The dorsal and medial raphe projections to the substantia nigra in the rat: Electrophysiological, biochemical and behavioural observations

Electrophysiological experiments have been performed in urethane anaesthetized rats to investigate the projections from the dorsal (DRN) and medial raphe nuclei (MRN) to the substantia nigra. The biochemical and behavioural effects following discrete electrolytic lesions in the dorsal and medial raphe have also been investigated.Stimulation of the DRN produced predominantly inhibition of spontaneous activity of single neurones in the substantia nigra though some neurones were also excited. Bilateral stimulation of the substantia nigra produced antidromic spikes in DRN and MRN neurones.Lesions of the DRN and MRN produced a significant reduction in substantia nigra 5-HT concentration. Additionally, DRN lesions reduced striatal 5-HT, while MRN lesions reduced hippocampal 5-HT. Both lesions increased substantia nigra HVA concentration but did not affect DA concentration. Neither DRN nor MRN lesions affected striatal HVA, although DA levels were significantly elevated after 14 days.Animals with DRN lesions explored more than controls or MRN-lesioned animals. However, this behaviour was transient and was not observed after 14 days. On the other hand, MRN-lesioned animals were significantly hyperactive.These observations suggest that the substantia nigra receives a direct monosynaptic inhibitory input from the DRN and MRN and that these pathways use 5-HT as a neurotransmitter serving to tonically inhibit dopaminergic neurones. While 5-HT and dopamine appear to be involved in the control of motor behaviour, the precise relationship between these serotoninergic and dopaminergic systems in this respect is unclear.     

Effect of ovarian hormones on conflict behavior

We injected ovariectomized female rats with estrogen and progesterone. Some of the injection regimens used are known to induce estrus, while others do not. The effects of these treatments on operant behavior were evaluated. Operant behavior was maintained under a reinforcement schedule, one segment of which involved experimentally induced conflict. Such behaviors previously have been shown to be modified by anti-anxiety drugs. Those hormone treatments effective in inducing estrus had behavioral effects similar to the effects observed for established anti-anxiety agents. Hormone-injection regimens not capable of inducing estrus were without effect on operant behavior. Our findings suggest that the reproductive cycles of female rats are associated with behavioral changes which may be indicative of changing anxiety levels mediated in part by changing titers of ovarian hormones. We suggest that the evaluation of hormonal influences on operant behaviors sensitive to tranquilizers should be a useful model system for studying possible mechanisms underlying emotional changes associated with reproductive cycles.     

Lateralized hunger: Ipsilateral attenuation of cortical spreading depression-induced feeding after unilateral 6-OHDA injection into the substantia nigra

Unilateral injections of 6-hydroxydopamine into the substantia nigra in the rat significantly attenuated cortical spreading depression (CSD)-induced eating from the hemisphere ipsilateral but not contralateral to the lesion. The lateralized decrease in elicited feeding was correlated with postlesion body weight loss, striatal catecholamine depletion (dopamine, 94%; norepinephrine, 52%) and amphetamine-induced ipsilateral turning, and can be characterized as an inability of the lesioned nigrostriatal system to maintain the CSD-elicited response rather than a failure to induce it. The interhemispheric control procedure allows us to exclude various general sensory and motor deficits to account for the decrement of feeding, and to attribute the feeding deficit to a reduced nigrostriatal transmission. It is suggested that CSD-induced feeding is due to an activation of integrative sensorimotor systems (especially the nigrostriatal dopamine system), rather than to homeostatic imbalances.     

Efferent connections of the substantia nigra and ventral tegmental area in the rat

Small injections of tritiated leucine and proline confined to the ventral tegmental area (AVT) were found to label fibers ascending: (a) to the entire ventromedial half of the striatum, but most massively to the ventral striatal zone that includes the nucleus accumbens; (b) to the thalamus: lateral habenular nucleus, nuclei reuniens and centralis medius, and the most medial zone of the mediodorsal nucleus; (c) to the posterior hypothalamic nucleus and possibly the lateral hypothalamic and preoptic region; (d) to the nuclei amygdalae centralis, lateralis and medialis; (e) to the bed nucleus of the stria terminalis, the nucleus of the diagonal band, and the medial half of the lateral septal nucleus; (f) to the anteromedial (frontocingulate) cortex; and (g) to the entorhinal area. Further AVT efferents descend to the medial half of the midbrain tegmentum including an anterior region of the median raphe nucleus, to the ventral half of the central grey substance including the dorsal raphe nucleus, to the parabrachial nuclei, and to the locus coeruleus. Similar injections centered in the pars compacta of the substantia nigra (SNC) label fibers that are distributed in the striatum in an orderly medial-to-lateral arrangement, and almost entirely avoid the nucleus accumbens and olfactory tubercle. With the exception of the lateral quarter of the substantia nigra, which apparently does not project to the extreme rostral pole of the striatum, each small SNC locus, regardless of its anteroposterior localization, distributes nigrostriatal fibers throughout the length of the striatum. Descending SNC efferents are distributed to the same general regions that receive descending AVT projections, except that no SNC fibers appear to enter the locus coeruleus. Isotope injections confined to the pars reticulata (SNR) label sparse nigrostriatal fibers, and numerous nigrothalamic fibers ascending mainly to the nucleus ventromedialis and in lesser number to the parafascicular nucleus and the paralamellar zone of the nucleus mediodorsalis. Descending SNR fibers leave the nigra as a voluminous fiber bundle that bifurcates into a large nigrotectal and a smaller nigrotegmental component, the latter terminating largely in the pedunculopontine nucleus of the pontomesencephalic tegmentum.     

A study of American immigrants to Israel utilizing the SRRQ

The stressfulness of migration to a new country was evaluated using the Social Readjustment Rating Questionnaire (SRRQ) with a group of 99 recent American immigrants to Israel. The migration experience was found to be only moderately stressful for this sample. SRRQ scores for the event ‘moving to a new country’ (MNC) reflected this finding. Individual SRRQ ratings of the stressfulness of migration correlated with the level of reported success in adjusting to the new life situation. The SRRQ may aid in the assessment of the impact of specific life events for groups and individuals.     

Iontophoretic application of opiates to the locus coeruleus.

The vast majority of morphine-sensitive single units in the area examined were localized to the locus coeruleus. This corresponds well with the known distribution of the highest densities of opiate receptor sites in this region of the midbrain. The effect of iontophoretically applied morphine was a marked and prolonged depression of spontaneous activity. Levorphanol, an opiate agonist, produced an effect similar to that of morphine while comparable doses of dextrorphan, it's clinically inactive stereoisomer, did not. Naloxone and levallorphan prevented as well as reversed the depression due to application of agonists. While the units were depressed following the application of opiate agonists, the cells were still excited by the neurotransmitter acetylcholine. We conclude that (1) neuronal sensitivity to opiates has a high positive correlation with autoradiographically determined opiate receptor sites, and (2) this sensitivity to opiates is blocked by opiate antagonists and is stereospecific in nature.     

Trans-synaptic regulation of the development of end organ innervation by sympathetic neurons.

To examine the regulation of development of end organ innervation the superior cervical ganglion (SCG), and two of its target organs, the iris and pineal gland, were studied using biochemical and histofluorescent approaches. During postnatal ontogeny the activity of tyrosine hydroxylase (T-OH), which is localized to adrenergic neurons, increased 50-fold in iris, and 34-fold in pineal nerve terminals of the rat. These increases paralleled the in vitro rise in iris [3H]norepinephrine ([3H]NE) uptake, a measure of the presence of functional nerve terminal membrane. These biochemical indices of end organ innervation correlated well with developmental increases in density of innervation, adrenergic ground plexus ramification and nerve fiber fluorescence intensity as determined by fluorescence microscopy. Unilateral transection of the presynaptic cholinergic nerves innervating the SCG in 2-3-day-old rats prevented the normal development of end organ innervation: T-OH activity, [3H]NE uptake, innervation density, plexus ramification and fluorescence intensity failed to develop normally in irides innervated by decentralized ganglia. It is concluded that trans-synaptic factors regulate the maturation of adrenergic nerve terminals, and the development of end organ innervation by SCG.     

Thermoregulatory responses to intraventricular norepinephrine in normal and hypothalamic-damaged rats.

We examined the effects of intraventricular injection of low doses of norepinephrine (NE) on internal temperature and on behavioral and reflexive thermoregulatory responses in unrestrained rats. NE lowered the body temperature of the rats in cold and neutral environments but had little effect in the heat. The hypothermia was blocked by alpha-adrenergic antagonists but unchanged by beta-adrenergic antagonists. In the cold, the hypothermia was caused primarily by a lowered metabolic rate. At ambient temperature 25 degrees C, it was caused primarily by vasodilatation while metabolic rate increased. Thus, reflexive responses were not integrated to lower body temperature. Behavioral responding compensated for the hypothermia. In the cold, rats increased responding to get heat after NE. In a warm environment, they did not increase responding to escape heat. Thus, both reflexive and behavioral results support the idea that the set-point is unchanged after intraventricular NE. Wherever in the brain the NE may be acting, it is not in the preoptic-anterior hypothalamic area, because when this area was ablated, the hypothermia in response to intraventricular NE was greatly exaggerated.     

Activity of neurons in the region of the substantia nigra during feeding in the monkey.

The activity of single neurons in the region of the substantia nigra of the monkey was recorded during feeding to investigate their function in ingestive behavior. It was observed that some neurons in the substantia nigra and the adjacent tegmentum altered their activity during feeding, in relation to mouth movements. The activity of these neurons was related to mouth movements in that the responses of the units were similar when the monkeys drank fluids with different tastes as long as the same movements were made, in that equally good responses could be obtained when the monkey moved his mouth to non-food objects, and in that in some units opposite responses were obtained when ipsilateral as compared with contralateral mouth movements were made. It was also shown that the responses of these units associated with mouth movements were similar when the monkeys were hungry and when they were satiated. These findings suggest that the activity of some neurons in the region of the substantia nigra is related to the execution of movements which may be involved in feeding, and that the activity of these neurons is not related to the initiation of feeding. Self-stimulation through the recording microelectrodes could be obtained just dorsal to the substantia nigra, but the neural basis of this self-stimulation is not known.     

Weight gain in adulthood in relation to socioeconomic factors,mental illness and personality traits: A prospective study of middle-aged women

The relationships between body weight change during a six-year follow-up period and a number of psychosocial variables were studied in a representative population sample of middle-aged women. Those women who had gained weight ? 5.0 kg were compared with the rest of the sample taking into account age, social class and initial level of obesity. Never-married women were over- represented among the women with weight gain ? 5.0 kg. Husband's social class (based on occupation) was inversely related with weight gain. Educational level, own social class and annual income were not significantly different between the two groups. There was a positive relation between mental illness (disability degree), depth of depression and weight gain. Use of psychotropic drugs, frequency of anxiety attacks and phobia grade were not related to weight gain, however. The personality trait order was positively related to weight gain, while there were no significant relationships between the other personality variables studied and weight gain. The study thus indicates that psychosocial factors might be of causal importance for the development of obesity in adult women. Further studies on the role of these factors for regulation of energy intake and expenditure seem to be justified.     

Behavioral deficits in cats following early selected visual exposure to contours of a single orientation

The ability of adult cats, whose early visual experience was confined to contours of a single orientation (either vertical or horizontal), to resolve gratings of different orientations was studied by operant methods. Following selective visual exposure during part or all of the first 4 months of life, the cats were trained on a simultaneous discrimination between gratings of various orientations and blank fields of the same mean luminance. The spatial frequency of the gratings was systematically altered in order to obtain an estimate of acuity based upon extrapolation to chance levels of performance. Selectively deprived cats performed as well as normally reared cats on gratings having the same orientation as that of the stripes they saw as kittens, but their performance on gratings orthogonal to these was poorer. The deficits in acuity for gratings perpendicular to the experienced orientation varied between 0.26 and 0.87 of an octave. On the other hand, control cats whose early visual experience alternated between vertical and horizontal stripes, or who were reared in an environment containing randomly oriented contours, failed to show any difference in their acuity for vertical and horizontal gratings. the acuity deficits shown by the selectively deprived animals are long-standing since they remain unchanged even after 30 months of normal visual exposure.It is argued that these perceptual deficits are a consequence of the changes in cortical physiology that other investigators^8,20 have described in cats who had undergone similar early visual deprivation. Taken together, these findings provide a basis for explaining a number of human perceptual disorders.     

The role of mesencephalic structures in thirst induced by centrally administered angiotensin II.

(1) In 27 animals microinjection of 25--100 ng of angiotensin II through chronic cannulae implanted in the preoptic region initiated drinking and in subsequent acute experiments influenced the spontaneous discharge rate of single neurons in the ipsi-lateral mesencephalon. Of 148 neurons for which recordings were made, 52 (35%) increased their frequency of spike potentials following administration of angiotensin II, 2 (1%) showed inhibition and 94 (64%) showed no change in firing rate. (2) In another series of 44 animals, unilateral or bilateral lesions of the midbrain ventral tegmentum or reticular formation were found to have little or no effect on water intake elicited by the microinjection of angiotensin II into the preoptic region. (3) In contrast to the effects of tegmental and reticular lesions, unilateral lesions located dorsally and laterally to the mammillary peduncle, in the area of passage of the medial forebrain bundle, significantly attenuated the dipsogenic response to either contralateral or ipsilateral injections of angiotensin II into the preoptic region. With bilateral lesions this effect was permanent. (4) Since the more caudal lesions were relatively ineffective in disrupting the elicited drinking, it is suggested that signals from angiotensin II receptors in the preoptic region are transmitted along pathways which diverge in the midbrain. (5) The possibility of a forebrain-hypothalamus-midbrain circuit mediating thirst initiated by activation of the renin-angiotensin system is discussed.     

The lipid and protein content of cholinergic synaptic vesicles from the electric organ of Torpedo marmorata purified to constant composition: implications for vesicle structure

The lipid, protein, acetylcholine and ATP content of cholinergic synaptic vesicles isolated from the richly innervated electric organ of Torpedo marmorata and purified to constant composition has been determined. The number of vesicles present in the preparations has been estimated by quantitative electron microscopy and the mean composition of the vesicle deduced. The acetylcholine content of the purest preparations was considerably greater than that previously attained and reached a mean of 6.10 mmole/g of protein and 2.6 X 10(5) molecules/vesicle; the mean values, for all determinations, were 4.1 +/- S.E.M. 0.6 and 2.6 X 10(5) +/- S.E.M. 0.6 X 10(5) respectively. The lipid and protein content of the vesicle (about 140 and 80 ag/vesicle respectively) is relatively low, indicating a thin, lipid-rich membrane and a highly hydrated core of which not more than 1-2% can be occupied by protein. These findings are consistent with conclusions drawn from recent density determinations made at different osmotic pressures using penetrating and non-penetrating gradients.     

Appearance of myelin proteins in rat sciatic nerve during development.

Rats between 5 and 45 days of age were sacrificed and their sciatic nerves dissected. Myelin was prepared from these sciatic nerves by a procedure involving purification on discontinuous sucrose gradients. The proteins of whole sciatic nerves at different ages and the proteins derived from the myelin isolated from these sciatic nerves were examined by discontinuous polyacrylamide gel electrophoresis in buffers containing sodium dodecyl sulfate. Over half of the proteins of sciatic nerve myelin migrated in a single band on the gel (P0). There were only minor changes in the protein distribution of sciatic nerve mylein during development. In contrast, the polyacrylamide gel patterns of whole sciatic nerve homogenate changed markedly during development between 5 and 15 days of age. The amount of P0 protein as a proportion of the total sciatic nerve protein increased from 3% at 5 days of age to 13% at 15 days of age after which it remained constant. Several other proteins which were also characteristic of the isolated myelin increased in relative importance during this time period. Parallel experiments dealing with a metabolic parameter of myelinogenesis, incorporation of intraperitoneally injected [35S]sulfate into sulfatide, were conducted. The maximum synthesis of sulfatide occurred between 6 and 16 days of age, coincident with the marked accumulation of myelin proteins in sciatic nerve.