Suckling behavior and intake control in the developing rat pup.

Studied the behavioral development of suckling and intake control in 2 experiments with Charles River CD strain rat pups. Ss were observed at the initiation, during the course, and at the termination of suckling from their anesthetized mothers. Diet was delivered intraorally through a fine tongue cannula which enabled control of timing and volume. The control of diet intake and the behavior at termination of suckling showed correlated changes from 5 to 20 days of age. When deprived of suckling (and food and water) for 8 hr, 5- and 10-day-old Ss consumed large volumes of diet (10% of body weight or greater) and terminated suckling only in the presence of extreme gastrointestinal filling. These Ss were immediately lethargic and slept after intake termination. Five-day-old Ss persisted in reattaching to the nipple when manually stimulated; 10-day-old Ss eventually refused to reattach. In contrast, 20-day-old Ss consumed more moderate volumes of diet (5% of body weight). These Ss also remained awake for a period after feeding and engaged in the exploratory and grooming activities characteristic of adult rats at the termination of feeding. These observations demonstrate major changes in suckling behavior during development. They suggest that intake control processes shift from indirect to direct and become more effective and specifically food intake related in older pups. (20 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Separation of opioid from nonopioid mediation of affect in neonatal rats: Nonopioid mechanisms mediate maternal contact influences.

Established a causal distinction in infant rats between opioid- (OP) and non-OP-mediated determinants of behavior. Contact influences were mediated by non-OP pathways, and gustatory influences were OP-mediated. Naltrexone (NTX) did not diminish quieting exerted by contact with an anesthetized dam but reversed the quieting effects of morphine in isolated Ss. Naloxone (NLX) did not affect the latencies with which nondeprived or 8-hr deprived Ss 9, 12, 15, and 18 days old attached to nipples (NPs) of anesthetized dams, nor did NLX cause systematic change in NP attachment in 10- and 18-day old Ss from the NP when milk letdown was induced by oxytocin. NLX did not reduce milk intake in Day-10 Ss that, while suckling, received milk via indwelling cannulae in the anterior portion of the lower jaw or in Ss that obtained milk directly from their awake mother. Milk intake was significantly reduced by NTX in Day-10 Ss that obtained milk by licking it off a saturated substrate. In Day-10 Ss, intake of milk delivered via cannulae was reduced by NLX in Ss that were either isolated, in contact with an anesthetized dam, or attached to her NPs. Behavioral influences of the tactile (and possibly olfactory) qualities of the dam were not mediated by OP systems. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Ontogeny of preference for nutritive over nonnutritive suckling in albino rats.

Investigated nutritive vs nonnutritive suckling in 48 10–21 day old Sprague-Dawley rat pups in a spatial discrimination task. Ss preferred nutritive to nonnutritive suckling on their anesthetized mother at l7 and 21 days of age, but no preference was apparent in 10- and 12-day-old Ss. Rearing in isolation from the mother during Days 11–26 did not impair the development of preference for nutritive suckling in 16 17-day-old Ss. Thus, the appetitive component of suckling of infant rats, like the consummatory component, appears to come under the direct control of nutritional factors at the start of the weaning period. (21 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Behaviorally functional opioid systems in infant rats: I. Evidence for olfactory and gustatory classical conditioning.

Conducted 2 series of experiments to characterize the behavioral function of opioid systems in neonatal rats. In the 1st series, the reinforcing properties of exogenous opioids were investigated in 112 5-day-old pups. Ss' ability to associate the novel taste of saccharin, received while suckling, with intraperitoneal morphine injections was assessed. Results show that Ss that received 0.5 ml of saccharin prior to morphine administration ingested considerably more saccharin on Day 10 than did control rats. The 2nd set of experiments was conducted to determine whether 144 rat pups could associate a novel odor with morphine administration. Five days after conditioning, that stimulus was highly preferred by morphine-treated Ss compared with saline control Ss. Thus positive associations were formed with either a novel taste stimulus experienced while suckling or with an odor experienced during social isolation. Conditioning was cue specific and was retained for at least 5 days. The formation of these associations was blocked with opioid antagonists given prior to conditioning. Data suggest behaviorally functional opioid receptors and raise the possibility of a functional role of the endogenous opioids in motivational processes in infant rats. (38 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Interactions between contact and chemosensory mechanisms in pain modulation in 10-day-old rats.

Antinociception was evaluated in 10-day-old rats while suckling or in contact with the mother. Testing occurred during, immediately after, or at 30 and 60 sec following milk-induced hyperextension. Hyperextension-induced hypoalgesia terminated immediately with stretch cessation. For suckling rats, baseline escape levels were reachieved within 1 min. For contact rats, baseline levels were also manifest at 30 sec but were elevated by 1 min. Sublingual infusions into the anterior portion of the mouth in rats that were either suckling or in contact caused a 20–25-sec increase in escape latencies. For suckling rats, escape latencies returned to baseline levels immediately at infusion termination. For contact rats, latencies continued to be elevated for at least 5 min postinfusion. Thus, 3 classes of mother–infant interactions, contact, suckling, and hyperextension during milk letdown, cause varying degrees of hypoalgesia in 10-day-old rats. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Ontogeny of amphetamine anorexia in rats: A behavioral analysis.

Conducted 4 experiments with 246 Sprague-Dawley rats to ascertain the effects of dextroamphetamine (DAM; 1 or 2 mg/kg) on the behaviors associated with feeding in weanling and preweanling rats. The 1st 2 experiments produced the following results: (a) In 5-day-old Ss, DAM increased speed of approach to an anesthetized mother; (b) at 15 days of age, DAM increased speed of approach to the mother and produced marked weight loss (relative to the weight of controls), slowed or reduced frequency of attachment to the nipple, and decreased time spent nursing; and (c) at 25 days of age, DAM disrupted all aspects of the feeding process except initial approach. Weight gain, time spent in contact with the mother, time spent nursing, and time attached to the nipple were all reduced by the drug. In Exps III and IV, milk was delivered to Ss at 5, 15, and 25 days of age through tongue cannulas, which allowed ingestion without suckling. Under these circumstances, DAM produced clear-cut anorexia in Ss of all 3 ages. It is concluded that in early development, the anorectic effects of DAM are overridden by the strong suckling response that is not disrupted by the drug. (17 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effect of initial-pecking consequences on subsequent pecking in young chicks.

White Leghorn cockeral chicks ? and 2? days old received saline or LiCl injection immediately following their 1st feeding experience. When retested 5 hrs later 2?-day-old Ss that had received saline increased their pecking rate, but ?-day-old Ss showed no change. Only 2?-day-old chicks, therefore, appear to associate ingestion of food with long-term positive consequences. Ss of both ages, on the other hand, greatly reduced pecking when retested 5 hrs after LiCl injection. Thus, ?- and 2?-day-old chicks are capable of forming an association between pecking and its long-term consequence when the consequence is aversive. When LiCl injection was not contingent on pecking, following the initial feeding session by 6 hrs, Ss did not reduce retest pecking rates. (7 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Suckling behavior in neonatal rats: Psychopharmacological investigations.

Examined the effects of various neurotransmitter antagonists on suckling behavior of 370 3- and 4-day-old Sprague-Dawley rat pups. Peripheral administration of 3 serotonergic antagonists (methysergide, methiothepin, and metergoline) and a cholinergic antagonist (scopolamine) were observed to markedly reduce suckling behavior of neonatal Ss. These effects appear to be centrally mediated, since intracisternal administration of small doses of all these drugs was observed to suppress suckling. The reduction in suckling induced by these antagonists did not appear to be a result of a debilitating effect of the drugs or to be due to any alteration in body temperature. In contrast, the opiate antagonist naloxone, the dopaminergic antagonist haloperidol, the alpha-noradrenergic antagonist phentolamine, and the beta-noradrenergic antagonist propranolol did not consistently produce any alteration in suckling behavior. Results suggest that the serotonergic and cholinergic systems may be functioning much earlier in ontogeny than previously suggested and may be involved in modulating suckling behavior in the early neonatal period. (26 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Activation and odor conditioning of suckling behavior in 3-day-old albino rats.

Investigated circumstances under which a novel odor could elicit nipple attachment behavior in 3-day-old Sprague-Dawley rats. In Exp I, Ss suckled washed nipples scented with citral (a lemon odor) only if they either had received tactile stimulation (by stroking with a soft brush) or had been administered amphetamine in the presence of citral prior to the suckling test. Ss stimulated in citral's absence or only exposed to citral without stimulation failed to suckle such nipples. In Exp II, Ss stimulated in a benzaldehyde (an almond odor) ambience suckled washed nipples scented with benzaldehyde but not those with citral scent. The opposite held for those stimulated in a citral-rich environment. The stimulus conditions that supported this conditioning were investigated in Exp III. Simultaneously increasing citral concentration and raising ambient temperature markedly attenuated the phenomenon. Exp IV demonstrated that not all classes of stimulation produced conditioning. Caffeine, in a wide range of doses, did not allow citral to elicit suckling on washed nipples. Findings are discussed within a framework of higher-order conditioning and may provide a mechanism by which naturally occurring stimuli come to elicit the species- and age-typical behavior of suckling. (29 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The ontogeny of feeding in rats: I. Ingestive and behavioral responses to oral infusions.

Reports on 3 experiments with Charles River rat pups. When milk infusions were made through oral cannulas in the front of their mouths, 1–20 day old Ss actively ingested the diet, and their intake was related to the length of deprivation. Ss decreased their ingestive responding after they had consumed large volumes of milk. In addition, 1-, 3-, and 6-day-old Ss, when 24-hr deprived, exhibited an intense behavioral activation in response to milk infusion. The behavioral activation appeared to be stimulated primarily by taste and the opportunity to swallow. Milk infusions did not produce activation in older Ss; their behavior was more exclusively ingestive and food directed. Results demonstrate that (a) from birth, rat pups are capable of an active form of ingestion, independent of normal suckling from the mother; (b) such ingestion is controlled by physiological factors; (c) food has arousing properties in young animals; and (d) as pups grow older, their ingestive responding is refined from a generalized and nondirected activation to specific and directed feeding responses. (57 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Appetitive learning and extinction in 11-day-old rat pups: Effects of various reinforcement conditions.

Studied the acquisition and extinction of approach behavior in 96 11-day-old albino Sprague-Dawley rat pups in 3 experiments. The reinforcement in Exps I & II was 15 sec of nonnutritive suckling on an anesthetized lactating female. In Exp I, detention duration, 0- or 15-sec in the goal box on nonreward (N) trials, was studied in 2 groups whose acquisition training consisted of alternating blocks of rewarded and nonrewarded trials with a short (5-sec) intertrial interval. Exp II combined an examination of the effect of detention length with whether or not the mother was physically present, though inaccessible, on N trials with partially or continuously rewarded groups. Detaining Ss on N trials slowed the rate of extinction when the mother was present but increased the rate of extinction when she was absent. There was no evidence of a partial reinforcement extinction effect in any of the groups. The effectiveness of 6 types of reinforcement on promoting acquisition of approach behavior was assessed in Exp III. Equally good acquisition, but differences in extinction was obtained with an adult conspecific as the reinforcer, independent of sex and suckling, but there was no acquisition of approach responding when a sibling or no conspecific was in the goal box. These data extend earlier findings of appetitive learning and extinction in infant rats. They do not support the view that inhibitory mechanisms are absent in the rat until the 3rd or 4th wk of life. (24 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Ontogeny of passive avoidance learning in domestic chicks: Punishment of key-peck and running responses.

Determined the effect of the number of prepunishment acquisition trials on the age dependency of passive avoidance (PA) learning of the chick in keypeck and runway tests. In 9 experiments, 1- and 4-day-old Ss were first trained to respond for heat reward. After a variable number of reinforced acquisition trials (ATs), Ss' responses were punished with aversive wing shocks. Results show that the age dependency of PA learning of the young S is related specifically to the number of reinforced training trials given prior to PA testing. When several prepunishment ATs were given, 1-day-old Ss learned as quickly as 4-day-old Ss to withhold responding when punished. However, when only a few ATs preceded PA testing, 1-day-old Ss showed significantly less response suppression than 4-day-old Ss. Rather, results suggest that the 1-day-old chick, compared with the 4-day-old chick, is deficient in learning or detecting changes in stimulus– and/or response–reinforcement contingencies. (25 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Arthroscopic-assisted anterior cruciate ligament reconstruction with the central third patellar tendon. A 5-8-year follow-up

We reviewed 89 arthroscopically assisted patellar tendon anterior cruciate ligament (ACL) reconstructions for chronic isolated injuries with an average follow-up of 7 years (range 5.4 to 8.6 years). Pain was present in 7 knees (8%). Giving-way symptoms were reported by 7 patients (8%). A KT-2000 side-to-side difference over 5 mm at 30 lbs was recorded in 12 cases (16%). The pivot shift was glide in 17 cases (19%) and clunk in 10 (11%). A 3 degrees-5 degrees extension loss compared with the normal side was present in 20 knees (22%) and 6 degrees-10 degrees in 4 knees (4%). The intra-articular exit of the femoral tunnel was misplaced in the anterior 50% of the condyles along the roof of the notch in 10% of the knees. This positioning significantly (P = 0.003) increased the frequency of graft failure (62.5%) compared with the cases with a more posterior placement (graft failure 12%). An anterior position of the intra-articular exit of the tibial tunnel (in the anterior 15% of the sagittal width of the tibia) significantly (P = 0.01) increased the frequency of extension loss > 5 degrees. Medial meniscectomy was associated with a 35% incidence of narrowing of the medial joint space, which was significantly higher compared with knees with normal menisci (9%; P = 0.04) or with medial meniscal repair (7%; P = 0.05). In conclusion this study showed satisfactory anterior stability (KT-2000 side-to-side difference up to 5 mm and pivot absent or glide) in 83% of the knees. This percentage increases to 88% in the knees with a correct posterior and proximal femoral tunnel placement. Accuracy in tunnel positioning is essential for the success of ACL surgery. Meniscal repair was effective in decreasing joint space narrowing and should be attempted when possible.     

Extent of recovery from neonatal damage to the cortical visual system in cats.

Cats that received either marginal or marginal plus extramarginal lesions as 3-day-old kittens were assessed on a series of tests of visually guided behavior. These Ss were not conspicuously different from normal controls in avoiding obstacles or in activity level. Yet these same operated Ss were severely impaired in performance on the visual cliff and in visual discrimination learning, even when lesions were limited to the geniculocortical portion of the visual system. Maximum losses in pattern and form discrimination learning were observed only in Ss with severe retrograde degeneration in both the lateral geniculate nucleus and the complex of the pulvinar and nucleus lateralis posterior. Photically evoked potentials were recorded in the lateral regions of the neocortex more reliably from operated Ss that had made fewer errors in discrimination learning than from more severely debilitated cases; this relation was present even among cases with nearly equivalent amounts of retrograde degeneration in the visual thalamus. These findings suggest that in the cat (a) recovery of vision is incomplete after neonatal lesions of the visual cortex, and (b) a cortical system lateral to the geniculocortical projections may be involved in pattern vision. (29 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Behaviorally functional opioid systems in infant rats: II. Evidence for pharmacological, physiological, and psychological mediation of pain and stress.

Two experiments, with 160 10-day-old Sprague-Dawley rat pups, examined the behavioral characteristics of the neonatal opioid system during distressful situations, using a modification of the hot-plate paw-lick test. Ss were analgesic to heat following intraperitoneal morphine (0.5 mg/kg). Subcutaneous naloxone (0.5 mg/kg) prevented the analgesia. Morphine analgesia was significantly greater in Ss group-isolated from the dam. Saline controls group-isolated from the dam exhibited longer latencies than their nest-housed siblings. Individual isolation for 5 min markedly increased paw-withdrawal latency, and this effect was naltrexone reversible. Analgesia was not seen when Ss were tested directly from the nest or when grouped with others for 5 min. It is suggested that the opioid systems for stress and pain are functional in 10-day-old rats and that short-term isolation from the dam is a probable natural stressor modulated by endogenous opioid release. (51 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Age of first appearance of simultaneous and successive negative contrast in infant rats.

Simultaneous (SimNC) and successive (SNC) negative contrast, 2 paradoxical effects that are related to shifts in reward magnitude, were studied in 148 rat pups. In Exps I and II, 11-, 14-, and 17-day-old Ss were able to discriminate between the large (milk suckling) and small (dry suckling) reward odor cues as measured by attachment latencies, but only the 14- and 17-day-olds showed SimNC. At none of the 3 ages was a discrimination formed to the differential odor cues in the alley in terms of runway speeds. In Exp III, Ss were placed directly on the dam's ventrum to facilitate attachment. As in the earlier experiment, the 11-day-olds discriminated between the odors signaling the 2 reward conditions but did not show the SimNC effect. In Exp IV, SNC was shown at 17 days but not at 14 days in the attachment latency measure and at neither age in the run measure. These 4 experiments extend earlier findings that the paradoxical effects that emerge out of intermittent schedules of reward magnitude occur earlier than those associated with single abrupt shifts in reward magnitude. (31 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A neuroanatomical investigation of enhanced cutaneous and gustatory responsivity associated with septal forebrain injury.

Observed enhanced reactivity to cutaneous stimulation (handling and footshock) in 14 male Sprague-Dawley rats sustaining either large septal lesions or medial forebrain bundle ablations at the level of the septum. Cutaneously elicited hyperreactivity was not noted in 7 unoperated controls or 28 Ss with smaller septal lesions placed in the anterior, posterior, or dorsal septum or with lesions in the stria terminalis. All septal ablations but neither the medial forebrain bundle nor the stria terminalis lesions produced a gustatory hyperreactivity in the form of altered intakes of quinine and saccharin solutions. The gustatory hyperreactivity to quinine was clearly maximal in Ss with posterior ventral septal injury. Significantly, this lesion always extended into the medial preoptic nucleus. These results point to different neuroanatomical mechanisms in the septum underlying cutaneous- vs. gustatory-elicited behavior. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effect of visual deprivation on depth discrimination of hooded rats.

In a study with hooded rats (N = 530), Ss raised in the dark were compared to light-reared controls. 21-day-old dark-reared (DR) Ss were not different from controls in the discrimination of 4-in depths, but 30-day-old DR Ss were deficient. 60-day-old DR Ss were deficient in discriminating 4-, 6-, and 8-in depths. 30-day-old DR Ss recovered the loss in depth discrimination after 48 hrs in the light. 60-day-old DR Ss had no noticeable recovery to the 4-in depth discrimination, but they did recover discrimination of the 6-in depth after 72 hrs in the light. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Methysergide-induced nipple attachment depends on suckling experience in juvenile rats.

These studies were designed to investigate the links between pharmacological and behavioral procedures that facilitate suckling in weanling rats by assessing the effects of methysergide on nipple attachment behavior following experiential manipulations known to either promote or attenuate suckling. In the first experiment, methysergide failed to stimulate suckling in 25-day-old rats separated from their dam on Day 20, although it facilitated suckling in rats kept with the dam until either Day 24 or Day 25. In the second experiment, methysergide did not facilitate suckling in 35-day-old rats separated on Day 25, although rats separated on Day 30 or 34 were induced to suckle. In the third experiment, rats were housed with preweanling litters until Day 35 and then separated, housed with 25-day-old litters, or housed with preweanling litters for another 10 days. Rats in a fourth group remained with their dams until Day 35 and were then separated for 10 days. When tested at Day 45, nipple attachment was facilitated by methysergide only in the three groups that had received extended suckling experience. These results demonstrate that serotonergic inhibitory mechanisms modulate nipple attachment only when suckling experience is recent or extensive. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Potentiation and overshadowing in preweanling and adult rats.

Four experiments that compared the aversion acquired by 599 18- and 60-day-old Sprague-Dawley rats to a flavor that was either tasted alone or in combination (simultaneously or successively) with another flavor when paired with illness were conducted to study temporal variables and theoretical issues pertinent to potentiation and overshadowing while investigating ontogenetic differences in these phenomena. Results show that when either preweanlings or adults were presented with a simultaneous compound flavor (sucrose/coffee) followed by LiCl-induced illness, greater sucrose aversions were found than for Ss conditioned on sucrose alone. Preweanlings demonstrated greater potentiation than adults, whether the CS–UCS delay was 0 or 1 hr. This potentiation was eliminated by nonreinforced presentations of the alternative CS element. Potentiation was not observed when the 2 flavors were presented successively as the CS; instead, overshadowing occurred. Tests of configuring by extinction procedures indicated a tendency for these Ss to form a configured representation of the simultaneous compound solution. This disposition for configuring was more pronounced for preweanlings than for adults. Ontogenetic differences in response to configuration, CS saliency, and generalization decrement were consistent with the observed ontogenetic differences in potentiation. (33 ref) (PsycINFO Database Record (c) 2011 APA, all rights reserved)