A method for assessing pain and analgesia in rats and cats is described. The procedure involves subcutaneous injection of dilute formalin into the forepaw, after which the animal's responses are rated according to objective behavioral criteria. The formalin test is a statistically valid technique which has two advantages over other pain tests: (1) little or no restraint is necessary, permitting unhindered observation of the complete range of behavioral responses; and (2) the pain stimulus is continuous rather than transient, thus bearing greater resemblance to most clinical pain. The analgesic effects of morphine, meperidine, and stimulation of the periaqueductal grey matter are evaluated using this test.

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To minimize the sensory loss associated with intradural posterior rhizotomy for medically refractory occipital neuralgia, partial sectioning of the upper cervical posterior rootlets was performed in 11 patients. The ventrolateral aspect of each posterior rootlet from C-1 to the upper portion of C-3 was divided at the root entry zone. In three patients with bilateral neuralgia, the procedure was performed on both sides, for a total of 14 partial rhizotomy procedures in the 11 patients. This resulted in satisfactory preservation of scalp sensation in all cases. Pain within the territory of the greater occipital nerve was consistently reduced or abolished by this procedure. The overall degree of pain relief was rated good or excellent after 10 of the 14 procedures. The other four procedures alleviated pain in the territory of the greater occipital nerve, but the results were marred by persistent periorbital or temporal pain. Two patients subsequently underwent complete C1-3 posterior rhizotomy without further improvement. Although partial posterior rhizotomy at C1-3 did not always relieve pain in the periorbital and temporal regions, this procedure did provide consistent long-term relief of severe occipital pain with minimal risk of postoperative vertigo, scalp anesthesia, or deafferentation syndrome.

We compared the pulsatile secretion of luteinizing hormone (LH) between 13 men with clinically and electrographically documented temporal lobe seizures and 8 age-matched controls. Serum for LH measurement was drawn every 15 minutes during 8 hours of EEG telemetry in both groups. The 2 groups did not differ significantly in average mean baseline LH secretion, total LH secretion, or average pulse amplitude. The group with seizures, however, showed a significantly greater (p less than 0.05) variability of baseline LH secretion and pulse frequency. Among the men with unilateral paroxysmal EEG findings, pulse frequency was significantly greater (p = 0.05) with right epileptiform discharges or left slowing (6.4 +/- 0.4) than with left epileptiform discharges or right slowing (3.0 +/- 1.3). The relationship of pulse frequency to the nature and laterality of paroxysmal discharges makes it unlikely that endocrine abnormalities can be attributed to medication alone and strengthens the notion that temporal lobe epileptiform discharges may disrupt hypothalamic regulation of pituitary secretion.

Single neuronal units with physiological characteristics of superficial dorsal-horn neurons were recorded extracellularly in laminae 1, 2, and 3 of cat spinal cord. When focal electrical stimulation was applied to the ipsilateral dorsal column, most of the units were excited transsynaptically at various latencies consistent with an effect mediated by large myelinated axons. Units recorded in laminae 2 and 3 had earlier latencies of activation than units in lamina 1. Units with cutaneous receptive fields only for noxious stimuli were activated at significantly longer latencies than units responsive to innocuous stimuli. The time course of these effects was consistent with the concept that many cells in laminae 1 to 3 receive direct excitatory synaptic input from collaterals of dorsal-column fibers, and some lamina 1 cells receive excitatory synaptic input from lamina 2 neurons. Previous reports have emphasized the inhibitory action of dorsal-column stimulation on nociceptive responses of cells in laminae 4 and 5 of the dorsal-horn, particularly those of the spinocervical tract in cats and the spinothalamic tract in primates. The present study suggests that some of this inhibition might be sustained by a network of interneurons in or near the substantia gelatinosa and marginal layer. The therapeutic efficiency of dorsal-column stimulation for pain relief in humans may depend in part on the activation of neurons in the superficial layers of the dorsal horn.