Bilateral cochlear ablation in postnatal rat disrupts development of banded pattern of projections from the dorsal nucleus of the lateral lemniscus to the inferior colliculus.

Axonal projections from the dorsal nucleus of the lateral lemniscus (DNLL) distribute contralaterally in a pattern of banded layers in the central nucleus of the inferior colliculus (IC). The banded pattern of DNLL projections is already in the IC by onset of hearing in postnatal rat pups. Previously, it was shown that unilateral cochlear ablation in neonatal rat pups disrupted the banded pattern in IC for the projections of the DNLL contralateral to the ablation but not those of the DNLL ipsilateral to the ablation. In the present study, bilateral cochlear ablation or sham surgery was performed at postnatal day 9 (P9) after which rat pups were killed at P12 and the brains removed to study axonal projections of the DNLL. A lipophilic carbocyanine dye, 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI), was placed in the dorsal tegmental commissure of Probst to label decussating DNLL axons that end in the central nucleus of the contralateral IC. The distribution of labeled fibers across the central nucleus of the IC was analyzed in digital images by comparing the pattern of labeling with a sine model of periodic distribution of banded layers. In the control group, labeled axons formed a regular pattern of dense banded layers in IC. In the bilateral cochlear ablation group, labeled axons in the IC were distributed diffusely and there was little or no regular pattern of dense bands of axonal labeling. The influence of the cochlea on developing auditory circuits possibly mediated by activity-dependent mechanisms is discussed.

Development of banded afferent compartments in the inferior colliculus before onset of hearing in ferrets.

Axonal projections from the lateral superior olivary nuclei (LSO), as well as from the dorsal cochlear nucleus (DCN) and dorsal nucleus of the lateral lemniscus (DNLL), converge in frequency-ordered layers in the central nucleus of the inferior colliculus (IC) where they distribute among different synaptic compartments. A carbocyanine dye, 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI), was used as a tracer to study the postnatal development of axonal projections in the ferret IC. The results indicated that projections from all three nuclei are present at birth, but are not segregated into bands. During the postnatal week between approximately postnatal days 4 and 12 (P4-P12), axons from LSO proliferate in IC, become more branched, and segregate into a series of bands composed of densely packed fibers and endings. LSO projections in these afferent bands course parallel to IC layers and are separated by intervening regions with few endings. A modest fit of a sine curve (R2>0.15) to the pattern of spacing of LSO projections in IC indicated that regularly spaced bands are forming by P7. Similarly, banded patterns of DCN and DNLL projections to IC have developed by the end of the first postnatal week. Thus, well before hearing onset in ferret (P28-30), three different afferent projections have segregated into banded compartments along layers in the central nucleus of the ferret IC. Possible mechanisms in circuit development are discussed.

Unilateral cochlear ablation before hearing onset disrupts the maintenance of dorsal nucleus of the lateral lemniscus projection patterns in the rat inferior colliculus.

During postnatal development, ascending and descending auditory inputs converge to form fibrodendritic layers within the central nucleus of the inferior colliculus (IC). Before the onset of hearing, specific combinations of inputs segregate into bands separated by interband spaces. These bands may define functional zones within the IC. Previous studies in our laboratory have shown that unilateral or bilateral cochlear ablation at postnatal day 2 (P2) disrupts the development of afferent bands from the dorsal nucleus of the lateral lemniscus (DNLL) to the IC. These results suggest that spontaneous activity propagated from the cochlea is required for the segregation of afferent bands within the developing IC. To test if spontaneous activity from the cochlea also may be required to maintain segregated bands of DNLL input, we performed cochlear ablations in rat pups at P9, after DNLL bands already are established. All animals were killed at P12 and glass pins coated with carbocyanine dye, DiI (1,1'-dioctodecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate), subsequently were placed in the commissure of Probst to label the crossed projections from both DNLLs. When compared with surgical controls, experimental results showed a similar pattern of DNLL bands in the IC contralateral to the ablated cochlea, but a disruption of DNLL bands in the IC ipsilateral to the cochlear ablation. The present results suggest that cochlear ablation after DNLL bands have formed may affect the maintenance of banded DNLL projections within the central nucleus of the IC.

Unilateral cochlear ablation in adult ferrets results in upregulation in calretinin immunostaining in the central nucleus of the inferior colliculus.

In the present study, unilateral cochlear ablations were performed in adult ferrets in order to determine whether an upregulation of the calretinin immunostained plexus in the central nucleus of the inferior colliculus occurs and if so, what the time course of this upregulation is. Accordingly, the mean gray level and the calretinin-immunostained area of the axonal plexus in the central nucleus of the inferior colliculus were evaluated at 1, 20 and 90 days after cochlear ablation. In unoperated animals, the calretinin-immunostained plexus was bilaterally symmetric. In ablated animals, both the mean gray level and the immunostained area of the plexus increased in the central nucleus of the inferior colliculus contralateral to the lesion compared with both the ipsilateral side and unoperated animals. This upregulation was present 24 h after the ablation and did not change at the two subsequent time points. In a previous study in young ferrets, the immunostained area of the plexus in the central nucleus of the inferior colliculus contralateral to the lesion increased 200% compared with control ferrets [J Comp Neurol 460 (2003) 585], whereas it increased only 33% in adult ferrets. These findings suggest that 1) calretinin upregulation in the contralateral central nucleus of the inferior colliculus following cochlear ablation occurs by 24 h after cochlear ablation and 2) there is an age-related decline in the magnitude of this upregulation after cochlear ablation.

Discriminative stimulus effects of a low dose of apomorphine in the rat.

The discriminative stimulus (DS) effect of apomorphine was investigated in rats trained in a two-lever, food-reinforcement procedure. Rats were given subcutaneous injections of saline or 0.1 mg/kg apomorphine HCl, 15 min before training sessions. The training dose of apomorphine was chosen to activate dopamine autoreceptors selectively. Stimulus generalization studies demonstrated that the DS effects generalized completely to other direct-acting dopaminergic agonists such as N-n-propylnorapomorphine (NPNA), pergolide, lergotrile, and bromocriptine. The indirect-acting dopamine agonists, (+)amphetamine, cocaine, and methylphenidate produced predominantly saline-appropriate lever responses. The DS effect of apomorphine at the training dose was incompletely antagonized by haloperidol or metoclopramide. The dopaminergic antagonists tested, however, also partially generalized to apomorphine. Both enantiomers of 3-(3-hydroxyphenyl)-N-n-propylpiperidine (3-PPP) produced apomorphine-appropriate lever choice with the (-) enantiomer being slightly more potent. The discriminative property of this (0.1 mg/kg) dose of apomorphine has characteristics consistent with selective dopamine autoreceptor activation.

Dopamine agonists facilitate footshock-elicited locomotion in rats, and suppress level-press responding for food.

Several dopamine agonists (apomorphine, quinpirole, 7-OH-DPAT, and U-91356A) suppressed locomotor activities of rats exploring a Y-maze, presumably through activation of dopamine autoreceptors. If brief electric shocks were applied to the grid floor during exploration, locomotion was unchanged in control rats, but the locomotor suppression from the dopamine agonists was converted to a profound stimulation. This locomotor stimulation was completely antagonized by pretreatment with sulpiride. SKF 38393 and clonidine produced no locomotor stimulation in the shock environment. To test whether the locomotor stimulant effect from dopamine agonists generalized to a food-reinforced behavior, rats were trained to lever-press for food according to a multiple (VI-10", VI-40") schedule. The above compounds only suppressed responding with no stimulation, and the suppressant effect on food-reinforced behavior was also blocked by sulpiride. It is concluded that the behavioral inhibitory effect from dopamine autoreceptor activation can be readily overcome by exteroceptive stimulation, which uncovers a powerful motor stimulant effect. This stimulant effect, however, did not generalize to lever-press responding for food.

Discriminative stimulus properties of the dopamine D3 antagonist PNU-99194A.

It was recently documented that the relatively selective dopamine D3 receptor antagonist, PNU-99194A, is capable of establishing discriminative stimulus control in rats and that the discriminative cue associated with this compound is not similar to that produced by psychostimulants. The present experiment further characterized the discriminative stimulus properties of PNU-99194A by examining several other dopaminergic agents for stimulus generalization in 23 male Sprague-Dawley rats trained to discriminate 10 mg/kg PNU-99194A (SC, 15 min) from vehicle in a two-choice discrimination procedure under an FR10 schedule of food reinforcement. Rats achieved a criterion of ten consecutive sessions with correct lever choice after a median of 35.5 sessions (range 23-78). In substitution tests, the non-selective D2 receptor antagonist, haloperidol (0.01- 0.1 mg/kg), and the mixed D2/D3 antagonists, amisulpiride (3.2-32 mg/kg) and sulpiride (32-200 mg/kg), failed to produce stimulus generalization, while the D3-preferring antagonists, (-)-DS121 (1-10 mg/kg) and (+)-AJ76 (3.2-32 mg/kg), produced complete stimulus generalization. Direct and indirect DA agonists, including apomorphine (0.01-0.32 mg/kg) and d-amphetamine (0.1-1 mg/kg), the D1 agonist SKF38393 (10-100 mg/kg), the D2 selective agonist PNU-95666E (0.32-3.2 mg/kg) and the D3-preferring agonist pramipexole (0.032-1 mg/kg), all produced non-significant amounts of drug-appropriate responding and significantly reduced response rate. It is concluded that PNU-99194A produces a distinctive subjective cue which is probably based on D3 receptor antagonism.

Anxiolytic-like effects of PNU-101017, a partial agonist at the benzodiazepine receptor.

PNU-101017 is a chemically novel ligand at the benzodiazepine recognition site of cloned GABAA receptors. It was reported to potentiate GABA-mediated chloride current in cultured cells with a moderate intrinsic activity and a biphasic dose-response relationship. In this study, we confirmed that PNU-101017 has a partial agonist-like effect in the antagonism of metrazole-induced seizures in mice. It produced no sedation or ataxia, but did antagonize diazepam-induced motor deficit of mice in the rotarod test. PNU-101017 was weakly active in anti-conflict anxiolytic tests, but attenuated the plasma corticosteroid response to mild stress in rats. It also antagonized stress-induced elevation of cerebellar cGMP levels in mice. Like chlordiazepoxide, it increased drinking of saline solution in thirsty rats. PNU-101017 did not potentiate the CNS-depressant effects of ethanol, and produced no evidence of physical dependence when administered repeatedly. Agonists with low intrinsic activity at the benzodiazepine receptor, such as PNU-101017, should be further explored for therapeutic uses.

Reversal of scopolamine-induced amnesia and alterations in energy metabolism by the nootropic piracetam: implications regarding identification of brain structures involved in consolidation of memory traces.

Pretreatment with scopolamine, 3 mg/kg, prevented the acquisition of a passive avoidance task in rats. These amnesic effects of scopolamine could largely be overcome by treatment with 100 mg/kg of the nootropic drug piracetam. In order to identify the brain structures involved, the effects of these drugs on regional energy metabolism were measured throughout the brain, utilizing Sokoloff's 2-deoxyglucose autoradiographic procedures. Scopolamine, 3 mg/kg, reduced glucose utilization in several areas of the cerebral cortex. These effects were largest in the parietal and temporal cortices. Other areas affected included the sensorimotor and cingulate cortices, the ventral and lateral thalamus, and the dendritic neuropil of the CA1, CA2, and CA3 regions of the hippocampus. The regional depressions in glucose metabolism observed following scopolamine treatment in the rat had some resemblance to depressions in glucose metabolism reported for Alzheimer's disease patients in positron emission tomography studies. Piracetam, 100 mg/kg, did not alter the energy metabolism of any of the 41 brain regions examined. However, this dose of piracetam completely reversed the scopolamine-induced depressions in the hippocampus. Piracetam partially but significantly reversed the scopolamine effects in the cingulate cortex. It is concluded that the data provide support for the hippocampal-cholinergic theory of memory as originally formulated by Meyers and Domino in 1964 and give insight into the mechanisms by which nootropics work.

Discriminative stimulus properties of physostigmine in rats.

Sprague-Dawley rats were trained to discriminate a subcutaneous injection of physostigmine (0.2 mg/kg) from a similar injection of saline in a two-lever, food-reinforced behavior paradigm. The training dose of physostigmine reduced the response rate to about 50% of that in saline sessions. The discriminative stimulus (DS) effect of physostigmine is mediated by a central cholinergic mechanism since it was antagonized by scopolamine (0.1 mg/kg), but was unaffected by methylscopolamine (1 mg/kg) or pirenzepine (3 mg/kg). Neostigmine produced predominantly saline-appropriate lever choice. Compounds which produced averages of greater than 80% responses on the physostigmine lever are: compound BM-5 (N-methyl-N-(1-methyl-4-pyrrolidino-2-butynyl)-acetamide), tetrahydroaminoacridine (THA), RS-86 (2-ethyl-8-methyl-2,8-diazaspiro-(4,5)-decan-1,3-dion hydrobromide), cis-AF30 (2-methyl-spiro-(1,3-dioxolane-4,3')-quinuclidine), and pilocarpine. In comparison, oxotremorine, aceclidine (3-acetoxy-quinuclidine), arecoline, and nicotine produced a maximum average responding of 40-70% on the physostigmine lever. The DS effect of physostigmine in rats appeared to involve a greater participation of M1 and M2 muscarinic or the nicotinic receptor in the brain.

Quinpirole-induced locomotor stimulation in rats develops rapid sensitization when combined with brief footshocks.

In rats exploring a symmetrical Y-maze, an acute injection of quinpirole or intermittent brief footshocks did not change the level of locomotion. The combined treatment of quinpirole and footshocks elicited an immediate locomotor stimulation. When the experimental session was repeated daily, there was a further increase of hyperlocomotion (i.e. sensitization). In parallel groups of rats treated with quinpirole and placed in the Y-maze daily without shock, or subjected only to daily footshock, locomotor activity did not increase. Footshock, therefore, has a synergistic effect in the development of sensitization to quinpirole. When the dose-response relationships of quinpirole were compared between naive and sensitized animals, the magnitude of stimulation differed, but the threshold stimulant dose did not change. Pretreatment with sulpiride completely antagonized the hyperlocomotion in both drug-naive and quinpirole-sensitized rats. The results support a view that quinpirole facilitates the emergence of patterned motor behaviors. Non-contingent, brief footshock elicits running as the prepotent behavior in the Y-maze, and hastens the development of behavioral sensitization to quinpirole.

Acquisition of brightness discrimination in the rat is impaired by opiates with psychotomimetic properties.

The acquisition of shock avoidance behavior by rats was studied in an automated Y-maze which incorporates a simultaneous brightness discrimination paradigm. When administered prior to each of 5 consecutive daily sessions, two opiate derivatives with psychotomimetic properties, cyclazocine and N-allylnormetazocine, impaired the acquisition of brightness discrimination at doses which also increased movements between trials. These effects were similar to those produced by phencyclidine, ketamine, and a high dose of d-amphetamine. Pretreatment with morphine, pentazocine and scopolamine at motor stimulant doses before each training session did not affect acquisition of brightness discrimination. Nalorphine, naltrexone, and chlorpromazine also had no effect on brightness discrimination, even at motor depressant doses. Whereas the motor stimulation produced by morphine or pentazocine was blocked by naltrexone, the motor stimulation and discrimination disruption produced by cyclazocine or N-allylnormetazocine were only incompletely antagonized by naltrexone. The results demonstrate similarities between psychotomimetic opiates and phencyclidine-like compounds and may reflect the sensory or cognitive disturbance produced by these drugs in man.

Amnesia produced by intracerebroventricular injections of hemicholinium-3 in mice was prevented by pretreatment with piracetam-like compounds.

Intracerebroventricular (ICV) injections of hemicholinium-3 (HC-3) to mice before the training trial in a passive avoidance task produced an amnesic effect at the 24-hour retention test. Pretreatment by IP injection of piracetam, etiracetam, or pramiracetam, 30 minutes before HC-3 injections antagonized the amnesic effects of HC-3. Pretreatment with choline was not effective. The depletion of cerebral acetylcholine by the HC-3 injection was not prevented by piracetam or etiracetam.

Phencyclidine-like behavioral effects of 2-methyl-3,3-diphenyl-3-propanolamine (2-MDP).

2-Methyl-3,3-diphenyl-3-propanolamine (2-MDP) produced effects in animals similar to those produced by the dissociative anesthetics such as phencyclidine (PCP). Specifically, it shared the discriminative stimulus properties of PCP in rats trained to discriminate PCP (1 mg/kg) from saline; at higher doses, it disrupted brightness discrimination and stimulated locomotor activities in rats trained to avoid shocks in an automated Y-maze; and it produced surgical anesthesia when injected IV to rhesus monkeys. These pharmacological activities were observed only with the levo-isomer of 2-MDP. The dextro-isomer was either inactive or produced opposite effects, depending on the tests. Among several related diphenylpropylamines, 2-MDP represents the optimal structure for potency of PCP-like effects since changes in the amino, 2-methyl and 3-hydroxy groups reduced the potencies of the PCP-like discriminative properties.

The discriminative stimulus effects of diazepam in rats at two training doses.

Two groups of rats were trained to discriminate either a low (1 mg/kg) or a high (10 mg/kg) intraperitoneal dose of diazepam from vehicle injections in a two-lever, food-reinforcement procedure. Comparison of the dose-response curves demonstrated a difference in the intensity of the stimulus effects. A number of benzodiazepine agonists and partial agonists were tested for stimulus generalization. The stimulus effect in both groups of rats generalized fully to triazolam, alprazolam, adinazolam and pentobarbital. Ro 17-1812 occasioned nearly full generalization in both groups of rats with a shallow dose-response slope. The low-, but not the high-dose stimulus effect generalized to the following compounds: CL 218872, ZK 91296 (ethyl-5-benzyloxy-4-methoxymethyl-B-carboline-3-carboxylate), CGS 20625 (2-(4-methoxyphenyl)-2,3,5,6,7,8,9,10-octahydrocyclohepta(b)pyrazo lo(3,4- d)pyridin-3-one) and U-78875 (3-(5-cyclo-propyl-1,2,4-oxadiazol-3-yl)-5-(1- methylethyl)imidazol(1,5-a)quinoxalin-4(5H)-o-ne). Flumazenil, FD-7142 (N-methyl-beta-carboline-3-carboxamide), buspirone and morphine occasioned predominantly vehicle-appropriate responses in both groups of rats. In the low-dose group, pretreatment with flumazenil (10 mg/kg) reduced responding on the diazepam-lever for the following compounds: diazepam, Ro 17-1812 (cyclopropylmethyl-(S)-8-chloro-12,12a-dihydro- 9-oxo-9H,11H-aceto(2,1-C)imidazo(1,5-a)(1,4)benzo-diazepine-1-carboxylat e), ZK 91296, CGS 20625, CL 218872 and U-78875.(ABSTRACT TRUNCATED AT 250 WORDS)

Disruption of brightness discrimination in a shock avoidance task by phencyclidine and its antagonism in rats.

Rats were trained to make a simultaneous brightness discrimination in order to avoid or escape foot shocks in an automated Y-maze. Brightness discrimination was completely disrupted by phencyclidine (PCP, 3 mg/kg), ketamine (30 mg/kg) and dexoxadrol (10 mg/kg). At these doses, there was increased locomotor activity between trials. The number of movement attempts to avoid shock during a trial were either unchanged or reduced. Several drugs with various clinical applications (chlorpromazine, haloperidol, diazepam, pentobarbital, d-amphetamine, propranolol, clonidine and prazosin) did not impair brightness discrimination in behavioral stimulant or depressant doses. The levoisomer of dexoxadrol, levoxadrol, was also inactive. Daily administration of PCP for 5 consecutive days produced progressive increases in locomotor stimulation with no tolerance to effects on brightness disruption. The disruption of brightness discrimination by PCP was not reversed by chlorpromazine, haloperidol, diazepam, propranolol or apomorphine at doses which reduced the locomotor stimulation by PCP. Both locomotor stimulation and discrimination disruption were blocked by prazosin and clonidine. A central adrenergic mechanism is implicated for some behavioral effects of PCP.

Adjustable sutures in strabismus surgery.

The benefits of the adjustable suture technique for strabismus surgery include the surgeon's ability to place the eye at the exact position desired in the immediate postoperative period. Depending on the type of deviation, this may be orthophoric, slight esophoric, or slight exophoric. Unexpected postoperative results are prevented which can occur when measurements and classical surgery are done in special problems such as paretic and restrictive strabismus and in reoperations. In addition precise alignment can be made in patients with weak fusion or fusion only in certain fields of gaze, and this should decrease the need for reoperation.

Behavioral effects of U-78875, a quinoxalinone anxiolytic with potent benzodiazepine antagonist activity.

U-78875 (3-(5-cyclopropyl-1,2,4-oxadiazol-3-yl)-5-(1-methylethyl) imidazo[1,5-a]-quinoxalin-4(5H)-one) is a chemically novel compound with a high affinity for the benzodiazepine receptors. It has anticonflict effects in both the Vogel and Cook-Davidson models of anxiety, with a potency similar to that of diazepam (1-3 mg/kg, i.p.). In unanesthetized rats implanted with cortical electrodes for EEG recording, i.p. injections of U-78875 (3-10 mg/kg) increased the EEG power density in frequencies above 12 Hz, and decreased EEG power at lower frequencies. This EEG effect is similar to that of diazepam, and was completely antagonized by pretreatment with flumazenil. In animal models measuring central nervous system depression, U-78875 is much weaker than diazepam. It produced minimal impairment of rotarod performance in rats at doses up to 30 mg/kg, but at lower doses completely reversed the impairment from 10 mg/kg of diazepam. In rats trained to avoid shocks in a shuttle box, U-78875 (3-10 mg/kg) increased avoidance responses and antagonized the suppression of avoidance from diazepam (10 mg/kg). In the mouse one-trial passive avoidance task, pretreatment with U-78875 (1-10 mg/kg) before training produced no anterograde amnesia, but completely blocked the amnesic effect from diazepam (10 mg/kg). The diazepam antagonist potency for U-78875 is 10 to 100 times that of flumazenil. This unusual profile of mixed agonist/antagonist activities suggests U-78875 to be a unique anxiolytic agent with a minimum of central nervous system depression.

PNU-96415E, a potential antipsychotic agent with clozapine-like pharmacological properties.

The atypical antipsychotic drug clozapine interacts with multiple transmitter systems, among them the D4 subtype of dopamine receptors. PNU-96415E is chemically unrelated to clozapine and has its highest binding affinity for the D4 and 5-HT2A receptors. In comparison to clozapine, PNU-96415E is weaker in binding to D1, D2, alpha1 and muscarinic receptors. PNU-96415E inhibited exploratory locomotor activity in mice and rats, and antagonized d-amphetamine-induced locomotor stimulation in rats. It antagonized apomorphine-induced cage climbing, and blocked head and body twitch produced by 5-HTP in mice. Like clozapine, but unlike haloperidol, PNU-96415E did not antagonize stereotypic behaviors produced by a high dose of d-amphetamine or methylphenidate in rats and mice. PNU-96415E blocked conditioned avoidance in rats but produced no catalepsy, a pattern similar to clozapine but different from haloperidol. In rats trained to discriminate clozapine from saline injections, the stimulus effect generalized completely with PNU-96415E, but not haloperidol. This profile of pharmacological activities is consistent with that of an atypical antipsychotic and, as in the case with clozapine, the behavioral effects of PNU-96415E cannot be ascribed to a single receptor mechanism.

Pharmacology of a mixed 5-hydroxytryptamine1A/dopamine agonist.

U-67413B (4-hydroxydipropylaminodihydrophenalene) bound with high affinity to both 5-hydroxytryptamine (HT)1A and D2-dopamine (DA) receptor sites. U-67413B depressed 5-HT and DA cell firing rates and depressed synthesis of both neurotransmitters. The drug depressed mouse body temperatures by an amount similar to that for buspirone, gepirone and ipsapirone, but less than that for 8-hydroxy-N,N-dipropyl-2-aminotetralin. In rats, it produced the 5-HT1A behavioral syndrome. In contrast to 5-HT1A agonists having DA antagonist effects, U-67413B mildly depressed rather than stimulated firing rates of noradrenaline (NA) neurons in the locus ceruleus by a non-alpha-2 receptor mechanism. In behavioral tests designed to measure anxiolytic activities, U-67413B was a slightly more effective anxiolytic than standard 5-HT1A anxiolytics (buspirone, gepirone and ipsapirone). The data are consistent with the hypothesis that effects of 5-HT1A agonists on NA neuron activity are mediated through effects on dopaminergic mechanisms, and that effects on NA neurons could modulate anxiolytic activities of 5-HT1A agonists.