Leonard Y. Koda

Hypothalamic enkephalin neurones may regulate the neurohypophysis.

WE have previously reported that significant amounts of immunoreactive (ir)-Leu5-enkephalin were present in extracts of the neurointermediate lobe of the rat pituitary1. Negligible amounts of the pentapeptide were detected in the anterior lobe. In these assays, the concentration of Leu5-enkephalin in the neurointermediate lobe was higher than in the globus pallidus, the brain region reported to contain the densest enkephalinergic innervation2. The high content of (ir)-Leu-enkephalin in the neurointermediate lobe of the pituitary led us to further investigation of its distribution and possible function. We report here that (ir)-enkephalins in the pituitary are concentrated in nerve fibres projecting from the hypothalamus to the pars nervosa and that this pathway may be involved in the regulation of neurohypophysial neurosecretion.

Visceral cortex: A direct connection from prefrontal cortex to the solitary nucleus in rat

Abstract Injections of the fluorescent retrograde axonal tracer, True Blue, into the solitary complex (a visceral and taste center in the medulla) labeled pyramidal cell bodies deep in the medial, prefrontal cortex and especially lateral prefrontal (or insular) cortex of the rat. Injections of the anterograde axonal tracer (wheat germ agglutinin conjugated to horseradish peroxidase) into the prefrontal cortex produced bilateral labeling throughout much of the solitary nucleus. The distribution of prefrontal cortical cells projecting directly to the solitary nucleus may provide one clear anatomical criterion for identifying regions of cerebral cortex that may influence visceral function.

Redistribution of endorphin and enkephalin immunoreactivity in the rat brain and pituitary after in vivo treatment with colchicine or cytochalasin B.

Abstract The effects of intracerebroventricular injection of colchicine or cytochalasin B were compared on radioimmunoassayable endorphin and enkephalin in several rat brain regions and pituitary gland. In addition, colchicine effects on brain immunoreactivity were also assessed by immunocytochemistry. Colchicine treatment increased endorphin levels in the hypothalamus without changing pituitary levels. Cytochalasin B did not change brain endorphin levels but increased pituitary content. These contrasting drug effects probably reflect the neuronal nature of the brain endorphin system and the endocrine nature of the pituitary system. Colchicine treatment also increased enkephalin radioimmunoreactivity in the hypothalamus with a corresponding decrease in the pituitary. This colchicine effect is compatible with reduced axonal transport of enkephalin in a hypothalamo-neurohypophysial pathway: immunocytochemistry after colchicine reveals stained hypothalamic neurons not seen normally. However, colchicine treatment did not alter enkephalin radioimmunoassay values in the other brain regions, even when these regions also revealed groups of cell bodies not seen in normal brain. This inconsistency between unchanged assay values and increased cell reactivity might be explained in part if most enkephalin neurons have short axons; thus, colchicine arrest of axonal transport might cause a local redistribution of enkephalin immunoreactive material that would not be detected by radioimmunoassay due to the limitations of tissue dissection. These results demonstrate the enhanced interpretive value of data obtained from both radioimmunoassay and immunocytochemistry.

Regional distribution of endorphin, met5-enkephalin and leu5-enkephalin in the pigeon brain

The distribution of beta-endorphin and enkephalin in the pigeon forebrain by immunohistochemistry and radioimmunoassay is essentially analogous to mammals. Both endorphin- and enkephalin-reactive fibers have a similar periventricular distribution, but the enkephalin fibers are more extensive and are also found in the paleostriatum, limbic regions and brain stem, pituitary stalk and notably, penetrating the organum vasculosum hypothalami. There was poor correlation between endorphin and enkephalin regional contents by radioimmunoassay. In contrast, a highly significant correlation was observed between Met5-enkephalin and Leu5-enkephalin regional distribution. These data support the view that enkephalin neurons and endorphin neurons are independent central neuronal systems.

Synaptic responses of neurons of the nucleus tractus solitarius in vitro

Postsynaptic responses of neurons in the nucleus tractus solitarius (NTS) have been studied in an in vitro slice preparation using extra- and intracellular recording. Single or paired pulse stimulations were delivered to afferent fibers within the tractus solitarius (TS) to activate orthodromic responses in these neurons. Most NTS neurons displayed an initial synaptic excitation followed by inhibition of spontaneous or evoked firing lasting up to 150-200 ms after stimulation. Excitatory postsynaptic potentials (EPSPs), recorded intracellularly, were increased in amplitude by membrane hyperpolarization. Large afterhyperpolarizations followed action potentials triggered by the EPSPs or evoked by intracellular current injections. Intracellular evidence for synaptic inhibition within the NTS included: (1) the presence, after Cl-injection, of flurries of spontaneous PSPs likely to be inverted inhibitory postsynaptic potentials; (2) reduction of the size of a test EPSP by a previous subthreshold TS conditioning volley; and (3) hyperpolarizing PSPs recorded in some neurons. Other NTS neurons exhibited prolonged excitatory responses to TS stimulation and could be local inhibitory interneurons. These results may help specify synaptic mechanisms in the NTS that could play an integrative role in the relay of visceral sensory inputs to higher order effectors.

Doxorubicin: a fluorescent neurotoxin retrogradely transported in the central nervous system.

Doxorubicin, a fluorescent cytotoxic antibiotic, was found to be both a retrograde neuron pathway tracer and neurotoxin to cells retrogradely labeled with it. Doxorubicin was injected into rat caudate-putamen and within 4 h the nuclei in the ipsilateral substantia nigra zona compacta (SNc) and ventral tegmental area (VTA) were stained with red fluorescent doxorubicin. After 2 weeks, portions, but not all of the ipsilateral SNc and VTA were depleted of neurons. Retrograde neurotoxicity was obvious following injections of 20%, 10%, 6%, 5% or 4% doxorubicin but not after 1% or 2%. Five months following doxorubicin treatment, the ipsilateral SNc and VTA were shrunken, distorted and nearly absent; the injected caudate was shrunken and replaced by ventricle. The ipsilateral thalamic parafasicular center median nucleus, a complex nucleus also known to project to the caudate, was depleted of large neurons 2 weeks following caudate injection. Doxorubicin can be transported over relatively long distances; lumbar spinal cord injections labeled cortical pyramidal neurons 3 days later. Doxorubicins unique pathway-specific neurotoxicity may be useful in future neuroscientific studies.

Penetration of fluorescein into the brain: a sex difference ☆

Fluorescein was found to penetrate into the brain via the circumventricular organs. Fluorescein penetrates beyond the borders of the circumventricular organs into the surrounding neuropile. This relationship was found for the area postrema and the nucleus tractus solitarius, the organum vasculosum lamina terminalis and the rostral suprachiasmatic area, the median eminence and the arcuate nucleus. The choroid plexus appears to take up fluorescein, but fluorescence does not appear in adjacent structures such as the corpus striatum and septum, but rather along the ependymal and plial surfaces. Fluorescein was found to accumulate to a greater extent in the brains of female as compared to male rats. This sex difference is not associated with the blood-brain barrier as cortex and cerebellum did not show increased fluorescence, but only midline structures containing circumventricular organs. Gonadectomy did not alter fluorescein accumulation.

Blood pressure following microinjection of somatostatin related peptides into the rat nucleus tractus solitarii

The possible role of medullary somatostatin as a neurotransmitter involved in blood pressure regulation was examined. Blood pressure and heart rate were measured in pentobarbital anesthetized rats while pmol quantities of somatostatin-28 (SS28), SS28-(15-28) (somatostatin-14), SS28-(1-12) or SS28-(1-10) were injected into the caudal nucleus tractus solitarii (NTS). Injection of artificial cerebrospinal fluid (ACSF; 500 nl/10 s) alone was followed by a small (2 mmHg) statistically insignificant decrease in blood pressure. SS28, SS28-(15-28) or SS28-(1-12) induced an immediate and statistically significant decrease in blood pressure as compared to vehicle alone. SS28-(1-10) had no significant effect. SS28 was tested at three doses. The lowest dose of SS28 (2.5 pmol) induced an 8 mmHg drop in blood pressure, the medium dose (25 pmol), an 11 mmHg drop and the highest dose (250 pmol) a 16 mmHg drop. The other peptide fragments were tested only at the higher 250 pmol dose. SS28-(1-12) induced a significantly (P less than 0.01) less drop in blood pressure (10 mmHg) when compared to either SS28 or SS28-(15-28) (18-19 mmHg). The hypotensive and bradycardiac effects of SS28 were prevented by pretreatment with methylscopolamine (5 mg/kg i.p.) 10 min prior to SS28. The cardiovascular effects of intramedullary injected SS28 were also blocked with an ipsilateral NTS injection of yohimbine or tolazoline 10 min prior to SS28.(ABSTRACT TRUNCATED AT 250 WORDS)

Distribution of Catecholamine-containing cell bodies and blood vessels in the rat nuclues tractus solitarius

Glyoxylic acid-induced monoamine fluorescence (GIF) was used to map the distribution of catecholamine-containing cell bodies and terminals in the rat nucleus tractus solitarius (NTS) and dorsal medulla. In addition, the relative vascularity of the NTS was quantified by examination of tissue perfused with Pontamine sky blue. The GIF-reactive cell bodies within the NTS complex were caudal to the rostral pole of the area postrema and are therefore considered to be the A2 cell body group as defined by Dahlström and Fuxe. The A2 cell body group was composed of 900 (890 +/- 43, n = 3) small to medium sized neurons (15-25 micron diameter) located on the dorsal and lateral edges of the dorsal motor nucleus of the vagus. GIF terminal density was found to be most dense in the medial portion of the NTS as compared to the lateral or midline portions of the NTS, dorsal motor nucleus of the vagus, or hypoglossal nucleus. Quantitative blood vessel analysis revealed that the NTS is significantly less vascularized than the surrounding nucleus gracilius, central gray, or dorsal motor nucleus of the vagus. A full serial section analysis of NTS, stained either for GIF cell bodies, terminals or blood vessels, has been obtained; this detailed presentation of catecholamine-containing profiles and blood vessels in the dorsal medulla may facilitate future studies aimed at examining central control of autonomic function.

Lithium treatment decreases blood pressure in genetically hypertensive rats

Chronic lithium treatment was examined for effects on the blood pressure of spontaneously hypertensive rats (SHRs). Treated rats were allowed continuous access to a pelleted lithium diet (1.7 g LiCl (40 mmol)/kg diet) for 21 days. Control SHRs were fed a similar diet lacking the lithium. Two groups of control rats were examined. One group had continuous access to control diet (ad lib controls); a second group was pair-fed a daily ration of control diet such that their mean body weight remained similar to the lithium treated group (pair-fed controls). Heart rate, systolic, diastolic and mean arterial blood pressures were recorded on day 21 from freely moving conscious rats. Systolic, diastolic and mean arterial blood pressure was significantly lower (approximately 15 mmHg) in the lithium treated SHRs as compared to either control group; the pair-fed and ad lib controls had similar blood pressures at the end of the treatment periods. Heart rate was increased in the lithium treated animals. All rats gained weight during the 21 days of treatment, although the lithium treated group and the pair-fed control group did not gain weight as much or as rapidly as the control group that had continuous access to control diet. Plasma and brain lithium levels were in the moderate range (0.3--0.4 meq/l) and all rats appeared healthy at the end of the experiment. These results suggest that chronic treatment may have clinically relevant effects on blood pressure.