the dose used in these experiments is hypothermic. However, it is unlikely that methysergide-treated pups suckle because they are cold, since we have found that cooling nondeprived pups to 32°C in a refrigerator does not stimulate suckling behavior. Furthermore, quipazine (10 mg/kg) which inhibits suckling, also appears to be slightly hypothermic. Thus, the changes in suckling behavior reported here do not appear to be related to drug-induced changes in body temperature. In addition, because reinstatement of suckling behavior was induced by acute pharmacological manipulations, it can not be attributed to chronic metabolic changes. Central 5-HT mechanisms have been implicated in the control of food intake in adult rats \[2, 4, 5, 27, 28, 29\], yet, it is unlikely that the reinstatement of suckling observed in this study is simply the result of making the nondeprived pups hungry. Two kinds of evidence support this statement. First, we have preliminary data which indicates that methysergide reliably stimulates suckling in 30-day-old pups (deprived and nondeprived). At this age, even 24 hr food deprivation fails to reliably stimulate suckling behavior. Thus, simply making a pup hungry is not a sufficient cause for it to suckle. Second, given the choice between eating rat chow or attaching to their mother's dry nipples, deprived 20-day-old pups eat food pellets and suckle while nondeprived methysergide-treated pups only suckle (Williams and Hall, unpublished observations). Therefore, food deprivation and methysergide treatment appear to have different effects on the appetitive behavior of 20-day-old rat pups. These data, in fact, suggest hypotheses about feeding effects obtained with serotonergic manipulations in adult animals \[10\]. Adult effects may be related to specific disinhibition or inhibition of only one component of the adult feeding system, rather than to general satiety or hunger processes. That is, a treatment in the weaning age pup which may alter perception of oral stimulation and reinstate suckling in preference to feeding, may in the adult lead to an increased attention to food and feeding in the absence of other appropriate oral manipulanda. In this way, the presumed reestablishment of suckling in the present study may also reflect the types of processes which underlie neurological regression and the reappearance of neonatal reflexes (e.g., suckling, rooting) in humans suffering from neurological trauma or senility \[2 5\]. In neonatal pups, suckling has the appearance of a reflex behavior. However, in the brief preweaning period, this initially simple behavior sequentially develops internal controls. The pharmacological stimulation and inhibition of suckling in 20-day-old rats reported here, suggest that, in part, the development of these controls may be related to the emergence of an inhibitory serotonergic system. This study also suggests that suckling may provide a behavioral system for investigating the emergence of neurotransmitter function and points to the usefulness of suckling as a model system for the study of the development of complex motivated behaviors. ACKNOWLEDGEMENTS Supported by USPHS Research Fellowship MH-05067 to W. G. Hall, USPHS Biomedical Research Support Grant RR-07059, and USPHS Center Grant MH-08604. We thank Jay S. Rosenblatt, Harvey H. Feder, Byron A. Campbell and Henry Szechtman for critical comments and Richard Wilson for assistance. Methysergide was generously supplied by Sandoz Pharmaceuticals and quipazine by Miles Labs., Inc. This is contribution No. 277 of the Institute of Animal Behavior, Rutgers - The State University.",
year = "1978",
month = mar,
doi = "10.1016/0091-3057(78)90316-7",
language = "English",
volume = "8",
pages = "277--280",
journal = "Pharmacology, Biochemistry and Behavior",
issn = "0091-3057",
number = "3",
}