Axoplasmic transport of norepinephrine in the locus coeruleus-hypothalamic system in the rat

The axoplasmic transport of norepinephrine (NE) between the nucleus locus coeruleus (LC) and the hypothalamus has been measured by three methods which employ the stereotaxic injection of [3H]catecholamines in the rat brain. [3H]NE is synthesized from [3H]dopamine (DA) injected into the LC and transported at a rate of 0.8-0.9 mm/h. This rate is probably an underestimate since it includes the time required for uptake and conversion of [3H]DA to [3H]NE prior to transport. Measurement of transport of [3H]NE between the posterior and anterior hypothalamus gives a rate of 2 mm/h which is independent of [3H]DA uptake and [3H]NE synthesis. This rate is in good agreement with the 1.9 mm/h figure calculated for [3H]NE transport in the system after LC injection of [3H]NE and represents a closer estimate of the true rate of axoplasmic transport than the 0.8-0.9 mm/h estimate. Transport of [3H]NE occurs through primarily ipsilateral NE fibers running in the median forebrain bundle and is blocked by 6-hydroxydopamine lesions in the bundle. Early appearing [3H]NE in the hypothalamus forms a relatively stable pool which is unaffected by median forebrain bundle lesions and is essentially unchanged by [3H]NE transported from the LC. This pool appears to be derived from non-specific spread of [3H]DA after injection, probably through the cerebrospinal fluid.

Iatrogenic muscle fibrosis. Arm levitation as an initial sign

Three patients had iatrogenic muscle fibrosis, without weakness or sensory loss. Deltoid muscle fibrosis produced the unique clinical sign of gradual, involuntary, and irreducible arm levitation. The third patient had both levitated arms and levitated legs, a result of injections in the rectus femoris muscles. Repeated intramuscular injections apparently resulted in muscle fibrosis and intramuscular nerve-twig damage. Pentazocine (Talwin) is a particularly offending agent. One patient showed an unusual tissue reaction to foreign material, which may have played a role in her muscle fibrosis. Nevertheless, dramatic recovery of muscle function followed surgical sectioning of the fibrous deltoid bands.

Loss of active avoidance of responding after lateral hypothalamic injections of 6-hydroxydopamine

After injections of 6-hydroxydopamine (6-OHDA) along the medial forebrain bundle in the lateral hypothalamus, rats failed to acquire a one-way active avoidance response or failed to perform a previously acquired active avoidance response. Such rats, however, acquired a passive avoidance response and a conditioned taste aversion normally. Thus the effect of lateral hypothalamic injections of 6-OHDA was not a total loss of the capacity to acquire or perform conditioned responses, but was a failure to initiate forward movement in the presence of a conditional stimulus. Most of these rats could initiate a similar forward movement to escape from the unconditioned stimulus (foot shock). Failure to acquire or perform the active avoidance response was correlated with the loss of hypothalamic, striatal and forebrain catecholamines produced by lateral hypothalamic 6-OHDA injections. Identical injections of 6-ohda placed along the medial hypothalamus produced a similar loss of regional catecholamines, but medial 6-OHDA injections did not affect active avoidance responding. We interpret this dissociation between loss of catecholamines and the capacity for active avoidance responding to mean that medial 6-OHDA injections did not damage the same catecholaminergic terminal fields as lateral 6-OHDA injections and that the integrity of the terminal fields damaged by lateral 6-OHDA injections is necessary for active avoidance responding.