Endoscope-assisted craniotomy: approach to the rostral brain stem.

We describe a surgical technique to improve visualization of deep brain structures during craniotomy. The technique, developed in a cadaveric model, combines the use of an operating microscope and a solid-rod lens endoscope. Addition of the endoscope during craniotomy allows the operator to visualize structures that otherwise might not have been seen. An approach to the brain stem is demonstrated.

Oscillopsia and primary cerebellar ectopia: case report and review of the literature.

Oscillopsia, the visual sensation of stationary objects swaying back and forth or vibrating, has been described in association with downbeat nystagmus in patients with primary cerebellar ectopia (Chiari I malformation). A patient with symptomatic oscillopsia without downbeat nystagmus, who was diagnosed by magnetic resonance imaging to have displaced cerebellar tonsils below the foramen magnum, is presented here. Suboccipital craniectomy and upper cervical laminectomy completely relieved the visual disturbance of the patient. The pathogenesis and surgical management of oscillopsia are discussed with respect to the current literature. Early recognition and surgical management of oscillopsia are lead to complete recovery in patients with minimal symptomatology.

Anatomic evidence of nociceptive inputs to primary somatosensory cortex: relationship between spinothalamic terminals and thalamocortical cells in squirrel monkeys.

This study examined anatomic pathways that are likely to transmit noxious and thermal cutaneous information to the primary somatosensory cortex. Anterograde and retrograde labeling techniques were combined to investigate the relationship between spinothalamic (STT) projections and thalamocortical neurons in the squirrel monkey (Saimiri sciureus). Large injections of diamidino yellow (DY) were placed in the physiologically defined hand region of primary somatosensory cortex (hSI), and wheat germ agglutinin-horseradish peroxidase (WGA-HRP) was injected in the contralateral cervical enlargement (C5-T1). Both DY-labeled neuronal cell bodies and HRP-labeled STT terminal-like structures were visualized within single thalamic sections in each animal. Quantitative analysis of the positions and numbers of retrogradely labeled neurons and anterogradely labeled terminal fields reveal that: 1) ventral posterior lateral (VPL), ventral posterior inferior (VPI), and central lateral (CL), combined, receive 87% of spinothalamic inputs originating from the cervical enlargement; 2) these three nuclei contain over 91% of all thalamocortical neurons projecting to hSI that are likely to receive STT input; and 3) these putatively contacted neurons account for less than 24% of all thalamic projections to hSI. These results suggest that three distinct spinothalamocortical pathways are capable of relaying nociceptive information to the hand somatosensory cortex. Moreover, only a small portion of thalamocortical neurons are capable of relaying STT-derived nociceptive and thermal information to the primary somatosensory cortex.

Decreased beta-adrenergic receptors in rat heart in streptozotocin-induced diabetes: role of thyroid hormones.

The effect of streptozotocin-induced diabetes on the beta-adrenergic receptor-coupled adenylate cyclase was studied in rat heart particulate fractions. Streptozotocin treatment decreased the number of myocardial beta-adrenergic receptors by 34% with no change in the apparent affinity of these receptors for [3H]dihydroalprenolol. The maximal isoproterenol-activated accumulation of cAMP in streptozotocin-treated rat hearts was decreased by only 10%. Insulin administration to streptozotocin-treated rats increased the number of myocardial beta-adrenergic receptors to near or above control levels. Administration of L-T4 to streptozotocin-treated rats had the same effect. Total T4, free T4, and total T3 levels were all significantly decreased in the diabetic animals. Administration of insulin to streptozotocin-treated rats increased the serum thyroid hormone levels toward or above the levels found in control animals. Streptozotocin-induced diabetes had no significant effect on cardiac beta-adrenergic receptor number in thyroidectomized rats. Insulin did not elevate cardiac beta-adrenergic receptor number in thyroidectomized diabetic rats. The decrease in the number of myocardial beta-adrenergic receptors occurring in diabetes mellitus is probably mediated through thyroid hormones.

Prelimbic cortex, mediodorsal thalamus, septum, and delayed alternation in rats.

Rats were trained preoperatively on contingently reinforced alternation in a T-maze. Then different matched groups of rats received lesions in the prelimbic cortex, mediodorsal thalamus, posterodorsal septum (aimed at transecting the precommissural fornix), and control operations (no brain lesions). Following a 2-week recovery period the rats were retested in the T-maze for retention of delayed alternation. Control rats were unaffected by the control operations and the testing hiatus of the recovery period. Rats with lesions in the prelimbic cortex performed at chance levels on the first postoperative session as did rats with posterodorsal septal lesions, but both groups recovered with continued experience, i.e., they could relearn the task. Rats with lesions in mediodorsal thalamus were only slightly affected by the lesions. The results suggest that a restricted field in the medial pregenual cortex, the prelimbic area, is critically involved in T-maze alternation. However, the data also suggest that a major subcortical source of afferents to prelimbic cortex, the mediodorsal nucleus of the thalamus, is not crucial for retention of contingently reinforced T-maze delayed alternation following interference with septo-hippocampal circuitry is consistent with data previously reported.

Behavioral characteristics of vasopressin-deficient rats (Brattleboro strain).

A group of vasopressin-deficient rats (Brattleboro strain--DI) and a group of normal Long-Evans rats were successively evaluated on visual discrimination, olfactory discrimination, delayed alternation at short and long intertrial intervals (ITIs), approach-avoidance conflict in a straight runway, and open-field behavior. It was found that DI rats adapted more slowly than normal rats in the T-maze, in the straight runway, and they were slower to emerge into the open field. The DI rats were impaired relative to normal animals on the discrimination tasks (visual and olfactory), but they were not impaired on delayed alternation (at least for short ITIs). DI rats also showed better retention of the punishment effect in the approach-avoidance conflict test than normal animals. It is suggested that DI rats have defective reference-memory mechanisms, fairly intact working-memory processes and altered adaptability (timidity or cautiousness).