Impaired learning and motor behavior in heterozygous Pafah1b1 (Lis1) mutant mice.

Heterozygous mutation or deletion of Pafab1b1 (LIS1) in humans is associated with syndromes with type 1 lissencephaly, a severe brain developmental disorder resulting from abnormal neuronal migration. We have created Lis1 heterozygous mutant mice by gene targeting. Heterozygous mutant mice are viable and fertile, but display global organizational brain defects as a result of impaired neuronal migration. To assess the functional impact of the mutation, Lis1 heterozygous mice and their wild-type littermates were evaluated on a wide variety of behavioral tests. Lis1 mutant mice displayed abnormal hindpaw clutching responses and were impaired on a rotarod test. Lis1 heterozygous mice were also impaired in the spatial learning version of the Morris water task. Impaired motor behavior and spatial learning and memory in Lis1 mutant mice indicates that impaired neuronal migration can have functional effects on complex behavioral responses. The behavioral findings also support the use of the Lis1 mutant mice as a model from human type 1 lissencephaly.

Behavioral effects of ivermectin in mice.

BACKGROUND AND PURPOSE: Ivermectin is a common anthelmintic drug, widely used in laboratory rodents for treatment of pinworm and mite infestations. We evaluated the action of ivermectin on sensitive behavioral tasks in mice during treatment for mites within a barrier facility. METHODS: A total of 21 (5 males, 16 females) mice (129/SvEv) were used for measuring body weight, open field locomotor activity, and rotarod motor coordination. For acoustic startle and prepulse inhibition, 20 C57BL/6J and 29 AKR/J mice were studied. For the Morris water task, the same 20 C57BL/6J mice were studied. Ivermectin (0.08% sheep drench) was administered in the drinking water of the home cage for 8 weeks. Control groups received normal tap water in identical bottles. RESULTS: Ivermectin did not affect general health, body weight, motor coordination, swimming behavior, or spatial learning in several inbred strains of mice. However, it induced a small but significant effect on some sensitive behaviors. CONCLUSIONS: A cautious approach to initiating ivermectin treatment in mice should be used for sensitive behavioral experiments.

Inbred strain differences in prepulse inhibition of the mouse startle response.

Prepulse inhibition is the phenomenon in which a weak prepulse stimulus suppresses the response to a startling stimulus. Patients with schizophrenia have impaired prepulse inhibition which is thought to reflect dysfunctional sensorimotor gating mechanisms. To investigate the potential genetic basis for differences in sensorimotor gating, the responses of 13 inbred strains of mice were evaluated using the prepulse inhibition paradigm. Ten male mice from A/J, AKR/J, BALB/cByJ, BUB/BnJ, C3H/HeJ, C57BL/6J, C57BL/10J, DBA/2J, FVB/NJ, ST/bJ, 129/J, 129/SvJ, 129/SvEvTac inbred strains were tested for acoustic prepulse inhibition of acoustic and tactile startle responses. There was a wide range of responses among the inbred strains of mice. Exact strain distributions were determined for each combination of prepulse sound level and startle stimulus. In general, mice from the 129/SvEvTac, AKR/J, 129/J, and 129/SvJ strains displayed high levels of prepulse inhibition of both the acoustic and tactile startle responses. C57BL/6J, C57BL/10J and BUB/BnJ mice showed low levels of prepulse inhibition. There was also a wide range in the amplitude of the acoustic and tactile startle responses. C57BL/10J and FVB/NJ mice displayed the greatest startle responses and DBA/2J, 129/J and 129/SvJ had the poorest startle responses. There was no correlation between the level of prepulse inhibition and the amplitude of the startle response. These findings indicate that inbred strains of mice may be a useful tool to study the genetic basis of sensorimotor gating.

Galanin receptor antagonists M40 and C7 block galanin-induced feeding.

Two peptide antagonists of the galanin receptor, M40 (galanin[1-13]-Pro-Pro-[Ala-Leu]2-Ala amide) and C7 (galanin[1-13]-spantide amide), significantly inhibited galanin-induced consumption of a palatable wet cookie mash, when microinjected intraventricularly to satiated rats. Antagonists were effective at doses equimolar to or less than the active doses of galanin. Feeding induced by an overnight fast was not significantly different in rats microinjected with saline as compared to M40 or C7, at doses which inhibited galanin-induced feeding. The activity of the chimeric compound, C7, did not appear to be linked to the properties of its C-terminal spantide-like sequence, as C7 did not induce barrel rolling at doses which inhibited galanin-induced feeding. The IC50 for displacement of 125I-[Tyr26]-porcine galanin 1-29 binding in rat hypothalamic membranes was 15 nM for M40, and 0.2 nM for C7, as compared to 0.8 nM for unlabelled porcine galanin(1-29). These two structurally different galanin antagonists, both demonstrating antagonist activity in vivo in awake, behaving rats, provide promising tools for further analyses of the functional activity of galanin in the mammalian brain.

Centrally administered cholecystokinin suppresses feeding through a peripheral-type receptor mechanism.

Agonists and antagonists selective for the brain-type [cholecystokinin (CCK)-B] and the peripheral-type (CCK-A) CCK receptor were used to localize the site(s) of action at which CCK inhibits food consumption. BC 264, a highly selective CCK-B receptor agonist, did not decrease consumption of a palatable meal when administered either i.p. or into the lateral ventricles of the brain, whereas CCK decreased feeding when administered i.p. at the same doses. CCK decreased feeding when administered i.v.t. at a high dose, 5 micrograms. L-364,718, an antagonist selective for the CCK-A receptor, blocked completely the action of centrally administered CCK, whereas L-365,260, a selective CCK-B receptor antagonist, had no effect on the ability of centrally administered CCK to inhibit feeding. To estimate the quantity of i.v.t. administered CCK which reached the periphery, a tracer of radiolabeled [3H]p-CCK8 ([3H]CCK octapeptide sulfate), combined with unlabeled pCCK8 (5 micrograms) was administered i.c.t. Thirty minutes after administration, intact radiolabeled pCCK8 was extracted from the plasma and measured in the blood in nanomolar concentrations, exceeding the amounts of CCK octapeptide sulfate reported previously to be present in the plasma after a meal. Intraventricularly administered CCK thus appears to reduce feeding in the rat through a mechanism involving a CCK-A receptor subtype in the periphery.

Activity of centrally administered galanin fragments on stimulation of feeding behavior and on galanin receptor binding in the rat hypothalamus.

Synthetic fragments of galanin 1-29 were administered intraventricularly or into the paraventricular nucleus of the hypothalamus for analysis of the critical amino acid sequence necessary to stimulate feeding behavior in rats. Galanin 1-29 and galanin fragment 1-16 significantly increased feeding at doses of 6 nmol microinjected into the lateral ventricles and 1 nmol microinjected into the hypothalamus. There was no significant effect of D-TRP2 galanin 1-16 microinjected into the hypothalamus, and no significant effect of galanin fragments 1-9, 10-20, 12-29, 17-29, or 21-29 microinjected intraventricularly, on food consumption. Synthetic fragments of galanin 1-29 were assayed for displacement of 125I-galanin 1-29 binding to rat hypothalamic membranes. The efficacies of the galanin fragments in the feeding paradigm were consistent with the relative affinities of these fragments for the hypothalamic galanin receptor in equilibrium binding experiments. The first 16 N-terminal amino acids appear to contain galanin agonist activity on increasing food consumption and to bind to the galanin receptor in the rat hypothalamus.

Anatomical analysis of frontal cortex sites at which carbachol induces motor seizures in the rat.

High amplitude spiking representative of seizures, accompanied by an unusual motor behavior pattern of rearing and forelimbic clonus resembling "boxing," was elicited by microinjection of the cholinergic agonist, carbachol, 4 micrograms, into the medial prefrontal cortex of the rat. A rating scale devised to score the behavior revealed a motor pattern elicited by carbachol from the medial anterior cortex which was similar to that described by Racine for electrical stimulation of the amygdala. Topographical analysis of the areas surrounding the medial anterior cortex region revealed that the motor manifestations of seizures were elicited over a wide region of the anterior cortex, with scores significantly lower at carbachol microinjection sites greater than 1 mm rostral, 2 and 3 mm caudal, and 2 mm lateral to the standard medial prefrontal cortex site. Unilateral microinjection of carbachol yielded motor seizures primarily from the contralateral forepaw, suggesting involvement of a crossed pathway. Retrograde tracing with fast blue dye, combined with immunostaining for choline acetyltransferase and NADPH-diaphorase, found that the cholinergic neurons innervating the standard microinjection site were the dorsolateral tegmental cells, as previously reported, which have been shown to also contain substance P and corticotropin releasing factor. In addition, cholinergic neurons of the nucleus basalis of Meynert region were found to innervate the standard microinjection site. These findings implicate cholinergic innervation of the rostral cortex in classical limbic seizures.

Site of action of anorectic drugs: glucoprivic- versus food deprivation-induced feeding.

Feeding induced by 2-deoxyglucose was compared with feeding induced by food deprivation in terms of antagonism by anorectic drugs and of anatomical site of action. Glucoprivic feeding was completely blocked by microinjection of amphetamine, fenfluramine, and mazindol into the paraventricular nucleus of the hypothalamus (PVN). Deprivation-induced feeding was not blocked by amphetamine, fenfluramine, or mazindol microinjected into the PVN. Neither the feeding induced by 2-deoxyglucose nor its reversal by amphetamine were blocked by pretreatment with the beta-adrenergic antagonist, propranolol. Amphetamine and fenfluramine blocked both glucoprivic- and deprivation-induced feeding when microinjected into the perifornical region of the lateral hypothalamus. These data suggest that food consumption induced by 2-deoxyglucose treatment can be antagonized by anorectic drugs acting at recognition sites present in several hypothalamic nuclei, while deprivation-induced feeding acts through different receptor mechanisms which may be specific to the perifornical region of the lateral hypothalamus.

Anxiolytic activity of an endogenous adrenal steroid.

The A-ring reduced metabolite of deoxycorticosterone, 3 alpha, 5 alpha-tetrahydrodeoxycorticosterone (THDOC) was recently shown to act at the gamma-aminobutyric acid receptor-chloride ion channel complex in rat brain. The behavioral profile of THDOC was investigated using two animal models of anxiety, the two-chambered mouse exploration test and the lick suppression conflict test. THDOC showed anxiolytic activity in both animal models, with an anxiolytic dose range, 5-15 mg/kg i.p., separable from the sedative dose range, above 20-30 mg/kg i.p.

Behavioral investigation of the coexistence of substance P, corticotropin releasing factor, and acetylcholinesterase in lateral dorsal tegmental neurons projecting to the medial frontal cortex of the rat.

Colocalization of substance P (SP), corticotropin releasing factor (CRF), and acetylcholinesterase (AChE) was detected by retrograde tracing and immunocytochemical staining in the nucleus tegmentalis dorsalis lateralis (ntdl) projecting to the medial frontal cortex (MFC), septum, and thalamus of the rat. The histochemical results suggest that SP and CRF coexist within a subpopulation of ntdl cholinergic neurons that project to a number of forebrain regions including the MFC. Behavioral studies of the effects of SP, CRF, and the cholinergic agonist, carbachol, employed microinjections into the MFC of rats. SP and CRF did not elicit any behavioral effects when administered alone. Carbachol (1-5 micrograms/side) produced a stereotyped motor behavior, consisting of rapid forepaw treading while in an upright posture, resembling "boxing." SP (1 micrograms/side) increased carbachol-induced "boxing." CRF (1-10 ng/side) decreased carbachol-induced "boxing." One possible functional significance of the coexistence of SP, CRF, and acetylcholinesterase, in neurons projecting to the medial frontal cortex in rats, appears to be a modulatory potentiation of cholinergic response by SP, and a modulatory inhibition of the cholinergic response by CRF.