Preservation of binocularity after monocular deprivation in the striate cortex of kittens treated with 6-hydroxydopamine

The change with age in biogenic amines and their metabolites in the striatum of the rat

The changes in the content of the biogenic amines and their metabolites in the striatum of the rat during the aging period (3-30 months) have been studied. The maximum levels of dopamine (DA) have been found at 6 months of age and this concentration is maintained until 24 months. Between 24 to 30 months there is a decrease in the concentration of this compound. At that time, there is a slight increase in 3,4-dihydroxyphenyl acetic acid (DOPAC) and homovanillic acid (HVA) concentration, the main metabolites of DA, which suggests a slight increase in DA metabolism. The 3-methoxytyramine (3-MT) concentration also increases at this time. The maximum concentration of noradrenaline (NA) was also found at 6 months of age. Tryptophan has the maximum concentration after DA and this is maintained over the life-span of the rat. The concentration of serotonin (5-HT) is high and does not change during this period. However, the concentration of 5-HT, as occurred with DA, decreased between 24 and 30 months. Also the DA/5-HT ratio does not change during the period studied.

Selective lesioning of forebrain noradrenaline neurons at birth abolishes the improved maze learning performance induced by rearing in complex environment

The effect of selective destruction of forebrain noradrenaline (NA) neurons induced by 6-hydroxydopamine (6-OHDA) at Day 1 after birth on Hebb-Williams maze performance was investigated in adult rats housed after weaning in a complex environment (EC) or an isolated (IC) environment for 35 days. Saline treated control rats raised in the EC made fewer errors than those raised in the IC. This effect of EC was completely abolished in 6-OHDA treated rats; for these animals no improved performance due to the housing condition was obtained. Protection of the NA neurons against 6-OHDA neurotoxicity by pretreatment with desipramine (DMI) resulted in an effect of EC identical to that seen in saline-treated controls. Postweaning housing in the IC led to an increased locomotion as compared to housing in EC, but this effect was not affected by neonatal 6-OHDA and/or DMI treatment. Neurochemical analysis confirmed cortical NA and metabolite depletion as well as a good protection by the DMI pretreatment. The present results indicate that central NA neurons are involved critically in mediating mainly the cognitive components of behavioral alterations induced by EC.

Effects of neonatal forebrain noradrenaline depletion on recovery from brain damage: performance on a spatial navigation task as a function of age of surgery and postsurgical housing

The experiments examined the contributions of forebrain noradrenaline and environmental enrichment to recovery of place navigation ability in rats after hemidecortication in infancy or adulthood. Noradrenaline depletion did not affect recovery from neonatal hemidecortication, although the early hemidecortications did allow sparing of function relative to adult operates. Noradrenaline depletion also failed to attenuate the positive effects of enriched housing on otherwise normal rats. Noradrenaline depletion did retard recovery of adult hemidecorticate rats housed in standard laboratory cages, but it did not retard recovery of adult hemidecorticate rats housed in enriched environments. The results suggest that noradrenaline is importantly involved in enhancing recovery from brain damage when other sources of compensation (e.g., neonatal injury, enriched environment) are absent.

Concentration-dependent suppression by beta-adrenergic antagonists of the shift in ocular dominance following monocular deprivation in kitten visual cortex

We showed that beta-adrenergic receptor antagonists blocked the shift in ocular dominance following brief monocular deprivation in young kittens. Localized microperfusion of propranolol into the kitten visual cortex reduced the expected shift in the ocular dominance approximately 2 mm away from the center of perfusion. The blocking effect, however, did not reach an area approximately 5 mm from the perfusion center, suggesting that beta blockers work in a concentration-dependent fashion in the present paradigm. We further studied the concentration-effect relationship by widely changing the concentration of beta blockers (propranolol and sotalol) stored in an osmotic minipump. The proportion of binocular cells increased from 0.13 to 0.67 when the concentration of propranolol was increased from 10(-6)M to 10(-2)M, giving the half-maximum effect (binocularity, 0.40) at about 10(-4)M propranolol. However, the maximum binocularity obtained with the sotalol perfusion under the comparable condition was apparently much lower (0.45) than that with propranolol. Accordingly, the half-maximum binocularity (0.30) was obtained at about 10(-5)M sotalol. We also noted the presence of a linear, inverse relation between the logarithmic concentration of the beta blockers and the extent of the shift in ocular dominance as measured by the proportion of monocular cells which responded exclusively to stimulation of the nondeprived eye. The latter decreased from 0.75 to 0.25, when the former was increased from 10(-6)M to 10(-2)M (in an osmotic minipump). The two beta blockers behaved similarly in this correlation. The intracortical spread of locally perfused [3H]propranolol was studied at the end of the cortical perfusion which lasted for a week. The radioactivity was highest at the perfusion center and rapidly declined with increasing distance, leveling off approximately 3 mm from the perfusion center. The average "dilution factor" of locally perfused [3H]propranolol was calculated as about 1/170 of the original solution in an area of physiological recordings (approximately 2 mm from the perfusion center). Applying the "dilution factor" of 1/170, we estimated the approximate concentration of beta blockers needed at the recording sites to obtain the half-maximum effect; it was about 5.8 X 10(-8)M for sotalol. Taken together, the present results were interpreted as suggesting that there is a positive correlation between the number of activated beta-adrenergic receptors within the visual cortex and the extent of changes in ocular dominance following monocular deprivation.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholine-rich neuronal grafts in the forebrain of rats: effects of environmental enrichment, neonatal noradrenaline depletion, host transplantation site and regional source of embryonic donor cells on graft size and acetylcholinesterase-positive fibre outgrowth

The importance of several factors influencing the survival of cholinergic-rich embryonic tissue transplanted to the adult rat forebrain and the extent of acetylcholinesterase-positive fibre innervation of the host brain was investigated in 3 experiments. In the first two experiments, embryonic ventral forebrain tissue was grafted to the neocortex of rats in which the intrinsic cortical cholinergic innervation had been removed by nucleus basalis lesions. Housing the host rats in an enriched environment produced a temporary enhancement of fibre outgrowth 4 weeks after transplantation, but this was not maintained after 10 weeks. Fibre outgrowth was greater when the grafts were transplanted to the noradrenaline-depleted neocortex than to the intact neocortex. Neither environmental enrichment nor noradrenaline depletion influenced graft survival or size. In the third experiment, the embryonic donor tissue was dissected to separate regions containing precursors of the nucleus basalis cholinergic cells from regions containing precursors of the septal cholinergic cells, and transplanted to either the neocortex following nucleus basalis lesions or to the hippocampus following fimbria-fornix lesions. Nucleus basalis grafts showed greater growth in size than septal grafts, and grafts placed into the hippocampus showed greater growth in size than grafts placed into the neocortex. More interestingly, the extent of fibre outgrowth depended on the appropriateness of the donor tissue to the host transplantation site: nucleus basalis tissue showed greater acetylcholinesterase-positive outgrowth than septal tissue in the neocortex, whereas septal tissue showed greater outgrowth than nucleus basalis tissue in the hippocampus.

The ontogeny of the laminar distribution of beta-adrenergic receptors in the visual cortex of cats, normally reared and dark-reared

Patterns of distribution of beta 1 and beta 2 adrenergic receptors were examined autoradiographically in slide-mounted sections from the visual cortical areas of 22 developing cat brains, using [125I]iodopindolol as the ligand in combination with displacers specific for beta 1 and beta 2 subtypes of adrenergic receptors. Within visual cortical areas 17 and 18 of adult brains, the density of beta 1 and beta 2 adrenergic receptors was highest in laminae I-III, lowest in lamina IV, and intermediate in laminae V-VI. For beta 1 adrenergic receptors, this laminar distribution was also seen in visual area 19 as well as in the non-visual area 7 that is lateral to area 19. By contrast, the distribution of beta 2 adrenergic receptors varied across cortical areas, such that its density was more homogeneous across the laminae in area 19, and decreased in all laminae in area 7. This pattern of distribution in adult brains was already formed at the beginning of the critical period and was not disturbed by dark-rearing.

Neonatal 6-hydroxydopamine lesion of forebrain norepinephrine does not eliminate critical period for behavioral effects of gonadal hormone manipulation

Newborn rats were injected s.c. with 6-hydroxydopamine to deplete forebrain norepinephrine (NE) or with the vehicle. The males were then castrated at 4 days and the females injected with testosterone at 5 days of age. Both sexes were tested for female-like sexual responsiveness to a stud male at 6 months of age. The loss of forebrain NE did not prevent the feminization of the males due to castration or the masculinization of the females due to testosterone. This result contraindicates a general permissive-requisite role for forebrain NE for the mammalian brain's plasticity during its critical periods.

Modulation of visual cortical plasticity by acetylcholine and noradrenaline

During a critical period of postnatal development, the temporary closure of one eye in kittens will permanently shift the ocular dominance (OD) of neurones in the striate cortex to the eye that remains open. The OD plasticity can be substantially reduced if the cortex is infused continuously with the catecholamine neurotoxin 6-hydroxydopamine (6-OHDA) during the period of monocular deprivation, an effect that has been attributed to selective depletion of cortical noradrenaline. However, several other methods causing noradrenaline (NA) depletion leave the plasticity intact. Here we present a possible explanation for the conflicting results. Combined destruction of the cortical noradrenergic and cholinergic innervations reduces the physiological response to monocular deprivation although lesions of either system alone are ineffective. We also find that 6-OHDA can interfere directly with the action of acetylcholine (ACh) on cortical neurones. Taken together, our results suggest that intracortical 6-OHDA disrupts plasticity by interfering with both cholinergic and noradrenergic transmission and raise the possibility that ACh and NA facilitate synaptic modifications in the striate cortex by a common molecular mechanism.

Autoradiographic study of beta 1-adrenergic receptor development in the mouse forebrain

The development of beta 1-adrenergic receptors has been studied in the mouse forebrain from embryonic day 14 (E14) to adulthood, using autoradiographic visualization of [125I]iodocyanopindolol (ICYP) binding sites. From E14, ICYP binding sites are detected in moderate amounts in the striatum and basal forebrain and in very low concentration in the cortical plate. At E17, binding sites have increased in number in the deep layers of the embryonic cortex and extend over the whole thickness of the cortical ribbon at birth. On postnatal day 4 (P4), ICYP binding sites are more abundant in the superficial than in the inner cortex. By P10 the adult pattern of ICYP binding site distribution is achieved, namely: a high concentration in ventral pallidum, striatum and cortical layers I, II and III, a moderate concentration in layers V and VI and a lower density in septal areas and in cortical layer IV. It is well established that norepinephrine fibers arrive in the embryonic cortex early in development. The present results show that the development of norepinephrine fiber and beta 1 receptor systems are coincident in the mouse.

The brain as a self-organizing system

Clinical evidence and numerous results from animal experimentation indicate that cognitive functions have to be learned. Brain structures subserving these functions require sensory experience for their maturation. Genetic instructions are in principle not sufficient to specify neuronal connections with sufficient precision. Self-organization processes are implemented in addition which allow to optimize genetically determined blue prints of connectivity by making use of functional criteria. Thus, neuronal activity becomes an important shaping factor in the development of the structural and functional architecture of the forebrain. To the extent that this neuronal activity is modulated by sensory signals, environmental factors can influence the development of neuronal networks. Recent experiments indicate that these shaping processes are additionally controlled by modulatory systems. Both, the noradrenergic projection from the locus coeruleus and the cholinergic projection from the basal forebrain facilitate activity-dependent long-term changes of neuronal connections during development. The activity of these modulatory systems in turn depends on central states such as arousal, attention, and perhaps also motivation. It is inferred from this evidence that experience-dependent self-organization should not be considered as a passive imprinting process but rather as an active dialogue between the brain and its environment. The hypothesis is discussed that many developmental disturbances which are commonly attributed to deprivation are in fact due to defaults of the CNS which either lead to the formulation of wrong questions or to the reduction of exploratory drive.

Visual behavior of monocularly deprived kittens treated with 6-hydroxydopamine

Several investigators have reported that treating the visual cortex with 6-hydroxydopamine (6-OHDA) preserves the ability of a monocularly deprived eye to drive cells in the visual cortex. If 6-OHDA provides useful protection from the effects of monocular deprivation, it should also prevent the behavioral blindness that normally accompanies monocular deprivation. To test this prediction we compared the visual behavior of monocularly deprived kittens pretreated with 6-OHDA with that of kittens similarly deprived, but not drug-treated. Kittens were trained on a visual discrimination task before drug treatment or suture. Starting at about 5 weeks of age the kittens were given 6-OHDA via ventricular cannula, given vehicle solution, or given no treatment at all. At about 6 weeks of age all kittens were monocularly deprived for one week. When the deprived eye was opened at 7 weeks of age, most kittens not receiving 6-OHDA were blind when tested with the deprived eye. In contrast, none of the kittens receiving 6-OHDA intraventricularly were blind when tested with the deprived eye. 6-OHDA had no effect on performance with the non-deprived eye. We conclude that 6-OHDA protects vision through the monocularly deprived eye without impairing vision through the non-deprived eye.

Disruption of corticospinal plasticity by 6-hydroxydopamine as measured by intracortical microstimulation in rats

Intracortical microstimulation in normal, adult rats evoked low-threshold contralateral and high-threshold ipsilateral forelimb movements. In comparison, stimulation of the intact cortex in adult rats that sustained unilateral cortical lesions at birth evoked ipsilateral movements at abnormally low-threshold levels in addition to normal contralateral movements. Depletion of cortical and spinal cord noradrenaline levels by treatment with 6-hydroxydopamine prior to the placement of neonatal cortical lesions eliminated the low-threshold ipsilateral movements when tested at maturity. These findings suggest that the noradrenergic system may influence corticospinal plasticity.

Clonidine and cortical plasticity: possible evidence for noradrenergic involvement

In order to test the hypothesis that noradrenergic transmission modulates ocular dominance plasticity in kitten visual cortex, we monocularly deprived kittens while administering the alpha-2 adrenergic agonist clonidine (CLON). To avoid bias in testing the hypothesis, we included, with a single blind technique, saline-treated control kittens in the series. First, using high-pressure liquid chromatography, we demonstrated that CLON treatments resulted in an average decline in cerebrospinal fluid levels of the norepinephrine metabolite, 3-methoxy-4-hydroxy phenylethylene glyolol (MHPG) of 44%. Then, single-unit recording in area 17 revealed the expected ocular dominance (OD) shift in monocularly deprived saline controls, but recording failed to find a significant shift in CLON-treated kittens. Our results support the notion that CLON treatment interferes with ocular dominance plasticity by inhibiting noradrenergic transmission in visual cortex. We discuss side effects of CLON, concluding that CLON's sedative effect may contribute to the lack of OD shift.

Noradrenaline and functional plasticity in kitten visual cortex: a re-examination

A quantitative re-examination was made of the influence of noradrenergic depletion on the epigenesis of kitten visual cortex. Two methods were used to deplete noradrenaline at the cortical level: stereotaxically controlled injection of 6-hydroxydopamine (6-OHDA) in the coeruleus complex, from which the noradrenergic input to visual cortex arises; intraventricular injection of 6-OHDA. The latter chemical lesion also depleted dopamine levels in the brain. Lesion of the noradrenergic or catecholaminergic systems was performed neonatally or at an age of 3-4 weeks in kittens submitted to five different rearing procedures: normal rearing, dark rearing, monocular rearing, monocular exposure following dark rearing and monocular deprivation following normal rearing. Forty-two kittens between 3 and 12 weeks of age were used for this biochemical and electrophysiological study. Noradrenaline and dopamine levels were measured by a radioenzymatic method in the primary visual cortex of twenty-six kittens. A total of 1263 cells were recorded in area 17 of twenty-six kittens. Combined biochemical and electrophysiological data were obtained in ten 6-OHDA-lesioned kittens. Whatever the mode of chemical lesion used, cortical noradrenergic depletion failed to block either maturation or vision-dependent processes which are known to affect orientation selectivity and/or ocular dominance during the critical period. However, in some cases, the amplitude of the epigenetic functional modifications was slightly reduced in 6-OHDA-treated kittens. The cortical effects of monocular deprivation starting from the age of 5 weeks were studied quantitatively both in lesioned and intact kittens. Disappearance of noradrenaline in area 17 did not prevent the loss of binocularity in cortical cells. However, even when monocular occlusion had been maintained for 2 or 3 weeks in 6-OHDA-treated kittens, ocular dominance shifts were limited to a stage equivalent to that observed in the intact kitten after 5-8 days of monocular occlusion. The amplitude of this partial protective effect was found to be unrelated either to the delay following the chemical lesion, or to the level of noradrenaline remaining in lesioned kitten cortex. Although a putative gating role of noradrenaline cannot be excluded in the development of the intact animal, this report shows that its presence is not required for functional plasticity to occur in kitten area 17.

Development of the A1 adenosine receptors in the visual cortex of cats, dark-reared and normally reared

The ontogeny of the distribution of the binding sites for [3H]chlorohydroxyladenosine, an A1 adenosine receptor-specific ligand, was visualized autoradiographically within coronal sections of the visual cortical areas of developing cats. In adults, the A1 adenosine receptors were found in all lamina except for lamina IV, and in particularly high concentration within laminas I-III. In brains of kittens 2 months old and younger who were within the critical period for the development of visual neural function, the receptor distribution was less defined and sparser, except that in contrast to adults, it was found in relatively high concentration within lamina VI. Animals dark-reared from birth, so that the critical period was postponed, exhibited an ontogenetic pattern identical to that of the normally reared animals. These results indicate that, at least with respect to ocular dominance determination, A1 adenosine receptors are probably not involved in determining the state of plasticity that is seen during the critical period.

Plasticity in cat visual cortex restored by electrical stimulation of the locus coeruleus

It has been proposed that the presence of noradrenaline (NA)-containing terminals and NA-related receptors within the visual cortex is necessary to maintain the high level of neuronal plasticity in the immature visual cortex of kittens. In the present study we wanted to show whether electrical stimulation of the locus coeruleus (LC), which contains the somata of these cortical NA fibers, can restore neuronal plasticity to the normally aplastic visual cortex of juvenile and adult cats. We consistently found a significant loss of binocular cells in the visual cortex of mature animals which had monocular vision for only 12 h dispersed over 6 days (2 h a day, otherwise kept in the dark) in combination with concurrent LC stimulation. This result was interpreted as indicating that endogenous NA released from NA terminals restored susceptibility to monocular vision in the mature visual cortex. We next examined how long the restored plasticity lasts in the same animals after the LC stimulation was ended. The animals revived from the first recording session were either returned to the same daily schedule of brief monocular exposure (light/dark = 2/22 h) as before, or subjected to the usual monocular lid suture and kept in a cat colony environment (light/dark = 16/8 h). The LC electrodes had been removed and no more electrical stimulation was delivered at this stage. In the animals subjected to reiteration of brief monocular exposure, the state of reduced binocularity gradually returned to normal over a period of 2-3 weeks after stopping LC stimulation. We calculated that the revived plasticity disappeared at an average rate of a 22% loss every 7 days. This result sharply contrasted with the result obtained in the animals subjected to usual monocular lid suture. In this test the state of reduced binocularity continued for at least the next 3 weeks, suggesting that the restored plasticity was sustained throughout a period of 3 weeks (longest term tested). The different results obtained in the two paradigms may be explained by the different strength of binocular imbalance in the two tests imposed on the visual cortex in which neuronal plasticity was restored partially.

Octopamine enhances neuromuscular transmission in developing and adult moths, Manduca sexta

The effect of octopamine on neuromuscular transmission was examined in developing and adult Manduca sexta. Intracellular recordings were made from the dorsal longitudinal muscle (DLM), superfused with solutions containing DL-octopamine or other amines. In untreated adult moths and pharate adults nearly ready to enclose (stage Day 19), stimulation of the motor nerve evokes a large excitatory junction potential (EJP), an active membrane response, and a twitch. In adults and Day 19 animals DL-octopamine (10(-7) to 10(-4)M) has no effect on the amplitude and rise-time of the electrical response in normal saline, but 10(-6) to 10(-4) M DL-octopamine increases the amplitude of the excitatory junction potential recorded in saline containing one-third the normal calcium concentration. Immature (Day 16) muscle, which normally produces only small EJPs following stimulation of its motor nerve, responds to 10(-6) to 10(-4) M DL-octopamine by an increase in the EJP above threshold for an active membrane response and a contraction. When the muscle has developed sufficiently to spike and contract in response to nerve stimulation in the absence of exogenous octopamine (Days 17 and 18), application of DL-octopamine increases the maximum rate at which the muscle contracts in response to each stimulus in a train (designated the maximum following frequency, MFF). The threshold dose for an effect on the MFF of Day 18 immature moths is less than 10(-10) M. At this stage 10(-8) M DL-octopamine increases the MFF four-fold. The effect on the MFF is dose-dependent over the range 10(-10) M to 10(-6) M. The biogenic amines DL-epinephrine, DL-norepinephrine, tyramine, DL-phenylethanolamine, 2-phenylethylamine, and dopamine, applied at concentrations of 10(-8) or 10(-4) M, do not change the MFF. Both DL-synephrine (10(-8) M) and serotonin (10(-7) M) mimic the action of 10(-10) M DL-octopamine on the MFF. The action of DL-octopamine (10(-7) M) is blocked by phentolamine (10(-4)M) but not by propranolol (10(-4)M). The octopamine content of hemolymph was determined with a radioenzymtic assay. The concentration of octopamine in the hemolymph increases 3.6-fold, from 5 X 10(-8) M on Day 18 (duration of adult development is 19 days) to 1.85 X 10(-7) M one day following eclosion.(ABSTRACT TRUNCATED AT 400 WORDS)

Laminar distribution of alpha 1- and beta 1-adrenoceptors in ferret visual cortex

The distribution of alpha 1- and beta 1-adrenoceptors has been examined in the ferret visual cortex (area 17), with an autoradiographic procedure using iodine-125 labeled hydroxy-iodophenyl-ethylaminomethyl-tetralone (HEAT) and iodocyanopindolol (ICYP), respectively. The density of ligand binding with ICYP, known to have selective affinity for beta-receptors, was heavy over layers I-III, very low over layer IV, and medium over V and VI. In contrast, binding sites for HEAT, a new ligand selective for alpha-receptors, were diffusely distributed, although preferentially concentrated in layer IV and the upper layers. The distinct laminar distribution of these two receptor types may imply two cortical channels for norepinephrine influence; alpha 1-receptors may be preferentially associated with enhancement of excitatory inputs to layer IV; beta 1-receptors, in contrast, with enhancement of inhibitory responses outside layer IV.

gamma-Aminobutyric acid enables synaptogenesis in the intact superior cervical ganglion of the adult rat

Local gamma-aminobutyric acid (GABA) application into the intact superior cervical ganglion (SCG) of the adult rat allows active innervation of a surgically implanted hypoglossal nerve in addition to the normal nerve supply of the ganglion. In GABA-treated SCG of the adult rat, action potentials could be obtained on stimulation of both the preganglionic nerve trunk and the implanted hypoglossal nerve. Both action potentials were reversibly sensitive to hexamethonium bromide indicating new cholinergic synapses established between axons in the hypoglossal nerve and principal sympathetic neurons. If GABA treatment of the ganglion was omitted, the double innervation did not develop after hypoglossal nerve implantation.

Surprisingly rich projection from locus coeruleus to the olfactory bulb in the rat

The brainstem nucleus, locus coeruleus (LC), is the major, if not the sole, source of noradrenergic (NE) innervation of the telencephalon. It is generally held that LC neurons project diffusely to the entire neuroaxis and this had been the basis for theories that postulate 'general' functions (sleep, attention, learning, etc.) for LC. We report that at least 40% of all LC neurons project to the olfactory bulb; the projection is almost 10 times greater than to any other part of the cerebral cortex. This unsuspectedly rich LC-olfactory bulb connection is consistent with current theories which implicate LC neurons in heightened sensory vigilance and trophic regulation of connectional development and plasticity.

Neural mechanisms distinguishing the neocortical EEG of C57BL/6 mice from that of DBA/2 mice

C57BL/6 inbred mice lack the 1-5 sec bursts of 6-7 cps spindles characteristic of the neocortical EEG of DBA/2 mice during waking. C57BL/6 mice (1) may be unable to generate any synchronized cortical EEG activity, (2) may lack the thalamocortical circuitry required to generate these brief spindle episodes (BSEs), (3) may lack mechanisms that can activate this circuitry or (4) may possess a potent mechanism to suppress BSE initiation and generation. Possibilities 1 and 2 have been eliminated because C57BL/6 mice generate pentobarbital, rostropontine-induced and sleep spindles, and because certain C57BL/6 sleep spindles resembled the BSEs seen in DBA/2 mice. Possibilities 3 and 4 were examined in the experiments reported here. In DBA/2 mice, pentylenetetrazol activates BSEs at subconvulsant doses. In contrast, neither 20 nor 50 mg/kg, IP, pentylenetetrazol activated BSEs in C57BL/6 mice, although the higher dose provoked 4-5 cps slow waves and myoclonic jerks. In DBA/2 mice, the beta-noradrenergic antagonist propranolol has been reported to powerfully release BSEs. In C57BL/6 mice, 10 and 15 mg/kg propanolol weakly released BSEs; fewer than 3 per hour occurred. Hence neither possibilities 3 and 4 are sufficient in themselves to explain the lack of BSEs during waking in C57BL/6 mice. However, simultaneous administration of 10 mg/kg propranolol and 20 mg/kg pentylenetetrazol provoked numerous BSEs in C57BL/6 mice. This suggests that perhaps C57BL/6 mice, as compared to DBA/2 mice, possess both a more powerful noradrenergic mechanism to suppress spindles and a more weakly functioning mechanism to activate BSEs. Hence possibilities 3 and 4 may both be correct.(ABSTRACT TRUNCATED AT 250 WORDS)

Intertectal neuronal plasticity in Xenopus laevis: persistence despite catecholamine depletion

In normal Xenopus, the tectum receives a direct projection from the contralateral retina and an indirect projection, via the intertectal system, from the ipsilateral eye. The two maps of binocular visual space, at each tectum, are in register. If one eye is rotated during larval development, the ipsilateral visuotectal projection compensates by changing its orientation. Rearrangement of the intertectal system brings the ipsilateral map back into register with the contralateral map. We sought to determine whether this intertectal plasticity required normal levels of brain monoamines. Animals received an eye rotation between stages 55-63 of larval life and were then placed in one of 3 groups. A first control group received no further treatment. A second control group was given intraventricular injections of ascorbate vehicle. The experimental group was given intraventricular injections of 6-hydroxydopamine in ascorbate vehicle. Two to 3 months after metamorphosis, visuotectal projections were mapped electrophysiologically and the brains were assayed for monoamines. Intertectal plasticity occurred in all 3 groups of animals, including animals in which brain catecholamine levels were severely reduced. We conclude that normal levels of brain catecholamines are not required for this form of neural plasticity.

Central control of developmental plasticity in the mammalian visual cortex

Visual experience influences the development of visual cortex functions. By manipulating retinal activity the efficacy of excitatory connections between the eyes and cortical neurones can be modified dramatically. A criterion for the enhancement or impairment of transmission is the temporal contiguity of pre- and postsynaptic activation. For a change to occur it is necessary that the cortical cells respond to retinal activity but this condition is not sufficient. Further permissive gating signals of nonretinal origin are required. It is proposed that these "now print" signals act by controlling the Ca2+-conductance of cortical dendrites. The possible role of these activity dependent modifications is discussed in the context of the development of cooperatively coupled cell assemblies.

Serotonin selectively inhibits growth cone motility and synaptogenesis of specific identified neurons

The motile activity of growth cones of specific identified neurons is inhibited by the neurotransmitter serotonin, although other identified neurons are unaffected. As a consequence, affected neurons are unable to form electrical synapses, whereas other neurons whose growth is unaffected can still interconnect. This result demonstrates that neurotransmitters can play a prominent role in regulating neuronal architecture and connectivity in addition to their classical role in neurotransmission.

Extrinsic visual and auditory cortical connections in the 4-day-old kitten

The major extrinsic projections to and from the visual and auditory cortical areas were examined in 4-day-old kittens using axonal transport of horseradish peroxidase (HRP) and/or tritiated proline. Six different afferent and seven different efferent systems were studied; all 13 were present by postnatal day 4 as revealed by either HRP, or autoradiography alone, or these two techniques combined. Topographical projections were found for the corticopetal pathways from the thalamus and claustrum and for the corticofugal pathways to the thalamus, claustrum, striatum, and tectum, as well as for the inter- and intrahemispheric pathways. No topographical relations were seen in projections to the cortex from the basal ganglia or the lower brainstem. The results of the present study indicate that most or all of the major extrinsic connections of the kitten's visual and auditory cortical areas are present neonatally, and that both the cells of origin and the axonal targets are arranged topographically much like those of adult cats. However, the origins of callosal projections from visual cortex are more widespread in newborn kittens than in adult cats. In addition, the laminar arrangements of the kitten's corticocortical connections differ from those of adult cats in a number of details. The results suggest that the sparing of some visual and auditory functions after neonatal lesions occurs despite the fact that the cortical areas removed have formed extrinsic connections.

Modifiability of responsiveness in a visual projection area of the chick brain: visual experience is only one of several factors involved

The effects of visual experience on neuronal responsiveness in the hyperstriatum accessorium, a visual projection area, were investigated in 4 groups of domestic chicks, each comprising dark-reared (total = 44) and visually experienced (total = 34) birds. Visually experienced birds were placed singly in running wheels facing a flashing red light for 3 h; wheel revolutions were used as a measure of the chicks' locomotor activity. At approximately equal to 48 h after hatching each chick was anaesthetized and a microelectrode advanced in 250 micron steps through the left Wulst. After each step the responsiveness of units to diffuse retinal illumination (light flashes) was tested. Each recording site at which responses greater than or equal to 5 successive flashes could be evoked was classified as a response site. In some chicks at least one site responding briskly to greater than or equal to 15 successive flashes was found deep to the hyperstriatum accessorium. The zone of markedly increased responsiveness is referred to as the visually responsive lamina. The effect of visual experience on the response of units in the hyperstriatum accessorium varied between the groups of chicks. Visual experience did not significantly effect neuronal responsiveness in this region for chicks without a visually responsive lamina. For chicks with a lamina there was an effect of visual experience, but the effect again varied between groups. When data from inactive, visually experienced chicks were excluded, the group-to-group variation ceased to be significant. Thus visual experience alone was not adequate consistently to bring about long-term changes in the responsiveness of neurones in the hyperstriatum accessorium. Such experience was likely to increase neuronal responsiveness provided the chicks: were behaviourally active; and possessed a visually responsive lamina.

Hyperpolarizing and age-dependent depolarizing responses of cultured locus coeruleus neurons to noradrenaline

The electrical activity and responses to noradrenaline (NA) of locus coeruleus (LC) neurons have been studied in organotypic cultures using intracellular recording. Most LC neurons were predominantly quiescent, though occasional bursts of activity were observed; a few cells were tonically active at rates of 0.5-5/s. In most cells tested, iontophoretic application of NA evoked responses which were initially hyperpolarizing, sometimes followed by a depolarizing phase and frequently followed by a period of increased excitatory synaptic activity. The enhanced synaptic activity appeared to be an indirect effect since it was blocked by bath application of tetrodotoxin (TTX). In the presence of TTX, responses to NA of all but one cell were simple hyperpolarizations or biphasic (hyperpolarization/depolarization) responses. The presence of the depolarizing component appeared to be age-dependent, since it was frequently observed in cultures grown in vitro for less than 26 days, while neurons in older cultures exhibited only hyperpolarizing responses. If such age-dependent depolarizing responses are present in vivo, they would represent a unique example of a transmitter response which is present only during a transient developmental phase.

Enhanced binocular interaction in the visual cortex of normal kittens subjected to intracortical norepinephrine perfusion

It was previously proposed that norepinephrine (NE)-containing nerve terminals in visual cortex are important for the maintenance of cortical plasticity. Observations at that time indicated that local microperfusion of exogenous NE for 1 week directly into kitten visual cortex, with no alteration of the visual environment, resulted in an unexpected bias in ocular dominance toward the contralateral eye. The proportion of binocular cells, however, remained close to normal. In the present study, we examined this contralateral bias in visual cortical neurons addressing the following two issues: the time needed for change in ocular dominance to occur, and its dependence on visually evoked activity. We found no bias in ocular dominance toward the contralateral eye when the continuous local perfusion of 48 microM NE lasted for 3 days. Such change became obvious after 1 week. However, if the animal was placed in the dark during the period of NE perfusion, no change whatsoever in ocular dominance was observed. These results suggest that NE itself does not affect ocular dominance circuitry directly, since both high levels of NE and an extended period of visually evoked activity are necessary for the observed change in ocular dominance to occur. We conclude that the present results are consistent with the previously proposed role for NE in the modulation of visual cortical plasticity.

Ontogenesis of muscarinic acetylcholine binding sites in cat visual cortex: reversal of specific laminar distribution during the critical period

Acetylcholine appears to act as a modulator of neuronal activity in cat visual cortex and, like noradrenaline, may be involved with cortical plasticity mechanisms during the critical period. To explore possible ACh involvement in these mechanisms we have examined acetylcholine binding sites in cat visual cortex during development using [3H]QNB, a muscarinic antagonist. At 3 days postnatal [3H]QNB preferentially labelled binding sites in layer IV. During development the pattern of binding reversed, so that by 95 days postnatal layer IV was the least densely labelled. The number of binding sites increased during development peaking at 1 month postnatal. The Kd of [3H]QNB binding sites increased to 95 days postnatal, with a peak value of 0.76 nM. The results show that during development, and especially within the critical period, changes in [3H]QNB binding site distribution, number and affinity occur.

Mutations in the dopa decarboxylase gene affect learning in Drosophila

Fruit flies synthesize several monoamine neurotransmitters. Dopa decarboxylase (Ddc) mutations affect synthesis of two of these, dopamine and serotonin. Both transmitters are implicated in vertebrate and invertebrate learning. Therefore, we bred flies of various Ddc genotypes and tested their learning ability in positively and negatively reinforced learning tasks. Mutations in the Ddc gene diminished learning acquisition approximately in proportion to their effect on enzymatic activity. Courtship and mating sequences of the mutants appeared normal, except for one aspect of male courtship that had previously been shown to be experience dependent. In contrast, the effect on behavior patterns that do not involve learning--phototaxis, geotaxis, olfactory acuity, responsiveness to sucrose--was relatively slight under these conditions. Moderate Ddc mutations affected the acquisition of learned responses while leaving memory retention unaltered. This is in contrast to the mutations dunce , rutabaga , and amnesiac , which primarily affect short-term memory.

Disruption of cortical activity prevents ocular dominance changes in monocularly deprived kittens

Abundant evidence now indicates that atypical visual exposure early in the life of cats and primates can cause profound alterations in cortical organization. In particular, it has been shown that preventing the use of one eye for vision early in life results in a marked shift of ocular preference among neurones of kitten visual cortex in favour of the exposed eye. The cellular mechanisms underlying these alterations remain uncertain, but much recent attention has focused on the possible role of pharmacological agents in modifying cortical plasticity, with particular reference to catecholamines. These experiments, which have shown that agents which modify cortical noradrenaline levels can alter the degree of cortical plasticity, do not specify the mechanism of action, and leave open the possibility that other neurotransmitter systems may also be involved in cortical modifiability. We now report that chronic intracortical administration of L-glutamate during a period of monocular vision imposed on young kittens largely prevents the ocular dominance shift which normally occurs under these circumstances.

Noradrenergic action in the developing rat cerebellum: interaction between norepinephrine and synaptically-evoked responses of immature Purkinje cells

This study was designed to characterize the influence of norepinephrine (NE), a putative cerebellar neurotransmitter, on immature synaptic activity during early postnatal periods of the developing cerebellar cortex. Norepinephrine was applied by microiontophoresis to single, young Purkinje cells to assess its effects on spontaneous and synaptically-mediated activities. Data from these studies indicate that the catecholamine exerts a profound modulatory-type influence on Purkinje cell responsiveness to activation of newly-established inputs. NE augmented climbing fiber-elicited excitatory burst responses by postnatal day 5 and enhanced 'off-beam' inhibitory activity by postnatal day 9, as soon as basket and stellate interneurons became functional. The functional implications of this noradrenergic facilitating effect, which is present throughout the maturation of the cerebellar cortical network, are discussed in terms of its possible contribution to the wiring of a definitive neuronal circuit.

Visual development in infancy and childhood

This article considers the development of vision in normal children, emphasizing new evaluative techniques that may eventually play an important role in clinical practice, and follows with a discussion of abnormal development, where recent discoveries in the laboratory and in clinical observation have already led to significant advances in the treatment of children with ophthalmologic problems.

Norepinephrine levels in developing pigeon brain: effect of monocular deprivation on the Wulst noradrenergic system

The endogenous level of norepinephrine (NE) was measured in discrete brain areas of the pigeon during post-hatching development. The pontine tegmentum showed the highest NE content, which remained constant during the post-hatching period. On the contrary, the NE content in the Wulst and cerebellum gradually decreased from hatching to 6 days. After this period, the Wulst NE level did not change significantly. In fact, there was no significant difference between NE values at 6 days and those at 6 months of age. In contrast, the difference between the cerebellar NE level at 6 days and that at the adult stage was highly significant. The NE content in the Wulst could be related to noradrenergic afferents originating in the ipsilateral locus coeruleus and substantia grisea centralis, since an electrolytic lesion of the pontine tegmentum caused a 60% reduction in the NE level in the ipsilateral Wulst. In line with the hypothesis that NE plays an important role in cortical plasticity, effects of early monocular deprivation on the Wulst NE content were also observed. After monocular deprivation during the first 6 months of life, the NE level increased by 40% in the Wulst ipsilateral to the deprived eye in comparison to the other side, where the NE level was normal. Monocular deprivation performed in adult animals did not affect the NE content in the Wulst. These results indicate that noradrenergic systems in the Wulst are affected by early, but not late visual deprivation.

Neonatal treatment with 6-OH dopamine and the elimination of polyneuronal innervation of skeletal muscle in the rat

The polyneuronal innervation of skeletal muscles of newborn rats was eliminated completely in spite of virtually complete destruction of the sympathetic nervous system with 6-OH dopamine (6-OHDA). There was, however, a moderate delay in the elimination of redundant nerve terminals which is probably a secondary effect of the treatment.

Amnesia-producing drugs affect hippocampal frequency potentiation

The effects of intravenous injections of lorazepam, scopolamine and propranolol upon hippocampal potentiation produced by commissural stimulation have been investigated in rats anaesthetized with urethane. Administration of 250 micrograms/kg or 500 micrograms/kg lorazepam significantly delayed the onset of secondary potentiation (frequency potentiation) of the population spikes recorded in subfields CA1 and CA3 of the dorsal hippocampus. Scopolamine also delayed the onset of frequency potentiation in CA1, but only at high dose (10 mg/kg). No other measured parameters of frequency potentiation, paired-pulse potentiation or post-tetanic potentiation were affected by any of the drugs. Lorazepam (greater than or equal to 250 micrograms/kg) and propranolol (3 mg/kg) reduced the severity of hippocampal after-discharge. Rhythmic entrainment of after-discharges was occasionally observed. The results are discussed in relation to the possible link between hippocampal potentiation and memory processes.

Changes in telencephalic catecholamine levels in the domestic chick. Effects of age and visual experience

The concentrations of adrenaline, dopamine and noradrenaline were measured in 3 regions of the domestic chick telencephalon: (a) the Wulst; (b) a medial forebrain sample comprising mainly the intermediate part of the medial hyperstriatum ventrale (IMHV); and (c) a basal forebrain sample comprising mainly paleostriatum augmentatum. There was no significant left/right hemispheric asymmetry in the concentration of any of these catecholamines in any region studied. Adrenaline was undetectable in the Wulst and medial forebrain samples and only trace amounts were found in the basal forebrain samples of 1-day-old, light-reared chicks. Dopamine concentrations of 9.13 +/- 1.13 (S.E.M.) ng/g were present in the Wulst, 16.66 +/- 2.56 ng/g in the medial forebrain and 121.19 +/- 33.06 ng/g in the basal forebrain samples at hatching. These levels did not alter with age or with visual experience of an imprinting stimulus during the first 50 h post-hatch. At hatching, noradrenaline concentrations of 35.83 +/- 8.61 ng/g were present in the Wulst, 26.09 +/- 3.75 ng/g in the medial forebrain and 53.13 +/- 7.85 in the basal forebrain samples. The noradrenaline concentrations in the Wulst and medial forebrain samples increased significantly over the first 50 h post-hatch in dark-reared chicks. Visual experience increased noradrenaline levels in all 3 regions of the telencephalon studied.

Imprinting and cortical plasticity: a comparative review

Results of research on imprinting and developmental neurobiology of the visual cortex are compared to evaluate the evidence for or against a frequently hypothesized linkage of the two phenomena. The comparison reveals striking similarities. In both paradigms a sensitive period exists. Once this sensitive period is over, the storage of early influences from the environment remains stable throughout life. Storage of "natural" stimuli is facilitated by a certain preorganisation of the receiving brain areas. It is stated that the two phenomena are not directly linked, but are two expressions of a developmental process, which may be common for the organisation of the connectivity of single cells as well as for complex neuronal networks as they are likely to be involved in imprinting. This process is basically self-organizing, but can be influenced by superimposed controls. Differences of the stability of storage of external influences might be explained by the difference in the overall amount of morphological alterations, which is large in the young and small in the adult animal. This holds for both the modifiability in the visual cortex and imprinting.

Development of the serotonergic system in the rat embryo: an immunocytochemical study

The development of central serotonergic neurons has been examined immunocytochemically utilizing an antiserum to serotonin (5-HT). Cells of the B4-B9 complex are first detected early on embryonic day 13 (E13; 7 mm crown rump length, CRL) and increase rapidly in number through E15 when they appear as bilateral columns situated from just caudal to the mesencephalic flexure to the pontine flexure. Aggregation of cells into subgroups is apparent soon after 5-HT neurons leave the ventricular zone, allowing the identification of certain subdivisions of the B4-B9 complex long before they assume their adult locations. The initial detection of 5-HT immunoreactive cells in the medulla occurs 1-2 days after the appearance of cells in the B4-B9 complex, although it has been reported that the time of origin of medullary raphe neurons (B1-B3) occurs before that of raphe neurons in the midbrain and pons (B4-B9). The first medullary 5-HT neurons, comprising the B3 subdivision occur ventro-laterally on E14 (10-11 mm CRL) at least 1-2 days before midline 5-HT neurons are visualized in the B1 and B2 groups. Thus, in contrast to cells in the B4-B9 complex, medullary 5-HT neurons complete much of their migration before they can be detected immunocytochemically, indicating that the time of onset of transmitter synthesis and storage may differ during differentiation of cells sharing a common neurotransmitter phenotype. The formation of ascending 5-HT fiber projections occurs rapidly from cells of the B4-B9 complex. Within 24 hours after the initial detection of 5-HT fiber immunoreactivity in such cells at E13, their axons are seen entering the caudal diencephalon (E14). These fibers have traversed the diencephalon and floor of the telencephalon by E15-E16 and reach the frontal neocortical pole by E17. The main ascending bundle of 5-HT axons courses through the diencephalon in the vicinity of the medial forebrain bundle, although some fibers also diverge and travel along certain pre-existing non-5HT pathways. However, examples are also found of acute directional changes in 5-HT fiber growth which do not appear to be associated with pre-formed non-5HT pathways. The pattern of ascending fiber outgrowth suggests a priority routing system which provides certain regions with 5-HT axons in a preferential sequence irrespective of the distance of these areas from 5-HT cell groups or from major bundles of ascending 5-HT fibers.

Ontogenesis of beta-adrenergic binding sites in kitten visual cortex and the effects of visual deprivation

We have determined maximum binding capacities for beta-adrenergic binding sites in developing cat visual cortex. These increase quickly from birth to 4 weeks, after which time a slower increase reaches maximal levels at 12 weeks. Dark-rearing and monocular eyelid suture have no influence on this developmental profile.

Two methods of catecholamine depletion in kitten visual cortex yield different effects on plasticity

As first clearly demonstrated by the experiments of Wiesel and Hubel, the developing visual cortex is exquisitely sensitive to sensory deprivation. Temporary closure of one eye of a kitten during a critical period that extends from 3 weeks to 3 months of age results in a dramatic cortical reorganization such that most neurones, originally binocularly driven, are dominated exclusively by the open eye. Recently, attention has been directed to chemical factors which may influence the degree of plasticity during the critical period. The work of Kasamatsu and pettigrew suggests that cortical catecholamines, especially noradrenaline (NA), are essential for the normal plastic response to visual deprivation. In an effort to clarify the role of NA in visual cortical plasticity, we have monocularly deprived kittens whose cortex had been depleted of catecholamines by the neurotoxin 6-hydroxydopamine (6-OHDA). We used two strategies to deplete cortical NA: the first, pioneered by Kasamatsu el al., utilized osmotic minipumps to deliver 6-OHDA to visual cortex; the second involved systemic neonatal injections of 6-OHDA, a technique which has proved effective in rodents. We found, using high-pressure liquid chromatography (HPLC), that both techniques produced a substantial reduction in the level of cortical NA. However, single unit recording in area 17 revealed that the plastic response to monocular deprivation (MD) was only diminished in the kittens depleted by minipump.