Neuroscience
-
Neurons containing a calcium-binding protein parvalbumin in the external plexiform layer of the rat olfactory bulb were identified light microscopically with the pre-embedding immunocytochemistry and were subsequently analysed with the electron microscopic serial-sectioning and three-dimensional reconstructions. In the present study we chose several different types of parvalbumin-immunoreactive neurons identified light microscopically as Van Gehuchten cell type, superficial short-axon cell type and multipolar cell type. Parvalbumin-immunoreactive somata were similar to one another in their ultrastructural characteristics, showing nuclear indentations, moderately developed Golgi apparatus and abundant mitochondria; these structural features appeared to resemble those of the short axon cells around the glomeruli and in the granule cell layer reported in previous electron microscopic studies. ⋯ Until now, it has been believed that in the external plexiform layer only granule cells form reciprocal synapses with mitral/tufted cells. However, the present study clearly demonstrates that interneurons different from granule cells, namely GABAergic neurons containing a calcium-binding protein parvalbumin, also make reciprocal synapses with mitral/tufted cells in the external plexiform layer. Therefore, neuronal processes making reciprocal synapses with mitral/tufted cells in the external plexiform layer cannot be determined a priori as granule cell processes.
-
Comparative Study
The serotonergic agent fluoxetine reduces neuropeptide Y levels and neuropeptide Y secretion in the hypothalamus of lean and obese rats.
Evidence suggests that serotonin and neuropeptide Y neurons in the hypothalamus, which respectively inhibit and stimulate food intake, may interact to control energy homoeostasis. We therefore investigated the effects of fluoxetine, which inhibits serotonin reuptake, on food intake and the activity of the neuropeptide Yergic arcuato-paraventricular projection in lean Wistar and Zucker rats. We also studied its effects in obese Zucker rats, in which obesity is postulated to be due to overactivity of the arcuato-paraventricular projection. ⋯ Furthermore, seven days fluoxetine treatment prevented the significant increases in hypothalamic neuropeptide Y messenger RNA which were induced in lean rats by food restriction which precisely matched the hypophagia induced by the drug. We conclude that fluoxetine inhibits various aspects of the activity of the neuropeptide Yergic arcuato-paraventricular neurons, and suggest that reduced neuropeptide Y release in the paraventricular nucleus may mediate, at least in part, the drug's hypophagic action. We further suggest that serotonin may influence food intake and energy balance by inhibiting the arcuato-paraventricular projection, and that the two neurotransmitters may act together to regulate feeding and energy homoeostasis.
-
Systemic administration or local injection to the rat hindpaw of leukemia inhibitory factor induced a prolonged, dose dependent, mechanical hypersensitivity of the hindpaw flexion withdrawal reflex. Mechanical stimuli which were innocuous prior to leukemia inhibitory factor administration, evoked a rapid hindpaw withdrawal reflex indicative of mechanical allodynia. Pre-administration of anti-leukemia inhibitory factor antibodies prevented this behavioural hypersensitivity. ⋯ Anti-leukemia inhibitory factor had no effect upon hindpaw withdrawal thresholds when injected alone nor influenced the mechanical hypersensitivity produced by a subcutaneous injection of nerve growth factor. Injection of the closely related cytokine ciliary neurotrophic factor did not affect mechanical or thermal reflex withdrawal thresholds. Elevation of the neuroactive cytokine leukemia inhibitory factor following peripheral nerve injury may be a contributory factor to the pathogenesis of neuropathic pain.
-
In the present study we demonstrate low level expression of the laminin alpha 2 chain in brain and localize the alpha 2 protein to the capillary basement membrane. While in peripheral basement membranes the laminin alpha 1 and alpha 2 chains have an almost mutually exclusive distribution, the present results suggest both alpha 1 and alpha 2 in the cerebral capillary basement membrane. ⋯ In contrast to the muscle and Schwann cell basement membrane, where alpha 2 deficiency causes structural basement membrane abnormalities, the present results show that the lack of the alpha 2 subunit in the cerebral capillary basement membrane is not detrimental to its structure. This observation might be explained by the fact that the cerebral capillary basement membrane expresses both alpha chains and therefore exhibits structural redundancy.
-
The functional organization of the cortico-nucleus accumbens-substantia nigra pars reticulata circuit was investigated in the rat using combined anatomical and electrophysiological approaches. The nucleus accumbens neurons which project to the substantia nigra pars reticulata are located in a circumscribed region of the core immediately adjacent and extending dorsally to the anterior commissure. As shown by retrograde and anterograde transports of wheatgerm agglutinin conjugated to horseradish peroxidase, the region of the nucleus accumbens related to the substantia nigra was found to receive bilateral inputs from restricted areas of the medial and lateral prefrontal cortex, i.e., prelimbic/medial orbital and dorsal agranular insular areas. ⋯ Furthermore, the present data also show that the stimulation of the medial prefrontal cortex results in a powerful inhibition of the tonic firing of the substantia nigra pars reticulata neurons. In conclusion, this study reveals the existence of a functional link between the prefrontal cortex (prelimbic/medial orbital and agranular insular areas) and the nucleus accumbens neurons which innervate the dorsomedial region of the substantia nigra pars reticulata. Since the dorsomedial region of substantia nigra pars reticulata is known to project to subfields of the mediodorsal and ventromedial thalamic nuclei related to the prefrontal cortex, the present data further demonstrate the existence of a prefrontal-nucleus accumbens-thalamo-cortical circuit involving the substantia nigra pars reticulata.