Action of CCK and 5-HT on lateral hypothalamic neurons depends on early postnatal nutrition.

Wistar rats grown up during the early postnatal life (3-21 days after birth) in artificially built normal, small or large lifters developed a significantly different body weight. This difference persisted also during adulthood when they had free access to food and water. The influence of iontophoretically administered cholecystokinin (CCK8S), serotonin (5-HT) or co-ejection of both on firing of lateral hypothalamic neurons was investigated in adult, urethane anesthetized rats of the three groups. The responsiveness to CCK8S was significantly higher in large- and small-litter rats than in the normal control group. The differences were greater in males than in females. They resulted in the male large-litter group from an increase of excitatory responses, whereas in the male small-litter group the proportion of inhibitory responses was augmented. Co-administration of 5-HT generally reduced the neuronal responsiveness. Especially in the large-litter group excitatory responses were significantly reduced. It may be speculated that the availability of food in the early postnatal life influences the development of the hypothalamic regulatory network in such a way that it stabilizes the high or low food ingestion all the life. At least in males, a changed responsiveness and type of response to cholecystokinin of lateral hypothalamic neurons might be involved in this altered regulation.

Action of cholecystokinin and serotonin on lateral hypothalamic neurons of rats.

Discharges of spontaneously active lateral hypothalamic neurons were extracellularly recorded during iontophoretic administration of cholecystokinin (CCK-8S) or/and serotonin (5-HT) in anesthetized rats. The main results are the following. (1) The proportion of neurons responsive to CCK-8S was 62% (61/99) and that responsive to 5-HT 42% (33/78). (2) Out of the neuronal sample, 36% were influenced by both transmitters, allowing an interaction between the two systems. (3) Co-ejection of CCK and 5-HT elicited a response in 40% of the tested neurons, which was a significantly smaller responsiveness than with separate ejection of CCK-8S. The effect resulted from a reduced number of excited neurons whereas the number of inhibitions did not change. The results show that effects of 5-HT and CCK can converge on the same neuron within the lateral hypothalamus. This might be of relevance in the regulation of feeding behavior.

Chondrotoxicity and toxicokinetics of sparfloxacin in juvenile rats.

Sparfloxacin is a fluoroquinolone with improved antibacterial activity against gram-positive pathogens. Like other quinolones, use of this drug is contraindicated in children and adolescents because of its potential chondrotoxicity in juveniles. We performed histological and immunohistochemical studies on the knee joint cartilage in 5-week-old rats after treatment with 600 or 1,800 mg of sparfloxacin/kg of body weight. Treatment with single or multiple oral doses of 600 mg of sparfloxacin/kg was not sufficient to induce joint cartilage lesions. However, five of eight rats treated with a single oral dose of 1,800 mg of sparfloxacin/kg of body weight showed typical cartilage lesions in the femoral part of the knee joint. The concentrations of the drug in plasma measured 0.25, 0.75, 1.5, 3, 6, 12, and 24 h after the administration of an oral dose of 600 mg of sparfloxacin/kg were 6.3 +/- 1.8, 9.2 +/- 1.7, 9.6 +/- 2.7, 13.0 +/- 1.8, 12.3 +/- 1.6, 3.4 +/- 0.4, and 0.30 +/- 0.20 mg/liter, respectively (mean +/- standard deviation [SD]; n = 5 to 6 per group). The concentrations in plasma measured 0.75, 1.5, 3, 6, 24, and 48 h after the administration of an oral dose of 1,800 mg of sparfloxacin/kg were 10.9 +/- 1.5, 15.9 +/- 1.6, 19.1 +/- 1.7, 14.9 +/- 3.1, 4.1 +/- 0.6, and 0.46 +/- 0.37 mg/liter, respectively (mean +/- SD; n = 3 to 4 per group). The concentrations of sparfloxacin in joint cartilage were significantly higher at all time points studied (114.8 +/- 80, 99.4 +/- 31.5, 84.9 +/- 16.8, 44.4 +/- 13.9, and 14.2 +/- 4.8 mg of sparfloxacin/kg at 1.5, 3, 6, 24, and 48 h after the administration of 1,800 mg/kg, respectively). The range of concentrations in bone were similar to the range of concentrations in cartilage (peak, 115 +/- 12 mg/kg after 3 h). Our data indicate that chondrotoxic doses of sparfloxacin in juvenile rats are approximately 300 times higher than the doses of sparfloxacin used therapeutically (1,800 versus approximately 6 mg/kg of body weight), but due to species differences in kinetics, concentrations in plasma differ by a factor of only approximately 15. More data on quinolone concentrations in cartilage from animals and humans could provide a better basis for a reasonable risk assessment.

Effects of magnesium deficiency on magnesium and calcium content in bone and cartilage in developing rats in correlation to chondrotoxicity.

Quinolone-induced arthropathy has been described in juvenile rats between 3 and 6 weeks of age, but not in adult rats. The mechanism of this chondrotoxic effect is probably related to the Mg2+-chelating properties of the drugs, since identical cartilage lesions were observed in magnesium-deficient juvenile rats without quinolone treatment. However, the reasons for the phase-specificity of the effect are unknown. In the present study, we fed a magnesium-deficient diet to Wistar rats at different postnatal developmental stages. Cartilage lesions were only observed in magnesium-deficient rats between 3 and 5 weeks of age, but not in rats receiving the magnesium-deficient diet during weeks 5 to 8, weeks 8 to 11, or months 15 to 16. The formation of cartilage lesions was not related to the magnesium concentration in plasma, since magnesium concentrations in plasma were similarly reduced in rats with and without cartilage lesions. However, chondrotoxicity correlated with magnesium content in articular cartilage. In articular cartilage (articular and epiphyseal cartilage in immature rats) and bone, magnesium content was more reduced in rats receiving the magnesium-deficient diet between 3 and 5 weeks of age as compared with rats receiving the magnesium-deficient diet during weeks 8 to 11 postnatally. It was not possible to reduce the magnesium content in bone tissue of 15-month-old Wistar rats, which suggests a lower magnesium turnover in aged rats. Magnesium content in epiphyseal cartilage of 2-week-old rats (total femoral head) was 41.9 +/- 16.9 mmol/kg dry weight. The magnesium content in joint hyaline cartilage was significantly lower in 4-week-old rats (19.5 +/- 3.6 mmol/kg dry weight) and increased subsequently again to 48.5 +/- 9.2 mmol/kg dry weight (mean +/- SD; n = 8 to 16). Increase of the magnesium content in femoral bone between weeks 4 and 6 postnatally was less pronounced (139 +/- 10 and 175 +/- 15 mmol/kg dry weight, respectively). Taken together, these data show that in 4-week-old rats, magnesium concentration in joint hyaline cartilage is significantly lower than at other times during postnatal development. Only at this developmental stage can cartilage lesions be induced by feeding rats a magnesium-deficient diet. This period correlates well with the sensitive phase of immature rats toward the chondrotoxic action of quinolones.

Quinolone-induced arthropathy: exposure of magnesium-deficient aged rats or immature rats, mineral concentrations in target tissues and pharmacokinetics.

Quinolone treatment or magnesium deficiency induce identical cartilage lesions in juvenile rats and show additive arthropathogenic effects. It has been shown previously that neither condition is arthropathogenic in 8-week-old rats. Joint cartilage from aged individuals is rather prone to pathological alterations but information on prolonged quinolone treatment and/or dietarily induced magnesium deficiency in aged animals is not available. We treated magnesium-deficient (n = 9) aged Wistar rats (age 15 months) and age-matched controls with daily doses of 600 mg ofloxacin/kg body wt. by gastric intubation for 28 days. Further groups of magnesium-deficient and control rats (n = 9 and n = 10, respectively) received the vehicle only. Peak plasma concentrations of ofloxacin in adult rats were 20.5 +/- 5.6 mg/l (mean +/- SD) following treatment with a single dose of 600 mg/kg body wt. At the end of the experiment the degree of magnesium deficiency was most pronounced in plasma (Mg2+-def., 0.33 +/- 0.12 mmol/l; control, 0.97 +/- 0.08 mmol/l) and less pronounced in sternal cartilage (Mg2+-def., 10.8 +/- 3.6 mmol/kg dry wt; control, 13.3 +/- 2.8 mmol/kg dry wt), whereas the magnesium concentration in femoral bone remained unchanged (Mg2+-def., 201 +/- 13 mmol/kg dry wt; control, 204 +/- 11 mmol/kg dry wt). Histological investigation of the knee joints revealed no cartilage lesions following ofloxacin treatment, magnesium deficiency or a combination of both conditions. By contrast, cartilage lesions such as scars and erosions of the joint surface, chondrocyte clusters within acellular areas of the cartilage matrix and persisting clefts were detectable in knee joints from 7 of 10 adult rats (age 9 months) which had been treated with 4 x 600 mg fleroxacin/kg body wt. at 5 weeks of age. Mean plasma concentration of fleroxacin in juvenile rats was approx. 50 mg/l between 1.5 and 6 h after dosing and the drug was still detectable in plasma 48 h after dosing (0.4 +/- 0.1 mg/l). Our data indicate that joint cartilage in aged rats is not altered by a 4-week quinolone treatment, even during magnesium deficiency. Cartilage lesions in adult rats were only detectable if the animals had been treated during the sensitive phase at 5 weeks postnatally.

Effects of dopamine on neurons of the lateral geniculate nucleus: an iontophoretic study.

In urethane anesthetized rats, the iontophoretic administration of dopamine (DA) induced an inhibition of flash-evoked activity in the majority of geniculate cells investigated. Excitatory effects of DA also were found in some neurons of the dorsal lateral geniculate nucleus. The observed excitatory effects of DA were blocked selectively by D2 receptor antagonists, and the majority of inhibitory effects could be blocked by D1 receptor antagonists. In some neurons, the D2 receptor antagonist also blocked the DA-induced inhibition. Nine of 33 neurons tested responded differently to DA according to the amount ejected: with lower iontophoretic currents they increased their rates of discharge, whereas higher DA ejecting currents resulted in a suppression of their activity. Iontophoretic administration of a D1 agonist (SKF 38393) for the most part induced a decrease in baseline activity, whereas the D2 agonist (quinpirole) frequently induced an increase. These effects of agonists were dose-dependent and reproducible. Effects of the D1 and D2 agonists could be reversed by the receptor-specific dopamine antagonists. Presumed local circuit interneurons appeared to be involved in mediation of some inhibitory effects of DA, since the D2-induced inhibitions could be abolished by the GABAA antagonist, bicuculline. The majority of cells also was affected by DA antagonists given alone; these cells' responses to light usually were of an inhibitory nature. The results show that like other monoamines, DA also is involved in certain aspects of visual processing at the level of the thalamus.

Inhibitory effects of cholecystokinin on rat's geniculate activity can be blocked by GABA-antagonists.

Cholecystokinin applied iontophoretically as the sulfated octapeptide (CCK-8S) or as highly selective CCKA- and CCKB-agonists induced excitatory as well as inhibitory effects on dorsal lateral geniculate unit activity. Inhibitory effects of CCK could be abolished by administration of GABAergic antagonists, especially bicuculline. Therefore, interneurons seem to be largely excited by CCK, and in this way, they appear to mediate the inhibition of the discharge rate in geniculate relay cells induced by CCK.

Effects of two newly synthetized cholecystokinin tetrapeptides on the activity of single hippocampal and thalamic neurons.

The influence of two iontophoretically administered newly developed cholecystokinin (CCK) tetrapeptides with high selectivity and affinity to CCK-B receptors on the impulse activity of single hippocampal and thalamic neurons were tested in in-vivo experiments, in comparison to the effect of the sulfated octapeptide (CCK8S). A very similar responsiveness to the compared drugs was found. Most neurons responded with an increase of their discharge frequency. Only a few suppressive effects were elicited by each drug and in each of the structures. There was a good correspondence between the compared drugs concerning the direction and relative response amplitude, resulting in a highly significant correlation of the effects of both CCK4s with the CCK8S effects. On a subsample of neurons, the blocking effect of the selective CCK-B receptor blocker PD135 was tested and found to be effective in 16 out of 20 CCK4 responses, including also one inhibition. The results show that the new compounds act as effective CCK agonist binding to the B-type CCK receptor. The few inhibitory effects obtained could be explained by possible indirect effects mediated via inhibitory interneurons which are known to exist in both investigated structures.

Cholecystokinin affects the neuronal discharge mode in the rat lateral geniculate body.

Neurons of the dorsal lateral geniculate body (dLGB) discharge either continuously with single spikes or in bursts, that is, groups of action potentials with an interspike interval < or = 4 ms. The influence of the sulphated octapeptide of cholecystokinin (CCK-8S) on the discharge mode of dLGB neurons was studied in rats anesthetized with urethane. Unit activity was recorded during repeated stimulation with diffuse light. The occurrence of bursts was determined during control conditions and during iontophoretic administration of CCK-8S and its antagonists. CCK-8S frequently increased the number of bursts. The percentage of spikes involved in bursts was mainly augmented in neurons that responded after short latency to light or were excited by light-off. It was predominantly reduced in units responding to light after long latency with a primary excitation. CCKA receptors seem to contribute to burst induction, since CCK-8S reduced bursting in the presence of the CCKA receptor antagonist Ge 410 and increased bursting when applied with the CCKB receptor antagonist PD 135,158. These bursts were frequently related to light stimuli.

Cholecystokinin-induced activity changes of dorsal lateral geniculate neurons in rats.

The effects of iontophoretically applied cholecystokinin fragments and cholecystokinin antagonists on neurons of the dorsal lateral geniculate nucleus were investigated with extracellular recordings in rats anesthetized with urethane. The peptide cholecystokinin-8S, which has affinity for both cholecystokinin-A and -B receptors, altered the baseline firing as well as the responses to visual stimuli of about one half of the investigated neurons (90 out of 190). Excitatory effects predominated (P < 0.01, Wilcoxon test), although inhibitory effects were also observed. The effects of cholecystokinin-8S were dose-dependent. Neurons sensitive to cholecystokinin-8S could be found in all regions of the dorsal lateral geniculate nucleus, but they differed in their susceptibility to cholecystokinin in relation to their location. The B-agonist, BOC-cholecystokinin-4, also changed the baseline firing as well as the light-evoked activity of dorsal lateral geniculate nucleus neurons. The effects were either excitatory or inhibitory. Changes induced by cholecystokinin-8S could be effectively blocked by the cholecystokinin-B antagonist, CAM 1028 (19 out of 22 cholecystokinin-sensitive neurons tested). The cholecystokinin-A antagonist, Ge 410, blocked cholecystokinin-induced effects in 10 out of 16 neurons. These results indicate that the modulation of geniculate cell firing by cholecystokinin is mediated by both A-and B-receptor types.

SLOW and FAST lateral geniculate neurons are differently influenced by acetylcholine.

In rats anesthetized with urethane, potentials of 108 neurons were recorded extracellularly in the dorsal part of the lateral geniculate body (dLGB). Neuronal responses to diffuse light stimuli were studied before and during the iontophoretic application of acetylcholine (ACh). Although individual cells of all groups of functionally different neuron types could be influenced by ACh, responses to flashes were most pronounced and uniformly enhanced in the groups of SLOW ON-like cells located in the dorsolateral and caudal parts of the dLGB. The activity in primary response phases to light flashes increased also in caudally located SLOW OFF-like cells. In the group of ventromedially located FAST OFF-like cells the postinhibitory offdischarge in the response to flash was significantly augmented. Only few cells of FAST ON-like groups were affected and some of them inhibited by ACh. off

Different modulation of flash responses of fast and slow relay cells by aversive electrical brain stimulation.

Electrical activity of single neurons of the dorsal lateral geniculate nucleus of rats was recorded from stereotactically fixed animals. The neurons were classified as fast or slow ones, according to their response latency to electrical stimulation of the chiasma opticum. After this, the responses to diffuse flashes, to aversive electrical stimulation of the brain (ESB) and to a combination of both, brain stimulation immediately followed by a flash, were recorded. One week prior to testing, bipolar nichrom electrodes had been implanted into the tectotegmental region for the ESB, and their effectiveness was tested behaviorally. Out of 78 neurons 56 fast and 22 slow ones were found. Fast neurons have a significantly higher background activity than slow neurons. Both classes show a modulation of flash evoked responses by the ESB, although the ESB has nearly no effect on the spontaneous discharge frequency in any of the neurons. The influence on the flash response differs according to the cell class: the class of fast neurons is predominantly facilitated up to 1100 ms after the flash application, whereas the class of slow neurons is inhibited during this period. Later on (up to 2260 ms after flash) fast cells show no clear net effect, and slow cells were still slightly inhibited.

Classification of geniculo-cortical relay cells of albino rat dorsal lateral geniculate nucleus by means of multivariate analysis.

It was tested if responses of geniculo-cortical relay (GCR-) cells in rat dorsal lateral geniculate nucleus (dLGN) to diffuse light flashes contain features permitting a separation of the cell population into slow and fast cells like the response latency to stimulation of optic chiasm (OX-latency). The location of neurons within the dLGN found additional consideration. Using hierarchical cluster analysis two clusters were obtained for on- as well as off-like neurons, which reflected to a high degree the classification into slow and fast cells by OX-latency. Two subgroups were detected in the cluster of slow cells. Multivariate discriminance analysis made it possible to separate the cell population into two classes. The latency of primary excitation to flash (primary inhibition for off-cells), the number of impulses in the first excitation peak (duration of inhibitory period) and the location of the cells within the dLGN were suited for this separation differing in 11 up to 17% from that achieved by OX-latency classification.

Regional distribution of fast and slow geniculo-cortical relay cells (GCR-cells) within the rat's dorsal lateral geniculate nucleus (LGNd).

Unit activity of 135 GCR-cells in rat's LGNd was recorded extracellularly using micropipettes filled with trypan blue for subsequent marking of recording sites. The latencies of responses to electrical stimulation of the optic chiasma (OX) were mapped, and in accordance with Fukuda (1973) each GCR-cells was classified as fast or slow. Fast cells predominate in the rostroventromedial subregion and slow cells in the caudal part. Both fast and slow subtypes were found in the remaining rostrodorsolateral zone where slow cells made up two thirds of the subsample. The results fit the suggestion that in the LGNd of rats a fast retino-geniculate pathway relays in the ventromedial region, whereas slow pathways exist in the caudal as well as in the dorsolateral zone.

[Effect of a conditioned emotional state on the discharging behavior of single neurons of the rat dorsal lateral geniculate body]. / Der Einfluss eines bedingten emotionellen Zustandes auf das Entladungsverhalten von Einzelzellen des doesalen Corpus geniculatum laterale der Ratte

1. The spike activity of 155 cells of the dorsal geniculate body of rats was recorded under the influence of flash and the combination of flash with a tone. For test animals the tone has an emotional relevance (ERT), because they had been trained to learn a conditioned emotional reaction with the tone as conditioned stimulus. Controls had been sham trained, i.e. the tone was never reinforced and therefore without emotional relevance (EIT). 2. In the controls there was no difference in the quantity of facilitatory and inhibitory responses to the tone, whereas under ERT there were more often facilitations than inhibitions. 3. The tone changed the reaction to flash. This variation depends on the emotional relevance of the acoustic stimulus. The ERT evoked a stronger increase in the number of excitations than the EIT. The number of inhibitions decreased equally under both conditions. Also, the ERT changed the strength of the flash response more often than the EIT did. An increasing trend of excitation was found especially in primary positive cells, an increasing trend of inhibition especially in primary negative ones. The time course of responses shows these differences to occur in the primary positive cells essentially later than 200 mse cafter the stimulus, in the primary negative cells, however, within this interval.